Angewandte Chemie International Edition

Generation of High‐Molecular‐Weight Polymers with Diverse Substituents: An Unusual Metal‐Free Synthesis of Poly(aminoborane)s ()
Angewandte Chemie International Edition, Volume 57, Issue 21, Page 5990-5992, May 22, 2018.
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Spotlights on our sister journals: Angew. Chem. Int. Ed. 21/2018 ()
Angewandte Chemie International Edition, Volume 57, Issue 21, Page 5982-5985, May 22, 2018.
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Chemical Institute of Canada and Canadian Society for Chemistry Awards ()
Angewandte Chemie International Edition, Volume 57, Issue 21, Page 5987-5988, May 22, 2018.
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Corrigendum: The Structural Fate of Individual Multicomponent Metal‐Oxide Nanoparticles in Polymer Nanoreactors ()
Angewandte Chemie International Edition, Volume 57, Issue 21, Page 5977-5977, May 22, 2018.
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Graphical Abstract: Angew. Chem. Int. Ed. 21/2018 ()
Angewandte Chemie International Edition, Volume 57, Issue 21, Page 5959-5977, May 22, 2018.
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Cover Picture: Magnetic Mesoporous Silica Nanoparticles Cloaked by Red Blood Cell Membranes: Applications in Cancer Therapy (Angew. Chem. Int. Ed. 21/2018) ()
Angewandte Chemie International Edition, Volume 57, Issue 21, Page 5955-5955, May 22, 2018.
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Frontispiece: Postsynthetic Functionalization of Three‐Dimensional Covalent Organic Frameworks for Selective Extraction of Lanthanide Ions ()
Angewandte Chemie International Edition, Volume 57, Issue 21, May 22, 2018.
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Back Cover: An Amorphous Noble‐Metal‐Free Electrocatalyst that Enables Nitrogen Fixation under Ambient Conditions (Angew. Chem. Int. Ed. 21/2018) ()
Angewandte Chemie International Edition, Volume 57, Issue 21, Page 6354-6354, May 22, 2018.
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Inside Back Cover: SrB5O7F3 Functionalized with [B5O9F3]6− Chromophores: Accelerating the Rational Design of Deep‐Ultraviolet Nonlinear Optical Materials (Angew. Chem. Int. Ed. 21/2018) ()
Angewandte Chemie International Edition, Volume 57, Issue 21, Page 6353-6353, May 22, 2018.
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Inside Cover: Enzymatic or In Vivo Installation of Propargyl Groups in Combination with Click Chemistry for the Enrichment and Detection of Methyltransferase Target Sites in RNA (Angew. Chem. Int. Ed. 21/2018) ()
Angewandte Chemie International Edition, Volume 57, Issue 21, Page 5956-5956, May 22, 2018.
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Pleading for a Dual Molecular‐Orbital/Valence‐Bond Culture ()
Angewandte Chemie International Edition, Volume 57, Issue 21, Page 5994-6002, May 22, 2018.
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Halogen Bonding in Solution: Anion Recognition, Templated Self‐Assembly, and Organocatalysis ()
Abstract The halogen bond is a supramolecular interaction between a Lewis‐acidic region of a covalently bound halogen and a Lewis base. It has been studied widely in silico and experimentally in the solid state; however, solution‐phase applications have attracted enormous interest in the last few years. This Minireview highlights selected recent developments in halogen bond interactions in solution, with a focus on the use of receptors based on halogen bonds in anion recognition and sensing, anion‐templated self‐assembly, as well as in organocatalysis.
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Modern Electrochemical Aspects for the Synthesis of Value‐Added Organic Products ()
Abstract The use of electricity instead of stoichiometric amounts of oxidizers or reducing agents in synthesis is very appealing for economic and ecological reasons, and represents a major driving force for research efforts in this area. To use electron transfer at the electrode for a successful transformation in organic synthesis, the intermediate radical (cation/anion) has to be stabilized. Its combination with other approaches in organic chemistry or concepts of contemporary synthesis allows the establishment of powerful synthetic methods. The aim in the 21st Century will be to use as little fossil carbon as possible and, for this reason, the use of renewable sources is becoming increasingly important. The direct conversion of renewables, which have previously mainly been incinerated, is of increasing interest. This Review surveys many of the recent seminal important developments which will determine the future of this dynamic emerging field.
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Oxygen Vacancies in ZnO Nanosheets Enhance CO2 Electrochemical Reduction to CO ()
Abstract As electron transfer to CO2 is generally considered to be the critical step during the activation of CO2, it is important to develop approaches to engineer the electronic properties of catalysts to improve their performance in CO2 electrochemical reduction. Herein, we developed an efficient strategy to facilitate CO2 activation by introducing oxygen vacancies into electrocatalysts with electronic‐rich surface. ZnO nanosheets rich in oxygen vacancies exhibited a current density of −16.1 mA cm−2 with a Faradaic efficiency of 83 % for CO production. Based on density functional theory (DFT) calculations, the introduction of oxygen vacancies increased the charge density of ZnO around the valence band maximum, resulting in the enhanced activation of CO2. Mechanistic studies further revealed that the enhancement of CO production by introducing oxygen vacancies into ZnO nanosheets originated from the increased binding strength of CO2 and the eased CO2 activation.
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A Persulfide Donor Responsive to Reactive Oxygen Species: Insights into Reactivity and Therapeutic Potential ()
Abstract Persulfides (RSSH) have been hypothesized as critical components in sulfur‐mediated redox cycles and as potential signaling compounds, similar to hydrogen sulfide (H2S). Hindering the study of persulfides is a lack of persulfide‐donor compounds with selective triggers that release discrete persulfide species. Reported here is the synthesis and characterization of a ROS‐responsive (ROS=reactive oxygen species), self‐immolative persulfide donor. The donor, termed BDP‐NAC, showed selectivity towards H2O2 over other potential oxidative or nucleophilic triggers, resulting in the sustained release of the persulfide of N‐acetyl cysteine (NAC) over the course of 2 h, as measured by LCMS. Exposure of H9C2 cardiomyocytes to H2O2 revealed that BDP‐NAC mitigated the effects of a highly oxidative environment in a dose‐dependent manner over relevant controls and to a greater degree than common H2S donors sodium sulfide (Na2S) and GYY4137. BDP‐NAC also rescued cells more effectively than a non‐persulfide‐releasing control compound in concert with common H2S donors and thiols.
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Intermolecular σ‐Bond Cross‐Exchange Reaction between Cyclopropenones and (Benzo)silacyclobutanes: Straightforward Access towards Sila(benzo)cycloheptenones ()
Abstract Described herein is the first intermolecular σ‐bond exchange reaction between the C−C bond of cyclopropenones and C−Si bond of (benzo)silacyclobutanes and it proceeds smoothly by treatment with either 1 mol % of a palladium or 2 mol % of a nickel catalyst. This reaction constitutes an unprecedented route for the synthesis of various sila(benzo)suberones. And it is also the first example of a σ‐bond exchange reaction involving cyclopropenones.
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Tunable Multicolor Phosphorescence of Crystalline Polymeric Complex Salts with Metallophilic Backbones ()
Abstract A total of 35 [Au(NHC)2][MX2] (NHC=N‐heterocyclic carbene; M=Au or Cu; X=halide, cyanide or arylacetylide) complex salts were synthesized by co‐precipitation of [Au(NHC)2]+ cations and [MX2]− anions. These salts contain crystallographically determined polymeric Au⋅⋅⋅Au or Au⋅⋅⋅Cu interactions and are highly phosphorescent with quantum yields up to unity and emission color tunable in the entire visible regions. The nature of the emissive excited states is generally assigned to ligand (anion)‐to‐ligand (cation) charge‐transfer transitions assisted by d10⋅⋅⋅d10 metallophilicity. The emission properties can be further tuned by controlled triple‐component co‐crystallization or by epitaxial growth. Correct recipes for white light‐emitting phosphors with quantum yields higher than 70 % have been achieved by screening the combinatorial pool.
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Trimethylsilyl‐Protected Alkynes as Selective Cross‐Coupling Partners in Titanium‐Catalyzed [2+2+1] Pyrrole Synthesis ()
Abstract Trimethylsilyl (TMS)‐protected alkynes served as selective alkyne cross‐coupling partners in titanium‐catalyzed [2+2+1] pyrrole synthesis. Reactions of TMS‐protected alkynes with internal alkynes and azobenzene under the catalysis of titanium imido complexes yielded pentasubstituted 2‐TMS‐pyrroles with greater than 90 % selectivity over the other nine possible pyrrole products. The steric and electronic effects of the TMS group were both identified to play key roles in this highly selective pyrrole synthesis. This strategy provides a convenient method to synthesize multisubstituted pyrroles as well as an entry point for further pyrrole diversification through facile modification of the resulting 2‐silyl pyrrole products, as demonstrated through a short formal synthesis of the marine natural product lamellarin R.
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Concerted Catalysis by Adjacent Palladium and Gold in Alloy Nanoparticles for the Versatile and Practical [2+2+2] Cycloaddition of Alkynes ()
Abstract A Pd‐Au alloy efficiently catalyzed the [2+2+2] cycloaddition of substituted alkynes. Whereas monometallic Pd and Au catalysts were totally ineffective, Pd‐Au alloy nanoparticle catalysts with a low Pd/Au molar ratio showed high activity to give the corresponding polysubstituted arenes in high yields. A variety of substituted alkynes participated in various modes of cycloaddition under Pd‐Au alloy catalysis. The Pd‐Au alloy catalysts exhibited high air tolerance and reusability.
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Local Atomic Arrangements and Band Structure of Boron Carbide ()
Abstract Boron carbide, the simple chemical combination of boron and carbon, is one of the best‐known binary ceramic materials. Despite that, a coherent description of its crystal structure and physical properties resembles one of the most challenging problems in materials science. By combining ab initio computational studies, precise crystal structure determination from diffraction experiments, and state‐of‐the‐art high‐resolution transmission electron microscopy imaging, this concerted investigation reveals hitherto unknown local structure modifications together with the known structural alterations. The mixture of different local atomic arrangements within the real crystal structure reduces the electron deficiency of the pristine structure CBC+B12, answering the question about electron precise character of boron carbide and introducing new electronic states within the band gap, which allow a better understanding of physical properties.
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Octacarbonyl Anion Complexes of Group Three Transition Metals [TM(CO)8]− (TM=Sc, Y, La) and the 18‐Electron Rule ()
Abstract We report the gas‐phase synthesis of stable 20‐electron carbonyl anion complexes of group 3 transition metals, TM(CO)8− (TM=Sc, Y, La), which are studied by mass‐selected infrared (IR) photodissociation spectroscopy. The experimentally observed species, which are the first octacarbonyl anionic complexes of a TM, are identified by comparison of the measured and calculated IR spectra. Quantum chemical calculations show that the molecules have a cubic (Oh) equilibrium geometry and a singlet (1A1g) electronic ground state. The 20‐electron systems TM(CO)8− are energetically stable toward loss of one CO ligand, yielding the 18‐electron complexes TM(CO)7− in the 1A1 electronic ground state; these exhibit a capped octahedral structure with C3v symmetry. Analysis of the electronic structure of TM(CO)8− reveals that there is one occupied valence molecular orbital with a2u symmetry, which is formed only by ligand orbitals without a contribution from the metal atomic orbitals. The adducts of TM(CO)8− fulfill the 18‐electron rule when only those valence electrons that occupy metal–ligand bonding orbitals are considered.
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Asymmetric Synthesis of Silicon‐Stereogenic Vinylhydrosilanes by Cobalt‐Catalyzed Regio‐ and Enantioselective Alkyne Hydrosilylation with Dihydrosilanes ()
Abstract The strategic carbon‐to‐silicon substitution at a stereogenic center can produce chiral silanes with significantly improved properties relative to their carbon congeners. We herein report an unprecedented cobalt‐catalyzed asymmetric hydrosilylation of unsymmetric alkynes with dihydrosilanes that furnishes silicon‐stereogenic vinylhydrosilanes with high regio‐ and enantioselectivity. The absolute configurations of the products were determined by chiroptical methods in combination with DFT calculations. The synthetic versatility of the vinylhydrosilanes as chiral building blocks was further demonstrated by asymmetric Si−H insertion and catalytic hydroboration reactions.
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Cyclic and Lasso Peptides: Sequence Determination, Topology Analysis, and Rotaxane Formation ()
Abstract A broadly applicable chemical cleavage methodology to facilitate MS/MS sequencing was developed for macrocyclic and lasso peptides, which hold promise as exciting new therapeutics. Existing methods such as Edman degradation, CNBr cleavage, and enzymatic digestion are either limited in scope or completely fail in cleavage of constrained nonribosomal peptides. Importantly, the new method was utilized for synthesizing a unique peptide‐based rotaxane (both cyclic and threaded) from the lasso peptide, benenodin‐1 ΔC5.
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From S,N‐Heteroacene to Large Discotic Polycyclic Aromatic Hydrocarbons (PAHs): Liquid Crystal versus Plastic Crystalline Materials with Tunable Mechanochromic Fluorescence ()
Abstract A novel type of discotic polycyclic aromatic hydrocarbon (PAH) based on an enlarged dibenzo[a,c]phenazine core has been developed. The large conjugated mesogenic core with increased dipole moment derived from S,N heteroatoms facilitates the formation of highly ordered columnar superstructures both in solution and bulk. Columnar mesophases, including liquid crystal (LC) and plastic crystal (PC) assemblies could form unprecedentedly based on the same PAH core. The cores are delicately modulated by the peripherical alkoxy chains. Both mesogens have mechanochromic fluorescent (MCF) character, which is also structure dependent and correlated with the different mesophase formation. For the first time, MCF properties can be realized in such a large conjugated mesogenic system.
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Selective Activation of a Prodrug by Thioredoxin Reductase Providing a Strategy to Target Cancer Cells ()
Abstract Elevated reactive oxygen species and antioxidant defense systems have been recognized as one of the hallmarks of cancer cells. As a major regulator of the cellular redox homeostasis, the selenoprotein thioredoxin reductase (TrxR) is increasingly considered as a promising target for anticancer drug development. The current approach to inhibit TrxR predominantly relies on the modification of the selenocysteine residue in the C‐terminal active site of the enzyme, in which it is hard to avoid the off‐target effects. By conjugating the anticancer drug gemcitabine with a 1,2‐dithiolane scaffold, an unprecedented prodrug strategy is disclosed that achieves a specific release of gemcitabine by TrxR in cells. As overexpression of TrxR is frequently found in different types of tumors, the TrxR‐dependent prodrugs are promising for further development as cancer chemotherapeutic agents.
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Enzymatic or In Vivo Installation of Propargyl Groups in Combination with Click Chemistry for the Enrichment and Detection of Methyltransferase Target Sites in RNA ()
Abstract m6A is the most abundant internal modification in eukaryotic mRNA. It is introduced by METTL3‐METTL14 and tunes mRNA metabolism, impacting cell differentiation and development. Precise transcriptome‐wide assignment of m6A sites is of utmost importance. However, m6A does not interfere with Watson–Crick base pairing, making polymerase‐based detection challenging. We developed a chemical biology approach for the precise mapping of methyltransferase (MTase) target sites based on the introduction of a bioorthogonal propargyl group in vitro and in cells. We show that propargyl groups can be introduced enzymatically by wild‐type METTL3‐METTL14. Reverse transcription terminated up to 65 % at m6A sites after bioconjugation and purification, hence enabling detection of METTL3‐METTL14 target sites by next generation sequencing. Importantly, we implemented metabolic propargyl labeling of RNA MTase target sites in vivo based on propargyl‐l‐selenohomocysteine and validated different types of known rRNA methylation sites.
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Reaction of B2(o‐tol)4 with CO and Isocyanides: Cleavage of the C≡O Triple Bond and Direct C−H Borylations ()
Abstract The reaction of highly Lewis acidic tetra(o‐tolyl)diborane(4) with CO afforded a mixture of boraindane and boroxine by the cleavage of the C≡O triple bond. 13C labeling experiments confirmed that the carbon atom in the boraindane stems from CO. Simultaneously, formation of boroxine 3 could be considered as borylene transfer to capture the oxygen atom from CO. The reaction of diborane(4) with tBu−NC afforded an azaallene, while the reaction with Xyl−NC furnished cyclic compounds by direct C−H borylations.
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Singly and Doubly 1,2‐Phenylene‐Inserted Porphyrin Arch‐Tape Dimers: Synthesis and Highly Contorted Structures ()
Abstract Singly and doubly 1,2‐phenylene‐inserted NiII porphyrin arch‐tape dimers 3 and 9 were synthesized from the corresponding β‐to‐β 1,2‐phenylene‐bridged NiII porphyrin dimers 5 and 11 via Ni0‐mediated reductive cyclization and DDQ/Sc(OTf)3‐promoted oxidative cyclization as key steps, respectively. Owing to the fused eight‐membered ring(s), 3 showed a more contorted structure than those of previously reported arch‐tape dimers 2 a and 2 b possessing a fused seven‐membered ring. Furthermore, 9 displayed much larger molecular contortion. As the molecular contortion increases, the Q band of the absorption spectrum becomes more red‐shifted and the electrochemcial HOMO–LUMO gap becomes smaller, reaching at 1294 nm and 0.77 eV in 9, respectively. The effect of molecular contortion on the electronic properties was studied by means of DFT calculations.
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A Multicontrolled Enamine Configurational Switch Undergoing Dynamic Constitutional Exchange ()
Abstract A multiresponsive enamine‐based molecular switch is presented, in which forward/backward configurational rotation around the C=C bond could be precisely controlled by the addition of an acid/base or metal ions. Fluorescence turn‐on/off effects and large Stokes shifts were observed while regulating the switching process with CuII. The enamine functionality furthermore enabled double dynamic regimes, in which configurational switching could operate in conjunction with constitutional enamine exchange of the rotor part. This behavior was used to construct a prototypical dynamic covalent switch system through enamine exchange with primary amines. The dynamic exchange process could be readily turned on/off by regulating the switch status with pH.
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Facile, Quick, and Gram‐Scale Synthesis of Ultralong‐Lifetime Room‐Temperature‐Phosphorescent Carbon Dots by Microwave Irradiation ()
Abstract Long‐lifetime room‐temperature phosphorescence (RTP) materials are important for many applications, but they are highly challenging materials owing to the spin‐forbidden nature of triplet exciton transitions. Herein, a facile, quick and gram‐scale method for the preparation of ultralong RTP (URTP) carbon dots (CDs) was developed via microwave‐assisted heating of ethanolamine and phosphoric acid aqueous solution. The CDs exhibit the longest RTP lifetime, 1.46 s (more than 10 s to naked eye) for CDs‐based materials to date. The doping of N and P elements is critical for the URTP which is considered to be favored by a n→π* transition facilitating intersystem crossing (ISC) for effectively populating triplet excitons. In addition, possibilities of formation of hydrogen bonds in the interior of the CDs may also play a significant role in producing RTP. Potential applications of the URTP CDs in the fields of anti‐counterfeiting and information protection are proposed and demonstrated.
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Synthesis and Stereochemical Revision of the C31–C67 Fragment of Amphidinol 3 ()
Abstract Amphidinol 3 (AM3) is a marine natural product produced by the dinoflagellate Amphidinium klebsii. Although the absolute configuration of AM3 was determined in 1999 by extensive NMR analysis and degradation of the natural product, it was a daunting task because of the presence of numerous stereogenic centers on the acyclic carbon chain and the limited availability from natural sources. Thereafter, revisions of the absolute configurations at C2 and C51 were reported in 2008 and 2013, respectively. Reported herein is the revised absolute configuration of AM3: 32S, 33R, 34S, 35S, 36S, and 38S based on the chemical synthesis of partial structures corresponding to the C31–C67 fragment of AM3 in combination with degradation of the natural product. The revised structure is unique in that both antipodal tetrahydropyran counterparts exist on a single carbon chain. The structural revision of AM3 may affect proposed structures of congeners related to the amphidinols.
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Alkyl Ethers as Traceless Hydride Donors in Brønsted Acid Catalyzed Intramolecular Hydrogen Atom Transfer ()
Abstract A new protocol for the deoxygenation of alcohols and the hydrogenation of alkenes under Brønsted acid catalysis has been developed. The method is based on the use of either a benzyl or isopropyl ether as a traceless hydrogen‐atom donor, and involves an intramolecular hydride transfer as a key step, which is achieved in a regio‐ and stereoselective manner.
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Synthesis of Densely Packaged, Ultrasmall Pt02 Clusters within a Thioether‐Functionalized MOF: Catalytic Activity in Industrial Reactions at Low Temperature ()
Abstract The gram‐scale synthesis, stabilization, and characterization of well‐defined ultrasmall subnanometric catalytic clusters on solids is a challenge. The chemical synthesis and X‐ray snapshots of Pt02 clusters, homogenously distributed and densely packaged within the channels of a metal–organic framework, is presented. This hybrid material catalyzes efficiently, and even more importantly from an economic and environmental viewpoint, at low temperature (25 to 140 °C), energetically costly industrial reactions in the gas phase such as HCN production, CO2 methanation, and alkene hydrogenations. These results open the way for the design of precisely defined catalytically active ultrasmall metal clusters in solids for technically easier, cheaper, and dramatically less‐dangerous industrial reactions.
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Selective Monomethylation of Amines with Methanol as the C1 Source ()
Abstract The N‐monomethyl functionality is a common motif in a variety of synthetic and natural compounds. However, facile access to such compounds remains a fundamental challenge in organic synthesis owing to selectivity issues caused by overmethylation. To address this issue, we have developed a method for the selective, catalytic monomethylation of various structurally and functionally diverse amines, including typically problematic primary aliphatic amines, using methanol as the methylating agent, which is a sustainable chemical feedstock. Kinetic control of the aliphatic amine monomethylation was achieved by using a readily available ruthenium catalyst at an adequate temperature under hydrogen pressure. Various substrates including bio‐related molecules and pharmaceuticals were selectively monomethylated, demonstrating the general utility of the developed method.
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Selective Polymerization Catalysis from Monomer Mixtures: Using a Commercial Cr‐Salen Catalyst To Access ABA Block Polyesters ()
Abstract ABA triblock polyesters are synthesized using a commercially available chromium salen catalyst, in one pot, from monomer mixtures comprising epoxide, anhydride and lactone. The catalysis is highly selective and applies a single catalyst in two distinct pathways. It occurs first by epoxide/anhydride ring‐opening copolymerization and subsequently by lactone ring‐opening polymerization. It is used to produce various new ABA polyester polyols; these polyols can undergo post‐functionalization and chain‐extension reactions. The ability to use a commercial catalyst and switchable catalysis with monomer mixtures is expected to facilitate future explorations of new classes of block polymers.
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Fast Sodium‐Ion Conductivity in Supertetrahedral Phosphidosilicates ()
Abstract Fast sodium‐ion conductors are key components of Na‐based all‐solid‐state batteries which hold promise for large‐scale storage of electrical power. We report the synthesis, crystal‐structure determination, and Na+‐ion conductivities of six new Na‐ion conductors, the phosphidosilicates Na19Si13P25, Na23Si19P33, Na23Si28P45, Na23Si37P57, LT‐NaSi2P3 and HT‐NaSi2P3, based entirely on earth‐abundant elements. They have SiP4 tetrahedra assembled interpenetrating networks of T3 to T5 supertetrahedral clusters and can be hierarchically assigned to sphalerite‐ or diamond‐type structures. 23Na solid‐state NMR spectra and geometrical pathway analysis show Na+‐ion mobility between the supertetrahedral cluster networks. Electrochemical impedance spectroscopy shows Na+‐ion conductivities up to σ (Na+)=4×10−4 S cm−1. The conductivities increase with the size of the supertetrahedral clusters through dilution of Na+‐ions as the charge density of the anionic networks decreases.
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In Situ Monitoring of RAFT Polymerization by Tetraphenylethylene‐Containing Agents with Aggregation‐Induced Emission Characteristics ()
Abstract A facile and efficient approach is demonstrated to visualize the polymerization in situ. A group of tetraphenylethylene (TPE)‐containing dithiocarbamates were synthesized and screened as agents for reversible addition fragmentation chain transfer (RAFT) polymerizations. The spatial‐temporal control characteristics of photochemistry enabled the RAFT polymerizations to be ON and OFF on demand under alternating visible light irradiation. The emission of TPE is sensitive to the local viscosity change owing to its aggregation‐induced emission characteristic. Quantitative information could be easily acquired by the naked eye without destroying the reaction system. Furthermore, the versatility of such a technique was well demonstrated by 12 different polymerization systems. The present approach thus demonstrated a powerful platform for understanding the controlled living radical polymerization process.
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Regioselective C−H Xanthylation as a Platform for Polyolefin Functionalization ()
Abstract Polyolefins that contain polar functional groups are important materials for next‐generation lightweight engineering thermoplastics. Post‐polymerization modification is an ideal method for the incorporation of polar groups into branched polyolefins; however, it typically results in chain scission events, which have deleterious effects on polymer properties. Herein, we report a metal‐free method for radical‐mediated C−H xanthylation that results in the regioselective functionalization of branched polyolefins without coincident polymer‐chain scission. This method enables a tunable degree of polymer functionalization and capitalizes on the versatility of the xanthate functional group to unlock a wide variety of C−H transformations previously inaccessible on branched polyolefins.
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Cleavable Binary Dyads: Simplifying Data Extraction and Increasing Storage Density in Digital Polymers ()
Abstract Digital polymers are uniform macromolecules that store monomer‐based binary sequences. Molecularly stored information is usually extracted from the polymer by a tandem mass spectrometry (MS/MS) measurement, in which the coded chains are fragmented to reveal each bit (i.e. basic coded monomer unit) of the sequence. Here, we show that data‐extraction can be greatly simplified by favoring the formation of MS/MS fragments containing two bits instead of one. In order to do so, digital poly(alkoxyamine phosphodiester)s, containing binary dyads in each repeat unit, were prepared by an orthogonal solid‐phase approach involving successive phosphoramidite and radical‐radical coupling steps. Three different sets of monomers were considered to build these polymers. In all cases, four coded building blocks—two hydroxy‐nitroxides and two phosphoramidite monomers—were required to build the dyads. Among the three studied monomer sets, one combination allowed synthesis of uniform sequence‐coded polymers. The resulting polymers led to clear dyad‐containing fragments in MS/MS and could therefore be efficiently decoded. Additionally, an algorithm was created to detect specific dyad fragments, thus enabling automated sequencing.
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Selective Hydrogenation of CO2 to Ethanol over Cobalt Catalysts ()
Abstract Methods for the hydrogenation of CO2 into valuable chemicals are in great demand but their development is still challenging. Herein, we report the selective hydrogenation of CO2 into ethanol over non‐noble cobalt catalysts (CoAlOx), presenting a significant advance for the conversion of CO2 into ethanol as the major product. By adjusting the composition of the catalysts through the use of different prereduction temperatures, the efficiency of CO2 to ethanol hydrogenation was optimized; the catalyst reduced at 600 ° gave an ethanol selectivity of 92.1 % at 140 °C with an ethanol time yield of 0.444 mmol g−1 h−1. Operando FT‐IR spectroscopy revealed that the high ethanol selectivity over the CoAlOx catalyst might be due to the formation of acetate from formate by insertion of *CHx, a key intermediate in the production of ethanol by CO2 hydrogenation.
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Dynamic Changes in the Structure, Chemical State and Catalytic Selectivity of Cu Nanocubes during CO2 Electroreduction: Size and Support Effects ()
Abstract In situ and operando spectroscopic and microscopic methods were used to gain insight into the correlation between the structure, chemical state, and reactivity of size‐ and shape‐controlled ligand‐free Cu nanocubes during CO2 electroreduction (CO2RR). Dynamic changes in the morphology and composition of Cu cubes supported on carbon were monitored under potential control through electrochemical atomic force microscopy, X‐ray absorption fine‐structure spectroscopy and X‐ray photoelectron spectroscopy. Under reaction conditions, the roughening of the nanocube surface, disappearance of the (100) facets, formation of pores, loss of Cu and reduction of CuOx species observed were found to lead to a suppression of the selectivity for multi‐carbon products (i.e. C2H4 and ethanol) versus CH4. A comparison with Cu cubes supported on Cu foils revealed an enhanced morphological stability and persistence of CuI species under CO2RR in the former samples. Both factors are held responsible for the higher C2/C1 product ratio observed for the Cu cubes/Cu as compared to Cu cubes/C. Our findings highlight the importance of the structure of the active nanocatalyst but also its interaction with the underlying substrate in CO2RR selectivity.
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Catalytic Asymmetric Dearomatization by Visible‐Light‐Activated [2+2] Photocycloaddition ()
Abstract A novel method for the catalytic asymmetric dearomatization by visible‐light‐activated [2+2] photocycloaddition with benzofurans and one example of a benzothiophene is reported, thereby providing chiral tricyclic structures with up to four stereocenters including quaternary stereocenters. The benzofurans and the benzothiophene are functionalized at the 2‐position with a chelating N‐acylpyrazole moiety which permits the coordination of a visible‐light‐activatable chiral‐at‐rhodium Lewis acid catalyst. Computational molecular modeling revealed the origin of the unusual regioselectivity and identified the heteroatom in the heterocycle to be key for the regiocontrol.
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Enantioselective Formal [3+2] Cycloaddition of Epoxides with Imines under Brønsted Base Catalysis: Synthesis of 1,3‐Oxazolidines with Quaternary Stereogenic Center ()
Abstract The formal [3+2] cycloaddition of epoxides and unsaturated compounds is a powerful methodology for the synthesis of densely functionalized five‐membered heterocyclic compounds containing oxygen. Described is a novel enantioselective formal [3+2] cycloaddition of epoxides under Brønsted base catalysis. The bis(guanidino)iminophosphorane as a chiral organosuperbase catalyst enabled the enantioselective reaction of β,γ‐epoxysulfones with imines, owing to its strong basicity and high stereocontrolling ability, to provide enantioenriched 1,3‐oxazolidines having two stereogenic centers, including a quaternary one, in a highly diastereo‐ and enantioselective manner.
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Divergent Control of Point and Axial Stereogenicity: Catalytic Enantioselective C−N Bond‐Forming Cross‐Coupling and Catalyst‐Controlled Atroposelective Cyclodehydration ()
Abstract Catalyst control over reactions that produce multiple stereoisomers is a challenge in synthesis. Control over reactions that involve stereogenic elements remote from one another is particularly uncommon. Additionally, catalytic reactions that address both stereogenic carbon centers and an element of axial chirality are also rare. Reported herein is a catalytic approach to each stereoisomer of a scaffold containing a stereogenic center remote from an axis of chirality. Newly developed peptidyl copper complexes catalyze an unprecedented remote desymmetrization involving enantioselective C−N bond‐forming cross‐coupling. Then, chiral phosphoric acid catalysts set an axis of chirality through an unprecedented atroposelective cyclodehydration to form a heterocycle with high diastereoselectivity. The application of chiral copper complexes and phosphoric acids provides access to each stereoisomer of a framework with two different elements of stereogenicity.
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Iridium‐Catalyzed Annulation Reactions of Thiophenes with Carboxylic Acids: Direct Evidence for a Heck‐type Pathway ()
Abstract The functionalization of thiophenes is a fundamental and important reaction. Herein, we disclose iridium‐catalyzed one‐pot annulation reactions of (benzo)thiophenes with (hetero)aromatic or α,β‐unsaturated carboxylic acids, which afford thiophene‐fused coumarin‐type frameworks. Dearomatization reactions of 2‐substituted thiophenes with α,β‐unsaturated carboxylic acids deliver various thiophene‐containing spirocyclic products. The occurrence of two interconnected reactions provides direct evidence for a Heck‐type pathway. The mechanistic scenario described herein is distinctly different from the SEAr and concerted metalation–protodemetalation (CMD) pathways encountered in the well‐described oxidative C−H/C−H cross‐coupling reactions of thiophenes with other heteroarenes.
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The Role of Bi3+ in Promoting and Stabilizing Iron Oxo Clusters in Strong Acid ()
Abstract Metal oxo clusters and metal oxides assemble and precipitate from water in processes that depend on pH, temperature, and concentration. Other parameters that influence the structure, composition, and nuclearity of “molecular” and bulk metal oxides are poorly understood, and have thus not been exploited. Herein, we show that Bi3+ drives the formation of aqueous Fe3+ clusters, usurping the role of pH. We isolated and structurally characterized a Bi/Fe cluster, Fe3BiO2(CCl3COO)8(THF)(H2O)2, and demonstrated its conversion into an iron Keggin ion capped by six Bi3+ irons (Bi6Fe13). The reaction pathway was documented by X‐ray scattering and mass spectrometry. Opposing the expected trend, increased cluster nuclearity required a pH decrease instead of a pH increase. We attribute this anomalous behavior of Bi/Fe(aq) solutions to Bi3+, which drives hydrolysis and condensation. Likewise, Bi3+ stabilizes metal oxo clusters and metal oxides in strongly acidic conditions, which is important in applications such as water oxidation for energy storage.
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Magnetic Mesoporous Silica Nanoparticles Cloaked by Red Blood Cell Membranes: Applications in Cancer Therapy ()
Abstract Targeted drug delivery is an emerging technological strategy that enables nanoparticle systems to be responsive for tumor therapy. Magnetic mesoporous silica nanoparticles (MMSNs) were cloaked with red blood cell membrane (RBC). This integrates long circulation, photosensitizer delivery, and magnetic targeting for cancer therapy. In vivo experiments demonstrate that RBC@MMSNs can avoid immune clearance and achieve magnetic field (MF)‐induced high accumulation in a tumor. When light irradiation is applied, singlet oxygen rapidly generates from hypocrellin B (HB)‐loaded RBC@MMSN and leads to the necrosis of tumor tissue. Such a RBC‐cloaked magnetic nanocarrier effectively integrates immunological adjuvant, photosensitizer delivery, MF‐assisted targeting photodynamic therapy, which provides an innovative strategy for cancer therapy.
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Multistate Photoswitches: Macrocyclic Dihydroazulene/Azobenzene Conjugates ()
Abstract Molecules comprised of three covalently linked bi‐stable switches can exist in states described by a combination of binary numbers, one for each individual switch: ⟨000⟩, ⟨001⟩, etc. Here we have linked three photo‐/thermoswitches together in a rigid macrocyclic structure, one azobenzene (bit no 1) and two dihydroazulenes (DHAs; bits no 2 and 3) and demonstrate how electronic interactions and unfavorable strain in some states can be used to control the speed by which a certain state is reached. More specifically, upon irradiation of state ⟨000⟩, the AZB isomerizes from trans to cis and the two DHAs to vinylheptafulvenes (VHFs), generating ⟨111⟩. The thermal VHF‐to‐DHA back‐reactions from this state also occur stepwise and can be accelerated by photo‐induced AZB cis‐to‐trans conversion, proceeding via ⟨011⟩ to ultimately furnish ⟨000⟩. Overall, the accessibility to a specific state of one bit was found to depend on the states of its neighboring bits.
