Angewandte Chemie International Edition

Transition Metal Nitride Core-Noble Metal Shell Nanoparticles as Highly CO Tolerant Catalysts ()
Core-shell architectures offer an effective way to tune and enhance the properties of noble metal catalysts. Here, we demonstrate the synthesis of Pt shell on titanium tungsten nitride core nanoparticles (Pt/TiWN) by high temperature ammonia nitridation of a parent core-shell carbide material (Pt/TiWC). X-ray photoelectron spectroscopy revealed significant core-level shifts for Pt shells supported on TiWN cores, corresponding to increased stabilization of the Pt valence d-states. The modulation of the electronic structure of the Pt shell by the nitride core translated into enhanced CO tolerance during hydrogen electrooxidation in the presence of CO. The ability to control shell coverage and vary the heterometallic composition of the shell and nitride core opens up attractive opportunities to synthesize a broad range of new materials with tunable catalytic properties.
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A Unified Continuous Flow Assembly Line Synthesis of Highly Substituted Pyrazoles and Pyrazolines ()
A rapid and modular continuous flow synthesis of highly functionalized fluorinated pyrazoles and pyrazolines has been developed. Flowing fluorinated amines through sequential reactor coils mediates diazoalkane formation and [3+2] cycloaddition to generate more than 30 azoles in a telescoped fashion. Pyrazole cores are then sequentially modified through additional reactor modules performing N-alkylation and arylation, deprotection, and amidation to install broad molecular diversity in short order. Continuous flow synthesis enables the safe handling of diazoalkanes at elevated temperatures, and the use of aryl alkyne dipolarphiles under catalyst free conditions. This assembly line synthesis provides a flexible approach for the synthesis of agrochemicals and pharmaceuticals, as demonstrated by a four-step, telescoped synthesis of measles therapeutic, AS-136A, in a total residence time of 31.7 min (1.76 g h-1).
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Cytoprotective Encapsulation of Individual Jurkat T Cells within Durable TiO2 Shells for T Cell Therapy ()
Lymphocytes, such as T cells and natural killer (NK) cells, have therapeutic promises in adoptive cell transfer (ACT) therapy, where the cells are activated and expanded in vitro, and then infused into a patient. However, the in vitro preservation of labile lymphocytes during transfer, manipulation, and storage has been one of the bottlenecks in the development and commercialization of therapeutic lymphocytes. Herein, we suggest a "cell-in-shell" (a.k.a. artificial spore) strategy to enhance the cell viability in the practical settings, while maintaining biological activities for therapeutic efficacy. A durable titanium oxide (TiO2) shell is formed on individual Jurkat T cells, and the CD3 and other antigens on cell surfaces remain accessible to the antibodies. Interleukin-2 (IL-2) secretion is also not hampered by the shell formation. This work suggests a chemical toolbox for effectively preserving lymphocytes in vitro and developing the lymphocyte-based cancer immunotherapy.
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Acoustic Emission from Organic Martensites ()
In salient effects, still crystals of solids that switch between phases acquire a momentum and are autonomously propelled due to rapid release of elastic energy accrued during a latent structural transition induced by heat, light or mechanical stimulation. Herein we report that when the mechanical reconfiguration is induced by change of temperature in thermosalient crystals, bursts of detectable acoustic waves are generated prior to their self-actuation. The results provide compelling evidence that the thermosalient transitions in organic and organic-containing crystals are molecular analogues of the martensitic transitions in some metals and metal alloys such as steel and shape memory alloys. Within a broader context, the results reveal that akin to metallic bonding, the intermolecular interactions in molecular solids are capable of gradual accrual and sudden release of substantial amount of strain during anisotropic thermal expansion.
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Highly Luminescent and Ultra-stable CsPbBr3 Pervoskite Quantum Dots-silica/alumina Monolith ()
We successfully prepared QDs-silica/alumina monolith (QDs-SAM) by a simple sol-gel reaction of Al-Si single precursors with CsPbBr3 QDs blended in toluene solution, without adding water and catalyst. The resultant transparent monolith exhibits high photoluminescence quantum yields (PLQY) up to 90%, and good photostability under strong illumination of blue light for 300 h. We demonstrated that the preliminary ligand exchange of didodecyl dimethyl ammonium bromide (DDAB) was very important to protect CsPbBr3 QDs from the surface damages during sol-gel reaction, which not only allowed us to maintain the original optical properties of CsPbBr3 QDs but also avoided the aggregation of QDs and make the monolith transparent. The CsPbBr3 QDs-SAM in powder form was easily mixed into resins and applied as color-converting layer with curing on blue light-emitting diodes (LED), and showed a high luminous efficacy of 80 lm/w and a narrow emission with a full width at half maximum (FWHM) of 25 nm.
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Mechanism-Based Enantiodivergence in Manganese Reduction Catalysis: A Chiral Pincer Complex for the Highly Enantioselective Hydroboration of Ketones ()
A manganese alkyl complex containing a chiral "boxmi" pincer ligand is a precatalyst for a catalyst of unprecedented activity and selectivity in the enantioselective hydroboration of ketones producing preparatively useful chiral alcohols in excellent yields and up to >99 %ee. It is applicable for both aryl alkyl and dialkyl ketone reduction under mild conditions (TOF >450 h-1 at -40°C) and an earth abundant base metal catalyst which operates at very low catalyst loadings (as low as 0.1 mol%) and with a high level of functional group tolerance. We provide evidence for the existence of two distinct mechanistic pathways for manganese-catalyzed hydride transfer and elaborate their role for enantiocontrol in the selectivity-determining step.
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Enantioselective Nickel-Catalyzed Intramolecular Allylic Alkenylations Enabled by Reversible Alkenylnickel E/Z Isomerization ()
Enantioselective nickel-catalyzed arylative cyclizations of substrates containing a Z-allylic phosphate tethered to an alkyne are described. These reactions give multisubstituted chiral aza- and carbocycles, and are initiated by the addition of an arylboronic acid to the alkyne, followed by cyclization of the resulting alkenylnickel species onto the allylic phosphate. The reversible E/Z isomerization of the alkenylnickel species is essential for the success of the reactions.
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Molecular Graph Paper ()
We present a self-assembled template of tetraphenylmethane-based variants on a Au(111) surface which feature a periodic lateral arrangement of acetyl groups sticking out of the molecular film. Using the tip of a scanning tunneling microscope, this acetyl group can be removed in a spatially controlled way without a significant effect on the remaining molecular assembly. The chemically modified molecule can readily be distinguished from the original ones such that information can be engraved in the molecular film. Both the modified nature of an individual molecule and the order of the molecular film are shown to persist at room temperature. We show that the mesh size of this molecular graph paper can be tuned by varying the length of the molecular spacer group so that writing and reading information on the nanoscale with variable letter size becomes possible.
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Strain stiffening hydrogels through self-assembly and covalent fixation of semi-flexible fibers ()
Biomimetic, strain-stiffening materials are reported, made through self-assembly and covalent fixation of small building blocks to form fibrous hydrogels able to stiffen by an order of magnitude in response to applied stress. The gels consist of semi-flexible rodlike micelles of bisurea bolaamphiphiles with oligo(ethylene oxide) (EO) outer blocks and a polydiacetylene (PDA) backbone. The micelles are fibers composed of 9-10 ribbons. A gelation method based on Cu-catalyzed azide-alkyne cycloaddition (CuAAC) was developed that leads to strain-stiffening hydrogels with unusual yet universal linear and nonlinear stress-strain response. Upon gelation, the X-ray scattering profile is unchanged, suggesting that crosslinks are formed at random positions along the fiber contour without fiber bundling. The work expands the current knowledge about the design principles and chemistries needed to achieve fully synthetic, biomimetic soft matter with on-demand, targeted mechanical properties.
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Photocatalytic Nanosheet Lithography: A New Concept for Photolithography based on Organically Modified Photoactive 2D Nanosheets ()
Harvesting the properties of nanosheets is not only crucial from a fundamental perspective, but also for the development of novel functional devices based on 2D nanosheets. Here, we demonstrate the processing of organically modified TBAxH1-xCa2Nb3O10 nanosheets into photonic thin films and study their colorimetric sensing properties in response to various aqueous and organic solvent vapors. Building on the enhanced solvent accessibility of TBA-containing nanosheets and their photocatalytic activity under UV irradiation, we develop a new concept for photocatalytic lithography using TBAxH1-xCa2Nb3O10 nanosheets as a negative photoresist to obtain high-fidelity micron-scale patterns of robust inorganic nanosheets. Photocatalytic nanosheet lithography (PNL) therefore adds a new resist-free, resource efficient direct patterning technique to the toolbox of photolithography.
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Ag Films with Hierarchical Chiralities ()
Preparing chiral metallic films is one of the primary challenges in materials science. Although physical fabrication methods for metal films with singular and large-sized chirality exist, chemical preparation of that with multi-structured chirality from atomic to larger scales have not been reported yet. Here, we report the chiral molecule-induced formation of chiral Ag films on a copper substrate through a redox reaction. Three levels of chirality were identified, primary twisted 'nanoflakes' with atomic crystal lattices, secondary helical stacking of these nanoflakes to form 'nanoplates' and tertiary micrometre-sized 'circinate' consisting of chiral arranged nanoplates. The chiral Ag films exhibited multiple plasmonic absorption- and scattering-based optical activities at UV-visible wavelengths based on their hierarchical chiralities; and showed chiral catalytic selectivity for amino acids in electrochemical reactions based on their primary atomic crystal lattices.
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Monofluoromethyl-Substituted Sulfonium Ylides: Electrophilic Monofluoromethylating Reagents with Broad Substrate Scopes ()
Two electrophilic monofluoromethylating reagents S-monofluoromethyl-S-phenyl-bis(carbomethoxy) methylide sulfonium ylide 3a and S-monofluoromethyl-S-(4-nitrophenyl)-bis(carbo -methoxy) methylide sulfonium ylide 3b and their reactions with a variety of nucleophiles such as alcohols and malonate derivatives, sulfonic and carboxylic acids, phenols, amides, and nitrogen of heteroarenes under mild conditions were described. Mechanistic studies by employing deuterated reagents 3a-D2/3b-D2 suggest that these monofluoromethylating reactions proceed via an electrophilic substitution pathway.
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Cofactor-Free, Direct Photoactivation of Enoate Reductases for Asymmetric Reduction of C=C Bonds ()
Enoate reductases from the family of Old Yellow Enzymes (OYEs) can catalyze stereoselective trans-hydrogenation of activated C=C bonds. Here, we report visible light-driven activation of OYEs through NAD(P)H-free, direct transfer of photoexcited electrons from xanthene dyes to the prosthetic flavin moiety. Our spectroscopic and electrochemical analyses verified spontaneous association of rose bengal and its derivatives with OYEs. Illumination of a white light-emitting-diode triggered photoreduction of OYEs by xanthene dyes, which facilitated the enantioselective reduction of C=C bonds in the absence of NADH. The photoenzymatic conversion of 2-methylcyclohexenone resulted in enantiopure (ee >99%) (R)-2-methylcyclohenanone with conversion yields as high as 80-90%. The photobiocatalytic platform was successfully applied to different homologues of OYEs. This work demonstrates a simple and versatile way of activating OYEs by direct coupling of OYE-catalysis with molecular photocatalysis.
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Recent progress of first principles calculations in CH3NH3PbI3 perovskite solar cells ()
Hybrid halide perovskite solar cells (PSCs) exceeding 22% power conversion efficiencies (PCEs) have attracted considerable global attention due to the intrinsic nature of perovskite. Although we all know about that perovskite plays a significant role in the operation of PSCs, the fundamental theories associated with perovskite have not been resolved by the exponential increase in research effort. This raises questions about whether the first-principles calculations are sufficiently addressing the underlying issues in perovskite. In this minireview, we assess the current understanding of structural and electronic properties, defects, ionic diffusion, and shift current for CH3NH3PbI3 perovskite based on the first-principles calculations, and the effect of ionic transport on the hysteresis of current-voltage curves in PSCs. The shift current connected to the possible presence of ferroelectricity is also discussed. The current state-of-the-art and some open questions regarding PSCs are also highlighted, and the benefits, challenges, and potentials of perovskite for use in PSCs are especially stressed.
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Secondary Structure-Driven Self-Assembly of Reactive Polypept(o)ides: Controlling Size, Shape and Function of Core Cross-Linked Nanostructures ()
Achieving precise control over morphology and function of polymeric nanoparticles during self-assembly remains a challenge in material as well as bio-medical sciences, especially when all these properties can be controlled independently. Herein, we report on nanostructures derived from amphiphilic block copolypept(o)ides by secondary structure directed self-assembly, presenting a strategy to adjust core polarity separately from particle preparation in a bio-reversible fashion. The peptide-inherent process of secondary structure-formation allows for the synthesis of spherical and worm-like core cross-linked architectures from the same block copolymer, introducing a simple yet powerful approach to versatile peptide-based nanoparticles.
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A high-valent non heme μ-oxo MnIV dimer generated from a thiolate-bound MnII complex and O2 ()
This study deals with the unprecedented reactivity of dinuclear non heme MnII-thiolate complexes with O2, which dependent on the protonation state of the initial MnII dimer selectively generates either a di-μ-oxo or μ-oxo-μ-hydroxo MnIV complex. Both dimers have been characterized by different techniques including single-crystal X-ray diffraction and mass spectrometry. Oxygenation reactions carried out with labeled 18O2 unambiguously shows that the oxygen atoms present in the MnIV dimers originate from O2. Based on experimental observations and DFT calculations, evidence is provided that these MnIV species comproportionate with a MnII precursor to yield μ-oxo and/or μ-hydroxo MnIII dimers. Our work highlights the delicate balance of reaction conditions to control the synthesis of non heme high-valent μ-oxo and μ-hydroxo Mn species from MnII precursors and O2.
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α-Radical Phosphines: Synthesis, Structure and Reactivity ()
A series of phosphines featuring a persistent radical were synthesized in two steps by condensation of dialkyl-/diarylchlorophosphines with stable cyclic (alkyl)(amino)carbenes (cAACs) followed by one-electron reduction of the corresponding cationic intermediates. Structural, spectroscopic and computational data indicate that the spin density in these phosphines is mainly localized on the original carbene carbon from the cAAC fragment; thus, it remains in the α-position to the central phosphorus. The potential of these α-radical phosphines to serve as spin-labeled ligands is demonstrated through the preparation of several Au(I) derivatives, which were also structurally characterized by single-crystal X-ray diffraction.
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Absolute Minimal Sampling of Homonuclear 2D NMR TOCSY Spectra for High-Throughput Applications of Complex Mixtures ()
Modern applications of 2D NMR spectroscopy to diagnostic screening, metabolomics, quality control, and other high-throughput applications are often limited by the time-consuming sampling requirements along the indirect time domain t1. 2D Total Correlation Spectroscopy (TOCSY) provides unique spin-connectivity information for the analysis of a large number of compounds in complex mixtures, but standard methods typically require >100 t1-increments for an accurate spectral reconstruction, rendering these experiments ineffective for high-throughput applications. Here, we demonstrate for a complex metabolite mixture how absolute minimal sampling (AMS), based on direct fitting of resonance frequencies and amplitudes in the time domain, yields an accurate spectral reconstruction of TOCSY spectra using as few as 16 t1-points. This permits the rapid collection of homonuclear 2D NMR experiments at high resolution with measurement times that previously were the realm of 1D experiments only.
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Synthesis of Aldehydes by Organocatalytic Formylation Reactions of Boronic Acids with Glyoxylic Acid ()
We report a conceptually novel organocatalytic strategy for formylation of boronic acids, in which a new reactivity is engineered into the α-amino acid forming Petasis reaction occurring between aryl boron acids, amines and glyoxylic acid. The feasibility and preparative power of the protocol was demonstrated by its use to prepare aldehydes from broadly accessible aryl and alkenyl boronic acids, glyoxylic acid, and the cheap N-alkylaniline derivatives, tetrahydroquinoline and indoline, as catalysts. Furthermore, the operational simplicity of the process, which is performed by simply mixing these reagents under ambient conditions, and its ability to generate structurally diverse and valued aryl, heteroaryl and α,β-unsaturated aldehydes containing a wide array of functional groups, demonstrates the practical utility of the newly unveiled synthetic strategy.
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Surface Modification of Two-Dimensional Metal-Organic Layers Creates Biomimetic Catalytic Microenvironments for Selective Oxidation ()
Microenvironments in enzymes play crucial roles in controlling the activities and selectivities of reaction centers. Herein we report the tuning of the catalytic microenvironments of metal-organic layers (MOLs), a two-dimensional version of metal-organic frameworks (MOFs) with thickness down to a monolayer, to control product selectivities. By modifying the secondary building units (SBUs) of MOLs with monocarboxylic acids such as gluconic acid, we successfully changed the hydrophobicity/hydrophilicity around the active sites and fine-tuned the selectivity in photocatalytic oxidation of tetrahydrofuran (THF) to exclusively afford butyrolactone (BTL), likely via prolonging residence time of reaction intermediates in the hydrophilic microenvironment of catalytic centers. Our work highlights new opportunities in using functional MOLs as highly tunable and selective two-dimensional catalytic materials.
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A Designed Approach to Enantiodivergent Enamine Catalysis ()
The rational design and implementation of enantiodivergent enamine catalysis is reported. A simple secondary amine catalyst, 2-methyl-L-proline, and its tetrabutylammonium salt function as an enantiodivergent catalyst pair delivering opposite enantiomers of α-functionalized aldehyde products in excellent enantioselectivities. This novel concept of 'designed enantiodivergence' is applied to the enantioselective α-amination, aldol and α-aminoxylation/α-hydroxyamination reactions of aldehydes.
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Multiple hydrogen bonding enables the self-healing of sensors for human-machine interaction ()
Despite its widespread use in signal collection, flexible sensor has been rarely used in human-machine interaction due to its indistinguishable signal, poor reliability and stability when suffered from unavoidable scratches and/or mechanical cuts. Here, we demonstrate a highly sensitive and self-healing sensor enabled by multiple hydrogen bonding network and nanostructured conductive network. The nanostructured supramolecular sensor displays extremely fast (~15 s) and repeatable self-healing ability with high healing efficiency (93% after the 3rd healing process). It can precisely detect tiny human motions, demonstrating highly distinguishable and reliable signals even after cutting-healing and bending over 20000 cycles. Furthermore, a human-machine interaction system is integrated to develop a facial expression control system and an electronic larynx, aiming to control the robot to assist the patient's daily life and help the dumb to realize real-time speaking.
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Frozen Acrylamide Gels as Dynamic Nuclear Polarization Matrices. ()
We show that aqueous acrylamide gels can be used to provide dynamic nuclear polarization (DNP) NMR signal enhancements of around 200 at 9.4 T and 100 K. The enhancements are shown to increase with cross linker concentration and low concentrations of the AMUPol biradical. We show that this DNP matrix can be used in situations where conventional incipient wetness methods fail, such as to obtain DNP surface enhanced NMR spectra from inorganic nanoparticles. In particular, we obtain 113Cd spectra from CdTe-COOH NPs in minutes. The spectra clearly indicate a highly-disordered cadmium rich surface.
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SERS- and Electrochemically-Active 3D Plasmonic Liquid Marble for Molecular-Level Spectroelectrochemical Investigation of Microliter Reaction ()
Liquid marbles are emerging microreactors due to their isolated environment and flexibility of materials used. Herein, we demonstrate plasmonic liquid marble (PLM) as the smallest spectroelectrochemical microliter-scale reactor for concurrent spectro- and electrochemical analyses. We exploit PLM's three-dimensional Ag shell as bifunctional surface-enhanced Raman scattering (SERS) platform and working electrode for redox process modulation. The combination of SERS and electrochemistry (EC) capability enable in situ molecular read-out of transient electrochemical species, and elucidation of potential-dependent and multi-step reaction dynamics. The 3D configuration of our PLM-based EC-SERS system exhibits 2-fold and 10-fold superior electrochemical and SERS performance than conventional 2D platforms. The rich molecular-level electrochemical insights and excellent EC-SERS capabilities offered by our 3D spectroelectrochemical system is pertinent in charge transfer processes.
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DNA barcoding meets nanotechnology: development of a smart universal tool for food authentication ()
Food trade globalization and the growing demand for selected food varieties have led to the intensification of adulteration cases, especially in the form of species substitution/mixing with cheaper taxa. This phenomenon acquired huge economic impact and sometimes even public health implications. DNA barcoding represents a well-proven molecular tool to assess the authenticity of food items, although its diffusion is hampered by analytical constraints and timeframes that are often prohibitive for food market. To address such issues, we have introduced a new technology, named NanoTracer, which allows for rapid and naked-eye molecular traceability of any food, employing limited instrumentation and cost-effective reagents. Moreover, unlike sequencing, this method allows to identify not only the substitution of a fine ingredient, but also its dilution with cheaper ones.
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Induced-fit recognition of CCG trinucleotide repeats by a nickel chromomycin complex results in large-scale DNA deformation ()
Small-molecule compounds targeting trinucleotide repeats in DNA have considerable potential as therapeutic or diagnostic agents against many neurological diseases. NiII(Chro)2 (Chro = chromomycin A3) was found to bind specifically to the minor groove of (CCG)n repeats in duplex DNA, with unique fluorescence features that may serve as a probe for disease detection. Crystallographic studies have revealed that the specificity originates from the large-scale spatial rearrangement of the DNA structure, including extrusion of consecutive bases and backbone distortions, with a sharp bending of the duplex accompanied by conformational changes in the Ni(II) chelate itself. The DNA deformation of CCG repeats upon binding forms a GGCC tetranucleotide tract, which is recognized by NiII(Chro)2. The extruded cytosine and last guanine nucleotides form water-mediated hydrogen bonds which aid in ligand recognition. The recognition can be accounted for by the classic induced-fit paradigm.
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Total Synthesis of (±)-Waihoensene ()
The first total synthesis of waihoensene, a tetracyclic diterpene containing an angular triquinane and a six-membered ring, with four contiguous quaternary carbon atoms, was achieved through the tandem cycloaddition reaction of an allenyl diazo substrate containing a six-membered ring via trimethylenemethane (TMM) diyl intermediate.
