Angewandte Chemie International Edition

European Restrictions on 1,2‐Dichloroethane: C−H Activation Research and Development Should Be Liberated and not Limited ()
Angewandte Chemie International Edition, Volume 57, Issue 43, Page 14286-14290, October 22, 2018.
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Spotlights on our sister journals: Angew. Chem. Int. Ed. 43/2018 ()
Angewandte Chemie International Edition, Volume 57, Issue 43, Page 13958-13962, October 22, 2018.
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European Young Chemist Award: A. Porchetta, M. Atzori, and S. Fabiano / EuChemS Award for Service: F. De Angelis, S. Facchetti, and R. Salzer ()
Angewandte Chemie International Edition, Volume 57, Issue 43, Page 13965-13966, October 22, 2018.
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Graphical Abstract: Angew. Chem. Int. Ed. 43/2018 ()
Angewandte Chemie International Edition, Volume 57, Issue 43, Page 13941-13956, October 22, 2018.
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Back Cover: Lithium Nitrate Solvation Chemistry in Carbonate Electrolyte Sustains High‐Voltage Lithium Metal Batteries (Angew. Chem. Int. Ed. 43/2018) ()
Angewandte Chemie International Edition, Volume 57, Issue 43, Page 14292-14292, October 22, 2018.
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Inside Back Cover: Merging Photoredox and Organometallic Catalysts in a Metal–Organic Framework Significantly Boosts Photocatalytic Activities (Angew. Chem. Int. Ed. 43/2018) ()
Angewandte Chemie International Edition, Volume 57, Issue 43, Page 14291-14291, October 22, 2018.
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Cover Picture: Vertical Assembly of Giant Double‐ and Triple‐Decker Spoked Wheel Supramolecular Structures (Angew. Chem. Int. Ed. 43/2018) ()
Angewandte Chemie International Edition, Volume 57, Issue 43, Page 13937-13937, October 22, 2018.
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Inside Cover: Rationally Designed Peptidyl Virus‐Like Particles Enable Targeted Delivery of Genetic Cargo (Angew. Chem. Int. Ed. 43/2018) ()
Angewandte Chemie International Edition, Volume 57, Issue 43, Page 13938-13938, October 22, 2018.
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Frontispiece: Tuning Charge Transport in Aromatic‐Ring Single‐Molecule Junctions via Ionic‐Liquid Gating ()
Angewandte Chemie International Edition, Volume 57, Issue 43, October 22, 2018.
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The Chaotropic Effect as an Assembly Motif in Chemistry ()
Abstract Following up on scattered reports on interactions of conventional chaotropic ions (for example, I−, SCN−, ClO4−) with macrocyclic host molecules, biomolecules, and hydrophobic neutral surfaces in aqueous solution, the chaotropic effect has recently emerged as a generic driving force for supramolecular assembly, orthogonal to the hydrophobic effect. The chaotropic effect becomes most effective for very large ions that extend beyond the classical Hofmeister scale and that can be referred to as superchaotropic ions (for example, borate clusters and polyoxometalates). In this Minireview, we present a continuous scale of water–solute interactions that includes the solvation of kosmotropic, chaotropic, and hydrophobic solutes, as well as the creation of void space (cavitation). Recent examples for the association of chaotropic anions to hydrophobic synthetic and biological binding sites, lipid bilayers, and surfaces are discussed.
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Taming the Cationic Beast: Novel Developments in the Synthesis and Application of Weakly Coordinating Anions ()
Abstract This Review gives a comprehensive overview of the most topical weakly coordinating anions (WCAs) and contains information on WCA design, stability, and applications. As an update to the 2004 review, developments in common classes of WCA are included. Methods for the incorporation of WCAs into a given system are discussed and advice given on how to best choose a method for the introduction of a particular WCA. A series of starting materials for a large number of WCA precursors and references are tabulated as a useful resource when looking for procedures to prepare WCAs. Furthermore, a collection of scales that allow the performance of a WCA, or its underlying Lewis acid, to be judged is collated with some advice on how to use them. The examples chosen to illustrate WCA developments are taken from a broad selection of topics where WCAs play a role. In addition a section focusing on transition metal and catalysis applications as well as supporting electrolytes is also included.
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XLSY: Extra‐Large NMR Spectroscopy ()
Abstract NMR studies of intrinsically disordered proteins and other complex biomolecular systems require spectra with the highest resolution and dimensionality. An efficient approach, extra‐large NMR spectroscopy, is presented for experimental data collection, reconstruction, and handling of very large NMR spectra by a combination of the radial and non‐uniform sampling, a new processing algorithm, and rigorous statistical validation. We demonstrate the first high‐quality reconstruction of a full seven‐dimensional HNCOCACONH and two five‐dimensional HACACONH and HN(CA)CONH experiments for a representative intrinsically disordered protein α‐synuclein. XLSY will significantly enhance the NMR toolbox in challenging biomolecular studies.
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Tuning Charge Transport in Aromatic‐Ring Single‐Molecule Junctions via Ionic‐Liquid Gating ()
Abstract Achieving gate control with atomic precision, which is crucial to the transistor performance on the smallest scale, remains a challenge. Herein we report a new class of aromatic‐ring molecular nanotransistors based on graphene–molecule–graphene single‐molecule junctions by using an ionic‐liquid gate. Experimental phenomena and theoretical calculations confirm that this ionic‐liquid gate can effectively modulate the alignment between molecular frontier orbitals and the Fermi energy level of graphene electrodes, thus tuning the charge‐transport properties of the junctions. In addition, with a small gate voltage (|VG|≤1.5 V) ambipolar charge transport in electrochemically inactive molecular systems (EG>3.5 eV) is realized. These results offer a useful way to build high‐performance single‐molecule transistors, thus promoting the prospects for molecularly engineered electronic devices.
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Lithium Nitrate Solvation Chemistry in Carbonate Electrolyte Sustains High‐Voltage Lithium Metal Batteries ()
Abstract The lithium metal anode is regarded as a promising candidate in next‐generation energy storage devices. Lithium nitrate (LiNO3) is widely applied as an effective additive in ether electrolyte to increase the interfacial stability in batteries containing lithium metal anodes. However, because of its poor solubility LiNO3 is rarely utilized in the high‐voltage window provided by carbonate electrolyte. Dissolution of LiNO3 in carbonate electrolyte is realized through an effective solvation regulation strategy. LiNO3 can be directly dissolved in an ethylene carbonate/diethyl carbonate electrolyte mixture by adding trace amounts of copper fluoride as a dissolution promoter. LiNO3 protects the Li metal anode in a working high‐voltage Li metal battery. When a LiNi0.80Co0.15Al0.05O2 cathode is paired with a Li metal anode, an extraordinary capacity retention of 53 % is achieved after 300 cycles (13 % after 200 cycles for LiNO3‐free electrolyte) and a very high average Coulombic efficiency above 99.5 % is achieved at 0.5 C. The solvation chemistry of LiNO3‐containing carbonate electrolyte may sustain high‐voltage Li metal anodes operating in corrosive carbonate electrolytes.
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Sigmatropic Dearomatization/Defluorination Strategy for C−F Transformation: Synthesis of Fluorinated Benzofurans from Polyfluorophenols ()
Abstract Facile synthesis of fluorinated benzofurans from polyfluorophenols has been accomplished by means of a sigmatropic dearomatization/defluorination strategy composed of three processes: (1) interrupted Pummerer reaction of ketene dithioacetal monoxides with polyfluorophenols followed by [3,3] sigmatropic rearrangement, (2) Zn‐mediated smooth reductive removal of fluoride from the dearomatized intermediate, and (3) acid‐promoted cyclization/aromatization. Mechanistic investigations revealed important characteristic reactivity of polyfluorophenols in the present system. Some of the fluorinated benzofuran products were transformed by utilizing the 2‐methylsulfanyl moieties.
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Catalytic Promiscuity of Galactose Oxidase: A Mild Synthesis of Nitriles from Alcohols, Air, and Ammonia ()
Abstract We report an unprecedented catalytically promiscuous activity of the copper‐dependent enzyme galactose oxidase. The enzyme catalyses the one‐pot conversion of alcohols into the related nitriles under mild reaction conditions in ammonium buffer, consuming ammonia as the source of nitrogen and dioxygen (from air at atmospheric pressure) as the only oxidant. Thus, this green method does not require either cyanide salts, toxic metals, or undesired oxidants in stoichiometric amounts. The substrate scope of the reaction includes benzyl and cinnamyl alcohols as well as 4‐ and 3‐pyridylmethanol, giving access to valuable chemical compounds. The oxidation proceeds through oxidation from alcohol to aldehyde, in situ imine formation, and final direct oxidation to nitrile.
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Coupling of Methane and Carbon Dioxide Mediated by Diatomic Copper Boride Cations ()
Abstract The use of CH4 and CO2 to produce value‐added chemicals via direct C−C coupling is a challenging chemistry problem because of the inertness of these two molecules. Herein, mass spectrometric experiments and high‐level quantum‐chemical calculations have identified the first diatomic species (CuB+) that can couple CH4 with CO2 under thermal collision conditions to produce ketene (H2C=C=O), an important intermediate in synthetic chemistry. The order to feed the reactants (CH4 and CO2) is important and CH4 should be firstly fed to produce the C2 product. Molecular‐level mechanisms including control of product selectivity have been revealed for coupling of CH4 with CO2 under mild conditions.
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In Situ Thermal Atomization To Convert Supported Nickel Nanoparticles into Surface‐Bound Nickel Single‐Atom Catalysts ()
Abstract The arrangement of the active sites on the surface of a catalysts can reduce the problem of mass transfer and enhance the atom economy. Herein, supported Ni metal nanoparticles can be transformed to thermal stable Ni single atoms, mostly located on the surface of the support. Assisted by N‐doped carbon with abundant defects, this synthetic process not only transform the nanoparticles to single atoms, but also creates numerous pores to facilitate the contact of dissolved CO2 and single Ni sites. The proposed mechanism is that the Ni nanoparticles could break surface C−C bonds drill into the carbon matrix, leaving pores on the surface. When Ni nanoparticles are exposed to N‐doped carbon, the strong coordination splits Ni atoms from Ni NPs. The Ni atoms are stabilized within the surface of carbon substrate. The continuous loss of atomic Ni species from the NPs would finally result in atomization of Ni NPs. CO2 electroreduction testing shows that the surface enriched with Ni single atoms delivers better performance than supported Ni NPs and other similar catalysts.
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A Versatile Bis‐Allylboron Reagent for the Stereoselective Synthesis of Chiral Diols ()
Abstract Allylboron reagents are popular in synthesis owing to their versatility and the predictable stereochemical outcomes of their reactions with carbonyl compounds. Herein, we describe the synthesis of (Z,Z)‐hexadienyl bis‐boronate 1, a configurationally stable, crystalline, and easy to handle compound, which represents a class of bis‐allylic boron reagents with heretofore untapped synthetic potential. In combination with a chiral phosphoric acid catalyst, the reagent can be employed for the enantioselective allyl transfer reaction to a variety of one‐pot transformations, enabling swift access to functionalized 1,n‐diols. The in situ conversion of the reagent into the corresponding bis‐borinic ester allows for the direct and diastereoselective two‐fold allyl transfer to aldehydes. This affords C2‐ or Ci‐symmetric stereotetrads containing a 1,4‐diol moiety for natural product synthesis. The usefulness of our method was demonstrated with a short synthesis of the lignan (±)‐neo‐olivil.
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Oxygen‐Delivery Materials: Synthesis of an Open‐Cage Fullerene Derivative Suitable for Encapsulation of H2O2 and O2 ()
Abstract An open‐cage [60]fullerene was prepared through a multiple‐step sequence based on peroxide‐mediated cage‐opening reactions. Key steps include repeated C60‐sensitized singlet‐oxygen oxidation of electron‐rich amino enol double bonds to form two lactone and two lactam moieties on the rim of the orifice. Single‐crystal X‐ray analysis shows that the 22‐membered orifice has an ellipsoid shape with the major axis at 6.7 Å and the minor axis at 3.5 Å. Encapsulation of H2O2 was observed under atmospheric pressure at room temperature. Oxygen is also effectively trapped during the process.
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Rationally Designed Peptidyl Virus‐Like Particles Enable Targeted Delivery of Genetic Cargo ()
Abstract We report a strategy to construct peptidyl virus‐like particles (pVLPs) by mimicking the human immunodeficiency virus and simian virus 40. We designed two viral peptides with cell/nucleus‐targeting capabilities that can co‐assemble in their active conformations into well‐defined nanoparticles. The self‐assembled nanoparticles can encapsulate the DNA of clustered regularly interspaced short palindromic repeat associated proteins 9 (CRISPR/Cas9) to form biodegradable pVLPs with excellent cell‐targeting ability and biocompatibility. The pVLPs can penetrate the cellular membrane and deliver genetic cargos into the nucleus through the viral entry route. The results provide a promising pathway for engineering artificial viruses with desired functions.
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Tetracationic Gallium Cluster Cations ()
Abstract The univalent salt Ga(PhF)2+[Al(ORF)4]− (RF=OC(CF3)3) forms the strongly metal–metal bonded cluster tetracations [GaII2(L)4]4+ and [GaI4(L′)8]4+, when it reacts with innocent ligands like phenanthroline (L=phen) or t‐butylisonitrile (L′=tBu‐NC). Their structures and energetics are discussed as a function of the employed ligands, supported by DFT calculations and Born–Fajans–Haber cycles.
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Site‐Specific Deoxyfluorination of Small Peptides with [18F]Fluoride ()
Abstract Radiolabeled receptor‐binding peptides are an important class of positron emission tomography tracers owing to achievable high binding affinities and their rapid blood clearance. Herein, a method to introduce a 4‐[18F]fluoro‐phenylalanine residue into peptide sequences is reported, by chemoselective radio‐deoxyfluorination of a tyrosine residue using a traceless activating group. The replacement of only one hydrogen atom with [18F]fluoride results in minimal structural perturbation of the peptide, which is desirable in the labeling of tracer candidates.
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Heterometallic Cluster‐Capped Tetrahedral Assemblies with Postsynthetic Modification of the Metal Cores ()
Abstract Combining the star‐shaped alkynyl ligands with low‐nuclearity gold–copper triphosphane clusters produces 3D metallocage aggregates, which demonstrate room temperature phosphorescence in solution (max Φem=0.6). Their luminescence mainly originates from cluster‐localized metal‐to‐ligand charge transfer excited state. These supramolecular assemblies can be easily converted into the isostructural gold‐silver congeners by the direct exchange of the metal ions. Such modification of the terminal metal cores switches the emission to the intraligand (alkyne) electronic transitions of the triplet manifold, that represents an unusual optical functionality among the metallocycle/metallocage complexes.
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A P−P Bond as a Redox Reservoir and an Active Reaction Site ()
Abstract The carbonylation of a nickel(II) anilido species 2 led to the formation of a dinickel(0)–CO complex (P2P‐PP2){Ni(CO)}2 3 with a P−P bond along with isocyanate generation. In this reaction, the central phosphide moiety of an anionic PPP ligand (PPP−=−P[2‐PiPr2C6H4]2) acts as a single‐electron donor to form a P radical. Alternatively, 3 can be synthesized from the reduction of (PPP)NiCl (1) in the presence of CO; thus, the reaction proceeds by radical coupling of a .P−Ni0−CO species. The reverse reaction occurred to generate 1 when 3 was treated with AgCl. Since the P−P bond is light‐sensitive, its homolysis is possible and was explored by EPR spectroscopy and DFT analysis. Finally, various bond‐activation reactions of 3 occurred under visible‐light conditions, thus indicating that a P−P bond can act as an active reaction site.
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Room‐Temperature Liquid Na–K Anode Membranes ()
Abstract The Na–K alloy is a liquid at 25 °C over a large compositional range. The liquid alloy is also immiscible in the organic‐liquid electrolytes of an alkali‐ion rechargeable battery, providing dendrite‐free liquid alkali‐metal batteries with a liquid–liquid anode‐electrolyte interface at room temperature. The two liquids are each immobilized in a porous matrix. In previous work, the porous matrix used to immobilize the alloy was a carbon paper that is wet by the alloy at 420 °C; the alloy remains in the paper at room temperature. Here we report a room‐temperature vacuum infiltration of the alloy into a porous Cu or Al membrane and a reversible stripping/plating of the liquid alloy with the immobilized organic‐liquid electrolyte; no self‐diacharge is observed since the liquid Na–K does not dissolve into the liquid carbonate electrolytes. The preparation and stripping/plating of the liquid alkali‐metal anode can both now be done safely at room temperature.
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Vertical Assembly of Giant Double‐ and Triple‐Decker Spoked Wheel Supramolecular Structures ()
Abstract The double‐ or triple‐decker 3D metallo‐hexagons were obtained by self‐assembly of multitopic tris‐terpyridines with Cd2+ ions in near‐quantitative yield. Comprising up to 72 ionic pairs, the multiple spoked wheels display characteristic reversible gelation properties under thermodynamic conditions. The supramolecular metallo‐nanoarchitectures were characterized by 1H NMR, 2D NMR (COSY and NOESY), and diffusion‐ordered spectroscopy (DOSY) and HR‐ESI‐MS, traveling‐wave ion mobility mass spectrometry (TWIM‐MS), TEM, and AFM. For the first time, the self‐assembly of 45 units at once was demonstrated to yield exceptional giant triple‐decker hexagons of up to circa 42 000 Da.
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Bottom‐Up Construction of an Adaptive Enzymatic Reaction Network ()
Abstract The reproduction of emergent behaviors in nature using reaction networks is an important objective in synthetic biology and systems chemistry. Herein, the first experimental realization of an enzymatic reaction network capable of an adaptive response is reported. The design is based on the dual activity of trypsin, which activates chymotrypsin while at the same time generating a fluorescent output from a fluorogenic substrate. Once activated, chymotrypsin counteracts the trypsin output by competing for the fluorogenic substrate and producing a non‐fluorescent output. It is demonstrated that this network produces a transient fluorescent output under out‐of‐equilibrium conditions while the input signal persists. Importantly, in agreement with mathematical simulations, we show that optimization of the pulse‐like response is an inherent trade‐off between maximum amplitude and lowest residual fluorescence.