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Singlet Oxygen and the Origin of Oxygen Functionalities on the Surface of Carbon Electrodes ()
Abstract The generation of oxygen‐containing functionalities on pristine carbon surfaces is investigated and shown to be light sensitive, specifically to infra‐red radiation. A mechanistic route involving singlet oxygen, 1O2, is proposed and evidenced.
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Phosphine‐Catalyzed Activation of Vinylcyclopropanes: Rearrangement of Vinylcyclopropylketones to Cycloheptenones ()
Abstract We report a phosphine‐catalyzed activation of electron‐deficient vinylcyclopropanes (VCPs) to generate an ambident C5 synthon that is poised to undergo consecutive reactions. The utility of the activation is demonstrated in a phosphine‐catalyzed rearrangement of vinylcyclopropylketones to cycloheptenones in good yields with a broad substrate scope. Mechanistic investigations support a stepwise process comprising homoconjugate addition, water‐assisted proton transfer, and 7‐endo‐trig SN2′ ring closure.
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Diverging Mechanisms: Cytochrome‐P450‐Catalyzed Demethylation and γ‐Lactone Formation in Bacterial Gibberellin Biosynthesis ()
Abstract Biosynthesis of the gibberellin (GA) plant hormones evolved independently in plants and microbes, but the pathways proceed by similar transformations. The combined demethylation and γ‐lactone ring forming transformation is of significant mechanistic interest, yet remains unclear. The relevant CYP112 from bacteria was probed by activity assays and 18O2‐labeling experiments. Notably, the ability of tert‐butyl hydroperoxide to drive this transformation indicates use of the ferryl‐oxo (Compound I) from the CYP catalytic cycle for this reaction. Together with the confirmed loss of C20 as CO2, this necessitates two catalytic cycles for carbon–carbon bond scission and γ‐lactone formation. The ability of CYP112 to hydroxylate the δ‐lactone form of GA15, shown by the labeling studies, is consistent with the implied use of a further oxygenated heterocycle in the final conversion of GA24 into GA9, with the partial labeling of GA9, thus demonstrating that CYP112 partitions its reactants between two diverging mechanisms.
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Biosynthesis of the Polycyclic System in the Antifungal HSAF and Analogues from Lysobacter enzymogenes ()
Abstract The biocontrol agent Lysobacter enzymogenes produces polycyclic tetramate macrolactams (PoTeMs), including the antifungal HSAF. To elucidate the biosynthesis of the cyclic systems, we identified eleven HSAF precursors/analogues with zero, one, two, or three rings through heterologous expression of the HSAF gene cluster. A series of combinatorial gene expression and deletion experiments showed that OX3 is the “gatekeeper” responsible for the formation of the first 5‐membered ring from lysobacterene A, OX1 and OX2 are responsible for formation of the second ring but with different selectivity, and OX4 is responsible for formation of the 6‐membered ring. In vitro experiments showed that OX4 is an NADPH‐dependent enzyme that catalyzes the reductive cyclization of 3‐dehydroxy alteramide C to form 3‐dehydroxy HSAF. Thus, the multiplicity of OX genes is the basis for the structural diversity of the HSAF family, which is the only characterized PoTeM cluster that involves four redox enzymes in the formation of the cyclic system.
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SrB5O7F3 Functionalized with [B5O9F3]6− Chromophores: Accelerating the Rational Design of Deep‐Ultraviolet Nonlinear Optical Materials ()
Abstract Fluorooxoborates, benefiting from the large optical band gap, high anisotropy, and ever‐greater possibility to form non‐centrosymmetric structures activated by the large polarization of [BOxF4−x](x+1)− building blocks, have been considered as the new fertile fields for searching the ultraviolet (UV) and deep‐UV nonlinear optical (NLO) materials. Herein, we report the first asymmetric alkaline‐earth metal fluorooxoborate SrB5O7F3, which is rationally designed by taking the classic Sr2Be2B2O7 (SBBO) as a maternal structure. Its [B5O9F3]6− fundamental building block with near‐planar configuration composed by two edge‐sharing [B3O6F2]5− rings in SrB5O7F3 has not been reported in any other borates. Solid state 19F and 11B magic‐angle spinning NMR spectroscopy verifies the presence of covalent B−F bonds in SrB5O7F3. Property characterizations reveal that SrB5O7F3 possesses the optical properties required for deep‐UV NLO applications, which make SrB5O7F3 a promising crystal that could produce deep‐UV coherent light by the direct SHG process.
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Bio‐inspired Domino oxa‐Michael/Diels–Alder/oxa‐Michael Dimerization of para‐Quinols ()
Abstract A bio‐inspired, pyrrolidine‐mediated, dimerization of para‐quinols has been developed. It represents one of the most complex, yet general, dimerization reactions ever disclosed, selectively forming four new bonds, four new rings, and eight new contiguous stereogenic centres. The para‐quinol starting materials are easily handled, bench‐stable compounds, accessed in just one step from aromatic feedstocks. The reaction can be scaled up to give grams of polycyclic material, primed for further elaboration.
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Mapping the Excited‐State Potential Energy Surface of a Photomolecular Motor ()
Abstract A detailed understanding of the operation and efficiency of unidirectional photomolecular rotary motors is essential for their effective exploitation in molecular nanomachines. Unidirectional motion relies on light‐driven conversion from a stable (1 a) to a metastable (1 b) conformation, which then relaxes through a thermally driven helix inversion in the ground state. The excited‐state surface has thus far only been experimentally characterised for 1 a. Here we probe the metastable, 1 b, excited state, utilising ultrafast transient absorption and femtosecond stimulated Raman spectroscopy. These reveal that the “dark” excited‐state intermediate between 1 a and 1 b has a different lifetime and structure depending on the initial ground‐state conformation excited. This suggests that the reaction coordinate connecting 1 a to 1 b differs to that for the reverse photochemical process. The result is contrasted with earlier calculations.
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Two Histidines in an α‐Helix: A Rigid Co2+‐Binding Motif for PCS Measurements by NMR Spectroscopy ()
Abstract Pseudocontact shifts (PCS) generated by paramagnetic metal ions present valuable long‐range information in the study of protein structural biology by nuclear magnetic resonance (NMR) spectroscopy. Faithful interpretation of PCSs, however, requires complete immobilization of the metal ion relative to the protein, which is difficult to achieve with synthetic metal tags. We show that two histidine residues in sequential turns of an α‐helix provide a binding site for a Co2+ ion, which positions the metal ion in a uniquely well‐defined and predictable location. Exchange between the bound and free cobalt is slow on the timescale defined by chemical shifts, but the NMR resonance assignments are nonetheless readily transferred from the diamagnetic to the paramagnetic NMR spectrum by an IzSz‐exchange experiment. The double‐histidine‐Co2+ motif offers a straightforward, inexpensive, and convenient way of generating precision PCSs in proteins.
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Localizing Antifungal Drugs to the Correct Organelle Can Markedly Enhance their Efficacy ()
Abstract A critical aspect of drug design is optimal target inhibition by specifically delivering the drug molecule not only to the target tissue or cell but also to its therapeutically active site within the cell. This study demonstrates, as a proof of principle, that drug efficacy can be increased considerably by a structural modification that targets it to the relevant organelle. Specifically, by varying the fluorescent dye segment an antifungal azole was directed from the fungal cell mitochondria to the endoplasmic reticulum (ER), the organelle that harbors the drug target. The ER‐localized azole displayed up to two orders of magnitude improved antifungal activity and also dramatically reduced the growth of drug‐tolerant fungal subpopulations in a panel of Candida species, which are the most prevalent causes of serious human fungal infections. The principle underlying the “target organelle localization” approach provides a new paradigm to improve drug potency and replenish the limited pipeline of antifungal drugs.
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Coadsorbate‐Induced Reversal of Solid–Liquid Interface Dynamics ()
Abstract Coadsorbed anions are well‐known to influence surface reactivity and dynamics at solid–liquid interfaces. Here we demonstrate that the chemical nature of these spectator species can entirely determine the microscopic dynamic behavior. Quantitative in situ video‐STM data on the surface diffusion of adsorbed sulfur atoms on Cu(100) electrodes in aqueous solution covered by bromide and chloride spectators, respectively, reveal in both cases a strong exponential potential dependence, but with opposite sign. This reversal is highly surprising in view of the isostructural adsorbate arrangement in the two systems. Detailed DFT studies suggest an anion‐induced difference in the sulfur diffusion mechanism, specifically an exchange diffusion on the Br‐covered surface. Experimental evidence for the latter is provided by the observation of Cu vacancy formation in the Br system, which can be rationalized by a side reaction of the sulfur exchange diffusion.
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Realization of Walnut‐Shaped Particles with Macro‐/Mesoporous Open Channels through Pore Architecture Manipulation and Their Use in Electrocatalytic Oxygen Reduction ()
Abstract Herein we report a simple dual‐soft‐template approach to prepare walnut‐shaped macro‐/mesoporous polydopamine particles with diameter of ca. 270 nm, highly accessible bicontinuous channels and wide pore size distribution from ca. 20 nm to ca. 95 nm. This approach provides great opportunities to tailor the soft template‐directed assembly processes and generate various polydopamine particles with controllable mesophase curvature. Walnut‐shaped mesoporous carbon particles with large open mesochannels in the range of ca. 13 nm to ca. 50 nm can be fabricated by subsequent thermal treatment under nitrogen atmosphere. Lastly, we demonstrate that the as‐derived walnut‐shaped carbon particles manifest enhanced electrocatalytic performance for oxygen reduction reaction in alkaline electrolyte.
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Copper‐Catalyzed Heteroarylboration of 1,3‐Dienes with 3‐Bromopyridines: A cine Substitution ()
Abstract A method for the heteroarylboration of 1,3‐dienes is presented. The process involves an unusual cine substitution of 3‐bromopyridine derivatives to deliver highly functionalized heterocyclic products. Mechanistic studies are included that clarify the details of this unusual process.
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Divergent Total Syntheses of Enmein‐Type Natural Products: (−)‐Enmein, (−)‐Isodocarpin, and (−)‐Sculponin R ()
Abstract Divergent total syntheses of the enmein‐type natural products (−)‐enmein, (−)‐isodocarpin, and (−)‐sculponin R have been achieved in a concise fashion. Key features of the strategy include 1) an efficient early‐stage cage formation to control succeeding diastereoselectivity, 2) a one‐pot acylation/akylation/lactonization to construct the C‐ring and C8 quarternary center, 3) a reductive alkenylation approach to construct the enmain D/E rings and 4) a flexible route to allow divergent syntheses of three natural products.
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Amyloid‐β Peptide Induces Prion Protein Amyloid Formation: Evidence for Its Widespread Amyloidogenic Effect ()
Abstract Transmissible spongiform encephalopathy is associated with misfolding of prion protein (PrP) into an amyloid β‐rich aggregate. Previous studies have indicated that PrP interacts with Alzheimer′s disease amyloid‐β peptide (Aβ), but it remains elusive how this interaction impacts on the misfolding of PrP. This study presents the first in vitro evidence that Aβ induces PrP‐amyloid formation at submicromolar concentrations. Interestingly, systematic mutagenesis of PrP revealed that Aβ requires no specific amino acid sequences in PrP, and induces the misfolding of other unrelated proteins (insulin and lysozyme) into amyloid fibrils in a manner analogous to PrP. This unanticipated nonspecific amyloidogenic effect of Aβ indicates that this peptide might be involved in widespread protein aggregation, regardless of the amino acid sequences of target proteins, and exacerbate the pathology of many neurodegenerative diseases.
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Fluorine‐Free Synthesis of High‐Purity Ti3C2Tx (T=OH, O) via Alkali Treatment ()
Abstract MXenes, 2D compounds generated from layered bulk materials, have attracted significant attention in energy‐related fields. However, most syntheses involve HF, which is highly corrosive and harmful to lithium‐ion battery and supercapacitor performance. Here an alkali‐assisted hydrothermal method is used to prepare a MXene Ti3C2Tx (T=OH, O). This route is inspired from a Bayer process used in bauxite refining. The process is free of fluorine and yields multilayer Ti3C2Tx with ca. 92 wt % in purity (using 27.5 m NaOH, 270 °C). Without the F terminations, the resulting Ti3C2Tx film electrode (ca. 52 μm in thickness, ca. 1.63 g cm−3 in density) is 314 F g−1 via gravimetric capacitance at 2 mV s−1 in 1 m H2SO4. This surpasses (by ca. 214 %) that of the multilayer Ti3C2Tx prepared via HF treatments. This fluorine‐free method also provides an alkali‐etching strategy for exploring new MXenes for which the interlayer amphoteric/acidic atoms from the pristine MAX phase must be removed.
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Two‐Dimensional Fullerene Assembly from an Exfoliated van der Waals Template ()
Abstract Two‐dimensional (2D) materials are commonly prepared by exfoliating bulk layered van der Waals crystals. The creation of synthetic 2D materials from bottom‐up methods is an important challenge as their structural flexibility will enable chemists to tune the materials properties. A 2D material was assembled using C60 as a polymerizable monomer. The C60 building blocks are first assembled into a layered solid using a molecular cluster as structure director. The resulting hierarchical crystal is used as a template to polymerize its C60 monolayers, which can be exfoliated down to 2D crystalline nanosheets. Derived from the parent template, the 2D structure is composed of a layer of inorganic cluster, sandwiched between two monolayers of polymerized C60. The nanosheets can be transferred onto solid substrates and depolymerized by heating. Electronic absorption spectroscopy reveals an optical gap of 0.25 eV, narrower than that of the bulk parent crystalline solid.
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Highly Efficient Supramolecular Catalysis by Endowing the Reaction Intermediate with Adaptive Reactivity ()
Abstract A new strategy of highly efficient supramolecular catalysis is developed by endowing the reaction intermediate with adaptive reactivity. The supramolecular catalyst, prepared by host–guest complexation between 2,2,6,6‐tetramethylpiperidin‐1‐oxyl (TEMPO) and cucurbit[7]uril (CB[7]), was used for biphasic oxidation of alcohols. Cationic TEMPO+, the key intermediate, was stabilized by the electrostatic effect of CB[7] in aqueous phase, thus promoting the formation of TEMPO+ and inhibiting side reactions. Moreover, through the migration into the organic phase, TEMPO+ was separated from CB[7] and recovered the high reactivity to drive a fast oxidation of substrates. The adaptive reactivity of TEMPO+ induced an integral optimization of the catalytic cycle and greatly improved the conversion of the reaction. This work highlights the unique advantages of dynamic noncovalent interactions on modulating the activity of reaction intermediates, which may open new horizons for supramolecular catalysis.
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Stereoselective Synthesis of 2‐Deoxyglycosides from Glycals by Visible‐Light‐Induced Photoacid Catalysis ()
Abstract The direct, photoacid‐catalyzed synthesis of 2‐deoxyglycosides from glycals is reported. A series of phenol‐conjugated acridinium‐based organic photoacids were rationally designed, synthesized, and studied alongside the commercially available phenolic catalyst eosin Y. In the presence of such a photoacid catalyst and light, synthetic glycals were activated and coupled with a range of alcohols to afford 2‐deoxyglycosides in good yields and with excellent α‐selectivity.
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Pb2BO3I: A Borate Iodide with the Largest Second‐Harmonic Generation (SHG) Response in the KBe2BO3F2 (KBBF) Family of Nonlinear Optical (NLO) Materials ()
Abstract Borate halides are an ideal materials class from which to design high‐performance nonlinear optical (NLO) materials. Currently, borate fluorides, chlorides, and bromides are extensively investigated while borate iodide materials discovery remains rare because of the perceived synthetic challenges. We report a new borate iodide, Pb2BO3I, synthesized by a straightforward hydrothermal method. The Pb2BO3I chemical formula conceals that the compound exhibits a structure similar to the well‐established KBe2BO3F2 (KBBF), which we show supports the highest second‐harmonic generation (SHG) at 1064 nm in the KBBF family, 10 × KH2PO4 (KDP), arising from the inclusion of Pb2+ and I− and the crystal chemistry. Our work shows that KBBF‐related compounds can be synthesized incorporating iodide and exhibit superior NLO responses.
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Homo‐Helical Rod Packing as a Path Toward the Highest Density of Guest‐Binding Metal Sites in Metal–Organic Frameworks ()
Abstract In porous materials, metal sites with coordinate solvents offer opportunities for many applications, especially those promoted by host–guest chemistry, but such sites are especially hard to create for Li‐based materials, because unlike transition metals, lithium does not usually possess a high‐enough coordination number for both framework construction and guest binding. This challenge is addressed by mimicking the functional group ratio and metal‐to‐ligand charge ratio in MOF‐74. A family of rod‐packing lithium–organic frameworks (CPM‐47, CPM‐48, and CPM‐49) were obtained. These materials exhibit an extremely high density of guest‐binding lithium sites. Also unusual is the homo‐helical rod‐packing in the CPM series, as compared to the hetero‐helical rod packing by helices of opposite handedness in MOF‐74. This work demonstrates new chemical and structural possibilities in developing a record‐setting high density of guest‐binding metal sites in inorganic–organic porous materials.
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Modulating the Folding Landscape of Superoxide Dismutase 1 with Targeted Molecular Binders ()
Abstract Amyotrophic lateral sclerosis, or Lou Gehrig's disease, is characterized by motor neuron death, with average survival times of two to five years. One cause of this disease is the misfolding of superoxide dismutase 1 (SOD1), a phenomenon influenced by point mutations spanning the protein. Herein, we used an epitope‐specific high‐throughput screen to identify a peptide ligand that stabilizes the SOD1 native conformation and accelerates its folding by a factor of 2.5. This strategy may be useful for fundamental studies of protein energy landscapes as well as designing new classes of therapeutics.
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Postsynthetic Functionalization of Three‐Dimensional Covalent Organic Frameworks for Selective Extraction of Lanthanide Ions ()
Abstract Chemical functionalization of covalent organic frameworks (COFs) is critical for tuning their properties and broadening their potential applications. However, the introduction of functional groups, especially to three‐dimensional (3D) COFs, still remains largely unexplored. Reported here is a general strategy for generating a 3D carboxy‐functionalized COF through postsynthetic modification of a hydroxy‐functionalized COF, and for the first time exploration of the 3D carboxy‐functionalized COF in the selective extraction of lanthanide ions. The obtained COF shows high crystallinity, good chemical stability, and large specific surface area. Furthermore, the carboxy‐functionalized COF displays high metal loading capacities together with excellent adsorption selectivity for Nd3+ over Sr2+ and Fe3+ as confirmed by the Langmuir adsorption isotherms and ideal adsorbed solution theory (IAST) calculations. This study not only provides a strategy for versatile functionalization of 3D COFs, but also opens a way to their use in environmentally related applications.
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Thiophene‐Fused‐Heteroaromatic Diones as Promising NIR Reflectors for Radiative Cooling ()
Abstract Developing appropriate NIR‐reflective materials to combat near–infrared (NIR) heat radiation (700–2500 nm) from sunlight, avoiding energy accumulation and reduce energy consumption, is important and highly desirable. In this research, four thiophene‐fused‐heteroaromatic diones were used as basic reflectors to investigate the relationship between their intrinsic molecular structures and NIR‐reflective properties. The reflectance intensity can be readily tuned by adjusting the length of the appended aliphatic side chains, as well as the strength of the electron‐donating groups. A methoxy‐substituted thiophene‐fused‐heteroaromatic dione showed the best performance in reflecting NIR, and it was used as a coating for a model glass house. The comparison of the internal temperature difference relative to a control house was measured and the maximum temperature was 12 °C lower than that in the control house.
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Palladium‐Catalyzed para‐Selective Alkylation of Electron‐Deficient Arenes ()
Abstract Intermolecular alkylations of electron‐deficient arenes proceed with good para selectivity. Palladium catalysts were used to generate nucleophilic alkyl radicals from alkyl halides, which then directly add onto the arenes. The arene scope and the site of alkylation are opposite to those of classical Friedel–Crafts alkylations, which prefer electron‐rich systems.
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Site‐Directed Dimerization of Bowl‐Shaped Radical Anions to Form a σ‐Bonded Dibenzocorannulene Dimer ()
Abstract Designed site‐directed dimerization of the monoanion radicals of a π‐bowl in the solid state is reported. Dibenzo[a,g]corannulene (C28H14) was selected based on the asymmetry of the charge/spin localization in the C28H14.− anion. Controlled one‐electron reduction of C28H14 with Cs metal in diglyme resulted in crystallization of a new dimer, [{Cs+(diglyme)}2(C28H14−C28H14)2−] (1), as revealed by single crystal X‐ray diffraction study performed in a broad range of temperatures. The C−C bond length between two C28H14.− bowls (1.560(8) Å) measured at −143 °C does not significantly change upon heating of the crystal to +67 °C. The single σ‐bond character of the C−C linker is confirmed by calculations. The trans‐disposition of two bowls in 1 is observed with the torsion angles around the central C−C bond of 172.3(5)° and 173.5(5)°. A systematic theoretical evaluation of dimerization pathways of C28H14.− radicals confirmed that the trans‐isomer found in 1 is energetically favored.
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An Amorphous Noble‐Metal‐Free Electrocatalyst that Enables Nitrogen Fixation under Ambient Conditions ()
Abstract N2 fixation by the electrocatalytic nitrogen reduction reaction (NRR) under ambient conditions is regarded as a potential approach to achieve NH3 production, which still heavily relies on the Haber–Bosch process at the cost of huge energy and massive production of CO2. A noble‐metal‐free Bi4V2O11/CeO2 hybrid with an amorphous phase (BVC‐A) is used as the cathode for electrocatalytic NRR. The amorphous Bi4V2O11 contains significant defects, which play a role as active sites. The CeO2 not only serves as a trigger to induce the amorphous structure, but also establishes band alignment with Bi4V2O11 for rapid interfacial charge transfer. Remarkably, BVC‐A shows outstanding electrocatalytic NRR performance with high average yield (NH3: 23.21 μg h−1 mg−1cat., Faradaic efficiency: 10.16 %) under ambient conditions, which is superior to the Bi4V2O11/CeO2 hybrid with crystalline phase (BVC‐C) counterpart.
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Bottleable Neutral Analogues of [B2H5]− as Versatile and Strongly Binding η2 Donor Ligands ()
Abstract Herein we report the discovery that two bottleable, neutral, base‐stabilized diborane(5) compounds are able to bind strongly to a number of copper(I) complexes exclusively through their B−B bond. The resulting complexes represent the first known complexes containing unsupported, neutral σB−B diborane ligands. Single‐crystal X‐ray analyses of these complexes show that the X−Cu moiety (X=Cl, OTf, C6F5) lies opposite the bridging hydrogen atom of the diborane and is near perpendicular to the B−B bond, interacting almost equally with both boron atoms and causing a B−B bond elongation. DFT studies show that σ donation from and π backdonation to the pseudo‐π‐like B−B bond account for their formation. Astoundingly, these copper σB−B complexes are inert to ligand exchange with pyridine under either heating or photoirradiation.
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Catalytic Dinitrogen Reduction to Ammonia at a Triamidoamine–Titanium Complex ()
Abstract Catalytic reduction of N2 to NH3 by a Ti complex has been achieved, thus now adding an early d‐block metal to the small group of mid‐ and late‐d‐block metals (Mo, Fe, Ru, Os, Co) that catalytically produce NH3 by N2 reduction and protonolysis under homogeneous, abiological conditions. Reduction of [TiIV(TrenTMS)X] (X=Cl, 1A; I, 1B; TrenTMS=N(CH2CH2NSiMe3)3) with KC8 affords [TiIII(TrenTMS)] (2). Addition of N2 affords [{(TrenTMS)TiIII}2(μ‐η1:η1‐N2)] (3); further reduction with KC8 gives [{(TrenTMS)TiIV}2(μ‐η1:η1:η2:η2‐N2K2)] (4). Addition of benzo‐15‐crown‐5 ether (B15C5) to 4 affords [{(TrenTMS)TiIV}2(μ‐η1:η1‐N2)][K(B15C5)2]2 (5). Complexes 3–5 treated under N2 with KC8 and [R3PH][I], (the weakest H+ source yet used in N2 reduction) produce up to 18 equiv of NH3 with only trace N2H4. When only acid is present, N2H4 is the dominant product, suggesting successive protonation produces [{(TrenTMS)TiIV}2(μ‐η1:η1‐N2H4)][I]2, and that extruded N2H4 reacts further with [R3PH][I]/KC8 to form NH3.
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Mark Stradiotto ()
Angewandte Chemie International Edition, Volume 57, Issue 21, Page 5986-5986, May 22, 2018.
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Machine Learning for Organic Synthesis: Are Robots Replacing Chemists? ()
Angewandte Chemie International Edition, EarlyView.
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Metal‐Free Nitrogen Fixation at Boron ()
Angewandte Chemie International Edition, EarlyView.
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Sustainable Phosphorus Chemistry: A Silylphosphide Synthon for the Generation of Value‐Added Phosphorus Chemicals ()
Angewandte Chemie International Edition, EarlyView.
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Catalysis: An Integrated Textbook for Students. Edited by Ulf Hanefeld and Leon Lefferts. ()
Angewandte Chemie International Edition, EarlyView.
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Super‐Resolution Microscopy. A Practical Guide. By Udo J. Birk. ()
Angewandte Chemie International Edition, EarlyView.
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CNRS Silver and Bronze Medals 2018 ()
Angewandte Chemie International Edition, EarlyView.
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Robert Foster Cherry Award for Neil K. Garg/Innovation Prize in Medicinal/Pharmaceutical Chemistry ()
Angewandte Chemie International Edition, EarlyView.
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Chemistry Has No Nationality ()
Angewandte Chemie International Edition, EarlyView.
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Heritage Science: A Future‐Oriented Cross‐Disciplinary Field ()
Angewandte Chemie International Edition, EarlyView.
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The Energy Challenge, Batteries, and Why Simple Math Matters ()
Angewandte Chemie International Edition, EarlyView.
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Thoughts on Chemistry and Scientific Truth in Post‐Factual Times ()
Angewandte Chemie International Edition, EarlyView.
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Global Food‐Related Challenges: What Chemistry Has Achieved and What Remains to Be Done ()
Angewandte Chemie International Edition, EarlyView.
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Christoph Rüchardt (1929–2018) ()
Angewandte Chemie International Edition, EarlyView.
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Porous Polyelectrolytes: The Interplay of Charge and Pores for New Functionalities ()
Angewandte Chemie International Edition, EarlyView.
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Cobalt‐Catalyzed Tandem C−H Activation/C−C Cleavage/C−H Cyclization of Aromatic Amides with Alkylidenecyclopropanes ()
Angewandte Chemie International Edition, EarlyView.
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Polyvalent Display of Biomolecules on Live Cells ()
Angewandte Chemie International Edition, EarlyView.
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A Regularly Channeled Lamellar Membrane for Unparalleled Water and Organics Permeation ()
Angewandte Chemie International Edition, EarlyView.
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Silica‐Protection‐Assisted Encapsulation of Cu2O Nanocubes into a Metal–Organic Framework (ZIF‐8) To Provide a Composite Catalyst ()
Angewandte Chemie International Edition, EarlyView.
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An Extra‐Large‐Pore Zeolite with 24×8×8‐Ring Channels Using a Structure‐Directing Agent Derived from Traditional Chinese Medicine ()
Angewandte Chemie International Edition, EarlyView.
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Electron Transfer around a Molecular Corner ()
Angewandte Chemie International Edition, EarlyView.
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G‐Quadruplex Secondary Structure Obtained from Circular Dichroism Spectroscopy ()
Angewandte Chemie International Edition, EarlyView.
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Rediscovering Ducos du Hauron's Color Photography through a Review of His Three‐Color Printing Processes and Synchrotron Microanalysis of His Prints ()
Angewandte Chemie International Edition, EarlyView.
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A Planar‐Chiral Rhodium(III) Catalyst with a Sterically Demanding Cyclopentadienyl Ligand and Its Application in the Enantioselective Synthesis of Dihydroisoquinolones ()
Angewandte Chemie International Edition, EarlyView.
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Transition‐Metal‐Like Behavior of Monovalent Boron Compounds: Reduction, Migration, and Complete Cleavage of CO at a Boron Center ()
Angewandte Chemie International Edition, EarlyView.
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A Dynamic Chemical Network for Cystinuria Diagnosis ()
Angewandte Chemie International Edition, EarlyView.
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Optogenetic Control of Voltage‐Gated Calcium Channels ()
Angewandte Chemie International Edition, EarlyView.
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Chemical Mapping by Macroscopic X‐Ray Powder Diffraction of Van Gogh's Sunflowers: Identification of Areas with Higher Degradation Risk ()
Angewandte Chemie International Edition, EarlyView.
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Control of Molar Mass Distribution by Polymerization in the Analytical Ultracentrifuge ()
Angewandte Chemie International Edition, EarlyView.
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Mapping the Relationship between Glycosyl Acceptor Reactivity and Glycosylation Stereoselectivity ()
Angewandte Chemie International Edition, EarlyView.
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Valency‐Controlled Framework Nucleic Acid Signal Amplifiers ()
Angewandte Chemie International Edition, EarlyView.
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Transient and Persistent Room‐Temperature Mechanoluminescence from a White‐Light‐Emitting AIEgen with Tricolor Emission Switching Triggered by Light ()
Angewandte Chemie International Edition, EarlyView.
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Emergence of Uranium as a Distinct Metal Center for Building Intrinsic X‐ray Scintillators ()
Angewandte Chemie International Edition, EarlyView.
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Visible‐Light‐Induced Nickel‐Catalyzed Negishi Cross‐Couplings by Exogenous‐Photosensitizer‐Free Photocatalysis ()
Angewandte Chemie International Edition, EarlyView.
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Engineering Fast Ion Conduction and Selective Cation Channels for a High‐Rate and High‐Voltage Hybrid Aqueous Battery ()
Angewandte Chemie International Edition, EarlyView.
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Another Unprecedented Wieland Mechanism Confirmed: Hydrogen Formation from Hydrogen Peroxide, Formaldehyde, and Sodium Hydroxide ()
Angewandte Chemie International Edition, EarlyView.
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Reversible Magnetic Agglomeration: A Mechanism for Thermodynamic Control over Nanoparticle Size ()
Angewandte Chemie International Edition, EarlyView.
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A Vastly Increased Chemical Variety of RNA Modifications Containing a Thioacetal Structure ()
Angewandte Chemie International Edition, EarlyView.
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From Linear to Angular Isomers: Achieving Tunable Charge Transport in Single‐Crystal Indolocarbazoles Through Delicate Synergetic CH/NH⋅⋅⋅π Interactions ()
Angewandte Chemie International Edition, EarlyView.
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Metal‐ and Base‐Free Room‐Temperature Amination of Organoboronic Acids with N‐Alkyl Hydroxylamines ()
Angewandte Chemie International Edition, EarlyView.
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A Synchrotron‐Based Study of the Mary Rose Iron Cannonballs ()
Angewandte Chemie International Edition, EarlyView.
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Transport of Nucleoside Triphosphates into Cells by Artificial Molecular Transporters ()
Angewandte Chemie International Edition, EarlyView.
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Rational Tuning of Fluorobenzene Probes for Cysteine‐Selective Protein Modification ()
Angewandte Chemie International Edition, EarlyView.
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Exploring the Performance Improvement of the Oxygen Evolution Reaction in a Stable Bimetal–Organic Framework System ()
Angewandte Chemie International Edition, EarlyView.
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Desktop NMR and Its Applications From Materials Science To Organic Chemistry ()
Abstract NMR spectroscopy is an indispensable method of analysis in chemistry, which until recently suffered from high demands for space, high costs for acquisition and maintenance, and operational complexity. This has changed with the introduction of compact NMR spectrometers suitable for small‐molecule analysis on the chemical workbench. These spectrometers contain permanent magnets giving rise to proton NMR frequencies between 40 and 80 MHz. The enabling technology is to make small permanent magnets with homogeneous fields. Tabletop instruments with inhomogeneous fields have been in use for over 40 years for characterizing food and hydrogen‐containing materials by relaxation and diffusion measurements. Related NMR instruments measure these parameters in the stray field outside the magnet. They are used to inspect the borehole walls of oil wells and to test objects nondestructively. The state‐of‐the‐art of NMR spectroscopy, imaging and relaxometry with compact instruments is reviewed.
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Microemulsions, Micelles, and Functional Gels: How Colloids and Soft Matter Preserve Works of Art ()
Abstract Colloid science provides fundamental knowledge to fields such as the pharmaceutical, detergency, paint, and food industry. An exciting application is art conservation, which poses a challenge owing to the complex range of interfacial interactions involved in restoring artefacts. Currently, the majority of the most performing and environmentally safe cleaning and consolidation agents for artworks belong to soft matter and colloids. The development and application of increasingly complex systems, from microemulsions to semi‐interpenetrating hydrogels containing such fluids, is presented. These systems have been used on diverse artefacts, from Renaissance frescos to works by Picasso and Pollock. Chemical design can be implemented to meet the requirements of curators, and knowledge of the colloid structure and dynamics can overcome serendipitous approaches of traditional conservation practice. Future perspectives for soft matter and colloid science in the field of cultural heritage preservation are also summarized.
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Cross‐Linking/Mass Spectrometry for Studying Protein Structures and Protein–Protein Interactions: Where Are We Now and Where Should We Go from Here? ()
Abstract Structural mass spectrometry (MS) is gaining increasing importance for deriving valuable three‐dimensional structural information on proteins and protein complexes, and it complements existing techniques, such as NMR spectroscopy and X‐ray crystallography. Structural MS unites different MS‐based techniques, such as hydrogen/deuterium exchange, native MS, ion‐mobility MS, protein footprinting, and chemical cross‐linking/MS, and it allows fundamental questions in structural biology to be addressed. In this Minireview, I will focus on the cross‐linking/MS strategy. This method not only delivers tertiary structural information on proteins, but is also increasingly being used to decipher protein interaction networks, both in vitro and in vivo. Cross‐linking/MS is currently one of the most promising MS‐based approaches to derive structural information on very large and transient protein assemblies and intrinsically disordered proteins.