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Single-Atom Electrocatalysts ()
Recent years have witnessed the increasing production of the sustainable and renewable energy. The limitations of electrochemical performances are closely associated with the search for highly efficient electrocatalysts with more rational control of size, shape, composition and structure. Specifically, the rapidly emerging studies on single-atom catalysts (SACs) have sparked new interests in electrocatalysis because of the unique properties such as high catalytic activity, selectivity and 100% atom utilization. In this review, we introduce the innovative synthesis and advanced characterizations of SACs and primarily focus on their electrochemical applications in oxygen reduction/evolution reaction, hydrogen evolution reaction, hydrocarbon conversion reactions for fuel cells (methanol, ethanol and formic acid electrooxidation) and other related fields. Significantly, this unique single atom-depended electrocatalytic performance together with the underlying mechanism will also be discussed. Furthermore, future research directions and challenges are proposed to further realize the ultimate goal of tailoring single-atoms for electrochemical applications.
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From Extended-Nano Fluidics to an Autonomous Solar Light Driven Micro Fuel Cell Device ()
Autonomous micro/nano mechanical, chemical and biomedical sensors require persistent power sources scaled to their size. Realization of autonomous micro-power sources is a challenging task, as it requires combination of wireless energy supply, conversion, storage and delivery to the sensor. In this work, we realized solar light driven power source that consists of a micro fuel cell (μFC) and a photocatalytic micro fuel generator (μFG) integrated on a single microfluidic chip. The μFG produces hydrogen by photocatalytic water splitting under solar light. The hydrogen is then consumed by the μFC to generate electricity. Importantly, the byproduct water returns back to the photocatalytic μFG via recirculation loop without losses. Functionality of both devices relies on novel phenomena in extended-nano fluidic channels that ensure ultra-fast proton transport. As a proof of concept, we demonstrate that μFG/μFC source achieves remarkable energy density of ~17.2 mWh cm-2 at room temperature.
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A Tunable Ionic Diode based on Biomimetic Structure-Tailorable Nanochannel ()
In this work, we reported a tunable ionic diode based on biomimetic structure-tailorable nanochannels, with the precise ions transport characteristics from ohmic behaviour to bidirectional rectification as well as the gating properties. The forward/reverse directions of the ionic diode and the degree of rectification can be well regulated by combining the patterned surface charge and the sophisticated structure. This system creates an ideal platform for precise transportation of ions and molecules, and anticipates to have potential applications in analytical sciences.
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Rhodium-Catalyzed Enantioselective Radical Addition of CX4 Reagents to Olefins ()
We describe an enantioselective addition of Br-CX3 (X = Cl or Br) to terminal olefins that introduces a trihalomethyl group and generates optically active secondary bromides. Computational and experimental evidence supports an asymmetric atom transfer radical addition (ATRA) mechanism in which the stereodetermining step involves outer-sphere bromine abstraction from a (bisphosphine)Rh(II)BrCl complex by a benzylic radical intermediate. Beyond the synthetic utility, this mechanism appears unprecedented in asymmetric catalysis.
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Eight-Electron Silver and Mixed Gold/Silver Nanoclusters Stabilized by Se-Donor Ligands ()
The first atomically and structurally precise silver-nanoclusters stabilized by Se-donor ligands, [Ag20{Se2P(OiPr)2}12] (3) and [Ag21{Se2P(OEt)2}12]+(4), have been isolated by ligand replacement reaction of [Ag20{S2P(OiPr)2}12] (1) and [Ag21{S2P(OiPr)2}12]+ (2), respectively. Further, doping reactions of 4 with Au(PPh3)Cl resulted in the formation of [AuAg20{Se2P(OEt)2}12]+, (5). Structures of 3, 4 and 5 were determined by single crystal X-ray diffraction. The anatomy of cluster 3 with an Ag20 core having C3 symmetry is very similar to that of its dithiophosphate analogue 1. Clusters 4 and 5 exhibit an Ag21 and Au@Ag20 core of Oh symmetry composed of eight silver capping atoms in a cubic arrangement and encapsulating an Ag13 and Au@Ag12 centered icosahedron, respectively. Both ligand exchange and heteroatom doping result in significant changes in optical and emissive properties for chalcogen-passivated silver nanoparticles, which have been theoretically proved as 8-electron superatoms.
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Phenotypic Identification of a Novel Autophagy Inhibitor Chemotype Targeting Lipid Kinase VPS34 ()
Autophagy is a critical regulator of cellular homeostasis and metabolism. Interference with this process is considered a new approach for the treatment of disease, in particular cancer and neurological disorders. Therefore, novel small molecule autophagy modulators are in high demand. We describe the discovery of autophinib, a potent autophagy inhibitor with a novel chemotype. Autophinib was identified by means of a phenotypic assay monitoring formation of autophagy-induced puncta indicating accumulation of lipidated cytosolic protein LC3 on the autophagosomal membrane. Target identification and validation revealed that autophinib inhibits autophagy induced by starvation or Rapamycin by targeting the lipid kinase VPS34.
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Catalytic Electrophilic Alkylation of p-Quinones via a Redox Chain Reaction ()
Allylation and benzylation of p-quinones is achieved by an unusual redox chain reaction. Mechanistic studies suggest that the trace existence of hydroquinone initiates a redox chain reaction that consists of a Lewis acid-catalyzed Friedel-Crafts alkylation and a subsequent redox equilibrium that regenerates hydroquinone. The electrophiles could be various allylic and benzylic esters. Addition of Hantzsch ester as initiator improves the efficiency of the reaction.
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Self-Assembled Biomimetic Chloroplast Coupled Photoenzymatic Reaction for Sustainable Synthesis of Fuel ()
Prototypes of biosystems provide good blueprints for the design and creation of biomimetic systems. However, mimicking both the sophisticated natural structures and their complex biological functions still remains a great challenge. Herein, biomimetic chloroplasts have been fabricated by one-step bio-inspired amino acid mineralization and simultaneous integration of catalytically active units. Hierarchically structured crystals are obtained by metal ion-directed self-assembly of cystine (the oxidized dimer form of the amino acid cysteine), with porous structure and stacking nanorods, which show similar architectural principles to chloroplasts. Porphyrin and enzyme molecules can be both encapsulated in the crystal during mineralization, endowing photocatalytic and enzymatic activity to the crystal, achieving efficient and sustainable synthesis of hydrogen and aldehyde via coupled photoenzymatic reaction.
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Direct Hydroxylation of Benzene to Phenol by Cytochrome P450BM3 Triggered by Amino Acid Derivatives ()
Selective hydroxylation of benzene to phenol, without formation of side products resulting from overoxidation, was catalyzed by cytochrome P450BM3 (P450BM3) with the assistance of amino acid derivatives as decoy molecules. The catalytic turnover rate and the total turnover number reached 259 min-1P450BM3-1 and 40,200 P450BM3-1 when N-heptyl-L-proline modified with L-phenyl alanine (C7-L-Pro-L-Phe) was used as the decoy molecule. This work shows that amino acid derivatives that have a totally different structure from fatty acids can be used as decoy molecules for aromatic hydroxylation by wild-type P450BM3. This methodology for nonnative substrate hydroxylation by wild-type P450BM3 has the potential to expand the utility of P450BM3 for biotransformations.
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Selected Copper-Based Reactions for C-N, C-O, C-S and C-C Bond Formation ()
The metal catalyzed cross-coupling reactions are one of the most important transformations in organic synthesis. Copper catalysis has received great attention due to its low toxicity and inexpensive nature. However, traditional Ullmann-type coupling reactions suffered from limited substrate scope and harsh reaction conditions. The introduction of some bidentate ligands such as amino acids, diamines, 1,3-diketones and oxalic diamides during the past two decades has totally changed its scenario, allowing the coupling reactions of aryl halides and nucleophiles to take place at both low reaction temperatures and catalytic loadings. The reaction scope has also been greatly expanded and makes this copper-based cross coupling attractive in both academia and industry. This review will summarize the latest progress in developing the useful reaction conditions for coupling of (hetero)aryl halides with different nucleophiles. Additionally, recent advances on Cu-catalyzed coupling reactions with aryl boronates and Cu-based trifluoromethylations of aromatic electrophiles will be introduced.
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Structural basis for copper-oxygen mediated C-H bond activation by the formylglycine-generating enzyme ()
The formylglycine-generating enzyme (FGE) is a unique copper-protein that catalyzes oxygen-dependent C-H activation. We describe 1.66 Å- and 1.28 Å-resolution crystal structures of FGE from Thermomonospora curvata in complex with either Ag (I) or Cd (II) providing definitive evidence for a high-affinity metal-binding site in this enzyme. The structures reveal a bis-cysteine linear coordination of the monovalent metal, and tetrahedral coordination of the bivalent metal. Similar coordinational change may occur in the active enzyme as a result of Cu (I)/(II) redox cycling. Complexation of copper by two cysteines is common among copper-trafficking proteins, but is unprecedented for redox-active copper-enzymes or synthetic copper catalysts.
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Reversing polarity: Carbonyl α-aminations with nitrogen nucleophiles ()
The synthesis of alpha-amino carbonyl compounds is an important challenge in synthesis en route to biologically essential structures. While classical approaches involve the use of enol or enolate chemistries in combination with an electrophilic source of nitrogen, those strategies usually necessitate further transformations in order to reach the desired targets. In recent years, a new approach arose involving the direct use of nucleophilic sources of nitrogen along with an oxidant. This advantageously leads in one-pot to the biologically relevant alpha-amino compounds, without further transformation required. This Minireview highlights the recent advances in the emerging field of oxidative alpha-amination reactions using nucleophilic sources of nitrogen.
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Black Tungsten Nitride as Metallic Photocatalyst for Overall Water Splitting Operable at up to 765 nm ()
Semiconductor photocatalysts are hardly to be employed for overall water splitting beyond 700 nm, owing to both thermodynamic aspects and activation barriers. Metallic materials as photocatalysts are known to overcome this limitation through interband transitions for creating electron-hole pairs, however, the application of metallic photocatalysts for overall water splitting has never been fulfilled. Here we report, for the first time, that the black tungsten nitride can be employed as metallic photocatalyst for overall water splitting at wavelengths of up to 765 nm. Experimental and theoretical results together confirm that metallic properties play a substantial role in exhibiting photocatalytic activity under red-light irradiation for tungsten nitride. This work represents the first red-light responsive photocatalyst for overall water splitting, and may open a promising venue in searching of metallic materials as efficient photocatalysts for solar energy utilization.
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Enantiopure cycloiridiated complexes bearing a pentahelicenic N-heterocyclic carbene and displaying long-lived circularly-polarized phosphorescence ()
A fused pi-helical N-heterocyclic (NHC) system has been prepared and examined through its diastereoisomerically pure cycloiridiated complexes. The latter display light-green phosphorescence with i) unusually long lifetimes and ii) circular polarization that depends on both the helical-NHC P/M and the iridium delta/lambda stereochemistry. These unprecedented features are attributed to extended pi-conjugation within helical carbenic ligand and efficient helicene-NHC-Ir interaction.
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Enzymatic engineering of live bacterial cell surface using butelase 1 ()
We show that butelase-mediated ligation (BML) can be used to modify live bacterial cell surfaces with diverse cargo molecules. Surface-displayed butelase recognition motif NHV was first introduced at the C-terminal end of the anchoring protein OmpA on E. coli cells. This then served as a handle of BML for the functionalization of E. coli cell surfaces with fluorescein and biotin tags, a tumor-associated monoglycosylated peptide and mCherry protein. The cell-surface ligation reaction was achieved at low concentrations of butelase and the labeling substrates. Furthermore, the fluorescein-labeled bacterial cells were used to show the interactions with cultured HeLa cells and with macrophages in live transgenic zebrafish, capturing the latter's powerful phagocytic effect in action. Together these results highlight the usefulness of butelase 1 in live bacterial cell surface engineering for novel applications.
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Tris(perfluorotolyl)borane - a Boron Lewis Superacid ()
Tris(tetrafluoro-4-(trifluoromethyl)phenyl)borane (BTolF) was prepared by reacting boron tribromide with tetrameric F3CC6F4-Cu(I). The latter was generated from F3CC6F4MgBr and copper(I) bromide. Lewis acidities of BTolF evaluated by the Gutmann-Beckett method and calculated fluoride ion affinities are 9 and 10%, respecttively, higher than that of tris(penta-fluorophenyl)borane (BCF) and even higher than that of SbF5. The molecular structures of BTolF and BCF were determined by gas electron diffraction, that of BTolF also by single crystal X-ray diffraction.
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Double-Caging Linker for AND-Type Fluorogenic Construction of Protein/Antibody Bioconjugates and in situ Quantification ()
We report on in situ fluorescent quantification of the conjugation efficiency between azide-terminated synthetic polymers/ imaging probes and thiol-functionalized antibodies/proteins/peptides, by utilizing a doubly caged profluorescent and heterodifunctional core molecule (C1) as the self-sorting bridging unit. Orthogonal dual 'click' coupling of C1 with azide- and thiol-functionalized precursors leads to highly fluorescent bioconjugates, whereas single click products of C1 remain essentially nonfluorescent. This 'AND' logic gate-type fluorogenic feature also enables further integration with FRET processes. For the construction of antibody-probe conjugates from an anti-carcinoembryonic antigen and a quinone-caged profluorescent naphthalimide derivative, the dual 'click' coupling process with C1 can be conveniently monitored via emission turn-on of C1, whereas prominent changes in FRET ratios occur for antibody-probe conjugates when triggered by specific tumor-associated enzymes.
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Synthesis of Highly Substituted Pyridines via Copper-Catalyzed Condensation of Oximes and α,β-Unsaturated Imines ()
A copper-catalyzed condensation reaction of oxime acetates and α,β-unsaturated ketimines into pyridine derivatives is reported. The reaction features mild conditions, high functional group compatibility, and high regioselectivity with respect to unsymmetrical oxime acetates, thus allowing for the preparation of a wide range of polysubstituted pyridines, many of which are not readily accessible by conventional condensation methods.
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Silica-Polypyrrole Hybrids as High-Performance Metal-Free Electrocatalysts for Hydrogen Evolution Reaction in Neutral Media ()
Constructing inorganic-organic hybrids with high abilities of water adsorption and activation will lead to significant enhancement of electrocatalytic activity for hydrogen evolution reaction (HER) in neutral media that is environmentally benign. Here we report SiO2-polypyrrole (PPy) hybrid nanotubes supported on carbon fibers (CFs) (SiO2/PPy NTs-CFs) as low-cost and high-performance electrocatalysts for HER in neutral media. Because of the strong electronic interactions between SiO2 and PPy, SiO2 uniquely serves as the centers of water adsorption and activation, and accordingly it will obviously promote HER. SiO2/PPy NTs-CFs as metal-free electrocatalysts achieve high catalytic performance for HER in neutral media, such as low onset potential, small Tafel slope and excellent long-term durability.
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Bandgap Engineering of Lead-Free Double Perovskite Cs2AgBiBr6 through Trivalent Metal Alloying ()
The double perovskite family, A2MIMIIIX6, represents a promising route to overcome the lead toxicity issue confronting current photovoltaic (PV) standout, CH3NH3PbI3. Given the generally large indirect bandgap within most known double perovskites, bandgap engineering provides an important approach for targeting outstanding PV performance within this family. Using Cs2AgBiBr6 as host, we demonstrate bandgap engineering through alloying of InIII/SbIII. Cs2Ag(Bi1-xMx)Br6 (M = In, Sb) accommodates up to 75% InIII with increased bandgap, and up to 37.5% SbIII with reduced bandgap—i.e., enabling ~0.41 eV bandgap modulation through introduction of the two metals, with smallest value of 1.86 eV for Cs2Ag(Bi0.625Sb0.375)Br6. Band structure calculations indicate that opposite bandgap shift directions associated with Sb/In substitution arise from different atomic configurations for these atoms. Associated photoluminescence and environmental stability of the three-metal systems are also assessed.
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Optochemical Control of Biological Processes in Cells and Animals ()
Achieving precise control of biological function represents a crucial tool for studying the mechanisms of cellular processes. Naturally, these processes occur in a strict spatially and temporally regulated fashion. In order to generate accurate models, the tools used to study these processes must also operate with high spatiotemporal resolution. To this end, the use of light as a conditional stimulus has found extensive applications for the activation and deactivation of small molecules, proteins, peptides, and oligonucleotides. Harnessing light has enabled significant advances in both research applications and holds promise toward clinical studies. This review showcases many of the most recent applications and methodology developments of optical control of biology. It focuses on the most recent developments in utilizing chemistry to optically manipulate living systems such as cells and animals.
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Quantifying hydrogen-bond populations in DMSO/water mixtures ()
Dimethyl sulfoxide (DMSO) disrupts the hydrogen-bond networks in water. DMSO's widespread uses as a cosolvent, along with its unusual attributes, have inspired numerous studies. In this study, infrared absorption spectroscopy of the S=O stretch combined with molecular dynamics and quantum chemistry models were used to directly quantify DMSO/water hydrogen bond populations in binary mixtures. Singly H-bonded species are dominant at 10 mol%, due to strong DMSO-water interactions. We found an unexpected increase in non-hydrogen-bonded DMSO near the eutectic point (~35 mol%) which also correlates with several abnormalities in the solution's bulk properties. We find evidence for three distinct regimes: 1. Strong DMSO-water interactions (<30 mol%); 2. ideal-solution-like (30-90 mol%); 3. self-interaction, or aggregation, regime (>90 mol%). We propose a "step in" mechanism, which involves hydrogen bonding between water and the DMSO aggregate species.
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Perovskite solar cells from the atomic to the film level ()
Organic-inorganic perovskites have made tremendous progress in recent years due to exceptional material properties such as high panchromatic absorption, charge carrier diffusion lengths and a sharp optical band edge. The combination of high-quality semiconductor with low-cost deposition techniques seems to be a match made in heaven creating great excitement and anticipation far beyond the academic ivory tower. This is particularly true for perovskite solar cells (PSCs) that have shown unprecedented gains in efficiency and stability over a time span of just 5 years. Now there are serious efforts for commercialisation with the hope that PSCs can make a major impact in generating inexpensive, sustainable solar electricity. In this review, we will focus on materials and devices from the atomic to the thin film level to highlight the remaining challenges and to anticipate the future developments of PSCs.
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Asymmetric Synthesis of Secondary and Tertiary Boronic Esters ()
Non-racemic chiral boronic esters are recognised as immensely valuable building blocks in modern organic synthesis. Their stereospecific transformation into a variety of functional group - from amines and halides to arenes and alkynes - along with their air and moisture stability, has established them as an important target for asymmetric synthesis. Efforts towards the stereoselective synthesis of secondary and tertiary alkyl boronic esters have spanned over five decades and are underpinned by a wealth of reactivity platforms, drawing on the unique and varied reactivity of boron. This review summarizes strategies for the asymmetric synthesis of alkyl boronic esters, from the seminal hydroboration methods of H. C. Brown to the current state of the art.
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Nanojunction polymer photoelectrode for efficient charge transport and separation ()
A novel nanojunction archiecture of metal-free photoanode, composed of B-doped carbon nitride nanolayer and bulk carbon nitride has been fabricated by a one-step construction approach. This type of nanojunction overcomes a few intrinsic drawbacks of carbon nitride film, e.g. severe bulk charge recombination and slow charge transfer. For the optium sample, the top layer of the nanojunction has a depth of ca. 100 nm and the bottom layer is ca. 900 nm. The nanojunction photoanode results into a 10 fold higher photocurrent than bulk graphitic carbon nitride and an extremely high incident photon-to-current efficiency (IPCE) of ca. 10% at 400 nm, which to the best of our knowledge is the highest for G-CN based polymer photoanodes in the absence of any sacrificial reagents. The EIS, MS and IMPS spectroscopies all prove such enhancement is mainly due to more than 10 times faster charge seperation rate and nearly 3 times higher conductivity due to the nanojunction architcutre.
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Encapsulation and Polymerization of White Phosphorus Inside Single-wall Carbon Nanotubes ()
Elemental phosphorus displays an impressive number of allotropes with highly diverse chemical and physical properties. Here, we report that white phosphorus can be filled into single-wall carbon nanotubes (SWCNTs) from the liquid and thereby stabilized against the highly exothermic reaction with atmospheric oxygen. The encapsulated tetraphosphorus molecules were visualized with transmission electron microscopy, but found to convert readily to chain structures inside the SWCNT 'nanoreactors'. The energies of the possible chain structures were determined computationally highlighting a delicate balance between the extent of polymerization and the SWCNT diameter. Experimentally, a single-stranded zig-zag chain of phosphorus atoms was observed which represents the lowest energy structure at small confinement diameters. These one-dimensional chains provide a glimpse into the very first steps of the transformation from white to red phosphorus.
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Lithium Bond Chemistry in Lithium-Sulfur Batteries ()
Lithium-sulfur (Li-S) battery is a promising high-energy-density energy storage system. The strong anchoring of intermediates is widely accepted to retard the shuttle of polysulfides in a working battery. However, the understanding of the intrinsic chemistry is still deficient. Inspired by the concept of hydrogen bond, herein we focus on the Li bond chemistry in Li-S batteries through sophisticated quantum chemical calculations, in combination with 7Li nuclear magnetic resonance (NMR). Identified as Li bond, the strong dipole-dipole interaction between Li polysulfides and Li-S cathode materials originates from the electron-rich donors (e.g., pyridinic nitrogen (pN)), and enhanced by the inductive and conjugative effect of scaffold materials with π-electrons (e.g., graphene). The chemical shift of Li polysulfides in 7Li NMR, being both theoretically predicted and experimentally verified, is suggested to serve as a quantitative descriptor of Li bond strength.
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High-Dimensional Neural Network Potentials for Complex Systems ()
Modern simulation techniques have reached a level of maturity, which allows addressing a wide range of problems in chemistry and materials science. Unfortunately, the application of first principles methods with predictive power is still limited to rather small systems, and in spite of the rapid evolution of computer hardware no fundamental change of this situation can be expected. Consequently, to reach an atomic level understanding of complex systems, the development of more efficient but equally reliable atomistic potentials has received considerable attention in recent years. A promising new development has been the introduction of machine learning (ML) methods to describe the atomic interactions. Once trained to electronic structure data, ML potentials can accelerate computer simulations by several orders of magnitude, while quantum mechanical accuracy is preserved. In this article, the methodology of an important class of ML potentials employing artificial neural networks is reviewed.