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Cationic Charges Leading to an Inverse Free‐Energy Relationship for N−N Bond Formation by MnVI Nitrides ()
Abstract MnVN Schiff‐base complexes incorporating a Na+ (1Na), K+ (1K), Ba2+ (1Ba), or Sr2+ (1Sr) ion in the ligand framework are reported. The MnVI/V reduction potentials for 1Na, 1K, 1Ba, and 1Sr are 0.591, 0.616, 0.805, and 0.880 V vs. Fe(C5H5)2+/0, respectively, exhibiting significant positive shifts compared to a MnN Schiff‐base complex in the same primary coordination environment but with no associated alkali or alkaline earth metal ion (A, E1/2=0.427 V vs. Fe(C5H5)2+/0). One‐electron oxidation of the MnVN complexes results in bimolecular coupling to form N2 with rates (k2) at 20 °C of 2166, 684, 857, and 99.7, an 87 m−1 s−1 for A, 1Na, 1K, 1Ba, and 1Sr respectively, following an inverse linear free energy relationship. Thus, increasing charge through proximal cations results in MnVIN complexes that are both more oxidizing and more stable to bimolecular coupling, a trend diametrically opposed to when complexes were modified by ligand substituents through inductive effects.
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Super‐resolution Geometric Barcoding for Multiplexed miRNA Profiling ()
Abstract MicroRNA (miRNA) expression profiles hold promise as biomarkers for diagnostics and prognosis of complex diseases. Herein, we report a super‐resolution fluorescence imaging‐based digital profiling method for specific, sensitive, and multiplexed detection of miRNAs. In particular, we applied the DNA‐PAINT (point accumulation for imaging in nanoscale topography) method to implement a super‐resolution geometric barcoding scheme for multiplexed single‐molecule miRNA capture and digital counting. Using synthetic DNA nanostructures as a programmable miRNA capture nano‐array, we demonstrated high‐specificity (single nucleotide mismatch discrimination), multiplexed (8‐plex, 2 panels), and sensitive measurements on synthetic miRNA samples, as well as applied one 8‐plex panel to measure endogenous miRNAs levels in total RNA extract from HeLa cells.
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Dynamic Kinetic Asymmetric Reductive Amination: Synthesis of Chiral Primary β‐Amino Lactams ()
Abstract A highly efficient ruthenium‐catalyzed asymmetric reductive amination (ARA) of racemic β‐keto lactams with molecular hydrogen and ammonium salts is disclosed for the synthesis of enantiomerically pure primary amino lactams through dynamic kinetic resolution (DKR). By this approach, a range of syn primary β‐amino lactams were obtained in high yields with high chemo‐, enantio‐, and diastereoselectivity (up to 98 % yield, 99 % ee, >20:1 d.r., syn products). The utility of the products has been demonstrated by rapid access to a key synthetic intermediate towards biologically active drug molecules. Meanwhile, mechanistic studies and control experiments indicate that the reaction may proceed through the hydrogenation of an iminium intermediate.
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Different Degrees of Electron Delocalization in Mixed Valence Ru‐Ru‐Ru Compounds by Cyanido‐/Isocyanido‐Bridge Isomerism ()
Abstract The two stable pairs of trimetallic compounds trans‐[Cp*(dppe)Ru(μ‐NC)Ru(dmap)4(μ‐CN)Ru(dppe)Cp*][PF6]n (1[PF6]n, n=2, 3; Cp*=1,2,3,4,5‐pentamethylcyclopentadiene; dppe=1,2‐bis‐(diphenylphosphino)ethane; dmap= 4‐dimethylaminopyridine) and trans‐[Cp*(dppe)Ru(μ‐CN)Ru(dmap)4(μ‐NC)Ru(dppe)Cp*][PF6]n (2[PF6]n, n=2, 3), which demonstrate cyanide/isocyanide isomerism, have been synthesized and fully characterized. 13+[PF6]3 and 23+[PF6]3 are the one‐electron oxidation products of 12+[PF6]2 and 22+[PF6]2, respectively. The results suggest that 1[PF6]3 is a class III mixed valence compound, whereas 2[PF6]3 might be an unusually symmetrical class II–III mixed valence compound composed of the two asymmetrical delocalized RuIII−NC−RuII mixed valence subunits.
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Realization of an Al≡Al Triple Bond in the Gas‐Phase Na3Al2− Cluster via Double Electronic Transmutation ()
Abstract The discovery of homodinuclear multiple bonds composed of Group 13 elements represents one of the most challenging frontiers in modern chemistry. A classical triple bond such as N≡N and HC≡CH contains one σ bond and two π bonds constructed from the p orbitals perpendicular to the σ bond. However, the traditional textbook triple bond between two Al atoms has remained elusive. Here we report an Al≡Al triple bond in the designer Na3Al2− cluster predicted in silico, which was subsequently generated by pulsed arc discharge followed by mass spectrometry and photoelectron spectroscopy characterizations. Being effectively Al2− due to the electron donation from Na, the Al atoms in Na3Al2− undergo a double electronic transmutation into Group 15 elements, thus the Al2−≡Al2− kernel mimics the P≡P and N≡N molecules. We anticipate this work will stimulate more endeavors in discovering materials using Al2−≡Al2− as a building block in the gas phase and in the solid state.
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Ultrastabilization of Zeolite Y Transforms Brønsted–Brønsted Acid Pairs into Brønsted–Lewis Acid Pairs ()
Abstract Two pairs of Brønsted acid sites have been identified in H,Na‐Y zeolite, located in the supercage and in the sodalite cage, which upon ultrastabilization (dealumination) are transformed into pairs of Brønsted and Lewis acid sites. This mild postsynthetic modification step is an important process for converting this material into an active catalyst for large‐scale commercial reactions. Pairing structures and their transformations have been investigated using 1H double‐quantum NMR spectroscopy experiments for dehydrated zeolite, H,Na‐Y, and its ultrastabilized form, H,Na‐USY. This approach enables the detection of pairs of Brønsted and Lewis acid sites with unprecedented 1H resolution and distinguishing them from isolated acid sites. The dealumination is also detected by static 27Al solid‐state NMR experiments.
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Direct Photocatalytic Synthesis of Medium‐Sized Lactams by C−C Bond Cleavage ()
Abstract Reported is a novel two‐step ring‐expansion strategy for expeditious synthesis of all ring sizes of synthetically challenging (hetero)aryl‐fused medium‐sized lactams from readily available 5–8‐membered cyclic ketones. This step‐economic approach features a remote radical (hetero)aryl migration from C to N under visible‐light conditions. Broad substrate scope, good functional‐group tolerance, high efficiency, and mild reaction conditions make this procedure very attractive. In addition, this method also provides expedient access to 13–15‐membered macrolactams upon an additional one‐step manipulation. Mechanistic studies indicate that the reaction involves an amidyl radical and is promoted by acid.
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Highly Efficient Electroreduction of CO2 to Methanol on Palladium–Copper Bimetallic Aerogels ()
Abstract Electrochemical reduction of CO2 to CH3OH is of great interest. Aerogels have fine inorganic superstructure with high porosity and are known to be exceptional materials. Now a Pd−Cu bimetallic aerogel electrocatalyst has been developed for conversion of CO2 into CH3OH. The current density and Faradaic efficiency of CH3OH can be as high as 31.8 mA cm−2 and 80.0 % over the Pd83Cu17 aerogel at a very low overpotential (0.24 V). The superior performance of the electrocatalyst results from efficient adsorption and stabilization of the CO2 radical anion, high Pd0/PdII and CuI+Cu0/CuII ratios, and sufficient Pd/Cu grain boundaries of aerogel nanochains.
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Multivalent Crown Ether Receptors Enable Allosteric Regulation of Anion Exchange in an Fe4L6 Tetrahedron ()
Abstract We report a strategy for regulating the rate of internally bound anion exchange within an Fe4L6 metal–organic tetrahedron through external coordination of tripodal tris(alkylammonium) cations. The cage features three flexible 18‐crown‐6 receptors at each of its FeII vertices, facilitating strong tritopic interactions with tris(ammonium) cations to “cap” the vertices of the tetrahedron. This capping mechanism restricts the flexibility of the cage framework, thereby reducing the rate of anion exchange within its central cavity by 20‐fold. Thus, we demonstrate the first use of an externally bound multivalent effector to allosterically control internal guest binding in a molecular cage.
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Construction of Porous Mo3P/Mo Nanobelts as Catalysts for Efficient Water Splitting ()
Abstract A novel synthesis strategy is demonstrated to prepare Mo3P/Mo nanobelts with porous structure for the first time. The growth and formation mechanism of the porous Mo3P/Mo nanobelt structure was disclosed by varying the contents of H2/PH3 and the reaction temperature. During the hydrogen evolution reaction (HER) catalysis, the optimized porous Mo3P/Mo nanobelts exhibited a small overpotential of 78 mV at a current density of 10 mA cm−2 and a low Tafel slope of 43 mV dec−1, as well as long‐term stability in alkaline media, surpassing Pt wire. Density functional theory (DFT) calculations reveal that the H2O dissociation on the surface of Mo3P is favorable during the HER.
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Electron‐Affinity‐Triggered Variations on the Optical and Electrical Properties of Dye Molecules Enabling Highly Efficient Dye‐Sensitized Solar Cells ()
Abstract The synthesis, characterization, and photovoltaic performance of a series of indacenodithiophene (IDT)‐based D‐π‐A organic dyes with varying electron‐accepting units is presented. By control of the electron affinity, perfectly matching energy levels were achieved with a copper(I/II)‐based redox electrolyte, reaching a high open‐circuit voltage (>1.1 V) while harvesting a large fraction of solar photons at the same time. Besides achieving high power conversion efficiencies (PCEs) for dye‐sensitized solar cells (DSCs), that is, 11.2 % under standard AM 1.5 G sunlight, and 28.4 % under a 1000 lux fluorescent light tube, this work provides a possible method for the design and fabrication of low‐cost highly efficient DSCs.
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Calcium(II)‐Catalyzed Intermolecular Hydroarylation of Deactivated Styrenes in Hexafluoroisopropanol ()
Abstract A challenging catalytic hydroarylation of highly electron deficient styrenes has been developed on the basis of efficient cooperation between a calcium(II) triflimide salt and hexafluoroisopropanol (HFIP). This method affords a large variety of diaryl alkanes, notably diaryl ethanes, in good to excellent yields, and is simple to implement and compatible with various functional groups. Furthermore, DFT calculations and deuterium labeling experiments were conducted to elucidate the function of this promoter system.
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Generation of the UFM1 Toolkit for Profiling UFM1‐Specific Proteases and Ligases ()
Abstract Ubiquitin‐fold modifier 1 (UFM1) is a reversible post‐translational modifier that is covalently attached to target proteins through an enzymatic cascade and removed by designated proteases. Abnormalities in this process, referred to as Ufmylation, have been associated with a variety of human diseases. Given this, the UFM1‐specific enzymes represent potential therapeutic targets; however, understanding of their biological function has been hampered by the lack of chemical tools for activity profiling. To address this unmet need, a diversifiable platform for UFM1 activity‐based probes (ABPs) utilizing a native chemical ligation (NCL) strategy was developed, enabling the generation of a variety of tools to profile both UFM1 conjugating and deconjugating enzymes. The use of the probes is demonstrated in vitro and in vivo for monitoring UFM1 enzyme reactivity, opening new research avenues.
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Facile Benzene Reduction by a Ca2+/AlI Lewis Acid/Base Combination ()
Abstract Attempted synthesis of the donor–acceptor complex (BDI)Ca+←AlI(BDI) complex by reaction of (BDI)Ca+ in the form of its B(C6F5)4− salt with (BDI)AlI in benzene led to dearomatization of the solvent and formation of (BDI)Ca+(C6H6)AlIII(BDI) (BDI=CH[C(CH3)N‐Dipp]2, Dipp=2,6‐diisopropylphenyl). The C6H62− anion is strongly puckered and its boat form features four long (ca. 1.50 Å) and two short (ca. 1.34 Å) C−C bond distances. The flagpole positions of the C6H62− anion chelate an AlIII cation giving a norbornadiene‐like fragment with Al in the 7‐position. The C=C double bonds of this alumina‐norbornadiene strongly coordinate to the Ca2+ metal ion. The complex is stable in solution up to 80 °C. Several mechanisms for its formation are discussed including a highly likely frustrated Lewis pair type mechanism in which benzene is activated by the Lewis acid (BDI)Ca+ followed by nucleophilic attack by the Lewis base (BDI)AlI.
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Iridium‐Catalyzed Electrooxidative C−H Activation by Chemoselective Redox‐Catalyst Cooperation ()
Abstract Iridium‐catalyzed electrochemical C−H activation was accomplished within a cooperative catalysis manifold, setting the stage for electrooxidative C−H alkenylations through weak O‐coordination. The iridium‐electrocatalyzed C−H activation featured high functional‐group tolerance through assistance of a metal‐free redox mediator through indirect electrolysis. Detailed mechanistic insights provided strong support for an organometallic C−H cleavage and a synergistic iridium(III/I)/redox catalyst regime, enabling the use of sustainable electricity as the terminal oxidant with improved selectivity features.
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Enzymatic Amide Tailoring Promotes Retro‐Aldol Amino Acid Conversion To Form the Antifungal Agent Aspirochlorine ()
Abstract Aspirochlorine is an unusual antifungal cyclopeptide produced by Aspergillus oryzae, an important mold used for food fermentation. Whereas its structure suggested that a non‐ribosomal peptide synthetase assembles the cyclopeptide from phenylalanine and glycine building blocks, labeling studies indicated that one Phe moiety is transformed into Gly after peptide formation. By means of genetic engineering, heterologous expression, biotransformations, and in vitro assays, we dissected and reconstituted four crucial steps in aspirochlorine biosynthesis, which involve two cytochrome P450 monooxygenases, (AclL and AclO), a methyltransferase (AclU), and a halogenase (AclH). We found that the installation of the N‐methoxylation of the peptide bond sets the stage for a retro‐aldol reaction that leads to the Phe‐to‐Gly conversion. The substrate scopes of the dedicated enzymes as well as bioassays revealed that the peptide editing has evolved to optimize the antifungal action of the natural product.
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Endohedral Functionalized Cage as a Tool to Create Frustrated Lewis Pairs ()
Abstract A frustrated Lewis pair (FLP) system was obtained by confinement of the Lewis base partner, a Verkade's superbase, in a molecular cavity. Whereas the model superbase lacking cavity displayed no catalytic activity in Morita–Baylis–Hillman (MBH) reactions, when associated to titanium (IV) chloride, the encaged superbase turns out to be an efficient catalyst under the same conditions. The crucial role of the endohedral functionalized cage on catalytic performance was further demonstrated by the fact that model superbases with bulky substituents were much less efficient to produce active catalysts, as well as by inhibition and substrate selection experiments. 31P NMR spectroscopy and mass spectrometry experiments evidenced that no interaction between the Lewis acidic and basic partners occurred when the superbase was capped by a cycloveratrylene (CTV) unit, thus creating a true FLP active system.
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Parallel and Precise Macroscopic Supramolecular Assembly through Prolonged Marangoni Motion ()
Abstract Macroscopic supramolecular assembly (MSA) is a rising concept in supramolecular science, in which building blocks with sizes exceeding 10 μm self‐assemble into larger structures. MSA faces the challenge of developing appropriate self‐propulsion strategies to improve the motility of the macroscopic building blocks. Although the Marangoni effect is an ideal driving force with random motion paths, excessive aggregation of the surfactant and fast decay of motion remain challenging problems. Hence, a molecular interference strategy to drive the self‐assembly over longer times by finely controlling the interfacial adsorption of surfactants using dynamic equilibria is proposed. Surfactant depletion through molecular recognition in the solution to oppose fast interfacial aggregation efficiently facilitates macroscopic motion and assembly. The resulting motility lifetime is extended remarkably from 120 s to 2200 s; with the improved kinetic energy, the assembly probability increases from 20 % to 100 %.
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Iridium‐Catalyzed α‐Selective Arylation of Styrenes by Dual C−H Functionalization ()
Abstract An IrI‐system modified with a ferrocene derived bisphosphine ligand promotes α‐selective arylation of styrenes by dual C−H functionalization. These studies offer a regioisomeric alternative to the Pd‐catalyzed Fujiwara–Moritani reaction.
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Total Synthesis of Asperchalasines A, D, E, and H ()
Abstract The first total syntheses of the cytochalasan dimers asperchalasines A, D, E, and H have been accomplished. The key steps of the synthesis include a highly stereoselective intermolecular Diels–Alder reaction and a Horner–Wadsworth–Emmons macrocyclization to establish the key monomer aspochalasin B, and an intermolecular Diels–Alder reaction followed by a biomimetic oxidative heterodimerization by 5+2 cycloaddition to furnish asperchalasine A. The synthetic efforts provide insight into the biosynthetic pathway of cytochalasan dimers and enables the further study of their biological properties.
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Total Syntheses of Asperchalasines A–E ()
Abstract The first total syntheses of asperchalasines A–E, a collection of unprecedented merocytochalasans, are reported. Aspochalasin B, a key tricyclic cytochalasan monomer, was first synthesized through a unified approach that hinges on a Diels–Alder reaction and a ring‐closing metathesis reaction. The bioinspired Diels–Alder reactions of aspochalasin B with different epicoccine precursors were then explored, which enabled the divergent access of the heterodimers asperchalasines B–E as well as related congeners. Furthermore, the heterotrimer asperchalasine A was obtained from one epicoccine unit and two aspochalasin B units through a biomimetic Diels–Alder reaction followed by an oxidative [5+2]‐cycloaddition.