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Signal Amplification by Reversible Exchange (SABRE): From Discovery to Diagnosis ()
Abstract Signal amplification by reversible exchange (SABRE) turns typically weak magnetic resonance responses into strong signals making previously impractical measurements possible. This technique has gained significant popularity because of its speed and simplicity. This Minireview tracks the development of SABRE from the initial hyperpolarization of pyridine in 2009 to the point in which 50 % 1H polarization levels have been achieved in a di‐deuterio‐nicotinate, a key step in the pathway to potential clinical use. Simple routes to highly efficient 15N hyperpolarization and the creation of hyperpolarized long‐lived magnetic states are illustrated. To conclude, we describe how the recently reported SABRE‐RELAY approach offers a route for parahydrogen to hyperpolarize a much wider array of molecular scaffolds, such as amides, alcohols, carboxylic acids, and phosphates, than was previously thought possible. We predict that collectively these developments ensure that SABRE will significantly impact on both chemical analysis and the diagnosis of disease in the future.
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Paleo‐inspired Systems: Durability, Sustainability, and Remarkable Properties ()
Abstract The process of mimicking properties of specific interest (such as mechanical, optical, and structural) observed in ancient and historical systems is designated here as paleo‐inspiration. For instance, recovery in archaeology or paleontology identifies materials that are a posteriori extremely resilient to alteration. All the more encouraging is that many ancient materials were synthesized in soft chemical ways, often using low‐energy resources and sometimes rudimentary manufacturing equipment. In this Minireview, ancient systems are presented as a source of inspiration for innovative material design in the Anthropocene.
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Cultural Heritage Studies with Mobile NMR ()
Abstract Nuclear magnetic resonance (NMR) provides in situ information about selected isotope densities in samples and objects, while also providing contrast through rotational and translational molecular dynamics. These parameters are probed not only in NMR spectroscopy and imaging but also in nondestructive materials testing by mobile stray‐field NMR, the unique properties of which are valuable in cultural heritage studies. We present recent progress in the analysis of cultural heritage with mobile 1H NMR stray‐field sensors, for which the detection zone is outside of the NMR magnet. Prominent applications include the analysis of stratigraphies in paintings and frescoes, and the assessment of material states changing under the impact of aging, conservation, and restoration.
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Stimuli‐Responsive NO Release for On‐Demand Gas‐Sensitized Synergistic Cancer Therapy ()
Abstract Featuring high biocompatibility, the emerging field of gas therapy has attracted extensive attention in the medical and scientific communities. Currently, considerable research has focused on the gasotransmitter nitric oxide (NO) owing to its unparalleled dual roles in directly killing cancer cells at high concentrations and cooperatively sensitizing cancer cells to other treatments for synergistic therapy. Of particular note, recent state‐of‐the‐art studies have turned our attention to the chemical design of various endogenous/exogenous stimuli‐responsive NO‐releasing nanomedicines and their biomedical applications for on‐demand NO‐sensitized synergistic cancer therapy, which are discussed in this Minireview. Moreover, the potential challenges regarding NO gas therapy are also described, aiming to advance the development of NO nanomedicines as well as usher in new frontiers in this fertile research area.
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The Pre‐exponential Factor in Electrochemistry ()
Abstract Like many branches of science, not to mention culture in general, electrochemistry has a number of recurring topics: Areas of research that are popular for a certain time, then fade away as their possibilities seem to have been exhausted, only to return decades later as progress in experimental or theoretical techniques offer new possibilities for their investigation. A prime example are fuel cells, which have undergone five such cycles, but here we discuss a general concept of kinetics—the pre‐exponential factor of a rate constant—which has undergone two such cycles. The first cycle was in the 1950–1980s, when the methods of electrochemical kinetics were developed, and the interpretation was based on transition‐state theory. The second was triggered by the re‐discovery of Kramers theory for reactions in condensed phases. This Minireview will show that the time has come for a third cycle based on recent progress in electrocatalysis.
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Photobiocatalysis: Activating Redox Enzymes by Direct or Indirect Transfer of Photoinduced Electrons ()
Abstract Biocatalytic transformation has received increasing attention in the green synthesis of chemicals because of the diversity of enzymes, their high catalytic activities and specificities, and mild reaction conditions. The idea of solar energy utilization in chemical synthesis through the combination of photocatalysis and biocatalysis provides an opportunity to make the “green” process greener. Oxidoreductases catalyze redox transformation of substrates by exchanging electrons at the enzyme′s active site, often with the aid of electron mediator(s) as a counterpart. Recent progress indicates that photoinduced electron transfer using organic (or inorganic) photosensitizers can activate a wide spectrum of redox enzymes to catalyze fuel‐forming reactions (e.g., H2 evolution, CO2 reduction) and synthetically useful reductions (e.g., asymmetric reduction, oxygenation, hydroxylation, epoxidation, Baeyer–Villiger oxidation). This Review provides an overview of recent advances in light‐driven activation of redox enzymes through direct or indirect transfer of photoinduced electrons.
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The Hydrogen Evolution Reaction in Alkaline Solution: From Theory, Single Crystal Models, to Practical Electrocatalysts ()
Abstract The hydrogen evolution reaction (HER) is a fundamental process in electrocatalysis and plays an important role in energy conversion for the development of hydrogen‐based energy sources. However, the considerably slow rate of the HER in alkaline conditions has hindered advances in water splitting techniques for high‐purity hydrogen production. Differing from well documented acidic HER, the mechanistic aspects of alkaline HER are yet to be settled. A critical appraisal of alkaline HER electrocatalysis is presented, with a special emphasis on the connection between fundamental surface electrochemistry on single‐crystal models and the derived molecular design principle for real‐world electrocatalysts. By presenting some typical examples across theoretical calculations, surface characterization, and electrochemical experiments, we try to address some key ongoing debates to deliver a better understanding of alkaline HER at the atomic level.
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Electrobiorefineries: Unlocking the Synergy of Electrochemical and Microbial Conversions ()
Abstract An integrated biobased economy urges an alliance of the two realms of “chemical production” and “electric power”. The concept of electrobiorefineries provides a blueprint for such an alliance. Joining the forces of microbial and electrochemical conversions in electrobiorefineries allows interfacing the production, storage, and exploitation of electricity as well as biobased chemicals. Electrobiorefineries are a technological evolution of biorefineries by the addition of (bio)electrochemical transformations. This interfacing of microbial and electrochemical conversions will result in synergies affecting the entire process line, like enlarging the product portfolio, increasing the productivity, or exploiting new feedstock. A special emphasis is given to the utilization of oxidative and reductive electroorganic reactions of microbially produced intermediates that may serve as privileged building blocks.
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Recent Advances in Analytical Pyrolysis to Investigate Organic Materials in Heritage Science ()
Abstract The molecular characterization of organic materials in samples from artworks and historical objects traditionally entailed qualitative and quantitative analyses by HPLC and GC. Today innovative approaches based on analytical pyrolysis enable samples to be analysed without any chemical pre‐treatment. Pyrolysis, which is often considered as a screening technique, shows previously unexplored potential thanks to recent instrumental developments. Organic materials that are macromolecular in nature, or undergo polymerization upon curing and ageing can now be better investigated. Most constituents of paint layers and archaeological organic substances contain major insoluble and chemically non‐hydrolysable fractions that are inaccessible to GC or HPLC. To date, molecular scientific investigations of the organic constituents of artworks and historical objects have mostly focused on the minor constituents of the sample. This review presents recent advances in the qualitative and semi‐quantitative analyses of organic materials in heritage objects based on analytical pyrolysis coupled with mass spectrometry.
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Carbon Nanozymes: Enzymatic Properties, Catalytic Mechanism, and Applications ()
Abstract Nanozymes have advantages over natural enzymes, such as facile production on large scale, long storage time, low costs, and high stability in harsh environments. Carbon nanomaterials (CNMs), including fullerenes, carbon nanotubes, graphene, carbon quantum dots, and graphene quantum dots, have become a star family in materials science. As a new class of nanozymes, the catalytic activity of CNMs and their hybrids has been extensively reported. In this Minireview, recent progress of CNMs based artificial enzymes, focusing on those with peroxidase‐like activity, has been summarized. The enzymatic properties, catalytic mechanisms, and novel applications of CNM nanozymes in sensing, therapy, and environmental engineering are discussed in detail. Additionally, we also highlight the remaining challenges and unsolved problems. With the fast development of bionanotechnology, the unique enzymatic properties and advantages of CNM nanozymes have received much attention and will continue to be an active and challenging field for the years to come.
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Synthesis and Applications of Compartmentalised Molecular Polymer Brushes ()
Abstract Polymer science is rapidly advancing towards the precise construction of synthetic macromolecules of formidable complexity. Beyond the impressive advances in control over polymer composition and uniformity enabled by the living polymerisation revolution, the introduction of compartmentalisation within polymer architectures can elevate their functionality beyond that of their constituent parts, thus offering immense potential for the production of tailor‐made nanomaterials. In this Minireview, we discuss synthetic routes to complex molecular brushes with discrete chemical compartments and highlight their potential in the development of advanced materials with applications in nanofabrication, optics and functional materials.
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Catalysis of Carbon Dioxide Photoreduction on Nanosheets: Fundamentals and Challenges ()
Abstract The transformation of CO2 into fuels and chemicals by photocatalysis is a promising strategy to provide a long‐term solution to mitigating global warming and energy‐supply problems. Achievements in photocatalysis during the last decade have sparked increased interest in using sunlight to reduce CO2. Traditional semiconductors used in photocatalysis (e.g. TiO2) are not suitable for use in natural sunlight and their performance is not sufficient even under UV irradiation. Some two‐dimensional (2D) materials have recently been designed for the catalytic reduction of CO2. These materials still require significant modification, which is a challenge when designing a photocatalytic process. An overarching aim of this Review is to summarize the literature on the photocatalytic conversion of CO2 by various 2D materials in the liquid phase, with special attention given to the development of novel 2D photocatalyst materials to provide a basis for improved materials.
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Bridging the Gap between Industrial and Well‐Defined Supported Catalysts ()
Abstract Many industrial catalysts contain isolated metal sites on the surface of oxide supports. Although such catalysts have been used in a broad range of processes for more than 40 years, there is often a very limited understanding about the structure of the catalytically active sites. This Review discusses how surface organometallic chemistry (SOMC) engineers surface sites with well‐defined structures and provides insight into the nature of the active sites of industrial catalysts; the Review focuses in particular on olefin production and conversion processes.
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Porous Polyelectrolytes: The Interplay of Charge and Pores for New Functionalities ()
Abstract The past decade has witnessed rapid advances in porous polyelectrolytes and there is tremendous interest in their synthesis as well as their applications in environmental, energy, biomedicine, and catalysis technologies. Research on porous polyelectrolytes is motivated by the flexible choice of functional organic groups and processing technologies as well as the synergy of the charge and pores spanning length scales from individual polyelectrolyte backbones to their nano‐/micro‐superstructures. This Review surveys recent progress in porous polyelectrolytes including membranes, particles, scaffolds, and high surface area powders/resins as well as their derivatives. The focus is the interplay between surface chemistry, Columbic interaction, and pore confinement that defines new chemistry and physics in such materials for applications in energy conversion, molecular separation, water purification, sensing/actuation, catalysis, tissue engineering, and nanomedicine.
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Synthesis of Vibegron Enabled by a Ketoreductase Rationally Designed for High pH Dynamic Kinetic Reduction ()
Abstract Described here is an efficient stereoselective synthesis of vibegron enabled by an enzymatic dynamic kinetic reduction that proceeds in a high‐pH environment. To overcome enzyme performance limitations under these conditions, a ketoreductase was evolved by a computationally and structurally aided strategy to increase cofactor stability through tighter binding.
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Enantioselective Synthesis of the Spirotropanyl Oxindole Scaffold through Bimetallic Relay Catalysis ()
Abstract Spirotropanyl oxindole alkaloids like alstonisine and chitosenine show a wide range of bioactivites. We report the first enantioselective synthesis of the spirotropanyl oxindole scaffold by means of a bimetallic relay catalysis strategy. A new class of E‐oximino α‐diazo ketones was developed for the intramolecular generation of transient azomethine ylides catalyzed by an achiral RhII complex and a subsequent intermolecular 1,3‐dipolar cycloaddition catalyzed by a chiral N,N′‐dioxide NdIII Lewis acid complex. The enantioselectively catalyzed transformation has broad scope and yields the desired spirotropanyl oxindole cycloadducts in high yields and with very high enantio‐ and diastereoselectivity.
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Fast, Efficient and Low E‐Factor One‐Pot Palladium‐Catalyzed Cross‐Coupling of (Hetero)Arenes ()
Abstract The homocoupling of aryl halides and the heterocoupling of aryl halides with either aryl bromides or arenes bearing an ortho‐lithiation directing group are presented. The use of a Pd catalyst, in combination with t‐BuLi, allows for the rapid and efficient formation of a wide range of polyaromatic compounds in a one pot procedure bypassing the need for the separate preformation of an organometallic coupling partner. These polyaromatic structures are obtained in high yields, in 10 min at room temperature, with minimal waste generation (E‐factors as low as 1.5) and without the need for strict inert conditions, making this process highly efficient and practical in comparison to classical methods. As illustration, several key intermediates of widely used BINOL‐derived structures are readily prepared.
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Conductive Microporous Covalent Triazine‐Based Framework for High‐Performance Electrochemical Capacitive Energy Storage ()
Abstract Nitrogen‐enriched porous nanocarbon, graphene, and conductive polymers attract increasing attention for application in supercapacitors. However, electrode materials with a large specific surface area (SSA) and a high nitrogen doping concentration, which is needed for excellent supercapacitors, has not been achieved thus far. Herein, we developed a class of tetracyanoquinodimethane‐derived conductive microporous covalent triazine‐based frameworks (TCNQ‐CTFs) with both high nitrogen content (>8 %) and large SSA (>3600 m2 g−1). These CTFs exhibited excellent specific capacitances with the highest value exceeding 380 F g−1, considerable energy density of 42.8 Wh kg−1, and remarkable cycling stability without any capacitance degradation after 10 000 cycles. This class of CTFs should hold a great potential as high‐performance electrode material for electrochemical energy‐storage systems.
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Standoff Mid‐Infrared Emissive Imaging Spectroscopy for Identification and Mapping of Materials in Polychrome Objects ()
Abstract Microscale mid‐infrared (mid‐IR) imaging spectroscopy is used for the mapping of chemical functional groups. The extension to macroscale imaging requires that either the mid‐IR radiation reflected off or that emitted by the object be greater than the radiation from the thermal background. Reflectance spectra can be obtained using an active IR source to increase the amount of radiation reflected off the object, but rapid heating of greater than 4 °C can occur, which is a problem for paintings. Rather than using an active source, by placing a highly reflective tube between the painting and camera and introducing a low temperature source, thermal radiation from the room can be reduced, allowing the IR radiation emitted by the painting to dominate. Thus, emissivity spectra of the object can be recovered. Using this technique, mid‐IR emissivity image cubes of paintings were collected at high collection rates with a low‐noise, line‐scanning imaging spectrometer, which allowed pigments and paint binders to be identified and mapped.
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Brønsted Acid‐Catalyzed Carbonyl‐Olefin Metathesis inside a Self‐Assembled Supramolecular Host ()
Abstract Carbonyl–olefin metathesis represents a powerful yet underdeveloped method for the formation of carbon–carbon bonds. So far, no Brønsted acid based method for the catalytic carbonyl–olefin metathesis has been described. Herein, a cocatalytic system based on a simple Brønsted acid (HCl) and a self‐assembled supramolecular host is presented. The developed system compares well with the current benchmark catalyst for carbonyl–olefin metathesis in terms of substrate scope and yield of isolated product. Control experiments provide strong evidence that the reaction proceeds inside the cavity of the supramolecular host. A mechanistic probe indicates that a stepwise reaction mechanism is likely.
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Polymer Film Dewetting by Water/Surfactant/Good‐Solvent Mixtures: A Mechanistic Insight and Its Implications for the Conservation of Cultural Heritage ()
Abstract Aqueous nanostructured fluids (NSFs) have been proposed to remove polymer coatings from the surface of works of art; this process usually involves film dewetting. The NSF cleaning mechanism was studied using several techniques that were employed to obtain mechanistic insight on the interaction of a methacrylic/acrylic copolymer (Paraloid B72) film laid on glass surfaces and several NSFs, based on two solvents and two surfactants. The experimental results provide a detailed picture of the dewetting process. The gyration radius and the reduction of the Tg of Paraloid B72 fully swollen in the two solvents is larger for propylene carbonate than for methyl ethyl ketone, suggesting higher mobility of polymer chains for the former, while a nonionic alcohol ethoxylate surfactant was more effective than sodium dodecylsulfate in favoring the dewetting process. FTIR 2D imaging showed that the dewetting patterns observed on model samples are also present on polymer‐coated mortar tiles when exposed to NSFs.
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Polyvalent Display of Biomolecules on Live Cells ()
Abstract Surface display of biomolecules on live cells offers new opportunities to treat human diseases and perform basic studies. Existing methods are primarily focused on monovalent functionalization, that is, the display of single biomolecules across the cell surface. Here we show that the surface of live cells can be functionalized to display polyvalent biomolecular structures through two‐step reactions under physiological conditions. This polyvalent functionalization enables the cell surface to recognize the microenvironment one order of magnitude more effectively than with monovalent functionalization. Thus, polyvalent display of biomolecules on live cells holds great potential for various biological and biomedical applications.
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Potassium‐Zincate‐Catalyzed Benzylic C−H Bond Addition of Diarylmethanes to Styrenes ()
Abstract Direct functionalization of the benzylic C−H bond of diarylmethanes is an important strategy for the synthesis of diarylmethine‐containing compounds. However, the methods developed to date for this purpose require a stoichiometric amount (usually more) of either a strong base or an oxidant. Reported here is the first catalytic benzylic C−H bond addition of diarylmethanes to styrenes and conjugated dienes. A potassium zincate complex, generated from potassium benzyl and zinc amide, acts as a catalyst and displays good activity and chemoselectivity. Considering the atom economy of the reaction and the ready availability of the catalyst, this reaction constitutes a practical, efficient method for diarylalkane synthesis.
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Glass and Alchemy in Early Modern Europe: An Analytical Study of Glassware from the Oberstockstall Laboratory in Austria ()
Abstract Glass distillation equipment from an early modern alchemical laboratory was analyzed for its technology of manufacture and potential origin. Chemical data show that the assemblage can be divided into sodium‐rich, colorless distillation vessels made with glass from Venice or its European imitation, and potassium‐rich dark‐brown non‐specialized forms produced within the technological tradition of forest glass typical for central and north‐western Europe. These results complete our understanding of the supply of technical apparatus at one of the best‐preserved alchemical laboratories and highlight an early awareness of the need for high‐quality instruments to guarantee the successful outcome of specialized chemical operations. This study demonstrates the potential of archaeological science to inform historical research around the practice of early chemistry and the development of modern science.
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Classifying Degraded Modern Polymeric Museum Artefacts by Their Smell ()
Abstract The use of VOC analysis to diagnose degradation in modern polymeric museum artefacts is reported. Volatile organic compound (VOC) analysis is a successful method for diagnosing medical conditions but to date has found little application in museums. Modern polymers are increasingly found in museum collections but pose serious conservation difficulties owing to unstable and widely varying formulations. Solid‐phase microextraction gas chromatography/mass spectrometry and linear discriminant analysis were used to classify samples according to the length of time they had been artificially degraded. Accuracies in classification of 50–83 % were obtained after validation with separate test sets. The method was applied to three artefacts from collections at Tate to detect evidence of degradation. This approach could be used for any material in heritage collections and more widely in the field of polymer degradation.
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Regiospecific ortho‐C−H Allylation of Benzoic Acids ()
Abstract A carboxylate‐directed ortho‐C−H functionalization has been developed and it allows the regiospecific introduction of allyl residues to benzoic acids. In the presence of a [Ru(p‐cymene)Cl2]2 and K3PO4, benzoic acids react with allyl acetates at only 50 °C to give the corresponding ortho‐allylbenzoic acids. The protocol is generally applicable to both electron‐rich and electron‐poor benzoic acids in combination with linear and branched allyl acetates. The products can be further functionalized in situ, for example, by double‐bond migration, lactonization, or decarboxylation.
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Layered Nano‐TiO2 Based Treatments for the Maintenance of Natural Stones in Historical Architecture ()
Abstract Layered treatments of natural stones based on dispersions of experimental nano‐TiO2 and commercial TEOS showing photocatalytic and self‐cleaning properties were set up and tested. To enhance nano‐TiO2 efficacy, a surface pre‐treatment with tetraethyl orthosilicate was proposed to avoid the penetration of NPs into the crystalline porous substrates and to improve their adhesion to the stone. Two treatment applications (wet‐on‐wet and wet‐on‐dry) were compared, showing different results. A strong interaction Si−O−Ti was the key factor for the successful treatment, leaving the band gap and relevant properties of nano‐TiO2 unaltered. The layered treatments were tested on a porous calcarenite (Noto stone) and a very compact marble (Carrara marble). The combined SiO2‐nano‐TiO2 treatments can find application in suitable cases where a surface consolidation is needed, ensuring a depolluting and self‐cleaning durable activity.
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Blending Non‐Group‐3 Transition Metal and Rare‐Earth Metal into a C80 Fullerene Cage with D5h Symmetry ()
Abstract Rare‐earth metals have been mostly entrapped into fullerene cages to form endohedral clusterfullerenes, whereas non‐Group‐3 transition metals that can form clusterfullerenes are limited to titanium (Ti) and vanadium (V), and both are exclusively entrapped within an Ih‐C80 cage. Non‐Group‐3 transition‐metal‐containing endohedral fullerenes based on a C80 cage with D5h symmetry, VxSc3−xN@D5h‐C80 (x=1, 2), have now been synthesized, which exhibit two variable cluster compositions. The molecular structure of VSc2N@D5h‐C80 was unambiguously determined by X‐ray crystallography. According to a comparative study with the reported Ti‐ and V‐containing clusterfullerenes based on a Ih‐C80 cage and the analogous D5h‐C80‐based metal nitride clusterfullerenes containing rare‐earth metals only, the decisive role of the non‐Group‐3 transition metal on the formation of the corresponding D5h‐C80‐based clusterfullerenes is unraveled.
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Synthesis of Alternating Donor–Acceptor Ladder‐Type Molecules and Investigation of Their Multiple Charge‐Transfer Pathways ()
Abstract We describe the synthesis as well as the optical and charge‐transport properties of a series of donor–acceptor (D‐A) ladder‐type heteroacenes. These molecules are stable, soluble, and contain up to 24 fused rings. Structural analyses indicated that the backbones of S 10r and Se 10r are bent in single crystals. The three 10‐ring heteroacenes were functionalized with thiol anchoring groups and used for single‐molecular conductance measurements. The highest conductance was observed for molecular wires containing a benzoselenadiazole (BSD) moiety, which exhibits the narrowest band gap. Multiple charge‐transport pathways were observed in molecular wires containing either benzothiadiazole (BTD) or BSD. The conductance is a complex function of both energy gap and orbital alignment.
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Time‐Dependent ATR‐FTIR Spectroscopic Studies on Fatty Acid Diffusion and the Formation of Metal Soaps in Oil Paint Model Systems ()
Abstract The formation of metal soaps (metal complexes of saturated fatty acids) is a serious problem affecting the appearance and structural integrity of many oil paintings. Tailored model systems for aged oil paint and time‐dependent attenuated total reflection Fourier transform infrared (ATR‐FTIR) spectroscopy were used to study the diffusion of palmitic acid and subsequent metal soap crystallization. The simultaneous presence of free saturated fatty acids and polymer‐bound metal carboxylates leads to rapid metal soap crystallization, following a complex mechanism that involves both acid and metal diffusion. Solvent flow, water, and pigments all enhance metal soap crystallization in the model systems. These results contribute to the development of paint cleaning strategies, a better understanding of oil paint degradation, and highlight the potential of time‐dependent ATR‐FTIR spectroscopy for studying dynamic processes in polymer films.
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Synthesis of a Helical Bilayer Nanographene ()
Abstract A rigid, inherently chiral bilayer nanographene has been synthesized as both the racemate and enantioenriched M isomer (with 93 % ee) in three steps from established helicenes. This folded nanographene is composed of two hexa‐peri‐hexabenzocoronene layers fused to a [10]helicene, with an interlayer distance of 3.6 Å as determined by X‐ray crystallography. The rigidity of the helicene linker forces the layers to adopt a nearly aligned AA‐stacked conformation, rarely observed in few‐layer graphene. By combining the advantages of nanographenes and helicenes, we have constructed a bilayer system of 30 fused benzene rings that is also chiral, rigid, and remains soluble in common organic solvents. We present this as a molecular model system of bilayer graphene, with properties of interest in a variety of potential applications.
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Catalytic C−H Trifluoromethoxylation of Arenes and Heteroarenes ()
Abstract The intermolecular C−H trifluoromethoxylation of arenes remains a long‐standing and unsolved problem in organic synthesis. Herein, we report the first catalytic protocol employing a novel trifluoromethoxylating reagent and redox‐active catalysts for the direct (hetero)aryl C−H trifluoromethoxylation. Our approach is operationally simple, proceeds at room temperature, uses easy‐to‐handle reagents, requires only 0.03 mol % of redox‐active catalysts, does not need specialized reaction apparatus, and tolerates a wide variety of functional groups and complex structures such as sugars and natural product derivatives. Importantly, both ground‐state and photoexcited redox‐active catalysts are effective. Detailed computational and experimental studies suggest a unique reaction pathway where photoexcitation of the trifluoromethoxylating reagent releases the OCF3 radical that is trapped by (hetero)arenes. The resulting cyclohexadienyl radicals are oxidized by redox‐active catalysts and deprotonated to form the desired products of trifluoromethoxylation.
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Continuous Heterogeneous Photocatalysis in Serial Micro‐Batch Reactors ()
Abstract Solid reagents, leaching catalysts, and heterogeneous photocatalysts are commonly employed in batch processes but are ill‐suited for continuous‐flow chemistry. Heterogeneous catalysts for thermal reactions are typically used in packed‐bed reactors, which cannot be penetrated by light and thus are not suitable for photocatalytic reactions involving solids. We demonstrate that serial micro‐batch reactors (SMBRs) allow for the continuous utilization of solid materials together with liquids and gases in flow. This technology was utilized to develop selective and efficient fluorination reactions using a modified graphitic carbon nitride heterogeneous catalyst instead of costly homogeneous metal polypyridyl complexes. The merger of this inexpensive, recyclable catalyst and the SMBR approach enables sustainable and scalable photocatalysis.
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Tailored Microstructured Hyperpolarizing Matrices for Optimal Magnetic Resonance Imaging ()
Abstract Tailoring the physical features and the porous network architecture of silica‐based hyperpolarizing solids containing TEMPO radicals, known as HYPSO (hybrid polarizing solids), enabled unprecedented performance of dissolution dynamic nuclear polarization (d‐DNP). High polarization values up to P(1H)=99 % were reached for samples impregnated with a mixture of H2O/D2O and loaded in a 6.7 T polarizer at temperatures around 1.2 K. These HYPSO materials combine the best performance of homogeneous DNP formulations with the advantages of solid polarizing matrices, which provide hyperpolarized solutions free of any—potentially toxic—additives (radicals and glass‐forming agents). The hyperpolarized solutions can be expelled from the porous solids, filtered, and rapidly transferred either to a nuclear magnetic resonance (NMR) spectrometer or to a magnetic resonance imaging (MRI) system.
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An Extra‐Large‐Pore Zeolite with 24×8×8‐Ring Channels Using a Structure‐Directing Agent Derived from Traditional Chinese Medicine ()
Abstract Extra‐large‐pore zeolites have attracted much interest because of their important applications because for processing larger molecules. Although great progress has been made in academic science and industry, it is challenging to synthesize these materials. A new extra‐large‐pore zeolite SYSU‐3 (Sun Yat‐sen University no. 3) has been synthesized by using a novel sophoridine derivative as an organic structure‐directing agent (OSDA). The framework structure was solved and refined using continuous rotation electron diffraction (cRED) data from nanosized crystals. SYSU‐3 exhibits a new zeolite framework topology, which has the first 24×8×8‐ring extra‐large‐pore system and a framework density (FD) as low as 11.4 T/1000 Å3. The unique skeleton of the OSDA plays an essential role in the formation of the distinctive zeolite structure. This work provides a new perspective for developing new zeolitic materials by using alkaloids as cost‐effective OSDAs.
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Electron Transfer around a Molecular Corner ()
Abstract The distance dependence of electron transfer (ET) is commonly investigated in linear rigid rod‐like compounds, but studies of molecular wires with integrated corners imposing 90° angles are very rare. By using spirobifluorene as a key bridging element and by substituting it at different positions, two isomeric series of donor‐bridge‐acceptor compounds with either nearly linear or angled geometries were obtained. Photoinduced ET in both series is dominated by rapid through‐bond hole hopping across oligofluorene bridges over distances of up to 70 Å. Despite considerable conformational flexibility, direct through‐space and through‐solvent ET is negligible even in the angled series. The independence of the ET rate constant on the total number of fluorene units in the angled series is attributed to a rate‐limiting tunneling step through the spirobifluorene corner. This finding is relevant for multidimensional ET systems and grids in which individual molecular wires are interlinked at 90° angles.
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Controllable Assembly of Enzymes for Multiplexed Lab‐on‐a‐Chip Bioassays with a Tunable Detection Range ()
Abstract Multiplexed analysis of molecules with different concentrations requires assays with a tunable detection range. A strategy is outlined that uses click chemistry to assemble horseradish peroxidase in a controlled fashion to generate enzyme assemblies as probes for multiplexed bioassays. This controllable assembly of enzymes on detection antibodies allows for lab‐on‐a‐chip immunoassays with a tunable detection range from pg mL−1 to μg mL−1. Simultaneous, multiplexed bioassays of clinically relevant inflammatory biomarkers in serum are demonstrated in one lab‐on‐a‐chip format, with a limit of detection of 0.47 pg mL−1 for interleukin‐6, 2.6 pg mL−1 for procalcitonin, and 40 ng mL−1 for C‐reactive protein. This controlled assembly technique provides a multiplexed platform for simultaneous and quantitative analyses of both low‐abundance and high‐abundance biomarkers with a broad detection range, which holds great promise as a point‐of‐care platform for biomedical diagnostics.
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A Regularly Channeled Lamellar Membrane for Unparalleled Water and Organics Permeation ()
Abstract Lamellar membranes show exceptional molecular permeation properties of key importance for many applications. However, their design and development need the construction of regular and straight interlayer channels and the establishment of corresponding transport rate equation. The fabrication of a uniformly lamellar membrane is reported using double‐layered Ti3C2Tx MXenes as rigid building blocks. This membrane possesses ordered and straight 2 nm channels formed via a direct self‐stacking, in contrast to the conventional irregular ones from flexible sheets. Such channels permit precise molecular rejection and unparalleled molecular permeation. The permeance of water and organics by this membrane reached 2300 and 5000 L m−2 h−1 bar−1, respectively. The molecular transfer mechanism in confined nanochannels, and the corresponding model equation are established, paving a way to nanoscale design of highly efficient channeled membranes for transport and separation applications.
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Silica‐Protection‐Assisted Encapsulation of Cu2O Nanocubes into a Metal–Organic Framework (ZIF‐8) To Provide a Composite Catalyst ()
Abstract The integration of metal/metal oxide nanoparticles (NPs) into metal–organic frameworks (MOFs) to form composite materials has attracted great interest due to the broad range of applications. However, to date, it has not been possible to encapsulate metastable NPs with high catalytic activity into MOFs, due to their instability during the preparation process. For the first time, we have successfully developed a template protection–sacrifice (TPS) method to encapsulate metastable NPs such as Cu2O into MOFs. SiO2 was used as both a protective shell for Cu2O nanocubes and a sacrificial template for forming a yolk–shell structure. The obtained Cu2O@ZIF‐8 composite exhibits excellent cycle stability in the catalytic hydrogenation of 4‐nitrophenol with high activity. This is the first report of a Cu2O@MOF‐type composite material. The TPS method provides an efficient strategy for encapsulating unstable active metal/metal oxide NPs into MOFs or maybe other porous materials.
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An Efficient 1064 nm NIR‐II Excitation Fluorescent Molecular Dye for Deep‐Tissue High‐Resolution Dynamic Bioimaging ()
Abstract A small‐molecule fluorophore FD‐1080 with both excitation and emission in the NIR‐II region has been successfully synthesized for in vivo imaging. A heptamethine structure is designed to shift the absorption and emission into NIR‐II region. Sulphonic and cyclohexene groups are introduced to enhance its water solubility and stability. The quantum yield of FD‐1080 is 0.31 %, and can be increased to 5.94 % after combining with fetal bovine serum (FBS). Significantly, 1064 nm NIR‐II excitation was demonstrated with the high tissue penetration depth and superior imaging resolution compared to previously reported NIR excitation from 650 nm to 980 nm. FD‐1080 is not only capable of realizing non‐invasive high‐resolution deep‐tissue hindlimb vasculature and brain vessel bioimaging, but also quantifying the respiratory rate based on the dynamic imaging of respiratory craniocaudal motion of the liver for the awake and anaesthetized mouse.
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From Linear to Angular Isomers: Achieving Tunable Charge Transport in Single‐Crystal Indolocarbazoles Through Delicate Synergetic CH/NH⋅⋅⋅π Interactions ()
Abstract Weak intermolecular interaction in organic semiconducting molecular crystals plays an important role in molecular packing and electronic properties. Here, four five‐ring‐fused isomers were rationally designed and synthesized to investigate the isomeric influence of linear and angular shapes in affecting their molecular packing and resultant electronic properties. Single‐crystal field‐effect transistors showed mobility order of 5,7‐ICZ (3.61 cm2 V−1 s−1) >5,11‐ICZ (0.55 cm2 V−1 s−1) >11,12‐ICZ (ca. 10−5 cm2 V−1 s−1) and 5,12‐ICZ (ca. 10−6 cm2 V−1 s−1). Theoretical calculations based on density functional theory (DFT) and polaron transport model revealed that 5,7‐ICZ can reach higher mobilities than the others thanks to relatively higher hole transfer integral that links to stronger intermolecular interaction due to the presence of multiple NH⋅⋅⋅π and CH⋅⋅⋅π(py) interactions with energy close to common NH⋅⋅⋅N hydrogen bonds, as well as overall lower hole‐vibrational coupling owing to the absence of coupling of holes to low frequency modes due to better π conjugation.
