Angewandte Chemie International Edition

Prototyping Instruments for the Chemical Laboratory Using Inexpensive Electronic Modules ()
Abstract Open‐source electronics and programming can augment chemical and biomedical research. Currently, chemists can choose from a broad range of low‐cost universal electronic modules (microcontroller boards and single‐board computers) and use them to assemble working prototypes of scientific tools to address specific experimental problems and to support daily research work. The learning time can be as short as a few hours, and the required budget is often as low as 50 USD. Prototyping instruments using low‐cost electronic modules gives chemists enormous flexibility to design and construct customized instrumentation, which can reduce the delays caused by limited access to high‐end commercial platforms.
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Spotlights on our sister journals: Angew. Chem. Int. Ed. 34/2018 ()
Angewandte Chemie International Edition, Volume 57, Issue 34, Page 10794-10798, August 20, 2018.
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Arthur C. Cope Scholar Awards: E. P. Balskus, N. Chatani, W. F. DeGrado, F. Glorius, R. R. Knowles, D. Ma, H. D. Maynard, J. P. Morken, G. K. S. Prakash, K. A. Woerpel / Priestley Medal: K. B. Sharpless ()
Angewandte Chemie International Edition, Volume 57, Issue 34, Page 10801-10802, August 20, 2018.
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Corrigendum: Spontaneously Self‐Assembled Naphthalimide Nanosheets: Aggregation‐Induced Emission and Unveiling a‐PET for Sensitive Detection of Organic Volatile Contaminants in Water ()
Angewandte Chemie International Edition, Volume 57, Issue 34, Page 10791-10791, August 20, 2018.
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Corrigendum: Shape‐Controllable and Fluorescent Supramolecular Organic Frameworks Through Aqueous Host–Guest Complexation ()
Angewandte Chemie International Edition, Volume 57, Issue 34, Page 10790-10790, August 20, 2018.
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Graphical Abstract: Angew. Chem. Int. Ed. 34/2018 ()
Angewandte Chemie International Edition, Volume 57, Issue 34, Page 10777-10777, August 20, 2018.
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Frontispiece: Graphene‐Oxide‐Catalyzed Direct CH−CH‐Type Cross‐Coupling: The Intrinsic Catalytic Activities of Zigzag Edges ()
Angewandte Chemie International Edition, Volume 57, Issue 34, August 20, 2018.
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Inside Cover: Amorphous Pure Organic Polymers for Heavy‐Atom‐Free Efficient Room‐Temperature Phosphorescence Emission (Angew. Chem. Int. Ed. 34/2018) ()
Angewandte Chemie International Edition, Volume 57, Issue 34, Page 10774-10774, August 20, 2018.
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Back Cover: A Regio‐ and Diastereoselective Anodic Aryl–Aryl Coupling in the Biomimetic Total Synthesis of (−)‐Thebaine (Angew. Chem. Int. Ed. 34/2018) ()
Angewandte Chemie International Edition, Volume 57, Issue 34, Page 11080-11080, August 20, 2018.
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Inside Back Cover: Chemoenzymatic Synthesis of Advanced Intermediates for Formal Total Syntheses of Tetrodotoxin (Angew. Chem. Int. Ed. 34/2018) ()
Angewandte Chemie International Edition, Volume 57, Issue 34, Page 11079-11079, August 20, 2018.
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Cover Picture: Remote Control of Anion–π Catalysis on Fullerene‐Centered Catalytic Triads (Angew. Chem. Int. Ed. 34/2018) ()
Angewandte Chemie International Edition, Volume 57, Issue 34, Page 10773-10773, August 20, 2018.
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From Electron Crystallography to Single Particle CryoEM (Nobel Lecture) ()
Angewandte Chemie International Edition, Volume 57, Issue 34, Page 10804-10825, August 20, 2018.
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On the Development of Electron Cryo‐Microscopy (Nobel Lecture) ()
Angewandte Chemie International Edition, Volume 57, Issue 34, Page 10842-10846, August 20, 2018.
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Single‐Particle Reconstruction of Biological Molecules—Story in a Sample (Nobel Lecture) ()
Angewandte Chemie International Edition, Volume 57, Issue 34, Page 10826-10841, August 20, 2018.
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Transmission of Unidirectional Molecular Motor Rotation to a Remote Biaryl Axis ()
Abstract Molecular motors undergo repetitive directional motions upon external energy input. A profound challenge is the defined transfer of directional motor motions to remote entities at the molecular scale. Herein, we present a molecular setup that allows for the transfer of the directional rotation of a light‐powered motor unit onto a remote biaryl axis via an ethylene glycol chain link. Based on a combination of X‐ray crystallographic analysis, ECD, and NMR experiments as well as a comprehensive theoretical assessment, we provide evidence for the coupled stepwise directional motions of both molecular units. With the presented setup, facile integration of molecular motor units into larger functional frameworks and complex molecular machines can be explored consciously in the future.
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Axially Chiral Dibenzazepinones by a Palladium(0)‐Catalyzed Atropo‐enantioselective C−H Arylation ()
Abstract Atropo‐enantioselective C−H functionalization reactions are largely limited to the dynamic kinetic resolution of biaryl substrates through the introduction of steric bulk proximal to the axis of chirality. Reported herein is a highly atropo‐enantioselective palladium(0)‐catalyzed methodology that forges the axis of chirality during the C−H functionalization process, enabling the synthesis of axially chiral dibenzazepinones. Computational investigations support experimentally determined racemization barriers, while also indicating C−H functionalization proceeds by an enantio‐determining CMD to yield configurationally stable eight‐membered palladacycles.
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Creating Zipper‐Like van der Waals Gap Discontinuity in Low‐Temperature‐Processed Nanostructured PbBi2nTe1+3n: Enhanced Phonon Scattering and Improved Thermoelectric Performance ()
Abstract Nanoengineered materials can embody distinct atomic structures which deviate from that of the bulk‐grain counterpart and induce significantly modified electronic structures and physical/chemical properties. The phonon structure and thermal properties, which can also be potentially modulated by the modified atomic structure in nanostructured materials, however, are seldom investigated. Employed here is a mild approach to fabricate nanostructured PbBi2nTe1+3n using a solution‐synthesized PbTe‐Bi2Te3 nano‐heterostructure as a precursor. The as‐obtained monoliths have unprecedented atomic structure, differing from that of the bulk counterpart, especially the zipper‐like van der Waals gap discontinuity and the random arrangement of septuple‐quintuple layers. These structural motifs break the lattice periodicity and coherence of phonon transport, leading to ultralow thermal conductivity and excellent thermoelectric z T.
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Total Synthesis and Biological Evaluation of the Glycosylated Macrocyclic Antibiotic Mangrolide A ()
Abstract The macrocyclic antibiotic mangrolide A has been described to exhibit potent activity against a number of clinically important Gram‐negative pathogens. Reported is the first enantioselective total synthesis of mangrolide A and derivatives. Salient features of this synthesis include a highly convergent macrocycle preparation, stereoselective synthesis of the disaccharide moiety, and two β‐selective glycosylations. The synthesis of mangrolide A and its analogues enabled the re‐examination of its activity against bacterial pathogens, and only minimal activity was observed.
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Graphene‐Oxide‐Catalyzed Direct CH−CH‐Type Cross‐Coupling: The Intrinsic Catalytic Activities of Zigzag Edges ()
Abstract The development of graphene oxide (GO)‐based materials for C−C cross‐coupling represents a significant advance in carbocatalysis. Although GO has been used widely in various catalytic reactions, the scope of reactions reported is quite narrow, and the relationships between the type of functional groups present and the specific activity of the GO are not well understood. Herein, we explore CH−CH‐type cross‐coupling of xanthenes with arenes using GO as real carbocatalysts, and not as stoichiometric reactants. Mechanistic studies involving molecular analogues, as well as trapped intermediates, were carried out to probe the active sites, which were traced to quinone‐type functionalities as well as the zigzag edges in GO materials. GO‐catalyzed cross‐dehydrogenative coupling is operationally simple, shows reusability over multiple cycles, can be conducted in air, and exhibits good functional group tolerance.
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Remote Control of Anion–π Catalysis on Fullerene‐Centered Catalytic Triads ()
Abstract The design, synthesis and evaluation of catalytic triads composed of a central C60 fullerene with an amine base on one side and polarizability enhancers on the other side are reported. According to an enolate addition benchmark reaction, fullerene–fullerene–amine triads display the highest selectivity in anion–π catalysis observed so far, whereas NDI–fullerene–amine triads are not much better than fullerene–amine controls (NDI=naphthalenediimide). These large differences in activity are in conflict with the small differences in intrinsic π acidity, that is, LUMO energy levels and π holes on the central fullerene. However, they are in agreement with the high polarizability of fullerene–fullerene–amine triads. Activation and deactivation of the fullerene‐centered triads by intercalators and computational data on anion binding further indicate that for functional relevance, intrinsic π acidity is less important than induced π acidity, that is, the size of the oriented macrodipole of polarizable π systems that emerges only in response to the interaction with anions and anionic transition states. The resulting transformation is thus self‐induced, the anionic intermediates and transition states create their own anion–π catalyst.