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Development of Biomass-Derived Non-Noble Metal Catalysts for Selective Hydrodehalogenation of Alkyl and (Hetero)Aryl Halides ()
Hydrodehalogenation represents a straightforward approach for detoxifications of anthropogenic harmful organohalide based pollutants as well as removal of halide protecting groups used in multistep synthesis. A novel sustainable catalytic material has been prepared from biowaste (chitosan) in a combination with earth-abundant cobalt salt. This heterogeneous catalyst was fully characterized by means of TEM, XRD as well as XPS analysis and applied successfully for hydrodehalogenation of alkyl and (hetero)aryl halides with broad scope (>40 examples) and excellent chemoselectivity using molecular hydrogen. The general usefulness of this methodology has been proven by the successful implementation for detoxification of non-degradable pesticides and fire retardants. In addition, its use in the multistep synthesis of (±)-Peronatin B (alkaloid) as deprotection tool showed its potential applicability.
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Meta-C‒H Arylation and Alkylation of Benzylsulfonamide Enabled by a Pd(II)/Isoquinoline Catalyst ()
Palladium(II)-catalyzed meta-C‒H arylation and alkylation of benzylsulfonamide using 2-carbomethoxynorbornene (NBE-CO2Me) as a transient mediator are realized using a newly developed electron-deficient directing group and isoquinoline as a ligand. This protocol features broad substrate scope and good functional group tolerance. The meta-substituted benyzlsulfonamide can be readily transformed to sodium sulfonate, sulfonate ester, sulfonamide, as well as styrenes via Julia-type olefination. The unique impact of the isoquinoline ligand underscores the importance of subtle matching between ligands and the directing groups.
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Electrochemically-Treated BiVO4 Photoanode for Efficient Photoelectrochemical Water Splitting ()
BiVO4 films with (040) facet grown vertically on fluorine doped SnO2 (FTO) glass substrates are prepared by a seed-assisted hydrothermal method. A simple electrochemical treatment process drastically enhances the photocatalytic activity of BiVO4, exhibiting a remarkable photocurrent density of 2.5 mA cm-2 at 1.23 V vs. reversible hydrogen electrode (RHE) under AM 1.5 G illumination, which is approximately 10 folds higher than that of the pristine one. Loading cobalt borate (CoBi) as cocatalyst, the photocurrent density of the BiVO4 photoanode can be further improved to 3.2 mA cm-2, delivering an applied bias photon-to-current efficiency (ABPE) of 1.1%. Systematic studies reveal that crystal facet orientation also synergistically boosts both charge separation and transfer efficiencies, resulting in remarkably enhanced photocurrent densities. The new findings provide a facile and effective approach for the development of efficient photoelectrodes for photoelectrochemical water splitting.
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The Narrow Road to the Deep Past ()
The sequence of events that gave rise to the first life on our planet took place in the Earth's deep past, seemingly forever beyond our reach. Perhaps for that very reason the idea of reconstructing our ancient story is tantalizing, almost irresistible. Understanding the processes that led to synthesis of the chemical building blocks of biology and the ways in which these molecules self-assembled into cells that could grow, divide and evolve, nurtured by a rich and complex environment, seems at times insurmountably difficult. And yet, to my own surprise, simple experiments have revealed robust processes that could have driven the growth and division of primitive cell membranes. The nonenzymatic replication of RNA is more complicated and less well understood, but here too significant progress has come from surprising developments. Even our efforts to combine replicating compartments and genetic materials into a full protocell model have moved forward in unexpected ways. Fortunately, many challenges remain before we will be close to a full understanding of the origin of life, so the future of research in this field is brighter than ever!
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Overcoming the instability of nanoparticle based catalyst films in alkaline electrolysers by self-assembling and self-healing films ()
Engineering stable electrodes using highly active catalyst nanopowders for electrochemical water splitting remains a notorious challenge. We report an innovative and general approach for attaining highly stable catalyst films with self-healing capability based on in-situ self-assembly of catalyst particles during electrolysis. The catalyst particles are added to the electrolyte forming a suspension that is pumped through the electrolyzer. Particles with negatively charged surfaces stick onto the anode, while particles with positively charged surfaces stick to the cathode. The self-assembled catalyst films possess self-healing properties as long as a sufficient amount of catalyst particles are present in the electrolyte. The proof-of-concept was demonstrated in a non-zero gap alkaline electrolyzer using NiFe LDH and NixB catalyst nanopowders for anode and cathode, respectively. Steady cell voltages were maintained for at least three weeks during continuous electrolysis at 50-100 mA cm-2
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Assessing the Influence of Mutation on GTPase Transition States by using X-ray Crystallography, 19F NMR, and DFT Approaches ()
We report X-ray crystallographic and 19F NMR studies of the G-protein RhoA complexed with MgF3−, GDP, and RhoGAP, which has the mutation Arg85′Ala. When combined with DFT calculations, these data permit the identification of changes in transition state (TS) properties. The X-ray data show how Tyr34 maintains solvent exclusion and the core H-bond network in the active site by relocating to replace the missing Arg85′ sidechain. The 19F NMR data show deshielding effects that indicate the main function of Arg85′ is electronic polarization of the transferring phosphoryl group, primarily mediated by H-bonding to O3G and thence to PG. DFT calculations identify electron-density redistribution and pinpoint why the TS for guanosine 5′-triphosphate (GTP) hydrolysis is higher in energy when RhoA is complexed with RhoGAPArg85′Ala relative to wild-type (WT) RhoGAP. This study demonstrates that 19F NMR measurements, in combination with X-ray crystallography and DFT calculations, can reliably dissect the response of small GTPases to site-specific modifications. In transit: Mutagenic removal of an arginine finger from the GTPase-activating protein RhoGAP leads to changed crystal structures and transposed 19F NMR data for MgFx transition-state analogue (TSA) complexes, owing to the exclusively electrostatic contribution of Arg85′. This was fully delineated through DFT computation of electron distribution in the transition state. Taken together the data show a later, more dissociative transition state for phosphoryl transfer.
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Bert M. Weckhuysen Honored/MRS Outstanding Young Investigator Award/VAAM Forschungspreis for Tobias J. Erb ()

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Control of Product Distribution and Mechanism by Ligation and Electric Field in the Thermal Activation of Methane ()
Selective oxidative coupling of methane using metal–oxide-based catalysts constitutes one of the central challenges in the valorization of this inert hydrocarbon. Ligands have been known for decades to profoundly affect the electronic character of metal centers with the benefit to fine-tune the chemical features of, for example, cationic metal oxides. A well-studied case concerns the axial-ligand effect exerted in iron–oxo complexes, wherein by changing the electronic structure, the axial ligand fine-tunes the reactivity. However, the electronic origin of ligand effects in the gas-phase C−H bond activation, mediated by metal–oxide catalysts, is not understood very well yet. A simple ligand turns off two of the three channels operative in the [ZnO].+/CH4 couple. As a result, only hydrogen-atom abstraction occurs for the [(CH3CN)ZnO].+/CH4 system. This remarkable ligand effect can be modeled well by an oriented external electric field. PCSET: proton-coupled single-electron transfer; OEEF: oriented external electric field; HAT: hydrogen-atom transfer.
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Supramolecular Interfacial Polymerization: A Controllable Method of Fabricating Supramolecular Polymeric Materials ()
A new method of supramolecular polymerization at the water–oil interface is developed. As a demonstration, an oil-soluble supramonomer containing two thiol end groups linked by two ureidopyrimidinone units and a water-soluble monomer bearing two maleimide end groups are employed. Supramolecular interfacial polymerization can be implemented by a thiol–maleimide click reaction at the water–chloroform interface to obtain supramolecular polymeric films. The glass transition temperature of such supramolecular polymers can be well-tuned by simply changing the polymerization time and temperature. It is highly anticipated that this work will provide a facile and general approach to realize control over supramolecular polymerization by transferring the preparation of supramolecular polymers from solutions to water–oil interfaces and construct supramolecular materials with well-defined properties. Border control: A method for supramolecular polymerization at the water–oil interface is developed. This process has many advantages, such as ease of operation, insensitivity to molar ratio and monomer concentration, and feasibility for immiscible monomers. It can be used to construct supramolecular materials with well-defined and controllable properties.
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Essential Reagents for Organic Synthesis. Edited by Philip L. Fuchs, André B. Charette, Tomislav Rovis, Jeffrey W. Bode. ()
John Wiley and Sons, Hoboken 2016. 640 pp., softcover, $ 115.00.—ISBN 978-1119278306
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Trapping a Silicon(I) Radical with Carbenes: A Cationic cAAC–Silicon(I) Radical and an NHC–Parent-Silyliumylidene Cation ()
The trapping of a silicon(I) radical with N-heterocyclic carbenes is described. The reaction of the cyclic (alkyl)(amino) carbene [cAACMe] (cAACMe=:C(CMe2)2(CH2)NAr, Ar=2,6-iPr2C6H3) with H2SiI2 in a 3:1 molar ratio in DME afforded a mixture of the separated ion pair [(cAACMe)2Si:.]+I− (1), which features a cationic cAAC–silicon(I) radical, and [cAACMe−H]+I−. In addition, the reaction of the NHC–iodosilicon(I) dimer [IAr(I)Si:]2 (IAr=:C{N(Ar)CH}2) with 4 equiv of IMe (:C{N(Me)CMe}2), which proceeded through the formation of a silicon(I) radical intermediate, afforded [(IMe)2SiH]+I− (2) comprising the first NHC–parent-silyliumylidene cation. Its further reaction with fluorobenzene afforded the CAr−H bond activation product [1-F-2-IMe-C6H4]+I− (3). The isolation of 2 and 3 confirmed the reaction mechanism for the formation of 1. Compounds 1–3 were analyzed by EPR and NMR spectroscopy, DFT calculations, and X-ray crystallography. Unusual intermediates: The reaction of a cyclic (alkyl)(amino) carbene with H2SiI2 afforded a separated ion pair containing a cationic cAAC–silicon(I) radical complex (see scheme, left). On the other hand, treatment of the NHC–iodosilicon(I) dimer [IAr(I)Si:]2 with a different NHC led to an NHC–parent-silyliumylidene cation (right).
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Betaine Catalysis for Hierarchical Reduction of CO2 with Amines and Hydrosilane To Form Formamides, Aminals, and Methylamines ()
An efficient, sustainable organocatalyst, glycine betaine, was developed for the reductive functionalization of CO2 with amines and diphenylsilane. Methylamines and formamides were obtained in high yield by tuning the CO2 pressure and reaction temperature. Based on identification of the key intermediate, that is, the aminal, an alternative mechanism for methylation involving the C0 silyl acetal and aminal is proposed. Furthermore, reducing the CO2 amount afforded aminals with high yield and selectivity. Therefore, betaine catalysis affords products with a diversified energy content that is, formamides, aminals and methylamines, by hierarchical two-, four- and six-electron reduction, respectively, of CO2 coupled with C−N bond formation. Hierarchical: Efficient and sustainable glycine betaine catalysis was developed for reductive functionalization of CO2 with amines and diphenylsilane. Such organocatalysis afforded products with diversified energy contents, that is, formamides, aminals, and methylamines, by hierarchical two-, four-, and six-electron reduction, respectively, of CO2 coupled with C−N bond formation.
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Evidence of Structure Sensitivity in the Fischer–Tropsch Reaction on Model Cobalt Nanoparticles by Time-Resolved Chemical Transient Kinetics ()
The Fischer–Tropsch process, or the catalytic hydrogenation of carbon monoxide (CO), produces long chain hydrocarbons and offers an alternative to the use of crude oil for chemical feedstocks. The observed size dependence of cobalt (Co) catalysts for the Fischer–Tropsch reaction was studied with colloidally prepared Co nanoparticles and a chemical transient kinetics reactor capable of measurements under non-steady-state conditions. Co nanoparticles of 4.3 nm and 9.5 nm diameters were synthesized and tested under atmospheric pressure conditions and H2/CO=2. Large differences in carbon coverage (ΘC) were observed for the two catalysts: the 4.3 nm Co catalyst has a ΘC less than one while the 9.5 nm Co catalyst supports a ΘC greater than two. The monomer units present on the surface during reaction are identified as single carbon species for both sizes of Co nanoparticles, and the major CO dissociation site is identified as the B5-B geometry. The difference in activity of Co nanoparticles was found to be a result of the structure sensitivity caused by the loss of these specific types of sites at smaller nanoparticle sizes. Size it up: Size-dependent activity of cobalt nanoparticles in Fischer–Tropsch synthesis is correlated with loss of carbon monoxide dissociation sites on small nanoparticles. Transient kinetic experiments and synchrotron spectroscopy reveal greater carbon accumulation on large nanoparticles. Carbon monoxide dissociation sites occur on face-centered cubic cobalt (221) steps.
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Confining Excitation Energy in Er3+-Sensitized Upconversion Nanocrystals through Tm3+-Mediated Transient Energy Trapping ()
A new class of lanthanide-doped upconversion nanoparticles are presented that are without Yb3+ or Nd3+ sensitizers in the host lattice. In erbium-enriched core–shell NaErF4:Tm (0.5 mol %)@NaYF4 nanoparticles, a high degree of energy migration between Er3+ ions occurs to suppress the effect of concentration quenching upon surface coating. Unlike the conventional Yb3+-Er3+ system, the Er3+ ion can serve as both the sensitizer and activator to enable an effective upconversion process. Importantly, an appropriate doping of Tm3+ has been demonstrated to further enhance upconversion luminescence through energy trapping. This endows the resultant nanoparticles with bright red (about 700-fold enhancement) and near-infrared luminescence that is achievable under multiple excitation wavelengths. This is a fundamental new pathway to mitigate the concentration quenching effect, thus offering a convenient method for red-emitting upconversion nanoprobes for biological applications. Contain your excitement: Core–shell design strategies are usually unable to prevent luminescence quenching caused by energy losses at lattice defects residing inside a nanocrystal. Through Tm3+-mediated transient energy trapping, Er3+-sensitized nanocrystals (NaErF4:Tm@NaYF4) displaying highly efficient upconversion emission are presented. These nanomaterials are capable of generating red and NIR emissions under multiple excitation wavelengths.
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Sensitization-Initiated Electron Transfer for Photoredox Catalysis ()
Photosynthetic organisms exploit antenna chromophores to absorb light and transfer excitation energy to the reaction center where redox reactions occur. In contrast, in visible-light chemical photoredox catalysis, a single species (i.e., the photoredox catalyst) absorbs light and performs the redox chemistry. Mimicking the energy flow of the biological model, we report a two-center photoredox catalytic approach in which the tasks of light energy collection and electron transfer (i.e., redox reactions) are assigned to two different molecules. Ru(bpy)3Cl2 absorbs the visible light and transfers the energy to polycyclic aromatic hydrocarbons that enable the redox reactions. This operationally simple sensitization-initiated electron transfer enables the use of arenes that do not absorb visible light, such as anthracene or pyrene, for photoredox applications. We demonstrate the merits of this approach by the reductive activation of chemical bonds with high reduction potentials for carbon–carbon and carbon–heteroatom bond formations. Inspired by nature: In the presented two-center photoredox catalytic approach, Ru(bpy)3Cl2 absorbs visible light and transfers the energy to polycyclic aromatic hydrocarbons, which in turn enable an efficient redox process. This method was used for the activation of (hetero)aryl halides for the formation of carbon–carbon and carbon–heteroatom bonds.
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The Dynamic Multisite Interactions between Two Intrinsically Disordered Proteins ()
Protein interactions involving intrinsically disordered proteins (IDPs) comprise a variety of binding modes, from the well-characterized folding upon binding to dynamic fuzzy complexes. To date, most studies concern the binding of an IDP to a structured protein, while the interaction between two IDPs is poorly understood. In this study, NMR, smFRET, and molecular dynamics (MD) simulation are combined to characterize the interaction between two IDPs, the C-terminal domain (CTD) of protein 4.1G and the nuclear mitotic apparatus (NuMA) protein. It is revealed that CTD and NuMA form a fuzzy complex with remaining structural disorder. Multiple binding sites on both proteins were identified by molecular dynamics and mutagenesis studies. This study provides an atomic scenario in which two IDPs bearing multiple binding sites interact with each other in dynamic equilibrium. The combined approach employed here could be widely applicable for investigating IDPs and their dynamic interactions. Fuzzy wuzzy: Combined NMR, molecular dynamics simulation, and single-molecule FRET studies reveal that the intrinsically disordered proteins 4.1G-CTD and NuMA form a dynamic fuzzy complex in which both remain disordered (see figure). The two proteins bearing multiple binding sites interact in dynamic equilibrium.
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Instant Hydrogelation Inspired by Inflammasomes ()
Based on the recent near-atomic structures of the PYRIN domain of ASC in the protein filament of inflammasomes and the observation that the active form of vitamin B6 (pyridoxal phosphate, P5P) modulates the self-assembly of ASC, we rationally designed an N-terminal capped nonapeptide (Nap-FFKKFKLKL, 1) to form supramolecular nanofibers consisting of α-helix. The addition of P5P to the solution of 1 results in a hydrogel almost instantly (about 4 seconds). Several other endogenous small molecules (for example, pyridoxal, folinic acid, ATP, and AMP) also convert the solution of 1 into a hydrogel. As the demonstration of correlating assemblies of peptides and the relevant protein epitopes, this work illustrates a bioinspired approach to develop supramolecular structures modulated by endogenous small molecules. Vitamin B6 and other similar endogenous small molecules induce instant hydrogelation of peptidic epitope from inflammasomes. This is a direct demonstration of correlating supramolecular assemblies of peptides and the relevant protein epitopes for developing instant supramolecular hydrogelation.
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Crystalline Hollow Microrods for Site-Selective Enhancement of Nonlinear Photoluminescence ()
A class of one-dimensional hollow microstructure is described, which was formed by a kinetically controlled crystal growth process. A hexagonal-phase NaYbF4 microrod comprising isolated holes along the longitudinal axis was synthesized by a one-pot hydrothermal method with the assistance of citrate ligands. The structural void feature modulates light intensity across the microrods as a result of interference arising from light scattering and reflection by the inner walls. A single crystal comprising a structural void was doped with upconverting lanthanide ions. Upon near-infrared excitation of the doped crystal spatially resolvable optical codes were produced. Hollow-structured microcrystals of hexagonal phase NaYbF4 produce nonlinear photoluminescence upon illumination with near-infrared light. Light scattering and reflection by the inner walls of the microrod modulate light intensity across the structure. Spatially resolved optical codes are attained when the irradiated material is doped with upconverting lanthanide ions.
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Common Fibril Structures Imply Systemically Conserved Protein Misfolding Pathways In Vivo ()
Systemic amyloidosis is caused by the misfolding of a circulating amyloid precursor protein and the deposition of amyloid fibrils in multiple organs. Chemical and biophysical analysis of amyloid fibrils from human AL and murine AA amyloidosis reveal the same fibril morphologies in different tissues or organs of one patient or diseased animal. The observed structural similarities concerned the fibril morphology, the fibril protein primary and secondary structures, the presence of post-translational modifications and, in case of the AL fibrils, the partially folded characteristics of the polypeptide chain within the fibril. Our data imply for both analyzed forms of amyloidosis that the pathways of protein misfolding are systemically conserved; that is, they follow the same rules irrespective of where inside one body fibrils are formed or accumulated. Never break the chain: Polypeptide chains form the same amyloid fibril structures in different tissues of the same body, indicating that the pathways of protein misfolding are conserved in vivo.
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Sulfation of the Human Cytomegalovirus Protein UL22A Enhances Binding to the Chemokine RANTES ()
UL22A is an 83 amino acid chemokine-binding protein produced by human cytomegalovirus that likely assists the virus in dampening the host antiviral response. We proposed that UL22A is sulfated on two tyrosine residues and tested this hypothesis through the chemical synthesis of a small library of differentially sulfated protein variants. The (sulfo)proteins were efficiently prepared using a novel β-selenoleucine motif to facilitate one-pot ligation–deselenization chemistry. Tyrosine sulfation of UL22A proved critical for RANTES binding, with the doubly sulfated variant exhibiting an improvement in binding of 2.5 orders of magnitude compared to the unmodified protein. Modifications matter: The chemokine-binding protein UL22A was predicted to be post-translationally sulfated on two tyrosine residues. A library of sulfated UL22A proteins was constructed through a one-pot synthesis using a novel β-selenoleucine-mediated peptide ligation reaction followed by deselenization chemistry. Binding experiments showed that sulfation of the tyrosine residues substantially enhances the binding affinity for the chemokine RANTES.
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Structure and Biosynthesis of Crocagins: Polycyclic Postranslationally Modified Ribosomal Peptides from Chondromyces crocatus ()
Secondary metabolome mining efforts in the myxobacterial multiproducer of natural products, Chondromyces crocatus Cm c5, resulted in the isolation and structure elucidation of crocagins, which are novel polycyclic peptides containing a tetrahydropyrrolo[2,3-b]indole core. The gene cluster was identified through an approach combining genome analysis, targeted gene inactivation in the producer, and in vitro experiments. Based on our findings, we developed a biosynthetic scheme for crocagin biosynthesis. These natural products are formed from the three C-terminal amino acids of a precursor peptide and thus belong to a novel class of ribosomally synthesized and post-translationally modified peptides (RiPPs). We demonstrate that crocagin A binds to the carbon storage regulator protein CsrA, thereby inhibiting the ability of CsrA to bind to its cognate RNA target. Ribosomally synthesized and post-translationally modified peptides (RiPPs) were isolated from a myxobacterial producer. The unusual tetracyclic peptide scaffold of these crocagins turned out to originate from a ribosomally assembled precursor peptide. Isolation, structure elucidation, mutagenesis of the producer, and in vitro experiments are presented.