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Rediscovering Ducos du Hauron's Color Photography through a Review of His Three‐Color Printing Processes and Synchrotron Microanalysis of His Prints ()
Abstract Louis Ducos du Huron (1837–1920) dedicated his entire life to the elaboration of physical–chemical processes for color photography. This study aimed at highlighting his unique contribution to three‐color printing through 1) an in‐depth review of the many protocols he published and 2) the synchrotron‐based IR and X‐ray microanalysis of fragments sampled in three artworks. Ducos du Hauron's method relied on the preparation and assembly of three monochromes (red, blue, yellow). This study brings to light complex multistep recipes based on photochemistry (carbon print), organic, and inorganic chemistry. The various ingredients involved (e.g., pigments, dichromate gelatin, collodion, resin) were identified and localized through their spectroscopic signature, confirming the relevance of synchrotron spectromicroscopy for the characterization of historical photographs. The impressive correlation between texts and chemical analyses calls for a wider application to the history of photography.
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Chemical Mapping by Macroscopic X‐ray Powder Diffraction (MA‐XRPD) of Van Gogh's Sunflowers: Identification of Areas with Higher Degradation Risk ()
Abstract The discoloration rate of chrome yellow (CY), a class of synthetic inorganic pigments (PbCr1−xSxO4) frequently used by Van Gogh and his contemporaries, strongly depends on its sulfate content and on its crystalline structure (either monoclinic or orthorhombic). Macroscopic X‐Ray powder diffraction imaging of selected areas on Van Gogh's Sunflowers (Van Gogh Museum, Amsterdam) revealed the presence of two subtypes of CY: the light‐fast monoclinic PbCrO4 (LF‐CY) and the light‐sensitive monoclinic PbCr1−xSxO4 (x≈0.5; LS‐CY). The latter was encountered in large parts of the painting (e.g., in the pale‐yellow background and the bright‐yellow petals, but also in the green stems and flower hearts), thus indicating their higher risk for past or future darkening. Overall, it is present in more than 50 % of the CY regions. Preferred orientation of LS‐CY allows observation of a significant ordering of the elongated crystallites along the direction of Van Gogh's brush strokes.
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Using Optical Coherence Tomography to Reveal the Hidden History of The Landsdowne Virgin of the Yarnwinder by Leonardo da Vinci and Studio ()
Abstract Optical coherence tomography (OCT) was used for non‐invasive examination of a well‐known, yet complex, painting from the studio of Leonardo da Vinci in combination with routine imaging in various bands of electromagnetic radiation. In contrast with these techniques, OCT provides depth‐resolved information. Three post‐processing modalities were explored: cross‐sectional views, maps of scattering from given depths, and their 3D models. Some hidden alterations of the painting owing to past restorations were traced: retouching and overpainting with their positioning within varnish layers as well as indications of a former transfer to canvas.
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A Synchrotron‐Based Study of the Mary Rose Iron Cannonballs ()
Abstract Post‐excavation iron corrosion may be accelerated by the presence of Cl−, leading to conservation methods designed to remove Cl. This study exploits a unique opportunity to assess 35 years of conservation applied to cast‐iron cannon shot excavated from the Mary Rose. A combination of synchrotron X‐ray powder diffraction (SXPD), absorption spectroscopy (XAS), and fluorescence (XRF) mapping have been used to characterise the impact of conservation on the crystalline corrosion products, chlorine distribution, and speciation. The chlorinated phase akaganeite, β‐FeO(OH,Cl), was found on shot washed in corrosion inhibitor Hostacor IT with or without an additional reduction stage. No chlorinated phases were observed on the surface of shot stored in sodium sesquicarbonate (Na2CO3/NaHCO3); however, hibbingite, β‐Fe2(OH)3Cl, was present in metal pores. It is proposed that surface β‐FeO(OH,Cl) formed in the early stages of active conservation owing to oxidation of β‐Fe2(OH)3Cl at near‐neutral pH.
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Egyptian Grave Goods of Kha and Merit Studied by Neutron and Gamma Techniques ()
Abstract Artifacts from the Egyptian grave goods of Kha and Merit preserved at the Museo Egizio in Turin were studied through a combination of non‐destructive and non‐invasive neutron and gamma techniques (namely neutron imaging, neutron diffraction and prompt gamma activation analysis). The results provide unprecedented morphological reconstructions of the inner parts of the two alabaster and metallic vases and their isotopic and phase composition, thereby extending our knowledge of the hitherto unknown content of the vases and their functions.
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Dual‐Functional Small Molecules for Generating an Efficient Cytochrome P450BM3 Peroxygenase ()
Abstract We report a unique strategy for the development of a H2O2‐dependent cytochrome P450BM3 system, which catalyzes the monooxygenation of non‐native substrates with the assistance of dual‐functional small molecules (DFSMs), such as N‐(ω‐imidazolyl fatty acyl)‐l‐amino acids. The acyl amino acid group of DFSM is responsible for bounding to enzyme as an anchoring group, while the imidazolyl group plays the role of general acid–base catalyst in the activation of H2O2. This system affords the best peroxygenase activity for the epoxidation of styrene, sulfoxidation of thioanisole, and hydroxylation of ethylbenzene among those P450–H2O2 system previously reported. This work provides the first example of the activation of the normally H2O2‐inert P450s through the introduction of an exogenous small molecule. This approach improves the potential use of P450s in organic synthesis as it avoids the expensive consumption of the reduced nicotinamide cofactor NAD(P)H and its dependent electron transport system. This introduces a promising approach for exploiting enzyme activity and function based on direct chemical intervention in the catalytic process.
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Combined In Situ Illumination‐NMR‐UV/Vis Spectroscopy: A New Mechanistic Tool in Photochemistry ()
Abstract Synthetic applications in photochemistry are booming. Despite great progress in the development of new reactions, mechanistic investigations are still challenging. Therefore, we present a fully automated in situ combination of NMR spectroscopy, UV/Vis spectroscopy, and illumination to allow simultaneous and time‐resolved detection of paramagnetic and diamagnetic species. This optical fiber‐based setup enables the first acquisition of combined UV/Vis and NMR spectra in photocatalysis, as demonstrated on a conPET process. Furthermore, the broad applicability of combined UVNMR spectroscopy for light‐induced processes is demonstrated on a structural and quantitative analysis of a photoswitch, including rate modulation and stabilization of transient species by temperature variation. Owing to the flexibility regarding the NMR hardware, temperature, and light sources, we expect wide‐ranging applications of this setup in various research fields.
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Calcium Fluoride Nanocrystals: Tracers for In Vivo 19F Magnetic Resonance Imaging ()
Abstract Inorganic nanocrystals (NCs) have been extensively developed for a variety of uses. The ability to obtain high‐resolution NMR signals from the core nuclei of NCs in solution could offer new opportunities in materials sciences and MR imaging. Herein, we demonstrate that small, water‐soluble 19F‐ionic NCs can average out homonuclear dipolar interactions, enabling one to obtain high‐resolution 19F NMR signals in solution that reflect the MR properties of F− in the crystal core. Decorating 19F‐NC surfaces with a biocompatible poly(ethylene glycol) coating maintains colloidal stability in water while preserving the NC high‐resolution 19F NMR properties, even after further functionalization. The high content and magnetic equivalence of the fluorides within the NCs enable their use as imaging tracers for in vivo 19F MRI by facilitating a “hot‐spot” display of their distribution.
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Transient and Persistent Room‐Temperature Mechanoluminescence from a White‐Light‐Emitting AIEgen with Tricolor Emission Switching Triggered by Light ()
Abstract Persistent luminescence from purely organic materials is basically triggered by light and electricity, which largely confines its practical applications. A purely organic AIEgen exhibits not only persistent photoluminescence, but also transient and persistent room‐temperature mechanoluminescence. By simply turning on and off a UV lamp, tricolor emission switching between blue, white, and yellow was achieved. The data from single‐crystal structure analysis and theoretical calculation suggest that mechanism of the observed persistent mechanoluminescence (pML) is correlated with the strong spin–orbit coupling of the bromine atom, as well as the formation of H‐aggregates and restriction of intramolecular motions in noncentrosymmetric crystal structure. These results outline a fundamental principle for the development of new pML materials, providing an important step forward in expanding the application scope of persistent luminescence.
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Rational Tuning of Fluorobenzene Probes for Cysteine‐Selective Protein Modification ()
Abstract Fluorobenzene probes for protein profiling through selective cysteine labeling have been developed by rational reactivity tuning. Tuning was achieved by selecting an electron‐withdrawing para substituent in combination with variation of the number of fluorine substituents. Optimized probes chemoselectively arylated cysteine residues in proteins under aqueous conditions. Probes linked to azide, biotin, or a fluorophore were applicable to labeling of eGFP and albumin. Selective inhibition of cysteine proteases was also demonstrated with the probes. Additionally, probes were tuned for site‐selective labeling of cysteine residues and for activity‐based protein profiling in cell lysates.
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Transition‐Metal‐Like Behavior of Monovalent Boron Compounds: Reduction, Migration, and Complete Cleavage of CO at a Boron Center ()
Abstract The borylene–carbonyl moiety in [bis(silylene)B(CO)][WBr(CO)5] shows diverse reactivity. Reduction, migration, and complete cleavage of CO have been observed at the boron center, leading to the formation of new types of borylenes. These reactions not only serve as new methods for the synthesis of various stable borylenes, but also demonstrate that main‐group‐element compounds can mimic the behavior of transition‐metal complexes.
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Cobalt‐Catalyzed Tandem C−H Activation/C−C Cleavage/C−H Cyclization of Aromatic Amides with Alkylidenecyclopropanes ()
Abstract A cobalt‐catalyzed chelation‐assisted tandem C−H activation/C−C cleavage/C−H cyclization of aromatic amides with alkylidenecyclopropanes is reported. This process allows the sequential formation of two C−C bonds, which is in sharp contrast to previous reports on using rhodium catalysts for the formation of C−N bonds. Here the inexpensive catalyst system exhibits good functional‐group compatibility and relatively broad substrate scope. The desired products can be easily transformed into polycyclic lactones with m‐CPBA. Mechanistic studies revealed that the tandem reaction proceeds through a C−H cobaltation, β‐carbon elimination, and intramolecular C−H cobaltation sequence.
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Synthesis of Non‐Classical Arylated C‐Saccharides through Nickel/Photoredox Dual Catalysis ()
Abstract The development of synthetic tools to introduce saccharide derivatives into functionally complex molecules is of great interest, particularly in the field of drug discovery. Herein, we report a new route toward highly functionalized, arylated saccharides, which involves nickel‐catalyzed cross‐coupling of photoredox‐generated saccharyl radicals with a range of aryl‐ and heteroaryl bromides, triggered by an organic photocatalyst. In contrast to existing methods, the mild reaction conditions achieve arylation of saccharide motifs while leaving the anomeric carbon available, thus providing access to a class of arylated glycosides that has been underexplored until now. To demonstrate the potential of this strategy in late‐stage functionalization, a variety of structurally complex molecules incorporating saccharide moieties were synthesized.
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Evidence for the Role of Intracellular Water Lifetime as a Tumour Biomarker Obtained by In Vivo Field‐Cycling Relaxometry ()
Abstract It was established through in vivo T1 measurements at low magnetic fields that tumour cells display proton T1 values that are markedly longer than those shown by healthy tissue. Moreover, it has been found that the elongation of T1 parallels the aggressiveness of the investigated tumour. The T1 lengthening is associated with an enhanced water exchange rate across the transcytolemmal membrane through an overexpression/upregulation of GLUT1 and Na+/K+ ATPase transporters. It follows that the intracellular water lifetime represents a hallmark of tumour cells that can be easily monitored by measuring T1 at different magnetic field strengths ranging from 0.2 to 200 mT.
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Measuring Spin Relaxation Rates Using Satellite Exchange NMR Spectroscopy ()
Abstract An approach to the indirect measurement of nuclear spin relaxation rates of low‐magnetogyric ratio (γ) nuclei using the process of satellite exchange is described. The method does not require the observation of, or even the ability to provide radio‐frequency pulses to, the low‐γ nucleus, but requires this to be scalar coupled to an NMR observable nucleus, such as 31P or 1H, making it especially attractive for the study of diamagnetic transition metals. In situations where spin relaxation is dominated by chemical shift anisotropy (CSA), the determination of the longitudinal spin relaxation time constant (T1) of the metal becomes possible, as illustrated for 195Pt and 107/109Ag.
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Optogenetic Control of Voltage‐Gated Calcium Channels ()
Abstract Voltage‐gated Ca2+ (CaV) channels mediate Ca2+ entry into excitable cells to regulate a myriad of cellular events following membrane depolarization. We report the engineering of RGK GTPases, a class of genetically encoded CaV channel modulators, to enable photo‐tunable modulation of CaV channel activity in excitable mammalian cells. This optogenetic tool (designated optoRGK) tailored for CaV channels could find broad applications in interrogating a wide range of CaV‐mediated physiological processes.
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Synthesis of Reversed C‐Acyl Glycosides through Ni/Photoredox Dual Catalysis ()
Abstract The incorporation of C‐glycosides in drug design has become a routine practice for medicinal chemists. These naturally occurring building blocks exhibit attractive pharmaceutical profiles, and have become an important target of synthetic efforts in recent decades. Described herein is a practical, scalable, and versatile route for the synthesis of non‐anomeric and unexploited C‐acyl glycosides through a Ni/photoredox dual catalytic system. By utilizing an organic photocatalyst, a range of glycosyl‐based radicals are generated and efficiently coupled with highly functionalized carboxylic acids at room temperature. Distinctive features of this transformation include its mild conditions, impressive compatibility with a wide array of functional groups, and most significantly, preservation of the anomeric carbon: a handle for further, late‐stage derivatization.
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Engineering Fast Ion Conduction and Selective Cation Channels for a High‐Rate and High‐Voltage Hybrid Aqueous Battery ()
Abstract The rechargeable aqueous metal‐ion battery (RAMB) has attracted considerable attention due to its safety, low costs, and environmental friendliness. Yet the poor‐performance electrode materials lead to a low feasibility of practical application. A hybrid aqueous battery (HAB) built from electrode materials with selective cation channels could increase the electrode applicability and thus enlarge the application of RAMB. Herein, we construct a high‐voltage K–Na HAB based on K2FeFe(CN)6 cathode and carbon‐coated NaTi2(PO4)3 (NTP/C) anode. Due to the unique cation selectivity of both materials and ultrafast ion conduction of NTP/C, the hybrid battery delivers a high capacity of 160 mAh g−1 at a 0.5 C rate. Considerable capacity retention of 94.3 % is also obtained after 1000 cycles at even 60 C rate. Meanwhile, high energy density of 69.6 Wh kg−1 based on the total mass of active electrode materials is obtained, which is comparable and even superior to that of the lead acid, Ni/Cd, and Ni/MH batteries.
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Strain‐Promoted Cycloaddition of Cyclopropenes with o‐Quinones: A Rapid Click Reaction ()
Abstract Novel click reactions are of continued interest in fields as diverse as bio‐conjugation, polymer science and surface chemistry. Qualification as a proper “click” reaction requires stringent criteria, including fast kinetics and high conversion, to be met. Herein, we report a novel strain‐promoted cycloaddition between cyclopropenes and o‐quinones in solution and on a surface. We demonstrate the “click character” of the reaction in solution and on surfaces for both monolayer and polymer brush functionalization.
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A Planar‐Chiral Rhodium(III) Catalyst with a Sterically Demanding Cyclopentadienyl Ligand and Its Application in the Enantioselective Synthesis of Dihydroisoquinolones ()
Abstract The rapid development of enantioselective C−H activation reactions has created a demand for new types of catalysts. Herein, we report the synthesis of a novel planar‐chiral rhodium catalyst [(C5H2tBu2CH2tBu)RhI2]2 in two steps from commercially available [(cod)RhCl]2 and tert‐butylacetylene. Pure enantiomers of the catalyst were obtained through separation of its diastereomeric adducts with natural (S)‐proline. The catalyst promoted enantioselective reactions of aryl hydroxamic acids with strained alkenes to give dihydroisoquinolones in high yields (up to 97 %) and with good stereoselectivity (up to 95 % ee).
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Visible‐Light‐Induced Nickel‐Catalyzed Negishi Cross‐Couplings by Exogenous‐Photosensitizer‐Free Photocatalysis ()
Abstract The merging of photoredox and transition‐metal catalysis has become one of the most attractive approaches for carbon–carbon bond formation. Such reactions require the use of two organo‐transition‐metal species, one of which acts as a photosensitizer and the other one as a cross‐coupling catalyst. We report herein an exogenous‐photosensitizer‐free photocatalytic process for the formation of carbon–carbon bonds by direct acceleration of the well‐known nickel‐catalyzed Negishi cross‐coupling that is based on the use of two naturally abundant metals. This finding will open new avenues in cross‐coupling chemistry that involve the direct visible‐light absorption of organometallic catalytic complexes.
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The Interaction of Guest Molecules with Co‐MOF‐74: A Vis/NIR and Raman Approach ()
Abstract Co‐MOF‐74 rod like crystals with a length of several hundred micrometers are synthesized by a solvothermal procedure and their interaction with different gases is evaluated for selective gas sensing. We show strongly anisotropic absorption behavior of the Co‐MOF‐74 crystals when illuminated with polarized light. The interactions of guests (CO2, propane, propene, Ar, MeOH, H2O) with Co‐MOF‐74, is studied by various spectroscopic techniques. Vis/NIR shows peak shifts of Co‐MOF‐74 depending on the interaction with the guest. In the visible and the NIR the maximum absorbance is shifted selectively corresponding to the intensity of the CoII–guest interaction. Even propene and propane could be distinguished at room temperature by their different interactions with Co‐MOF‐74. Raman spectroscopy was used to detect a modified vibrational behavior of Co‐MOF‐74 upon gas adsorption. We show that the adsorption of H2O leads to a characteristic shift of the peak maxima in the Raman spectra.
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Polycarboxylate‐Templated Coordination Polymers: Role of Templates for Superprotonic Conductivities of up to 10−1 S cm−1 ()
Abstract Three coordination polymers (CPs) have been synthesized based on a [Co(bpy)(H2O)4]2+ chain (bpy=4,4′‐bipyridine) by a template approach. The frameworks are neutralized by different templated polycarboxylate anions (furan di‐carboxylate (fdc) in Co‐fdc, benzene tri‐carboxylate (btc) in Co‐tri and benzene tetra‐carboxylate (btec) in Co‐tetra). These templates with different degrees of protonation and ionic carrier concentration played significant role on crystal packing as well as formation of well‐directed H‐bonded networks which made these CPs perform well in proton conduction (PC). The PC value reaches to 1.49×10−1 S cm−1 under 80 °C and 98 % relative humidity (R.H.) for Co‐tri, which is the highest among CPs/MOFs/COFs and is an example of conductivity in the order of 10−1 S cm−1. Co‐tri and Co‐tetra are excellent proton conductors at mild temperature (40 °C) and 98 % R.H. (conductivities up to 2.92×10−2 and 1.38×10−2 S cm−1, respectively).
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Valency‐Controlled Framework Nucleic Acid Signal Amplifiers ()
Abstract Weak ligand–receptor recognition events are often amplified by recruiting multiple regulatory biomolecules to the action site in biological systems. However, signal amplification in in vitro biomimetic systems generally lack the spatiotemporal regulation in vivo. Herein we report a framework nucleic acid (FNA)‐programmed strategy to develop valence‐controlled signal amplifiers with high modularity for ultrasensitive biosensing. We demonstrated that the FNA‐programmed signal amplifiers could recruit nucleic acids, proteins, and inorganic nanoparticles in a stoichiometric manner. The valence‐controlled signal amplifier enhanced the quantification ability of electrochemical biosensors, and enabled ultrasensitive detection of tumor‐relevant circulating free DNA (cfDNA) with sensitivity enhancement of 3–5 orders of magnitude and improved dynamic range.
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Control of Molar Mass Distribution by Polymerization in the Analytical Ultracentrifuge ()
Abstract Molar mass distributions are of high interest in macromolecular chemistry because they directly determine the physical and chemical properties of polymers. A principal approach to obtain and control the shape of broad molar mass distributions is adjusting the initiator concentration in free radical polymerizations. A controlled gradient of the initiator concentration should potentially lead to tailored molar mass distributions. Here we use analytical ultracentrifugation (AUC) to adjust and measure a macroinitiator's concentration gradient. Subsequent photopolymerization of a uniformly distributed monomer leads to desired chain length distributions. Resulting distributions are described and calculated by a Schulz–Flory approach. The desired concentration profiles are simulated in advance and can be detected anytime by the optical systems in the centrifuge. Therefore, tailored broad molar mass distributions can now be produced using predictions from simulations using the established theory of AUC.
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Emergence of Uranium as a Distinct Metal Center for Building Intrinsic X‐ray Scintillators ()
Abstract The combination of high atomic number and high oxidation state in UVI materials gives rise to both high X‐ray attenuation efficiency and intense green luminescence originating from ligand‐to‐metal charge transfer. These two features suggest that UVI materials might act as superior X‐ray scintillators, but this postulate has remained substantially untested. Now the first observation of intense X‐ray scintillation in a uranyl–organic framework (SCU‐9) that is observable by the naked eye is reported. Combining the advantage in minimizing the non‐radiative relaxation during the X‐ray excitation process over those of inorganic salts of uranium, SCU‐9 exhibits a very efficient X‐ray to green light luminescence conversion. The luminescence intensity shows an essentially linear correlation with the received X‐ray intensity, and is comparable with that of commercially available CsI:Tl. SCU‐9 possesses an improved X‐ray attenuation efficiency (E>20 keV) as well as enhanced radiation resistance and decreased hygroscopy compared to CsI:Tl.
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Catalytic Reduction of Molecular Dinitrogen to Ammonia and Hydrazine Using Vanadium Complexes ()
Abstract Newly designed and prepared vanadium complexes bearing anionic pyrrole‐based PNP‐type pincer and aryloxy ligands were found to work as effective catalysts for the direct conversion of molecular dinitrogen into ammonia and hydrazine under mild reaction conditions. This is the first successful example of vanadium‐catalyzed dinitrogen reduction under mild reaction conditions.
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A Dynamic Chemical Network for Cystinuria Diagnosis ()
Abstract The study of molecular networks represents a conceptual revolution in chemistry. Building on previous knowledge and after understanding the rules of non‐covalent interactions, the design of stimulus‐responsive chemical systems is possible. Herein we report a new strategy, based on the reorganization of a dynamic chemical network that generates new fluorescent associations in the presence of cysteine or cystine. The binding and sensing units are encoded in the components that dynamically assemble and disassemble responding to external stimuli as a successful tool to detect both cysteine and cystine in aqueous media. Moreover, the dynamic sensing system works in human urine, as a prospective application for cystinuria diagnosis.
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Direct Synthesis of a Covalent Triazine‐Based Framework from Aromatic Amides ()
Abstract There have been extensive efforts to synthesize crystalline covalent triazine‐based frameworks (CTFs) for practical applications and to realize their potential. The phosphorus pentoxide (P2O5)‐catalyzed direct condensation of aromatic amide instead of aromatic nitrile to form triazine rings. P2O5‐catalyzed condensation was applied on terephthalamide to construct a covalent triazine‐based framework (pCTF‐1). This approach yielded highly crystalline pCTF‐1 with high specific surface area (2034.1 m2 g−1). At low pressure, the pCTF‐1 showed high CO2 (21.9 wt % at 273 K) and H2 (1.75 wt % at 77 K) uptake capacities. The direct formation of a triazine‐based COF was also confirmed by model reactions, with the P2O5‐catalyzed condensation reaction of both benzamide and benzonitrile to form 1,3,5‐triphenyl‐2,4,6‐triazine in high yield.
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Fused Isoindigo Ribbons with Absorption Bands Reaching Near‐Infrared ()
Abstract Through fusing isoindigo (IID) units at 6,7;6′,7′‐positions, a series of new near‐infrared (NIR) absorbing and stable ribbon‐like conjugated molecules, namely nIIDs in which n represents the number of IID units, have been synthesized. The optical band gaps of the molecules are lowered from 2.03 eV of 1IID to 1.12 eV of 6IID with the increase of the conjugation length. 3IID, 4IID, and 6IID have strong absorption in the NIR region and exhibit photothermal conversion efficiencies of greater than 50 % under laser irradiation at λ=808 nm.
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Core Electron Topologies in Chemical Compounds: Case Study of Carbon versus Silicon ()
Abstract The similarities and differences between carbon and silicon have attracted the curiosity of chemists for centuries. Similarities and analogies can be found in their saturated compounds, but carbon exhibits a cornucopia of unsaturated compounds that silicon (and most other elements) cannot replicate. While this qualitative difference is empirically well known, quantum chemistry has previously only described quantitative differences related to orbital overlap, steric effects, or orbital energies. We study C2 and Si2 and their hydrides X2H2n (X=C, Si; n=1, 2, 3) by first‐principles quantum chemical calculation, and find a qualitative difference in the topologies of the core electrons: carbon has the propensity to alter its core electron topology when forming unsaturated compounds, and silicon has not. We draw a connection between the core electron topologies and ionization energies, and identify other elements we expect to have similarly flexible core topologies as carbon.
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Bioinspired Oxidative Cyclization of the Geissoschizine Skeleton for the Total Synthesis of (−)‐17‐nor‐Excelsinidine ()
Abstract We report the first total synthesis of (−)‐17‐nor‐excelsinidine, a zwitterionic monoterpene indole alkaloid that displays an unusual N4−C16 connection. Inspired by the postulated biosynthesis, we explored an oxidative coupling approach from the geissoschizine framework to forge the key ammonium–acetate connection. Two strategies allowed us to achieve this goal, namely an intramolecular nucleophilic substitution on a 16‐chlorolactam with the N4 nitrogen atom or a direct I2‐mediated N4−C16 oxidative coupling from the enolate of geissoschizine.
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Kinetic Resolution of α‐Hydroxy‐Substituted Oxime Ethers by Enantioselective Cu−H‐Catalyzed Si−O Coupling ()
Abstract A catalyst‐controlled enantioselective alcohol silylation by Cu−H‐catalyzed dehydrogenative Si−O coupling of hydroxy groups α to an oxime ether and simple hydrosilanes is reported. The selectivity factors reached in this kinetic resolution are generally high (s≈50), and these reactions thereby provide reliable access to highly enantioenriched α‐hydroxy‐substituted oxime ethers. The synthetic usefulness of these compounds is also demonstrated.
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Miniaturized Biosensors to Preserve and Monitor Cultural Heritage: from Medical to Conservation Diagnosis ()
Abstract The point‐of‐care testing concept has been exploited to design and develop portable and cheap bioanalytical systems that can be used on‐site by conservators. These systems employ lateral flow immunoassays to simultaneously detect two proteins (ovalbumin and collagen) in artworks. For an in‐depth study on the application of these portable biosensors, both chemiluminescent and colorimetric detections were developed and compared in terms of sensitivity and feasibility. The chemiluminescent system displayed the best analytical performance (that is, two orders of magnitude lower limits of detection than the colorimetric system). To simplify its use, a disposable cartridge was designed ad hoc for this specific application. These results highlight the enormous potential of these inexpensive, easy‐to‐use, and minimally invasive diagnostic tools for conservators in the cultural heritage field.
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Oxidative Coupling of Anionic Abnormal N‐Heterocyclic Carbenes: Efficient Access to Janus‐Type 4,4′‐Bis(2H‐imidazol‐2‐ylidene)s ()
Abstract The oxidative coupling of anionic imidazol‐4‐ylidenes protected at the C2 position with [MnCp(CO)2] or BH3 led to the corresponding 4,4′‐bis(2H‐imidazol‐2‐ylidene) complexes or adducts, in which the two carbene moieties are connected through a single C−C bond. Subsequent acidic treatment of the later species led to the corresponding 4,4′‐bis(imidazolium) salts in good yields. The overall procedure offers practical access to a novel class of Janus‐type bis(NHC)s. Strikingly, the coplanarity of the two NHC rings within the mesityl derivative 4,4′‐bis(IMes), favored by steric hindrance along with stabilizing intramolecular C−H⋅⋅⋅π aryl interactions, allows the alignment of the π‐systems and, as a direct consequence, significant electron communication through the bis(carbene) scaffold.
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Noncontinuous Super‐Diffusive Dynamics of a Light‐Activated Nanobottle Motor ()
Abstract We report a carbonaceous nanobottle (CNB) motor for near infrared (NIR) light‐driven jet propulsion. The bottle structure of the CNB motor is fabricated by soft‐template‐based polymerization. Upon illumination with NIR light, the photothermal effect of the CNB motor carbon shell causes a rapid increase in the temperature of the water inside the nanobottle and thus the ejection of the heated fluid from the open neck, which propels the CNB motor. The occurrence of an explosion, the on/off motion, and the swing behavior of the CNB motor can be modulated by adjusting the NIR light source. Moreover, we simulated the physical field distribution (temperature, fluid velocity, and pressure) of the CNB motor to demonstrate the mechanism of NIR light‐driven jet propulsion. This NIR light‐powered CNB motor exhibits fuel‐free propulsion and control of the swimming velocity by external light and has great potential for future biomedical applications.
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G‐Quadruplex Secondary Structure Obtained from Circular Dichroism Spectroscopy ()
Abstract A curated library of circular dichroism spectra of 23 G‐quadruplexes of known structure was built and analyzed. The goal of this study was to use this reference library to develop an algorithm to derive quantitative estimates of the secondary structure content of quadruplexes from their experimental CD spectra. Principal component analysis and singular value decomposition were used to characterize the reference spectral library. CD spectra were successfully fit to obtain estimates of the amounts of base steps in anti–anti, syn–anti or anti–syn conformations, in diagonal or lateral loops, or in other conformations. The results show that CD spectra of nucleic acids can be analyzed to obtain quantitative structural information about secondary structure content in an analogous way to methods used to analyze protein CD spectra.
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Ultrashort Broadband Cooperative Pulses for Multidimensional Biomolecular NMR Experiments ()
Abstract NMR spectroscopy at ultra‐high magnetic fields requires improved radiofrequency (rf) pulses to cover the increased spectral bandwidth. Optimized 90° pulse pairs were introduced as Ramsey‐type cooperative (Ram‐COOP) pulses for biomolecular NMR applications. The Ram‐COOP element provides broadband excitation with enhanced sensitivity and reduced artifacts even at magnetic fields >1.0 GHz 1H Larmor frequency (23 T). A pair of 30 μs Ram‐COOP pulses achieves an excitation bandwidth of 100 kHz with a maximum rf field of 20 kHz, more than three‐fold improved compared to excitation by rectangular pulses. Ram‐COOP pulses exhibit little offset‐dependent phase errors and are robust to rf inhomogeneity. The performance of the Ram‐COOP element is experimentally confirmed with heteronuclear multidimensional NMR experiments, applied to proteins and nucleic acids. Ram‐COOP provides broadband excitation at low rf field strength suitable for application at current magnetic fields and beyond 23 T.
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Spectroscopic Identification of H2NSO and syn‐ and anti‐HNSOH Radicals ()
Abstract The simplest aminosulfinyl radical H2NSO has been generated in the gas phase through flash vacuum pyrolysis of CF3S(O)NH2 at approximately 1000 K. Upon UV light irradiation (365 nm), 1,3‐H migration occurs in H2NSO and furnishes an elusive N‐amidyl radical HNSOH in syn and anti conformations in cryogenic matrices (N2 or Ar, 15 K). Further 266 nm laser irradiation results in dissociation of HNSOH to H2O and SN and concomitant reformation of H2NSO in trace amount. The identification of H2NSO, syn‐HNSOH, and anti‐HNSOH by matrix‐isolation IR spectroscopy is supported by high‐level quantum chemical computations.
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Combined Non‐invasive PIXE/PIGE Analyses of Mammoth Ivory from Aurignacian Archaeological Sites ()
Abstract Among the earliest Homo sapiens societies in Eurasia, the Aurignacian phase of the Early Upper Paleolithic, approximately 40 000–30 000 years ago, mammoth ivory assumed great social and economic significance, and was used to create hundreds of personal ornaments as well as the earliest known works of three‐dimensional figurative art in the world. This paper reports on the results of micro‐PIXE/PIGE analyses of mammoth‐ivory artifacts and debris from five major sites of Aurignacian ivory use. Patterns of variable fluorine content indicate regionally distinctive strategies of ivory procurement that correspond to apparent differences in human–mammoth interactions. Preserved trace elements (Br, Sr, Zn) indicate that differences at the regional level are applicable to sourcing Paleolithic ivory at the regional scale.
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Modified High‐Nickel Cathodes with Stable Surface Chemistry Against Ambient Air for Lithium‐Ion Batteries ()
Abstract High‐Ni layered oxides are promising next‐generation cathodes for lithium‐ion batteries owing to their high capacity and lower cost. However, as the Ni content increases over 70 %, they have a high dynamic affinity towards moisture and CO2 in ambient air, primarily reacting to form LiOH, Li2CO3, and LiHCO3 on the surface, which is commonly termed “residual lithium”. Air exposure occurs after synthesis as it is common practice to handle and store them under ambient conditions. The air exposure leads to significant performance losses, and hampers the electrode fabrication, impeding their practical viability. Herein, we show that substituting a small amount of Al for Ni in the crystal lattice notably improves the chemical stability against air by limiting the formation of LiOH, Li2CO3, LiHCO3, and NiO in the near‐surface region. The Al‐doped high‐Ni oxides display a high capacity retention with excellent rate capability and cycling stability after being exposed to air for 30 days.
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A Highly Efficient Near‐Infrared‐Emissive Copolymer with a N=N Double‐Bond π‐Conjugated System Based on a Fused Azobenzene–Boron Complex ()
Abstract Fused azobenzene–boron complexes (BAzs) show highly efficient near‐infrared (NIR) emission from the nitrogen–nitrogen double bond (N=N) containing π‐conjugated copolymer. Optical measurements showed that BAz worked as a strong electron acceptor because of the intrinsic electron deficiency of the N=N double bond and the boron–nitrogen (B−N) coordination which dramatically lowered the energy of the lowest unoccupied molecular orbital (LUMO) of the azobenzene ligand. The simple donor–acceptor (D–A) type copolymer of bithiophene (BT) and BAz exhibited intense photoluminescence (PL) in the NIR region both in the dilute solution (λPL=751 nm, ΦPL=0.25) and in the film (λPL=821 nm, ΦPL=0.038). The BAz monomer showed slight PL in the dilute solution, and aggregation‐induced emission (AIE) was detected. We proposed that N=N double bonds should be attractive and functional building blocks for designing π‐conjugated materials.