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Zwitterionic Design Principle of Nickel(II) Catalysts for Carbonylative Polymerization of Cyclic Ethers ()
Abstract Zwitterionic structure is necessary for NiII complexes to catalyze carbonylative polymerization (COP) of cyclic ethers. The cationic charge at the NiII center imparts sufficient electrophilicity to the Ni–acyl bond for it to react with cyclic ethers to give an acyl‐cyclic ether oxonium intermediate, while the ligand‐centered anionic charge ensures that the resultant oxonium cation is ion‐paired with the Ni0 nucleophile. The current catalysts give non‐alternating copolymers of carbon monoxide and cyclic ethers and are the most effective when both ethylene oxide and tetrahydrofuran are present as the cyclic ether monomers.
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Synthesis of N‐Heterocycles by Dehydrogenative Annulation of N‐Allyl Amides with 1,3‐Dicarbonyl Compounds ()
Abstract Dehydrogenative annulation under oxidizing reagent‐free conditions is an ideal strategy to construct cyclic structures. Reported herein is an unprecedented synthesis of pyrrolidine and tetrahydropyridine derivatives through electrochemical dehydrogenative annulation of N‐allyl amides with 1,3‐dicarbonyl compounds. The electrolytic method employs an organic redox catalyst, which obviates the need for oxidizing reagents and transition‐metal catalysts. In these reactions, the N‐allyl amides serve as a four‐atom donor to react with dimethyl malonate to give pyrrolidines by a (4+1) annulation, or with β‐ketoesters to afford tetrahydropyridine derivatives by a (4+2) annulation.
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Merging Photoredox and Organometallic Catalysts in a Metal–Organic Framework Significantly Boosts Photocatalytic Activities ()
Abstract Metal–organic frameworks (MOFs) have been extensively used for single‐site catalysis and light harvesting, but their application in multicomponent photocatalysis is unexplored. We report here the successful incorporation of an IrIII photoredox catalyst and a NiII cross‐coupling catalyst into a stable Zr12 MOF, Zr12‐Ir‐Ni, to efficiently catalyze C−S bond formation between various aryl iodides and thiols. The proximity of the IrIII and NiII catalytic components to each other (ca. 0.6 nm) in Zr12‐Ir‐Ni greatly facilitates electron and thiol radical transfers from Ir to Ni centers to reach a turnover number of 38 500, an order of magnitude higher than that of its homogeneous counterpart. This work highlights the opportunity in merging photoredox and organometallic catalysts in MOFs to effect challenging organic transformations.
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C−H Bond Activation for the Synthesis of Heterocyclic Atropisomers Yields Hedgehog Pathway Inhibitors ()
Abstract Axially chiral 4‐arylisoquinolones are endowed with pronounced bioactivity, and methods for their efficient synthesis have gained widespread attention. However, enantioselective synthesis of axially chiral 4‐arylisoquinolones by means of C−H activation has not been reported to date. Described here is a rhodium (III)‐catalyzed C−H bond activation and annulation for the atroposelective synthesis of axially chiral 4‐arylisoquinolones. The method employs chiral cyclopentadienyl ligands embodying a piperidine ring as backbone and yields the atropisomers with good to excellent yields and enantioselectivity. Biological relevance of the 4‐arylisoquinolones was demonstrated by their investigation in different cellular assays, leading to the discovery of novel non‐SMO (SMO= smoothened) binding Hedgehog pathway inhibitors.
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Gold‐Catalyzed Double Cycloisomerization of 1‐Ene‐4,10‐diynyl Esters to Bicyclo[6.3.0]undeca‐2,4,9‐trienyl Esters ()
Abstract A synthetic method to prepare bicyclo[6.3.0]undeca‐2,4,9,trienyl esters efficiently from gold(I)‐catalyzed Rautenstrauch rearrangement/1,5‐hydride shift/8‐endo‐dig cyclization of 1‐ene‐4,10‐diynyl esters is described. The suggested double cycloisomerization mechanism delineates the first example of an unactivated all‐carbon tethered 1,7‐enyne, either preformed or formed in situ, which undergoes an 8‐endo‐dig cyclization pathway to give a cyclooctane motif. It also offers an extremely rare synthetic method in organic chemistry that can sequentially assemble both ring components of the bicyclic motif from an acyclic precursor in one step.
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3D‐Printed Carbon Electrodes for Neurotransmitter Detection ()
Abstract Implantable neural microsensors have significantly advanced neuroscience research, but the geometry of most probes is limited by the fabrication methods. Therefore, new methods are needed for batch‐manufacturing with high reproducibility. Herein, a novel method is developed using two‐photon nanolithography followed by pyrolysis for fabrication of free‐standing microelectrodes with a carbon electroactive surface. 3D‐printed spherical and conical electrodes were characterized with slow scan cyclic voltammetry (CV). With fast‐scan CV, the electrodes showed low dopamine LODs of 11±1 nm (sphere) and 10±2 nm (cone), high sensitivity to multiple neurochemicals, and high reproducibility. Spherical microelectrodes were used to detect dopamine in a brain slice and in vivo, demonstrating they are robust enough for tissue implantation. This work is the first demonstration of 3D‐printing of free‐standing carbon electrodes; and the method is promising for batch fabrication of customized, implantable neural sensors.
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Ultrafast PhotoRAFT Block Copolymerization of Isoprene and Styrene Facilitated through Continuous‐Flow Operation ()
Abstract Polymers made from isoprene and styrene resemble an important class of synthetic macromolecules found in a wide range of everyday commodity products. Their synthesis is usually limited to radical emulsion or anionic polymerization. Herein, we report on ultrafast photoiniferter reversible addition‐fragmentation chain transfer (RAFT) polymerization of isoprene and styrene in a continuous‐flow microreactor. The cooperative action of a high photoinitiation efficiency and use of elevated temperatures considerably reduces the reaction times to less than half an hour to give high monomer conversions, allowing for the first time polyisoprene to be yielded from controlled radical polymerization in high definition and reasonable reaction times. High chain‐end fidelities are maintained and block copolymers were prepared including a polystyrene‐block‐polyisoprene‐block‐polystyrene (PS‐b‐PI‐b‐PS) triblock copolymer.
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Exploring the “Goldilocks Zone” of Semiconducting Polymer Photocatalysts by Donor–Acceptor Interactions ()
Abstract Water splitting using polymer photocatalysts is a key technology to a truly sustainable hydrogen‐based energy economy. Synthetic chemists have intuitively tried to enhance photocatalytic activity by tuning the length of π‐conjugated domains of their semiconducting polymers, but the increasing flexibility and hydrophobicity of ever‐larger organic building blocks leads to adverse effects such as structural collapse and inaccessible catalytic sites. To reach the ideal optical band gap of about 2.3 eV, A library of eight sulfur and nitrogen containing porous polymers (SNPs) with similar geometries but with optical band gaps ranging from 2.07 to 2.60 eV was synthesized using Stille coupling. These polymers combine π‐conjugated electron‐withdrawing triazine (C3N3) and electron donating, sulfur‐containing moieties as covalently bonded donor–acceptor frameworks with permanent porosity. The remarkable optical properties of SNPs enable fluorescence on‐off sensing of volatile organic compounds and illustrate intrinsic charge‐transfer effects.
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Near‐Infrared Semiconducting Polymer Brush and pH/GSH‐Responsive Polyoxometalate Cluster Hybrid Platform for Enhanced Tumor‐Specific Phototheranostics ()
Abstract Tumor‐specific phototheranostics is conducive to realizing precise cancer therapy. Herein, a novel tumor microenvironment (TME)‐responsive phototheranostic paradigm based on the combination of semiconducting polymer brushes and polyoxometalate clusters (SPB@POM) is rationally designed. The acidic TME could drive the self‐assembly of SPB@POM into bigger aggregates for enhanced tumor retention and accumulation, while the reducing TME could significantly enhance the NIR absorption of SPB@POM for significant improvement of photoacoustic imaging contrast and photothermal therapy efficacy. Therefore, the smart pH/glutathione (GSH)‐responsive SPB@POM allows for remarkable phototheranostic enhancement under the unique TME, which has potential for precise tumor‐specific phototheranostics with minimal side effects.
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Selective C(sp3)−H and C(sp2)−H Fluorination of Alcohols Using Practical Auxiliaries ()
Abstract Selective introduction of fluorine into molecules by the cleavage of inert C−H bonds is of central academic and synthetic interest, yet remains challenging. Given the central role of alcohols in organic chemistry as the most ubiquitous building blocks, a versatile and selective C(sp3)−H and C(sp2)−H fluorination of simple alcohols, enabled by novel designed exo‐directing groups, is described. C(sp2)−H bond fluorination was achieved by using a simple acetone oxime as auxiliary, whereas a new, modular and easily accessible bidentate auxiliary was developed for the efficient and site‐selective fluorination of various primary methyl, methylene, and benzylic C(sp3)−H bonds. Fluorinated alcohols can readily be accessed by the removal of auxiliaries, and significantly expands the synthetic prospect of the present procedure.
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Air‐Stable Blue Phosphorescent Tetradentate Platinum(II) Complexes as Strong Photo‐Reductant ()
Abstract Strong photo‐reductants have applications in photo‐redox organic synthesis involving reductive activation of C−X(halide) and C=O bonds. We report herein air‐stable PtII complexes supported by tetradentate bis(phenolate‐NHC) ligands having peripheral electron‐donating N‐carbazolyl groups. Photo‐physical, electrochemical, and computational studies reveal that the presence of N‐carbazolyl groups enhances the light absorption and redox reversibility because of its involvement into the frontier MOs in both ground and excited states, making the complexes robust strong photo‐reductant with E([Pt]+/*) over −2.6 V vs. Cp2Fe+/0. The one‐electron reduced [Pt]− species are stronger reductants with EPC([Pt]0/−) up to −3.1 V vs. Cp2Fe+/0. By virtue of the strong reducing nature of these species generated upon light excitation, they can be used in light‐driven reductive coupling of carbonyl compounds and reductive debromination of a wide range of unactivated aryl bromides.
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Structure, Total Synthesis, and Biosynthesis of Chloromyxamides: Myxobacterial Tetrapeptides Featuring an Uncommon 6‐Chloromethyl‐5‐methoxypipecolic Acid Building Block ()
Abstract Soil‐living microbes are an important resource for the discovery of new natural products featuring great structural diversity that are reflective of the underlying biosynthetic pathways as well as incorporating a wide range of intriguing small‐molecule building blocks. We report here the full structural elucidation, total synthesis, and biosynthesis of chloromyxamides, a new class of tetrapeptides that display an unprecedented 6‐chloromethyl‐5‐methoxypipecolic acid (CMPA) substructure. Chemical synthesis—including an approach to access the CMPA unit—was pursued to confirm the structure of the chloromyxamides and enabled determination of the absolute configuration in the CMPA ring. A model for the nonribosomal assembly of chloromyxamides was devised on the basis of the combined evaluation of the biosynthetic gene cluster sequence and the feeding of stable isotope‐labeled precursors. This provided insight into the formation of the various chloromyxamide derivatives and the biogenesis of the CMPA unit.
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Molecular Conformation‐Dependent Mechanoluminescence: Same Mechanical Stimulus but Different Emissive Color over Time ()
Abstract A phenothiazine derivative of FCO‐CzS with changeable mechanoluminescence is reported, which, upon continuous mechanical stimulus, shows mechanoluminescent emission from blue to white and yellow. Careful analysis of the experimental results, coupled with the well‐understood photoluminescence theory, show that the molecular conformation transition of the phenothiazine group from quasi‐axial to quasi‐equatorial is responsible for this dynamic mechanoluminescence effect.
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Intensely Photoluminescent Diamidophosphines of the Alkaline‐Earth Metals, Aluminum, and Zinc ()
Abstract The positively charged and weakly polarizable s‐block metals commonly do not usually have phosphine ligands in molecular complexes. Herein, we report mono‐ and dinuclear small diamidophosphine complexes of the alkaline‐earth metals Mg, Ca, and Sr, which were prepared from simple precursors and a phosphine‐functionalized diamine ligand N,N‐bis(2‐(diphenyl‐phosphino)phenyl)ethane‐1,2‐diamine (PNHNHP). The alkaline‐earth metal based complexes [(PNNP)Mg]2 and [(PNNP)M(thf)3] (M=Ca, Sr), exhibit unusual coordination spheres and show bright fluorescence, both in the solid state and in solution. For comparison, the even stronger luminescent Al and Zn complexes [(PNNP)Zn]2 and [(PNNP)AlCl] were prepared. Emission lifetimes in the nanosecond range and high photoluminescence quantum yields up to 93 % are observed at room temperature.
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Genome Editing Reveals Novel Thiotemplated Assembly of Polythioamide Antibiotics in Anaerobic Bacteria ()
Abstract Closthioamide (CTA) is a unique symmetric nonribosomal peptide with six thioamide moieties that is produced by the Gram‐positive obligate anaerobe Ruminiclostridium cellulolyticum. CTA displays potent inhibitory activity against important clinical pathogens, making it a promising drug candidate. Yet, the biosynthesis of this DNA gyrase‐targeting antibiotic has remained enigmatic. Using a combination of genome mining, genome editing (targeted group II intron, CRISPR/Cas9), and heterologous expression, we show that CTA biosynthesis involves specialized enzymes for starter unit biosynthesis, amide bond formation, thionation, and dimerization. Surprisingly, CTA biosynthesis involves a novel thiotemplated peptide assembly line that markedly differs from known nonribosomal peptide synthetases. These findings provide the first insights into the biosynthesis of thioamide‐containing nonribosomal peptides and offer a starting point for the discovery of related natural products.
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Sheng‐Gui He ()
Angewandte Chemie International Edition, Volume 57, Issue 43, Page 13964-13964, October 22, 2018.
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Hydrogen Atom Transfer Reactions via Photoredox Catalyzed Chlorine Atom Generation ()
Abstract The selective functionalization of chemically inert C−H bonds remains to be fully realized in achieving organic transformations that are redox‐neutral, waste‐limiting, and atom‐economical. The catalytic generation of chlorine atoms from chloride ions is one of the most challenging redox processes, where the requirement of harsh and oxidizing reaction conditions renders it seldom utilized in synthetic applications. We report the mild, controlled, and catalytic generation of chlorine atoms as a new opportunity for access to a wide variety of hydrogen atom transfer (HAT) reactions owing to the high stability of HCl. The discovery of the photoredox mediated generation of chlorine atoms with Ir‐based polypyridyl complex, [Ir(dF(CF3)ppy)2(dtbbpy)]Cl, under blue LED irradiation is reported.
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Synthesis of the Campylobacter jejuni 81‐176 Strain Capsular Polysaccharide Repeating Unit Reveals the Absolute Configuration of its O‐Methyl Phosphoramidate Motif ()
Abstract The O‐methyl phosphoramidate (MeOPN) motif is a non‐stoichiometric modification of capsular polysaccharides (CPS) in ≈70 % of all Campylobacter jejuni strains. Infections by C. jejuni lead to food‐borne illnesses and the CPS they produce are key virulence factors. The MeOPN phosphorus atom in these CPS is stereogenic and is found as a single stereoisomer. However, to date, the absolute stereochemistry at this atom has been undefined. We report the synthesis of the three repeating units found in C. jejuni 81‐176 CPS; one of these possesses a MeOPN group. In the course of these studies we established that the stereochemistry of the phosphorus atom in this MeOPN group is R. These studies represent the first unequivocal proof of stereochemistry of this group in any C. jejuni CPS. The compounds produced are anticipated to be useful tools in investigations targeting the function and biosynthesis of this structurally‐interesting modification, which so far has only been identified in campylobacter.
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High‐Flux High‐Selectivity Metal–Organic Framework MIL‐160 Membrane for Xylene Isomer Separation by Pervaporation ()
Abstract Separation of p‐xylene (kinetic diameter ca. 0.58 nm) from its bulkier isomers (o‐xylene and m‐xylene, ca. 0.68 nm) is challenging, but important in the petrochemical industry. Herein, we developed a highly selective and stable metal–organic framework (MOF) MIL‐160 membrane for selective separation of p‐xylene from its isomers by pervaporation. The suitable pore size (0.5∼0.6 nm) of the MIL‐160 membrane selectively allows p‐xylene to pass through, while excluding the bulkier o‐xylene and m‐xylene. For the separation of equimolar binary p‐/o‐xylene mixtures at 75 °C, high p‐xylene flux of 467 g m−2 h−1 and p‐/o‐xylene selectivity of 38.5 could be achieved. The stability of MIL‐160, ensured the separation performance of the MIL‐160 membrane was unchanged over a 24 h measurement. The high separation performance combined with its high thermal and chemical stability makes the MIL‐160 membrane a promising candidate for the separation of xylene isomers.
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Xiaodong Chen ()
Angewandte Chemie International Edition, EarlyView.
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Copper‐Catalyzed Radical Cross‐Coupling of Redox‐Active Oxime Esters, Styrenes, and Boronic Acids ()
Abstract A visible‐light‐driven, copper‐catalyzed three‐component radical cross‐coupling of oxime esters, styrenes, and boronic acids has been developed. Key steps of this protocol involve catalytic generation of an iminyl radical from a redox‐active oxime ester and subsequent C−C bond cleavage to generate a cyanoalkyl radical. Upon its addition to styrene, the newly formed benzylic radical undergoes coupling with a boronic‐acid‐derived ArCuII complex to achieve 1,1‐diarylmethane‐containing alkylnitriles.
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Société Chimique de France Prizes 2018 / And also in the News ()
Angewandte Chemie International Edition, EarlyView.
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Ammonia Storage by Reversible Host–Guest Site Exchange in a Robust Metal–Organic Framework ()
Angewandte Chemie International Edition, EarlyView.
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Solid‐Phase Conversion of Four Stereoisomers into a Single Enantiomer ()
Abstract Viedma ripening is an emerging method for the solid‐phase deracemization of mixtures of enantiomers. Up to now, the scope of the method has remained limited to molecules with a single stereocenter. We show here that this method can be extended to obtain a single enantiomer from a mixture of stereoisomers with two different stereocenters. In addition, we show that by using tailor‐made chiral additives, the conversion time can be reduced by a factor of 100.