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Total Synthesis Establishes the Biosynthetic Pathway to the Naphterpin and Marinone Natural Products ()
Abstract The naphterpins and marinones are naphthoquinone meroterpenoids with an unusual aromatic oxidation pattern that is biosynthesized from 1,3,6,8‐tetrahydroxynaphthalene (THN). We propose that cryptic halogenation of THN derivatives by vanadium‐dependent chloroperoxidase (VCPO) enzymes is key to this biosynthetic pathway, despite the absence of chlorine in these natural products. This speculation inspired a total synthesis to mimic the naphterpin/marinone biosynthetic pathway. In validation of this biogenetic hypothesis, two VCPOs were discovered that interconvert several of the proposed biosynthetic intermediates.
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Molecular Recognition of the Hybrid‐2 Human Telomeric G‐Quadruplex by Epiberberine: Insights into Conversion of Telomeric G‐Quadruplex Structures ()
Abstract Human telomeres can form DNA G‐quadruplex (G4), an attractive target for anticancer drugs. Human telomeric G4s bear inherent structure polymorphism, challenging for understanding specific recognition by ligands or proteins. Protoberberines are medicinal natural‐products known to stabilize telomeric G4s and inhibit telomerase. Here we report epiberberine (EPI) specifically recognizes the hybrid‐2 telomeric G4 predominant in physiologically relevant K+ solution and converts other telomeric G4 forms to hybrid‐2, the first such example reported. Our NMR structure in K+ solution shows EPI binding induces extensive rearrangement of the previously disordered 5′‐flanking and loop segments to form an unprecedented four‐layer binding pocket specific to the hybrid‐2 telomeric G4; EPI recruits the (−1) adenine to form a “quasi‐triad” intercalated between the external tetrad and a T:T:A triad, capped by a T:T base pair. Our study provides structural basis for small‐molecule drug design targeting the human telomeric G4.
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Simultaneous Stabilization of Potassium Metal and Superoxide in K–O2 Batteries on the Basis of Electrolyte Reactivity ()
Abstract In superoxide batteries based on O2/O2− redox chemistry, identifying an electrolyte to stabilize both the alkali metal and its superoxide remains challenging owing to their reactivity towards the electrolyte components. Bis(fluorosulfonyl)imide (FSI−) has been recognized as a “magic anion” for passivating alkali metals. The KFSI–dimethoxyethane electrolyte passivates the potassium metal anode by cleavage of S−F bonds and the formation of a KF‐rich solid–electrolyte interphase (SEI). However, the KFSI salt is chemically unstable owing to nucleophilic attack by superoxide and/or hydroxide species. On the other hand, potassium bis(trifluorosulfonyl)imide (KTFSI) is stable to KO2, but results in mossy potassium deposits and irreversible plating and stripping. To circumvent this dilemma, we developed an artificial SEI for the metal anode and thus long‐cycle‐life K–O2 batteries. This study will guide the development of stable electrolytes and artificial SEIs for metal–O2 batteries.
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Modular One‐Step Three‐Component Synthesis of Tetrahydroisoquinolines Using a Catellani Strategy ()
Abstract Reported is a modular one‐step three‐component synthesis of tetrahydroisoquinolines using a Catellani strategy. This process exploits aziridines as the alkylating reagents, through palladium/norbornene cooperative catalysis, to enable a Catellani/Heck/aza‐Michael addition cascade. This mild, chemoselective, and scalable protocol has broad substrate scope (43 examples, up to 90 % yield). The most striking feature of this protocol is the excellent regioselectivity and diastereoselectivity observed for 2‐alkyl‐ and 2‐aryl‐substituted aziridines to access 1,3‐cis‐substituted and 1,4‐cis‐substituted tetrahydroisoquinolines, respectively. Moreover, this is a versatile process with high step and atom economy.
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Nickel Doping in Atomically Thin Tin Disulfide Nanosheets Enables Highly Efficient CO2 Reduction ()
Abstract Engineering electronic properties by elemental doping is a direct strategy to design efficient catalysts towards CO2 electroreduction. Atomically thin SnS2 nanosheets were modified by Ni doping for efficient electroreduction of CO2. The introduction of Ni into SnS2 nanosheets significantly enhanced the current density and Faradaic efficiency for carbonaceous product relative to pristine SnS2 nanosheets. When the Ni content was 5 atm %, the Ni‐doped SnS2 nanosheets achieved a remarkable Faradaic efficiency of 93 % for carbonaceous product with a current density of 19.6 mA cm−2 at −0.9 V vs. RHE. A mechanistic study revealed that the Ni doping gave rise to a defect level and lowered the work function of SnS2 nanosheets, resulting in the promoted CO2 activation and thus improved performance in CO2 electroreduction.
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Robust Ultramicroporous Metal–Organic Frameworks with Benchmark Affinity for Acetylene ()
Abstract Highly selective separation and/or purification of acetylene from various gas mixtures is a relevant and difficult challenge that currently requires costly and energy‐intensive chemisorption processes. Two ultramicroporous metal–organic framework physisorbents, NKMOF‐1‐M (M=Cu or Ni), offer high hydrolytic stability and benchmark selectivity towards acetylene versus several gases at ambient temperature. The performance of NKMOF‐1‐M is attributed to their exceptional acetylene binding affinity as revealed by modelling and several experimental studies: in situ single‐crystal X‐ray diffraction, FTIR, and gas mixture breakthrough tests. NKMOF‐1‐M exhibit better low‐pressure uptake than existing physisorbents and possesses the highest selectivities yet reported for C2H2/CO2 and C2H2/CH4. The performance of NKMOF‐1‐M is not driven by the same mechanism as current benchmark physisorbents that rely on pore walls lined by inorganic anions.
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Hybrid Organic–Inorganic Rotaxanes, Including a Hetero‐Hybrid [3]Rotaxane Featuring Two Distinct Heterometallic Rings and a Molecular Shuttle ()
Abstract [2] and [3] hybrid rotaxanes are reported based on {Ti7M} rings (M is a trivalent metal such as FeIII or GaIII). NMR studies show that [2]rotaxanes can act as molecular shuttles, while EPR studies of [3]rotaxanes show weak interactions between the paramagnetic components of the supramolecular assemblies.
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Noble‐Metal‐Free Single‐Atom Catalysts CuAl4O7–9− for CO Oxidation by O2 ()
Abstract The single copper atom doped clusters CuAl4O7–9− can catalyze CO oxidation by O2. The CuAl4O7–9− clusters are the first group of experimentally identified noble‐metal free single atom catalysts for such a prototypical reaction. The reactions were characterized by mass spectrometry and density functional theory calculations. The CuAl4O9CO− is much more reactive than CuAl4O9− in the reaction with CO to generate CO2. One adsorbed CO is crucial to stabilize Cu of CuAl4O9− around +I oxidation state and promote the oxidation of another CO. The widely emphasized correlation between the catalytic reactivity of CO oxidation and Cu oxidation state can be understood at the strictly molecular level. The remarkable difference between Cu catalysis and noble‐metal catalysis was discussed.
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Superprotonic Conductivity in Flexible Porous Covalent Organic Framework Membranes ()
Abstract Poor mechanical stability of the polymer electrolyte membranes remains one of the bottlenecks towards improving the performance of the proton exchange membrane (PEM) fuel cells. The present work proposes a unique way to utilize crystalline covalent organic frameworks (COFs) as a self‐standing, highly flexible membrane to further boost the mechanical stability of the material without compromising its innate structural characteristics. The as‐synthesized p‐toluene sulfonic acid loaded COF membranes (COFMs) show the highest proton conductivity (as high as 7.8×10−2 S cm−1) amongst all crystalline porous organic polymeric materials reported to date, and were tested under real PEM operating conditions to ascertain their practical utilization as proton exchange membranes. Attainment of 24 mW cm−2 power density, which is the highest among COFs and MOFs, highlights the possibility of using a COF membrane over the other state‐of‐the‐art crystalline porous polymeric materials reported to date.
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Molecular Ruby under Pressure ()
Abstract The intensely luminescent chromium(III) complexes [Cr(ddpd)2]3+ and [Cr(H2tpda)2]3+ show surprising pressure‐induced red shifts of up to −15 cm−1 kbar−1 for their sharp spin‐flip emission bands (ddpd=N,N′‐dimethyl‐N,N′‐dipyridine‐2‐yl‐pyridine‐2,6‐diamine; H2tpda=2,6‐bis(2‐pyridylamino)pyridine). These shifts surpass that of the established standard, ruby Al2O3:Cr3+, by a factor of 20. Beyond the common application in the crystalline state, the very high quantum yield of [Cr(ddpd)2]3+ enables optical pressure sensing in aqueous and methanolic solution. These unique features of the molecular rubies [Cr(ddpd)2]3+ and [Cr(H2tpda)2]3+ pave the way for highly sensitive optical pressure determination and unprecedented molecule‐based pressure sensing with a single type of emitter.