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Shell‐Isolated Tip‐Enhanced Raman and Fluorescence Spectroscopy ()
Abstract Tip‐enhanced Raman spectroscopy can provide molecular fingerprint information with ultrahigh spatial resolution, but the tip will be easily contaminated, thus leading to artifacts. It also remains a great challenge to establish tip‐enhanced fluorescence because of the quenching resulting from the proximity of the metal tip. Herein, we report shell‐isolated tip‐enhanced Raman and fluorescence spectroscopies by employing ultrathin shell‐isolated tips fabricated by atomic layer deposition. Such shell‐isolated tips not only show outstanding electromagnetic field enhancement in TERS but also exclude interference by contaminants, thus greatly promoting applications in solution. Tip‐enhanced fluorescence has also been achieved using these shell‐isolated tips, with enhancement factors of up to 1.7×103, consistent with theoretical simulations. Furthermore, tip‐enhanced Raman and fluorescence signals are acquired simultaneously, and their relative intensities can be manipulated by changing the shell thickness. This work opens a new avenue for ultrahigh resolution surface analysis using plasmon‐enhanced spectroscopies.
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Mapping the Relationship between Glycosyl Acceptor Reactivity and Glycosylation Stereoselectivity ()
Abstract The reactivity of both coupling partners—the glycosyl donor and acceptor—is decisive for the outcome of a glycosylation reaction, in terms of both yield and stereoselectivity. Where the reactivity of glycosyl donors is well understood and can be controlled through manipulation of the functional/protecting‐group pattern, the reactivity of glycosyl acceptor alcohols is poorly understood. We here present an operationally simple system to gauge glycosyl acceptor reactivity, which employs two conformationally locked donors with stereoselectivity that critically depends on the reactivity of the nucleophile. A wide array of acceptors was screened and their structure–reactivity/stereoselectivity relationships established. By systematically varying the protecting groups, the reactivity of glycosyl acceptors can be adjusted to attain stereoselective cis‐glucosylations.
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Reversible Magnetic Agglomeration: A Mechanism for Thermodynamic Control over Nanoparticle Size ()
Abstract We present a method for the synthesis and precise size control of magnetic nanoparticles in a reversible magnetic agglomeration mechanism. In this approach, nanoparticles nucleate and grow until a critical susceptibility is reached, in which magnetic attraction overcomes dispersive forces, leading to agglomeration and precipitation. This phase change in the system arrests nanoparticle growth and gives true thermodynamic control over the size of nanoparticles. We then show that increasing the alkyl chain length of the surfactant, and hence increasing steric stabilization, allows nanoparticles to grow to larger sizes before agglomeration occurs. Therefore, simply by choosing the correct surfactant, the size and magnetic properties of iron nanoparticles can be tailored for a particular application. With the continuous addition of the precursor solution, we can repeat the steps of nucleation, growth, and magnetic agglomeration indefinitely, making the approach suitable for large scale syntheses.
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Expanding the Chemistry of the Class C Radical SAM Methyltransferase NosN by Using an Allyl Analogue of SAM ()
Abstract The radical S‐adenosylmethionine (SAM) superfamily enzymes cleave SAM reductively to generate a highly reactive 5′‐deoxyadenosyl (dAdo) radical, which initiates remarkably diverse reactions. Unlike most radical SAM enzymes, the class C radical SAM methyltransferase NosN binds two SAMs in the active site, using one SAM to produce a dAdo radical and the second as a methyl donor. Here, we report a mechanistic investigation of NosN in which an allyl analogue of SAM (allyl‐SAM) was used. We show that NosN cleaves allyl‐SAM efficiently and the resulting dAdo radical can be captured by the olefin moieties of allyl‐SAM or 5′‐allylthioadenosine (ATA), the latter being a derivative of allyl‐SAM. Remarkably, we found that NosN produced two distinct sets of products in the presence and absence of the methyl acceptor substrate, thus suggesting substrate‐triggered production of ATA from allyl‐SAM. We also show that NosN produces S‐adenosylhomocysteine from 5′‐thioadenosine and homoserine lactone. These results support the idea that 5′‐methylthioadenosine is the direct methyl donor in NosN reactions, and demonstrate great potential to modulate radical SAM enzymes for novel catalytic activities.
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Enzymatic Formation of a Skipped Methyl‐Substituted Octaprenyl Side Chain of Longestin (KS‐505a): Involvement of Homo‐IPP as a Common Extender Unit ()
Abstract Longestin (KS‐505a), a specific inhibitor of phosphodiesterase, is a meroterpenoid that consists of a unique octacyclic terpene skeleton with branched methyl groups at unusual positions (C1 and C12). Biochemical analysis of Lon23, a methyltransferase involved in the biosynthesis of longestin, demonstrated that it methylates homoisopentenyl diphosphate (homo‐IPP) to afford (3Z)‐3‐methyl IPP. This compound, along with IPP, is selectively accepted as extender units by Lon22, a geranylgeranyl diphosphate (GGPP) synthase homologue, to yield dimethylated GGPP (dmGGPP). The absolute configuration of dmGGPP was determined to be (4R,12R) by degradation and chiral GC analysis. These findings allowed us to propose an enzymatic sequence for key steps of the biosynthetic pathway of the unusual homoterpenoid longestin.
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Redox‐Divergent Synthesis of Fluoroalkylated Pyridines and 2‐Pyridones through Cu‐Catalyzed N−O Cleavage of Oxime Acetates ()
Abstract Cu‐catalyzed redox‐divergent [3+3] coupling of oxime esters with β‐CF3 enones and acrylates is described. This redox‐neutral coupling with enones and acrylates affords trifluoromethylated pyridines and pyridones, respectively. Under reductive conditions, difluoromethylated pyridines, difluoromethlated pyridones, and trifluoromethylated dihydropyridones are obtained. The reactions occur under mild conditions with broad substrate scope and regio/redox selectivity.
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Polar Fluorooxoborate, NaB4O6F: A Promising Material for Ionic Conduction and Nonlinear Optics ()
Abstract The search of new borates with improved functional properties has attracted considerable attention. Herein, a new polar fluorooxoborate, NaB4O6F (NBF) was prepared by high‐temperature solid‐state reaction. NBF belongs to the AB4O6F family (A=alkali metal or ammonium), a series of compounds that undergoes significant cation‐dependent structural changes. NBF is of particular interest owing to the special cation position. Temperature‐dependent ionic conductivity measurements show that NBF is a solid ionic conductor, and it has the lowest active energy of 32.5 kJ mol−1 of fluorooxoborates. NBF also shows a second‐harmonic generation (SHG) response of 0.9×KH2PO4 and 0.2×β‐BaB2O4, at 1064 and 532 nm, respectively, and it has a short UV cutoff edge below 180 nm. Based on bond valence (BV) concepts, symmetry analysis, and the first principles calculation, the unique [B4O6F]∞ layer can be regarded as the “multifunctional unit”, which is responsible for the observed properties of NBF.
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Stishovite's Relative: A Post‐Coesite Form of Phosphorus Oxonitride ()
Abstract Phosphorus oxonitride (PON) is isoelectronic with SiO2 and may exhibit a similar broad spectrum of intriguing properties as silica. However, PON has only been sparsely investigated under high‐pressure conditions and there has been no evidence on a PON polymorph with a coordination number of P greater than 4. Herein, we report a post‐coesite (pc) PON polymorph exhibiting a stishovite‐related structure with P in a (5+1) coordination. The pc‐PON was synthesized using the multianvil technique and characterized by powder X‐ray diffraction, solid‐state NMR spectroscopy, TEM measurements and in situ synchrotron X‐ray diffraction in diamond anvil cells. The structure model was verified by single‐crystal X‐ray diffraction at 1.8 GPa and the isothermal bulk modulus of pc‐PON was determined to K0=163(2) GPa. Moreover, an orthorhombic PON polymorph (o‐PON) was observed under high‐pressure conditions and corroborated as the stable modification at pressures above 17 GPa by DFT calculations.
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Preparation of Cyclobutene Acetals and Tricyclic Oxetanes through Photochemical Tandem and Cascade Reactions ()
Abstract We describe a photochemical reaction using two starting materials, a cyclopent‐2‐enone and an alkene, which are transformed in a controlled manner via the initial [2+2]‐photocycloaddition adducts into cyclobutene aldehydes (conveniently trapped as stable acetals) or unprecedented angular tricyclic 4:4:4 oxetane‐containing skeletons. These compounds are formed through tandem or triple cascade photochemical reaction processes, respectively. Small libraries of each compound class were prepared, thus suggesting that this photochemistry approach opens new opportunities for synthesis design and for widening molecular diversity.
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A Unified Approach for the Assembly of Atisine‐ and Hetidine‐type Diterpenoid Alkaloids: Total Syntheses of Azitine and the Proposed Structure of Navirine C ()
Abstract A tetracyclic dinitrile was synthesized in twelve steps from cyclohex‐2‐en‐1‐one by using a chelation‐triggered conjugate addition to a γ‐hydroxy‐substituted α,β‐unsaturated nitrile and an oxidative dearomatization/Diels–Alder cycloaddition cascade as the key steps. The first total synthesis of azitine (in 17 steps) was achieved through a simple reductive cyclization of this intermediate and subsequent transformations while the total synthesis of the proposed structure of navirine C (in 19 steps) was accomplished by a hydrogen‐atom‐transfer reaction of the tetracyclic dinitrile, Pd/C‐catalyzed reductive cyclization, and subsequent functional group manipulation.
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Rapid Aqueous Late‐Stage Radiolabelling of [GaF3(BnMe2‐tacn)] by 18F/19F Isotopic Exchange: Towards New PET Imaging Probes ()
Abstract A simple and rapid method for 18F radiolabelling of [GaF3(BnMe2‐tacn)] by 18F/19F isotopic exchange is described. The use of MeCN/H2O or EtOH/H2O (75:25) and aqueous [18F]F− (up to 200 MBq) with heating (80 °C, 10 min) gave 66±4 % 18F incorporation at a concentration of 268 nm, and 37±5 % 18F incorporation at even lower concentration (27 nm), without the need for a Lewis acid promoter. A solid‐phase extraction method was established to give [Ga18F19F2(BnMe2‐tacn)] in 99 % radiochemical purity in an EtOH/H2O mixture.
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An Organogold(III) Difluoride with a trans Arrangement ()
Abstract The trans isomer of the organogold(III) difluoride complex [PPh4][(CF3)2AuF2] has been obtained in a stereoselective way and in excellent yield by reaction of [PPh4][CF3AuCF3] with XeF2 under mild conditions. The compound is both thermally stable and reactive. Thus, the fluoride ligands are stereospecifically replaced by any heavier halide or by cyanide, the cyanide affording [PPh4][trans‐(CF3)2Au(CN)2]. The organogold fluoride complexes [CF3AuFx]− (x=1, 2, 3) have been experimentally detected to arise upon collision‐induced dissociation of the [trans‐(CF3)2AuF2]− anion in the gas phase. Their structures have been calculated by DFT methods. In the isomeric forms identified for the open‐shell species [CF3AuF2]−, the spin density residing on the metal center is found to strongly depend on the precise stereochemistry. Based on crystallographic evidence, it is concluded that Auiii and Agiii have similar covalent radii, at least in their most common square‐planar geometry.
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Site‐Selective Cysteine–Cyclooctyne Conjugation ()
Abstract We report a site‐selective cysteine–cyclooctyne conjugation reaction between a seven‐residue peptide tag (DBCO‐tag, Leu‐Cys‐Tyr‐Pro‐Trp‐Val‐Tyr) at the N or C terminus of a peptide or protein and various aza‐dibenzocyclooctyne (DBCO) reagents. Compared to a cysteine peptide control, the DBCO‐tag increases the rate of the thiol–yne reaction 220‐fold, thereby enabling selective conjugation of DBCO‐tag to DBCO‐linked fluorescent probes, affinity tags, and cytotoxic drug molecules. Fusion of DBCO‐tag with the protein of interest enables regioselective cysteine modification on proteins that contain multiple endogenous cysteines; these examples include green fluorescent protein and the antibody trastuzumab. This study demonstrates that short peptide tags can aid in accelerating bond‐forming reactions that are often slow to non‐existent in water.
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Formation of Aminocyclopentadienes from Silyldihydropyridines: Ring Contractions Driven by Anion Stabilization ()
Abstract Highly functionalized aminocyclopentadienes can be formed through the rearrangement of anions generated from readily prepared 6‐silyl‐1,2‐dihydropyridines by desilylation with fluoride. The scope and generality of the reaction was defined, and diverse transformations were performed on the highly functionalized products. A mechanism and driving force for the rearrangement were identified from experiments and DFT calculations.
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Creating a Low‐Potential Redox Polymer for Efficient Electroenzymatic CO2 Reduction ()
Abstract Increasing greenhouse gas emissions have resulted in greater motivation to find novel carbon dioxide (CO2) reduction technologies, where the reduction of CO2 to valuable chemical commodities is desirable. Molybdenum‐dependent formate dehydrogenase (Mo‐FDH) from Escherichia coli is a metalloenzyme that is able to interconvert formate and CO2. We describe a low‐potential redox polymer, synthesized by a facile method, that contains cobaltocene (grafted to poly(allylamine), Cc‐PAA) to simultaneously mediate electrons to Mo‐FDH and immobilize Mo‐FDH at the surface of a carbon electrode. The resulting bioelectrode reduces CO2 to formate with a high Faradaic efficiency of 99±5 % at a mild applied potential of −0.66 V vs. SHE.
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Metal‐Free Fluorine‐Doped Carbon Electrocatalyst for CO2 Reduction Outcompeting Hydrogen Evolution ()
Abstract The electrochemical CO2 reduction (ECDRR), as a key reaction in artificial photosynthesis to implement renewable energy conversion/storage, has been inhibited by the low efficiency and high costs of the electrocatalysts. Herein, we synthesize a fluorine‐doped carbon (FC) catalyst by pyrolyzing commercial BP 2000 with a fluorine source, enabling a highly selective CO2‐to‐CO conversion with a maximum Faradaic efficiency of 90 % at a low overpotential of 510 mV and a small Tafel slope of 81 mV dec−1, outcompeting current metal‐free catalysts. Moreover, the higher partial current density of CO and lower partial current density of H2 on FC relative to pristine carbon suggest an enhanced inherent activity towards ECDRR as well as a suppressed hydrogen evolution by fluorine doping. Fluorine doping activates the neighbor carbon atoms and facilitates the stabilization of the key intermediate COOH* on the fluorine‐doped carbon material, which are also blocked for competing hydrogen evolution, resulting in superior CO2‐to‐CO conversion.
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Dynamic Nuclear Polarization‐Enhanced Biomolecular NMR Spectroscopy at High Magnetic Field with Fast Magic‐Angle Spinning ()
Abstract Dynamic nuclear polarization (DNP) is a powerful way to overcome the sensitivity limitation of magic‐angle‐spinning (MAS) NMR experiments. However, the resolution of the DNP NMR spectra of proteins is compromised by severe line broadening associated with the necessity to perform experiments at cryogenic temperatures and in the presence of paramagnetic radicals. High‐quality DNP‐enhanced NMR spectra of the Acinetobacter phage 205 (AP205) nucleocapsid can be obtained by combining high magnetic field (800 MHz) and fast MAS (40 kHz). These conditions yield enhanced resolution and long coherence lifetimes allowing the acquisition of resolved 2D correlation spectra and of previously unfeasible scalar‐based experiments. This enables the assignment of aromatic resonances of the AP205 coat protein and its packaged RNA, as well as the detection of long‐range contacts, which are not observed at room temperature, opening new possibilities for structure determination.
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Generation and Rearrangement of N,O‐Dialkenylhydroxylamines for the Synthesis of 2‐Aminotetrahydrofurans ()
Abstract A new diastereoselective route to 2‐aminotetrahydrofurans has been developed from N,O‐dialkenylhydroxylamines. These intermediates undergo a spontaneous C−C bond‐forming [3,3]‐sigmatropic rearrangement followed by a C−O bond‐forming cyclization. A copper‐catalyzed N‐alkenylation of an N‐Boc‐hydroxylamine with alkenyl iodides, and a base‐promoted addition of the resulting N‐hydroxyenamines to an electron‐deficient allene, provide modular access to these novel rearrangement precursors. The scope of this de novo synthesis of simple nucleoside analogues has been explored to reveal trends in diastereoselectivity and reactivity. In addition, a base‐promoted ring‐opening and Mannich reaction has been discovered to covert 2‐aminotetrahydrofurans to cyclopentyl β‐aminoacid derivatives or cyclopentenones.
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Enantioselective Formation of 2‐Azetidinones by Ring‐Assisted Cyclization of Interlocked N‐(α‐Methyl)benzyl Fumaramides ()
Abstract The synthesis of optically active interlocked and non‐interlocked 2‐azetidinones by intramolecular cyclization of N‐(α‐methyl)benzyl fumaramide [2]rotaxanes is described. Two different strategies of asymmetric induction were tested in which the chiral group was located either proximal or distal to the reacting center of the thread. During these experiments, an interesting equilibration process inside the macrocyclic void occurred, thus leading to the cyclization through the (α‐methyl)benzyl carbon atom and giving rise to β‐lactams, with a quaternary carbon atom, in an enantio‐ and diastereocontrolled manner. This cyclization also proceeds in kinetically stable chiral pseudo[2]rotaxanes, thus allowing further dethreading to provide enantioenriched 3,4‐disubstituted trans‐2‐azetidinones. The stereochemical outcomes of the cyclizations inside and outside the macrocycle demonstrated noticeable differences.
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Rational Fabrication of Anti‐Freezing, Non‐Drying Tough Organohydrogels by One‐Pot Solvent Displacement ()
Abstract Tough hydrogels, polymeric network structures with excellent mechanical properties (such as high stretchability and toughness), are emerging soft materials. Despite their remarkably mechanical features, tough hydrogels exhibit two flaws (freezing around the icing temperatures of water and drying under arid conditions). Inspired by cryoprotectants (CPAs) used in the inhibition of the icing of water in biological samples, a versatile and straightforward method is reported to fabricate extreme anti‐freezing, non‐drying CPA‐based organohydrogels with long‐term stability by partially displacing water molecules within the pre‐fabricated hydrogels. CPA‐based Ca‐alginate/polyacrylamide (PAAm) tough hydrogels were successfully fabricated with glycerol, glycol, and sorbitol. The CPA‐based organohydrogels remain unfrozen and mechanically flexible even up to −70 °C and are stable under ambient conditions or even vacuum.
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A Vastly Increased Chemical Variety of RNA Modifications Containing a Thioacetal Structure ()
Abstract Recently discovered new chemical entities in RNA modifications have involved surprising functional groups that enlarge the chemical space of RNA. Using LC‐MS, we found over 100 signals of RNA constituents that contained a ribose moiety in tRNAs from E. coli. Feeding experiments with variegated stable isotope labeled compounds identified 37 compounds that are new structures of RNA modifications. One structure was elucidated by deuterium exchange and high‐resolution mass spectrometry. The structure of msms2i6A (2‐methylthiomethylenethio‐N6‐isopentenyl‐adenosine) was confirmed by methione‐D3 feeding experiments and by synthesis of the nucleobase. The msms2i6A contains a thioacetal, shown in vitro to be biosynthetically derived from ms2i6A by the radical‐SAM enzyme MiaB. This enzyme performs thiomethylation, forming ms2i6A from i6A in a first turnover. The new thioacetal is formed by a second turnover. Along with the pool of 36 new modifications, this work describes a new layer of RNA modification chemistry.
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Crowding Shifts the FMN Recognition Mechanism of Riboswitch Aptamer from Conformational Selection to Induced Fit ()
Abstract In bacteria, the binding between the riboswitch aptamer domain and ligand is regulated by environmental cues, such as low Mg2+ in macrophages during pathogenesis to ensure spatiotemporal expression of virulence genes. Binding was investigated between the flavin mononucleotide (FMN) riboswitch aptamer and its anionic ligand in the presence of molecular crowding agent without Mg2+ ion, which mimics pathogenic conditions. Structural, kinetic, and thermodynamic analyses under the crowding revealed more dynamic conformational rearrangements of the FMN riboswitch aptamer compared to dilute Mg2+‐containing solution. It is hypothesized that under crowding conditions FMN binds through an induced fit mechanism in contrast to the conformational selection mechanism previously demonstrated in dilute Mg2+solution. Since these two mechanisms involve different conformational intermediates and rate constants, these findings have practical significance in areas such as drug design and RNA engineering.
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Synthesis, Structure, and Anion Binding Properties of Electron‐Deficient Tetrahomocorona[4]arenes: Shape Selectivity in Anion–π Interactions ()
Abstract Tetrahomocorona[2]arene[2]tetrazines were constructed by means of a fragment coupling strategy based on nucleophilic aromatic substitution reaction starting from 3,6‐dichlorotetrazine and o‐, m‐, and p‐bis(hydroxymethyl)benzenes. The unprecedented macrocycles gave rectangular box‐like cavities with tunable cavity sizes and deficient electronic properties depending on the substitution pattern of phenylene. Due to anion–π interactions, they formed complexes selectively with azide and thiocyanate owing to complementary shapes between host and guest.
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How Changing the Bridgehead Can Affect the Properties of Tripodal Ligands ()
Abstract Although a multitude of studies have explored the coordination chemistry of classical tripodal ligands containing a range of main‐group bridgehead atoms or groups, it is not clear how periodic trends affect ligand character and reactivity within a single ligand family. A case in point is the extensive family of neutral tris‐2‐pyridyl ligands E(2‐py)3 (E=C−R, N, P), which are closely related to archetypal tris‐pyrazolyl borates. With the 6‐methyl substituted ligands E(6‐Me‐2‐py)3 (E=As, Sb, Bi) in hand, the effects of bridgehead modification alone on descending a single group in the periodic table were assessed. The primary influence on coordination behaviour is the increasing Lewis acidity (electropositivity) of the bridgehead atom as Group 15 is descended, which not only modulates the electron density on the pyridyl donor groups but also introduces the potential for anion selective coordination behaviour.
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A Very Short Uranium(IV)–Rhodium(I) Bond with Net Double‐Dative Bonding Character ()
Abstract Reaction of [U{C(SiMe3)(PPh2)}(BIPM)(μ‐Cl)Li(TMEDA)(μ‐TMEDA)0.5]2 (BIPM=C(PPh2NSiMe3)2; TMEDA=Me2NCH2CH2NMe2) with [Rh(μ‐Cl)(COD)]2 (COD=cyclooctadiene) affords the heterotrimetallic UIV−RhI2 complex [U(Cl)2{C(PPh2NSiMe3)(PPh[C6H4]NSiMe3)}{Rh(COD)}{Rh(CH(SiMe3)(PPh2)}]. This complex has a very short uranium–rhodium distance, the shortest uranium–rhodium bond on record and the shortest actinide–transition metal bond in terms of formal shortness ratio. Quantum‐chemical calculations reveal a remarkable Rh UIV net double dative bond interaction, involving RhI 4d ‐ and 4dxy/xz‐type donation into vacant UIV 5f orbitals, resulting in a Wiberg/Nalewajski–Mrozek U−Rh bond order of 1.30/1.44, respectively. Despite being, formally, purely dative, the uranium–rhodium bonding interaction is the most substantial actinide–metal multiple bond yet prepared under conventional experimental conditions, as confirmed by structural, magnetic, and computational analyses.
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Chemiluminescent Probes for Activity‐Based Sensing of Formaldehyde Released from Folate Degradation in Living Mice ()
Abstract Formaldehyde (FA) is a common environmental toxin that is also produced naturally in the body through a wide range of metabolic and epigenetic processes, motivating the development of new technologies to monitor this reactive carbonyl species (RCS) in living systems. Herein, we report a pair of first‐generation chemiluminescent probes for selective formaldehyde detection. Caging phenoxy‐dioxetane scaffolds bearing different electron‐withdrawing groups with a general 2‐aza‐Cope reactive formaldehyde trigger provides chemiluminescent formaldehyde probes 540 and 700 (CFAP540 and CFAP700) for visible and near‐IR detection of FA in living cells and mice, respectively. In particular, CFAP700 is capable of visualizing FA release derived from endogenous folate metabolism, providing a starting point for the use of CFAPs and related chemical tools to probe FA physiology and pathology, as well as for the development of a broader palette of chemiluminescent activity‐based sensing (ABS) probes that can be employed from in vitro biochemical to cell to animal models.
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Diferrocenylmercury‐Bridged Diphosphine: A Chiral, Ambiphilic, and Redox‐Active Bidentate Ligand ()
Abstract A diphosphine chelate ligand with a wide and flexible bite angle, a unique stereochemical environment, and redox‐active and ambiphilic character is reported. Initially generated as its HgCl2 complex by reaction of 1,2‐fc(PPh2)(SnMe3) (fc=ferrocenediyl) with HgCl2 in acetone, treatment with [n‐Bu4N]CN readily liberates the free chiral bidentate ligand. An intermolecular ClHg−Cl→Hgfc2 (2.9929(13) Å) interaction that is unprecedented in ambiphilic ligand chemistry is seen in the solid structure of Hg(fcPPh2)2⋅HgCl2 where the bridging mercury atom acts as a σ‐acceptor. Furthermore, a bis‐[Rh(COD)Cl] complex is introduced, which displays relatively short Rh⋅⋅⋅Hg contacts of 3.4765(5) and 3.4013(1) Å. Wiberg indices of 0.12 are determined for these Rh⋅⋅⋅Hg interactions and an AIM analysis reveals bond paths with an electron density ρ(r) of 1.2×10−2 and 1.4×10−2 e/a03 at the bond critical points.
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Selective Conversion of CO2 into Isocyanate by Low‐Coordinate Iron Complexes ()
Abstract Discovery of the mechanisms for selective transformations of CO2 into organic compounds is a challenge. Herein, we describe the reaction of low‐coordinate Fe silylamide complexes with CO2 to give trimethylsilyl isocyanate and the corresponding Fe siloxide complex. Kinetic studies show that this is a two‐stage reaction, and the presence of a single equivalent of THF influences the rates of both steps. Isolation of a thermally unstable intermediate provides mechanistic insight that explains both the effect of THF in this reaction, and the way in which the reaction achieves high selectivity for isocyanate formation.
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Design of Trifluoroalkenyl Iodonium Salts for a Hypervalency‐Aided Alkenylation–Cyclization Strategy: Metal‐Free Construction of Aziridine Rings ()
Abstract The synthesis of fluorinated compounds and their use as pharmaceutical ingredients or synthetic building blocks have been in the focus of chemical and medicinal research. However, the efficient synthesis of trifluoromethylated nitrogen heterocycles is sometimes challenging. Herein, we disclose a simple aziridination process that relies on the use of amines and novel alkenyl iodonium reagents for the synthesis of strained, trifluoromethylated heterocycles. With the utilization of a newly designed and bench‐stable but highly reactive hypervalent alkenyl iodonium species, these three‐membered‐ring heterocyclic compounds can be efficiently constructed from simple amines under mild conditions in the absence of transition‐metal catalysts. The special reactivity of the new trifluoropropenyl synthon towards nucleophilic centers could be exploited in more general cyclization and alkenylation reactions in the future.
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Atomically Precise Nanocluster Assemblies Encapsulating Plasmonic Gold Nanorods ()
Abstract The self‐assembled structures of atomically precise, ligand‐protected noble metal nanoclusters leading to encapsulation of plasmonic gold nanorods (GNRs) is presented. Unlike highly sophisticated DNA nanotechnology, this strategically simple hydrogen bonding‐directed self‐assembly of nanoclusters leads to octahedral nanocrystals encapsulating GNRs. Specifically, the p‐mercaptobenzoic acid (pMBA)‐protected atomically precise silver nanocluster, Na4[Ag44(pMBA)30], and pMBA‐functionalized GNRs were used. High‐resolution transmission and scanning transmission electron tomographic reconstructions suggest that the geometry of the GNR surface is responsible for directing the assembly of silver nanoclusters via H‐bonding, leading to octahedral symmetry. The use of water‐dispersible gold nanoclusters, Au≈250(pMBA)n and Au102(pMBA)44, also formed layered shells encapsulating GNRs. Such cluster assemblies on colloidal particles are a new category of precision hybrids with diverse possibilities.
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CuH‐Catalyzed Asymmetric Hydroamidation of Vinylarenes ()
Abstract A CuH‐catalyzed enantioselective hydroamidation reaction of vinylarenes has been developed using readily accessible 1,4,2‐dioxazol‐5‐ones as electrophilic amidating reagents. This method provides a straightforward and efficient approach to synthesize chiral amides in good yields with high levels of enantiopurity under mild conditions. Moreover, this transformation tolerates substrates bearing a broad range of functional groups.
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Another Unprecedented Wieland Mechanism Confirmed: Hydrogen Formation from Hydrogen Peroxide, Formaldehyde, and Sodium Hydroxide ()
Abstract In 1923, Wieland and Wingler reported that in the molecular hydrogen producing reaction of hydrogen peroxide with formaldehyde in basic solution, free hydrogen atoms (H.) are not involved. They postulated that bis(hydroxymethyl)peroxide, HOCH2OOCH2OH, is the intermediate, which decomposes to yield H2 and formate, proposing a mechanism that would nowadays be considered as a “concerted process”. Since then, several other (conflicting) “mechanisms” have been suggested. Our NMR and Raman spectroscopic and kinetic studies, particularly the determination of the deuterium kinetic isotope effect (DKIE), now confirm that in this base‐dependent reaction, both H atoms of H2 derive from the CH2 hydrogen atoms of formaldehyde, and not from the OH groups of HOCH2OOCH2OH or from water. Quantum‐chemical CBS‐QB3 and W1BD computations show that H2 release proceeds through a concerted process, which is strongly accelerated by double deprotonation of HOCH2OOCH2OH, thereby ruling out a free radical pathway.
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Generation of Aryl and Heteroaryl Magnesium Reagents in Toluene by Br/Mg or Cl/Mg Exchange ()
Abstract The alkylmagnesium alkoxide sBuMgOR⋅LiOR (R=2‐ethylhexyl), which was prepared as a 1.5 m solution in toluene, undergoes very fast Br/Mg exchange with aryl and heteroaryl bromides, producing aryl and heteroaryl magnesium alkoxides (ArMgOR⋅LiOR) in toluene. These Grignard reagents react with a broad range of electrophiles, including aldehydes, ketones, allyl bromides, acyl chlorides, epoxides, and aziridines, in good yields. Remarkably, the related reagent sBu2Mg⋅2 LiOR (R=2‐ethylhexyl) undergoes Cl/Mg exchange with various electron‐rich aryl chlorides in toluene, producing diorganomagnesium species of type Ar2Mg⋅2 LiOR, which react well with aldehydes and allyl bromides.
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Side Methyl Groups Control the Conformation and Contribute to Symmetry Breaking of Isoprenoid Chromophores ()
Abstract Ab initio DFT computations reveal that the essential structural and photophysical features of the conjugated π‐electron system of retinal and carotenoids are dictated by “innocent” methyl substituents. These methyl groups shape the conformation and symmetry of the isoprenoid chromophores by causing a sigmoidal distortion of the polyene skeleton and increasing its flexibility, which facilitates fitting to their binding pockets in proteins. Comparison of in vacuo conformations of the chromophores with their native (protein‐bound) conformations showed, surprisingly, that the peripheral groups and interactions with the protein environment are much less significant than the methyl side groups in tuning their structural features. The methyl side groups also contribute to a loss of symmetry elements specific to linear polyenes. In effect, the symmetry‐imposed restrictions on the chromophore electronic properties are disabled, which is of tremendous relevance to their photophysics. This is evidenced by their non‐negligible permanent dipole moments and by the simulated and experimentally measured circular dichroism spectra, which necessarily reflect the chirality of the conjugated π‐electron system.
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Reactions of Fluoroalkenes with an Aluminium(I) Complex ()
Abstract A series of industrially relevant fluoroalkenes react with a monomeric AlI complex. These reactions break strong sp2 and sp3 C−F bonds, and result in the formation of a diverse array of organoaluminium compounds. Mechanistic studies show that two mechanisms are likely in operation: 1) direct oxidative addition of the C−F bond to AlI occurs with retention of alkene stereochemistry, and 2) stepwise formation and decomposition of a metallocyclopropane intermediate occurs with inversion of alkene stereochemistry. As part of this mechanistic analysis, we have isolated the first aluminium metallocyclopropane complex from oxidative addition of an alkene to AlI. Remarkably this reaction is reversible and reductive elimination of the alkene occurs at higher temperature reforming AlI. Furthermore, in selected cases the organoaluminium products are susceptible toward β‐fluoride elimination to yield a double C−F activation pathway.
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Electrochemical Functional‐Group‐Tolerant Shono‐type Oxidation of Cyclic Carbamates Enabled by Aminoxyl Mediators ()
Abstract An electrochemical method has been developed for α‐oxygenations of cyclic carbamates by using a bicyclic aminoxyl as a mediator and water as the nucleophile. The mediated electrochemical process enables substrate oxygenation to proceed at a potential that is approximately 1 V lower than the redox potential of the carbamate substrate. This feature allows for functional‐group compatibility that is inaccessible with conventional Shono oxidations, which proceed by direct electrochemical substrate oxidation. This reaction also represents the first α‐functionalization of non‐activated cyclic carbamates with oxoammonium oxidants.
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Graphene‐Like Molecules with Four Zigzag Edges ()
Abstract An efficient synthetic method toward graphene‐like molecules (GLMs), having four zigzag edges, is described. They were obtained as stable materials and their structures were confirmed by X‐ray crystallographic analysis. They exhibit topology‐ and size‐dependent electronic properties and global aromaticity, which are all different from GLMs having either all‐armchair edges, or three zigzag edges, or two armchair/two zigzag edges. They can be reversibly oxidized and reduced into stable charged species, which show fragmental aromatic character to minimize anti‐aromaticity. Our studies give some new insights into the electronic structures and properties of a new type of rarely studied GLMs.