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Isomerism of the Aniline Trimer ()
Abstract Weaker intermolecular forces expand the isomerization alternatives for molecular aggregation, as observed for the prototype models of the aniline trimer (An3) and the monohydrated aniline dimer (An2‐W) when compared to the phenol trimer. In this experiment the aniline clusters were generated in a jet‐cooled expansion and probed using broadband (chirped‐pulsed) microwave spectroscopy. Three isomers of the aniline trimer and two isomers of the hydrated dimer were detected and characterized in the rotational spectrum. In the homotrimer the weak N−H⋅⋅⋅N hydrogen bonds are assisted by subtle combinations of N−H⋅⋅⋅π and C−H⋅⋅⋅π interactions, producing several competing low‐lying ring species in the gas phase. One of the aniline trimers is a symmetric top, topologically equivalent to the only observed phenol trimer. Conversely, addition of a water molecule to the aniline dimer introduces a leading O−H⋅⋅⋅N interaction, making water to behave as dominant hydrogen‐bond pivot between the two aniline molecules. This combination of weak intermolecular interactions critically tests the performance of dispersion‐corrected or parametrized density‐functional methods. Evaluation of the B3LYP‐D3(BJ) and M06‐2X methods revealed deficiencies of the Truhlar functional to reproduce the experimental rotational data.
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Text ()
Angewandte Chemie International Edition, EarlyView.
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Mannich‐type Reactions of Cyclic Nitrones: Effective Methods for the Enantioselective Synthesis of Piperidine‐containing Alkaloids ()
Abstract Even though there are dozens of biologically active 2‐substituted and 2,6‐disubstituted piperidines, only a limited number of approaches exist for their synthesis. Herein is described two Mannich‐type additions to nitrones, one using β‐ketoacids under catalyst‐free conditions and another using methyl ketones in the presence of chiral thioureas, which can generate a broad array of such 2‐substituted materials, as well as other ring variants, in the form of β‐N‐hydroxy‐aminoketones. Both processes have broad scope, with the latter providing products with high enantioselectivity (up to 98 %). The combination of these methods, along with other critical steps, has enabled 8‐step total syntheses of the 2,6‐disubstituted piperidine alkaloids (−)‐lobeline and (−)‐sedinone.
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All‐Inorganic Ionic Porous Material Based on Giant Spherical Polyoxometalates Containing Core‐Shell K6@K36‐Water Cage ()
Abstract This work demonstrates that the use of high‐negative and high‐symmetry lacunary polyoxometalates (POMs) for the clustering of alkali metal ions is a feasible strategy not only for the formation of rare high‐nuclearity alkali‐metal clusters but also for the construction of new‐type all‐inorganic ionic porous materials. By the strategy, an unprecedented high‐nuclearity K‐H2O cluster {K42(H2O)60} with core–shell K6@K36 configuration is stabilized by 8 C3v‐symmetry trivacant POMs [GeW9O34]10−, forming a novel giant ionic alkali‐metal‐POM composite cluster {K42Ge8W72O272(H2O)60} with more than 100 metal centers. The incorporated 42‐nuclearity K‐H2O cluster {K42(H2O)60} exhibits the highest‐nuclearity alkali‐metal‐water cluster known to date in POM chemistry. Further, the giant {K42Ge8W72O272(H2O)60} clusters can be linked by another kind of alkali metal ions Na+ to generate a fascinating three‐dimensional all‐inorganic ionic porous framework with high chemical stability, proton conductivity, and water vapor adsorption.
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Highly Enantiospecific Borylation for Chiral α‐Amino Tertiary Boronic Esters ()
Abstract Herein we report a highly efficient and enantiospecific borylation method to synthesize a wide range of enantiopure (>99 % ee) α‐amino tertiary boronic esters. The configurationally stable α‐N‐Boc substituted tertiary organolithium species and pinacolborane (HBpin) underwent enantiospecific borylation at −78 °C with the formation of a new stereogenic C−B bond. This reaction has a broad scope, enabling the synthesis of various α‐amino tertiary boronic esters in excellent yields and, importantly, with universally excellent enantiospecificity (>99 % es) and complete retention of configuration.
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MXene Aerogel Scaffolds for High‐Rate Lithium Metal Anodes ()
Abstract Li metal is considered to be an ultimate anode for metal batteries owing to its extremely high theoretical capacity and lowest potential. However, numerous issues such as short lifespan and infinite volume expansion caused by the dendrite growth during Li plating/stripping hinder its practical usage. These challenges become more grievous under high current densities. Herein, 3D porous MXene aerogels are proposed as scaffolds for high‐rate Li metal anodes using Ti3C2 as an example. With high metallic electron conductivity, fast Li ion transport capability, and abundant Li nucleation sites, such scaffolds could deliver high cycling stability and low overpotential at current density up to 10 mA cm−2. High rate performance is also demonstrated in full cells with LiFePO4 as cathodes. This work provides a new type of scaffolds for Li metal anodes and paves the way for the application of non‐graphene 2D materials toward high energy density Li metal batteries.
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Tuning Intramolecular Förster Resonance Energy Transfer and Activating Intramolecular Singlet Fission ()
Abstract The synergy of panchromatic absorption throughout most of the visible range of the solar spectrum and intramolecular singlet fission (SF) has been realized in a series of conjugates featuring different light‐harvesting subphthalocyanines (SubPcs) and an energy accepting pentacene dimer (Pnc2). At the focal point was a modular SubPc approach, which was based on decorating the SubPc core with different peripheral substituents to tailor and fine‐tune their optical properties. Transient absorption measurements assisted in corroborating that the SubPcs act as energy‐transfer antennas by means of unidirectional and quantitative intramolecular Förster resonance energy transfer (FRET) to the Pnc2, where an intramolecular SF affords triplet quantum yields reaching unity.
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The H2S Dimer is Hydrogen‐Bonded: Direct Confirmation from Microwave Spectroscopy ()
Angewandte Chemie International Edition, EarlyView.
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High‐Density RNA Microarrays Synthesized In Situ by Photolithography ()
Abstract While high‐density DNA microarrays have been available for over three decades, the synthesis of equivalent RNA microarrays has proven intractable until now. Herein we describe the first in situ synthesis of mixed‐based, high‐density RNA microarrays using photolithography and light‐sensitive RNA phosphoramidites. With coupling efficiencies comparable to those of DNA monomers, RNA oligonucleotides at least 30 nucleotides long can now efficiently be prepared using modified phosphoramidite chemistry. A two‐step deprotection route unmasks the phosphodiester, the exocyclic amines and the 2′ hydroxyl. Hybridization and enzymatic assays validate the quality and the identity of the surface‐bound RNA. We show that high‐density is feasible by synthesizing a complex RNA permutation library with 262144 unique sequences. We also introduce DNA/RNA chimeric microarrays and explore their applications by mapping the sequence specificity of RNase HII.
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How [Fe]‐Hydrogenase from Methanothermobacter is Protected Against Light and Oxidative Stress ()
Abstract [Fe]‐hydrogenase (Hmd) catalyzes the reversible hydrogenation of methenyltetrahydromethanopterin (methenyl‐H4MPT+) with H2. Hmd contains the iron–guanylylpyridinol (FeGP) cofactor, which is sensitive to light and oxidative stress. A natural protection mechanism is reported for Hmd based on structural and biophysical data. Hmd from Methanothermobacter marburgensis (mHmd) was found in a hexameric state, where an expanded oligomerization loop is detached from the dimer core and intrudes into the active site of a neighboring dimer. An aspartic acid residue from the loop ligates to FeII of the FeGP cofactor and thus blocks the postulated H2‐binding site. In solution, this enzyme is in a hexamer‐to‐dimer equilibrium. Lower enzyme concentrations, and the presence of methenyl‐H4MPT+, shift the equilibrium toward the active dimer side. At higher enzyme concentrations—as present in the cell—the enzyme is predominantly in the inactive hexameric state and is thereby protected against light and oxidative stress.
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Sessler Early Career Researcher Prize for Mindy Levine / International Award of the Society of Polymer Science, Japan / The Chemical Record Lectureship for Keiji Maruoka ()
Angewandte Chemie International Edition, EarlyView.
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Fast Magic‐Angle Spinning 19F NMR Spectroscopy of HIV‐1 Capsid Protein Assemblies ()
Abstract 19F NMR spectroscopy is an attractive and growing area of research with broad applications in biochemistry, chemical biology, medicinal chemistry, and materials science. We have explored fast magic angle spinning (MAS) 19F solid‐state NMR spectroscopy in assemblies of HIV‐1 capsid protein. Tryptophan residues with fluorine substitution at the 5‐position of the indole ring were used as the reporters. The 19F chemical shifts for the five tryptophan residues are distinct, reflecting differences in their local environment. Spin‐diffusion and radio‐frequency‐driven‐recoupling experiments were performed at MAS frequencies of 35 kHz and 40–60 kHz, respectively. Fast MAS frequencies of 40–60 kHz are essential for consistently establishing 19F–19F correlations, yielding interatomic distances of the order of 20 Å. Our results demonstrate the potential of fast MAS 19F NMR spectroscopy for structural analysis in large biological assemblies.
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Structurally Ordered Intermetallic Cobalt Stannide Nanocrystals for High‐Performance Electrocatalytic Overall Water‐Splitting ()
Abstract The synthesis of structurally ordered non‐noble intermetallic cobalt stannide (CoSn2) nanocrystals and their utilization for high‐performance electrocatalytic overall water‐splitting is presented. The structurally and electronically beneficial properties of the tetragonal CoSn2 exhibit a considerably low overpotential for the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) on fluorine‐doped tin oxide (FTO) and Ni foam (NF). Loss of Sn from the crystal lattices and oxidation of Co under strongly alkaline conditions furnishes highly disordered amorphous active CoOx(H), the catalytically active structure for OER. The Co0 atoms in the CoSn2 act as active sites for HER and the presence of Sn provides efficient electrical conductivity. This intermetallic phase is a novel type of cost‐effective and competitive bifunctional electrocatalysts and predestinated for overall water‐splitting devices: A two‐electrode electrolyzer with CoSn2 on NF delivers a cell voltage of merely 1.55 V at 10 mA cm−2 maintaining long‐term stability.
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Single‐Electron Transfer Reactions in Frustrated and Conventional Silylium Ion/Phosphane Lewis Pairs ()
Abstract Silylium ions undergo a single‐electron reduction with phosphanes, leading to transient silyl radicals and the corresponding stable phosphoniumyl radical cations. As supported by DFT calculations, phosphanes with electron‐rich 2,6‐disubstituted aryl groups are sufficiently strong reductants to facilitate this single‐electron transfer (SET). Frustration as found in kinetically stabilized triarylsilylium ion/phosphane Lewis pairs is not essential, and silylphosphonium ions, which are generated by conventional Lewis adduct formation of solvent‐stabilized trialkylsilylium ions and phosphanes, engage in the same radical mechanism. The trityl cation, a Lewis acid with a higher electron affinity, even oxidizes trialkylphosphanes, such as tBu3P, which does not react with either B(C6F5)3 or silylium ions.
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Carbon Nanotubes with Cobalt Corroles for Hydrogen and Oxygen Evolution in pH 0–14 Solutions ()
Abstract Water splitting is promising to realize a hydrogen‐based society. The practical use of molecular water‐splitting catalysts relies on their integration onto electrode materials. We describe herein the immobilization of cobalt corroles on carbon nanotubes (CNTs) by four strategies and compare the performance of the resulting hybrids for H2 and O2 evolution. Co corroles can be covalently attached to CNTs with short conjugated linkers (the hybrid is denoted as H1) or with long alkane chains (H2), or can be grafted to CNTs via strong π–π interactions (H3) or via simple adsorption (H4). An activity trend H1≫H3>H2≈H4 is obtained for H2 and O2 evolution, showing the critical role of electron transfer ability on electrocatalysis. Notably, H1 is the first Janus catalyst for both H2 and O2 evolution reactions in pH 0–14 aqueous solutions. Therefore, this work is significant to show potential uses of electrode materials with well‐designed molecular catalysts in electrocatalysis.
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Palladium‐Catalyzed Enantioselective Addition of Chiral Metal Enolates to In Situ Generated ortho‐Quinone Methides ()
Abstract We describe herein a conceptually novel, cooperative Brønsted acid/base catalyzed process for the conjugate addition of cyclic β‐keto esters to ortho‐quinone methides both generated in situ. Upon hemiacetalization, densely functionalized chiral chromans with two adjacent quaternary and additionally a tertiary stereogenic center were obtained with very good diastereoselectivity (up to >95:5 d.r.) and typically excellent enantioselectivity (up to >99 % ee). The striking feature and key to success is the dual catalytic activation of both nucleophile and electrophile in two separate cycles with a single chiral catalyst.
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Design of a Multicompartment Hydrogel that Facilitates Time‐Resolved Delivery of Combination Therapy and Synergized Killing of Glioblastoma ()
Abstract There is significant current interest in identifying new combination therapies that synergize to treat disease, and it is becoming increasingly clear that the temporal resolution of their administration greatly impacts efficacy. To facilitate effective delivery, a multicompartment hydrogel material was developed that is composed of spherical vesicles interlaced within a self‐assembled peptide‐based network of physically crosslinked fibrils that allows time‐resolved independent co‐delivery of small molecules. This material architecture effectively delivers the EGFR kinase inhibitor Erlotinib (ERL) and Doxorubicin (DOX, DNA intercalator) in an ERL→DOX sequential manner to synergistically kill glioblastoma, the most aggressive form of brain cancer.
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Facile Synthesis of a Stable Dihydroboryl {BH2}− Anion ()
Abstract While the one‐electron reduction of (CAACMe)BH2Br (CAACMe=1‐(2,6‐diisopropylphenyl)‐3,3,5,5‐tetramethylpyrrolidin‐2‐ylidene) yields a hydride‐shift isomer of the corresponding tetrahydrodiborane, a further reversible reduction leads to the first stable parent boryl anion, [(CAACMe)BH2]−, which acts as a powerful boron nucleophile.
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Room‐Temperature Linear Light Upconversion in a Mononuclear Erbium Molecular Complex ()
Abstract To date, the piling up of successive photons of low energies (near infrared; NIR) using a single lanthanide center and linear optics to ultimately produce upconverted visible emission was restricted to low‐phonon solid materials and nanoparticles. Now we show that the tight helical wrapping of three terdentate N‐donor ligands around a single nine‐coordinate trivalent erbium cation provides favorable conditions for a mononuclear molecular complex to exhibit unprecedented related upconverted emission. Low power NIR laser excitations into the metal‐centered transitions Er(4I11/2←4I15/2) at 801 nm or Er(4I13/2←4I15/2) at 966 nm result in upconverted blue–green emissions, where two or three photons respectively are successively absorbed by a molecular lanthanide complex possessing high‐energy vibrations.
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The Mackay‐Type Cluster [Cu43Al12](Cp*)12: Open‐Shell 67 Electron Superatom with Emerging Metal‐Like Electronic Structure ()
Angewandte Chemie International Edition, EarlyView.
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Ultrafast Dynamics of a “Super” Photobase ()
Angewandte Chemie International Edition, EarlyView.
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Bing‐Feng Shi ()
Angewandte Chemie International Edition, EarlyView.
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Methane Hydration‐Shell Structure and Fragility ()
Abstract The influence of oily molecules on the structure of liquid water is a question of importance to biology and geology and many other fields. Previous experimental, theoretical, and simulation studies of methane in liquid water have reached widely conflicting conclusions regarding the structure of hydrophobic hydration‐shells. Herein we address this question by performing Raman hydration‐shell vibrational spectroscopic measurements of methane in liquid water from −10 °C to 300 °C (at 30 MPa, along a path that parallels the liquid‐vapor coexistence curve). We show that, near ambient temperatures, methane's hydration‐shell is slightly more tetrahedral than pure water. Moreover, the hydration‐shell undergoes a crossover to a more disordered structure above ca. 85 °C. Comparisons with the crossover temperature of aqueous methanol (and other alcohols) reveal the stabilizing influence of an alcohol OH head‐group on hydrophobic hydration‐shell fragility.
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Enantioselective Synthesis of Indolines, Benzodihydrothiophenes, and Indanes by C−H Insertion of Donor/Donor Carbenes ()
Abstract We employ a single catalyst/oxidant system to enable the asymmetric syntheses of indolines, benzodihydrothiophenes, and indanes by C−H insertion of donor/donor carbenes. This methodology enables the rapid construction of densely substituted five‐membered rings that form the core of many drug targets and natural products. Furthermore, oxidation of hydrazones to the corresponding diazo compounds proceeds in situ, enabling a relatively facile one‐ or two‐pot protocol in which isolation of potentially explosive diazo alkanes is avoided. Regioselectivity studies were performed to determine the impact of sterics and electronics in donor/donor metal carbene C−H insertions to form indolines. This methodology was applied to a variety of substrates in high yield, diastereomeric, and enantiomeric ratios and to the synthesis of a patented indane estrogen receptor agonist with anti‐cancer activity.
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C2‐Symmetric Bicyclic Bisborane Catalysts: Kinetic or Thermodynamic Products of a Reversible Hydroboration of Dienes ()
Abstract We prepared a new class of chiral C2‐symmetric bicyclic bisborane catalysts by addition reactions of internal dienes with the Piers borane, HB(C6F5)2, and an analogue, HB(p‐C6F4H)2. The dependence of the addition pattern on the reaction temperature allowed us to selectively prepare two diastereomeric catalysts from a single diene precursor. The bisboranes prepared in situ exhibited excellent activity (turnover numbers up to 200 at −40 °C) and enantioselectivity (up to 95 % ee) in imine hydrogenation reactions.
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A Stereodynamic Redox‐Interconversion Network of Vicinal Tertiary and Quaternary Carbon Stereocenters in Hydroquinone–Quinone Hybrid Dihydrobenzofurans ()
Abstract Reversible redox processes involving hydroquinones and quinones are ubiquitous in biological reaction networks, materials science, and catalysis. While extensively studied in intermolecular settings, less is known about intramolecular scenarios. Herein, we report hydroquinone–quinone hybrid molecules that form two‐stereocenter dihydrobenzofurans via intramolecular cyclization under thermodynamic control. A π‐methylhistidine peptide‐catalyzed kinetic resolution allowed us to study the stereodynamic behavior of enantio‐ and diastereo‐enriched dihydrofurans. In the course of this study, it was revealed that a reversible intramolecular redox‐interconversion network connects all four possible stereoisomers via inversion of a quaternary carbon stereocenter without achiral intermediates. As a result, these findings on hydroquinone‐quinone hybrid molecules provide insights into potential natural origin and synthetic access of the common dihydrobenzofuran motif.