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Assembly of a Wheel‐Like Eu24Ti8 Cluster under the Guidance of High‐Resolution Electrospray Ionization Mass Spectrometry ()
Abstract A building blocks strategy is an effective approach for constructing the large molecular systems. Herein, we demonstrate that high‐resolution electro‐spray ionization mass spectrometry (HRESI‐MS) provides an effective chance to insight the assemble process of the building blocks and guides the construction of high‐nuclearity metal clusters on the basis of the reaction of Ti(OiPr)4, Eu(acac)3, and salicylic acid. The time‐dependent HRESI‐MS indicates that not only a Eu3Ti building block can be formed, but that it can further assemble into a Eu24Ti8 compound. Temperature‐dependent HRESI‐MS reveals that increase of the reaction temperature favors the formation and crystallization of the stable Eu24Ti8 structure. Single‐crystal structural analysis demonstrates that the Eu24Ti8 has a wheel‐like structure with diameter of ca. 4.1 nm and is the highest nuclearity lanthanide‐titanium oxo cluster reported to date.
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A Regio‐ and Diastereoselective Anodic Aryl–Aryl Coupling in the Biomimetic Total Synthesis of (−)‐Thebaine ()
Abstract The biosynthesis of thebaine is based on the regioselective, intramolecular, oxidative coupling of (R)‐reticuline. For decades, chemists have sought to mimic this coupling by using stoichiometric oxidants. However, all approaches to date have suffered from low yields or the formation of undesired regioisomers. Electrochemistry would represent a sustainable alternative in this respect but all attempts to accomplish an electrochemical synthesis of thebaine have failed so far. Herein, a regio‐ and diastereoselective anodic coupling of 3′,4′,5′‐trioxygenated laudanosine derivatives is presented, which finally enables electrochemical access to (−)‐thebaine.
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Multistage Microfluidic Platform for the Continuous Synthesis of III–V Core/Shell Quantum Dots ()
Abstract We present a fully continuous chip microreactor‐based multistage platform for the synthesis of quantum dots with heterostructures. The use of custom‐designed chip reactors enables precise control of heating profiles and flow distribution across the microfluidic channels while conducting multistep reactions. The platform can be easily reconfigured by reconnecting the differently designed chip reactors allowing for screening of various reaction parameters during the synthesis of nanocrystals. III–V core/shell quantum dots are chosen as model reaction systems, including InP/ZnS, InP/ZnSe, InP/CdS and InAs/InP, which are prepared in flow using a maximum of six chip reactors in series.
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Surfactant Assembly within Pickering Emulsion Droplets for Fabrication of Interior‐Structured Mesoporous Carbon Microspheres ()
Abstract Large‐sized carbon spheres with controllable interior architecture are highly desired, but there is no method to synthesize these materials. Here, we develop a novel method to synthesize interior‐structured mesoporous carbon microspheres (MCMs), based on the surfactant assembly within water droplet‐confined spaces. Our approach is shown to access a library of unprecedented MCMs such as hollow MCMs, multi‐chambered MCMs, bijel‐structured MCMs, multi‐cored MCMs, “solid” MCMs, and honeycombed MCMs. These novel structures, unattainable for the conventional bulk synthesis even at the same conditions, suggest an intriguing effect arising from the droplet‐confined spaces. This synthesis method and the hitherto unfound impact of the droplet‐confined spaces on the microstructural evolution open up new horizons in exploring novel materials for innovative applications.
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An Immobilized‐Dirhodium Hollow‐Fiber Flow Reactor for Scalable and Sustainable C−H Functionalization in Continuous Flow ()
Abstract A scalable flow reactor is demonstrated for enantioselective and regioselective rhodium carbene reactions (cyclopropanation and C−H functionalization) by developing cascade reaction methods employing a microfluidic flow reactor system containing immobilized dirhodium catalysts in conjunction with the flow synthesis of diazo compounds. This allows the utilization of the energetic diazo compounds in a safe manner and the recycling of the dirhodium catalysts multiple times. This approach is amenable to application in a bulk‐scale synthesis employing asymmetric C−H functionalization by stacking multiple fibers in one reactor module. The products from this sequential flow–flow reactor are compared with a conventional batch reactor or flow–batch reactor in terms of yield, regioselectivity, and enantioselectivity.
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Catalytic Oxo/Imido Heterometathesis by a Well‐Defined Silica‐Supported Titanium Imido Complex ()
Abstract Grafting Ti(=NtBu)(Me2Pyr)2(py)2 (Me2Pyr= 2,5‐dimethylpyrrolyl, py=pyridine) onto the surface of silica partially dehydroxylated at 700 °C gives the well‐defined silica‐supported Ti imido complex (≡SiO)Ti(=NtBu)(Me2Pyr)(py)2, which is fully characterized by IR and solid‐state NMR spectroscopy as well as elemental and mass balance analyses. While stoichiometric imido‐transfer reactivity is typical for Ti imides, the obtained surface complex is unique in that it enables catalytic transformations involving Ti imido and oxo intermediates. In particular, it efficiently catalyzes imidation of carbonyl compounds with N‐sulfinylamines by oxo/imido heterometathesis.
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Rhodium‐Catalyzed Intermolecular trans‐Disilylation of Alkynones with Unactivated Disilanes ()
Abstract Disilylation of alkynes could provide rapid entry to synthetically useful 1,2‐bissilyl‐alkenes, but is currently limited to activated disilanes reacting in an intramolecular fashion. Reported herein is an efficient rhodium(I)‐catalyzed intermolecular disilylation of a wide array of alkynones with unactivated disilanes. Importantly, this reaction produces exclusively trans‐disilylation products, selectivity that has been rarely reported. These disilylation products were transformed into interesting pentacyclic vinyl silane ethers, among other additional synthetic manipulations. Mechanistic studies uncovered that the unactivated disilanes underwent facile Si−Si activation and crossover under the reaction conditions.
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Chemoenzymatic Synthesis of Advanced Intermediates for Formal Total Syntheses of Tetrodotoxin ()
Abstract Advanced intermediates for the syntheses of tetrodotoxin reported by the groups of Fukuyama, Alonso, and Sato were prepared. Key steps include the toluene dioxygenase mediated dihydroxylation of either iodobenzene or benzyl acetate. The resulting diene diols were transformed into Fukuyama's intermediate in six steps, into Alonso's intermediate in nine steps, and into Sato's intermediate in ten steps.
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A Two‐Dimensional Hole‐Transporting Material for High‐Performance Perovskite Solar Cells with 20 % Average Efficiency ()
Abstract A readily available small molecular hole‐transporting material (HTM), OMe‐TATPyr, was synthesized and tested in perovskite solar cells (PSCs). OMe‐TATPyr is a two‐dimensional π‐conjugated molecule with a pyrene core and four phenyl‐thiophene bridged triarylamine groups. It can be readily synthesized in gram scale with a low lab cost of around US$ 50 g−1. The incorporation of the phenyl‐thiophene units in OMe‐TATPyr are beneficial for not only carrier transportation through improved charge delocalization and intermolecular stacking, but also potential trap passivation via Pb–S interaction as supported by depth‐profiling XPS, photoluminescence, and electrochemical impedance analysis. As a result, an impressive best power conversion efficiency (PCE) of up to 20.6 % and an average PCE of 20.0 % with good stability has been achieved for mixed‐cation PSCs with OMe‐TATPyr with an area of 0.09 cm2. A device with an area of 1.08 cm2 based on OMe‐TATPyr demonstrates a PCE of 17.3 %.
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Selective Functionalization of Aminoheterocycles by a Pyrylium Salt ()
Abstract The functionalization of aminoheterocycles by using a pyrylium tetrafluoroborate reagent (Pyry‐BF4) is presented. This reagent efficiently condenses with a great variety of heterocyclic amines and primes the C−N bond for nucleophilic aromatic substitution. More than 60 examples for the formation of C−O, C−N, C−S, or C−SO2R bonds are disclosed herein. In contrast to C−N activation through diazotization and polyalkylation, this method is characterized by its mild conditions and impressive functional‐group tolerance. In addition to small‐molecule derivatization, Pyry‐BF4 allows the introduction of functional groups in a late‐stage fashion to furnish highly functionalized structures.
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Alkali Metal Species in the Reversible Activation of H2 ()
Abstract MP(tBu)2 (M=Li, Na, K), KH and KN(SiMe3)2 are shown to activate HD reversibly. In the case of MP(tBu)2 this leads to isotopic scrambling and the formation of H2, D2, H(D)P(tBu)2 and MH(D) in C6D6. In toluene, KP(tBu)2 reacts with H2 but also leads to isotopic scrambling into the methyl groups of the solvent toluene. DFT calculations reveal that these systems effect H2 activation via cooperative interactions with the Lewis acidic alkali metal and the basic phosphorus, carbanion, or hydride centres, mimicking frustrated Lewis pair (FLP) behaviour.