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Transport of Nucleoside Triphosphates into Cells by Artificial Molecular Transporters ()
Abstract Chemically modified nucleoside triphosphates (NTPs) are widely exploited as unnatural metabolites in chemical biology and medicinal chemistry. Because anionic NTPs do not permeate cell membranes, their corresponding neutral precursors are employed in cell‐based assays. These precursors become active metabolites after enzymatic conversion, which often proceeds insufficiently. Here we show that metabolically‐active NTPs can be directly transported into eukaryotic cells and bacteria by the action of designed synthetic nucleoside triphosphate transporters (SNTTs). The transporter is composed of a receptor, which forms a non‐covalent complex with a triphosphate anion, and a cell‐penetrating agent, which translocates the complex across the plasma membrane. NTP is then released from the complex in the intracellular milieu and accumulates in nuclei and nucleoli in high concentration. The transport of NTPs proceeds rapidly (seconds to minutes) and selectively even in the presence of other organic anions. We demonstrate that this operationally simple and efficient means of transport of fluorescently labelled NTPs into cells can be used for metabolic labeling of DNA in live cells.
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Concerted Bimetallic Nanocluster Synthesis and Encapsulation via Induced Zeolite Framework Demetallation for Shape and Substrate Selective Heterogeneous Catalysis ()
Abstract Bimetallic nanoparticle encapsulation in microporous zeolite crystals is a promising route for producing catalysts with unprecedented reaction selectivities. Herein, a novel synthetic approach was developed to produce PtZnx nanoclusters encapsulated inside zeolite micropores by introducing Pt2+ cations into a zincosilicate framework via ion exchange, and subsequent controlled demetallation and alloying with framework Zn. The resulting zeolites featured nanoclusters with sizes of approximately 1 nm, having an interatomic structure corresponding to a PtZnx alloy as confirmed by pair distribution function (PDF) analysis. These materials featured simultaneous shape and substrate specificity demonstrated by the selective production of p‐chloroaniline from the competitive hydrogenation of p‐chloronitrobenzene and 1,3‐dimethyl‐5‐nitrobenzene.
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Enantioselective Synthesis of Medium‐Sized Lactams via Chiral α,β‐Unsaturated Acylammonium Salts ()
Abstract Medium‐sized lactams are important structural motifs found in a variety of bioactive compounds and natural products but are challenging to prepare, especially in optically active form. A Michael addition/proton transfer/lactamization organocascade process is described that delivers medium‐sized lactams, including azepanones, benzazepinones, azocanones, and benzazocinones, in high enantiopurity through the intermediacy of chiral α,β‐unsaturated acylammonium salts. An unexpected indoline synthesis was also uncovered, and the benzazocinone skeleton was transformed into other complex heterocyclic derivatives, including spiroglutarimides, isoquinolinones, and δ‐lactones.
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Divergent Coupling of Anilines and Enones by Integration of C−H Activation and Transfer Hydrogenation ()
Abstract Cp*RhIII/IrIII complexes are known to play important roles in both C−H activation and transfer hydrogenation (TH). However, these two areas evolved separately. They have been integrated in redox‐ and chemodivergent coupling reactions of N‐pyridylanilines with enones. The iridium‐catalyzed coupling with enones leads to the efficient synthesis of tetrahydroquinolines through TH from iPrOH. Counterintuitively, iPrOH does not serve as the sole hydride source, and the major reaction pathway involves disproportionation of a dihydroquinoline intermediate, followed by the convergent and iterative reduction of quinolinium species.
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The Cooperative Effect of both Molecular and Supramolecular Chirality on Cell Adhesion ()
Abstract Although helical nanofibrous structures have great influence on cell adhesion, the role played by chiral molecules in these structures on cells behavior has usually been ignored. The chirality of helical nanofibers is inverted by the odd–even effect of methylene units from homochiral l‐phenylalanine derivative during assembly. An increase in cell adhesion on left‐handed nanofibers and weak influence of cell behaviors on right‐handed nanofibers are observed, even though both were derived from l‐phenylalanine derivatives. Weak and negative influences on cell behavior was also observed for left‐ and right‐handed nanofibers derived from d‐phenylalanine, respectively. The effect on cell adhesion of single chiral molecules and helical nanofibers may be mutually offset.
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Cobalt‐Catalyzed Intramolecular Reactions between a Vinylcyclopropane and an Alkyne: Switchable [5+2] Cycloaddition and Homo‐Ene Pathways ()
Abstract Cobalt–diphosphine catalysts have been found to promote intramolecular reactions between a vinylcyclopropane and an alkyne to selectively afford either the [5+2] cycloaddition product or the homo‐ene reaction product under solvent control. The former product is exclusively formed in noncoordinating 1,2‐dichloroethane, whereas the latter is dominant in coordinating solvents, such as acetonitrile and dimethylacetamide. Furthermore, a highly enantioselective variant of the homo‐ene reaction afforded chiral tetrahydrofuran, pyrrolidine, and cyclopentane derivatives bearing 1,3‐diene and alkylidene substituents.
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Dissipative Synthetic DNA‐Based Receptors for the Transient Loading and Release of Molecular Cargo ()
Abstract Supramolecular chemistry is moving into a direction in which the composition of a chemical equilibrium is no longer determined by thermodynamics but by the efficiency with which kinetic states can be populated by energy consuming processes. Herein, we show that DNA is ideally suited for programming chemically fueled dissipative self‐assembly processes. Advantages of the DNA‐based systems presented in this study include a perfect control over the activation site for the chemical fuel in terms of selectivity and affinity, highly selective fuel consumption that occurs exclusively in the activated complex, and a high tolerance for the presence of waste products. Finally, it is shown that chemical fuels can be used to selectively activate different functions in a system of higher complexity embedded with multiple response pathways.
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Placement of Single Proteins within the SERS Hot Spots of Self‐Assembled Silver Nanolenses ()
Abstract This study demonstrates the bottom‐up synthesis of silver nanolenses. A robust coating protocol enabled the functionalization of differently sized silver nanoparticles with DNA single strands of orthogonal sequence. Coated particles 10 nm, 20 nm, and 60 nm in diameter were self‐assembled by DNA origami scaffolds to form silver nanolenses. Single molecules of the protein streptavidin were selectively placed in the gap of highest electric field enhancement. Streptavidin labelled with alkyne groups served as model analyte in surface‐enhanced Raman scattering (SERS) experiments. By correlated Raman mapping and atomic force microscopy, SERS signals of the alkyne labels of a single streptavidin molecule, from a single silver nanolens, were detected. The discrete, self‐similar aggregates of solid silver nanoparticles are promising for plasmonic applications.
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Genetically Engineered Supercharged Polypeptide Fluids: Fast and Persistent Self‐Ordering Induced by Touch ()
Abstract Mechanically induced disorder–order transitions have been studied in fluid surfactant solutions or polymer thermotropic liquid crystals. However, isothermally induced ordered phases do not persist after cessation of shear, which limits their technological applicability. Moreover, no such stimuli‐responsive materials involving biomacromolecules have been reported although biopolymer liquids are gaining a lot of attention. A biological fluid system is introduced in which anionic polypeptides are complexed with cationic surfactants. The resulting fluids exhibited very sensitive isotropic–nematic transition triggered by shear. The formed liquid crystal was preserved after cessation of mechanical stimulus. Self‐ordering behavior of the material was achieved through water flow and finger pressing. The latter mechanical induction resulted in the formation of complex pattern that can be read out by birefringence, allowing the recording of fingerprint information.
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From a Helix to a Small Cycle: Metadynamics‐Inspired αvβ6 Integrin Selective Ligands ()
Abstract The RGD‐recognizing αvβ6 integrin has only recently emerged as a major target for cancer diagnosis and therapy. Thus, the development of selective, low‐molecular‐weight ligands of this receptor is still in great demand. Here, a metadynamics‐driven design strategy allowed us to successfully convert a helical nonapeptide into a cyclic pentapeptide (6) showing remarkable potency and αvβ6 specificity. NMR and docking studies elucidated the reasons for the high affinity and selectivity of this compound, setting the ground for the rational design of new αvβ6‐specific small peptides or even peptidomimetics. In vivo PET imaging studies demonstrated the potential use of 6 for medical applications.
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Supramolecular Copolymerization as a Strategy to Control the Stability of Self‐Assembled Nanofibers ()
Abstract A major challenge in supramolecular polymerization is controlling the stability of the polymers formed, that is, controlling the rate of monomer exchange in the equilibrium between monomer and polymer. The exchange dynamics of supramolecular polymers based on benzene‐1,3,5‐tricarboxamide (BTA) can be regulated by copolymerizing molecules with dendronized (dBTA) and linear (nBTA) ethylene glycol‐based water‐soluble side chains. Whereas nBTAs form long nanofibers in water, dBTAs do not polymerize, forming instead small spherical aggregates. The copolymerization of the two BTAs results in long nanofibers. The exchange dynamics of both the BTA monomers in the copolymer are significantly slowed down in the mixed systems, leading to a more stable copolymer, while the morphology and spectroscopic signature of the copolymers are identical to that of nBTA homopolymer. This copolymerization is the supramolecular counterpart of styrene/ maleic anhydride copolymerization.
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Efficient CO2 Insertion and Reduction Catalyzed by a Terminal Zinc Hydride Complex ()
Abstract The terminal zinc hydride complex [Tntm]ZnH (2; Tntm=tris(6‐tert‐butyl‐3‐thiopyridazinyl)methanide) is an efficient hydrosilylation catalyst of CO2 at room temperature without the need of Lewis acidic additives. The inherent electrophilicity of the system leads to selective formation of the monosilylated product (MeO)3SiO2CH (at room temperature with a TOF of 22.2 h−1 and at 45 °C with a TOF of 66.7 h−1). In absence of silanes, the intermediate formate complex [Tntm]Zn(O2CH) (3) is quantitatively formed within 5 min. All complexes were fully characterized by 1H and 13C NMR spectroscopy and single‐crystal X‐ray diffraction analyses. Density functional theory (DFT) calculations reveal a high positive charge on zinc and the increased preference of the ligand to adopt a κ3‐coordination mode.
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Optically Matched Semiconductor Quantum Dots Improve Photophosphorylation Performed by Chloroplasts ()
Abstract A natural–artificial hybrid system was constructed to enhance photophosphorylation. The system comprises chloroplasts modified with optically matched quantum dots (chloroplast–QD) with a large Stokes shift. The QDs possess a unique optical property and transform ultraviolet light into available and highly effective red light for use by chloroplasts. This favorable feature enables photosystem II contained within the hybrid system to split more water and produce more protons than chloroplasts would otherwise do on their own. Consequently, a larger proton gradient is generated and photophosphorylation is improved. At optimal efficiency activity increased by up to 2.3 times compared to pristine chloroplasts. Importantly, the degree of overlap between emission of the QDs and absorption of chloroplasts exerts a strong influence on the photophosphorylation efficiency. The chloroplast–QD hybrid presents an efficient solar energy conversion route, which involves a rational combination of a natural system and an artificial light‐harvesting nanomaterial.
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Versatile Three‐Dimensional Porous Cu@Cu2O Aerogel Networks as Electrocatalysts and Mimicking Peroxidases ()
Abstract A facile strategy is presented to form 3D porous Cu@Cu2O aerogel networks by self‐assembling Cu@Cu2O nanoparticles with the diameters of ca. 40 nm for constructing catalytic interfaces. Unexpectedly, the prepared Cu@Cu2O aerogel networks display excellent electrocatalytic activity to glucose oxidation at a low onset potential of ca. 0.25 V. Moreover, the Cu@Cu2O aerogels also can act as mimicking‐enzymes including horseradish peroxidase and NADH peroxidase, and show obvious enzymatic catalytic activities to the oxidation of dopamine (DA), o‐phenyldiamine (OPD), 3,3,5,5‐tetramethylbenzidine (TMB), and dihydronicotinamide adenine dinucleotide (NADH) in the presence of H2O2. These 3D Cu@Cu2O aerogel networks are a new class of porous catalytic materials as mimic peroxidases and electrocatalysts and offer a novel platform to construct catalytic interfaces for promising applications in electrochemical sensors and artificial enzymatic catalytic systems.
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Direct Access to Aryl Bis(trifluoromethyl)carbinols from Aryl Bromides or Fluorosulfates: Palladium‐Catalyzed Carbonylation ()
Abstract A palladium‐catalyzed carbonylative approach for the direct conversion of (hetero)aryl bromides into their α,α‐bis(trifluoromethyl)carbinols is described, and it employs only stoichiometric amounts of carbon monoxide and trifluoromethyltrimethylsilane. In addition, aryl fluorosulfates proved highly compatible with these reaction conditions. The method is tolerant of a diverse set of functional groups, and it is adaptable to late‐stage carbon‐isotope labeling.
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Bulky Diamine Ligand Promotes Cross‐Coupling of Difluoroalkyl Bromides by Iron Catalysis ()
Abstract Although iron‐catalyzed cross‐coupling of Grignard reagents with alkyl halides has been well established, the adoption of the reaction for fluoroalkylations has not been reported because traditional catalytic systems often lead to defluorination reactions. Described herein is the investigation of an iron‐catalyzed cross‐coupling between arylmagnesium bromides and difluoroalkyl bromides with modified N,N,N′,N′‐tetramethyl‐ethane‐1,2‐diamine (TMEDA) as a ligand. The use of this bulky diamine, in which a butylene is substituted at one carbon atom of the ethylene backbone in TMEDA, enables the iron‐catalyzed difluoroalkylation under mild reaction conditions with a wide range of difluoroalkyl bromides, including vulnerable bromodifluoromethane, thus providing a general and cost‐efficient route for applications in medicinal chemistry.
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Chiral Atropisomeric Indenocorannulene Bowls: Critique of the Cahn–Ingold–Prelog Conception of Molecular Chirality ()
Abstract Chiral corannulenes abound, but suffer generally from configurational lability associated with bowl‐to‐bowl inversion, thus obviating questions of stereogenicity and stereoelement construction. In contrast, peri‐annulated corannulenes show greatly increased barriers for bowl‐to‐bowl inversion; specifically indenocorannulenes invert on a time scale too slow to observe by normal NMR methods and raise the possibility of creating chiral atropisomeric bowl‐shaped aromatics. Two methods for preparing indenocorannulene from simple 2‐haloarylcorannulenes—silyl cation C–F activation, and Pd‐mediated C–Cl activation[5]—enable the synthesis of an array of such chiral atropisomeric indenocorannulenes. Resolution of the enantiomers by high‐performance liquid chromatography over chiral support phases motivates the study of chiroptical properties, the assignment of absolute “Cartesian” configuration, and the assessment of configurational stability. These studies bring into question any systematic assignment of nontrivial stereoelements (i.e. not the molecule in its entirety) and refute any assertion of congruence between “Cahn–Ingold–Prelog elements” and the physical or “Cartesian” basis of chirality.
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Trifluoromethanesulfonic Anhydride as a Low‐Cost and Versatile Trifluoromethylation Reagent ()
Abstract A large number of reagents have been developed for the synthesis of trifluoromethylated compounds. However, an ongoing challenge in trifluoromethylation reaction is the use of less expensive and practical trifluoromethyl sources. We report herein the unprecedented direct trifluoromethylation of (hetero)arenes using trifluoromethanesulfonic anhydride as a radical trifluoromethylation reagent by merging photoredox catalysis and pyridine activation. Furthermore, introduction of both the CF3 and OTf groups of the trifluoromethanesulfonic anhydride into internal alkynes to access tetrasubstituted trifluoromethylated alkenes was achieved. Since trifluoromethanesulfonic anhydride is a low‐cost and abundant chemical, this method provides a cost‐efficient and practical route to trifluoromethylated compounds.
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Distinct Electron Conductance Regimes in Bacterial Decaheme Cytochromes ()
Abstract Shewanella oneidensis MR‐1 gains energy by extracellular electron transfer to solid surfaces. They employ c‐type cytochromes in two Mtr transmembrane complexes, forming a multiheme wire for electron transport across the cellular outer membrane. We investigated electron‐ and hole‐transfer mechanisms in the external terminal of the two complexes, MtrC and MtrF. Comparison of computed redox potentials with previous voltammetry experiments in distinct environments (isolated and electrode‐bound conditions of PFV or in vivo) suggests that these systems function in different regimes depending on the environment. Analysis of redox potential shifts in different regimes indicates strong coupling between the hemes via an interplay between direct Coulomb and indirect interactions through local structural reorganization. The latter results in the screening of Coulomb interactions and explains poor correlation of the strength of the heme‐to‐heme interactions with the distance between the hemes.
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Reconstruction of Supported Metal Nanoparticles in Reaction Conditions ()
Abstract Metal nanoparticles (NPs) dispersed on a high‐surface‐area support are normally used as heterogeneous catalysts. Recent in situ experiments have shown that structure reconstruction of the NP occurs in real catalysis. However, the role played by supports in these processes is still unclear. Supports can be very important in real catalysis because of the new active sites at the perimeter interface between nanoparticles and supports. Herein, using a developed multiscale model coupled with in situ spherical aberration‐corrected (Cs‐corrected) TEM experiments, we show that the interaction between the support and the gas environment greatly changes the contact surface area between the metal and support, which further leads to the critical change in the perimeter interface. The dynamic changes of the interface in reactive environments can thus be predicted and be included in the rational design of supported metal nanocatalysts. In particular, our multiscale model shows quantitative consistency with experimental observations. This work offers possibilities for obtaining atomic‐scale structures and insights beyond the experimental limits.
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Palaeoproteomic Profiling of Conservation Layers on a 14th Century Italian Wall Painting ()
Abstract Ahead of display, a non‐original layer was observed on the surface of a fragment of a wall painting by Ambrogio Lorenzetti (active 1319, died 1348/9). FTIR analysis suggested proteinaceous content. Mass spectrometry was used to better characterise this layer and revealed two protein components: sheep and cow glue and chicken and duck egg white. Analysis of post‐translational modifications detected several photo‐oxidation products, which suggest that the egg experienced prolonged exposure to UV light and was likely applied long before the glue layer. Additionally, glycation products detected may indicate naturally occurring glycoprotein degradation or reaction with a carbohydrate material such as starch, identified by ATR‐FTIR in a cross‐section of a sample taken from the painting. Palaeoproteomics is shown to provide detailed characterisation of organic layers associated with mural paintings and therefore aids reconstruction of the conservation history of these objects.
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Exploring the Performance Improvement of the Oxygen Evolution Reaction in a Stable Bimetal–Organic Framework System ()
Abstract Despite wide applications of bimetallic electrocatalysis in oxygen evolution reaction (OER) owing to their superior performance, the origin of the improved performance remains elusive. The underlying mechanism was explored by designing and synthesizing a series of stable metal–organic frameworks (MOFs: NNU‐21–24) based on trinuclear metal carboxylate clusters and tridentate carboxylate ligands. Among the examined stable MOFs, NNU‐23 exhibits the best OER performance; particularly, compared with monometallic MOFs, all the bimetallic MOFs display improved OER activity. DFT calculations and experimental results demonstrate that introduction of the second metal atom can improve the activity of the original atom. The proposed model of bimetallic electrocatalysts affecting their OER performance can facilitate design of efficient bimetallic catalysts for energy storage and conversion, and investigation of the related catalytic mechanisms.
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Bottom‐up Construction of π‐Extended Arenes by a Palladium‐Catalyzed Annulative Dimerization of o‐Iodobiaryl Compounds ()
Abstract A straightforward method was developed for construction of aromatic compounds with a triphenylene core. The method involves Pd‐catalyzed annulative dimerization of o‐iodobiaryl compounds by double C−I and C−H bond cleavage steps. Simple reaction conditions are needed, requiring neither a ligand nor an oxidant, and the reaction tolerates a wide range of coupling partners without compromising efficiency or scalability. Significantly, the tetrachloro‐substituted synthon, 1,6,11‐trichloro‐4‐(4‐chlorophenyl)triphenylene, can be generated and used to prepare a series of fully fused, small graphene nanoribbons by a late‐stage arylation with arylboronic acids and a subsequent Scholl reaction. The synthetic strategy enables bottom‐up access to extended π‐systems in a controlled manner.
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Regioselective Formation of (E)‐β‐Vinylstannanes with a Topologically Controlled Molybdenum‐Based Alkyne Hydrostannation Catalyst ()
Abstract The regioselective formation of (E)‐β‐vinylstannanes has been a long‐standing challenge in transition‐metal‐catalyzed alkyne hydrostannation. Herein, we report a well‐defined molybdenum‐based system featuring two encumbering m‐terphenyl isocyanides that reliably and efficiently delivers (E)‐β‐vinylstannanes from a range of terminal and internal alkynes with high regioselectivity. The system is particularly effective for aryl alkynes and can discriminate between alkyl chains of low steric hindrance in unsymmetrically substituted dialkyl alkynes. Catalytic hydrostannation with this system is also characterized by an electronic effect that leads to a decrease in regioselectivity when electron‐withdrawing groups are present on the alkyne substrate.
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Enantioselective Rhodium‐Catalyzed Dimerization of ω‐Allenyl Carboxylic Acids: Straightforward Synthesis of C2‐Symmetric Macrodiolides ()
Abstract Herein, we report on the first enantioselective and atom‐efficient catalytic one‐step dimerization method to selectively transform ω‐allenyl carboxylic acids into C2‐symmetric 14‐ to 28‐membered bismacrolactones (macrodiolides). This convenient asymmetric access serves as an attractive route towards multiple naturally occuring homodimeric macrocyclic scaffolds and demonstrates excellent efficiency to construct the complex, symmetric core structures. By utilizing a rhodium catalyst with a modified chiral cyclopentylidene‐diop ligand, the desired diolides were obtained in good to high yields, high diastereoselectivity, and excellent enantioselectivity.
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Long‐Lasting Efficacy of Coatings for Bronze Artwork Conservation: The Key Role of Layered Double Hydroxide Nanocarriers in Protecting Corrosion Inhibitors from Photodegradation ()
Abstract The photodegradation kinetics of 2‐mercaptobenzothiazole (MBT), a corrosion inhibitor for copper‐based alloys, is studied in high amorphous polyvinyl alcohol coatings subjected to either UV irradiation or indoor light exposure. The photodegradation process proceeds rapidly, thus compromising the anticorrosion ability of the coating. The encapsulation of MBT into layered double hydroxide (LDH) nanocarriers slows down its decomposition kinetics by a factor of three. Besides preserving the corrosion inhibitor, such a strategy allows a controlled release of MBT triggered by corrosion‐related stimuli, for example, presence of chloride species and acid pH. The developed coating guarantees long‐lasting corrosion protection even at low amounts of inhibitor‐loaded LDH nanocarriers (ca. 5 wt %). This also reflects in a high transparency, which makes the protective coating suitable for demanding applications, such as the conservation of high‐value metal works of art.
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Organocatalytic Atroposelective Intramolecular [4+2] Cycloaddition: Synthesis of Axially Chiral Heterobiaryls ()
Abstract The enantioselective construction of axially chiral aryl‐naphthopyran skeletons was realized by organocatalytic atroposelective intramolecular [4+2] cycloaddition of in situ generated vinylidene ortho‐quinone methides, from 2‐ethynylphenol derivatives, with alkynes. Through this method, the heteroatropisomers were obtained with excellent yields and enantioselectivities. Moreover, a speculative model of the stereochemical outcome is proposed based on preliminary mechanistic studies. The products having various functional groups can be easily transformed into valuable intermediates as either potential ligands or organocatalysts.
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Ultrathin Chiral Metal–Organic‐Framework Nanosheets for Efficient Enantioselective Separation ()
Abstract Chiral metal–organic framework (CMOF) nanosheets only a few layers thick remain a virgin land waiting for exploration. Herein, the first examples of ultrathin CMOF nanosheets are prepared by the confinement growth of two‐dimensional (2D) chiral layers, which are assembled by helical metal–organic chains within microemulsion. This convenient and easily scaled up inverse microemulsion method gives a series of 2D CMOF nanosheets composed of variable metal nodes or chiral ligands. More significantly, thanks to the exceptionally large number of chiral sites exposed on surfaces, the as‐obtained CMOF nanosheets exhibit much higher enantioselectivity in chiral separation compared with their bulk counterparts.
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Tunneling Mode of Scanning Electrochemical Microscopy: Probing Electrochemical Processes at Single Nanoparticles ()
Abstract Electrochemical experiments at individual nanoparticles (NPs) can provide new insights into their structure–activity relationships. By using small nanoelectrodes as tips in a scanning electrochemical microscope (SECM), we recently imaged individual surface‐bound 10–50 nm metal NPs. Herein, we introduce a new mode of SECM operation based on tunneling between the tip and a nanoparticle immobilized on the insulating surface. The obtained current vs. distance curves show the transition from the conventional feedback response to electron tunneling between the tip and the NP at separation distances of less than about 3 nm. In addition to high‐resolution imaging of the NP topography, the tunneling mode enables measurement of the heterogeneous kinetics at a single NP without making an ohmic contact with it. The developed method should be useful for studying the effects of nanoparticle size and geometry on electrocatalytic activity in real‐world applications.
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Free‐Standing Air Cathodes Based on 3D Hierarchically Porous Carbon Membranes: Kinetic Overpotential of Continuous Macropores in Li‐O2 Batteries ()
Abstract Free‐standing macroporous air electrodes with enhanced interfacial contact, rapid mass transport, and tailored deposition space for large amounts of Li2O2 are essential for improving the rate performance of Li‐O2 batteries. An ordered mesoporous carbon membrane with continuous macroporous channels was prepared by inversely topological transformation from ZnO nanorod array. Utilized as a free‐standing air cathode for Li‐O2 battery, the hierarchically porous carbon membrane shows superior rate performance. However, the increased cross‐sectional area of the continuous macropores on the cathode surface leads to a kinetic overpotential with large voltage hysteresis and linear voltage variation against Butler–Volmer behavior. The kinetics were investigated based on the rate‐determining step of second electron transfer accompanied by migration of Li+ in solid or quasi‐solid intermediates. These discoveries shed light on the design of the air cathode for Li‐O2 batteries with high‐rate performance.
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Development of the Vinylogous Pictet–Spengler Cyclization and Total Synthesis of (±)‐Lundurine A ()
Abstract A novel vinylogous Pictet–Spengler cyclization has been developed for the generation of indole‐annulated medium‐sized rings. The method enables the synthesis of tetrahydroazocinoindoles with a fully substituted carbon center, a prevalent structural motif in many biologically active alkaloids. The strategy has been applied to the total synthesis of (±)‐lundurine A.
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Molecular Insight into the Mg2+‐Dependent Allosteric Control of Indole Prenylation by Aromatic Prenyltransferase AmbP1 ()
Abstract AmbP1 is a cyanobacterial aromatic prenyltransferase and a dedicated synthase for (R)‐3‐geranyl‐3‐isocyanovinyl indolenine (2), the biogenetic precursor for hapalindole‐type alkaloids. The regioselective geranylation of cis‐indolyl vinyl isonitrile (1) by the standalone AmbP1 to give 2 has been shown to require a magnesium ion (Mg2+) to suppress the formation of cis‐2‐geranylindolyl vinyl isonitrile (3). Here, we report high‐resolution crystal structures of AmbP1 in complex with 1 and geranyl S‐thiodiphosphate (GSPP) in the presence and absence of a Mg2+ effector. The comparative study of these structures revealed a unique allosteric binding site for Mg2+ that modulates the conformation of 1 in the active site of AmbP1 for its selective geranylation. This work defines the structural basis for AmbP1 catalysis in the biogenesis of hapalindole‐type alkaloids and provides the first atomic‐level insight to the allosteric regulation of prenyltransferases.
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Catalytic Direct‐Type Addition Reactions of Alkylarenes with Imines and Alkenes ()
Abstract Catalytic addition reactions of very weakly acidic nonactivated alkylarenes such as toluene and its derivatives were developed by using a strongly basic mixed catalyst system under mild reaction conditions. The addition reactions with imines and alkenes proceeded smoothly under proton‐transfer conditions to afford the desired products in good to high yields, and high levels of regio‐ and stereoselectivity were achieved. It was also revealed that the asymmetric addition reaction of an alkylarene was possible.
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Electronic Communication between two [10]cycloparaphenylenes and Bis(azafullerene) (C59N)2 Induced by Cooperative Complexation ()
Abstract The complex of [10]cycloparaphenylene ([10]CPP) with bis(azafullerene) (C59N)2 is investigated experimentally and computationally. Two [10]CPP rings are bound to the dimeric azafullerene giving [10]CPP⊃(C59N)2⊂[10]CPP. Photophysical and redox properties support an electronic interaction between the components especially when the second [10]CPP is bound. Unlike [10]CPP⊃C60, in which there is negligible electronic communication between the two species, upon photoexcitation a partial charge transfer phenomenon is revealed between [10]CPP and (C59N)2 reminiscent of CPP‐encapsulated metallofullerenes. Such an alternative electron‐rich fullerene species demonstrates C60‐like ground‐state properties and metallofullerene‐like excited‐state properties opening new avenues for construction of functional supramolecular architectures with organic materials.
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Spectral Imaging and Archival Data in Analysing Madonna of the Rabbit Paintings by Manet and Titian ()
Abstract A concise insight into the outputs provided by the latest prototype of visible‐near infrared (Vis‐NIR) multispectral scanner (National Research Council‐National Institute of Optics, CNR‐INO, Italy) is presented. The analytical data acquired on an oil painting Madonna of the Rabbit by É. Manet are described. In this work, the Vis‐NIR was complemented with X‐ray fluorescence (XRF) mapping for the chemical and spatial characterization of several pigments. The spatially registered Vis‐NIR data facilitated their processing by spectral correlation mapping (SCM) and artificial neural network (ANN) algorithm, respectively, for pigment mapping and improved visibility of pentimenti and of underdrawing style. The data provided several key elements for the comparison with a homonymous original work by Titian studied within the ARCHive LABoratory (ARCHLAB) transnational access project.
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High‐Performance Sodium Metal Anodes Enabled by a Bifunctional Potassium Salt ()
Abstract Developing Na metal anodes that can be deeply cycled with high efficiency for a long time is a prerequisite for rechargeable Na metal batteries to be practically useful despite their notable advantages in theoretical energy density and potential low cost. Their high chemical reactivity with the electrolyte and tendency for dendrite formation are two major issues limiting the reversibility of Na metal electrodes. In this work, we introduce for the first time potassium bis(trifluoromethylsulfonyl)imide (KTFSI) as a bifunctional electrolyte additive to stabilize Na metal electrodes, in which the TFSI− anions decompose into lithium nitride and oxynitrides to render a desirable solid electrolyte interphase layer while the K+ cations preferentially adsorb onto Na protrusions and provide electrostatic shielding to suppress dendritic deposition. Through the cooperation of the cations and anions, we have realized Na metal electrodes that can be deeply cycled at a capacity of 10 mAh cm−2 for hundreds of hours.
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Highly Efficient and Stereoselective Thioallylation of Alkynes: Possible Gold Redox Catalysis with No Need for a Strong Oxidant ()
Abstract Stereoselective thioallylation of alkynes under possible gold redox catalysis was accomplished with high efficiency (as low as 0.1 % catalyst loading, up to 99 % yield) and broad substrate scope (various alkynes, inter‐ and intramolecular fashion). The gold(I) catalyst acts as both a π‐acid for alkyne activation and a redox catalyst for AuI/III coupling, whereas the sulfonium cation generated in situ functions as a mild oxidant. This novel methodology provides an exciting system for gold redox catalysis without the need for a strong oxidant.
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Direct Aryloxylation/Alkyloxylation of Dialkyl Phosphonates for the Synthesis of Mixed Phosphonates ()
Abstract A strategy for the direct functionalization strategy of inertial dialkyl phosphonates with hydroxy compounds to afford diverse mixed phosphonates with good yields and functional‐group tolerance has been developed. Mechanistic investigations involving both NMR studies and DFT studies suggest that an unprecedented highly reactive PV species (phosphoryl pyridin‐1‐ium salt), a key intermediate for this new synthetic transformation, is generated in situ from dialkyl phosphonate in the presence of Tf2O/pyridine.
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A General, Activator‐Free Palladium‐Catalyzed Synthesis of Arylacetic and Benzoic Acids from Formic Acid ()
Abstract A new catalyst for the carboxylative synthesis of arylacetic and benzoic acids using formic acid (HCOOH) as the CO surrogate was developed. In an improvement over previous work, CO is generated in situ without the need for any additional activators. Key to success was the use of a specific system consisting of palladium acetate and 1,2‐bis((tert‐butyl(2‐pyridinyl)phosphinyl)methyl)benzene. The generality of this method is demonstrated by the synthesis of more than 30 carboxylic acids, including non‐steroidal anti‐inflammatory drugs (NSAIDs), under mild conditions in good yields.
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Insights into the Crystallization and Structural Evolution of Glycine Dihydrate by In Situ Solid‐State NMR Spectroscopy ()
Abstract In situ solid‐state NMR spectroscopy is exploited to monitor the structural evolution of a glycine/water glass phase formed on flash cooling an aqueous solution of glycine, with a range of modern solid‐state NMR methods applied to elucidate structural properties of the solid phases present. The glycine/water glass is shown to crystallize into an intermediate phase, which then transforms to the β polymorph of glycine. Our in situ NMR results fully corroborate the identity of the intermediate crystalline phase as glycine dihydrate, which was first proposed only very recently.
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Synthesis of 1,4‐Cyclohexanedimethanol, 1,4‐Cyclohexanedicarboxylic Acid and 1,2‐Cyclohexanedicarboxylates from Formaldehyde, Crotonaldehyde and Acrylate/Fumarate ()
Abstract Valuable polyester monomers and plasticizers—1,4‐cyclohexanedimethanol (CHDM), 1,4‐cyclohexanedicarboxylic acid (CHDA), and 1,2‐cyclohexanedicarboxylates—have been prepared by a new strategy. The synthetic processes involve a proline‐catalyzed formal [3+1+2] cycloaddition of formaldehyde, crotonaldehyde, and acrylate (or fumarate). CHDM is produced after a subsequent hydrogenation step over a commercially available Cu/Zn/Al catalyst and a one‐pot hydrogenation/oxidation/hydrolysis process yields CHDA, whereas 1,2‐cyclohexanedicarboxylate is obtained by a Pd/C‐catalyzed tandem decarbonylation/hydrogenation step.
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De novo Biosynthesis of “Non‐Natural” Thaxtomin Phytotoxins ()
Abstract Thaxtomins are diketopiperazine phytotoxins produced by Streptomyces scabies and other actinobacterial plant pathogens that inhibit cellulose biosynthesis in plants. Due to their potent bioactivity and novel mode of action there has been considerable interest in developing thaxtomins as herbicides for crop protection. To address the need for more stable derivatives, we have developed a new approach for structural diversification of thaxtomins. Genes encoding the thaxtomin NRPS from S. scabies, along with genes encoding a promiscuous tryptophan synthase (TrpS) from Salmonella typhimurium, were assembled in a heterologous host Streptomyces albus. Upon feeding indole derivatives to the engineered S. albus strain, tryptophan intermediates with alternative substituents are biosynthesized and incorporated by the NRPS to deliver a series of thaxtomins with different functionalities in place of the nitro group. The approach described herein, demonstrates how genes from different pathways and different bacterial origins can be combined in a heterologous host to create a de novo biosynthetic pathway to “non‐natural” product target compounds.