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Local and Global Dynamics in Intrinsically Disordered Synuclein ()
Abstract Intrinsically disordered proteins (IDPs) experience a diverse spectrum of motions that are difficult to characterize with a single experimental technique. Herein we combine high‐ and low‐field nuclear spin relaxation, nanosecond fluorescence correlation spectroscopy (nsFCS), and long molecular dynamics simulations of alpha‐synuclein, an IDP involved in Parkinson disease, to obtain a comprehensive picture of its conformational dynamics. The combined analysis shows that fast motions below 2 ns caused by local dihedral angle fluctuations and conformational sampling within and between Ramachandran substates decorrelate most of the backbone N−H orientational memory. However, slow motions with correlation times of up to ca. 13 ns from segmental dynamics are present throughout the alpha‐synuclein chain, in particular in its C‐terminal domain, and global chain reconfiguration occurs on a timescale of ca. 60 ns. Our study demonstrates a powerful strategy to determine residue‐specific protein dynamics in IDPs at different time and length scales.
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Construction of Heterostructured Fe2O3‐TiO2 Microdumbbells for Photoelectrochemical Water Oxidation ()
Abstract Designing advanced structures for heterojunction photocatalysts is an effective approach to enhance their performance toward solar‐energy conversion. Herein we develop a facile synthetic strategy for the fabrication of Fe2O3‐TiO2 microdumbbells. With the assistance of preferentially adsorbed hexadecylamine molecules, amorphous TiO2 nanospheres with tunable size are grown at the two ends of Fe‐based metal–organic compound microrods. Subsequent annealing of the hybrid obtained leads to the formation of a novel heterostructured Fe2O3‐TiO2 microdumbbell photocatalyst. Owing to the heterojunction formed and the unique structure, Fe2O3‐TiO2 microdumbbells with optimized composition and morphology show enhanced performance for photoelectrochemical water oxidation, compared to monophasic Fe2O3 and TiO2 materials as well as physical mixtures thereof.
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An Efficient Anti‐poisoning Catalyst against SOx, NOx, and POx: P, N‐Doped Carbon for Oxygen Reduction in Acidic Media ()
Abstract Electrocatalysts are readily poisoned during the catalysis of the oxygen reduction reaction (ORR); even air containing traces of SOx and/or NOx significantly decrease the activity and the durability of H2–O2 fuel cells. Now, a metal‐free strategy is reported to develop an efficient anti‐poisoning ORR catalyst, which involves the pyrolysis of PDAP‐phytic acid super‐molecular aggregate (PPSA). The pyrolyzed co‐doped carbon acting as a metal‐free electrocatalyst shows an enhanced activity for ORR in acidic medium, even under poisoning conditions (SOx, NOx, and POx). Moreover, P‐doping also changes the ORR pathway by yielding less than 4 % of H2O2, indicating a four‐electron pathway whereas more than>20 % of H2O2 was recorded for N‐doped carbon synthesized from PDAP.
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A Modular Approach to Sensitized Two‐Photon Patterning of Photodegradable Hydrogels ()
Abstract Photodegradable hydrogels have emerged as useful platforms for research on cell function, tissue engineering, and cell delivery as their physical and chemical properties can be dynamically controlled by the use of light. The photo‐induced degradation of such hydrogel systems is commonly based on the integration of photolabile o‐nitrobenzyl derivatives to the hydrogel backbone, because such linkers can be cleaved by means of one‐ and two‐photon absorption. Herein we describe a cytocompatible click‐based hydrogel containing o‐nitrobenzyl ester linkages between a hyaluronic acid backbone, which is photodegradable in the presence of cells. It is demonstrated for the first time that by using a cyclic benzylidene ketone‐based small molecule as photosensitizer the efficiency of the two‐photon degradation process can be improved significantly. Biocompatibility of both the improved two‐photon micropatterning process as well as the hydrogel itself is confirmed by cell culture studies.
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A Charge‐Separated State that Lives for Almost a Second at a Conductive Metal Oxide Interface ()
Abstract Transparent conductive oxides (TCOs) are widely used commercially available materials for opto‐electronic applications, yet they have received very little attention for dye‐sensitization applications. Now, mesoporous thin films of conductive indium‐doped tin oxide (ITO) nanocrystallites are shown to support long‐lived charge separation with first‐order recombination kinetics (k=1.5 s−1). A layer‐by‐layer technique was utilized to spatially arrange redox and/or chromophoric molecular components on ITO. Spectroelectrochemical measurements demonstrated that upon light absorption, each component provided a free‐energy gradient to direct electron transfer at the conductive oxide interface. The long‐lived nature of the photogenerated charge separated states provide favorable conditions for photocatalytic solar fuel production. Furthermore, the first‐order recombination kinetics are most ideal for the fundamental understanding of interfacial charge separation dynamics.
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A Highly Active Molybdenum Phosphide Catalyst for Methanol Synthesis from CO and CO2 ()
Abstract Methanol is a major fuel and chemical feedstock currently produced from syngas, a CO/CO2/H2 mixture. Herein we identify formate binding strength as a key parameter limiting the activity and stability of known catalysts for methanol synthesis in the presence of CO2. We present a molybdenum phosphide catalyst for CO and CO2 reduction to methanol, which through a weaker interaction with formate, can improve the activity and stability of methanol synthesis catalysts in a wide range of CO/CO2/H2 feeds.
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Total Syntheses of Bisdehydroneostemoninine and Bisdehydrostemoninine by Catalytic Carbonylative Spirolactonization ()
Abstract The first total syntheses of the stemona alkaloids bisdehydroneostemoninine and bisdehydrostemoninine in racemic forms have been achieved. The synthetic strategy features a novel palladium‐catalyzed carbonylative spirolactonization of a hydroxycyclopropanol to rapidly construct the oxaspirolactone moiety. It also features a Lewis acid promoted tandem Friedel–Crafts cyclization and lactonization to form the 5‐7‐5 tricyclic core of the target stemona alkaloids.
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Reprogramming Human Siderocalin To Neutralize Petrobactin, the Essential Iron Scavenger of Anthrax Bacillus ()
Angewandte Chemie International Edition, EarlyView.
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Selective C−N Borylation of Alkyl Amines Promoted by Lewis Base ()
Abstract An efficient method for the metal‐free deaminative borylation of alkylamines, using bis(catecholato)diboron as the boron source, to directly synthesize various alkyl potassium trifluoroborate salts is introduced. The key to this high reactivity is the utilization of pyridinium salt activated alkylamines, with a catalytic amount of a bipyridine‐type Lewis base as a promoter. This transformation shows good functional‐group compatibility (e.g., it is unimpeded by the presence of a ketone, indole, internal alkene, or unactivated alkyl chloride) and can serve as a powerful synthetic tool for borylation of amine groups in complex compounds. Mechanistic experiments and computations suggest a mechanism in which the Lewis base activated B2cat2 unit intercepts an alkyl radical generated by single‐electron transfer (SET) from a boron‐based reductant.
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Iodospirocyclization of Tryptamine‐Derived Isocyanides: Formal Total Synthesis of Aspidofractinine ()
Abstract The N‐iodosuccinimide‐mediated spirocyclization of tryptamine‐derived isocyanides to generate spiroindolenines is reported. The products contain both an imine and an imidoyl iodide as flexible handles for follow‐up chemistry. Nucleophilic addition typically occurs chemoselectively on the imine moiety with complete diastereoselectivity, providing opportunities for the construction of complex molecular frameworks. The synthetic potential of the method was showcased in the formal total synthesis of (±)‐aspidofractinine.
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B(C6F5)3/Amine‐Catalyzed C(sp)−H Silylation of Terminal Alkynes with Hydrosilanes: Experimental and Theoretical Studies ()
Abstract Transition metal catalyzed C−H functionalization of organic compounds has proved to be a useful atom‐efficient strategy in organic synthesis. In contrast, main‐group‐element‐based catalytic processes for C−H functionalization have remained underexplored to date. Reported herein is the catalytic C(sp)−H silylation of a wide range of terminal alkynes with hydrosilanes by using a combination of B(C6F5)3 and an organic base such as triethylenediamine (DABCO). This protocol constitutes the first example of boron‐catalyzed C(sp)−H functionalization, offering a convenient route for the synthesis of a variety of alkynylsilanes. Experimental and computational studies have revealed that DABCO plays two crucial roles (Lewis base and Brønsted base) in this catalytic transformation.
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Chemistry / Physics, and Physiology or Medicine ()
Angewandte Chemie International Edition, EarlyView.
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Electrophilic Phosphonium Cation‐Mediated Phosphane Oxide Reduction Using Oxalyl Chloride and Hydrogen ()
Abstract The metal‐free reduction of phosphane oxides with molecular hydrogen (H2) using oxalyl chloride as activating agent was achieved. Quantum‐mechanical investigations support the heterolytic splitting of H2 by the in situ formed electrophilic phosphonium cation (EPC) and phosphane oxide and subsequent barrierless conversion to the phosphane and HCl. The reaction can also be catalyzed by the frustrated Lewis pair (FLP) consisting of B(2,6‐F2C6H3)3 and 2,6‐lutidine or phosphane oxide as Lewis base. This novel reduction was demonstrated for triaryl and diaryl phosphane oxides providing access to phosphanes in good to excellent yields (51–93 %).
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Adenine‐Driven Structural Switch from a Two‐ to Three‐Quartet DNA G‐Quadruplex ()
Abstract A G‐rich sequence found in the regulatory region of the RANKL gene, which is associated with homeostasis of bone metabolism, folds into a two‐quartet basket‐type G‐quadruplex stabilized by A⋅G⋅A and G⋅G⋅G base‐triads. Perusal of local structural features together with G/A‐to‐T modifications uncovered the critical role of A5 for the formation of a distinct antiparallel two‐quartet topology and not the three‐quartet topology that would be expected based on the sequence with four GGG‐tracts alone. The structural changes induced by the A5‐to‐T5 modification include a switch in orientation and relative positions of G‐strands that together with anti to syn reorientation of G12 provide insights into the complexity of the interactions that influence the folding of G‐rich DNA. Understanding the impact of loop residues on the stability and formation of G‐quadruplexes advances our knowledge and ability to predict structures adopted by G‐rich sequences, which are involved in regulatory mechanisms in the cell, and may also facilitate drug design.
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Stereoselective Synthesis of Mechanically Planar Chiral Rotaxanes ()
Abstract Chiral interlocked molecules in which the mechanical bond provides the sole stereogenic unit are typically produced with no control over the mechanical stereochemistry. Here we report a stereoselective approach to mechanically planar chiral rotaxanes in up to 98:2 d.r. using a readily available α‐amino acid‐derived azide. Symmetrization of the covalent stereocenter yields a rotaxane in which the mechanical bond provides the only stereogenic element.
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Mechanically Responsive Crystalline Coordination Polymers with Controllable Elasticity ()
Abstract Crystalline coordination polymers tend to be brittle and inelastic, however, we now describe a family of such compounds that are capable of displaying mechanical elasticity in response to external pressure. The design approach successfully targets structural features that are critical for producing the desired mechanical output. The elastic crystals all comprise 1D cadmium(II) halide polymeric chains with adjacent metal centres bridged by two halide ions resulting in the required stacking interactions and short “4 Å” crystallographic axes. These polymeric chains (structural “spines”) are further organized via hydrogen bonds and halogen bonds perpendicular to the direction of the chains. By carefully altering the strength and the geometry of these non‐covalent interactions, we have demonstrated that it is possible to control the extent of elastic bending in crystalline coordination compounds.
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The Curious Case of Ketene in Zeolite Chemistry and Catalysis ()
Angewandte Chemie International Edition, EarlyView.
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Divergent Reactivity of Stannane and Silane in the Trifluoromethylation of PdII: Cyclic Transition State versus Difluorocarbene Release ()
Abstract The transmetalation is a key elementary step in cross‐coupling reactions. Yet, the precise nature of its mechanism and transition state geometry are frequently elusive. This report discloses our study of the transmetalation of [PdII]‐F complexes with the silane‐ and stannane‐based trifluoromethylation agents, R3SiCF3 and R3SnCF3. A divergent reactivity was uncovered, with the stannane showing selective R‐group transfer, and the silane selective CF3‐group transfer. Using a combined experimental and computational approach, we uncovered a hitherto unrecognized transmetalation mechanism with the widely employed R3SiCF3 reagent, explaining its unique activity in metal‐catalyzed trifluoromethylations. While the stannane reacts via a cyclic, 4‐membered transition state, the silane undergoes a fundamentally different pathway and releases a difluorocarbene in the transmetalation event. Molecular dynamics studies clearly reinforced the liberation of a free CF2 carbene, which reacts with [PdII]‐F to ultimately generate [PdII]‐CF3.
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Origin of the Chemiresistive Response of Ultrathin Films of Conductive Metal–Organic Frameworks ()
Abstract Conductive metal–organic frameworks are opening new perspectives for the use of these porous materials for applications traditionally limited to more classical inorganic materials, such as their integration into electronic devices. This has enabled the development of chemiresistive sensors capable of transducing the presence of specific guests into an electrical response with good selectivity and sensitivity. By combining experimental data with computational modelling, a possible origin for the underlying mechanism of this phenomenon in ultrathin films (ca. 30 nm) of Cu‐CAT‐1 is described.
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Nucleophilic versus Electrophilic Reactivity of Bioinspired Superoxido Nickel(II) Complexes ()
Abstract The formation and detailed spectroscopic characterization of the first biuret‐containing monoanionic superoxido‐NiII intermediate [LNiO2]− as the Li salt [2; L=MeN[C(=O)NAr)2; Ar=2,6‐iPr2C6H3)] is reported. It results from oxidation of the corresponding [Li(thf)3]2[LNiIIBr2] complex M with excess H2O2 in the presence of Et3N. The [LNiO2]− core of 2 shows an unprecedented nucleophilic reactivity in the oxidative deformylation of aldehydes, in stark contrast to the electrophilic character of the previously reported neutral Nacnac‐containing superoxido‐NiII complex 1, [L′NiO2] (L′=CH(CMeNAr)2). According to density‐functional theory (DFT) calculations, the remarkably different behaviour of 1 versus 2 can be attributed to their different charges and a two‐state reactivity, in which a doublet ground state and a nearby spin‐polarized doublet excited‐state both contribute in 1 but not in 2. The unexpected nucleophilicity of the superoxido‐NiII core of 2 suggests that such a reactivity may also play a role in catalytic cycles of Ni‐containing oxygenases and oxidases.
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Avenues to Characterize the Interactions of Extended N‐Glycans with Proteins by NMR Spectroscopy: The Influenza Hemagglutinin Case ()
Abstract Long‐chain multiantenna N‐glycans are extremely complex molecules. Their inherent flexibility and the presence of repetitions of monosaccharide units in similar chemical environments hamper their full characterization by X‐ray diffraction or standard NMR methods. Herein, the successful conformational and interaction analysis of a sialylated tetradecasaccharide N‐glycan presenting two LacNAc repetitions at each arm is presented. This glycan has been identified as the receptor of the hemagglutinin protein of pathogenic influenza viruses. To accomplish this study, a N‐glycan conjugated with a lanthanide binding tag has been synthesized, enabling analysis of the system by paramagnetic NMR. Under paramagnetic conditions, the NMR signals of each sugar unit in the glycan have been determined. Furthermore, a detailed binding epitope of the tetradecasaccharide N‐glycan in the presence of HK/68 hemagglutinin is described.
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Palladium/Graphitic Carbon Nitride (g‐C3N4) Stabilized Emulsion Microreactor as a Store for Hydrogen from Ammonia Borane for Use in Alkene Hydrogenation ()
Abstract Direct hydrogenation of C=C double bonds is a basic transformation in organic chemistry which is vanishing from simple practice because of the need for pressurized hydrogen. Ammonia borane (AB) has emerged as a hydrogen source through its safety and high hydrogen content. However, in conventional systems the hydrogen liberated from the high‐cost AB cannot be fully utilized. Herein, we develop a novel Pd/g‐C3N4 stabilized Pickering emulsion microreactor, in which alkenes are hydrogenated in the oil phase with hydrogen originating from AB in the water phase, catalysed by the Pd nanoparticles at the interfaces. This approach is advantageous for more economical hydrogen utilization over conventional systems. The emulsion microreactor can be applied to a range of alkene substrates, with the conversion rates achieving >95 % by a simple modification.
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A General Amino Acid Synthesis Enabled by Innate Radical Cross‐Coupling ()
Abstract The direct union of primary, secondary, and tertiary carboxylic acids with a chiral glyoxylate‐derived sulfinimine provides rapid access into a variety of enantiomerically pure α‐amino acids (>85 examples). Characterized by operational simplicity, this radical‐based reaction enables the modular assembly of exotic α‐amino acids, including both unprecedented structures and those of established industrial value. The described method performs well in high‐throughput library synthesis, and has already been implemented in three distinct medicinal chemistry campaigns.
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Defect‐Rich Bi12O17Cl2 Nanotubes Self‐Accelerating Charge Separation for Boosting Photocatalytic CO2 Reduction ()
Abstract Solar‐driven reduction of CO2, which converts inexhaustible solar energy into value‐added fuels, has been recognized as a promising sustainable energy conversion technology. However, the overall conversion efficiency is significantly limited by the inefficient charge separation and sluggish interfacial reaction dynamics, which resulted from a lack of sufficient active sites. Herein, Bi12O17Cl2 superfine nanotubes with a bilayer thickness of the tube wall are designed to achieve structural distortion for the creation of surface oxygen defects, thus accelerating the carrier migration and facilitating CO2 activation. Without cocatalyst and sacrificing reagent, Bi12O17Cl2 nanotubes deliver high selectivity CO evolution rate of 48.6 μmol g−1 h−1 in water (16.8 times than of bulk Bi12O17Cl2), while maintaining stability even after 12 h of testing. This paves the way to design efficient photocatalysts with collaborative optimizing charge separation and CO2 activation towards CO2 photoreduction.