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Cyclopentene Annulations of Alkene Radical Cations with Vinyl Diazo Species Using Photocatalysis ()
Abstract A direct (3+2) cycloaddition between alkenes and vinyl diazo reagents using either Cr or Ru photocatalysis is described. The intermediacy of a radical cation species enables a nucleophilic interception by vinyl diazo compounds, a departure from their traditional electrophilic behavior. A variety of cyclopentenes are synthesized using this method, and experimental insights implicate a direct cycloaddition instead of a cyclopropanation/rearrangement process.
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Electron‐Transporting Bis(heterotetracenes) with Tunable Helical Packing ()
Abstract A novel kind of electron‐deficient bis(heterotetracenes) namely perylenotetrathiophenediimides (PTTIs) involving double S‐hetero[5]helicene diimides, is developed by a fourfold thienannulation route via ortho‐functionalization of perylene diimides (PDIs). PTTIs exhibit significantly red‐shifted absorption capacity with lowest‐energy transition maxima beyond 700 nm and narrowed HOMO–LUMO energy gaps. Through delicately tuning the side‐chain substitution, the distorted propeller‐like framework could self‐assemble into unprecedented 1D helical π‐stacking structures with short π–π contacts and rich nonbonding interactions from alternating arrangements of P/M enantiomeric couples or tetrads. Excellent electron transporting efficiency in racemate PTTI crystals with 0.40 cm2 V−1 s−1 for 5 a and 0.90 cm2 V−1 s−1 for 5 b, was witnessed in single‐crystalline transistors, signifying the prospects of the chiral π‐helix in optoelectronic applications.
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Nickel‐Catalyzed Amination of Silyloxyarenes through C–O Bond Activation ()
Abstract Silyloxyarenes were utilized as electrophilic coupling partners with amines in the synthesis of aniline derivatives. A diverse range of amine substrates were used, including cyclic or acyclic secondary amines, secondary anilines, and sterically hindered primary anilines. Additionally, a range of sterically hindered and unhindered primary aliphatic amines were employed, which have previously been challenging with other classes of aryl ether electrophiles. Orthogonal couplings of silyloxyarenes with aryl methyl ethers are illustrated, where selectivity between the two C−O electrophiles is determined by ligand control, thereby allowing complementary and selective late‐stage diversification of either electrophile. Finally, a sequential coupling displays the utility of this amination method along with the reversal in intrinsic reactivity between aryl methyl ethers and silyloxyarenes.
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Asymmetric Synthesis of Spirocyclic β‐Lactams through Copper‐Catalyzed Kinugasa/Michael Domino Reactions ()
Abstract The first copper‐catalyzed highly chemo‐, regio‐, diastereo‐, and enantioselective Kinugasa/Michael domino reaction for the desymmetrization of prochiral cyclohexadienones is described. In the presence of a chiral copper catalyst, alkyne‐tethered cyclohexadienones couple with nitrones to generate the chiral spirocyclic lactams with excellent stereoselectivity (up to 97 % ee, >20:1 dr). The new method provides direct access to versatile highly functionalized spirocyclic β‐lactams possessing four contiguous stereocenters, including one quaternary and one tetra‐substituted stereocenter.
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Facile Preparation of Hydrophobic Colloidal MFI and CHA Crystals and Oriented Ultrathin Films ()
Abstract We report novel routes for synthesis of defect‐free, hydrophobic and monodispersed 10 nm (5 unit cells) thick MFI crystals and 100 nm CHA crystals. The crystals are obtained in high yield and display very high 1‐butanol adsorption from aqueous solution. These crystals are assembled in monolayers for the growth of ultrathin and uniformly oriented films with thicknesses of 36 nm and 330 nm, respectively, using a synthesis gel in the form of a powder. This method is very simple and may open up for industrial preparation of materials with improved performances.
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Repeat Module‐Based Rational Design of a Photoswitchable Protein for Light‐Driven Control of Biological Processes ()
Abstract Light‐driven control of biological processes using photoswitchable proteins allows high spatiotemporal interrogation or manipulation of such processes, assisting in understanding their functions. Despite considerable advances, however, the wide spread use of optical control has been hampered by a limited repertoire of photoswitchable proteins and a lack of generalized design strategy. Herein, we present a repeat module‐based rational design of a photoswitchable protein composed of LRR (Leucine‐rich repeat) modules using azobenzene as a photochromic ligand. Our design approach involves the rational selection of a Cβ pair between two nearby modules within a convex region and subsequent cross‐linking with a photochromic ligand. We demonstrate the general utility and potential of our strategy by showing the design of three target‐specific photoswitchable proteins and a light‐driven modulation of the cell signaling. With an abundance of LRR proteins in nature, our approach can expand the repertoire of photoswitchable proteins for light‐driven control of biological processes.
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Amorphous Pure Organic Polymers for Heavy‐Atom‐Free Efficient Room‐Temperature Phosphorescence Emission ()
Abstract Pure organic, heavy‐atom‐free room‐temperature phosphorescence (RTP) materials have attracted much attention and have potential applications in photoelectric and biochemical material fields owing to their rich excited state properties. They offer long luminescent lifetime, diversified design, and facile preparation. However, recent achievements of efficient phosphorescence under ambient conditions mainly focus on ordered crystal lattices or embedding into rigid matrices, which require strict growth conditions and have poor reproducibility. Herein, we developed a concise approach to give RTP with a decent quantum yield and ultralong phosphorescence lifetime in the amorphous state by radical binary copolymerization of acrylamide and different phosphors with oxygen‐containing functional groups. The cross‐linked hydrogen‐bonding networks between the polymeric chains immobilize phosphors to suppress non‐radiative transitions and provide a microenvironment to shield quenchers.
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Dry Chemistry of Ferrate(VI): A Solvent‐Free Mechanochemical Way for Versatile Green Oxidation ()
Abstract The +6 oxidation state of iron generally exists in the form of ferrate(VI) with high redox potential and environmentally friendly nature. Although ferrate(VI) has been known for over a century, its chemistry is still limited to the solvent‐based reactions that suffers from the insolubility/instability of this oxidant and the environmental issues caused by hazardous solvents. Herein, we explore the solvent‐free reactivity of ferrate(VI) under mechanical milling, revealing that its strong oxidizing power is accessible in the “dry” solid state towards a broad variety of substrates, for example, aromatic alcohols/aldehydes and carbon nanotubes. More significantly, solvent‐free mechanochemistry also reshapes the oxidizing ability of ferrate(VI) due to the underlying solvent‐free effect and the promotive mechanical actions. This study opens up a new chemistry of ferrate(VI) with promising application in green oxidative transformation of both organic and inorganic substrates.
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A Deprotonation Approach to the Unprecedented Amino‐Trimethylenemethane Chemistry: Regio‐, Diastereo‐, and Enantioselective Synthesis of Complex Amino Cycles ()
Abstract The first realization of the amino‐trimethylenemethane chemistry is reported using a deprotonation strategy to simplify the synthesis of the amino‐trimethylenemethane donor in two steps from commercial and inexpensive materials. A broad scope of cycloaddition acceptors (seven different classes) participated in the chemistry, chemo‐, regio‐, diastereo‐, and enantioselectively generating various types of highly valuable complex amino cycles. Multiple derivatization reactions that further elaborated the initial amino cycles were performed without isolation of the crude product. Ultimately, we applied the amino‐trimethylenemethane chemistry to synthesize a potential pharmaceutical in 8 linear steps and 7.5 % overall yield, which previously was achieved in 18 linear steps and 0.6 % overall yield.
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Reaction of CO2 with a Vanadium(II) Aryl Oxide: Synergistic Activation of CO2/Oxo Groups towards H‐Atom Radical Abstraction ()
Abstract Treatment of divalent (ONNO)V(TMEDA) (1; ONNO=[2,4‐Me2‐2‐(OH)C6H2CH2]2N(CH2)2NMe2) with CO2 afforded [(ONNO)V]2(μ‐OH)(μ‐formate) (2). Whereas the bridging hydroxo and formate groups both originated from CO2, the H atoms present on the two residues were obtained through H‐atom radical abstraction from the solvent. DFT calculations revealed an initially linear CO2 bonding mode, followed by deoxygenation, and highlighted a synergistic effect between the so‐formed oxo group and an additional bridging CO2 residue in promoting radical behavior.
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Nonlinear Unmixing of Hyperspectral Datasets for the Study of Painted Works of Art ()
Abstract Nonlinear unmixing of hyperspectral reflectance data is one of the key problems in quantitative imaging of painted works of art. The approach presented is to interrogate a hyperspectral image cube by first decomposing it into a set of reflectance curves representing pure basis pigments and second to estimate the scattering and absorption coefficients of each pigment in a given pixel to produce estimates of the component fractions. This two‐step algorithm uses a deep neural network to qualitatively identify the constituent pigments in any unknown spectrum and, based on the pigment(s) present and Kubelka–Munk theory to estimate the pigment concentration on a per‐pixel basis. Using hyperspectral data acquired on a set of mock‐up paintings and a well‐characterized illuminated folio from the 15th century, the performance of the proposed algorithm is demonstrated for pigment recognition and quantitative estimation of concentration.