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The N‐Methylpyrrolidone (NMP) Effect in Iron‐Catalyzed Cross‐Coupling with Simple Ferric Salts and MeMgBr ()
Abstract The use of N‐methylpyrrolidone (NMP) as a co‐solvent in ferric salt catalyzed cross‐coupling reactions is crucial for achieving the highly selective, preparative scale formation of cross‐coupled product in reactions utilizing alkyl Grignard reagents. Despite the critical importance of NMP, the molecular level effect of NMP on in situ formed and reactive iron species that enables effective catalysis remains undefined. Herein, we report the isolation and characterization of a novel trimethyliron(II) ferrate species, [Mg(NMP)6][FeMe3]2 (1), which forms as the major iron species in situ in reactions of Fe(acac)3 and MeMgBr under catalytically relevant conditions where NMP is employed as a co‐solvent. Importantly, combined GC analysis and 57Fe Mössbauer spectroscopic studies identified 1 as a highly reactive iron species for the selective formation generating cross‐coupled product. These studies demonstrate that NMP does not directly interact with iron as a ligand in catalysis but, alternatively, interacts with the magnesium cations to preferentially stabilize the formation of 1 over [Fe8Me12]− cluster generation, which occurs in the absence of NMP.
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Tunable and Photoswitchable Chemically Induced Dimerization for Chemo‐optogenetic Control of Protein and Organelle Positioning ()
Abstract The spatiotemporal dynamics of proteins and organelles play an important role in controlling diverse cellular processes. Optogenetic tools using photosensitive proteins and chemically induced dimerization (CID), which allow control of protein dimerization, have been used to elucidate the dynamics of biological systems and to dissect the complicated biological regulatory networks. However, the inherent limitations of current optogenetic and CID systems remain a significant challenge for the fine‐tuning of cellular activity at precise times and locations. Herein, we present a novel chemo‐optogenetic approach, photoswitchable chemically induced dimerization (psCID), for controlling cellular function by using blue light in a rapid and reversible manner. Moreover, psCID is tunable; that is, the dimerization and dedimerization degrees can be fine‐tuned by applying different doses of illumination. Using this approach, we control the localization of proteins and positioning of organelles in live cells with high spatial (μm) and temporal (ms) precision.
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Reversible Response of Luminescent Terbium(III)–Nanocellulose Hydrogels to Anions for Latent Fingerprint Detection and Encryption ()
Abstract Fingerprint fluorescence imaging has become one of the most prominent technologies in the field of forensic medicine, but it seldom considers the security protection of detection information, which is of great importance in modern society. Herein we demonstrate that luminescent TbIII–carboxymethyl cellulose (CMC) complex binding aptamer hydrogels that are reversibly responsive to ClO−/SCN− can be used for the selective detection, protection, and storage of fingerprint information. The imaging information of the fingerprint can be quenched and recovered by ClO−/SCN− regulation, respectively, resulting in reversible on/off conversion of the luminescence signals for the encryption and decryption of multiple levels of information. The present study opens new avenues for multilevel imaging, data recording, and security protection of fingerprint information with tunable fluorescent hydrogels.
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Catholyte‐Free Electrocatalytic CO2 Reduction to Formate ()
Abstract Electrochemical reduction of carbon dioxide (CO2) into value‐added chemicals is a promising strategy to reduce CO2 emission and mitigate climate change. One of the most serious problems in electrocatalytic CO2 reduction (CO2R) is the low solubility of CO2 in an aqueous electrolyte, which significantly limits the cathodic reaction rate. This paper proposes a facile method of catholyte‐free electrocatalytic CO2 reduction to avoid the solubility limitation using commercial tin nanoparticles as a cathode catalyst. Interestingly, as the reaction temperature rises from 303 K to 363 K, the partial current density (PCD) of formate improves more than two times with 52.9 mA cm−2, despite the decrease in CO2 solubility. Furthermore, a significantly high formate concentration of 41.5 g L−1 is obtained as a one‐path product at 343 K with high PCD (51.7 mA cm−2) and high Faradaic efficiency (93.3 %) via continuous operation in a full flow cell at a low cell voltage of 2.2 V.
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Catalyst‐Dependent Chemoselective Formal Insertion of Diazo Compounds into C−C or C−H Bonds of 1,3‐Dicarbonyl Compounds ()
Abstract A catalyst‐dependent chemoselective one‐carbon insertion of diazo compounds into the C−C or C−H bonds of 1,3‐dicarbonyl species is reported. In the presence of silver(I) triflate, diazo insertion into the C(=O)−C bond of the 1,3‐dicarbonyl substrate leads to a 1,4‐dicarbonyl product containing an all‐carbon α‐quaternary center. This reaction constitutes the first example of an insertion of diazo‐derived carbenoids into acyclic C−C bonds. When instead scandium(III) triflate was applied as the catalyst, the reaction pathway switched to formal C−H insertion, affording 2‐alkylated 1,3‐dicarbonyl products. Different reaction pathways are proposed to account for this powerful catalyst‐dependent chemoselectivity.
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Metal‐ and Base‐Free Room‐Temperature Amination of Organoboronic Acids with N‐Alkyl Hydroxylamines ()
Abstract We have found that readily available N‐alkyl hydroxylamines are effective reagents for the amination of organoboronic acids in the presence of trichloroacetonitrile. This amination reaction proceeds rapidly at room temperature and in the absence of added metal or base, it tolerates a remarkable range of functional groups, and it can be used in the late‐stage assembly of two complex units.
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Universal pH‐Responsive and Metal‐Ion‐Free Self‐Assembly of DNA Nanostructures ()
Abstract pH‐responsiveness has been widely pursued in dynamic DNA nanotechnology, owing to its potential in biosensing, controlled release, and nanomachinery. pH‐triggering systems mostly depend on specific designs of DNA sequences. However, sequence‐independent regulation could provide a more general tool to achieve pH‐responsive DNA assembly, which has yet to be developed. Herein, we propose a mechanism for dynamic DNA assembly by utilizing ethylenediamine (EN) as a reversibly chargeable (via protonation) molecule to overcome electrostatic repulsions. This strategy provides a universal pH‐responsivity for DNA assembly since the regulation originates from externally co‐existing EN rather than specific DNA sequences. Furthermore, it endows structural DNA nanotechnology with the benefits of a metal‐ion‐free environment including nuclease resistance. The concept could in principle be expanded to other organic molecules which may bring unique controls to dynamic DNA assembly.
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Control of the Spin Dynamics of Single‐Molecule Magnets by using a Quasi One‐Dimensional Arrangement ()
Abstract Magnetic dipole interactions are dominate in quasi one‐dimensional (1D) molecular magnetic materials, in which TbNcPc units (Tb3+=terbium(III) ion, Nc2−=naphthalocyaninato, Pc2−=phthalocyaninato) adopt a structure similar to TbPc2 single‐molecule magnets (SMMs). The magnetic properties of the [TbNcPc]0/+ (neutral 1 and cationic 2) with 1D structures are significantly different from those of a magnetically diluted sample (3). In particular, the magnetic relaxation time (τ) of 2 in the low‐temperature region is five orders of magnitude slower than that of 3. Furthermore, the coercivity (HC) of 2 remained up to about 20 K. The single‐ion anisotropy of Tb3+ ions in a 1D structure and the magnetic dipole interactions acting among molecules determines the direction of the magnetic properties. These results show that the spin dynamics can be improved by manipulating the arrangement of SMMs in the solid state.
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Iron‐Catalyzed Ring‐Closing C−O/C−O Metathesis of Aliphatic Ethers ()
Abstract Among all metathesis reactions known to date in organic chemistry, the metathesis of multiple bonds such as alkenes and alkynes has evolved into one of the most powerful methods to construct molecular complexity. In contrast, metathesis reactions involving single bonds are scarce and far less developed, particularly in the context of synthetically valuable ring‐closing reactions. Herein, we report an iron‐catalyzed ring‐closing metathesis of aliphatic ethers for the synthesis of substituted tetrahydropyrans and tetrahydrofurans, as well as morpholines and polycyclic ethers. This transformation is enabled by a simple iron catalyst and likely proceeds via cyclic oxonium intermediates.
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In Vitro Biosynthesis of the Nonproteinogenic Amino Acid Methoxyvinylglycine ()
Abstract Oxyvinylglycines are a family of nonproteinogenic amino acids featuring an essential vinyl ether conferring mechanism‐based inhibition of pyridoxal phosphate enzymes. The gene clusters for a few oxyvinylglycines are known, yet the biosynthetic origin of the vinyl ether is elusive. The in vitro biosynthesis of methoxyvinylglycine or l‐2‐amino‐4‐methoxy‐trans‐3‐butenoic acid (AMB) is reported. It is shown that AMB is made from glutamate as an alanyl‐AMB dipeptide and the rationale is provided for the N‐term Ala. Using a chemical capture method, the order and timing of the modifications on non‐ribosomal peptide synthetase (NRPS)‐bound substrates was determined, including a cryptic hydroxylation of the Glu β‐carbon. Eliminating this hydroxy group likely generates a key α,β‐dehydroamino acid intermediate that facilitates decarboxylation. This work sheds light on vinyl ether biosynthesis and uncovers new NRPS chemistry.
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Complexing DNA Origami Frameworks through Sequential Self‐Assembly Based on Directed Docking ()
Abstract Ordered DNA origami arrays have the potential to compartmentalize space into distinct periodic domains that can incorporate a variety of nanoscale objects. Herein, we used the cavities of a preassembled 2D DNA origami framework to incorporate square‐shaped DNA origami structures (SQ‐origamis). The framework was self‐assembled on a lipid bilayer membrane from cross‐shaped DNA origami structures (CR‐origamis) and subsequently exposed to the SQ‐origamis. High‐speed AFM revealed the dynamic adsorption/desorption behavior of the SQ‐origamis, which resulted in continuous changing of their arrangements in the framework. These dynamic SQ‐origamis were trapped in the cavities by increasing the Mg2+ concentration or by introducing sticky‐ended cohesions between extended staples, both from the SQ‐ and CR‐origamis, which enabled the directed docking of the SQ‐origamis. Our study offers a platform to create supramolecular structures or systems consisting of multiple DNA origami components.
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Gold‐Catalyzed Regiospecific C−H Annulation of o‐Ethynylbiaryls with Anthranils: π‐Extension by Ring‐Expansion En Route to N‐Doped PAHs ()
Abstract We describe a novel, short, and flexible approach to diverse N‐doped polycyclic aromatic hydrocarbons (PAHs) through gold‐catalyzed π‐extension of anthranils with o‐ethynylbiaryls as reagents. This strategy uses easily accessible starting materials, is simple due to high step and atom economy, and shows good functional‐group compatibility as well as scale‐up potential. Mechanistically, the tandem reaction is proposed to involve a nucleophilic addition/ring opening/regiospecific C−H annulation/protodeauration sequence terminated by a Friedel–Crafts‐type cyclization. Photophysical studies of the products indicated violet‐blue fluorescence emission with quantum yields up to 0.45.
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From Open‐Shell Singlet Diradicaloid to Closed‐Shell Global Antiaromatic Macrocycles ()
Abstract A dithieno[a,h]‐s‐indacene‐ (DTI‐) based diradicaloid DTI‐2Br was synthesized and its open‐shell singlet diradical character was validated by magnetic measurements. On the other hand, its macrocyclic trimer DTI‐MC3 and tetramer DTI‐MC4 turned out to be closed‐shell compounds with global antiaromaticity, which was supported by X‐ray crystallographic analysis and NMR spectroscopy, assisted by ACID and 2D‐ICSS calculations. Such change can be explained by a subtle balance between two types of antiferromagnetic spin–spin coupling along the π‐conjugated macrocycles. The dications of DTI‐MC3 and DTI‐MC4 turned out to be open‐shell singlet diradical dications, with a singlet–triplet energy gap of −2.90 and −2.60 kcal mol−1, respectively. At the same time, they are both global aromatic. Our studies show that intramolecular spin–spin interactions play important roles on electronic properties of π‐conjugated macrocycles.
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Dynamic Nuclear Polarization NMR Spectroscopy of Polymeric Carbon Nitride Photocatalysts: Insights into Structural Defects and Reactivity ()
Abstract Metal‐free polymeric carbon nitrides (PCNs) are promising photocatalysts for solar hydrogen production, but their structure–photoactivity relationship remains elusive. Two PCNs were characterized by dynamic‐nuclear‐polarization‐enhanced solid‐state NMR spectroscopy, which circumvented the need for specific labeling with either 13C‐ or 15N‐enriched precursors. Rapid 1D and 2D data acquisition was possible, providing insights into the structural contrasts between the PCNs. Compared to PCN_B with lower performance, PCN_P is a more porous and more active photocatalyst that is richer in terminal N−H bonds not associated with interpolymer chains. It is proposed that terminal N−H groups act as efficient carrier traps and reaction sites.
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Robust SnO2−x Nanoparticle‐Impregnated Carbon Nanofibers with Outstanding Electrochemical Performance for Advanced Sodium‐Ion Batteries ()
Abstract The sluggish sodium reaction kinetics, unstable Sn/Na2O interface, and large volume expansion are major obstacles that impede practical applications of SnO2‐based electrodes for sodium‐ion batteries (SIBs). Herein, we report the crafting of homogeneously confined oxygen‐vacancy‐containing SnO2−x nanoparticles with well‐defined void space in porous carbon nanofibers (denoted SnO2−x/C composites) that address the issues noted above for advanced SIBs. Notably, SnO2−x/C composites can be readily exploited as the working electrode, without need for binders and conductive additives. In contrast to past work, SnO2−x/C composites‐based SIBs show remarkable electrochemical performance, offering high reversible capacity, ultralong cyclic stability, and excellent rate capability. A discharge capacity of 565 mAh g−1 at 1 A g−1 is retained after 2000 cycles.
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Modeling the Evolution of Crosslinked and Extractable Material in an Oil‐Based Paint Model System ()
Abstract The construction of mechanistic models for the autoxidation of fatty acid or ester substrates found in oil paint binders is a challenging undertaking due to the complexity of the large crosslinked species that form, and the small molecules that volatilize. Building models that capture this product diversity are made possible by automating the process of network generation. This work presents a microkinetic model for the autoxidation of ethyl linoleate catalyzed by cobalt(II) 2‐ethyl hexanoate. The mechanism size was controlled by using a rate‐based criterion to include the most kinetically relevant reactions from among the millions of possible reactions generated. The resulting model was solved and compared to experimental metrics. Quantities such as hexanal production and the consumption of unsaturated moieties were in good agreement with experiment. Finally, the model was used to explore the effect of the catalyst concentration and temperature on key measurables.
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Halogen–Aromatic π Interactions Modulate Inhibitor Residence Times ()
Abstract Prolonged drug residence times may result in longer‐lasting drug efficacy, improved pharmacodynamic properties, and “kinetic selectivity” over off‐targets with high drug dissociation rates. However, few strategies have been elaborated to rationally modulate drug residence time and thereby to integrate this key property into the drug development process. Herein, we show that the interaction between a halogen moiety on an inhibitor and an aromatic residue in the target protein can significantly increase inhibitor residence time. By using the interaction of the serine/threonine kinase haspin with 5‐iodotubercidin (5‐iTU) derivatives as a model for an archetypal active‐state (type I) kinase–inhibitor binding mode, we demonstrate that inhibitor residence times markedly increase with the size and polarizability of the halogen atom. The halogen–aromatic π interactions in the haspin–inhibitor complexes were characterized by means of kinetic, thermodynamic, and structural measurements along with binding‐energy calculations.
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Photochemical Generation of Chiral N,B,X‐Heterocycles by Heteroaromatic C−X Bond Scission (X=S, O) and Boron Insertion ()
Abstract Chiral organoboron compounds with a chelate backbone and mesityl/heterocycle substituents (thienyl, furyl, and derivatives thereof) undergo a quantitative phototransformation that yields rare, chiral N,B,X‐containing heterocycles, such as base‐stabilized 1,2‐thiaborinines and 1,2‐oxaborinines. Boriranes were observed as intermediates in some of these transformations. The oxaborinines display further reactivity, generating 4a,12b‐dihydrobenzo[h][1,2]oxaborinino[4,3‐f]quinolines through a sequential conrotatory electrocyclization and a [1,5]‐H shift. The N,B,X‐containing heterocycles display strong blue‐green to orange‐red emission in the solid state. Combined DFT//CASP2T calculations suggest that a common biradical intermediate is responsible for the formation of these compounds as well as their interconversion.
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A Durable Nickel Single‐Atom Catalyst for Hydrogenation Reactions and Cellulose Valorization under Harsh Conditions ()
Abstract Hydrothermally stable, acid‐resistant nickel catalysts are highly desired in hydrogenation reactions, but such a catalyst remains absent owing to the inherent vulnerability of nickel under acidic conditions. An ultra‐durable Ni‐N‐C single‐atom catalyst (SAC) has now been developed that possesses a remarkable Ni content (7.5 wt %) required for practical usage. This SAC shows not only high activities for hydrogenation of various unsaturated substrates but also unprecedented durability for the one‐pot conversion of cellulose under very harsh conditions (245 °C, 60 bar H2, presence of tungstic acid in hot water). Using integrated spectroscopy characterization and computational modeling, the active site structure is identified as (Ni‐N4)⋅⋅⋅N, where significantly distorted octahedral coordination and pyridinic N constitute a frustrated Lewis pair for the heterolytic dissociation of dihydrogen, and the robust covalent chemical bonding between Ni and N atoms accounts for its ultrastability.
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Pigment and Binder Concentrations in Modern Paint Samples Determined by IR and Raman Spectroscopy ()
Abstract Knowledge of the techniques employed by artists, such as the composition of the paints, colour palette, and painting style, is of crucial importance not only to attribute works of art to the workshop or artist but also to develop strategies and measures for the conservation and restoration of the art. While much research has been devoted to investigating the composition of an artist's materials from a qualitative point of view, little effort has been made in terms of quantitative analyses. This study aims to quantify the relative concentrations of binders (acrylic and alkyd) and inorganic pigments in different paint samples by IR and Raman spectroscopies. To perform this quantitative evaluation, reference samples of known concentrations were prepared to obtain calibration plots. In a further step, the quantification method was verified by additional test samples and commercially available paint tubes. The results obtained confirm that the quantitative method developed for IR and Raman spectroscopy is able to efficiently determine different pigment and binder concentrations of paint samples with high accuracy.
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Nanosecond Dynamics Regulate the MIF‐Induced Activity of CD74 ()
Abstract Macrophage migration inhibitory factor (MIF) activates CD74, which leads to severe disorders including inflammation, autoimmune diseases and cancer under pathological conditions. Molecular dynamics (MD) simulations up to one microsecond revealed dynamical correlation between a residue located at the opening of one end of the MIF solvent channel, previously thought to be a consequence of homotrimerization, and residues in a distal region responsible for CD74 activation. Experiments verified the allosteric regulatory site and identified a pathway to this site via the MIF β‐strands. The reported findings provide fundamental insights on a dynamic mechanism that controls the MIF‐induced activation of CD74.
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Photomechanically Induced Magnetic Field Response by Controlling Molecular Orientation in 9‐Methylanthracene Microcrystals ()
Abstract A surfactant‐assisted seeded‐growth method is used to form single‐crystal platelets composed of 9‐methylanthracene with two different internal molecular orientations. The more stable form exhibits a photoinduced twisting, as observed previously for 9‐methylanthracene microribbons grown by the floating drop method. However, the newly discovered elongated hexagonal platelets undergo a photoinduced rolling‐up and unrolling. The ability of the rolled‐up cylindrical shape to trap superparamagnetic nanoparticles enables it to be carried along in a magnetic field gradient. The new photoinduced shape change, made possible by a novel surfactant‐assisted crystal growth method, opens up the possibility of using light to modulate the crystal translational motion.
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Stereospecific Nucleophilic Substitution with Arylboronic Acids as Nucleophiles in the Presence of a CONH Group ()
Abstract Stereospecific nucleophilic substitution was achieved for the first time with arylboronic acids as nucleophiles. This transition‐metal‐free coupling between chiral α‐aryl‐α‐mesylated acetamides and arylboronic acids provided access to a series of chiral α,α‐diaryl acetamides with excellent enantioselectivity and moderate to good yields. The CONH functionality proved to be crucial for bridging the reactants and promoting the reaction. Efficient syntheses of a cannabinoid CB1 receptor ligand, the antidepressant (S)‐diclofensine, and a key chiral building block of the inhibitor implitapide were successfully accomplished by using this method.
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A Facile Method for Producing Selenocysteine‐Containing Proteins ()
Abstract Selenocysteine (Sec, U) confers new chemical properties on proteins. Improved tools are thus required that enable Sec insertion into any desired position of a protein. We report a facile method for synthesizing selenoproteins with multiple Sec residues by expanding the genetic code of Escherichia coli. We recently discovered allo‐tRNAs, tRNA species with unusual structure, that are as efficient serine acceptors as E. coli tRNASer. Ser‐allo‐tRNA was converted into Sec‐allo‐tRNA by Aeromonas salmonicida selenocysteine synthase (SelA). Sec‐allo‐tRNA variants were able to read through five UAG codons in the fdhF mRNA coding for E. coli formate dehydrogenase H, and produced active FDHH with five Sec residues in E. coli. Engineering of the E. coli selenium metabolism along with mutational changes in allo‐tRNA and SelA improved the yield and purity of recombinant human glutathione peroxidase 1 (to over 80 %). Thus, our allo‐tRNAUTu system offers a new selenoprotein engineering platform.
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Two‐fold Bioorthogonal Derivatization by Different Formylglycine‐Generating Enzymes ()
Abstract Formylglycine‐generating enzymes are of increasing interest in the field of bioconjugation chemistry. They catalyze the site‐specific oxidation of a cysteine residue to the aldehyde‐containing amino acid Cα‐formylglycine (FGly). This non‐canonical residue can be generated within any desired target protein and can subsequently be used for bioorthogonal conjugation reactions. The prototypic formylglycine‐generating enzyme (FGE) and the iron‐sulfur protein AtsB display slight variations in their recognition sequences. We designed specific tags in peptides and proteins that were selectively converted by the different enzymes. Combination of the different tag motifs within a single peptide or recombinant protein enabled the independent and consecutive introduction of two formylglycine residues and the generation of heterobifunctionalized protein conjugates.
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Heavy Carbene Analogues: Donor‐Free Bismuthenium and Stibenium Ions ()
Abstract Kinetically stabilized congeners of carbenes, R2C, possessing six valence electrons (four bonding electrons and two non‐bonding electrons) have been restricted to Group 14 elements, R2E (E=Si, Ge, Sn, Pb; R=alkyl or aryl) whereas isoelectronic Group 15 cations, divalent species of type [R2E]+ (E=P, As, Sb, Bi; R=alkyl or aryl), were unknown. Herein, we report the first two examples, namely the bismuthenium ion [(2,6‐Mes2C6H3)2Bi][BArF4] (1; Mes=2,4,6‐Me3C6H2, ArF=3,5‐(CF3)2C6H3) and the stibenium ion [(2,6‐Mes2C6H3)2Sb][B(C6F5)4] (2), which were obtained by using a combination of bulky meta‐terphenyl substituents and weakly coordinating anions.
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Oxidation Catalysis by an Aerobically Generated Dess–Martin Periodinane Analogue ()
Abstract Hypervalent iodine(V) reagents, such as Dess–Martin periodinane (DMP) and 2‐iodoxybenzoic acid (IBX), are broadly useful oxidants in chemical synthesis. Development of strategies to generate these reagents from dioxygen (O2) would immediately enable use of O2 as a terminal oxidant in a broad array of substrate oxidation reactions. Recently we disclosed the aerobic synthesis of I(III) reagents by intercepting reactive oxidants generated during aldehyde autoxidation. In this work, aerobic oxidation of iodobenzenes is coupled with disproportionation of the initially generated I(III) compounds to generate I(V) reagents. The aerobically generated I(V) reagents exhibit substrate oxidation chemistry analogous to that of DMP. The developed aerobic generation of I(V) has enabled the first application of I(V) intermediates in aerobic oxidation catalysis.
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Stabilization of Lewis Acidic AuF3 as an N‐Heterocyclic Carbene Complex: Preparation and Characterization of [AuF3(SIMes)] ()
Abstract Two different reaction routes are described to access the unprecedented trifluoridoorganogold(III) complex [AuF3(SIMes)]. The compound bears the N‐heterocyclic carbene SIMes (1,3‐bis(2,4,6‐trimethylphenyl)‐4,5‐dihydroimidazol‐2‐ylidene) as a ligand for a molecular Lewis acidic AuF3 unit and was characterized by NMR spectroscopy as well as X‐ray crystallography. Apart from the use of a [AuF4]− salt as precursor, the strong oxidizing compound AuF3 can be employed neat as starting material. The reaction proceeded even in organic solvents in the presence of SIMes as the ligand precursor. Decomposition reactions with the solvent can, therefore, be prevented by using this strategy.
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Cucurbit[7]uril‐Dimethyllysine Recognition in a Model Protein ()
Abstract Here, we provide the first structural characterization of host–guest complexation between cucurbit[7]uril (Q7) and dimethyllysine (KMe2) in a model protein. Binding was dominated by complete encapsulation of the dimethylammonium functional group. While selectivity for the most sterically accessible dimethyllysine was observed both in solution and in the solid state, three different modes of Q7‐KMe2 complexation were revealed by X‐ray crystallography. The crystal structures revealed also entrapped water molecules that solvated the ammonium group within the Q7 cavity. Remarkable Q7‐protein assemblies, including inter‐locked octahedral cages that comprise 24 protein trimers, occurred in the solid state. Cucurbituril clusters appear to be responsible for these assemblies, suggesting a strategy to generate controlled protein architectures.
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Aggregation of Giant Cerium–Bismuth Tungstate Clusters into a 3D Porous Framework with High Proton Conductivity ()
Abstract The exploration of high nuclearity molecular metal oxide clusters and their reactivity is a challenge for chemistry and materials science. Herein, we report an unprecedented giant molecular cerium–bismuth tungstate superstructure formed by self‐assembly from simple metal oxide precursors in aqueous solution. The compound, {[W14CeIV6O61]([W3Bi6CeIII3(H2O)3O14][B‐α‐BiW9O33]3)2}34− was identified by single‐crystal X‐ray diffraction and features 104 metal centers, a relative molar mass of ca. 24 000 and is ca. 3.0×2.0×1.7 nm3 in size. The cluster anion is assembled around a central {Ce6} octahedron which is stabilized by several molecular metal oxide shells. Six trilacunary Keggin anions ([B‐α‐BiW9O33]9−) cap the superstructure and limit its growth. In the crystal lattice, water‐filled channels with diameters of ca. 0.5 nm are observed, and electrochemical impedance spectroscopy shows pronounced proton conductivity even at low temperature.
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Divergent Synthesis of CF3‐Substituted Allenyl Nitriles by Ligand‐Controlled Radical 1,2‐ and 1,4‐Addition to 1,3‐Enynes ()
Abstract A ligand‐controlled system that enables regioselective trifluoromethylcyanation of 1,3‐enynes has been identified, which provides access to a variety of CF3‐containing tri‐ and tetrasubstituted allenyl nitriles. We disclose that the involved propargylic radicals can be selectively trapped by (Box)CuII cyanide, while the tautomerized allenyl radicals are trapped by (phen)CuII cyanide (Box= bisoxazoline, phen=phenanthroline). In addition, the reaction features broad substrate scope and excellent functional group compatibility. Moreover, this protocol represents a novel regioselectivity‐tunable functionalization of 1,3‐enynes via radicals, which we believe will have great implications for the development of catalytic systems for selectivity control in radical and organometallic chemistry.
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Affinity‐Driven Covalent Modulator of the Glyceraldehyde‐3‐Phosphate Dehydrogenase (GAPDH) Cascade ()
Abstract Traditional medicines provide a fertile ground to explore potent lead compounds, yet their transformation into modern drugs is fraught with challenges in deciphering the target that is mechanistically valid for its biological activity. Herein we reveal that (Z)‐(+)‐isochaihulactone (1) exhibited significant inhibition against multiple‐drug‐resistant (MDR) cancer cell lines and mice xenografts. NMR spectroscopy showed that 1 resisted an off‐target thiolate, thus indicating that 1 was a target covalent inhibitor (TCI). By identifying the pharmacophore of 1 (α,β‐unsaturated moiety), a probe derived from 1 was designed and synthesized for TCI‐oriented activity‐based proteome profiling. By MS/MS and computer‐guided molecular biology approaches, an affinity‐driven Michael addition of the noncatalytic C247 residue of GAPDH was found to control the “ON/OFF” switch of apoptosis through non‐canonically nuclear GAPDH translocation, which bypasses the common apoptosis‐resistant route of MDR cancers.
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Bottom‐up Synthesis and Self‐Assembly of Copper Clusters into Permanent Excimer Supramolecular Nanostructures ()
Abstract Metal clusters with appropriate molecular ligands have been shown to be suitable subnanometer building blocks for supramolecular architectures with controlled secondary interactions, providing access to physical regimes not achievable with conventional intermolecular motifs. An example is the excimer photophysics exhibited by individual cluster‐based superstructures produced by top‐down etching of gold nanoparticles. Now, a supramolecular architecture of copper clusters is presented with controlled optical properties and efficient non‐resonant luminescence produced via a novel bottom‐up synthesis using mild green reductants followed by a ligand exchange reaction and spontaneous supramolecular assembly. Spectroscopic experiments confirm the formation of the intercluster network and reveal the permanent nature of their excimer‐like behavior, thus extending the potential impact and applicability of metal cluster superstructures as efficient and stable non‐resonant single‐particle emitters.
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Stereoretentive Reactions at the Anomeric Position: Synthesis of Selenoglycosides ()
Abstract Reported is the stereospecific cross‐coupling of anomeric stannanes with symmetrical diselenides, resulting in the synthesis of selenoglycosides with exclusive anomeric control. The reaction proceeds without the need for directing groups and is compatible with free hydroxy groups as demonstrated in the preparation of glycoconjugates derived from mono‐, di‐, and trisaccharides and peptides (35 examples). Given its generality and broad substrate scope, the glycosyl cross‐coupling method presented herein can find use in the synthesis of selenium‐containing glycomimetics and glycoconjugates.
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Lewis Base Free Oxophosphonium Ions: Tunable, Trigonal‐Planar Lewis Acids ()
Abstract Oxophosphonium ions (R2P=O)+ are fascinating chemical intermediates related to the well‐known acylium cations (RC=O)+, and comprise a tricoordinate phosphorus(V) center with a phosphorus–oxygen double bond. Here, we report the synthesis of two oxophosphonium ions stabilized by bulky imidazolin‐2‐imine and imidazolin‐2‐olefin substituents attached to phosphorus. The novel species were characterized by NMR spectroscopy and single‐crystal X‐ray diffraction analysis, and the bonding situation was probed by DFT calculations. Determination of the acceptor number and the fluoride ion affinity revealed that the choice of the substituents has a strong influence on the electrophilicity of the phosphorus center. Additionally, the formation of Lewis base adducts with pyridine derivatives and the reactivity with isopropyl alcohol was explored.
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Polycyclic Indoline‐Benzodiazepines through Electrophilic Additions of α‐Imino Carbenes to Tröger Bases ()
Abstract Polycyclic indoline‐benzodiazepines can be accessed through the intermolecular reaction of Tröger bases with N‐sulfonyl‐1,2,3‐triazoles. Under RhII catalysis, α‐imino carbenes are generated and a subsequent cascade of [1,2]‐Stevens, Friedel–Crafts, Grob, and aminal formation reactions yield the polycyclic heterocycles as single isomers (d.r.>49:1, four stereocenters including two bridgehead N atoms). Further ring expansion by insertion of a second α‐imino carbene leads to elaborated polycyclic 9‐membered‐ring triazonanes.
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Asymmetric Reductive Carbocyclization Using Engineered Ene Reductases ()
Abstract Ene reductases from the Old Yellow Enzyme (OYE) family reduce the C=C double bond in α,β‐unsaturated compounds bearing an electron‐withdrawing group, for example, a carbonyl group. This asymmetric reduction has been exploited for biocatalysis. Going beyond its canonical function, we show that members of this enzyme family can also catalyze the formation of C−C bonds. α,β‐Unsaturated aldehydes and ketones containing an additional electrophilic group undergo reductive cyclization. Mechanistically, the two‐electron‐reduced enzyme cofactor FMN delivers a hydride to generate an enolate intermediate, which reacts with the internal electrophile. Single‐site replacement of a crucial Tyr residue with a non‐protic Phe or Trp favored the cyclization over the natural reduction reaction. The new transformation enabled the enantioselective synthesis of chiral cyclopropanes in up to >99 % ee.
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Monitoring of the ADP/ATP Ratio by Induced Circularly Polarised Europium Luminescence ()
Abstract A series of three europium complexes bearing picolyl amine moieties was found to possess differing binding affinities towards Zn2+ and three nucleotides: AMP, ADP, and ATP. A large increase in the total emission intensity was observed upon binding Zn2+, followed by signal amplification upon the addition of nucleotides. The resulting adducts possessed strong induced circularly polarised emission, with ADP and ATP signals of opposite sign. Model DFT geometries of the adducts suggest the Δ diastereoisomer is preferred for ATP and the Λ isomer for ADP/AMP. This change in sign allows the ADP/ATP (or AMP/ATP) ratio to be assessed by monitoring changes in the emission dissymmetry factor, gem.
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An O3‐type Oxide with Low Sodium Content as the Phase‐Transition‐Free Anode for Sodium‐Ion Batteries ()
Abstract Layered transition metal oxides NaxMO2 (M=transition metal) with P2 or O3 structure have attracted attention in sodium‐ion batteries (NIBs). A universal law is found to distinguish structural competition between P2 and O3 types based on the ratio of interlayer distances of the alkali metal layer d(O‐Na‐O) and transition‐metal layer d(O‐M‐O). The ratio of about 1.62 can be used as an indicator. O3‐type Na0.66Mg0.34Ti0.66O2 oxide is prepared as a stable anode for NIBs, in which the low Na‐content (ca. 0.66) usually undergoes a P2‐type structure with respect to NaxMO2. This material delivers an available capacity of about 98 mAh g−1 within a voltage range of 0.4–2.0 V and exhibits a better cycling stability (ca. 94.2 % of capacity retention after 128 cycles). In situ X‐ray diffraction reveals a single‐phase reaction in the discharge–charge process, which is different from the common phase transitions reported in O3‐type electrodes, ensuring long‐term cycling stability.