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Matthieu Sollogoub ()
Angewandte Chemie International Edition, EarlyView.
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Simple Alkaline‐Earth Metal Catalysts for Effective Alkene Hydrogenation ()
Abstract Alkaline earth metal amides (AeN′′2: Ae=Ca, Sr, Ba, N′′=N(SiMe3)2) catalyze alkene hydrogenation (80–120 °C, 1–6 bar H2, 1–10 mol % cat.), with the activity increasing with metal size. Various activated C=C bonds (styrene, p‐MeO‐styrene, α‐Me‐styrene, Ph2C=CH2, trans‐stilbene, cyclohexadiene, 1‐Ph‐cyclohexene), semi‐activated C=C bonds (Me3SiCH=CH2, norbornadiene), or non‐activated (isolated) C=C bonds (norbornene, 4‐vinylcyclohexene, 1‐hexene) could be reduced. The results show that neutral Ca or Ba catalysts are active in the challenging hydrogenation of isolated double bonds. For activated alkenes (e.g. styrene), polymerization is fully suppressed due to fast protonation of the highly reactive benzyl intermediate by N′′H (formed in the catalyst initiation). Using cyclohexadiene as the H source, the first Ae metal catalyzed H‐transfer hydrogenation is reported. DFT calculations on styrene hydrogenation using CaN′′2 show that styrene oligomerization competes with styrene hydrogenation. Calculations also show that protonation of the benzylcalcium intermediate with N′′H is a low‐energy escape route, thus avoiding oligomerization.
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Creating Elastic Organic Crystals of π‐Conjugated Molecules with Bending Mechanofluorochromism and Flexible Optical Waveguide ()
To create low band‐gap, fluorescent, and elastic organic crystal emitters, we focused on an extended π‐conjugated system based on: (i) a planar conformation, (ii) a rigid structure, and (iii) controlled intermolecular interactions. Here, we report on two fluorescent and highly flexible organic crystals (1 and 2) which were capable of bending under an applied stress. The bent crystals rapidly recover their straight shape upon release of the stress. Crystal 1 with a tetrafluoropyridyl terminal unit and a lower band‐gap energy (orange emission, λem = 573 nm, ΦF = 0.50, FWHM = 56 nm), showed no bending mechanofluorochromism and had superior performance as an optical waveguide with reddish orange emission. Loss coefficients of the straight and bent crystals measured at 600 nm were particularly low, as little as 0.043 and 0.047 dB/mm, respectively. The waveguide performance of the crystal did not decrease under bending stress. For crystal 2 with a pentafluorophenyl terminal unit (green emission, λem = 500 nm, ΦF = 0.38, FWHM = 53 nm), the original waveguide performance decreased under an applied bending stress; however, this crystal showed a unique bending mechanofluorochromism.
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Mechanistic Studies in Photocatalysis ()
The fast‐moving fields of photoredox and photocatalysis have recently provided fresh opportunities to expand the potential of synthetic organic chemistry. Advances in light‐mediated processes have mainly been guided so far by empirical findings and the quest for reaction invention. The general perception, however, is that photocatalysis is entering a more mature phase where the combination of experimental and mechanistic studies will play a dominant role in sustaining further innovation. This Minireview outlines the key mechanistic studies to consider when developing a photochemical process, and the best techniques available for acquiring relevant information. The discussion will use selected case studies to highlight how mechanistic investigations can be instrumental in guiding the invention and development of synthetically useful photocatalytic transformations
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A Solid Phase Approach to Accessing Bisthioether Stapled Peptides Resulting in a Potent Inhibitor of PRC2 Catalytic Activity ()
Stapled peptides have emerged as a new class of therapeutics to effectively target intractable protein‐protein interactions. Thus, efficient and versatile methods granting easy access to this class of compounds and expanding the scope(s) of the currently available ones are of great interest. Here, we describe a solid phase approach for the synthesis of bisthioether stapled peptides with multiple architectures, including single‐, double‐turn and double‐stapled macrocycles. This methodology allows for ligation with all‐hydrocarbon linkers of various lengths, avoiding the use of unnatural amino acids and expensive catalysts, and affords cyclopeptides with remarkable resistance to proteolytic degradation. The potential of this procedure is demonstrated by applying it to generate a stapled peptide that shows potent in vitro inhibition of methyltransferase activity of the polycomb repressive complex 2 (PRC2) of proteins.
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Intramolecular Charge Transfer Controls Switching Between Room Temperature Phosphorescence and Thermally Activated Delayed Fluorescence ()
Chemical modification of phenothiazine–benzophenone derivatives is shown to tune the emission behavior from triplet states by selecting the molecular geometry of the intramolecular charge transfer (ICT) state. A fundamental principle of planar ICT (PICT) and twisted ICT (TICT) is demonstrated to obtain selectively either room temperature phosphorescence (RTP) or highly efficient thermally activated delayed fluorescence (TADF), respectively. Time‐resolved spectroscopy and time‐dependent density functional theory (TD‐DFT) investigations on polymorphic single crystals demonstrate the roles of PICT and TICT states in the underlying photophysics. This has resulted in a RTP molecule OPM, where the triplet states contribute with 89% of the luminescence, and an isomeric TADF molecule OMP, where the triplet states contribute with 95% of the luminescence.
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Predicting Monomers for use in Polymerization Induced Self‐Assembly ()
We report an in silico method to predict monomers suitable for use in polymerization‐induced self‐assembly (PISA). By calculating the dependence of LogPoct/SA on the length of the growing polymer chain, the change in hydrophobicity during polymerization was determined. This allowed for evaluation of the capability of a monomer to polymerize to form self‐assembled structures during chain extension. Using this method, we identified five new monomers for use in PISA via reversible addition‐fragmentation chain transfer (RAFT) polymerization, and confirmed that these all successfully underwent PISA to product nanostructures of various morphologies. The results obtained using this method correlated well with and predicted the differences in morphology obtained from the PISA of block copolymers of similar molecular weight but different chemical structures. Thus, we propose this method can be utilized for the discovery new monomers for PISA and also prediction of their self‐assembly behavior.
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Simultaneously Trapping C2H2 and C2H6 into a Robust Metal‐Organic Framework from a Ternary Mixture of C2H2/C2H4/C2H6 for Purification of C2H4 ()
The removal of C2H2 and C2H6 from C2H4 streams is of great significance for the purification of feedstock to produce polyethylene and other commodity chemicals, while the simultaneous absorption of C2H6 and C2H2 over C2H4 from a ternary mixture has never been realized. Herein, a robust metal‐organic framework TJT‐100 was design and synthesized, which demonstrates remarkably selective adsorption of C2H2 and C2H6 over C2H4. Breakthrough experiments show that TJT‐100 can be used as an absorbent for high‐performance purification of C2H4 from a ternary mixture of C2H2/C2H4/C2H6 (0.5/99/0.5), to afford a C2H4 purity greater than 99.997%, beyond that required for ethylene polymerization. Computational studies reveal that the uncoordinated carboxylate oxygen atoms and coordinated water molecules towards the pore can trap C2H2 and C2H6 through the formation of multiple C‐H•••O electrostatic interactions, while the corresponding 'C2H4‐framework' interaction is unfavorable.
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Myths and Realities of Graphene Oxide: Carbocatalyst or Reagent ()
Metal‐free heterogeneous carbon‐based materials have the potential to facilitate a wide range of organic transformations in an economical and environmentally‐friendly manner. Often times, however, the mechanism of their action is obfuscated by their ill‐defined nature, so careful analysis of the reaction products is essential before they can be labelled ‘catalysts’ according to IUPAC’s definition. We present here our findings on the archetypal ‘carbocatalytic’ conversion of benzyl alcohol to benzaldehyde, in which graphene oxide is reduced and a major side product – dibenzyl ether, is also formed. Thus, our work re‐classifies graphene oxide as a reagent and presents an important step in the proper evaluation of reactions in the nascent field of carbocatalysis.
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Null Exciton Splitting in Chromophoric Greek Cross (+) Aggregate ()
Exciton interactions in molecular aggregates play a crucial role in tailoring the optical behavior of π‐conjugated materials. Though vital for optoelectronic applications, ideal Greek cross‐dipole (α = 90°) stacking of chromophores remains elusive. We report a novel Greek cross (+) assembly of 1,7‐dibromoperylene‐3,4,9,10‐tetracarboxylic tetrabutylester (PTE‐Br2) which exhibits null exciton coupling mediated monomer‐like optical characteristics in crystalline state. Contrastingly, nonzero exciton coupling in X‐type (α = 70.2°, PTE‐Br0) and J‐type (α = 0°, θ = 48.4°, PTE‐Br4) assemblies render perturbed optical properties. Additionally, the semi‐classical Marcus theory of charge‐transfer rates predicts a selective hole transport phenomenon in the orthogonally stacked PTE‐Br2. Precise rotation angle dependent optoelectronic properties in crystalline PTE‐Br2 can have consequences in the rational design of novel π‐conjugated materials for photonic and molecular electronic applications.
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Transition Metal‐Free [4+3]‐Cycloaddition of ortho‐Quinone Methides and Isomünchnones: Catalytic and Diastereoselective Assembly of Oxa‐bridged Oxazocine Scaffolds ()
Cycloadditions are powerful processes to synthesize complex polycyclic scaffolds. Herein, we disclose a [4+3]‐cycloaddition between an in situ generated ortho‐quinone methide and an isomünchnone to yield oxa‐bridged oxazocine cores, generating N2 and H2O as the sole by‐products. Using only catalytic amounts of camphorsulfonic acid, it is possible to generate both reactive intermediates in one step, eliminating the need for rhodium catalysts generally employed for isomünchnone formation. Spectroscopic data and X‐ray crystallography indicate the formation of the syn diastereomer, with the main side‐product arising from a hydrate participating in a competing [4+2]‐cycloaddition pathway.
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Chemo‐enzymatic synthesis of pyrazines and pyrroles ()
Herein we report the biocatalytic synthesis of substituted pyrazines and pyrroles using a transaminase to mediate the key amination of the ketone precursors. Treatment of α‐diketones with ATA‐113 in the presence of a suitable amine donor yielded the corresponding α‐amino ketones which underwent oxidative dimerization to the pyrazines. Selective amination of α‐diketones in the presence of β‐keto esters afforded substituted pyrroles in a biocatalytic equivalent of the classical Knorr pyrrole synthesis. Finally we have shown that pyrroles can be prepared by internal amine transfer catalyzed by a transaminase in which no external amine donor is required.
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Direct Synthesis and Pseudomorphic Transformation of Mixed Metal Oxide Nanostructures with Non‐Close‐Packed Hollow Sphere Arrays ()
While bottom‐up syntheses of ordered nanostructured materials at colloidal length scales have been successful at producing close‐packed materials, it is more challenging to synthesize non‐close‐packed (ncp) structures. Here, a metal oxide nanostructure with ncp hollow sphere arrays was synthesized by combining a polymeric colloidal crystal template (CCT) with a Pechini precursor. The CCT provided defined confinement through its tetrahedral (Td) and octahedral (Oh) voids where the three‐dimensionally (3D) ordered, ncp hollow sphere arrays formed as a result of a crystallization‐induced rearrangement. This nanostructure, consisting of alternating, interconnected large and small hollow spheres, is distinct from the inverse opal structures typically generated from these CCTs. The morphology of the ncp hollow sphere arrays was retained in pseudomorphic transformations involving sulfidation and reoxidation cycling despite the segregation of zinc during these steps.
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Switching Chemoselectivity: Using Mechanochemistry to Alter Reaction Kinetics ()
A reaction manifold has been discovered in which the chemoselectivity can be altered by switching between neat milling and liquid assisted grinding (LAG) with polar additives. After investigation of the reaction mechanism, it has been established that this switching in reaction pathway is due to the neat mechanochemical conditions exhibiting different kinetics for a key step in the transformation. This proof of concept study demonstrates that mechanochemistry can be used to trap the kinetic product of a reaction. It is envisaged that, if this concept can be successfully applied to other transformations, novel synthetic processes could be discovered and known reaction pathways perturbed or diverted.
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Proton‐Activated "Off‐On" Room‐Temperature Phosphorescence from Purely Organic Thioethers ()
Room‐temperature phosphorescence (RTP)‐based sensors have distinctive advantages over the fluorescence counterparts, such as larger Stokes shifts and longer lifetimes. Unfortunately, almost all RTP sensors are operated on quenching‐based mechanisms given the sensitive nature of the emissive triplet state. Here we report a type of thioether RTP molecules that shows RTP “turn‐on” when volatile acid vapors such as HCl are in contact. To elucidate the underlying mechanism, model thioethers containing different donor/acceptor combinations are investigated via fluorescence spectroscopy and theoretical calculations aided by molecular coordinates obtained from single‐crystal X‐ray diffraction. It is revealed that a charge‐transfer character in the phosphorescence state is crucial. The “turn‐on” design concept may significantly broaden the sensing application scope for organic RTP molecules.
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Dynamic covalent self‐assembly based on oxime condensation ()
Oxime, whose dynamic nature was reported to be switchable between ON/OFF by tuning the acidity, could be employed as a novel type of dynamic covalent approach that is amenable to use in water for self‐assembly of purely organic molecules. In strong‐acidic conditions, the dynamic nature of oxime is turned ON, allowing occurrence of error‐checking and therefore a catenane and a macrocycle were successfully self‐assembled in high yields. In neutral conditions, oxime becomes an irreversible bond, which helps to trap the self‐assembled products. We envision that this switchable behaviour might help, at least partially, to resolve a commonly‐encountered drawbacks of dynamic covalent chemistry, namely that the intrinsic stability of the self‐assembled products containing dynamic bonds are often jeopardized by their reversible nature.
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The Origin of Reduced Reductive Stability of Ion–Solvent Complexes on Alkali and Alkaline Earth Metal Anodes ()
The intrinsic instability of organic electrolytes seriously impedes the practical applications of high‐capacity metal anodes, such as lithium and sodium metal anodes. The ion–solvent complexes can even further promote the decomposition of electrolytes on metal anodes. Herein, first‐principles calculations were performed to investigate the origin of the reduced reductive stability of ion–solvent complexes. Both ester and ether electrolyte solvents are selected to interact with Li+, Na+, K+, Mg2+, and Ca2+. The LUMO energy levels of ion–ester complexes exhibit a linear relationship with the binding energy, regulated by the ratio of carbon atomic orbital in the LUMO. While LUMOs of ion–ether complexes are composed by the metal atomic orbitals. This work uncovers the intrinsic reasons why ion–solvent complexes can reduce the reductive stability of electrolytes, reveals two different mechanisms for ester and ether electrolytes, and provides a theoretical understanding of the electrolyte–anode interfacial reactions and a mechanistic guidance to electrolyte and metal anode design for safe rechargeable batteries.
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Topochemical Synthesis of 2D Carbon Hybrids through Self‐Boosting Catalytic Carbonization of Metal‐Polymer Framework ()
Two‐dimensional (2D) carbon hybrids have demonstrated promising application in various areas like energy storage and catalysis. Yet, the exploration of simple methods for controllable fabrication of 2D graphitic carbon hybrids in a scalable manner remains challenging. Herein, a novel microwave assisted strategy for mass production of 2D carbon hybrids based on self‐boosting catalytic carbonization of metal‐agarose framework is demonstrated. Hybrids including hollow Fe3C nanoparticles, Ni/Co nanoparticles, and hollow FeOx nanoparticles uniformly embedded in 2D graphitic carbon nanosheets (GCNs) are obtained respectively, demonstrating the generality of the approach. Metal‐polymer coordination and microwave enabled fast catalytic decomposition of precursors are found to play vital roles in facilitating the formation of the nanosheet structure. The resulting FeOx‐GCNs hybrid exhibits superior lithium‐storage performance (i.e. 1118 mAh g‐1 at 500 mA g‐1 and 818 mAh g‐1 at 2000 mA g‐1 after 1200 cycles).
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A Metal‐Organic Framework with Tetrahedral Aluminate Sites as a Single‐Ion Li+ Solid Electrolyte ()
We demonstrate the synthesis of the first anionic aluminum metal‐organic framework (MOFs) constructed from tetrahedral AlO4 sites. Al‐Td‐MOF‐1 was obtained in a simple two‐step synthesis by condensation of 1,4‐dihydroxybenzene and lithium aluminum hydride into an amorphous aluminate framework before applying a solvothermal treatment under basic conditions to obtain the crystalline Al‐Td‐MOF‐1 with a chemical composition of Li[Al(C6H4O2)2]. The overall Al‐Td‐MOF‐1 structure consists of one‐dimensional chains of alternating edge‐sharing AlO4 and LiO4 tetrahedral sites describing unidirectional pore channels with a square window aperture of ~ 5 x 5 Å2, best described topologically as a uninodal 6‐coordinated snp rod net. Al‐Td‐MOF‐1 features the highest Li+ loading reported to date for a MOF (2.50 wt%) and proved to be an effective single‐ion solid electrolyte. An ionic conductivity of 5.7 x 10‐5 S·cm‐1 was measured for Al‐Td‐MOF‐1 and the beneficial contribution of crystallinity was evidenced by an 8‐fold increase in conductivity between the disordered and crystalline material.
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Flexible Films of Covalent Organic Framework with Ultralow Dielectric Constants under High Humidity ()
Covalent organic framework (COF) films combine the processibility of polymers with porosity and atomic precision of crystalline porous materials are long‐sought‐after in electronics yet hard to realize. Here, we prepared four flexible COF films with different alkoxy side chains via interfacial polymerization. The COF films exhibit ultralow dielectric constant (κ = 1.19 ± 0.04 at 105 Hz), small dielectric loss (< 0.02, 103 ~ 106 Hz), high breakdown voltage (> 63 kV cm‒1) and low leakage current (10‒10 A cm‒2 at 1 kV cm‒1). They adopt considerable mechanical strength, and ability to withstand high humidity (RH 70% for 10 days) and repeated bending (1000 times) without losing their dielectric properties. Extension of the alkoxy chains reduces the film's κ and enhances its moisture resistance, while incorporation of guest molecules further increase the κ value up to 43 times. This study demonstrates that the potentials of COF films as promising candidate for portable electronic devices.