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Site‐Specific Labeling of Affimers for DNA‐PAINT Microscopy ()
Abstract Optical super‐resolution techniques allow fluorescence imaging below the classical diffraction limit of light. From a technology standpoint, recent methods are approaching molecular‐scale spatial resolution. However, this remarkable achievement is not easily translated to imaging of cellular components, since current labeling approaches are limited by either large label sizes (antibodies) or the sparse availability of small and efficient binders (nanobodies, aptamers, genetically‐encoded tags). In this work, we combined recently developed Affimer reagents with site‐specific DNA modification for high‐efficiency labeling and imaging using DNA‐PAINT. We assayed our approach using an actin Affimer. The small DNA‐conjugated affinity binders could provide a solution for efficient multitarget super‐resolution imaging in the future.
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Photoinduced Miyaura Borylation by a Rare‐Earth‐Metal Photoreductant: The Hexachlorocerate(III) Anion ()
Abstract The first photoinduced carbon(sp2)–heteroatom bond forming reaction by a rare‐earth‐metal photoreductant, a Miyaura borylation, has been achieved. This simple, scalable, and novel borylation method that makes use of the hexachlorocerate(III) anion ([CeIIICl6]3−, derived from CeCl3) has a broad substrate scope and functional‐group tolerance and can be conducted at room temperature. Combined with Suzuki–Miyaura cross‐coupling, the method is applicable to the synthesis of various biaryl products, including through the use of aryl chloride substrates.
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Chiral Phosphoric Acid Catalyzed Asymmetric Synthesis of Hetero‐triarylmethanes from Racemic Indolyl Alcohols ()
Abstract The direct enantioselective 1,4‐ and 1,8‐arylations of 7‐methide‐7H‐indoles and 6‐methide‐6H‐indoles, respectively, generated in situ from diarylmethanols, with electron‐rich arenes as nucleophiles, has been achieved in the presence of chiral phosphoric acids (CPAs). These two remote activation protocols provide an efficient approach for the construction of diverse hetero‐triarylmethanes in high yields (up to 97 %) and with excellent enantioselectivities (up to 96 %). Mechanistically inspired experiments tentatively indicate that the catalytic enantioselective 1,4‐addition as well as the formal SN1 substitution could proceed efficiently in the similar catalytic systems. Furthermore, the modification of the catalytic system and diarylmethanol structure successfully deviates the reactivity toward a remote, highly enantioselective 1,8‐arylation reaction. This flexible activation mode and novel reactivity of diarylmethanols expand the synthetic potential of chiral phosphoric acids.
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Nickel–Iron Layered Double Hydroxide Hollow Polyhedrons as a Superior Sulfur Host for Lithium–Sulfur Batteries ()
Abstract We have designed and synthesized novel hollow Ni/Fe layered double hydroxide (LDH) polyhedrons as an advanced sulfur host for enhancing the performance of lithium–sulfur (Li–S) batteries. The Ni/Fe LDH host shows multiple advantages. First, the Ni/Fe LDH shells can provide sufficient sulfiphilic sites for chemically bonding with polysulfides. Second, the hollow architecture can provide sufficient inner space for both loading a large amount of sulfur and accommodating its large volumetric expansion. Moreover, once the active material is confined within the host, the shells could easily restrict the outward diffusion of polysulfides, guaranteeing prolonged cycle life even with high sulfur loading. As a result, the S@Ni/Fe LDH cathode has successfully solved the main issues related to sulfur electrodes, and it exhibits significantly improved electrochemical performances with prolonged life over 1000 cycles and excellent rate properties.
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Control of the Alternating Sequence for N‐Isopropylacrylamide (NIPAM) and Methacrylic Acid Units in a Copolymer by Cyclopolymerization and Transformation of the Cyclopendant Group ()
Abstract An alternating copolymer of methacrylic acid and N‐isopropyl acrylamide (NIPAM) was synthesized by selective cyclopolymerization of a special divinyl monomer and transformation of repeating cyclo‐units in the resultant cyclopolymer. Crucial to the breakthrough is the monomer design in view of two types of cleavable bonds (3° ester and activated ester) in the pendant group of the monomer and the lower reactivity ratio of the two double bonds (methacrylate and electron‐poor acrylate) for the polymerizable groups. The thus‐obtained cyclopolymer was transformed into the alternating copolymer by transformation of the activated ester into amide by isopropyl amine and cleavage of the 3° ester by trifluoroacetic acid. The resultant copolymer showed thermal and pH response in aqueous solution that was different from the 1:1 random copolymer as well as the homopolymers.
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Copper‐Catalyzed Ring‐Opening Silylation of Benzofurans with Disilane ()
Abstract The catalytic ring‐opening silylation of benzofurans has been achieved by employing a copper catalyst and 1,2‐di‐tert‐butoxy‐1,1,2,2‐tetramethyldisilane, which could be easily prepared and handled without special care. The reaction afforded (E)‐o‐(β‐silylvinyl)phenols with complete stereoselectivity. The scope of benzofurans was well explored, and functional groups such as chloro, fluoro, and acetal were compatible with the reaction conditions. DFT calculations were used to determine the energy profile of the silylation and the origin of the stereoselectivity. The silylated product was proven to be useful as a synthetic intermediate and subsequently underwent transformations such as Pd‐catalyzed cross‐coupling with iodoarenes.
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RGB‐Color Intensiometric Indicators to Visualize Spatiotemporal Dynamics of ATP in Single Cells ()
Abstract Adenosine triphosphate (ATP) provides energy for the regulation of multiple cellular processes in living organisms. Capturing the spatiotemporal dynamics of ATP in single cells is fundamental to our understanding of the mechanisms underlying cellular energy metabolism. However, it has remained challenging to visualize the dynamics of ATP in and between distinct intracellular organelles and its interplay with other signaling molecules. Using single fluorescent proteins, multicolor ATP indicators were developed, enabling the simultaneous visualization of subcellular ATP dynamics in the cytoplasm and mitochondria of cells derived from mammals, plants, and worms. Furthermore, in combination with additional fluorescent indicators, the dynamic interplay of ATP, cAMP, and Ca2+ could be visualized in activated brown adipocyte. This set of indicator tools will facilitate future research into energy metabolism.
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Qichun Zhang ()
Angewandte Chemie International Edition, Volume 57, Issue 34, Page 10800-10800, August 20, 2018.
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A Practical and General Amidation Method from Isocyanates Enabled by Flow Technology ()
Abstract The addition of carbon nucleophiles to isocyanates represents a conceptually flexible and efficient approach to the preparation of amides. This general synthetic strategy has, however, been relatively underutilized owing to narrow substrate tolerance and the requirement for less favourable reaction conditions. Herein, we disclose a high‐yielding, mass‐efficient, and scalable method with appreciable functional group tolerance for the formation of amides by reaction of Grignard reagents with isocyanates. Through the application of flow chemistry and the use of substoichiometric amounts of CuBr2, this process has been developed to encompass a broad range of substrates, including reactants found to be incompatible with previously published procedures.
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2D Organic Photonics: An Asymmetric Optical Waveguide in Self‐Assembled Halogen‐Bonded Cocrystals ()
Abstract Anisotropic organic molecular construction and packing are crucial for the optoelectronic properties of organic crystals. Two‐dimensional (2D) organic crystals with regular morphology and good photon confinement are potentially suitable for a chip‐scale planar photonics system. Herein, through the bottom‐up process, 2D halogen‐bonded DPEpe‐F4DIB cocrystals were fabricated that exhibit an asymmetric optical waveguide with the optical‐loss coefficients of RBackward=0.0346 dB μm−1 and RForward=0.0894 dB μm−1 along the [010] crystal direction, which can be attributed to the unidirectional total internal reflection caused by the anisotropic molecular packing mode. Based on this crystal direction‐oriented asymmetric photon transport, these as‐prepared 2D cocrystals have been demonstrated as a microscale optical logic gate with multiple input/out channels, which will offer potential applications as the 2D optical component for the integrated organic photonics.
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Yujie Xiong ()
Angewandte Chemie International Edition, EarlyView.
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ORCHEM Prizes for Ivana Fleischer and Florian Beuerle / Emil Fischer Medal for Thorsten Bach / Leonidas Zervas Award for Christian P. R. Hackenberger / Hanwha‐Total IUPAC Young Scientist Award for Andreas Walther / Thieme–IUPAC Prize for Seth Herzon / Greifswald Research Award for Uwe T. Bornscheuer / Melvin Calvin Award for Troels Skrydstrup ()
Angewandte Chemie International Edition, EarlyView.
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Jishan Wu ()
Angewandte Chemie International Edition, EarlyView.
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Ryoji Noyori ACES Award for Martin G. Banwell / Liebig Memorial Medal for Wolfgang Schnick / Izatt–Christensen Award for Philip A. Gale / Cram Lehn Pedersen Prize for Rafal Klajn ()
Angewandte Chemie International Edition, EarlyView.