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Total Synthesis of (±)-Corymine ()
The first total synthesis of the hexacyclic indole alkaloid (±)-corymine is described. Starting from the readily available N-protected tryptamine, the title compound was achieved in 21 steps in 3.4 % overall yield. Key steps of the synthesis include: a) the addition of a malonate to a 3-bromooxindole to afford 3,3-disubstituted oxindole, b) the formation of a 12-membered cyclic enol ether by intramolecular O-propargylation, immediately followed by propargyl Claisen rearrangement to provide the α-allenyl ketone stereospecifically, c) DMDO oxidation to install a hydroxy group in a highly stereoselective manner, and d) the SmI2-mediated reductive C−O bond cleavage to remove the α-keto carboxyl group. To the cor(ymine): The first total synthesis of (±)-corymine has been accomplished in 21 steps starting from N-nosyl-protected tryptamine. The synthesis features the intramolecular O-propargylation to generate a 12-membered cyclic enol ether, and subsequent propargyl Claisen rearrangement to provide, stereospecifically, the corresponding 3-vinylideneazocane as a key intermediate.
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Enantioselective Dearomative Difunctionalization of Indoles by Palladium-Catalyzed Heck/Sonogashira Sequence ()
Palladium-catalyzed enantioselective dearomative arylalkynylation of N-substituted indoles, through a Heck/Sonogashira sequence, was established using a new BINOL-based phosphoramidite as the chiral ligand. A wide range of 2,3-disubstituted indolines, bearing vicinal quaternary and tertiary stereocenters, were efficiently constructed in one step with excellent enantioselectivities (up to 97 % ee) and diastereoselectivities (>20:1). Double the function: A highly enantioselective dearomative arylalkynylation of N-substituted indoles with alkynes has been established by using palladium and a BINOL-based phosphoramidite as the chiral ligand. A wide range of 2,3-disubstituted indolines, bearing vicinal tertiary and quaternary stereocenters, were constructed in one step with excellent enantio- and diastereoselectivities.
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An Unsaturated Quinolone N-Oxide of Pseudomonas aeruginosa Modulates Growth and Virulence of Staphylococcus aureus ()
Chemical interactions of competing bacteria have major implications for health and disease of their human host. In their Communication (DOI: 10.1002/anie.201702944), D. Szamosvári and T. Böttcher report an unsaturated quinolone N-oxide produced by Pseudomonas aeruginosa with unprecedented efficacy and activity against Staphylococcus aureus affecting both growth and virulence. These results provide insight into a major metabolite by which P. aeruginosa modulates growth and behavior of its competitors.
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Total Synthesis of Aplydactone by a Conformationally Controlled C−H Functionalization ()
A concise, protecting-group-free total synthesis of the unusual brominated sesquiterpene aplydactone is described. Our synthesis features a [2+2] photocycloaddition, a Wolff ring contraction, an unusual remote C−H functionalization to establish the highly strained tetracyclic core, and a hydrogen-atom transfer (HAT) reaction to access the bromine-containing stereocenter. A finely tuned conformation of the α-diazoketone precursor is the key for the success of the late-stage transannular C−H insertion to deliver a bridged six-membered ring and a quaternary stereocenter (C6) between two quaternary carbon atoms (C1 and C7). HAT in hand: A concise, protecting-group-free total synthesis of aplydactone has been achieved. The synthesis features a transannular six-membered-ring C−H insertion and a hydrogen atom transfer (HAT) reaction. A finely tuned conformation, as supported by theoretical calculations, is key to the success of the challenging C−H insertion.
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Modified Tetrathiafulvalene as an Organic Conductor for Improving Performances of Li−O2 Batteries ()
Large over-potentials owing to the sluggish kinetics of battery reactions have always been the drawbacks of Li−O2 batteries, which lead to short cycle life. Although redox mediators have been intensively investigated to overcome this issue, side-reactions are generally induced by the solvated nature of redox mediators. Herein, we report an alternative method to achieve more efficient utilization of tetrathiafulvalene (TTF) in Li−O2 batteries. By coordinating TTF+ with LiCl during charging, an organic conductor TTF+Clx− precipitate covers Li2O2 to provide an additional electron-transfer pathway on the surface, which can significantly reduce the charge over-potential, improve the energy efficiency of Li−O2 batteries, and eliminate side-reactions between the lithium metal anode and TTF+. When a porous graphene electrode is used, the Li−O2 battery combined with TTF and LiCl shows an outstanding performance and prolonged cycle life. A pinch of salt: TTF+Clx− precipitates on the surface of the Li2O2 discharge product upon the addition of LiCl to tetrathiafulvalene-containing electrolytes during charging. This efficiently reduces the risk of side-reactions and enhances the cycling performances of Li−O2 batteries.
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Rapid Production of High-Purity Hydrogen Fuel through Microwave-Promoted Deep Catalytic Dehydrogenation of Liquid Alkanes with Abundant Metals ()
Hydrogen as an energy carrier promises a sustainable energy revolution. However, one of the greatest challenges for any future hydrogen economy is the necessity for large scale hydrogen production not involving concurrent CO2 production. The high intrinsic hydrogen content of liquid-range alkane hydrocarbons (including diesel) offers a potential route to CO2-free hydrogen production through their catalytic deep dehydrogenation. We report here a means of rapidly liberating high-purity hydrogen by microwave-promoted catalytic dehydrogenation of liquid alkanes using Fe and Ni particles supported on silicon carbide. A H2 production selectivity from all evolved gases of some 98 %, is achieved with less than a fraction of a percent of adventitious CO and CO2. The major co-product is solid, elemental carbon. Stop CO2! Microwave-promoted, catalytic deep dehydrogenation of liquid alkanes using the abundant metals iron and nickel as catalysts produces CO2-free hydrogen, signaling a route to the decarbonization of fossil fuels.
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Biocatalytic Friedel–Crafts Acylation and Fries Reaction ()
The Friedel–Crafts acylation is commonly used for the synthesis of aryl ketones, and a biocatalytic version, which may benefit from the chemo- and regioselectivity of enzymes, has not yet been introduced. Described here is a bacterial acyltransferase which can catalyze Friedel–Crafts C-acylation of phenolic substrates in buffer without the need of CoA-activated reagents. Conversions reach up to >99 %, and various C- or O-acyl donors, such as DAPG or isopropenyl acetate, are accepted by this enzyme. Furthermore the enzyme enables a Fries-like rearrangement reaction of resorcinol derivatives. These findings open an avenue for the development of alternative and selective C−C bond formation methods. Order up on Fries: The biocatalytic acylation of resorcinol substrates, catalyzed by an acyltransferase, leads to C-acylated products. The Friedel–Crafts bio-C-acylation allows use of simple activated esters, such as isopropenyl acetate, as an acyl source. Additionally the enzyme enables a Fries-like rearrangement reaction.
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Facile Access to NaOC≡As and Its Use as an Arsenic Source to Form Germylidenylarsinidene Complexes ()
A facile, one-pot synthesis of [Na(OC≡As)(dioxane)x] (x=2.3–3.3) in 78 % yield is reported through the reaction of arsine gas with dimethylcarbonate in the presence of NaOtBu and 1,4-dioxane. It has been employed for the synthesis of the first arsaketenyl-functionalized germylene [LGeAsCO] (2, L=CH[CMeN(Dipp)]2; Dipp=2,6-iPr2C6H3) from the reaction with LGeCl (1). Upon exposure to ambient light, 2 undergoes CO elimination to form the 1,3-digerma-2,4-diarsacyclobutadiene [L2Ge2As2] (3), which contains a symmetric Ge2As2 ring with ylide-like Ge=As bonds. Remarkably, the CO ligand located at the arsenic center of 2 can be exchanged with PPh3 or an N-heterocyclic carbene iPrNHC donor (iPrNHC=1,3-diisopropyl-4,5-dimethylimidazol-2-ylidene) to afford the novel germylidenylarsinidene complexes [LGe-AsPPh3] (4) and [LGe-As(iPrNHC)] (5), respectively, demonstrating transition-metal-like ligand substitution at the arsinidene-like As atom. The formation of 2–5 and their electronic structures have been studied by DFT calculations. Germanium meets arsenic: A convenient, one-pot synthesis of Na(OC≡As) starts from arsine as an arsenic source. This reagent reacts straightforwardly with a chloro-β-diketiminato germylene to form the first arsaketenyl-functionalized germylene 1. Compound 1 undergoes CO release to afford, via the arsagermyne intermediate 2, the unprecedented isolable 1,3-digerma-2,4-diarsacyclobutadiene 3 with ylide-like Ge=As bonds.
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Self-Optimization of the Active Site of Molybdenum Disulfide by an Irreversible Phase Transition during Photocatalytic Hydrogen Evolution ()
The metallic 1T-MoS2 has attracted considerable attention as an effective catalyst for hydrogen evolution reactions (HERs). However, the fundamental mechanism about the catalytic activity of 1T-MoS2 and the associated phase evolution remain elusive and controversial. Herein, we prepared the most stable 1T-MoS2 by hydrothermal exfoliation of MoS2 nanosheets vertically rooted into rigid one-dimensional TiO2 nanofibers. The 1T-MoS2 can keep highly stable over one year, presenting an ideal model system for investigating the HER catalytic activities as a function of the phase evolution. Both experimental studies and theoretical calculations suggest that 1T phase can be irreversibly transformed into a more active 1T′ phase as true active sites in photocatalytic HERs, resulting in a “catalytic site self-optimization”. Hydrogen atom adsorption is the major driving force for this phase transition. An irreversible phase transition of MoS2 during the photocatalytic hydrogen evolution was decrypted. Hydrogen atom adsorption is the driving force for this phase transition. The distorted structure could be stabilized by both strain and S vacancies. This phase-transition-induced catalytic activity improvement was defined as a “self-optimization” mechanism.
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Chain Multiplication of Fatty Acids to Precise Telechelic Polyethylene ()
Starting from common monounsaturated fatty acids, a strategy is revealed that provides ultra-long aliphatic α,ω-difunctional building blocks by a sequence of two scalable catalytic steps that virtually double the chain length of the starting materials. The central double bond of the α,ω-dicarboxylic fatty acid self-metathesis products is shifted selectively to the statistically much-disfavored α,β-position in a catalytic dynamic isomerizing crystallization approach. “Chain doubling” by a subsequent catalytic olefin metathesis step, which overcomes the low reactivity of this substrates by using waste internal olefins as recyclable co-reagents, yields ultra-long-chain α,ω-difunctional building blocks of a precise chain length, as demonstrated up to a C48 chain. The unique nature of these structures is reflected by unrivaled melting points (Tm=120 °C) of aliphatic polyesters generated from these telechelic monomers, and by their self-assembly to polyethylene-like single crystals. Double the fun: Common monounsaturated fatty acids are used to provide ultra-long aliphatic α,ω-difunctional building blocks of precise chain length. A sequence of two scalable catalytic steps (isomerization and “chain doubling”) virtually double the chain length of the starting materials.
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Construction of Chiral Tetrahydro-β-Carbolines: Asymmetric Pictet–Spengler Reaction of Indolyl Dihydropyridines ()
A highly efficient synthesis of the enantioenriched tetrahydro-β-carbolines was developed by using a chiral phosphoric acid catalyzed Pictet–Spengler reaction of indolyl dihydropyridines. The reaction proceeds under mild reaction conditions to afford the desired chiral tetrahydro-β-carbolines in good to excellent yields (up to 96 %) and high enantioselectivities (up to 99 % ee). With this method, a formal synthesis of tangutorine and a total synthesis of deplancheine were achieved in a highly efficient manner. New twist, old reaction: A highly efficient synthesis of the enantioenriched title compounds was developed by using a chiral phosphoric acid (CPA) catalyzed Pictet–Spengler reaction of indolyl dihydropyridines. The reaction proceeds under mild reaction conditions to afford the desired chiral tetrahydro-β-carbolines in good to excellent yields and high enantioselectivities. The method was used in the formal synthesis of tangutorine and a total synthesis of deplancheine.
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Base-Selective Five- versus Six-Membered Ring Annulation in Palladium-Catalyzed C–C Coupling Cascade Reactions: New Access to Electron-Poor Polycyclic Aromatic Dicarboximides ()
Palladium-catalyzed base-selective annulation of dibromonaphthalimide to different aryl boronate esters by combined Suzuki–Miyaura cross-coupling and direct C−H arylation afforded a series of new five- and six-membered ring annulated electron-poor polycyclic aromatic hydrocarbons. Cesium carbonate (Cs2CO3) as auxiliary base in these C−C coupling cascade reactions led exclusively to six-membered ring annulation, while the use of organic base diazabicycloundecene (DBU) afforded the corresponding five-membered ring annulated products. This base-dependent selective mode of annulation is attributed to different mechanistic pathways directed by the applied base. The selective annulation was revealed by single crystal X-ray analysis of the respective five- and six-membered ring annulated products. The optical and redox properties of the new polycyclic aromatic dicarboximides were characterized by UV/Vis absorption and fluorescence spectroscopy and cyclic voltammetry. Polycycles: Depending on the auxiliary bases applied in Pd-catalyzed C−C coupling reactions electron-poor polycyclic aromatic hydrocarbons are obtained by selective five- or six-membered ring annulation.
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Carbon Monoxide Dehydrogenase Reduces Cyanate to Cyanide ()
The biocatalytic function of carbon monoxide dehydrogenase (CODH) has a high environmental relevance owing to its ability to reduce CO2. Despite numerous studies on CODH over the past decades, its catalytic mechanism is not yet fully understood. In the present combined spectroscopic and theoretical study, we report first evidences for a cyanate (NCO−) to cyanide (CN−) reduction at the C-cluster. The adduct remains bound to the catalytic center to form the so-called CN−-inhibited state. Notably, this conversion does not occur in crystals of the Carboxydothermus hydrogenoformans CODH enzyme (CODHIICh), as indicated by the lack of the corresponding CN− stretching mode. The transformation of NCO−, which also acts as an inhibitor of the two-electron-reduced Cred2 state of CODH, could thus mimic CO2 turnover and open new perspectives for elucidation of the detailed catalytic mechanism of CODH. Take-O-way: By combining spectroscopic and theoretical studies, the C-cluster of carbon monoxide dehydrogenase (CODH) was found to catalyze the reduction of cyanate to cyanide. The adduct remains bound to the catalytic center to form the so-called CN−-inhibited state. The transformation of NCO− could thus mimic CO2 turnover and open new perspectives for elucidation of the detailed catalytic mechanism of CODH.
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Unexpected Direct Synthesis of N-Vinyl Amides through Vinyl Azide–Enolate [3+2] Cycloaddition ()
The unexpected synthesis of industrially important N-vinyl amides directly from aldehydes and α,β-unsaturated N-vinyl amides from esters is reported. This reaction probably proceeds through an initial [3+2] azide–enolate cycloaddition involving a vinyl azide generated in situ. A survey of the reaction scope and preliminary mechanistic findings supported by quantum computational analysis are reported, with implications for the future development of atom-efficient amide synthesis. Intriguingly, this study suggests that (cautious) reevaluation of azidoethene as a synthetic reagent may be warranted. Worth another look: Industrially important N-vinyl amides were synthesized directly from aldehydes/esters and 1-azido-2-iodoethane. Quantum-chemical calculations support the proposed mechanism involving [3+2] cycloaddition of the enolate derived from the aldehyde or ester with a vinyl azide generated in situ (see scheme). The results suggest that azidoethene itself may be worth (cautious) reevaluation as an atom-efficient synthetic reagent.
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High-Fidelity, Narcissistic Self-Sorting in the Synthesis of Organometallic Assemblies from Poly-NHC Ligands ()
Highly selective, narcissistic self-sorting has been observed in the one-pot synthesis of three organometallic molecular cylinders of type [M3{L-(NHC)3}2](PF6)3 (M=Ag+, Au+; L=1,3,5-benzene, triphenylamine, or 1,3,5-triphenylbenzene) from L-(NHC)3 and silver(I) or gold(I) ions. The molecular cylinders contain only one type of tris-NHC ligand with no crossover products detectable. Transmetalation of the tris-NHC ligands from Ag+ to Au+ in a one-pot reaction with retention of the supramolecular structures is also demonstrated. High-fidelity self-sorting was also observed in the one-pot reaction of benzene-bridged tris-NHC and tetrakis-NHC ligands with Ag2O. This study for the first time extends narcissistic self-sorting in metal–ligand interactions from Werner-type complexes to organometallic derivatives. Perfect sorting! Unique narcissistic self-sorting has been observed in the one-pot reaction of three different trigonal trisimidazolium salts with Ag2O. Only three cylinder-like trinuclear complexes each bearing two identical tris-NHC ligands were obtained from this reaction. Self-sorting was also observed in the subsequent transmetalation of the tris-NHC ligands from the three silver(I) complexes to give three gold(I) complexes.
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Unprecedented Carbon Signal Enhancement in Liquid-State NMR Spectroscopy ()
We shall overcome: As a result of efforts to overcome the sensitivity challenge of liquid-state NMR spectroscopy, a thousand-fold signal enhancement was achieved by dynamic nuclear polarization (DNP) for 13C signals at high magnetic field (3.4 T) and room temperature, thereby exceeding the predicted limitations of high-field liquid-state in situ DNP.
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Self-Assembly of Conjugated Metallopolymers with Tunable Length and Controlled Regiochemistry ()
Self-assembled materials can be designed to express useful optoelectronic properties; however, achieving structural control is a necessary precondition for the optimization of desired properties. Here we report a simple, metal-templated polymerization process that generates helical metallopolymer strands over 75 repeat units long (28 kDa) from a single bifunctional monomer and CuI. The resulting polymer consists of a double helix of two identical conjugated organic strands enclosing a central column of metal ions. The length of this metallopolymer can be controlled by adding monofunctional subcomponents to end-cap the conjugated ligands. The use of ditopic and bulky monotopic subcomponents, respectively, allows a head-to-head or head-to-tail double helix to be generated. Spectroscopic measurements of different polymer lengths demonstrate how control over polymer length leads to control over the electronic and luminescent properties of the resulting material, thereby enabling tunable white-light emission. Polymers with a twist: The self-assembly of bifunctional subcomponents around CuI to yield long, double helical metallopolymers is reported. Terminating groups are employed that govern the regiochemistry of the two strands within the polymer. Varying the stoichiometry of monomer to terminating group alters the polymer length, thereby enabling tunable white-light emission.
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Mild, Redox-Neutral Formylation of Aryl Chlorides through the Photocatalytic Generation of Chlorine Radicals ()
We report a redox-neutral formylation of aryl chlorides that proceeds through selective 2-functionalization of 1,3-dioxolane through nickel and photoredox catalysis. This scalable benchtop approach provides a distinct advantage over traditional reductive carbonylation in that no carbon monoxide, pressurized gas, or stoichiometric reductant is employed. The mild conditions give unprecedented scope from abundant and complex aryl chloride starting materials. Born to be mild: Aromatic aldehydes are generated from abundant aryl chlorides through nickel-photocatalyzed C−H functionalization of the inexpensive solvent 1,3-dioxolane. The mild conditions and absence of pressurized carbon monoxide or stoichiometric reductant lead to broad functional-group tolerance and scope.
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Morphological Control of Heteroleptic cis- and trans-Pd2L2L′2 Cages ()
Control over the integrative self-sorting of metallo-supramolecular assemblies opens up possibilities for introducing increased complexity and function into a single self-assembled architecture. Herein, the relationship between the geometry of three ligand components and morphology of three self-sorted heteroleptic [Pd2L2L′2]4+ cages is examined. Pd-mediated assembly of two bis-monodentate pyridyl ligands with native bite angles of 75° and 120° affords a cis-[Pd2L2L′2]4+ cage while the same reaction with two ligands with bite angles of 75° and 60° gives an unprecedented, self-penetrating structural motif; a trans-[Pd2(anti-L)2L′2]4+ heteroleptic cage with a “doubly bridged figure eight” topology. Each heteroleptic assembly can be formed by cage-to-cage conversion of the homoleptic precursors and morphological control of [Pd2L2L′2] cages is achieved by selective ligand displacement transformations in a system of three ligands and at least six possible cage products. A doubly bridged figure eight: Integrative self-sorting of geometrically distinct ligands and cages is regulated to form new [Pd2L2L′2] structures. For one example, X-ray analysis reveals a doubly bridged figure-eight topology which is an unprecedented motif for metallo-supramolecular structures. Furthermore, morphological control of a system of cages is achieved by highly selective ligand displacement transformations.
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A Structurally Characterized Fluoroalkyne ()
The facile synthesis of a stable and isolable compound with a fluoroalkynyl group, M−C≡CF, is reported. Reaction of [Ru(C≡CH)(η5-C5Me5)(dppe)] with an electrophilic fluorinating agent (NFSI) results in the formation of the fluorovinylidene complex [Ru(=C=CHF)(η5-C5Me5)(dppe)][N(SO2Ph)2]. Subsequent deprotonation with LiN(SiMe3)2 affords the fluoroalkynyl complex [Ru(C≡CF)(η5-C5Me5)(dppe)]. In marked contrast to the rare and highly reactive examples of fluoroalkynes that have been reported previously, this compound can be readily isolated and structurally characterized. This has allowed the structure and bonding in the CCF motif to be explored. Further electrophilic fluorination of this species yields the difluorovinylidene complex [Ru(C=CF2)(η5-C5Me5)(dppe)][N(SO2Ph)2]. Fancy a fluorine? In contrast to other fluorinated alkynes, structurally characterized {M−C≡CF} exhibits considerable long-term stability. Structural, spectroscopic and computational analyses reveal that this longevity is underpinned by kinetic stabilization by a half-sandwich ruthenium substituent. Subsequent fluorination provides facile access to a rare example of a difluorovinylidene complex.
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A Membrane-Free Neutral pH Formate Fuel Cell Enabled by a Selective Nickel Sulfide Oxygen Reduction Catalyst ()
Polymer electrolyte membranes employed in contemporary fuel cells severely limit device design and restrict catalyst choice, but are essential for preventing short-circuiting reactions at unselective anode and cathode catalysts. Herein, we report that nickel sulfide Ni3S2 is a highly selective catalyst for the oxygen reduction reaction in the presence of 1.0 m formate. We combine this selective cathode with a carbon-supported palladium (Pd/C) anode to establish a membrane-free, room-temperature formate fuel cell that operates under benign neutral pH conditions. Proof-of-concept cells display open circuit voltages of approximately 0.7 V and peak power values greater than 1 mW cm−2, significantly outperforming the identical device employing an unselective platinum (Pt) cathode. The work establishes the power of selective catalysis to enable versatile membrane-free fuel cells. A highly selective catalyst: Nickel sulfide (Ni3S2) selectively catalyzes the oxygen reduction reaction (ORR) in the presence of 1.0 m formate, enabling a membrane-free formate fuel cell that operates under benign neutral pH conditions. The Ni3S2–Pd fuel cell achieves higher open circuit voltage and power density than a Pt–Pd configuration.