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Formation of Hypoxanthine Tetrad by Reaction with Sodium Chloride: From Planar to Stereo ()
By reacting with NaCl on Au(111), the formation of hypoxanthine (HX) tetrads is demonstrated at the atomic scale in real space. These results directly demonstrate for the first time that alternative purine tetrads can be formed in both planar and non‐planar configuration, and that ionic bonding plays a crucial role for the formation and planar‐to‐stereo transformation of the tetrads, providing deeper insight for constructing artificial DNA/RNA quadruplexes. Moreover, both the tilted HXs and Na show strong charge transfer with the substrate in the non‐planar phase. The insights gained by this work also opens up new routes to tune the electrostatic nature of metal‐organic interfaces and design stereo‐nanostructures on surfaces.
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Plasma‐Triggered Synergy of Exfoliation, Phase Transformation and Surface Engineering in Cobalt Diselenide for Enhanced Water Oxidation ()
Various strategies, such as increasing active site numbers, structural and surface engineering, have been used to improve the oxygen evolution reaction (OER) performance of transition metal dichalcogenide. However, it is still a grand challenge to combine these strategies in one material system to realize the full catalytic potential. Herein, we firstly report an Ar/O2 plasma method to simultaneously induce exfoliation, surface reorganization (formation of an oxidative layer with rich oxygen vacancies) and phase transformation (cubic‐to‐orthorhombic) on cobalt diselenide (CoSe2) to generate an exceptionally outstanding OER electrocatalysts. The as‐made samples only require an overpotential of 251 mV at 10 mA cm‐2, outperforming commercial RuO2 and most reported OER catalysts. As demonstrated by a systematic experimental and theoretical study, the striking catalytic activity originates from the optimized chemical and electronic environment. Our work provides valuable insights into the design of promising OER electrocatalysts with high natural abundance via multilevel structural modulation.
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Chemoselective α,β‐Dehydrogenation of Saturated Amides ()
We report a method for the selective a,b‐dehydrogenation of amides in the presence of other carbonyl moieties under mild conditions. Our strategy relies on electrophilic activation coupled to in situ selective selenium‐mediated dehydrogenation. The a,b‐unsaturated products are obtained in moderate to excellent yields and their synthetic versatility is demonstrated by a range of transformations. Mechanistic experiments suggest formation of an electrophilic Se(IV) species.
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Recent Advanced in Flexible Perovskite Solar Cell: Fabrication and Application ()
Flexible perovskite solar cells have attracted widespread research effort because of their promising potential in light‐weight wearable, portable, flyable and deployable for ultralight‐weight space and near‐space applications. During just the past few years, the efficiency has exceeded 18% due to the high quality perovskite film achieved by various low‐temperature fabrication methods and the great achievements in developing matched interface and electrode materials. This review focuses on the recent progress of flexible perovskite solar cells concerning: Low‐temperature fabrication methods to improve the properties of perovskite films, such as full coverage, uniform morphology and good crystallinity; The demonstrated interface layers used in flexible perovskite solar cells, considering key figure‐of‐merit such as high transmittance, high carrier mobility, suitable band gap and easy fabrication via low‐temperature methods; The flexible transparent electrode materials developed to enhance the mechanical stability of the devices; Mechanical and long‐term environmental stability of flexible perovskite device; Outlook of flexible perovskite solar cell in portable electronic device and its cost; Prospective of commercialization feasibility of the flexible perovskite solar cells.
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Metal‐Free Radical Borylation of Alkyl and Aryl Iodides ()
A method for metal‐free radical borylation of alkyl and aryl iodides with bis(catecholato)diboron (B₂cat₂) as the boron source under mild conditions is introduced. The developed borylation reaction is operationally easy to conduct and shows high functional group tolerance and broad substrate scope. Radical clock experiments and density functional theory calculations provide insights into the mechanism and rate constants for C‐radical borylation with B₂cat₂ are disclosed.
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The Promising Application of Optical Hexagonal TaN in Photocatalytic Reactions ()
Searching for highly active and efficient photocatalysts for photo‐induced/photo‐assisted reactions is always the most challenging task for solar energy utilization. In previous studies, the search for such materials has mainly focused on precious plasmonic metals (Au, Ag, Cu, etc) and semiconductor oxides (TiO2, ZnO, WO3, etc). Here, we report the potential application of hexagonal tantalum mononitride (TaN) as optical support in photocatalytic reactions, which could harness visible light to assist CO2 conversion and decompose organic pollutants. Theoretical study indicated that the improved electron‐hole separation over asymmetrically polar TaN under visible light illumination was critical for its utilizations in photocatalytic area. This study is forecasted to guide TaN to various photocatalytic reactions and wider optical application domains.
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Biocatalytic "Oxygen‐Fueled" Atom Transfer Radical Polymerization ()
Atom Transfer Radical Polymerization (ATRP) was carried out in a flask completely open to air using a biocatalytic system composed of Glucose Oxidase (GOx) and Horse Radish Peroxidase (HRP) with an active copper catalyst complex. Nanomolar concentrations of the enzymes and ppm amounts of Cu provided excellent control over the polymerization of oligo(ethylene oxide) methyl ether methacrylate (OEOMA500), generating polymers with high molecular weight (Mn > 70,000) and low dispersities (1.13 ≤ Đ ≤ 1.27) in less than an hour. The continuous oxygen supply was necessary for the generation of radicals and polymer chain growth as demonstrated via temporal control and by inducing hypoxic conditions. In addition, the enzymatic cascade polymerization triggered by oxygen was used for a protein and DNA functionalized with initiators to form protein‐b‐POEOMA and DNA‐b‐POEOMA bioconjugates, respectively.
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An Effective Chemical Way via Anchoring of Highly Oxidized Cluster toward Superior Electrocatalytic Activity and High Functionality as a Catalyst for Li‐O₂ Batteries ()
An effective chemical way to optimize the oxygen electrocatalyst and Li−O₂ electrode functionalities of metal oxide can be developed by the control of chemical bond nature with the surface anchoring of highly‐oxidized selenate (SeO₄²−) clusters. The bond competition between (Se6+−O) and (Mn−O) bonds is quite effective in stabilizing Jahn‐Teller‐active Mn3+ state and in increasing oxygen electron density of α‐MnO₂ nanowire (NW). The selenate‐anchored α‐MnO₂ NW shows excellent oxygen electrocatalytic activity and electrode performance for Li−O₂ batteries, which is due to the improved charge transfer kinetics and reversible formation/decomposition of Li₂O₂. The present study underscores that the surface anchoring of highly‐oxidized cluster can provide a facile effective way of improving the oxygen electrocatalyst and electrochemical performances of nanostructured metal oxide in Li−O₂ cells.
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Enantioselective Formal C(sp3)‐H Bond Activation in the Synthesis of Bioactive Spiropyrazolone Derivatives ()
Herein we report the first enantioselective annulation of α‐arylidene pyrazolones through a formal C(sp3)‐H activation under mild conditions enabled by highly variable Rh(III)‐Cpx catalysts. The method has wide substrate scope proceeds with good to excellent yields and enantioselectivity. Its synthetic utility was demonstrated by late‐stage functionalization of drugs and natural products as well as preparation of enantioenriched [3]‐dendralenes. Preliminary biological investigation also identified the spiropyrazolones as a novel class of Hedgehog pathway inhibitors.
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Functionalization of Carbon Monoxide and tert‐Butyl Nitrile by Intramolecular Proton Transfer in a Bis(Phosphido) Thorium Complex ()
We report examples of intramolecular proton transfer reactions to functionalize carbon monoxide and tert‐butyl nitrile from a bis(phosphido) thorium complex. The reaction of (C5Me5)2Th[PH(Mes)]2, Mes = 2,4,6‐Me3C6H2, with 1 atm of CO yields (C5Me5)2Th(κ2‐(O,O)‐OCH2PMes‐C(O)PMes), in which one CO molecule is inserted into each thorium‐phosphorus bond. Concomitant transfer of two protons, formerly coordinated to phosphorus, are now bound to one of the carbon atoms from one of the inserted CO molecules. Density functional theory calculations were employed to determine the lowest energy pathway and show a proton coupled electron transfer (PCET) reaction. With tert‐butyl nitrile, tBuCN, only one nitrile inserts into a thorium‐phosphorus bond, but the proton is transferred to nitrogen with one phosphido remaining unperturbed affording (C5Me5)2Th[PH(Mes)][κ2‐(P,N)‐N(H)C(CMe3)P(Mes)]. Surprisingly, reaction of this compound with KN(SiMe3)2 removes the proton bound to nitrogen, not phosphorus. These reactions represent unprecedented intramolecular proton transfer reactivity, not previously observed in molecular complexes, and provides new insight into CO and tert‐butyl nitrile functionalization.
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Tuning Cu/Cu2O Interfaces for Reduction of Carbon Dioxide to Methanol in Aqueous Solutions ()
Artificial photosynthesis can store solar energy and reduce CO2 into fuels to potentially alleviate global warming and energy crisis. Compared to gas products, it remains a grand challenge to tune the product distribution of artificial photosynthesis to liquid fuels, such as CH3OH, that are suitable for storage and transport. This paper describes the introduction of metallic Cu nanoparticles (NPs) on Cu2O films to change the product distribution from gas products on bare Cu2O to predominant CH3OH via CO2 reduction in aqueous solutions. The specifically designed Cu/Cu2O interfaces could balance the binding strengths of H* and CO* intermediates, which plays critical roles in CH3OH production. With TiO2 model photoanode to construct a photoelectrochemical cell, Cu/Cu2O dark cathode exhibited a Faradaic efficiency up to 53.6% for CH3OH production. This work demonstrates the feasibility and mechanism of interface engineering to enhance the CH3OH production from CO2 reduction in aqueous electrolytes.
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Water‐soluble Blue Emissive Tricyclic 2‐Aminopyridinium Salts by Three‐component Coupling‐(3+3)‐Anellation Synthesis ()
The (3+3) anellation of alkynones and cyclic amidines is a novel and unexpected approach to intensively blue luminescent tricyclic 2‐aminopyridinium salts with quantum yields Φf up to 63% in water. By implementation into a consecutive three‐component reaction these title compounds are obtained rapidly and efficiently in a diversity‐oriented fashion. Most interestingly, these bi‐ and tricyclic 2‐aminopyridinium salts emit in dichloromethane and water solutions, making them interesting novel luminophore probes for bioanalytics, as well as in the solid state as blue emitters with tunable efficiency.
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Heavy and Guilty: Isolation of a TMTAA‐Based Radical in Uranium bis‐TMTAA Complexes ()
We report the synthesis, characterization, and electronic structure studies of a series of thorium(IV) and uranium(IV) bis‐tetramethyltetraazaannulene complexes. These sandwich complexes show remarkable stability towards air and moisture, even at elevated temperatures. Electrochemical studies show the uranium complex to be stable in three different oxidation states; isolation of the oxidized species revealed a rare case of a non‐innocent TMTAA ligand.
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Low net heat of adsorption of ethylene achieved by major solid‐state structural rearrangement of a discrete copper complex ()
The trinuclear copper(I) pyrazolate complex [Cu3] rearranges to the dinuclear analogue [Cu2•(C2H4)2] when exposed to ethylene gas. Remarkably, the [Cu3] ↔ [Cu2•(C2H4)2] rearrangement occurs reversibly in the solid state. Furthermore, this transformation emulates solution chemistry. The bond‐making and breaking processes associated with the rearrangement in the solid‐state result in an observed heat of adsorption ( 13 ± 1 kJ mol 1 per Cu – C2H4 interaction) significantly lower than other Cu – C2H4 interactions (≥ 24 kJ mol‐1). The low overall heat of adsorption, ‘step’ isotherms, high ethylene capacity (2.76 mmol∙g 1; 7.6 wt% at 293 K), and high ethylene/ethane selectivity (136:1 at 293 K) make [Cu3] an interesting basis for the rational design of materials for low‐energy ethylene/ethane separations
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Iron metal‐organic framework as highly efficient catalyst for ozone decomposition ()
Ozone pollution is an increasingly prominent concern worldwide, and catalysts with high and unchanged activity under ambient conditions and good processability into devices are urgently required for ozone amelioration especially in practical air filtration applications. Herein, we present the unique advantages of an iron metal‐organic framework, MIL‐100(Fe), for ozone removal. MIL‐100(Fe) exhibits long‐lasting ozone conversion efficiency of 100% for over 100 h under RH of 45% and space velocity of 1.9 × 105 h‐1 at room temperature, which is well beyond the performance of most porous or metal catalysts like activated carbon and α‐MnO2 (quickly drop to 18% and 60% of ozone conversion respectively after 12 h under the same condition). We also investigated the impact of humidity level and elucidated the plausible reaction mechanism, which is further confirmed by DFT calculation. Furthermore, MIL‐100(Fe) can be processed into MOF films and used as filtration layer in a mask to protect personnel against ozone contamination. This study demonstrates the promising potential of MOFs in ozone pollution control, and also offers new insights for the design of ozone decomposition catalyst.
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Emerging Application of Nanotechnology for Controlling Cell Surface Receptors Clustering ()
The spatial organization of cell surface receptors plays an important role in defining cell fate. Recently, the development of strategies for direct regulation of receptors clustering using nanomaterials has aroused enormous interest. In this review, we discuss the mechanisms and features of recent developed nanomaterial‐based strategies to control the nanoscale distribution of cell binding ligands and regulate cell behavior. We expect this review to inspire innovative work on manipulating cell functions by controlling cell surface receptors clustering.
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Water Splitting Carbon Nitride Photoelectrochemical Cell with Efficient Charge Separation and Remarkably Low Onset Potential ()
Here we report a simple method to grow a closely‐packed carbon nitride (CN) film by the crystallization of CN monomers on a conductive substrate followed by a thermal condensation. The as‐synthesized CN exhibits excellent performance as photoanode material in photoelectrochemical cell. Detailed (photo)electrochemical and transient absorption measurements indicate excellent charge separation properties, high hole‐extraction efficiency (up to 50%), a long electron lifetime, and low amount of defect states below the CN conduction band. Consequently, the CN photoanode exhibits a markedly low overpotential of 0.25 V versus reversible hydrogen electrode (RHE), which is comparable with the state‐of‐the‐art metal‐based photoanodes, an impressive photocurrent density of 116 µA/cm2 at 1.23 V versus RHE in an alkaline solution without sacrificial agent, as well as excellent stability over a wide pH range (0‐13).
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Achieving Atomic Dispersion of Highly Loaded Transition Metals in Small‐pore Zeolite SSZ‐13: A New Class of High‐capacity and High‐efficiency Low Temperature CO and NOx Adsorbers ()
The majority of harmful atmospheric CO and NOx emissions comes from vehicles’ exhaust. Although there has been success addressing NOx emissions at temperatures above 250 ºC with the aid of selective catalytic reduction technology that relies on the Cu/SSZ‐13 material and sacrificial urea source, emissions during vehicle cold start (when the temperature is below 150 ºC), are a major challenge. Herein, we show we can completely eliminate both CO and NOx emissions simultaneously under realistic exhaust flow, using a highly‐loaded (2 wt %) atomically dispersed palladium in the extra‐framework positions of the small‐pore chabazite material as a low‐temperature CO and passive NOx adsorber. Until now, atomically dispersed highly loaded (> 0.3 wt%) transition metal/SSZ‐13 materials have not been known: we therefore devised a general simple and scalable route to prepare such materials for Pt(II) and Pd(II) via systematic investigation of synthetic methods; this also allowed us to explain the discrepancies in the available metal/zeolite literature that stem from the lack of systematic knowledge on the synthesis of such materials. With the aid of spectroscopy and materials testing with various specifications of Pd, we show that both CO and NOx can be simultaneously completely abated with 100% efficiency (NO/Pd and CO/Pd ratio 1 which is the maximum theoretical limit) even in the presence of significant water amounts, due to the formation of mixed carbonyl‐nitrosyl palladium complex in chabazite micropore
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Iridium‐Catalyzed Intramolecular Asymmetric Allylic Dearomatization Reaction of Benzene Derivatives ()
Guided by the mechanistic insights from computational studies, we have developed an Ir‐catalyzed asymmetric intramolecular allylic dearomatization reaction of benzene derivatives. Under the optimized conditions consisting of a readily available Ir‐catalyst, a series of spiro[4.5]cyclohexadiene compounds were delivered in reasonable yields (up to 79%) with good enantioselectivity (up to 99% ee). The introduction of a malonate diester‐type substituent serves as a key strategy to guide the nucleophilic reactivity of the benzene ring.
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Facile Synthesis of Sequence‐Regulated Synthetic Polymers Using Orthogonal SuFEx and CuAAC Click Reactions ()
Orthogonal sulfur‐fluoride exchange reaction (SuFEx) and copper(I) catalyzed azide–alkyne cycloaddition (CuAAC) are employed to synthesize sequence‐regulated synthetic polymers. The high efficiency and broad tolerance of SuFEx and CuAAC to diverse chemical functionalities enable one‐pot synthesis of polydispersed sequence‐controlled polymers via step‐growth copolymerization in high yield and sequence complexity. Furthermore, iterative SuFEx and CuAAC coupling reactions on the solid support without the need of protecting groups afford monodispersed sequence‐defined oligomers. The use of this orthogonal pair of click reactions provides new opportunities to facilely access sequence‐regulated synthetic polymers with a high degree of structural diversity.
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Platinum‐catalyzed Desaturation of Lactams, Ketones and Lactones ()
The development of a general platinum‐catalyzed desaturation of N‐protected lactams, ketones, and lactones to their conjugated α,β‐unsaturated counterparts is reported. The reaction is operated under mildly acidic conditions at room temperature or 50 oC. It is scalable and tolerates a wide range of functional groups. The complementary reactivity to the palladium‐catalyzed desaturation is demonstrated in the efficient conversion of iodide, bromide and sulfur‐containing substrates.