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Three‐Dimensional Heterocycles by Iron‐Catalyzed Ring‐Closing Sulfoxide Imidation ()
Abstract A general and atom‐economical method for the synthesis of cyclic sulfoximines by intramolecular imidations of azido‐containing sulfoxides using a commercially available FeII phthalocyanine (FeIIPc) as catalyst has been developed. The method conveys a broad functional group tolerance and the resulting three‐dimensional heterocycles can be modified by cross‐coupling reactions.
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Combining Electrodeposition and Optical Microscopy for Probing Size‐Dependent Single‐Nanoparticle Electrochemistry ()
Abstract Electrodeposition of nanoparticles (NPs) is a promising route for the preparation of highly electroactive nanostructured electrodes. By taking advantage of progressive electrodeposition, disordered arrays with a wide size distribution of Ag NPs are produced. Combined with surface‐reaction monitoring by using highly sensitive backside absorbing‐layer optical microscopy (BALM), such arrays offer a platform for screening size‐dependent electrochemistry at the single NP level. In particular, this strategy allows rationalizing the electrodeposition dynamics at the single‐NP level (>10 nm), up to the point of quantifying the presence of metal nanoclusters (<2 nm), and probing easier NP oxidation with size decrease, either through electrochemical or galvanic reactions.
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Multidirectional Activity Control of Cellular Processes by a Versatile Chemo‐optogenetic Approach ()
Abstract The spatiotemporal dynamics of proteins or organelles plays a vital role in controlling diverse cellular processes. However, acute control of activity at distinct locations within a cell is challenging. A versatile multidirectional activity control (MAC) approach is presented, which employs a photoactivatable system that may be dimerized upon chemical inducement. The system comprises second‐generation SLF*‐TMP (S*T) and photocaged NvocTMP‐Cl dimerizers; where, SLF*‐TMP features a synthetic ligand of the FKBP(F36V) binding protein, Nvoc is a caging group, and TMP is the antibiotic trimethoprim. Two MAC strategies are demonstrated to spatiotemporally control cellular signaling and intracellular cargo transport. The novel platform enables tunable, reversible, and rapid control of activity at multiple compartments in living cells.
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Capturing the Genesis of an Active Fischer–Tropsch Synthesis Catalyst with Operando X‐ray Nanospectroscopy ()
Abstract A state‐of‐the‐art operando spectroscopic technique is applied to Co/TiO2 catalysts, which account for nearly half of the world's transportation fuels produced by Fischer–Tropsch catalysis. This allows determination of, at a spatial resolution of approximately 50 nm, the interdependence of formed hydrocarbon species in the inorganic catalyst. Observed trends show intra‐ and interparticular heterogeneities previously believed not to occur in particles under 200 μm. These heterogeneities are strongly dependent on changes in H2/CO ratio, but also on changes thereby induced on the Co and Ti valence states. We have captured the genesis of an active FTS particle over its propagation to steady‐state operation, in which microgradients lead to the gradual saturation of the Co/TiO2 catalyst surface with long chain hydrocarbons (i.e., organic film formation).
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Chiral N,N Ligands Enabling Palladium‐Catalyzed Enantioselective Intramolecular Heck–Matsuda Carbonylation Reactions by Sequential Migratory and CO Insertions ()
Abstract Unprecedented enantioselective intramolecular Heck carbonylation reactions of arenediazonium salts were enabled by a chiral N,N ligand. This reaction constitutes the first enantioselective Heck carbonylation that proceeds through migratory insertion followed by CO insertion. The enantioenriched functionalized dihydrobenzofurans were obtained in good to high yields and enantiomeric ratios of up to 98:2 under mild and operationally simple reaction conditions.
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Emerging Methods and Design Principles for Cell‐Penetrant Peptides ()
Abstract Biomolecules such as antibodies, proteins, and peptides are important tools for chemical biology and leads for drug development. They have been used to inhibit a variety of extracellular proteins, but accessing intracellular proteins has been much more challenging. In this review, we discuss diverse chemical approaches that have yielded cell‐penetrant peptides and identify three distinct strategies: masking backbone amides, guanidinium group patterning, and amphipathic patterning. We summarize a growing number of large data sets, which are starting to reveal more specific design guidelines for each strategy. We also discuss advantages and disadvantages of current methods for quantifying cell penetration. Finally, we provide an overview of best‐odds approaches for applying these new methods and design principles to optimize cytosolic penetration for a given bioactive peptide.
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The Relationship between the Relative Solvating Power of Electrolytes and Shuttling Effect of Lithium Polysulfides in Lithium–Sulfur Batteries ()
Abstract Relative solvating power, that is, the ratio of the coordination ratios between a solvent and the reference solvent, was used to probe the quantitative structure–activity relationship of electrolyte solvents and the lithium polysulfide (LiPS) dissolution in lithium–sulfur batteries. Internally referenced diffusion‐ordered nuclear magnetic resonance spectroscopy (IR‐DOSY) was used to determine the diffusion coefficient and coordination ratio, from which the relative solvating power can be easily measured. The higher the relative solvating power of an ethereal solvent, the more severe will be the LiPS dissolution and the lower the coulombic efficiency of the lithium–sulfur battery. A linear relationship was established between the logarithm of relative solvating power of a solvent and the degree of LiPS dissolution, rendering relative solvating power an important parameter in choosing the electrolyte solvent for lithium–sulfur batteries.
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Giant Hysteretic Single‐Molecule Electric Polarisation Switching above Room Temperature ()
Abstract Continual progress has been achieved in information technology through unrelenting miniaturisation of the single memory bit in integrated ferromagnetic, ferroelectric, optical, and related circuits. However, as miniaturisation approaches its theoretical limit, new memory materials are being sought. Herein, we report a unique material exhibiting single‐molecule electric polarisation switching that can operate above room temperature. The phenomenon occurs in a Preyssler‐type polyoxometalate (POM) cluster we call a single‐molecule electret (SME). It exhibits all the characteristics of ferroelectricity but without long‐range dipole ordering. The SME affords bi‐stability as a result of the two potential positions of localisation of a Tb3+ ion trapped in the POM, resulting in extremely slow relaxation of the polarisation and electric hysteresis with high spontaneous polarisation and coercive electric fields. Our findings suggest that SMEs can potentially be applied to ultrahigh‐density memory and other molecular‐level electronic devices operating above room temperature.
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Thermally Induced Valence Tautomeric Transition in a Two‐Dimensional Fe‐Tetraoxolene Honeycomb Network ()
Abstract A novel tetraoxolene‐bridged Fe two‐dimensional honeycomb layered compound, (NPr4)2[Fe2(Cl2An)3] ⋅2 (acetone)⋅H2O (1), where Cl2Ann−=2,5‐dichloro‐3,6‐dihydroxy‐1,4‐benzoquinonate and NPr4+=tetrapropylammonium cation, has been synthesized. 1 revealed a thermally induced valence tautomeric transition at T1/2=236 K (cooling)/237 K (heating) between Fem+ (m=2 or 3) and Cl2Ann− (n=2 or 3) that induced valence modulations between [FeIIHSFeIIIHS(Cl2An2−)2(Cl2An.3−)]2− at T>T1/2 and [FeIIIHSFeIIIHS(Cl2An2−)(Cl2An.3−)2]2− at T
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N‐Heterocyclic Carbene Iron(III) Porphyrin‐Catalyzed Intramolecular C(sp3)–H Amination of Alkyl Azides ()
Abstract Metal‐catalyzed intramolecular C−H amination of alkyl azides constitutes an appealing approach to alicyclic amines; challenges remain in broadening substrate scope, enhancing regioselectivity, and applying the method to natural product synthesis. Herein we report an iron(III) porphyrin bearing axial N‐heterocyclic carbene ligands which catalyzes the intramolecular C(sp3)–H amination of a wide variety of alkyl azides under microwave‐assisted and thermal conditions, resulting in selective amination of tertiary, benzylic, allylic, secondary, and primary C−H bonds with up to 95 % yield. 14 out of 17 substrates were cyclized selectively at C4 to give pyrrolidines. The regioselectivity at C4 or C5 could be tuned by modifying the reactivity of the C5–H bond. Mechanistic studies revealed a concerted or a fast re‐bound mechanism for the amination reaction. The reaction has been applied to the syntheses of tropane, nicotine, cis‐octahydroindole, and leelamine derivatives.
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Highly Diastereo‐ and Enantioselective Synthesis of Cyclohepta[b]indoles by Chiral‐Phosphoric‐Acid‐Catalyzed (4+3) Cycloaddition ()
Abstract A highly enantio‐ and diastereoselective formal (4+3) cycloaddition of 1,3‐diene‐1‐carbamates with 3‐indolylmethanols in the presence of a chiral phosphoric acid catalyst is reported. The approach described herein provides efficient access to 6‐aminotetrahydrocyclohepta[b]indoles in good yields with mostly complete diastereoselectivity and excellent levels of enantioselectivity (>98:2 dr and up to 98 % ee). Mild reaction conditions, facile scale‐up, and versatile derivatization highlight the practicality of this methodology. A mechanistic study suggests that cycloaddition occurs in a stepwise fashion, after the formation of an ion pair between the chiral catalytic phosphate and the intermediate carbocation.