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Intermolecular Arrangement of Fullerene Acceptors Proximal to Semiconducting Polymers in Mixed Bulk Heterojunctions ()
Abstract Precise control of the molecular arrangements at the interface between the electron donor and acceptor in mixed bulk heterojunctions (BHJs) remains challenging, despite the correlation between structural characteristics and efficiency in organic photovoltaics (OPVs). This study reveals that the substitution patterns of linear and branched alkyl side chains on electron‐donating/‐accepting alternating copolymers can control the positions of an acceptor molecule (C60) around the π‐conjugated main chains in mixed BHJs. Two‐dimensional solid‐state NMR demonstrates a marked difference in the location of C60 in the blend films. A copolymer with an electron‐accepting unit positioned in close proximity to C60 demonstrated higher OPV performance in combination with various fullerene derivatives. This molecular design offers precise control over the interfacial molecular structure, thereby paving the way for overcoming the current limitations of OPVs comprising mixed BHJs.
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Ligand‐Unsupported Cuprophilicity in the Preparation of Dodecacopper(I) Complexes and Raman Studies ()
Abstract Synthesis and characterization of two dodecacopper(I) extended metal atom chains (EMAC) assembled by two hexadentate bis(pyridylamido)amidinate‐supported hexacopper(I) string complexes (monomers) via the ligand‐unsupported cuprophilicity are described. In addition to short unsupported Cu−Cu contacts, two hexacopper fragments in these two dodecacopper EMACs show a bent conformation based on X‐ray crystallography. Compared with their THF‐bound hexacopper(I) monomers and protonated ligands, these ligand‐unsupported cuprophilic interactions are shown to be weak by Raman spectroscopy. DFT calculations suggest the ligand‐unsupported cuprophilicity originate from weak attractive orbital interactions, and the strength is estimated to be 2.4 kcal mol−1.
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7‐Step Flow Synthesis of the HIV Integrase Inhibitor Dolutegravir ()
Abstract Dolutegravir (DTG), an important active pharmaceutical ingredient (API) used in combination therapy for the treatment of HIV, has been synthesized in continuous flow. By adapting the reported GlaxoSmithKline process chemistry batch route for Cabotegravir, DTG was produced in 4.5 h in sequential flow operations from commercially available materials. Key features of the synthesis include rapid manufacturing time for pyridone formation, one‐step direct amidation of a functionalized pyridone, and telescoping of multiple steps to avoid isolation of intermediates and enable for greater throughput.
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Polymeric Nanoparticles with a Glutathione‐Sensitive Heterodimeric Multifunctional Prodrug for In Vivo Drug Monitoring and Synergistic Cancer Therapy ()
Abstract Polymeric micelle‐based drug delivery systems have dramatically improved the delivery of small molecular drugs, yet multiple challenges remain to be overcome. A polymeric nanomedicine has now been engineered that possesses an ultrahigh loading (59 %) of a glutathione (GSH)‐sensitive heterodimeric multifunctional prodrug (HDMP) to effectively co‐deliver two synergistic drugs to tumors. An HDMP comprising of chemotherapeutic camptothecin (CPT) and photosensitizer 2‐(1‐hexyloxyethyl)‐2‐devinyl pyropheophorbide‐α (HPPH) was conjugated via a GSH‐cleavable linkage. The intrinsic fluorogenicity and label‐free radio‐chelation (64Cu) of HPPH enabled direct drug monitoring by fluorescence imaging and positron emission tomography (PET). Through quantitative PET imaging, HDMP significantly improves drug delivery to tumors. The high synergistic therapeutic efficacy of HDMP‐loaded NPs highlights the rational design of HDMP, and presents exciting opportunities for polymer NP‐based drug delivery.
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A Long Cycle Life, Self‐Healing Zinc–Iodine Flow Battery with High Power Density ()
Abstract A zinc–iodine flow battery (ZIFB) with long cycle life, high energy, high power density, and self‐healing behavior is prepared. The long cycle life was achieved by employing a low‐cost porous polyolefin membrane and stable electrolytes. The pores in the membrane can be filled with a solution containing I3− that can react with zinc dendrite. Therefore, by consuming zinc dendrite, the battery can self‐recover from micro‐short‐circuiting resulting from overcharging. By using KI, ZnBr2, and KCl as electrolytes and a high ion‐conductivity porous membrane, a very high power density can be achieved. As a result, a ZIFB exhibits an energy efficiency (EE) of 82 % at 80 mA cm−2, which is 8 times higher than the currently reported ZIFBs. Furthermore, a stack with an output of 700 W was assembled and continuously run for more than 300 cycles. We believe this ZIFB can lead the way to development of new‐generation, high‐performance flow batteries.
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Block–Stereoblock Copolymers of Poly(ϵ‐Caprolactone) and Poly(Lactic Acid) ()
Abstract A magnesium complex of the type {ONNN}Mg‐HMDS wherein {ONNN} is a sequential tetradentate monoanionic ligand is introduced. In the presence of an alcohol initiator this complex catalyzes the living and immortal homopolymerization of the lactide enantiomers and ϵ‐caprolactone at room‐temperature with exceptionally high activities, as well as the precise block copolymerization of these monomers in a one‐pot synthesis by sequential monomer addition. Copolymers of unprecedented microstructures such as the PCL‐b‐PLLA‐b‐PDLA and PDLA‐b‐PLLA‐b‐PCL‐b‐PLLA‐b‐PDLA block–stereoblock microstructures that feature unique thermal properties are readily accessed.
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A Universal Organic Cathode for Ultrafast Lithium‐ and Multivalent Metal Batteries ()
Abstract Low‐cost multivalent battery chemistries (Mg2+, Al3+) have been extensively investigated for large‐scale energy storage applications. However, their commercialization is plagued by the poor power density and cycle life of cathodes. A universal polyimides@CNT (PI@CNT) cathode is now presented that can reversibly store various cations with different valences (Li+, Mg2+, Al3+) at an extremely fast rate. The ion‐coordination charge storage mechanism of PI@CNT is systemically investigated. Full cells using PI@CNT cathodes and corresponding metal anodes exhibit long cycle life (>10000 cycles), fast kinetics (>20 C), and wide operating temperature range (−40 to 50 °C), making the low‐cost industrial polyimides universal cathodes for different multivalent metal batteries. The stable ion‐coordinated mechanism opens a new foundation for the development of high‐energy and high‐power multivalent batteries.
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Enantioselective Hydroamidation of Enals by Trapping of a Transient Acyl Species ()
Abstract An enantioselective synthesis of β‐chiral amides through asymmetric and redox‐neutral hydroamidation of enals is reported. In this reaction, a chiral N‐heterocyclic carbene (NHC) catalyst reacts with enals to generate the homoenolate intermediate. Upon highly enantioselective β‐protonation through proton‐shuttle catalysis, the resulting azolium intermediate reacts with imidazole to yield the key β‐chiral acyl species. This transient intermediate provides access to diversified β‐chiral carbonyl derivatives, such as amides, hydrazides, acids, esters, and thioesters. In particular, β‐chiral amides can be prepared in excellent yield and ee (40 chiral amides, up to 95 % yield and 99 % ee). This modular strategy overcomes the challenge of disruption of the highly selective proton‐shuttling process by basic amines.
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A Nanohelicoidal Nematic Liquid Crystal Formed by a Non‐Linear Duplexed Hexamer ()
Abstract The twist‐bend modulated nematic liquid‐crystal phase exhibits formation of a nanometre‐scale helical pitch in a fluid and spontaneous breaking of mirror symmetry, leading to a quasi‐fluid state composed of chiral domains despite being composed of achiral materials. This phase was only observed for materials with two or more mesogenic units, the manner of attachment between which is always linear. Non‐linear oligomers with a H‐shaped hexamesogen are now found to exhibit both nematic and twist‐bend modulated nematic phases. This shatters the assumption that a linear sequence of mesogenic units is a prerequisite for this phase, and points to this state of matter being exhibited by a wider range of self‐assembling structures than was previously envisaged. These results support the double helix model of the TB phase as opposed to the simple heliconical model. This new class of materials could act as low‐molecular‐weight surrogates for cross‐linked liquid‐crystalline elastomers.
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The Contribution of Pyroelectricity of AgI Crystals to Ice Nucleation ()
Abstract The pyroelectricity of AgI crystals strongly affects the icing temperature of super‐cooled water, as disentangled from that of epitaxy. This deduction was achieved by the design of polar crystalline ceramic pellets of AgI, with experimentally determined sense of polarity. These pellets are suitable for measuring both their pyroelectric properties as well as the icing temperature of super‐cooled water, separately on each of the expressed Ag+ and I− hemihedral surfaces. The positive pyroelectric charge at the silver‐enriched side elevates the icing temperature, whereas the negative charge at the iodide side decreases that temperature. Moreover, the effect of pyroelectric charge remains dominant despite the presence of contaminants on both the silver and the iodide‐enriched surfaces. Consequently an electrochemical process for ice nucleation is suggested, which might be of relevance for understanding the role played by electric charges in heterogeneous icing processes in general.
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LiAlH4: From Stoichiometric Reduction to Imine Hydrogenation Catalysis ()
Abstract Imine‐to‐amine conversion with catalytic instead of stoichiometric quantities of LiAlH4 is demonstrated (85 °C, catalyst loading≥2.5 mol %, pressure≥1 bar). The effects of temperature, pressure, solvent, and catalyst modifications, as well as the substrate scope are discussed. Experimental investigations and preliminary DFT calculations suggest that the catalytically active species is generated in situ: LiAlH4+Ph(H)C=NtBu→LiAlH2[N(tBu)CH2Ph]2. A cooperative mechanism in which Li and Al both play a prominent role is proposed.
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Molecular Vise Approach to Create Metal‐Binding Sites in MOFs and Detection of Biomarkers ()
Abstract We report a new approach to create metal‐binding site in a series of metal–organic frameworks (MOFs), where tetratopic carboxylate linker, 4′,4′′,4′′′,4′′′′‐methanetetrayltetrabiphenyl‐4‐carboxylic acid, is partially replaced by a tritopic carboxylate linker, tris(4‐carboxybiphenyl)amine, in combination with monotopic linkers, formic acid, trifluoroacetic acid, benzoic acid, isonicotinic acid, 4‐chlorobenzoic acid, and 4‐nitrobenzoic acid, respectively. The distance between these paired‐up linkers can be precisely controlled, ranging from 5.4 to 10.8 Å, where a variety of metals, Mg2+, Al3+, Cr3+, Mn2+, Fe3+, Co2+, Ni2+, Cu2+, Zn2+, Ag+, Cd2+ and Pb2+, can be placed in. The distribution of these metal‐binding sites across a single crystal is visualized by 3D tomography of laser scanning confocal microscopy with a resolution of 10 nm. The binding affinity between the metal and its binding‐site in MOF can be varied in a large range (observed binding constants, Kobs from 1.56×102 to 1.70×104 L mol−1), in aqueous solution. The fluorescence of these crystals can be used to detect biomarkers, such as cysteine, homocysteine and glutathione, with ultrahigh sensitivity and without the interference of urine, through the dissociation of metal ions from their binding sites.
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Indanol‐Based Chiral Organoiodine Catalysts for Enantioselective Hydrative Dearomatization ()
Abstract Rapid development in the last decade has rendered chiral organoiodine(I/III) catalysis a reliable methodology in asymmetric catalysis. However, due to the severely limited numbers of effective organoiodine catalysts, many reactions still give low to modest enantioselectivity. We report herein a solution to this issue through the introduction of a pivotal indanol scaffold to the catalyst design. Our catalyst architecture exhibits the advantage of high modularity and thereby expedites catalyst optimization. The catalyst was optimized for the challenging and highly sought‐after hydrative dearomatization of 2‐substituted phenols at the 4‐position.
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A Biomimetic Nickel Complex with a Reduced CO2 Ligand Generated by Formate Deprotonation and Its Behaviour towards CO2 ()
Abstract Reduced CO2 species are key intermediates in a variety of natural and synthetic processes. In the majority of systems, however, they elude isolation or characterisation owing to high reactivity or limited accessibility (heterogeneous systems), and their formulations thus often remain uncertain or are based on calculations only. We herein report on a Ni−CO22− complex that is unique in many ways. While its structural and electronic features help understand the CO2‐bound state in Ni,Fe carbon monoxide dehydrogenases, its reactivity sheds light on how CO2 can be converted into CO/CO32− by nickel complexes. In addition, the complex was generated by a rare example of formate β‐deprotonation, a mechanistic step relevant to the nickel‐catalysed conversion of HxCOyz− at electrodes and formate oxidation in formate dehydrogenases.
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SnI4⋅(S8)2: A Novel Adduct‐Type Infrared Second‐Order Nonlinear Optical Crystal ()
Abstract A simple adduct from tin tetraiodide SnI4 and octasulfur S8, SnI4⋅(S8)2 (1), is obtained employing a facile reaction. The combination of Sn4+ ions with d10 electron configuration, acentric SnI4 tetrahedra, and lone‐pair effects of S8, makes 1 a phase‐matchable infrared NLO crystal with a moderate second‐harmonic generation (SHG) response and a very high laser‐induced damage threshold (LIDT), which is well confirmed by the DFT calculations.
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Propagation of Enzyme‐Induced Surface Events inside Polymer Nanoassemblies for a Fast and Tunable Response ()
Abstract We report a new molecular design strategy that allows for the propagation of surface enzymatic events inside a supramolecular assembly for accelerated molecular release. The approach addresses a key shortcoming encountered with many of the currently available enzyme‐induced disassembly strategies, which rely on the unimer–aggregate equilibria of amphiphilic assemblies. The enzymatic response of the host to predictably tune the kinetics of guest‐molecule release can be programmed by controlling substrate accessibility through electrostatic complexation with a complementary polymer. Accelerated guest release in response to the enzyme is shown to be accomplished by a cooperative mechanism of enzyme‐triggered supramolecular host disassembly and host reorganization.
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Janus Graft Block Copolymers: Design of a Polymer Architecture for Independently Tuned Nanostructures and Polymer Properties ()
Abstract The graft‐through synthesis of Janus graft block copolymers (GBCPs) from branched macromonomers composed of various combinations of homopolymers is presented. Self‐assembly of GBCPs resulted in ordered nanostructures with ultra‐small domain sizes down to 2.8 nm (half‐pitch). The grafted architecture introduces an additional parameter, the backbone length, which enables control over the thermomechanical properties and processability of the GBCPs independently of their self‐assembled nanostructures. The simple synthetic route to GBCPs and the possibility of using a variety of polymer combinations contribute to the universality of this technique.
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“Precipitation on Nanoparticles”: Attractive Intermolecular Interactions Stabilize Specific Ligand Ratios on the Surfaces of Nanoparticles ()
Abstract Confining organic molecules to the surfaces of inorganic nanoparticles can induce intermolecular interactions between them, which can affect the composition of the mixed self‐assembled monolayers obtained by co‐adsorption from solution of two different molecules. Two thiolated ligands (a dialkylviologen and a zwitterionic sulfobetaine) that can interact with each other electrostatically were coadsorbed onto gold nanoparticles. The nanoparticles favor a narrow range of ratios of these two molecules that is largely independent of the molar ratio in solution. Changing the solution molar ratio of the two ligands by a factor of 5 000 affects the on‐nanoparticle ratio of these ligands by only threefold. This behavior is reminiscent of the formation of insoluble inorganic salts (such as AgCl), which similarly compensate positive and negative charges upon crystallizing. Our results pave the way towards developing well‐defined hybrid organic–inorganic nanostructures.
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Electron‐Catalyzed Cross‐Coupling of Arylboron Compounds with Aryl Iodides ()
Abstract Arylboroxines in combination with zinc chloride and potassium tert‐butoxide were found to undergo the electron‐catalyzed cross‐coupling with aryl iodides to give the corresponding biaryls without the aid of transition‐metal catalysis.
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Synthesis of Renewable meta‐Xylylenediamine from Biomass‐Derived Furfural ()
Abstract We report the synthesis of biomass‐derived functionalized aromatic chemicals from furfural, a building block nowadays available in large scale from low‐cost biomass. The scientific strategy relies on a Diels–Alder/aromatization sequence. By controlling the rate of each step, it was possible to produce exclusively the meta aromatic isomer. In particular, through this route, we describe the synthesis of renewably sourced meta‐xylylenediamine (MXD). Transposition of this work to other furfural‐derived chemicals is also discussed and reveals that functionalized biomass‐derived aromatics (benzaldehyde, benzylamine, etc.) can be potentially produced, according to this route.
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Beryllium Complexes with Bio‐Relevant Functional Groups: Coordination Geometries and Binding Affinities ()
Abstract The coordination mode around beryllium in proteins and the binding affinity towards the peptide are unknown because there have been no coordination compounds of beryllium with ligands bearing bio‐relevant functional groups. We report the first comprehensive study on Be complexes with monodentate carboxylic acids, esters, aldehydes, and alcohols. Through solution and solid‐state techniques we determined that the binding affinities of Be2+ ions towards the functional groups are: carboxylate > alcohol > aldehyde > ester. Crystal structures of all the compounds have been determined including the unprecedented dodeca‐nuclear macrocyclic ring structure of non‐basic beryllium benzoate, which is the first example of those beryllium carboxylates. These findings enable the evaluation of potential beryllium binding sites inside proteins and is required to understand the mechanism of metal‐triggered immune responses.
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Highly Luminescent Inks: Aggregation‐Induced Emission of Copper–Iodine Hybrid Clusters ()
Abstract Aggregation‐induced emission (AIE) is an attractive phenomenon in which materials display strong luminescence in the aggregated solid states rather than in the conventional dissolved molecular states. However, highly luminescent inks based on AIE are hard to be obtained because of the difficulty in finely controlling the crystallinity of AIE materials at nanoscale. Herein, we report the preparation of highly luminescent inks via oil‐in‐water microemulsion induced aggregation of Cu–I hybrid clusters based on the highly soluble copper iodide‐tris(3‐methylphenyl)phosphine (Cu4I4(P‐(m‐Tol)3)4) hybrid. Furthermore, we can synthesize a series of AIE inks with different light‐emission colors to cover the whole visible spectrum range via a facile ligand exchange processes. The assemblies of Cu–I hybrid clusters with AIE characteristics will pave the way to fabricate low‐cost highly luminescent inks.
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Raman Microspectroscopic Evidence for the Metabolism of a Tyrosine Kinase Inhibitor, Neratinib, in Cancer Cells ()
Abstract Tyrosine kinase receptors are one of the main targets in cancer therapy. They play an essential role in the modulation of growth factor signaling and thereby inducing cell proliferation and growth. Tyrosine kinase inhibitors such as neratinib bind to EGFR and HER2 receptors and exhibit antitumor activity. However, little is known about their detailed cellular uptake and metabolism. Here, we report for the first time the intracellular spatial distribution and metabolism of neratinib in different cancer cells using label‐free Raman imaging. Two new neratinib metabolites were detected and fluorescence imaging of the same cells indicate that neratinib accumulates in lysosomes. The results also suggest that both EGFR and HER2 follow the classical endosome lysosomal pathway for degradation. A combination of Raman microscopy, DFT calculations, and LC‐MS was used to identify the chemical structure of neratinib metabolites. These results show the potential of Raman microscopy to study drug pharmacokinetics.
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Eosin Y as a Direct Hydrogen‐Atom Transfer Photocatalyst for the Functionalization of C−H Bonds ()
Abstract Eosin Y, a well‐known economical alternative to metal catalysts in visible‐light‐driven single‐electron transfer‐based organic transformations, can behave as an effective direct hydrogen‐atom transfer catalyst for C−H activation. Using the alkylation of C−H bonds with electron‐deficient alkenes as a model study revealed an extremely broad substrate scope, enabling easy access to a variety of important synthons. This eosin Y‐based photocatalytic hydrogen‐atom transfer strategy is promising for diverse functionalization of a wide range of native C−H bonds in a green and sustainable manner.
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High Electromagnetic Field Enhancement of TiO2 Nanotube Electrodes ()
Abstract We present the fabrication of TiO2 nanotube electrodes with high biocompatibility and extraordinary spectroscopic properties. Intense surface‐enhanced resonance Raman signals of the heme unit of the redox enzyme Cytochrome b5 were observed upon covalent immobilization of the protein matrix on the TiO2 surface, revealing overall preserved structural integrity and redox behavior. The enhancement factor could be rationally controlled by varying the electrode annealing temperature, reaching a record maximum value of over 70 at 475 °C. For the first time, such high values are reported for non‐directly surface‐interacting probes, for which the involvement of charge‐transfer processes in signal amplification can be excluded. The origin of the surface enhancement is exclusively attributed to enhanced localized electric fields resulting from the specific optical properties of the nanotubular geometry of the electrode.
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Bismesitoylphosphinic Acid (BAPO‐OH): A Ligand for Copper Complexes and Four‐Electron Photoreductant for the Preparation of Copper Nanomaterials ()
Abstract Bismesitoylphosphinic acid, (HO)PO(COMes)2 (BAPO‐OH), is an efficient photoinitiator for free‐radical polymerizations of olefins in aqueous phase. Described here are the structures of various copper(II) and copper(I) complexes with BAPO‐OH as the ligand. The complex CuII(BAPO‐O)2(H2O)2 is photoactive, and under irradiation with UV light in aqueous phase, it serves as a source of metallic copper in high purity and yield (>80 %). Simultaneously, the radical polymerization of acrylates can be initiated and allows the preparation of nanoparticle/polymer nanocomposites in which the metallic Cu nanoparticles are protected against oxidation. The determination of the stoichiometry of the photoreductions suggests an almost quantitative conversion from CuII into Cu0 with half an equivalent of BAPO‐OH, which serves as a four‐electron photoreductant.
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Exposing the Origins of Irreproducibility in Fluorine NMR Spectroscopy ()
Abstract Fluorine chemistry has taken a pivotal role in chemical reaction discovery, drug development, and chemical biology. NMR spectroscopy, arguably the most important technique for the characterization of fluorinated compounds, is rife with highly inconsistent referencing of fluorine NMR chemical shifts, producing deviations larger than 1 ppm. Herein, we provide unprecedented evidence that both spectrometer design and the current unified scale system underpinning the calibration of heteronuclear NMR spectra have unintentionally led to widespread variation in the standardization of 19F NMR spectral data. We demonstrate that internal referencing provides the most robust, practical, and reproducible method whereby chemical shifts can be consistently measured and confirmed between institutions to less than 30 ppb deviation. Finally, we provide a comprehensive table of appropriately calibrated chemical shifts of reference compounds that will serve to calibrate 19F spectra correctly.
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Near‐Infrared Sensitized Photoinduced Atom‐Transfer Radical Polymerization (ATRP) with a Copper(II) Catalyst Concentration in the ppm Range ()
Abstract NIR‐sensitized photoinduced atom‐transfer radical polymerization (ATRP) is possible by using ppm of CuII/tris(2‐pyridylmethyl)amine (TPMA) as the catalyst, a polymethine as the photosensitizer, and α‐bromophenylacetate as the alkyl halide initiator. Among the polymethines investigated with cationic, zwitterionic, or anionic structures, only the zwitterionic 2 exhibited sensitization activity under NIR light at room temperature resulting in the formation of polymers with controlled molecular weight characteristics and functionalities. The barbital group placed at the meso‐position of 2 caused the activity in this photo‐ATRP framework. The chain‐end fidelity of the polymers was confirmed by chain extension and block copolymerization experiments. The polymerization system exhibits high photostability under NIR light exposure and irradiation dependency as demonstrated by light on/off experiments.
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Simultaneous Quantification of Multiple Cancer Biomarkers in Blood Samples through DNA‐Assisted Nanopore Sensing ()
Abstract Protein biomarkers in blood have been widely used in the early diagnosis of disease. However, simultaneous detection of many biomarkers in a single sample remains challenging. Herein, we show that the combination of a sandwich assay and DNA‐assisted nanopore sensing could unambiguously identify and quantify several antigens in a mixture. We use five barcode DNAs to label different gold nanoparticles that can selectively bind specific antigens. After the completion of the sandwich assay, barcode DNAs are released and subject to nanopore translocation tests. The distinct current signatures generated by each barcode DNA allow simultaneous quantification of biomarkers at picomolar level in clinical samples. This approach would be very useful for accurate and multiplexed quantification of cancer‐associated biomarkers within a very small sample volume, which is critical for non‐invasive early diagnosis of cancer.
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Wood‐Derived Ultrathin Carbon Nanofiber Aerogels ()
Abstract Carbon aerogels with 3D networks of interconnected nanometer‐sized particles exhibit fascinating physical properties and show great application potential. Efficient and sustainable methods are required to produce high‐performance carbon aerogels on a large scale to boost their practical applications. An economical and sustainable method is now developed for the synthesis of ultrathin carbon nanofiber (CNF) aerogels from the wood‐based nanofibrillated cellulose (NFC) aerogels via a catalytic pyrolysis process, which guarantees high carbon residual and well maintenance of the nanofibrous morphology during thermal decomposition of the NFC aerogels. The wood‐derived CNF aerogels exhibit excellent electrical conductivity, a large surface area, and potential as a binder‐free electrode material for supercapacitors. The results suggest great promise in developing new families of carbon aerogels based on the controlled pyrolysis of economical and sustainable nanostructured precursors.
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Cu[B2(SO4)4] and Cu[B(SO4)2(HSO4)]—Two Silicate Analogue Borosulfates Differing in their Dimensionality: A Comparative Study of Stability and Acidity ()
Abstract Borosulfates are an ever‐expanding class of compounds and the extent of their properties is still elusive. Herein, the first two copper borosulfates Cu[B2(SO4)4] and Cu[B(SO4)2(HSO4)] are presented, which are structurally related but show different dimensionalities in their substructure: While Cu[B2(SO4)4] reveals an anionic chain, [B(SO4)4/2]−, with both a twisted and a unique chair conformation of the B(SO4)2B subunits, Cu[B(SO4)2(HSO4)] reveals isolated [B2(SO4)4(HSO4)2]4− anions showing exclusively a twisted conformation. The complex anion can figuratively be obtained as a cut‐out from the anionic chain by protons. Comparative DFT calculations based on magnetochemical measurements complement the experimental studies. Calculation of the pKa values of the two conformers of the [B2(SO4)4(HSO4)2]4− anion revealed them to be more similar to silicic than to sulfuric acid, highlighting the close relationship to silicates.
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Remote Central‐to‐Axial Chirality Conversion: Direct Atroposelective Ester to Biaryl Transformation ()
Abstract A strategy for the remote central‐to‐axial chirality conversion by simultaneous planarization of an encoding and a transient stereocenter is presented. Based on a diastereoselective double addition of a chiral 1,5‐bifunctional organomagnesium alkoxide reagent to a broad range of aryl ester substrates, axially chiral biaryls are directly obtained upon in situ reduction. Various structurally distinct atropisomeric biaryl silanes that serve as valuable chiral biaryl anion surrogates are accessible in one step with e.r. values of up to 98:2.
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The Discovery of a Palladium(II)‐Initiated Borono‐Catellani Reaction ()
Abstract Reported is a novel palladium(II)‐initiated Catellani‐type reaction that utilizes widely accessible aryl boronic acids as the substrates instead of aryl halides, thereby greatly expanding the existing scope of this powerful transformation. This borono‐Catellani reaction was promoted by cooperative catalysis between Pd(OAc)2 and the inexpensive 5‐norbornene‐2‐carbonitrile. Practicality is the striking feature of the reaction: it is run open to air at ambient temperature and no phosphine ligand is needed. This mild, chemoselective, and scalable protocol is compatible with a large range of readily available functionalized aryl boronic acids and bromides, as well as terminating olefins (50 examples, 39–97 % yields). Moreover, the orthogonal reactivity between the borono‐Catellani and classical Catellani reaction was demonstrated. This work is expected to open new avenues for developing novel Catellani‐type reactions.
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A Copper(I)‐Catalyzed Enantioselective γ‐Boryl Substitution of Trifluoromethyl‐Substituted Alkenes: Synthesis of Enantioenriched γ,γ‐gem‐Difluoroallylboronates ()
Abstract The first catalytic enantioselective γ‐boryl substitution of CF3‐substituted alkenes is reported. A series of CF3‐substituted alkenes was treated with a diboron reagent in the presence of a copper(I)/Josiphos catalyst to afford the corresponding optically active γ,γ‐gem‐difluoroallylboronates in high enantioselectivity. The thus obtained products could be readily converted into the corresponding difluoromethylene‐containing homoallylic alcohols using highly stereospecific allylation reactions.
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Separation of Acetylene from Carbon Dioxide and Ethylene by a Water‐Stable Microporous Metal–Organic Framework with Aligned Imidazolium Groups inside the Channels ()
Abstract Separation of acetylene from carbon dioxide and ethylene is challenging in view of their similar sizes and physical properties. Metal–organic frameworks (MOFs) in general are strong candidates for these separations owing to the presence of functional pore surfaces that can selectively capture a specific target molecule. Here, we report a novel 3D microporous cationic framework named JCM‐1. This structure possesses imidazolium functional groups on the pore surfaces and pyrazolate as a metal binding group, which is well known to form strong metal‐to‐ligand bonds. The selective sorption of acetylene over carbon dioxide and ethylene in JCM‐1 was successfully demonstrated by equilibrium gas adsorption analysis as well as dynamic breakthrough measurement. Furthermore, its excellent hydrolytic stability makes the separation processes highly recyclable without a substantial loss in acetylene uptake capacity.
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Frustrated Helicity: Joining the Diverging Ends of a Stable Aromatic Amide Helix to Form a Fluxional Macrocycle ()
Abstract Macrocyclization of a stable two‐turn helical aromatic pentamide, that is, an object with diverging ends that are not prone to cyclization, was made possible by the transient introduction of disruptors of helicity in the form of acid‐labile dimethoxybenzyl tertiary amide substituents. After removal of the helicity disruptors, NMR, X‐ray crystallography, and computational studies show that the macrocycle possesses a strained structure that tries to gain as high a helical content as possible despite being cyclic. Two points of disruption of helicity remain, in particular a cis amide bond. This point of disruption of helicity can propagate along the cycle in a fluxional manner according to defined trajectories to produce ten degenerate conformations.
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Hydroxyl‐Mediated Non‐oxidative Propane Dehydrogenation over VOx/γ‐Al2O3 Catalysts with Improved Stability ()
Abstract Supported vanadium oxides are one of the most promising alternative catalysts for propane dehydrogenation (PDH) and efforts have been made to improve its catalytic performance. However, unlike Pt‐based catalysts, the nature of the active site and surface structure of the supported vanadium catalysts under reductive reaction conditions still remain elusive. This paper describes the surface structure and the important role of surface‐bound hydroxyl groups on VOx / γ‐Al2O3 catalysts under reaction conditions employing in situ DRIFTS experiments and DFT calculations. It is shown that hydroxyl groups on the VOx /Al2O3 catalyst (V−OH) are produced under H2 pre‐reduction, and the catalytic performance for PDH is closely connected to the concentration of V−OH species on the catalyst. The hydroxyl groups are found to improve the catalyst that leads to better stability by suppressing the coke deposition.
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Palladium‐Catalyzed Insertion of Isocyanides into the C−S Bonds of Heteroaryl Sulfides ()
Abstract Insertion of tert‐butyl isocyanide into the C(sp2)−S bonds of heteroaryl sulfides is catalyzed by a palladium diphosphine complex. Thioimidates generated through this reaction could be readily hydrolyzed under acidic conditions to yield the corresponding thioesters, which are of synthetic use. This insertion is useful because starting heteroaryl sulfides were readily prepared by either conventional ways or through sulfur‐specific extended Pummerer reactions.
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A Desulfurative Strategy for the Generation of Alkyl Radicals Enabled by Visible‐Light Photoredox Catalysis ()
Abstract Herein, we present a new desulfurative method for generating primary, secondary, and tertiary alkyl radicals through visible‐light photoredox catalysis. A process that involves the generation of N‐centered radicals from sulfinamide intermediates, followed by subsequent fragmentation, is critical to forming the corresponding alkyl radical species. This strategy has been successfully applied to conjugate addition reactions that features mild reaction conditions, broad substrate scope (>60 examples), and good functional‐group tolerance.
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Stephan Irle ()
Angewandte Chemie International Edition, EarlyView.
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Abderrahmane Amgoune ()
Angewandte Chemie International Edition, EarlyView.
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Shangfeng Yang ()
Angewandte Chemie International Edition, EarlyView.
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Jian‐Hua Xie ()
Angewandte Chemie International Edition, EarlyView.
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Hajime Ito ()
Angewandte Chemie International Edition, EarlyView.
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Hidetoshi Tokuyama ()
Angewandte Chemie International Edition, EarlyView.
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Norbert W. Mitzel ()
Angewandte Chemie International Edition, EarlyView.
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David R. Spring ()
Angewandte Chemie International Edition, EarlyView.
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Yuemin Wang ()
Angewandte Chemie International Edition, EarlyView.
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Ralf I. Kaiser ()
Angewandte Chemie International Edition, EarlyView.
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Kallol Ray ()
Angewandte Chemie International Edition, EarlyView.
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Kurt Vesterager Gothelf ()
Angewandte Chemie International Edition, EarlyView.
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Carlo Unverzagt ()
Angewandte Chemie International Edition, EarlyView.
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Eva Hevia ()
Angewandte Chemie International Edition, EarlyView.
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Yi‐Chou Tsai ()
Angewandte Chemie International Edition, EarlyView.
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Marc T. M. Koper ()
Angewandte Chemie International Edition, EarlyView.
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Seth M. Cohen ()
Angewandte Chemie International Edition, EarlyView.
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Juyoung Yoon ()
Angewandte Chemie International Edition, EarlyView.
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Qichun Zhang ()
Angewandte Chemie International Edition, EarlyView.
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Yu Lan ()
Angewandte Chemie International Edition, EarlyView.
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Suning Wang ()
Angewandte Chemie International Edition, EarlyView.
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Jose M. Goicoechea ()
Angewandte Chemie International Edition, EarlyView.
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Sanzhong Luo ()
Angewandte Chemie International Edition, EarlyView.
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