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Rapid structure determination of microcrystalline molecular compounds using electron diffraction ()
Chemists of all fields currently publish about 50,000 crystal structures per year, the vast majority of which are X‐ray structures. We determined two molecular structures employing electron‐ rather than X‐ray diffraction. For this purpose an EIGER hybrid pixel detector was fitted to a transmission electron microscope yielding an electron diffractometer. The structure of a new methylene blue derivative was determined at 0.9 Å resolution from a crystal smaller than 1×2 μm². Several thousand active pharmaceutical ingredients (API) are only available as submicrocrystalline powder. To illustrate the potential of electron crystallography for the pharmaceutical industry, we also determined the structure of an API from its pill. We demonstrate that electron crystallography complements X‐ray crystallography and is the technique of choice for all unsolved cases in which submicron sized crystals were the limiting factor.
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Palladium‐Catalysed C‐H Alkenylation of Arenes with Alkynes: Stereoselective Synthesis of Vinyl Chlorides via a 1,4‐Chlorine Migration ()
A directing group‐free, ligand‐promoted palladium‐catalysed C‐H arylation of internal alkynes with simple arenes was developed, and alkenyl chlorides via 1,4‐chlorine migration or trisubstituted alkenes were produced in moderate to good yields depending on the type of alkyne.
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2D MoN‐VN Heterostructure as a Model Sulfur Host to Regulate Polysulfides for Highly Efficient Lithium‐Sulfur Batteries ()
Lithium‐sulfur batteries hold promise for next‐generation batteries. A problem however is rapid capacity fading. Moreover, atomic‐level understanding of the chemical interaction between sulfur host and polysulfides is poorly elucidated from a theoretical perspective. Here, a two‐dimensional (2D) heterostructured MoN‐VN is fabricated and investigated as a new model sulfur host. Theoretical calculations indicate that electronic structure of MoN can be tailored by incorporation of V. This leads to enhanced polysulfides adsorption. Additionally, in situ synchrotron X‐ray Diffraction and electrochemical measurements reveal effective regulation and utilization of the polysulfides in the MoN‐VN. The MoN‐VN‐based lithium‐sulfur batteries have a capacity of 708 mA h g‐1 at 2 C and a capacity decay as low as 0.068% per cycle during 500 cycles with sulfur loading of 3.0 mg cm‐2.
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Existence of a Precipitation Threshold in the Electrostatic Precipitation of Oppositely Charged Nanoparticles ()
Oppositely charged nanoparticles precipitate rapidly only at the point of electroneutrality, wherein their charges are macroscopically compensated. We investigated the aggregation and precipitation of oppositely charged nanoparticles at concentrations ranging from 10 to 10−3 mM (based on gold atoms) by using UV‐vis measurements. We employed solutions of equally sized (4.6 nm) gold nanoparticles, which were functionalized and stabilized with either positively or with negatively charged alkanethiols. Results showed that oppositely charged nanoparticles do not precipitate if their concentration is below a certain threshold even if the electroneutrality condition is fulfilled. This finding suggests the universal behavior of chemical systems comprising oppositely charged building blocks such as ions and charged nanoparticles.
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Hierarchical Self‐Assembly of BODIPY Dyes as a Tool to Improve the Antitumor Activity of Capsaicin in Prostate Cancer ()
Capsaicin (CAP) has been long known for its analgesic properties and more recently for its antitumor activity in various cell types. However, its pungency and the high doses needed to achieve a significant activity have precluded its application in cancer therapy. Herein, we propose a straightforward novel strategy to improve the antitumor effect of CAP based on the enhancement of its aggregation propensity in aqueous media by covalent attachment of a BODIPY (BDP) dye. The target CAP‐BDP 1 self‐assembles in aqueous solutions into weakly fluorescent globular assemblies that become highly emissive upon cell uptake‐induced disassembly. Remarkably, due to the improved delivery of material upon aggregation, we have succeeded in reducing the doses of CAP‐based drugs in vivo in prostate cancer two orders of magnitude while maintaining a substantial antitumor activity.
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Nitromethane as a Recursive Carbanion Source for Domino Benzoannulation with Ynones: One‐pot Synthesis of Polyfunctional Naphthalenes and a Total Synthesis of Macarpine ()
A one‐pot, transition‐metal‐free, domino Michael‐SNAr protocol of general applicability has been devised for the regioselective synthesis of polyfunctional naphthalenes employing nitromethane and ortho‐haloaryl ynones. Utilization of nitromethane as one carbon recursive carbanion source that is subsumed into a variety of ynones to end up as aromatic nitro substituent has been demonstrated. Besides many interesting examples, the application of this domino process towards a total synthesis of polycyclic alkaloid macarpine vouch for the efficacy of this methodology. The conceptually simple approach to affect regioselective, multifunctional benzoannulation of ynones displays wide substrate scope and functional group tolerance and has been implemented with substituted nitromethanes, reacting through a ‘split and subsume’ process, as well as with alicyclic o‐haloynones.
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A Long‐Lived Halogen‐Bonding Anion Triple Helicate Accommodates Rapid Guest Exchange ()
Anion‐templated helical structures are emerging as a dynamic and tractable class of supramolecules that exhibit anion‐switchable self‐assembly. We present the first kinetic studies of an anion helicate by utilizing halogen‐bonding m‐arylene‐ethynylene oligomers. These ligands formed high‐fidelity triple helicates in solution with surprisingly long lifetimes on the order of seconds even at elevated temperatures. We propose an associative ligand‐exchange mechanism that proceeded slowly on the same timescale. In contrast, intrachannel anion exchange occurred rapidly within milliseconds or faster as determined by stopped‐flow visible spectroscopy. Additionally, the helicate accommodated bromide in solution and the solid state, while the thermodynamic stability of the triplex favored larger halide ions (bromide ≈ iodide >> chloride). Taken together, we elucidate a new class of kinetically stable helicates. These anion‐switchable triplexes maintain their architectures while accommodating fast intrachannel guest exchange.
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Quadruply Twisted Hückel Aromatic Dodecaphyrin ()
Molecular topology of π‐conjugated circuits becomes increasingly important in the chemistry of aromatic and antiaromatic compounds. meso‐Pentafluorophenyl‐substituted 5,35‐(1,4‐phenylene)bridged [56]dodecaphyrin was synthesized by condensation of 1,4‐phenylene‐bridged dicarbinol dimer and 5,10,15‐tris‐(pentafluorophenyl)tetrapyrrane followed by oxidation with DDQ and was oxidized to its [54]‐ and [52]congeners in a stepwise manner. Metalation of the [52]dodecaphyrin with Pd2(dba)3 gave two bis‐PdII complexes that are isomers of metalation sites, anti and syn with regard to the 1,4‐phenylene bridge. The anti‐isomer was easily oxidized to its N‐fused form, a quadruply twisted non‐aromatic or weakly aromatic macrocycle. On the other hand, the syn ‐isomer was revealed to be the first example of Hückel aromatic molecule with a quadruply twisted structure.
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Strain‐promoted reactivity of alkyne‐containing cycloparaphenylenes ()
A family of angle‐strained, yet stable cycloalkynes with different sizes were repared in concise syntheses. Detailed analysis of their size‐dependent structural and electronic properties provide evidence for the considerable distortion of the alkyne unit incorporated into the cycloparaphenylene derived macrocycle. The remarkable increase of the alkyne reactivity with decreasing macrocycle size in [2+2]cycloaddition‐retrocyclization (CA‐RC) was investigated by joint experimental and theoretical studies, which aided to unravel the thermodynamic and kinetic parameters that govern this reaction. The findings presented herein pave the way to the application of alkyne‐containing CPPs as 'clickable' macrocyclic architectures.
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Non‐3d Metal Modulation of Cobalt Imidazolate Framework for Excellent Electrocatalytic Oxygen Evolution in Neutral Media ()
Cobalt imidazolate frameworks are classical electrocatalysts for the oxygen evolution reaction (OER) but suffer from the relatively low activity. Here, we report a non‐3d metal modulation strategy for enhancing the OER activity of cobalt imidazolate frameworks. Two isomorphous frameworks [Co4(MO4)(eim)6] (M = Mo or W, Heim = 2‐ethylimidazole) having Co(eim)3(MO4) units, as well as high water stabilities, were designed and synthesized. In different neutral medias, the Mo‐modulated framework coated on glassy carbon electrode shows the best OER performances (e.g. 1 mA cm‐2 at overpotential of 210 mV in CO2‐saturated 0.5 M KHCO3 electrolyte and 2/10/22 mA cm‐2 at overpotential of 388/490/570 mV in phosphate buffer solution) among non‐precious metal catalysts and even outperforming RuO2. X‐ray photoelectron spectroscopy (XPS) and computational calculations revealed that the non‐3d metals modulate the electronic structure of Co for optimum reactant/product adsorption, and tailor the energy of rate‐determining step to a more moderate value.
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Selective CO2 Splitting by Doubly Reduced Aryl Boranes to Give CO and [CO3]2– ()
Alkali metal salts M2[1] (M = Li, Na) of doubly reduced 9,10‐dimethyl‐9,10‐dihydro‐9,10‐diboraanthracene (1) instantaneously add the C=O bond of CO2 across their boron centers to furnish formal [4+2]‐cycloadducts M2[2]. If only 1 equiv of CO2 is supplied, these products are stable. In the presence of excess CO2, however, C‒O‐bond cleavage occurs and an O2– equivalent is transferred to CO2 to furnish CO and [CO3]2–. With M = Li, Li2CO3 precipitates and the neutral 1 is liberated such that it can be reduced again to establish a catalytic cycle. With M = Na, [CO3]2– remains coordinated to both boron atoms in a bridging mode (Na2[4]). A mechanistic scenario is proposed, based on isolated intermediates and model reactions.
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The Chemical Properties of Hydrogen Atoms Adsorbed on M°‐Nanoparticles Suspended in Aqueous Solutions: The Case of Ag°‐NPs and Au°‐NPs Reduced by BD₄¯ ()
The nature of H‐atoms adsorbed on M°‐nanoparticles is of major importance in many catalyzed reduction processes. Using isotope labeling, we determined that hydrogen evolution from transient {(M°‐NP)‐Hn}n¯ proceeds mainly via the Heyrovsky mechanism when n is large (i.e., the hydrogens behave as hydrides) but mainly via the Tafel mechanism when n is small (i.e., the hydrogens behave as atoms). Additionally, the relative contributions of the two mechanisms differ considerably when M = Au & Ag. The results are analogous to those recently reported for the M°‐NP‐catalyzed de‐halogenation processes.
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Enantioconvergent and Concise Synthesis of Lasonolide A ()
Efficient access to medicinally significant natural product is an essential basis for the development of pharmaceuticals. The limited availability of marine natural products impedes broad biological evaluation. Despite several elegant syntheses of (‐)‐lasonolide A having been reported, a practical synthesis of this potent anticancer polyketide remains elusive. Based on application of borane as a traceless protection and development of an unprecedented bissulfone reagent for Julia olefination, (‐)‐lasonolide A was assembled in an enantioconvergent manner by application of stereoselective hydroboration, allylation, and oxidation. This concise route may provide a realistic solution for accessing derivatives and analogs.
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A Molecular Secret Sharing Scheme ()
A method for implementing a secret sharing scheme at the molecular level is presented. By creating molecular code‐generators that are self‐assembled from several molecular components, we established a means for distributing distinct code‐activating elements among several participants. In this way, an authorization code can only be generated when all the participants are present, which ensures that highly secured systems cannot be operated by unauthorized individuals or disloyal users. Additional layers of protection result from the ability to program the security code by replacing one or several molecular components and by subjecting the system to distinct chemical inputs.
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Open‐shell 3d Transition Metal Nitridophosphates MIIP8N14 (MII = Fe, Co, Ni) by High‐pressure Metathesis ()
3d transition metal nitridophosphates MIIP8N14 (MII = Fe, Co, Ni) were prepared by high‐pressure metathesis indicating that this route might give a systematic access to a structurally rich family of M‐P‐N compounds. Their structures, which are stable in air up to at least 1273 K, were determined through powder X‐ray diffraction and consist of highly condensed tetra‐layers of PN4 tetrahedra and MN6 octahedra. Magnetic measurements revealed paramagnetic behavior of CoP8N14 and NiP8N14 down to low temperatures while, FeP8N14 exhibits an antiferromagnetic transition at TN = 3.5(1) K. Curie‐Weiss fits of the paramagnetic regime indicate that the transition metal cations are in a oxidation state +II, which was corroborated by Mössbauer spectroscopy for FeP8N14. The ligand field exerted by the nitride ions in CoP8N14 and NiP8N14 was determined from UV/Vis/NIR data and is comparable to that of aqua‐ligands and oxophosphates.
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Flexible Li‐air battery in Ambient Air with an In‐Situ Formed Gel Electrolyte ()
Flexible Li‐air batteries (LABs) have been considered as promising power sources for wearable electronics due to its higher energy density. However, when operated in ambient air, it suffers tremendous issues including Li anode passivation, poor cycle life as well as leakage of liquid electrolyte. Herein, we present a LAB with a tetraethylene glycol dimethyl ether (TEGDME, G4) gel electrolyte, in which the gel is in‐situ formed through a cross‐linking reaction between the liquid G4 and the Lithium Ethylenediamine (LiEDA) grown on the surface of Li anode. We demonstrate that the gel can efficiently alleviate the corrosion of Li anode, and thus the LAB shows a cycle performance more than 1175 hours (humidity: 10% to 40%), which is much superior to previous reports. Furthermore, the in situ formed gel enhances the electrode/electrolyte interfacial contact, which thus enables the cable‐type LAB to exhibit a robust flexibility.
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A Multi‐Ion Strategy towards Rechargeable Sodium‐Ion Full Batteries with High Working Voltage and Rate Capability ()
Sodium‐ion batteries (SIBs) are a promising alternative for the large‐scale energy storage owing to the natural abundance of sodium. However, the practical application of SIBs is still hindered by the low working voltage, poor rate performance, and insufficient cycling stability. Herein, we first report a sodium‐ion based full battery using a multi‐ion design. The optimized full batteries delivered a high working voltage of ~4.0 V, which is the best result of reported sodium‐ion full batteries. Moreover, this multi‐ion battery exhibited good rate performance up to 30 C and a high capacity retention of 95% over 500 cycles at 5 C. Although the electrochemical performance of this multi‐ion battery may be further enhanced via optimizing electrolyte and electrode materials, etc., the results presented here clearly indicate the feasibility of this multi‐ion strategy to improve the electrochemical performance of SIBs for possible energy storage applications.
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Iron‐Catalyzed Carbenoid Transfer Reactions of Vinyl Sulfoxonium Ylides: An Experimental and Computational Study ()
A method for the generation of unprecedented vinyl carbenoids from sulfoxonium ylides has been developed and applied in the synthesis of a diverse array of heterocycles such as indolizines, pyrroles, 3‐pyrrolin‐2‐ones, and furans. The reactions proceed under FeBr2 catalysis at mild reaction conditions with a broad substrate scope. A reaction pathway involving iron carbenoids is proposed based on a series of control experiments and DFT calculations.
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Solid State Umbrella‐type Inversion of a VO5 Square Pyramidal Unit in a Bowl‐type Dodecavanadate Induced by Insertion and Elimination of a Guest Molecule ()
Design of cavities for a target molecule and the elucidation of the corresponding host‐guest interactions are important for molecular manipulation. A discrete dodecavanadate bowl, [V12O32]4− (V12), possessing an entrance diameter of 4.4 Å and an electron‐rich guest at the center of the bowl, was stabilized via unique electrostatic interactions. Herein, we report a unique characteristic of the host V12, i.e., a solid‐state polytopal rearrangement during guest elimination and recapture. A guest‐free type dodecavanadate, [V12O32]4− (V12‐free), was prepared by the removal of the guest from dichloromethane‐inserted V12 under vacuum at 50 °C. Single crystal X‐ray analysis revealed that one of the VO5 square pyramids at the bottom of V12‐free was inverted to fill the void of the bowl cavity. The exposure of V12‐free to the guest molecule vapors of dichloromethane, 1,2‐dichloroethane, MeNO2, MeCN, and MeBr resulted in the selective insertion of the guest through the cavity entrance of the bowl to reform the guest‐inserted V12 framework. In addition, whereas CO2 could be inserted in the V12 bowl, CH4 and CO could not be inserted.
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Total Synthesis of An Atropisomer of the Schisandra Triterpenoid Schiglautone A ()
A diastereoselective approach for the total synthesis of an unusual atropisomer of the Schisandra triterpenoid (±)‐schiglautone A is described. The efficient synthetic strategy features three key transformations: 1) two sequential titanium(III)‐catalyzed radical cyclization and homologation reactions to construct the trans‐fused [6,7] bicycle as well as install the quaternary carbons at C10 and C14 with desired stereochemistry; 2) a Claisen rearrangement followed by a ring‐closing metathesis to forge the strained nine‐membered ring; and 3) a substrate‐controlled Michael addition to enable the introduction of the C17 side chain with good diastereoselectivity.
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Enhancing the efficacy of photodynamic therapy (PDT) through a porphyrin/POSS alternating copolymer ()
Aggregation‐induced quenching (AIQ) of photosensitizers greatly reduces the quantum yield of singlet oxygen generation and mitigates the efficacy of photodynamic therapy (PDT). We have prepared an alternating copolymer starting from 4‐vinylbenzyl‐terminated tetraphenylporphyrin (VBTPP) and maleimide isobutyl polyhedral oligomeric silsesquioxane (MIPOSS), via alternating reversible addition‐fragmentation chain transfer (RAFT) polymerization. Porphyrin and POSS are installed on the amphiphilic block copolymers backbone in an alternating fashion and POSS completely inhibits the aggregation of porphyrin units via stacking. The amphiphilic block copolymer can self‐assemble into nanoparticles and its application in PDT treatment was tested. These porphyrin‐containing polymeric nanoparticles display high photochemical yield and phototoxicity in vitro and in vivo, providing a novel strategy to enhance the PDT efficacy.
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