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A Rotaxane‐like Cage‐in‐Ring Structural Motif for a Metallosupramolecular Pd6L12 Aggregate ()
Abstract A BODIPY‐based bis(3‐pyridyl) ligand undergoes self‐assembly upon coordination to tetravalent palladium(II) cations to form a Pd6L12 metallosupramolecular assembly with an unprecedented structural motif that resembles a rotaxane‐like cage‐in‐ring arrangement. In this assembly the ligand adopts two different conformations—a C‐shaped one to form a Pd2L4 cage which is located in the center of a Pd4L8 ring consisting of ligands in a W‐shaped conformation. This assembly is not mechanically interlocked in the sense of catenation but it is stabilized only by attractive π‐stacking between the peripheral BODIPY chromophores and the ligands’ skeleton as well as attractive van der Waals interactions between the long alkoxy chains. As a result, the co‐arrangement of the two components leads to a very efficient space filling. The overall structure can be described as a rotaxane‐like assembly with a metallosupramolecular cage forming the axle in a metallosupramolecular ring. This unique structural motif could be characterized via ESI mass spectrometry, NMR spectroscopy, and X‐ray crystallography.
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NHC‐Catalyzed Electrophilic Trifluoromethylation: Efficient Synthesis of γ‐Trifluoromethyl α,β‐Unsaturated Esters ()
Abstract Described herein is a highly regioselective and efficient N‐heterocyclic‐carbene‐catalyzed γ‐trifluoromethylation of vinylogous enolates. Control experiments and DFT calculations provided important insight into the reaction mechanism.
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Metal‐Free Synthesis of Pharmaceutically Important Biaryls by Photosplicing ()
Abstract Many pharmaceuticals feature biaryl motifs that are crucial for their binding to the target. Yet, benchmark methods for selective cross‐couplings rely on highly toxic heavy metal catalysts, which are unfavorable in the synthesis of pharmaceuticals. Metal‐free coupling reactions, on the other hand, may require harsh conditions and lack selectivity. We report a novel, metal‐free cross‐coupling reaction that involves the tethering of two phenyl groups by a temporary, traceless sulfonamide linker that directs a photochemical aryl fusion into a single coupling product. The perfect regio‐ and chemoselectivity of the reaction could be rationalized by a cyclic intermediate, which fragments into the biaryl and volatile side products. Using a flow reactor, we synthesized numerous substituted biaryl building blocks for important therapeutics in high yields, such as antibiotics, antitumor, neuroprotective and cholesterol‐lowering agents as well as antiarthritic non‐steroidal antiinflammatory drugs (NSAIDs). The new method was successfully employed in a total synthesis of cannabinol, an important analgesic and antiemetic therapeutic. We also report a metal‐free synthesis of key building blocks used for the preparation of sartans, antihypertensive agents that rank among the top blockbuster drugs worldwide. This safe and convenient protocol is a valuable alternative for the widely used metal‐dependent aryl cross‐coupling methods.
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Experimental Evidence for a Triboluminescent Antiperovskite Ferroelectric: Tris(trimethylammonium) catena‐Tri‐μ‐chloro‐manganate(II) Tetrachloromanganate(II) ()
Abstract The perovskite structure is rich in ferroelectricity. In contrast, ferroelectric antiperovskites have been scarcely confirmed experimentally since the discovery of M3AB‐type antiperovskites in the 1930s. Ferroelectricity is now revealed in an organic–inorganic hybrid X3AB antiperovskite structure, which exhibits a clear ferroelectric phase transition 6/mmmF6mm with a high Curie point of 480 K. The physical properties across the phase transition are obviously changed along with the symmetry requirements, providing solid experimental evidence for the ferroelectric phase transition. More interestingly, the discovered antiperovskite shows intense photoluminescence and triboluminescence properties. The confirmation of the triboluminescent ferroelectric antiperovskite will open new avenues to explore excellent optoelectronic properties in the antiperovskite family.
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Chiral Carboxylic Acid Enabled Achiral Rhodium(III)‐Catalyzed Enantioselective C−H Functionalization ()
Abstract Reported is an achiral CpxRhIII/chiral carboxylic acid catalyzed asymmetric C−H alkylation of diarylmethanamines with a diazomalonate, followed by cyclization and decarboxylation to afford 1,4‐dihydroisoquinolin‐3(2H)‐one. Secondary alkylamines as well as nonprotected primary alkylamines underwent the transformation with high enantioselectivities (up to 98.5:1.5 e.r.) by using a newly developed chiral carboxylic acid as the sole source of chirality to achieve enantioselective C−H cleavage by a concerted metalation‐deprotonation mechanism.
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Light‐Triggered Release of Trapped Charges in Molecular Assemblies ()
Abstract We demonstrate the mediation of charge transport and release in thin films and devices by shifting the redox properties of layers of metal complexes by light. The nanoscale surface arrangement of both photo‐ and electrochemically‐active components is essential for the function of the thin films. Layers of well‐defined ruthenium complexes on indium‐tin‐oxide electrodes provide electron‐transport channels that allow the electrochemical addressing of layers of isostructural cobalt complexes. These cobalt complexes are electrochemically inactive when assembled directly on transparent metal‐oxide electrodes. The interlayer of ruthenium complexes on such electrodes allows irreversible oxidation of the cobalt complexes. However, shifting the redox properties of the ruthenium complexes by excitation with light opens up an electron‐transport channel to reduce the cobalt complexes; hence releasing the trapped positive charges.
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Photochromic Benzo[b]phosphole Alkynylgold(I) Complexes with Mechanochromic Property to Serve as Multistimuli‐Responsive Materials ()
Abstract A series of novel benzo[b]phosphole alkynylgold(I) complexes has been demonstrated to display photochromic and mechanochromic properties upon applying the respective stimuli of light and mechanical force. Promising multistimuli‐responsive properties of this series of gold(I) complexes have been successfully achieved through judicious molecular design, which involves incorporation of the photochromic dithienylethene‐containing benzo[b]phosphole into the triphenylamine‐containing arylethynyl ligand that is susceptible to mechanical force‐induced color changes via gold(I) complexation. With excellent thermal irreversibility and robust fatigue resistance of this series of gold(I) complexes, multicolor states controlled by the photochromism and mechanochromism have been realized. Repeatable photochromic and mechanochromic cycles without apparent loss of reactivity have also been observed under ambient conditions. The present work provides important insight and an alternative strategy for the molecular design of multistimuli‐responsive materials, paving the way for further development of the underexplored photoresponsive gold(I) complexes and the multistate photocontrolled system.
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Copper‐Catalyzed Tandem Hydrocupration and Diastereo‐ and Enantioselective Borylalkyl Addition to Aldehydes ()
Abstract We report the copper‐catalyzed stereoselective addition of in situ generated chiral boron‐α‐alkyl intermediates to various aldehydes including α,β‐unsaturated aldehydes under mild conditions. This tandem and multicomponent method facilitated the synthesis of enantiomerically enriched 1,2‐hydroxyboronates bearing contiguous stereocenters in good yield with high diastereo‐ and enantioselectivity up to a ratio greater than 98:2. In particular, α,β‐unsaturated aldehydes were successfully used as electrophiles in Cu−H catalysis through 1,2‐addition without significant reduction. The resulting 1,2‐hydroxyboronates were used in various transformations.
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Visible Light Mediated Aryl Migration by Homolytic C−N Cleavage of Aryl Amines ()
Abstract The photocatalytic preparation of aminoalkylated heteroarenes from haloalkylamides via a 1,4‐aryl migration from nitrogen to carbon, conceptually analogous to a radical Smiles rearrangement, is reported. This method enables the substitution of amino groups in heteroaromatic compounds with aminoalkyl motifs under mild, iridium(III)‐mediated photoredox conditions. It provides rapid access to thienoazepinone, a pharmacophore present in multiple drug candidates for potential treatment of different conditions, including inflammation and psychotic disorders.
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Exponential Isothermal Amplification of Nucleic Acids and Assays for Proteins, Cells, Small Molecules, and Enzyme Activities: An EXPAR Example ()
Abstract Isothermal exponential amplification techniques, such as strand‐displacement amplification (SDA), rolling circle amplification (RCA), loop‐mediated isothermal amplification (LAMP), nucleic acid sequence based amplification (NASBA), helicase‐dependent amplification (HDA), and recombinase polymerase amplification (RPA), have great potential for on‐site, point‐of‐care, and in situ assay applications. These amplification techniques eliminate the need for temperature cycling, as required for the polymerase chain reaction (PCR), while achieving comparable amplification yields. We highlight here recent advances in the exponential amplification reaction (EXPAR) for the detection of nucleic acids, proteins, enzyme activities, cells, and metal ions. The incorporation of fluorescence, colorimetric, chemiluminescence, Raman, and electrochemical approaches enables the highly sensitive detection of a variety of targets. Remaining issues, such as undesirable background amplification resulting from nonspecific template interactions, must be addressed to further improve isothermal and exponential amplification techniques.