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Direct Nucleophilic Substitution Reaction of Cage B−H Bonds by Grignard Reagents: A Route to Regioselective B4-Alkylation of o-Carboranes ()
Direct nucleophilic substitution reaction of cage B−H bonds of o-carboranes by Grignard reagents in the absence of any transition metals has been achieved for the first time, and leads to the regioselective synthesis of a series of 4-alkyl-1,2-diaryl-o-carboranes in very high yields. The presence of two electron-withdrawing aryl groups on the cage carbon atoms is crucial to realizing the reaction. The regioselectivity is controlled by both electronic and steric factors. This work represents a new strategy for the development of methods for carborane functionalization. Rattled cage: The title reaction proceeds in the absence of transition metals and leads to 4-alkyl-1,2-diaryl-o-carboranes in high yields. The presence of two electron-withdrawing aryl groups on the cage carbon atoms is crucial for the reaction, and the regioselectivity is controlled by both electronic and steric factors.
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Luminescence, Plasmonic, and Magnetic Properties of Doped Semiconductor Nanocrystals ()
Introducing a few atoms of impurities or dopants in semiconductor nanocrystals can drastically alter the existing properties or even introduce new properties. For example, mid-gap states created by doping tremendously affect photocatalytic activities and surface controlled redox reactions, generate new emission centers, show thermometric optical switching, make FRET donors by enhancing the excited state lifetime, and also create localized surface plasmon resonance induced low energy absorption. In addition, researchers have more recently started focusing their attention on doped nanocrystals as an important and alternative material for solar energy conversion to meet the current demand for renewable energy. Moreover, the electrical and magnetic properties of the host are also strongly altered on doping. These beneficial dopant-induced changes suggest that doped nanocrystals with proper selections of dopant–host pairs may be helpful for generating designer materials for a wide range of current technological needs. How properties relate to the doping of a variety of semiconductor nanocrystals are summarized in this Review. Doping control: Doping semiconductor nanocrystals combines properties of both the dopant ion and the quantum confinement effect of the nanocrystal. This Review presents recent advances in synthesis, luminescence, photocatalysis, photovoltaic, plasmonic, magnetic, and magneto-optic properties of doped semiconductor nanocrystals.
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Antivitamin B12 Inhibition of the Human B12-Processing Enzyme CblC: Crystal Structure of an Inactive Ternary Complex with Glutathione as the Cosubstrate ()
B12 antivitamins are important and robust tools for investigating the biological roles of vitamin B12. Here, the potential antivitamin B12 2,4-difluorophenylethynylcobalamin (F2PhEtyCbl) was prepared, and its 3D structure was studied in solution and in the crystal. Chemically inert F2PhEtyCbl resisted thermolysis of its Co−C bond at 100 °C, was stable in bright daylight, and also remained intact upon prolonged storage in aqueous solution at room temperature. It binds to the human B12-processing enzyme CblC with high affinity (KD=130 nm) in the presence of the cosubstrate glutathione (GSH). F2PhEtyCbl withstood tailoring by CblC, and it also stabilized the ternary complex with GSH. The crystal structure of this inactivated assembly provides first insight into the binding interactions between an antivitamin B12 and CblC, as well as into the organization of GSH and a base-off cobalamin in the active site of this enzyme. Antivitamins in action: A new, chemically robust antivitamin B12 was used for biochemical analysis of the inhibition of CblC, the key B12-processing enzyme of humans. The crystal structure of the inactive enzyme complex provides detailed insight into CblC loaded with a cobalamin and its cosubstrate glutathione.
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Gold-Catalyzed Cadiot–Chodkiewicz-Type Cross-Coupling of Terminal Alkynes with Alkynyl Hypervalent Iodine Reagents: Highly Selective Synthesis of Unsymmetrical 1,3-Diynes ()
A new and efficient method for the synthesis of unsymmetrical 1,3-butadiynes by gold-catalyzed C(sp)–C(sp) cross-coupling of terminal alkynes with alkynyl hypervalent iodine(III) reagents has been developed. The reaction features high selectivity and efficiency, mild reaction conditions, wide substrate scope, and functional-group compatibility, and is a highly attractive complement to existing methods. Mechanistic studies reveal that formation of a phenanthrolinyl-ligated gold(I) complex is crucial for the efficiency and selectivity of the target transformation. All the hype: A new method for the title reaction has been developed. The reaction features high selectivity and efficiency, mild reaction conditions, wide substrate scope, and functional-group compatibility. Mechanistic studies reveal that the formation of a phenanthrolinyl-ligated gold(I) complex is crucial for the efficiency and selectivity of the target transformation.
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A Modular Flow Design for the meta-Selective C−H Arylation of Anilines ()
Described herein is an effective and practical modular flow design for the meta-selective C−H arylation of anilines. The design consists of four continuous-flow modules (i.e., diaryliodonium salt synthesis, meta-selective C−H arylation, inline copper extraction, and aniline deprotection) which can be operated either individually or consecutively to provide direct access to meta-arylated anilines. With a total residence time of 1 hour, the desired product could be obtained in high yield and excellent purity without the need for column chromatography, and the residual copper content meets the standards for parenterally administered pharmaceutical substances. One by one or all in one: meta-Arylated anilines are key moieties in a variety of high-value chemicals. To access these compounds, four key flow steps were identified, including synthesis of the diaryliodonium salt, meta-selective C−H arylation, and the removal of both the copper catalyst and the directing group. Each module has great individual potential, however, combining them allowed straightforward access to meta-arylated anilines within a reasonable time scale and with good purity.
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Discovery of EGF Receptor Inhibitors that are Selective for the d746-750/T790M/C797S Mutant through Structure-Based de Novo Design ()
Next-generation epidermal growth factor receptor (EGFR) inhibitors against the d746-750/T790M/C797S mutation were discovered through two-track virtual screening and de novo design. A number of nanomolar inhibitors were identified using 2-aryl-4-aminoquinazoline as the molecular core and the modified binding energy function involving a proper dehydration term, which provides important structural insight into the key principles for high inhibitory activities against the d746-750/T790M/C797S mutant. Furthermore, some of these EGFR inhibitors showed a greater than 1000-fold selectivity for the d746-750/T790M/C797S mutant over the wild type, as well as nanomolar activity against the mutant. Mutant selective: Next-generation epidermal growth factor receptor (EGFR) inhibitors against the d746-750/T790M/C797S mutation were discovered through two-track virtual screening and de novo design. A number of nanomolar 2-aryl-4-aminoquinazoline-based inhibitors exhibited more than 1000-fold selectivity for the triple mutant over the wild type. High inhibitory activity was achieved by strengthening the interactions in the ATP-binding site.
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Catalytic Asymmetric [3+1]-Cycloaddition Reaction of Ylides with Electrophilic Metallo-enolcarbene Intermediates ()
The first asymmetric [3+1]-cycloaddition was successfully achieved by copper(I) triflate/double-sidearmed bisoxazoline complex catalyzed reactions of β-triisopropylsilyl-substituted enoldiazo compounds with sulfur ylides. This methodology delivered a series of chiral cyclobutenes in good yields with high enantio- and diastereoselectivities (up to 99 % ee, and >20:1 d.r.). Additionally, the [3+1]-cycloaddition of catalytically generated metallo-enolcarbenes was successfully extended to reaction with a stable benzylidene dichlororuthenium complex. Three plus one: β-Triisopropylsilyl-substituted enoldiazo compounds react with sulfur ylides in a [3+1]-cycloaddition reaction catalyzed by copper(I) triflate/double-sidearmed bisoxazoline complex (see figure) to give cyclobutenes. The asymmetric version proceeds in good yield with high enantio- and diastereoselectivity.
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Redox-Sensitive Stomatocyte Nanomotors: Destruction and Drug Release in the Presence of Glutathione ()
The development of artificial nanomotor systems that are stimuli-responsive is still posing many challenges. Herein, we demonstrate the self-assembly of a redox-responsive stomatocyte nanomotor system, which can be used for triggered drug release under biological reducing conditions. The redox sensitivity was introduced by incorporating a disulfide bridge between the hydrophilic poly(ethylene glycol) block and the hydrophobic polystyrene block. When incubated with the endogenous reducing agent glutathione at a concentration comparable to that within cells, the external PEG shells of these stimuli-responsive nanomotors are cleaved. The specific bowl-shaped stomatocytes aggregate after the treatment with glutathione, leading to the loss of motion and triggered drug release. These novel redox-responsive nanomotors can not only be used for remote transport but also for drug delivery, which is promising for future biomedical applications. Destruction on demand: A redox-responsive stomatocyte nanomotor was developed by incorporating disulfide bridges between the hydrophilic PEG and hydrophobic PS moieties of the copolymer. When incubated in vitro with the endogenous reducing agent glutathione, the external PEG shells of the nanomotors are cleaved, which results in the loss of motion and can be used for drug release.
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Oxidative Neutralization of Mustard-Gas Simulants in an On-Board Flow Device with In-Line NMR Monitoring ()
The fast and effective neutralization of the mustard-gas simulant 2-chloroethyl ethyl sulfide (CEES) using a simple and portable continuous flow device is reported. Neutralization takes place through a fully selective sulfoxidation by a stable source of hydrogen peroxide (alcoholic solution of urea–H2O2 adduct/MeSO3H freshly prepared). The reaction progress can be monitored with an in-line benchtop NMR spectrometer, allowing a real-time adjustment of reaction conditions. Inherent features of millireactors, that is, perfect control of mixing, heat and reaction time, allowed the neutralization of 25 g of pure CEES within 46 minutes in a 21.5 mL millireactor (tR=3.9 minutes). This device, which relies on affordable and nontoxic reagents, fits into a suitcase, and can be deployed by police/military forces directly on the attack site. Mustard-gas simulant 2-chloroethyl ethyl sulfide (CEES) was fully neutralized by selective oxidation to sulfoxide (CEESO) under continuous flow with in-line NMR monitoring. Pure CEES (25 g) has been converted almost completely into CEESO within 46 minutes in a 21.5 mL millireactor. This flow device is small enough to be moved by security forces and used directly on the site of a chemical threat.
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Observation of CH⋅⋅⋅π Interactions between Methyl and Carbonyl Groups in Proteins ()
Protein structure and function is dependent on myriad noncovalent interactions. Direct detection and characterization of these weak interactions in large biomolecules, such as proteins, is experimentally challenging. Herein, we report the first observation and measurement of long-range “through-space” scalar couplings between methyl and backbone carbonyl groups in proteins. These J couplings are indicative of the presence of noncovalent C−H⋅⋅⋅π hydrogen-bond-like interactions involving the amide π network. Experimentally detected scalar couplings were corroborated by a natural bond orbital analysis, which revealed the orbital nature of the interaction and the origins of the through-space J couplings. The experimental observation of this type of CH⋅⋅⋅π interaction adds a new dimension to the study of protein structure, function, and dynamics by NMR spectroscopy. Don't neglect the little ones: Solution NMR spectroscopy and DFT calculations showed the existence of weak, hydrogen-bond-like C−H⋅⋅⋅π interactions in proteins between methyl donor groups and peptide-bond acceptor groups (see picture). As large numbers of C−H⋅⋅⋅πCO interactions are present in proteins, they presumably make an important cumulative contribution to protein structure, dynamics, and function.
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Deprotonation of a Seemingly Hydridic Diborane(6) to Build a B−B Bond ()
Deprotonation of the doubly arylene-bridged diborane(6) derivative 1H2 with (Me3Si)3CLi or (Me3Si)2NK gives the B−B σ-bonded species M[1H] in essentially quantitative yields (THF, room temperature; M=Li, K, arylene=4,4′-di-tert-butyl-2,2′-biphenylylene). With nBuLi as the base, the yield of Li[1H] drops to 20 % and the 1,1-bis(9-borafluorenyl)butane Li[2H] is formed as a side product (30 %). In addition to the 1,1-butanediyl fragment, the two boron atoms of Li[2H] are linked by a μ-H bridge. In the closely related molecule Li[3H], the corresponding μ-H atom can be abstracted with (Me3Si)3CLi to afford the B−B-bonded conjugated base Li2[3] (THF, 150 °C; 15 %). Li[1H] and Li[2H] were characterized by NMR spectroscopy and X-ray crystallography. Fluid identity: A B−B bond was formed through the deprotonation of a doubly arylene-bridged diborane(6) derivative. The reaction shows that organoboranes are not necessarily hydridic and paves the way for new access routes to electron-precise diboranes.
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Methylammonium-Mediated Evolution of Mixed-Organic-Cation Perovskite Thin Films: A Dynamic Composition-Tuning Process ()
Methylammonium-mediated phase-evolution behavior of FA1−xMAxPbI3 mixed-organic-cation perovskite (MOCP) is studied. It is found that by simply enriching the MOCP precursor solutions with excess methylammonium cations, the MOCPs form via a dynamic composition-tuning process that is key to obtaining MOCP thin films with superior properties. This simple chemical approach addresses several key challenges, such as control over phase purity, uniformity, grain size, composition, etc., associated with the solution-growth of MOCP thin films with targeted compositions. Under control: FA1−xMAxPbI3 mixed-organic-cation iodide perovskite (MOCP) thin films have been synthesized. By simply enriching the precursor solutions with methylammonium cations, the MOCPs form via a dynamic composition-tuning process that is key to obtaining thin films with superior properties, exact composition, excellent uniformity, and extra-large grains.
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Biofunctional Microgel-Based Fertilizers for Controlled Foliar Delivery of Nutrients to Plants ()
Foliar application of micronutrients (e.g. Fe3+) onto plants over an extended time is challenging and often not possible due to insufficient rainfastness. Smart delivery systems which enable micronutrient release over several weeks would offer innovative and sustainable options to improve plant health and food production. Herein, we report a novel foliar fertilizer delivery system based on functional pH-responsive biohybrid microgels that have orthogonal functionality as carriers of micronutrients and employ peptides (termed anchor peptides) as foliar adhesion promoters. The anchor peptides bind to hydrophobic surfaces and the waxy “islands” of plant leaves. Our system requires no auxiliaries and is loadable, storable, and applicable from aqueous dispersion. We report the synthesis and functionalization of microgels, their loading with Fe3+ ions, and a proof of concept for the biofunctional microgel-based fertilizer system is demonstrated for iron-deficient cucumber plants. Gel nourished: Foliar application of micronutrients onto plants over an extended time offers sustainable options for plant health and food production. Novel biohybrid microgels modified with iron binding ligands and anchor peptides as foliar adhesion promoters can be employed as a micronutrients carrier system. A proof of concept is presented for iron-deficient cucumber plants.
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Elucidating the Role of Dissolution in CeO2 Nanoparticle Plant Uptake by Smart Radiolabeling ()
The identification of major uptake pathways in plants is an important factor when evaluating the fate of manufactured nanoparticles in the environment and the associated risks. Using different radiolabeling techniques we were able to show a predominantly particulate uptake for CeO2 nanoparticles in contrast to a possible uptake in the form of ionic cerium. Ce-ing and doing: Two radiolabeling techniques for CeO2 nanoparticles were developed which produce radiolabeled [139Ce]CeO2 nanoparticles with different activity release kinetics upon dissolution. Using these showed a predominantly particular uptake and translocation route of CeO2 along the water current in plants, with a slow dissolution inside the plant.
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A Long-Life Lithium–Air Battery in Ambient Air with a Polymer Electrolyte Containing a Redox Mediator ()
Lithium–air batteries when operated in ambient air generally exhibit poor reversibility and cyclability, because of the Li passivation and Li2O2/LiOH/Li2CO3 accumulation in the air electrode. Herein, we present a Li–air battery supported by a polymer electrolyte containing 0.05 m LiI, in which the polymer electrolyte efficiently alleviates the Li passivation induced by attacking air. Furthermore, it is demonstrated that I−/I2 conversion in polymer electrolyte acts as a redox mediator that facilitates electrochemical decomposition of the discharge products during recharge process. As a result, the Li–air battery can be stably cycled 400 times in ambient air (relative humidity of 15 %), which is much better than previous reports. The achievement offers a hope to develop the Li–air battery that can be operated in ambient air. An oxygen-breathing battery: A long-life lithium–air battery in ambient air was developed by using a gel polymer electrolyte containing the redox mediator I−/I2 (see picture). The polymer electrolyte and the redox mediator alleviate lithium passivation induced by attacking air and improve the charge–discharge efficiency of the battery.
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Non-Pincer-Type Manganese Complexes as Efficient Catalysts for the Hydrogenation of Esters ()
Ester reduction with manganese catalysis is enabled by balancing the reactivity of the Mn(I) species with simple bidentate P,N ligands and alkoxide base. In their Communication (http://doi.org/10.1002/anie.201701365), E. A. Pidko and co-workers report highly active Mn-based catalyst systems for selective ester hydrogenation. Their performance is the result of a delicate balance between the complex catalytic and deactivation paths, which depend on the choice of the solvent, base and the reaction conditions.
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Mechanical Deformation Accelerates Protein Ageing ()
A hallmark of tissue ageing is the irreversible oxidative modification of its proteins. We show that single proteins, kept unfolded and extended by a mechanical force, undergo accelerated ageing in times scales of minutes to days. A protein forced to be continuously unfolded completely loses its ability to contract by folding, becoming a labile polymer. Ageing rates vary among different proteins, but in all cases they lose their mechanical integrity. Random oxidative modification of cryptic side chains exposed by mechanical unfolding can be slowed by the addition of antioxidants such as ascorbic acid, or accelerated by oxidants. By contrast, proteins kept in the folded state and probed over week-long experiments show greatly reduced rates of ageing. We demonstrate a novel approach whereby protein ageing can be greatly accelerated: the constant unfolding of a protein for hours to days is equivalent to decades of exposure to free radicals under physiological conditions. Time will tell: Accelerated ageing occurs when a protein is held unfolded under force for long periods of time. Maintaining a protein extended for more 20 h blocks its ability to refold. This loss of folding contraction is triggered by the exposure of cryptic side chains to the oxidative environment, and can be greatly slowed by antioxidants. This kind of oxidative damage is a hallmark of the loss of tissue elasticity that occurs during ageing.
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An Aggregating Amphiphilic Squaraine: A Light-up Probe That Discriminates Parallel G-Quadruplexes ()
G-quadruplexes (G4s) are peculiar DNA or RNA tertiary structures that are involved in the regulation of many biological events within mammalian cells, bacteria, and viruses. Although their role as versatile therapeutic targets has been emphasized for 35 years, G4 selectivity over ubiquitous double-stranded DNA/RNA, as well as G4 differentiation by small molecules, still remains challenging. Here, a new amphiphilic dicyanovinyl-substituted squaraine, SQgl, is reported to act as an NIR fluorescent light-up probe discriminating an extensive panel of parallel G4s while it is non-fluorescent in the aggregated state. The squaraine can form an unconventional sandwich π-complex binding two quadruplexes, which leads to a strongly fluorescent (ΦF=0.61) supramolecular architecture. SQgl is highly selective against non-quadruplex and non-parallel G4 sequences without altering their topology, as desired for applications in selective in vivo high-resolution imaging and theranostics. In parallel: An amphiphilic squaraine that self-assembles into a non-fluorescent aggregated state in water has been designed as a near-infrared light-up probe with high selectivity for G-quadruplexes (G4s) with parallel topology. The strong fluorescence is based on the formation of an unconventional sandwich π-complex between the squaraine and two parallel G4s.
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Significant Enhancement of C2H2/C2H4 Separation by a Photochromic Diarylethene Unit: A Temperature- and Light-Responsive Separation Switch ()
Adjusting adsorption selectivity and separation in photochromic metal–organic frameworks (MOFs) just by external stimuli is highly important but still rare. In their Communication (http://doi.org/10.1002/anie.201702484), F. Luo, G.-C. Guo, and co-workers employ a photochromic diarylethene unit as a light-triggered selectivity and separation regulator, leading to ultrahigh adsorption selectivity and improvement in adsorption selectivity, for example for C2H2/C2H4.
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A Membrane-Free Neutral pH Formate Fuel Cell Enabled by a Selective Nickel Sulfide Oxygen Reduction Catalyst ()
A membrane-free fuel cell relies on the selectivity of catalysts at both the anode and the cathode. In their Communication (DOI: 10.1002/anie.201702578), Y. Surendranath et al. show that the sulfide N3S2 selectively catalyzes the oxygen reduction reaction (ORR) in the presence of a high concentration of formate. Paired with the known formate oxidation catalyst Pd/C the selective ORR catalyst Ni3S2 enables the construction of a membrane-free formate fuel cell that operates at neutral pH and outperforms the Pt–Pd device.
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Solution NMR Structure of a Ligand/Hybrid-2-G-Quadruplex Complex Reveals Rearrangements that Affect Ligand Binding ()
Telomeric G-quadruplexes have recently emerged as drug targets in cancer research. Herein, we present the first NMR structure of a telomeric DNA G-quadruplex that adopts the biologically relevant hybrid-2 conformation in a ligand-bound state. We solved the complex with a metalorganic gold(III) ligand that stabilizes G-quadruplexes. Analysis of the free and bound structures reveals structural changes in the capping region of the G-quadruplex. The ligand is sandwiched between one terminal G-tetrad and a flanking nucleotide. This complex structure involves a major structural rearrangement compared to the free G-quadruplex structure as observed for other G-quadruplexes in different conformations, invalidating simple docking approaches to ligand–G-quadruplex structure determination. Conformation matters: G-quadruplexes are emerging drug targets in cancer research. The first NMR structure determination of a telomeric DNA G-quadruplex in the hybrid-2 conformation in complex with a ligand is reported. The structure reveals major changes in the capping regions of the G-quadruplex, highlighting the importance of obtaining a ligand-bound structure to aid rational drug design.
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Arylative Intramolecular Allylation of Ketones with 1,3-Enynes Enabled by Catalytic Alkenyl-to-Allyl 1,4-Rhodium(I) Migration ()
Alkenyl-to-allyl 1,4-rhodium(I) migration enables the generation of nucleophilic allylrhodium(I) species by remote C−H activation. This new mode of reactivity was employed in the diastereoselective reaction of arylboron reagents with substrates containing a 1,3-enyne tethered to a ketone, to give products containing three contiguous stereocenters. The products can be obtained in high enantioselectivities using a chiral sulfur-alkene ligand. On the move: The title migration enables the generation of nucleophilic allylrhodium(I) species by remote C−H activation. This new mode of reactivity was employed in the diastereoselective reaction of arylboron reagents with substrates containing a 1,3-enyne tethered to a ketone, to give products containing three contiguous stereocenters. The products can be obtained in high enantioselectivities using a chiral sulfur-alkene ligand.
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Paul Hagenmuller ()
Paul Hagenmuller, honorary professor at the Université de Bordeaux, passed away at the age of 95 on January 7, 2017. Hagenmuller was one of the founders of solid-state chemistry at the interface between chemistry, physics, and material science, with contributions including high oxidation states in transition metal oxides, magnesium hydride for hydrogen-storage applications, and synthesis of copper perovskites.
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Cover Picture: Mo2B4O9—Connecting Borate and Metal-Cluster Chemistry (Angew. Chem. Int. Ed. 23/2017) ()
Two fields are united in Mo2B4O9, the first borate compound incorporating transition-metal clusters into its crystal structure. It thus constitutes the hitherto unknown interface between two previously separated fields of research—borate and metal cluster chemistry. In their Communication on page 6449 ff., H. Huppertz and co-workers show how the planned reduction of a reagent in a high-pressure experiment smoothed the way to this novel substance class.
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Inside Cover: Solvent-Assisted Metal Metathesis: A Highly Efficient and Versatile Route towards Synthetically Demanding Chromium Metal–Organic Frameworks (Angew. Chem. Int. Ed. 23/2017) ()
Owing to their extraordinary robustness and high porosity, chromium(III)-based metal–organic frameworks (Cr-MOFs) have great potential, but they are currently difficult to synthesize. In their Communication on page 6478 ff., J. H. Wang, X. M. Zhang et al. describe the preparation of a variety of Cr-MOFs from the corresponding Fe-MOFs under mild conditions by solvent-assisted metal metathesis. This efficient and versatile strategy constitutes a promising route for the synthesis of stable MOFs.
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Inside Back Cover: Synthesis and Bowl-in-Bowl Assembly of a Geodesic Phenylene Bowl (Angew. Chem. Int. Ed. 23/2017) ()
A carbon-rich geodesic dome has been synthesized by linking 20 trigonal planar 1,3,5-linked phenylenes through 25 biaryl linkages. H. Isobe et al. describe in their Communication on page 6511 ff. how the geodesic, corannulenoidal combination of one pentagon and five hexagons leads to the nanometer-sized bowl. Concave–convex molecular recognition results in the formation of a bowl-in-bowl dimer in both the crystalline state and in solution.
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Back Cover: Fluorophores for Excited-State Intramolecular Proton Transfer by an Yttrium Triflate Catalyzed Reaction of Isocyanides with Thiocarboxylic Acids (Angew. Chem. Int. Ed. 23/2017) ()
The one-pot synthesis of 5-amino-4-carboxamidothiazole molecules by the yttrium triflate catalyzed reaction of thiocarboxylic acids with isocyanides is reported by J. Zhu et al. in their Communication on page 6599 ff. The resulting heterocycles are novel prototypical structures for the double excited-state intramolecular proton transfer (ESIPT) process and could serve as templates for designing ESICT-to-ESIPT-coupled molecules (CT=charge transfer).
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Frontispiece: The Structure of the Elusive Simplest Dipeptide Gly-Gly ()
Dipeptide Structures In their Communication on page 6420 ff., J. L. Alonso et al. provide the first experimental information on the structure of the simplest dipeptide Gly-Gly by using laser ablation of solid samples combined with FT microwave spectroscopy in a supersonic expansion.
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Graphical Abstract: Angew. Chem. Int. Ed. 23/2017 ()

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Spotlights on our sister journals: Angew. Chem. Int. Ed. 23/2017 ()

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Makoto Yamashita ()
“I lose track of time when I am solving crystal structures. The most important thing I learned from my parents is optimism ...” This and more about Makoto Yamashita can be found on page 6372.
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IUAPC 2017 Distinguished Women in Chemistry or Chemical Engineering ()

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Gerd Becker (1940–2017) ()

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Oxidative Cross-Coupling Reactions. By Aiwen Lei, Wei Shi, Chao Liu, Wei Liu, Hua Zhang and Chuan He. ()
Wiley-VCH, Weinheim, 2016. 229 pp., hardcover, € 129.00.—ISBN 978-3527336883
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Hydronium Ion Batteries: A Sustainable Energy Storage Solution ()
Hydronium ions have been reversibly stored for the first time in an electrode of crystalline 3,4,9,10-perylenetetracarboxylic dianhydride (PTCDA). A highly reversible discharge–charge behavior of PTCDA was observed in an aqueous acidic electrolyte of 1 m H2SO4. The capacity and the operation potentials are comparable to that of Na-ion storage in the same electrode.
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On-Chip Microsupercapacitors Based on Coordination Polymer Frameworks for Alternating Current Line-Filtering ()
AC line-filtering on-chip micro-supercapacitors (MSCs) based on coordination polymer frameworks were fabricated by a facile layer-by-layer method. The reported on-chip MSCs showed a low impedance phase angle of −73° at 120 Hz and a high power density of up to 1323 W cm−3 with a low relaxation time constant of 0.27 ms.
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Transition-Metal-Catalyzed Utilization of Methanol as a C1 Source in Organic Synthesis ()
Methanol is used as a common solvent, cost-effective reagent, and sustainable feedstock for value-added chemicals, pharmaceuticals, and materials. Among the various applications, the utilization of methanol as a C1 source for the formation of carbon–carbon, carbon–nitrogen, and carbon–oxygen bonds continues to be important in organic synthesis and drug discovery. In particular, the synthesis of C-, N-, and O-methylated products is of central interest because these motifs are found in a large number of natural products as well as fine and bulk chemicals. In this Minireview, we summarize the utilization of methanol as a C1 source in methylation, methoxylation, formylation, methoxycarbonylation, and oxidative methyl ester formation reactions. Sustainable C1 source: Methanol serves as a sustainable feedstock for value-added chemicals, materials, and life science molecules. It has also been used as a C1 source in methylation, methoxylation, formylation, methoxycarbonylation, and oxidative methyl ester formation reactions for the synthesis of C-methylated products, N-methylamines, formamides, urea derivatives, ethers, esters, and heterocycles.
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Synthetic Biology—The Synthesis of Biology ()
Synthetic biology concerns the engineering of man-made living biomachines from standardized components that can perform predefined functions in a (self-)controlled manner. Different research strategies and interdisciplinary efforts are pursued to implement engineering principles to biology. The “top-down” strategy exploits nature's incredible diversity of existing, natural parts to construct synthetic compositions of genetic, metabolic, or signaling networks with predictable and controllable properties. This mainly application-driven approach results in living factories that produce drugs, biofuels, biomaterials, and fine chemicals, and results in living pills that are based on engineered cells with the capacity to autonomously detect and treat disease states in vivo. In contrast, the “bottom-up” strategy seeks to be independent of existing living systems by designing biological systems from scratch and synthesizing artificial biological entities not found in nature. This more knowledge-driven approach investigates the reconstruction of minimal biological systems that are capable of performing basic biological phenomena, such as self-organization, self-replication, and self-sustainability. Moreover, the syntheses of artificial biological units, such as synthetic nucleotides or amino acids, and their implementation into polymers inside living cells currently set the boundaries between natural and artificial biological systems. In particular, the in vitro design, synthesis, and transfer of complete genomes into host cells point to the future of synthetic biology: the creation of designer cells with tailored desirable properties for biomedicine and biotechnology. Exciting times for synthetic biology: Cells are being engineered to produce drugs and biofuels, entire genomes are being synthesized from scratch, proteins and DNA molecules are being equipped with unnatural functions, and recent progress in genome engineering promises to revolutionize biomedicine and biotechnology. This Review gives a comprehensive overview of different research areas in synthetic biology.
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The Structure of the Elusive Simplest Dipeptide Gly-Gly ()
Among the hundreds of peptide compounds for which conformations have been determined by using different spectroscopic techniques, the structure of the simplest dipeptide glycylglycine (Gly-Gly) is conspicuously absent. Herein, for the first time, solid samples of Gly-Gly have been vaporized by laser ablation and three different structures have been revealed in a supersonic expansion by Fourier transform microwave spectroscopy. The intramolecular hydrogen bonding interactions that stabilize the observed forms have been established based on the 14N nuclear quadrupole hyperfine structure. We have illustrated how conformer interconversion distorts the equilibrium conformational distribution, giving rise to missing conformers in the conformational landscape. Exposed! Structural secrets of Gly-Gly: The conformational landscape of the simplest dipeptide glycylglycine (Gly-Gly) has been unveiled for the first time by laser ablation coupled with Fourier transform microwave spectroscopy. The three identified conformers, along with those not observed because of conformer interconversion, provide the first global structural picture of Gly-Gly, which is, to some extent, dynamic.
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Elusive Terminal Copper Arylnitrene Intermediates ()
We report herein three new modes of reactivity between arylazides N3Ar with a bulky copper(I) β-diketiminate. Addition of N3ArX3 (ArX3=2,4,6-X3C6H2; X=Cl or Me) to [iPr2NN]Cu(NCMe) results in triazenido complexes from azide attack on the β-diketiminato backbone. Reaction of [iPr2NN]Cu(NCMe) with bulkier azides N3Ar leads to terminal nitrenes [iPr2NN]Cu]=NAr that dimerize via formation of a C−C bond at the arylnitrene p-position to give the dicopper(II) diketimide 4 (Ar=2,6-iPr2C6H3) or undergo nitrile insertion to give diazametallocyclobutene 8 (Ar=4-Ph-2,6-iPr2C6H2). Importantly, reactivity studies reveal both 4 and 8 to be “masked” forms of the terminal nitrenes [iPr2NN]Cu=NAr that undergo nitrene group transfer to PMe3, tBuNC, and even into a benzylic sp3 C−H bond of ethylbenzene. Attempts at isolating terminal arylnitrenes [Cu]=NAr result in a dicopper diketimide (see scheme, left) formed through reversible C−C coupling at the para position of the NAr group or acetonitrile insertion to give a diazametallacyclobutene (right). Experimental and theoretical studies reveal that both intermediates serve as “masked” sources of the corresponding terminal nitrene [Cu]=NAr that undergoes nitrene transfer to PMe3, CNtBu, and benzylic C−H bonds.
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Intramolecular Cross-Linking: Addressing Mechanochemistry with a Bioinspired Approach ()
Many of the attractive properties in polymers are a consequence of their high molecular weight and therefore, scission of chains due to mechanochemistry leads to deterioration in properties and performance. Intramolecular cross-links are systematically added to linear chains, slowing down mechanochemical degradation to the point where the chains become virtually invincible to shear in solution. Our approach mimics the immunoglobulin-like domains of Titin, whose structure directs mechanical force towards the scission of sacrificial intramolecular hydrogen bonds, absorbing mechanical energy while unfolding. The kinetics of the mechanochemical reactions supports this hypothesis, as the polymer properties are maintained while high rates of mechanochemistry are observed. Our results demonstrate that polymers with intramolecular cross-links can be used to make solutions which, even under severe shear, maintain key properties such as viscosity. Unbreakable polymers: Random covalent intramolecular cross-links in single-chain polymer nanoparticles break preferably during ultrasonication, making the polymers resistant to mechanochemistry in solution. Above a certain cross-link density, the nanoparticles become virtually invincible to shear in solution.
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Partial Reduction and Selective Transfer of Hydrogen Chloride on Catalytic Gold Nanoparticles ()
HCl in solution accepts electron density from Au NPs and partially reduces at room temperature, as occurs with other simple diatomic molecules, such as O2 and H2. The activation can be run catalytically in the presence of alkynes to give exclusively E-vinyl chlorides, after the regio- and stereoselective transfer of HCl. Based also on this method, vinyl chloride monomer (VCM) can be produced in a milder and greener way than current industrial processes. A helping hand from gold: Hydrogen chloride is partially reduced by supported gold nanoparticles at room temperature. It is catalytically added to alkynes to give, regio- and stereoselectively, E-α-vinyl chlorides. This approach enabled the synthesis of vinyl chloride monomer from acetylene in continuous mode.
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Synthesis of Intrinsically Disordered Fluorinated Peptides for Modular Design of High-Signal 19F MRI Agents ()
19F MRI is valuable for in vivo imaging due to the only trace amounts of fluorine in biological systems. Because of the low sensitivity of MRI however, designing new fluorochemicals remains a significant challenge for achieving sufficient 19F signal. Here, we describe a new class of high-signal, water-soluble fluorochemicals as 19F MRI imaging agents. A polyamide backbone is used for tuning the proteolytic stability to avoid retention within the body, which is a limitation of current state-of-the-art perfluorochemicals. We show that unstructured peptides containing alternating N-ϵ-trifluoroacetyllysine and lysine provide a degenerate 19F NMR signal. 19F MRI phantom images provide sufficient contrast at micromolar concentrations, showing promise for eventual clinical applications. Finally, the degenerate high signal characteristics were retained when conjugated to a large protein, indicating potential for in vivo targeting applications, including molecular imaging and cell tracking. Disordered symmetry: A new class of water-soluble, peptide-based fluorochemicals as high-signal 19F MRI imaging agents is described. The design strategy utilizes an alternating sequence of positive charges and fluorinated amino acids to produce a disordered peptide with overlapping 19F resonances that give a singular intense signal for use as a 19F MRI agent.
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An Organic Semiconductor Organized into 3D DNA Arrays by “Bottom-up” Rational Design ()
A 3D array of organic semiconductors was assembled using a DNA scaffold. An octameric aniline molecule (“octaniline”) was incorporated into a DNA building block based on a dimeric tensegrity triangle. The construct self-assembled to form a 3D crystal. Reversible redox conversion between the pernigraniline and leucoemeraldine states of the octaniline is retained in the crystal. Protonic doping gave emeraldine salt at pH 5, corresponding to the conductive form of polyaniline. Redox cycling within the crystal was visualized by color changes and Raman microscopy. The ease of conversion between the octaniline states suggests that it is a viable electronic switch within a unique 3D structure. Foresee and see: Three decades after the prediction, molecules of an organic semiconductor (octaniline) were templated by a DNA nanostructure and self-assembled into a macroscopic crystal by rational design (see picture). The oxidation and conducting states of octaniline are readily controlled inside of the crystal and visualized by the corresponding color changes.
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Mo2B4O9—Connecting Borate and Metal-Cluster Chemistry ()
We report on the first thoroughly characterized molybdenum borate, which was synthesized in a high-pressure/high-temperature experiment at 12.3 GPa/1300 °C using a Walker-type multianvil apparatus. Mo2B4O9 incorporates tetrahedral molybdenum clusters into an anionic borate crystal structure—a structural motif that has never been observed before in the wide field of borate crystal chemistry. The six bonding molecular orbitals of the [Mo4] tetrahedron are completely filled with 12 electrons, which are fully delocalized over the four molybdenum atoms. This finding is in agreement with the results of the magnetic measurements, which confirmed the diamagnetic character of Mo2B4O9. The two four-coordinated boron sites can be differentiated in the 11B MAS-NMR spectrum because of the strongly different degrees of local distortions. Experimentally obtained IR and Raman bands were assigned to vibrational modes based on DFT calculations. Come together: In the field of borate crystal chemistry, Mo2B4O9 is the first compound incorporating transition-metal clusters into its crystal structure. The tetrahedral molybdenum clusters and the face-capping oxygen atoms form heterocubane-like [Mo4O4] units. The reduction of a reagent in a high-pressure experiment enabled the combination of two hitherto separated fields of research and revealed an approach to this novel substance class.
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Direct Experimental Evidence for Halogen–Aryl π Interactions in Solution from Molecular Torsion Balances ()
We dissected halogen–aryl π interactions experimentally using a bicyclic N-arylimide based molecular torsion balances system, which is based on the influence of the non-bonded interaction on the equilibria between folded and unfolded states. Through comparison of balances modulated by higher halogens with fluorine balances, we determined the magnitude of the halogen–aryl π interactions in our unimolecular systems to be larger than −5.0 kJ mol−1, which is comparable with the magnitude estimated in the biomolecular systems. Our study provides direct experimental evidence of halogen–aryl π interactions in solution, which until now have only been revealed in the solid state and evaluated theoretically by quantum-mechanical calculations. Weighty evidence: Molecular torsion balances containing an N-aryl imide and an additional aromatic moiety provided direct experimental evidence for halogen–aryl π interactions in solution (see picture). The magnitude of the halogen–aryl π interactions in the unimolecular systems described herein are found to be larger than −5.0 kJ mol−1.
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Enhancing Light Absorption and Charge Transfer Efficiency in Carbon Dots through Graphitization and Core Nitrogen Doping ()
Single-source precursor syntheses have been devised for the preparation of structurally similar graphitic carbon dots (CDs), with (g-N-CD) and without (g-CD) core nitrogen doping for artificial photosynthesis. An order of magnitude improvement has been realized in the rate of solar (AM1.5G) H2 evolution using g-N-CD (7950 μmolH2 (gCD)−1 h−1) compared to undoped CDs. All graphitized CDs show significantly enhanced light absorption compared to amorphous CDs (a-CD) yet undoped g-CD display limited photosensitizer ability due to low extraction of photogenerated charges. Transient absorption spectroscopy showed that nitrogen doping in g-N-CD increases the efficiency of hole scavenging by the electron donor and thereby significantly extends the lifetime of the photogenerated electrons. Thus, nitrogen doping allows the high absorption coefficient of graphitic CDs to be translated into high charge extraction for efficient photocatalysis. Carbon dots are investigated for solar H2 production and a number of critical structure–activity relationships are determined for the first time. Nitrogen-doping of the core structure is established as a strategy to enhance charge-transfer reactions in graphitic carbons dots, which also demonstrate strong light absorption.
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Structure-Selective Cation Exchange in the Synthesis of Zincblende MnS and CoS Nanocrystals ()
The ability to selectively form one crystal structure among several options in a polymorphic system is an important goal in solid-state synthesis. Nanocrystal cation exchange, which proceeds rapidly under mild conditions, can retain key structural features and yield otherwise inaccessible phases, but the extent to which crystal structure can be retained and therefore selectively targeted during such reactions has been limited. Here, we show that nanocrystals of digenite Cu2−xS transform to zincblende MnS and CoS upon cation exchange. Zincblende MnS and CoS, which are metastable in bulk, retain both the tetrahedral cation coordination and cubic close packed anion sublattice of digenite Cu2−xS. Comparison with wurtzite MnS and CoS, which have been accessed previously through analogous cation exchange of roxbyite Cu2−xS, demonstrates the selective formation of the related zincblende vs. wurtzite polymorphs by cation exchange of structurally distinct templates. This structure, not that one! The anion and cation sublattices of digenite Cu2−xS nanocrystals are retained upon cation exchange to form zincblende MnS and CoS, which are metastable compounds in bulk. Using this synthesis pathway, multiple phases in the same system can now be accessed selectively and rationally.
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Enhanced Catalytic Activity of Cobalt Porphyrin in CO2 Electroreduction upon Immobilization on Carbon Materials ()
In a comparative study of the electrocatalytic CO2 reduction, cobalt meso-tetraphenylporphyrin (CoTPP) is used as a model molecular catalyst under both homogeneous and heterogeneous conditions. In the former case, employing N,N-dimethylformamide as solvent, CoTPP performs poorly as an electrocatalyst giving low product selectivity in a slow reaction at a high overpotential. However, upon straightforward immobilization of CoTPP onto carbon nanotubes, a remarkable enhancement of the electrocatalytic abilities is seen with CO2 becoming selectively reduced to CO (>90 %) at a low overpotential in aqueous medium. This effect is ascribed to the particular environment created by the aqueous medium at the catalytic site of the immobilized catalyst that facilitates the adsorption and further reaction of CO2. This work highlights the significance of assessing an immobilized molecular catalyst from more than homogeneous measurements alone. Heterogeneous vs. homogeneous: When cobalt meso-tetraphenylporphyrin (CoTPP) is immobilized on carbon nanotubes, a remarkably enhanced catalytic activity in CO2 electroreduction is observed, with [CoITPP]− serving as the active species. The simple approach for heterogenization enables facile screening and evaluation of molecular catalysts under heterogeneous conditions.
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Reversible Supracolloidal Self-Assembly of Cobalt Nanoparticles to Hollow Capsids and Their Superstructures ()
The synthesis and spontaneous, reversible supracolloidal hydrogen bond-driven self-assembly of cobalt nanoparticles (CoNPs) into hollow shell-like capsids and their directed assembly to higher order superstructures is presented. CoNPs and capsids form in one step upon mixing dicobalt octacarbonyl (Co2CO8) and p-aminobenzoic acid (pABA) in 1,2-dichlorobenzene using heating-up synthesis without additional catalysts or stabilizers. This leads to pABA capped CoNPs (core ca. 5 nm) with a narrow size distribution. They spontaneously assemble into tunable spherical capsids (d≈50–200 nm) with a few-layered shells, as driven by inter-nanoparticle hydrogen bonds thus warranting supracolloidal self-assembly. The capsids can be reversibly disassembled and reassembled by controlling the hydrogen bonds upon heating or solvent exchanges. The superparamagnetic nature of CoNPs allows magnetic-field-directed self-assembly of capsids to capsid chains due to an interplay of induced dipoles and inter-capsid hydrogen bonds. Finally, self-assembly on air–water interface furnishes lightweight colloidal framework films. Chain of CoNP capsids: In situ, template-free, and reversible supracolloidal self-assembly of superparamagnetic cobalt nanoparticles to hollow spherical capsids and their directed assembly to higher order superstructures is reported.
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Solvent-Assisted Metal Metathesis: A Highly Efficient and Versatile Route towards Synthetically Demanding Chromium Metal–Organic Frameworks ()
Chromium(III)-based metal–organic frameworks (Cr-MOFs) are very attractive in a wide range of investigations because of their robustness and high porosity. However, reports on Cr-MOFs are scarce owing to the difficulties in their direct synthesis. Recently developed postsynthetic routes to obtain Cr-MOFs suffered from complicated procedures and a lack of general applicability. Herein, we report a highly efficient and versatile strategy, namely solvent-assisted metal metathesis, to obtain Cr-MOFs from a variety of FeIII-MOFs, including several well-known MOFs and a newly synthesized one, through judicious selection of a coordinating solvent. The versatility of this strategy was demonstrated by producing Cr-MIL-100, Cr-MIL-142A/C, Cr-PCN-333, and Cr-PCN-600 from their FeIII analogues and Cr-SXU-1 from a newly synthesized MOF precursor, Fe-SXU-1, in acetone as the solvent under very mild conditions. We have thus developed a general approach for the preparation of robust Cr-MOFs, which are difficult to synthesize by direct methods. Chromium exchange: An efficient and versatile strategy for the synthesis of chromium(III)-based metal–organic frameworks (Cr-MOFs) from a variety of FeIII-MOFs has been developed based on solvent-assisted metal metathesis. These transformations proceeded in a judiciously chosen coordinating solvent (acetone) under very mild conditions.
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Chromatin Regulates Genome Targeting with Cisplatin ()
Cisplatin derivatives can form various types of DNA lesions (DNA-Pt) and trigger pleiotropic DNA damage responses. Here, we report a strategy to visualize DNA-Pt with high resolution, taking advantage of a novel azide-containing derivative of cisplatin we named APPA, a cellular pre-extraction protocol and the labeling of DNA-Pt by means of click chemistry in cells. Our investigation revealed that pretreating cells with the histone deacetylase (HDAC) inhibitor SAHA led to detectable clusters of DNA-Pt that colocalized with the ubiquitin ligase RAD18 and the replication protein PCNA. Consistent with activation of translesion synthesis (TLS) under these conditions, SAHA and cisplatin cotreatment promoted focal accumulation of the low-fidelity polymerase Polη that also colocalized with PCNA. Remarkably, these cotreatments synergistically triggered mono-ubiquitination of PCNA and apoptosis in a RAD18-dependent manner. Our data provide evidence for a role of chromatin in regulating genome targeting with cisplatin derivatives and associated cellular responses. Treatment of cancer cells with cisplatin derivatives and a histone deacetylase inhibitor leads to the production of clusters of platinated DNA lesions that synergistically activate translesion synthesis and apoptosis signaling. These findings provide evidence for a role of chromatin in regulating genome targeting with cisplatin derivatives and associated cellular responses.
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Fullerene C70 as a Nanoflask that Reveals the Chemical Reactivity of Atomic Nitrogen ()
To investigate the intrinsic reactivity of atomic nitrogen, which had previously been accomplished only by examining its decay in the gas phase using special equipment, a nitrogen atom was inserted into a series of molecule-encapsulating C60 and C70 fullerenes. Among the studied endofullerenes, H2@C70 was able to encapsulate an additional nitrogen atom within the fullerene cage under radiofrequency plasma conditions. The product was analyzed by ESR spectroscopy and mass spectrometry in solution, which revealed that the nitrogen atom with a quartet ground state does not react but weakly interact with the H2 molecule, thus demonstrating the utility of such fullerenes as “nanoflasks”. A weak interaction: Atomic nitrogen was encapsulated in a series of molecule-encapsulating endohedral C60 and C70 fullerenes in order to investigate the intrinsic reactivity of the N atom. Among the studied endofullerenes, H2@C70 accommodated an additional N atom within its fullerene cage under radiofrequency plasma conditions. The obtained product was analyzed by ESR spectroscopy and mass spectrometry in solution.
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Activatable Singlet Oxygen Generation from Lipid Hydroperoxide Nanoparticles for Cancer Therapy ()
Reactive oxygen species (ROS)-induced apoptosis is a widely practiced strategy for cancer therapy. Although photodynamic therapy (PDT) takes advantage of the spatial–temporal control of ROS generation, the meticulous participation of light, photosensitizer, and oxygen greatly hinders the broad application of PDT as a first-line cancer treatment option. An activatable system has been developed that enables tumor-specific singlet oxygen (1O2) generation for cancer therapy, based on a Fenton-like reaction between linoleic acid hydroperoxide (LAHP) tethered on iron oxide nanoparticles (IO NPs) and the released iron(II) ions from IO NPs under acidic-pH condition. The IO-LAHP NPs are able to induce efficient apoptotic cancer cell death both in vitro and in vivo through tumor-specific 1O2 generation and subsequent ROS mediated mechanism. This study demonstrates the effectiveness of modulating biochemical reactions as a ROS source to exert cancer death. Singlet oxygen generation through an activatable biochemical reaction between lipid hydroperoxide and catalytic iron(II) ions from iron oxide nanoparticles was engineered as a novel cancer therapy strategy, which showed promise to exert apoptotic cancer cell death both in vitro and in vivo.
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Color-Change Photoswitching of an Alkynylpyrene Excimer Dye ()
We describe a photoswitchable DNA-based dimeric dye that visibly changes fluorescence from green to blue upon UV irradiation. A novel bis-alkyne-dependent [2+2+2] cycloaddition is proposed as a mechanism for the color change in air. The photoinduced structural switching results in spatial separation of stacked pyrene units, thereby causing selective loss of the excimer emission. We demonstrate and suggest several applications for this novel photoswitch. DNA-based photoswitch: A DNA-based dimeric dye that visibly changes color from green to blue upon UV irradiation is described. A novel bis-alkyne [2+2+2] cycloaddition with oxygen is proposed as a mechanism for the color change in air (see picture).
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Tyrosine or Tryptophan? Modifying a Metalloradical Catalytic Site by Removal of the Cys–Tyr Cross-Link in the Galactose 6-Oxidase Homologue GlxA ()
The concerted redox action of a metal ion and an organic cofactor is a unique way to maximize the catalytic power of an enzyme. An example of such synergy is the fungal galactose 6-oxidase, which has inspired the creation of biomimetic copper oxidation catalysts. Galactose 6-oxidase and its bacterial homologue, GlxA, possess a metalloradical catalytic site that contains a free radical on a covalently linked Cys–Tyr and a copper atom. Such a catalytic site enables for the two-electron oxidation of alcohols to aldehydes. When the ability to form the Cys–Tyr in GlxA is disrupted, a radical can still be formed. Surprisingly, the radical species is not the Tyr residue but rather a copper second-coordination sphere Trp residue. This is demonstrated through the introduction of a new algorithm for Trp-radical EPR spectra simulation. Our findings suggest a new mechanism of free-radical transfer between aromatic residues and that the Cys–Tyr cross-link prevents radical migration away from the catalytic site. Breaking the bond is still radical: Copper radical oxidases contain an unusual Cys–Tyr redox cofactor capable of housing a stable protein radical required for their catalytic activity. Breaking the Cys–Tyr bond still yields a radical, surprisingly not on the Tyr but on the π-stacking Trp residue.
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Oligonucleotide-Addressed Covalent 3′-Terminal Derivatization of Small RNA Strands for Enrichment and Visualization ()
The HEN1 RNA 2′-O-methyltransferase plays important roles in the biogenesis of small non-coding RNAs in plants and proved a valuable tool for selective transfer of functional groups from cofactor analogues onto miRNA and siRNA duplexes in vitro. Herein, we demonstrate the versatile HEN1-mediated methylation and alkylation of small RNA strands in heteroduplexes with a range of complementary synthetic DNA oligonucleotides carrying user-defined moieties such as internal or 3′-terminal extensions or chemical reporter groups. The observed DNA-guided covalent functionalization of RNA broadens our understanding of the substrate specificity of HEN1 and paves the way for the development of novel chemo-enzymatic tools with potential applications in miRNomics, synthetic biology, and nanomedicine. Versatile RNA tagging: A method for addressable chemo-enzymatic labeling of miRNAs and siRNAs, which exploits the activity of HEN1 2′-O-methyltransferase to transfer functional groups to the 3′-end of the RNA strand in DNA/RNA heteroduplexes, is presented. This method permits a variety of user-defined single- or dual-reporter applications, in which one tag can be synthetically incorporated into the DNA probe and the second is covalently attached by HEN1 to the target RNA.
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Synthesis and Bowl-in-Bowl Assembly of a Geodesic Phenylene Bowl ()
A phenylene multiring with a corannulenoidal skeleton was synthesized. Geodesic constraints over 20 phenylene panels resulted in its nanometer-sized, bowl-shaped molecular structure, which was unequivocally revealed by crystallographic analysis. The crystal structure also showed the presence of a bowl-in-bowl dimeric assembly, which was driven by entropic factors in solution. Shape sorting: Geodesic constraints arising from the coupling of trigonal planar phenylenes into a pentagon surrounded by five hexagons resulted in a nanometer-sized bowl-shaped molecule. Concave–convex molecular recognition resulted in the molecules assembling in a bowl-in-bowl fashion. The shape recognition was driven by an entropy gain for the assembly of the large 120 π-systems.
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Vesicle Origami: Cuboid Phospholipid Vesicles Formed by Template-Free Self-Assembly ()
Phospholipid liposomes are archetypical self-assembled structures. To minimize the surface tension, the vesicles typically are spherical. Deciphering the bilayer code, the basic physical interactions between phospholipids would allow these molecules to be utilized as building blocks for novel, non-spherical structures. A 1,2-diamidophospholipid is presented that self-assembles into a cuboid structure. Owing to intermolecular hydrogen bonding, the bilayer membranes form an exceptionally tight subgel packing, leading to a maximization of flat structural elements and a minimization of any edges. These conditions are optimized in the geometrical structure of a cube. Surprisingly, the lateral surface pressure in the membrane is only one third of the value typically assumed for a bilayer membrane, questioning a long-standing rule-of-thumb. Cuboid vesicles: A 1,2-diamidophospholipid is presented that self-assembles into the first non-template phospholipid cube. Owing to intermolecular hydrogen bonding, the bilayer membranes form an exceptionally tight subgel packing, leading to a maximization of flat structural elements and a minimization of any edges. These conditions are optimized in the geometrical structure of a cube.
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Anaerobic Respiration on Self-Doped Conjugated Polyelectrolytes: Impact of Chemical Structure ()
We probe anaerobic respiration of bacteria in the presence of conjugated polyelectrolytes (CPEs). Three different CPEs were used to probe how structural variations impact biocurrent generation from Shewanella oneidensis MR-1. For the self-doped anionic CPE only, absorption spectroscopy shows that the addition of S. oneidensis MR-1 leads to the disappearance of the polaron (radical cation) band at >900 nm and an increase in the band at 735 nm due to the neutral species, consistent with electron transfer from microbe to polymer. Microbial three-electrode electrochemical cells (M3Cs) show an increase in the current generated by S. oneidensis MR-1 with addition of the self-doped CPE relative to other CPEs and controls. These experiments combined with in situ cyclic voltammetry suggest that the doped CPE facilitates electron transport to electrodes and reveal structure–function relationships relevant to developing materials for biotic/abiotic interfaces. Building better bioelectrodes: Abiotic–biotic interfacial contact resistance remains a limiting feature in the performance of bioelectronic devices. Anionic self-doped conjugated polyelectrolytes improve bioelectricity generation from anode-respiring Shewanella oneidensis MR-1 by acting as a conductive extension of the electrode and increasing colonization.
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Crack-Free, Soft Wrinkles Enable Switchable Anisotropic Wetting ()
Soft skin layers on elastomeric substrates are demonstrated to support mechano-responsive wrinkle patterns that do not exhibit cracking under applied strain. Soft fluoropolymer skin layers on pre-strained poly(dimethylsiloxane) slabs achieved crack-free surface wrinkling at high strain regimes not possible by using conventional stiff skin layers. A side-by-side comparison between the soft and hard skin layers after multiple cycles of stretching and releasing revealed that the soft skin layer enabled dynamic control over wrinkle topography without cracks or delamination. We systematically characterized the evolution of wrinkle wavelength, amplitude, and orientation as a function of tensile strain to resolve the crack-free structural transformation. We demonstrated that wrinkled surfaces can guide water spreading along wrinkle orientation, and hence switchable, anisotropic wetting was realized. Wrinkles without the worry: Soft fluoropolymer skin layers on elastomer substrates produced wrinkles that could undergo numerous stretch-and-release cycles without delamination or formation of cracks. A side-by-side comparison with conventional hard skin layers highlighted the integrity and robustness of wrinkles in a soft skin layer as well as their unique properties such as switchable anisotropic water spreading.
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Lead-free Perovskite Materials (NH4)3Sb2IxBr9−x ()
A family of perovskite light absorbers (NH4)3Sb2IxBr9−x (0≤x≤9) was prepared. These materials show good solubility in ethanol, a low-cost, hypotoxic, and environmentally friendly solvent. The light absorption of (NH4)3Sb2IxBr9−x films can be tuned by adjusting I and Br content. The absorption onset for (NH4)3Sb2IxBr9−x films changes from 558 nm to 453 nm as x changes from 9 to 0. (NH4)3Sb2I9 single crystals were prepared, exhibiting a hole mobility of 4.8 cm2 V−1 s−1 and an electron mobility of 12.3 cm2 V−1 s−1. (NH4)3Sb2I9 solar cells gave an open-circuit voltage of 1.03 V and a power conversion efficiency of 0.51 %. Unleaded: Lead-free perovskite materials (NH4)3Sb2IxBr9−x (0≤x≤9) were developed by using ethanol as the solvent. (NH4)3Sb2I9 single crystals were prepared and the crystal structure was analyzed. Solar cells were made by using (NH4)3Sb2IxBr9−x as the light absorbers. (NH4)3Sb2I9 solar cells gave a high open-circuit voltage of 1.03 V and a power conversion efficiency of 0.51 %.
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The Effect of Surface Site Ensembles on the Activity and Selectivity of Ethanol Electrooxidation by Octahedral PtNiRh Nanoparticles ()
Direct ethanol fuel cells are attractive power sources based on a biorenewable, high energy-density fuel. Their efficiency is limited by the lack of active anode materials which catalyze the breaking of the C−C bond coupled to the 12-electron oxidation to CO2. We report shape-controlled PtNiRh octahedral ethanol oxidation electrocatalysts with excellent activity and previously unachieved low onset potentials as low as 0.1 V vs. RHE, while being highly selective to complete oxidation to CO2. Our comprehensive characterization and in situ electrochemical ATR studies suggest that the formation of a ternary surface site ensemble around the octahedral Pt3Ni1Rhx nanoparticles plays a crucial mechanistic role for this behavior. It's the shape, that matters: The efficient and complete electrooxidation of ethanol at low overpotentials has been a prime research target for a long time. The unique combination of a ternary Pt-Ni-Rh ensemble on defined octahedral {111} facets now shows promising activity coupled with good selectivity in this transformation.
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Phenol-Catalyzed Discharge in the Aprotic Lithium-Oxygen Battery ()
Discharge in the lithium-O2 battery is known to occur either by a solution mechanism, which enables high capacity and rates, or a surface mechanism, which passivates the electrode surface and limits performance. The development of strategies to promote solution-phase discharge in stable electrolyte solutions is a central challenge for development of the lithium-O2 battery. Here we show that the introduction of the protic additive phenol to ethers can promote a solution-phase discharge mechanism. Phenol acts as a phase-transfer catalyst, dissolving the product Li2O2, avoiding electrode passivation and forming large particles of Li2O2 product—vital requirements for high performance. As a result, we demonstrate capacities of over 9 mAh cm−2areal, which is a 35-fold increase in capacity compared to without phenol. We show that the critical requirement is the strength of the conjugate base such that an equilibrium exists between protonation of the base and protonation of Li2O2. Battery balancing: Discharge in the Li-O2 battery occurs either by a desired solution mechanism or an unfavored surface mechanism, which passivates the electrode surface. The introduction of phenol promotes solution-phase discharge. Phenol acts as a phase-transfer catalyst (see scheme), dissolving the product Li2O2, avoiding electrode passivation and forming large particles of Li2O2—vital requirements for high performance.
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Amide-Directed C−H Sodiation by a Sodium Hydride/Iodide Composite ()
A new protocol for amide-directed ortho and lateral C−H sodiation is enabled by sodium hydride (NaH) in the presence of either sodium iodide (NaI) or lithium iodide (LiI). The transient organosodium intermediates could be transformed into functionalized aromatic compounds. New direction: An amide-directed ortho and lateral C−H sodiation is enabled by sodium hydride (NaH) in the presence of either sodium iodide (NaI) or lithium iodide (LiI). The transient organosodium intermediates could be transformed into functionalized aromatic compounds.
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Preparation of Waterproof Organometal Halide Perovskite Photonic Crystal Beads ()
Herein, we report on an innovative method for the preparation of a series of organometal halide perovskite (OHP) photonic crystal beads with pronounced and tunable photonic stop bands by using self-assembled polystyrene spheres as a mold. After infiltration of the mold with OHP precursor solution and slow drying, the OHPs crystallized in the voids of the polystyrene arrays. By controlling the diameter of the polystyrene spheres, the photonic stop band of the OHPs could be precisely tuned. The overlap between the photonic stop band of the beads and the band gap of the OHPs enhances the light harvesting of the perovskite because of the slow photon effect, which arises from the photonic crystal beads. Moreover, the stability of the composite was greatly enhanced by coating with the transparent polymer PDMS without blocking the light propagation. The coated OHP photonic beads kept their composition even after having been in contact with water for 24 h. Waterproof organometal halide perovskite/photonic crystal bead composites were prepared. The band gap of the halide perovskite and the stop band of the photonic crystal beads can be tuned to overlap with each other, which is promising for enhancing the light harvesting under visible-light irradiation through the slow photon effect. The composite was very stable in water after coating with PDMS.
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Pressure-Induced Polymerization of Acetylene: Structure-Directed Stereoselectivity and a Possible Route to Graphane ()
Geometric isomerism in polyacetylene is a basic concept in chemistry textbooks. Polymerization to cis-isomer is kinetically preferred at low temperature, not only in the classic catalytic reaction in solution but also, unexpectedly, in the crystalline phase when it is driven by external pressure without a catalyst. Until now, no perfect reaction route has been proposed for this pressure-induced polymerization. Using in situ neutron diffraction and meta-dynamic simulation, we discovered that under high pressure, acetylene molecules react along a specific crystallographic direction that is perpendicular to those previously proposed. Following this route produces a pure cis-isomer and more surprisingly, predicts that graphane is the final product. Experimentally, polycyclic polymers with a layered structure were identified in the recovered product by solid-state nuclear magnetic resonance and neutron pair distribution functions, which indicates the possibility of synthesizing graphane under high pressure. From acetylene to graphane: By using neutron diffraction and theoretical calculations the domination of cis-polyacetylene in the pressure-induced polymerization of C2H2 is explained. Graphane is predicted as the final product and a layered polycyclic polymer was identified experimentally as an intermediate between polyacetylene and graphane.
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Switchable Site-Selective Catalytic Carboxylation of Allylic Alcohols with CO2 ()
A switchable site-selective catalytic carboxylation of allylic alcohols has been developed in which CO2 is used with dual roles, both facilitating C−OH cleavage and as a C1 source. This protocol is characterized by its mild reaction conditions, absence of stoichiometric amounts of organometallic reagents, broad scope, and exquisite regiodivergency which can be modulated by the type of ligand employed. Double agent: In the title reaction, CO2 serves as both a facilitator for the C−OH cleavage and as a C1 source. This reaction is the first example of a cross-electrophile coupling of unprotected alcohols in the absence of stoichiometric amounts of organometallic species. The procedure has broad scope and an exquisite regiodivergency which can be modulated by the ligand-type employed.
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Non-Enzymatic RNA Backbone Proofreading through Energy-Dissipative Recycling ()
Non-enzymatic oligomerization of activated ribonucleotides leads to ribonucleic acids that contain a mixture of 2′,5′- and 3′,5′-linkages, and overcoming this backbone heterogeneity has long been considered a major limitation to the prebiotic emergence of RNA. Herein, we demonstrate non-enzymatic chemistry that progressively converts 2′,5′-linkages into 3′,5′-linkages through iterative degradation and repair. The energetic costs of this proofreading are met by the hydrolytic turnover of a phosphate activating agent and an acylating agent. With multiple rounds of this energy-dissipative recycling, we show that all-3′,5′-linked duplex RNA can emerge from a backbone heterogeneous mixture, thereby delineating a route that could have driven RNA evolution on the early earth. If at first you don't succeed, try, try again: With enzymes not available on the early Earth, energy-dissipative cycles might have contributed to the correction and recycling of ribonucleic acids, which defines a plausible scenario for the prebiotic evolution of RNA.
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Mizoroki–Heck Cyclizations of Amide Derivatives for the Introduction of Quaternary Centers ()
We report non-decarbonylative Mizoroki–Heck reactions of amide derivatives. The transformation relies on the use of nickel catalysis and proceeds using sterically hindered tri- and tetrasubstituted olefins to give products containing quaternary centers. The resulting polycyclic or spirocyclic products can be obtained in good yields. Moreover, a diastereoselective variant of this method gives access to an adduct bearing vicinal, highly substituted sp3 stereocenters. These results demonstrate that amide derivatives can be used as building blocks for the assembly of complex scaffolds. Adding complexity: A non-decarbonylative Mizoroki–Heck reaction of Boc-activated amide derivatives is reported. The transformation relies on the use of nickel catalysis and proceeds using sterically hindered tri- and tetrasubstituted olefins to give products containing quaternary centers. The results demonstrate that amide derivatives can be used as building blocks for the assembly of complex scaffolds.
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Crystallinity-Modulated Electrocatalytic Activity of a Nickel(II) Borate Thin Layer on Ni3B for Efficient Water Oxidation ()
The exploration of new efficient OER electrocatalysts based on nonprecious metals and the understanding of the relationship between activity and structure of electrocatalysts are important to advance electrochemical water oxidation. Herein, we developed an efficient OER electrocatalyst with nickel boride (Ni3B) nanoparticles as cores and nickel(II) borate (Ni-Bi) as shells (Ni-Bi@NB) via a very simple and facile aqueous reaction. This electrocatalyst exhibited a small overpotential of 302 mV at 10 mA cm−2 and Tafel slope of 52 mV dec−1. More interestingly, it was found that the OER activity of Ni-Bi@NB was closely dependent on the crystallinity of the Ni-Bi shells. The partially crystalline Ni-Bi catalyst exhibited much higher activity than the amorphous or crystalline analogues; this higher activity originated from the enhanced intrinsic activity of the catalytic sites. These findings open up opportunities to explore nickel(II) borates as a new class of efficient nonprecious metal OER electrocatalysts, and to improve the electrocatalyst performance by modulating their crystallinity. A new winner! Crystallinity-dependent activity was demonstrated on a new efficient electrocatalyst for the oxygen evolution reaction (OER) which consists of a nickel(II) borate thin layer on nickel boride (NB) nanoparticles (Ni-Bi@NB) (see figure). The partially crystalline Ni-Bi catalyst exhibits excellent OER performance.
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Discovery of Hexagonal Structured Pd–B Nanocrystals ()
We report on hexagonal close-packed (hcp) palladium (Pd)–boron (B) nanocrystals (NCs) by heavy B doping into face-centered cubic (fcc) Pd NCs. Scanning transmission electron microscopy–electron energy loss spectroscopy and synchrotron powder X-ray diffraction measurements demonstrated that the B atoms are homogeneously distributed inside the hcp Pd lattice. The large paramagnetic susceptibility of Pd is significantly suppressed in Pd–B NCs in good agreement with the reduction of density of states at Fermi energy suggested by X-ray absorption near-edge structure and theoretical calculations. A change in behavior: Hexagonal close-packed (hcp) Pd–B nanocrystals (NCs) are synthesized by B doping into face-centered cubic (fcc) Pd NCs. Analyses (HR-HAADF-STEM, EELS, and synchrotron PXRD) of Pd–B NCs demonstrate that B atoms are homogeneously distributed inside an hcp Pd lattice. The large paramagnetic susceptibility of Pd NCs is suppressed in Pd–B NCs, in good agreement with the reduction of density of states at Fermi energy suggested by XANES and theoretical calculations.
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Iron Oxide Photoelectrode with Multidimensional Architecture for Highly Efficient Photoelectrochemical Water Splitting ()
Nanostructured metal oxide semiconductors have shown outstanding performances in photoelectrochemical (PEC) water splitting, but limitations in light harvesting and charge collection have necessitated further advances in photoelectrode design. Herein, we propose anodized Fe foams (AFFs) with multidimensional nano/micro-architectures as a highly efficient photoelectrode for PEC water splitting. Fe foams fabricated by freeze-casting and sintering were electrochemically anodized and directly used as photoanodes. We verified the superiority of our design concept by achieving an unprecedented photocurrent density in PEC water splitting over 5 mA cm−2 before the dark current onset, which originated from the large surface area and low electrical resistance of the AFFs. A photocurrent of over 6.8 mA cm−2 and an accordingly high incident photon-to-current efficiency of over 50 % at 400 nm were achieved with incorporation of Co oxygen evolution catalysts. In addition, research opportunities for further advances by structual and compositional modifications are discussed, which can resolve the low fill factoring behavior and improve the overall performance. An anodized iron foam photoelectrode with multidimensional nano/micro-architecture leads to extremely large photocurrent generation and high Faradaic efficiency in photoelectrochemical water splitting. Morphologies of anodic iron oxides and activation of photoelectrode by phase-transition phenomena were also investigated.
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Enhanced Electrocatalytic Oxygen Evolution in Au–Fe Nanoalloys ()
Oxygen evolution reaction (OER) is the most critical step in water splitting, still limiting the development of efficient alkaline water electrolyzers. Here we investigate the OER activity of Au–Fe nanoalloys obtained by laser-ablation synthesis in solution. This method allows a high amount of iron (up to 11 at %) to be incorporated into the gold lattice, which is not possible in Au–Fe alloys synthesized by other routes, due to thermodynamic constraints. The Au0.89Fe0.11 nanoalloys exhibit strongly enhanced OER in comparison to the individual pure metal nanoparticles, lowering the onset of OER and increasing up to 20 times the current density in alkaline aqueous solutions. Such a remarkable electrocatalytic activity is associated to nanoalloying, as demonstrated by comparative examples with physical mixtures of gold and iron nanoparticles. These results open attractive scenarios to the use of kinetically stable nanoalloys for catalysis and energy conversion. Splitting water: Au–Fe nanoparticles synthesized by laser ablation in solution exhibit enhanced activity in the oxygen evolution reaction (see diagram). The results open exciting perspectives for using nanoalloys in catalysis and energy conversion.
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Directing Reaction Pathways through Controlled Reactant Binding at Pd–TiO2 Interfaces ()
Recent efforts to design selective catalysts for multi-step reactions, such as hydrodeoxygenation (HDO), have emphasized the preparation of active sites at the interface between two materials having different properties. However, achieving precise control over interfacial properties, and thus reaction selectivity, has remained a challenge. Here, we encapsulated Pd nanoparticles (NPs) with TiO2 films of regulated porosity to gain a new level of control over catalyst performance, resulting in essentially 100 % HDO selectivity for two biomass-derived alcohols. This catalyst also showed exceptional reaction specificity in HDO of furfural and m-cresol. In addition to improving HDO activity by maximizing the interfacial contact between the metal and metal oxide sites, encapsulation by the nanoporous oxide film provided a significant selectivity boost by restricting the accessible conformations of aromatics on the surface. Nanoscale morphology control over active sites consisting of Pd and TiO2 specifies binding orientation of reactant molecules to provide unprecedented reaction specificity toward hydrodeoxygenation during catalytic conversion of biomass-derived aromatic alcohols/aldehydes and phenolic compounds.
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Fluorophores for Excited-State Intramolecular Proton Transfer by an Yttrium Triflate Catalyzed Reaction of Isocyanides with Thiocarboxylic Acids ()
Discovery of new chemical reactivity of a given functional group can often result in innovative synthesis of important chemical entities that possess unprecedented properties. We designed and developed a one-step synthesis of 5-amino-4-carboxamidothiazoles 1 by an yttrium-triflate-catalyzed reaction of thiocarboxylic acids 2 with isocyanides 3. In this reaction, both reactants 2 and 3 deviated from their normal reactivities because of metal coordination. The resulting heterocycles are novel prototypical structures for the double ESIPT process. Some of them were excited by visible light irradiation and emitted fluorescence at the NIR region with large Stokes shift, high quantum yield, and strong solvatochromism. Colorful reactivity: The reaction of thiocarboxylic acids with isocyanides in the presence of a catalytic amount of yttrium triflate afforded 5-amino-4-carboxamidothiazoles in good to excellent yields. Some of these heterocycles were excited by visible light and emitted fluorescence in the near-infrared region with large Stokes shift, high quantum yield, and strong positive solvatochromism.
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A Rhodium(II)-Catalyzed Formal [4+1]-Cycloaddition toward Spirooxindole Pyrrolone Construction Employing Vinyl Isocyanates as 1,4-Dipoles ()
A RhII-catalyzed, formal [4+1]-cycloaddition between diazooxindoles as electrophilic C1 synthons and 1,3-heterodienes for the construction of spirooxindole pyrrolones is described. Employing vinyl isocyanates as 1,4-dipoles, the cycloannulation occurs under relatively mild conditions and provides the corresponding pyrrolones in good to excellent yields. Put a ring on it: The title reaction between diazooxindoles as electrophilic C1 synthons and 1,3-heterodienes enables the construction of spirooxindole pyrrolones. Employing vinyl isocyanates as 1,4-dipoles, the cycloannulation occurs under relatively mild conditions and provides the corresponding pyrrolones in good to excellent yields.
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Total Synthesis of Rishirilide B by Organocatalytic Oxidative Kinetic Resolution: Revision of Absolute Configuration of (+)-Rishirilide B ()
Described herein is the enantioselective syntheses of (+)- and (−)-rishirilide B from the corresponding optically active β-substituted tetralones, which were obtained by oxidative kinetic resolution based on α-hydroxylation in the presence of a chiral guanidine-bisurea bifunctional organocatalyst. Benzylic oxidation of the tetralones at C1 followed by regioselective isomerization of the oxabenzonorbornadiene structure led to rishirilide B. Our findings lead to the revision of the previously proposed (2R,3R,4R) absolute configuration of (+)-rishirilide B to (2S,3S,4S). Reconfigured: Enantioselective synthesis of (+)- and (−)-rishirilide B has been achieved from optically active β-substituted tetralone, which was obtained by oxidative kinetic resolution using a guanidine-bisurea bifunctional organocatalyst. This synthetic studies led to revision of the previously proposed absolute configuration of (+)-rishirilide B to (2S,3S,4S).
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A Short Synthesis of (±)-3-Demethoxyerythratidinone by Ligand-Controlled Selective Heck Cyclization of Equilibrating Enamines ()
A short, 5-step total synthesis of (±)-3-demethoxyerythratidinone from a simple pyrrole derivative is described. Features include the formation of gram quantities of a key tricylic aziridine from a challenging photochemical cascade reaction through the use of flow photochemistry. The final step involved a highly unusual Heck cyclization whereby ligand control enabled efficient formation of the natural product in 69 % yield from the minor isomer present in an equilibrating mixture of labile enamines. Five steps to success: A short total synthesis of (±)-3-demethoxyerythratidinone (1) has been completed using a combination of photochemistry and Pd-catalyzed Heck cyclization. A key feature was the ability to control the outcome of the Heck cyclization onto an equilibrating mixture of labile enamines by ligand choice.
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Atroposelective Synthesis of Axially Chiral Biaryls by Palladium-Catalyzed Asymmetric C−H Olefination Enabled by a Transient Chiral Auxiliary ()
Atroposelective synthesis of axially chiral biaryls by palladium-catalyzed C−H olefination, using tert-leucine as an inexpensive, catalytic, and transient chiral auxiliary, has been realized. This strategy provides a highly efficient and straightforward access to a broad range of enantioenriched biaryls in good yields (up to 98 %) with excellent enantioselectivities (95 to >99 % ee). Kinetic resolution of trisubstituted biaryls bearing sterically more demanding substituents is also operative, thus furnishing the optically active olefinated products with excellent selectivity (95 to >99 % ee, s-factor up to 600). No attachements: The title reaction employs tert-leucine as a transient chiral auxiliary and provides efficient access to enantioenriched biaryls in good yields (up to 98 %) with excellent enantioselectivities (up to >99 % ee). Kinetic resolution of trisubstituted biaryls bearing sterically more demanding substituents is also operative, thus furnishing the optically active olefinated products with excellent selectivity (up to >99 % ee, s-factor up to 600).
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Insights Into How Heme Reduction Potentials Modulate Enzymatic Activities of a Myoglobin-based Functional Oxidase ()
Heme-copper oxidase (HCO) is a class of respiratory enzymes that use a heme-copper center to catalyze O2 reduction to H2O. While heme reduction potential (E°′) of different HCO types has been found to vary >500 mV, its impact on HCO activity remains poorly understood. Here, we use a set of myoglobin-based functional HCO models to investigate the mechanism by which heme E°′ modulates oxidase activity. Rapid stopped-flow kinetic measurements show that increasing heme E°′ by ca. 210 mV results in increases in electron transfer (ET) rates by 30-fold, rate of O2 binding by 12-fold, O2 dissociation by 35-fold, while decreasing O2 affinity by 3-fold. Theoretical calculations reveal that E°′ modulation has significant implications on electronic charge of both heme iron and O2, resulting in increased O2 dissociation and reduced O2 affinity at high E°′ values. Overall, this work suggests that fine-tuning E°′ in HCOs and other heme enzymes can modulate their substrate affinity, ET rate and enzymatic activity. A four-electron reduction of O2 to H2O in heme-copper oxidase (HCO) requires an efficient control of electron transfer, O2 binding/dissociation rates, and O2 affinity. By employing a functional model of HCO, it is shown that the heme reduction potential plays a key role in controlling these parameters, the electronics of bound O2, and thus the overall enzymatic activity.
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Synthesis of Layered Carbonitrides from Biotic Molecules for Photoredox Transformations ()
The construction of layered covalent carbon nitride polymers based on tri-s-triazine units has been achieved by using nucleobases (adenine, guanine, cytosine, thymine and uracil) and urea to establish a two-dimensional semiconducting structure that allows band-gap engineering applications. This biomolecule-derived binary carbon nitride polymer enables the generation of energized charge carrier with light-irradiation to induce photoredox reactions for stable hydrogen production and heterogeneous organosynthesis of C−O, C−C, C−N and N−N bonds, which may enrich discussion on chemical reactions in prebiotic conditions by taking account of the photoredox function of conjugated carbonitride semiconductors that have long been considered to be stable HCN-derived organic macromolecules in space. A prebiotic photocatalyst? Graphitic carbon nitrides synthesized from nucleobases and urea enable the photogeneration of charge carriers to induce photoredox reactions for H2 production and heterogeneous organosynthesis of C−O, C−C, C−N, and N−N bonds. The findings enrich the concept of photochemical reactions in the primordial soup.
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C−N Bond Activation and Ring Opening of a Saturated N-Heterocyclic Carbene by Lateral Alkali-Metal-Mediated Metalation ()
Combining alkali-metal-mediated metalation (AMMM) and N-heterocyclic carbene (NHC) chemistry, a novel C−N bond activation and ring-opening process is described for these increasingly important NHC molecules, which are generally considered robust ancillary ligands. Here, mechanistic investigations on reactions of saturated NHC SIMes (SIMes=[:C{N(2,4,6-Me3C6H2)CH2}2]) with Group 1 alkyl bases suggest this destructive process is triggered by lateral metalation of the carbene. Exploiting co-complexation and trans-metal-trapping strategies with lower polarity organometallic reagents (Mg(CH2SiMe3)2 and Al(TMP)iBu2), key intermediates in this process have been isolated and structurally defined. Co-lateral damage! Lateral metalation of saturated N-heterocyclic carbene [:C{N(2,4,6-Me3C6H2)CH2}2] (SIMes) triggers a destructive process, inducing C−N bond activation and ring opening of the five-membered heterocyclic ring.
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Palladium-Catalyzed Regioselective Synthesis of 3-Arylindoles from N-Ts-Anilines and Styrenes ()
A Pd-catalyzed intermolecular oxidative annulation between N-Ts-anilines and styrenes was developed. This method offers a straightforward and robust approach to a wide range of 3-arylindoles using readily available starting materials with good functional-group tolerance and high regioselectivity and efficiency. Further elaboration of the products obtained from this process provided access to highly functionalized and structurally diverse indoles, for example, 3-(indol-3-yl)carbazoles, 1,9-dihydropyrrolo-[2,3-b]carbazoles, and 3′-aryl-3,5′-biindoles. Hello from the other side: A Pd-catalyzed intermolecular oxidative annulation for one-pot C−C/C−N bond formation was developed. In contrast to the opposite regioselectivity pattern of related methods, this method offers facile access to the synthetically valuable 3-arylindoles, which were previously inaccessible from styrenes and anilines, with high efficiency and excellent regioselectivity.
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Palladium-Catalyzed Cascade sp2 C−H Functionalization/Intramolecular Asymmetric Allylation: From Aryl Ureas and 1,3-Dienes to Chiral Indolines ()
A chiral PdII-catalyzed cascade sp2 C−H functionalization/intramolecular asymmetric allylation reaction is reported. A new chiral sulfoxide–oxazoline (SOX) ligand bearing single chiral center on the sulfur was identified as the optimal ligand for the reaction, being efficient both in the C−H cleavage step and the stereocontrol of the allylation step. The broad scope of this method with respect to aryl ureas and 1,3-dienes enables the rapid construction of valuable chiral indoline derivatives with high yields and enantioselectivities (up to 99 % yield, up to 95:5 e.r.). Efficiency and chirality: A chiral PdII-catalyzed cascade sp2 C−H functionalization/intramolecular asymmetric allylation reaction is described. A chiral sulfoxide–oxazoline (SOX) ligand bearing a single chiral center on the sulfur was identified as the optimal ligand for the reaction, being efficient both in the C−H cleavage step and the stereocontrol of the allylation step.
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Copper(I)-Catalyzed Enantioselective Nucleophilic Borylation of Aliphatic Ketones: Synthesis of Enantioenriched Chiral Tertiary α-Hydroxyboronates ()
A new method was developed for the first catalytic enantioselective borylation of aliphatic ketones. A variety of substrates reacted efficiently with bis(pinacolato)diboron in the presence of a copper(I)/chiral N-heterocyclic carbene complex catalyst to furnish optically active tertiary α-hydroxyboronates with moderate to high enantioselectivities (up to 94 % ee). Notably, the product could be converted into the chiral tertiary alcohol derivative using a stereospecific boron functionalization process. The theoretical study of the mechanism for the enantioselectivity is also described. Ketone functionalization: The first catalytic enantioselective borylation of ketones is presented. A variety of aliphatic ketones reacted efficiently with bis(pinacolato)diboron in the presence of a copper(I)/chiral N-heterocyclic carbene complex to furnish the corresponding tertiary α-hydroxyboronate esters with moderate to high enantioselectivities.
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Palladium-Catalyzed Enantioselective Redox-Relay Heck Alkynylation of Alkenols To Access Propargylic Stereocenters ()
An enantioselective redox-relay Heck alkynylation of di- and trisubstituted alkenols to construct propargylic stereocenters is disclosed using a new pyridine oxazoline ligand. This strategy allows direct access to chiral β-alkynyl carbonyl compounds employing allylic alcohol substrates in contrast to more traditional conjugate addition methods. Heck alkynylation: A convenient redox-relay Heck strategy to synthesize enantiomerically enriched β-alkynyl carbonyl compounds from allylic alcohols with high functional group tolerance is described. Trisubstituted allylic alcohols are also promising substrates allowing for the formation of propargylic quaternary stereocenters.
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Different Reactivity of As4 towards Disilenes and Silylenes ()
The activation of yellow arsenic is possible with the silylene [PhC(NtBu)2SiN(SiMe3)2] (1) and the disilene [(Me3Si)2N(η1-Me5C5)Si=Si(η1-Me5C5)N(SiMe3)2] (3). The reaction of As4 with 1 leads to the unprecedented As10 cage compound [(LSiN(SiMe3)2)3As10] (2; L=PhC(NtBu)2) with an As7 nortricyclane core stabilized by arsasilene moieties containing silicon(II)bis(trimethylsilyl)amide substituents. In contrast, the compound [Cp*{(SiMe3)2N}SiAs]2 (4) containing a butterfly-like diarsadisilabicyclo[1.1.0]butane unit is formed by the reaction of As4 with the disilene 3. Both compounds were characterized by single-crystal X-ray diffraction analysis, NMR spectroscopy, and mass spectrometry. The reaction outcomes demonstrate the different reaction behavior of yellow arsenic (As4) compared to white phosphorus (P4) in the reactions with the corresponding silylenes and disilenes. As revealed: The reaction of yellow arsenic with the silylene [PhC(NtBu)2SiN(SiMe3)2] and the disilene [(Me3Si)2N(η1-Me5C5)Si=Si(η1-Me5C5)N(SiMe3)2] gives an As10 cage compound with a nortricyclane core and a diarsadisila-butterfly derivative, respectively. These reactions demonstrate the different reaction behavior of yellow arsenic As4 and white phosphorus P4 with the corresponding silicon derivatives.
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Manganese(I)-Catalyzed Regioselective C−H Allenylation: Direct Access to 2-Allenylindoles ()
A MnI-catalyzed regioselective C−H allenylation is reported that allows a broad range of 2-allenylindoles to be synthesized regioselectively on a gram scale under simple conditions. Notably, a highly efficient chirality transfer was observed (up to 93 % ee) in this transformation. This procedure was further found to allow, for the first time, the direct preparation of ketones by MnI-catalyzed C−H activation. Mechanistic investigations revealed that the precoordination of the oxygen atom to the manganese center as well as the congested tertiary carbon atom in the propargylic carbonates play a crucial role. Magic manganese! The title reaction allows simple access to a broad range of 2-allenylindoles with efficient chirality transfer, and for the first time also allows the direct preparation of ketones by MnI-catalyzed C−H activation. The coordination of the carbonate oxygen atom to the Mn catalyst and the congested tertiary carbon atom play crucial roles in the reaction mechanism.
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Biosynthesis of the β-Lactone Proteasome Inhibitors Belactosin and Cystargolide ()
Belactosins and cystargolides are natural product proteasome inhibitors from Actinobacteria. Both feature dipeptidic backbones and a unique β-lactone building block. Herein, we present a detailed investigation of their biosynthesis. Identification and analysis of the corresponding gene clusters indicated that both compounds are assembled by rare single-enzyme amino acid ligases. Feeding experiments with isotope-labeled precursors and in vitro biochemistry showed that the formation of the β-lactone warhead is unprecedented and reminiscent of leucine biosynthesis, and that it involves the action of isopropylmalate synthase homologues. Lactone synthesis: The biosynthesis of belactosins and cystargolides, which are peptidic β-lactone proteasome inhibitors, follows an NRPS- and PKS-independent pathway. The distinct β-lactone moiety is assembled by isopropylmalate synthase like enzymes in a process that is reminiscent of leucine metabolism. The formation of the peptidic backbones is directed by discrete amino acid ligases.
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Ultrafast Delamination of Graphite into High-Quality Graphene Using Alternating Currents ()
To bridge the gap between laboratory-scale studies and commercial applications, mass production of high quality graphene is essential. A scalable exfoliation strategy towards the production of graphene sheets is presented that has excellent yield (ca. 75 %, 1–3 layers), low defect density (a C/O ratio of 21.2), great solution-processability, and outstanding electronic properties (a hole mobility of 430 cm2 V−1 s−1). By applying alternating currents, dual exfoliation at both graphite electrodes enables a high production rate exceeding 20 g h−1 in laboratory tests. As a cathode material for lithium storage, graphene-wrapped LiFePO4 particles deliver a high capacity of 167 mAh g−1 at 1 C rate after 500 cycles. A great alternative: A facile, cost-effective and highly efficient strategy has been developed to delaminate graphite into high-quality graphene by means of alternating currents. This procedure shows great potential to bridge the gap between laboratory-scale research and commercial applications.
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