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Heteroatom‐Doped Carbon Dots (CDs) as a Class of Metal‐Free Photocatalysts for PET‐RAFT Polymerization under Visible Light and Sunlight ()
Abstract A key challenge of photoregulated living radical polymerization is developing efficient and robust photocatalysts. Now carbon dots (CDs) have been exploited for the first time as metal‐free photocatalysts for visible‐light‐regulated reversible addition–fragmentation chain‐transfer (RAFT) polymerization. Screening of diverse heteroatom‐doped CDs suggested that the P‐ and S‐doped CDs were effective photocatalysts for RAFT polymerization under mild visible light following a photoinduced electron transfer (PET) involved oxidative quenching mechanism. PET‐RAFT polymerization of various monomers with temporal control, narrow dispersity (Đ≈1.04), and chain‐end fidelity was achieved. Besides, it was demonstrated that the CD‐catalyzed PET‐RAFT polymerization was effectively performed under natural solar irradiation.
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Direct Conversion of Syngas into Methyl Acetate, Ethanol, and Ethylene by Relay Catalysis via the Intermediate Dimethyl Ether ()
Abstract Selective conversion of syngas (CO/H2) into C2+ oxygenates is a highly attractive but challenging target. Herein, we report the direct conversion of syngas into methyl acetate (MA) by relay catalysis. MA can be formed at a lower temperature (ca. 473 K) using Cu‐Zn‐Al oxide/H‐ZSM‐5 and zeolite mordenite (H‐MOR) catalysts separated by quartz wool (denoted as Cu‐Zn‐Al/H‐ZSM‐5|H‐MOR) and also at higher temperatures (603–643 K) without significant deactivation using spinel‐structured ZnAl2O4|H‐MOR. The selectivity of MA and acetic acid (AA) reaches 87 % at a CO conversion of 11 % at 643 K. Dimethyl ether (DME) is the key intermediate and the carbonylation of DME results in MA with high selectivity. We found that the relay catalysis using ZnAl2O4|H‐MOR|ZnAl2O4 gives ethanol as the major product, while ethylene is formed with a layer‐by‐layer ZnAl2O4|H‐MOR|ZnAl2O4|H‐MOR combination. Close proximity between ZnAl2O4 and H‐MOR increases ethylene selectivity to 65 %.
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Shunsuke Chiba ()
Angewandte Chemie International Edition, EarlyView.
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Assessing Human Exposure to Organic Pollutants in the Indoor Environment ()
Abstract There is an ongoing probing of the role of chemicals in the indoor environment. The majority of potential target substances are so‐called very volatile, volatile, and semi‐volatile organic compounds (VVOCs, VOCs, and SVOCs). Depending on their physical properties and the mass transfer conditions, they are distributed in or between the gas phase, particle phase, settled house dust, surface films, clothing, and other fabrics as well as the exposed skin and hair of the occupants themselves. Therefore, inhalation, ingestion, and dermal uptake all must be considered as relevant pathways for exposure assessment in human habitats. Exposure to VVOCs, VOCs, and SVOCs can be estimated by measuring their concentrations in relevant indoor compartments or by determining the amounts of the target compounds and/or their metabolites in urine and blood. Assessing the various routes of exposure often requires a combination of sophisticated and interdisciplinary theoretical background and experimental techniques. Consequently, close communication and collaboration between chemical and exposure scientists are needed to achieve a better understanding of human exposure to chemical substances in various indoor environments. Embedded in the toxicological context, this is the basis for assessing the corresponding health risks and for determining control strategies or approaches to limit such risks.
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Gideon J. Davies ()
Angewandte Chemie International Edition, EarlyView.
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Jonathan A. Ellman ()
Angewandte Chemie International Edition, EarlyView.
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Metal‐Free Synthetic Approach to 3‐Monosubstituted Unsymmetrical 1,2,4,5‐Tetrazines Useful for Bioorthogonal Reactions ()
Abstract A facile, efficient and metal‐free synthetic approach to 3‐monosubstituted unsymmetrical 1,2,4,5‐tetrazines is presented. Dichloromethane (DCM) is for the first time recognized as a novel reagent in the synthetic chemistry of tetrazines. Using this novel approach 11 3‐aryl/alkyl 1,2,4,5‐tetrazines were prepared in excellent yields (up to 75 %). The mechanism of this new reaction, including the role of DCM in the tetrazine ring formation, has been investigated by 13C labeling of DCM, and is also presented and discussed as well as the photophysical and electrochemical properties.
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A Continuously Regenerable Chiral Ammonia Borane for Asymmetric Transfer Hydrogenations ()
Abstract A novel chiral ammonia borane was designed and developed through the dehydrogenation of ammonia borane with a chiral phosphoric acid, which was highly effective for the asymmetric transfer hydrogenation of imines and β‐enamino esters to afford high levels of reactivities and enantioselectivities. Significantly, this chiral ammonia borane can be continuously regenerated during the transfer hydrogenation with the assistance of water and ammonia borane, which made it possible to obtain satisfactory results using only 0.1 mol % of the chiral phosphoric acid. Notably, the role of chiral phosphoric acid is to produce the chiral ammonia borane.
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Total Synthesis and Structural Revision of the Antibiotic Tetrapeptide GE81112A ()
Abstract The total synthesis of the naturally occurring antibiotic GE81112A, a densely functionalized tetrapeptide, is reported. Comparison of spectral data with those of the natural product and the lack of biological activity of the synthesized compound led us to revise the published configuration of the 3‐hydroxypipecolic acid moiety. This hypothesis was fully validated by the synthesis of the corresponding epimer.
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Guest‐Induced Structural Transformations in a Porous Halogen‐Bonded Framework ()
Abstract Structural evidence obtained from in situ X‐ray diffraction shows that halogen bonding is responsible for the formation of a dynamic porous molecular solid. This material is surprisingly robust and undergoes reversible switching of its pore volume by activation or by exposure to a series of gases of different sizes and shapes. Volumetric gas sorption and pressure‐gradient differential scanning calorimetry (P‐DSC) data provide further mechanistic insight into the breathing behavior.
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Chemical Design of Non‐Ionic Polymer Brushes as Biointerfaces: Poly(2‐oxazine)s Outperform Both Poly(2‐oxazoline)s and PEG ()
Abstract The era of poly(ethylene glycol) (PEG) brushes as a universal panacea for preventing non‐specific protein adsorption and providing lubrication to surfaces is coming to an end. In the functionalization of medical devices and implants, in addition to preventing non‐specific protein adsorption and cell adhesion, polymer‐brush formulations are often required to generate highly lubricious films. Poly(2‐alkyl‐2‐oxazoline) (PAOXA) brushes meet these requirements, and depending on their side‐group composition, they can form films that match, and in some cases surpass, the bioinert and lubricious properties of PEG analogues. Poly(2‐methyl‐2‐oxazine) (PMOZI) provides an additional enhancement of brush hydration and main‐chain flexibility, leading to complete bioinertness and a further reduction in friction. These data redefine the combination of structural parameters necessary to design polymer‐brush‐based biointerfaces, identifying a novel, superior polymer formulation.
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Cottrell Scholars / TREE Awardees / Humboldt and Bessel Research Awards 2017/2018 ()
Angewandte Chemie International Edition, EarlyView.
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Modulation of Hydrophobic Interaction by Mediating Surface Nanoscale Structure and Chemistry, not Monotonically by Hydrophobicity ()
Abstract The hydrophobic (HB) interaction plays a critical role in many colloidal and interfacial phenomena, biophysical and industrial processes. Surface hydrophobicity, characterized by the water contact angle, is generally considered the most dominant parameter determining the HB interaction. Herein, we quantified the HB interactions between air bubbles and a series of hydrophobic surfaces with different nanoscale structures and surface chemistry in aqueous media using a bubble probe atomic force microscopy (AFM). Surprisingly, it is discovered that surfaces of similar hydrophobicity can show different ranges of HB interactions, while surfaces of different hydrophobicity can have similar ranges of HB interaction. The increased heterogeneity of the surface nanoscale structure and chemistry can effectively decrease the decay length of HB interaction from 1.60 nm to 0.35 nm. Our work provides insights into the physical mechanism of HB interaction.
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Dynamic Covalent Identification of an Efficient Heparin Ligand ()
Abstract Despite heparin being the most widely used macromolecular drug, the design of small‐molecule ligands to modulate its effects has been hampered by the structural properties of this polyanionic polysaccharide. Now a dynamic covalent selection approach is used to identify a new ligand for heparin, assembled from extremely simple building blocks. The amplified molecule strongly binds to heparin (KD in the low μm range, ITC) by a combination of electrostatic, hydrogen bonding, and CH–π interactions as shown by NMR and molecular modeling. Moreover, this ligand reverts the inhibitory effect of heparin within an enzymatic cascade reaction related to blood coagulation. This study demonstrates the power of dynamic covalent chemistry for the discovery of new modulators of biologically relevant glycosaminoglycans.
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Chemo‐Enzymatic Synthesis of Position‐Specifically Modified RNA for Biophysical Studies including Light Control and NMR Spectroscopy ()
Abstract The investigation of non‐coding RNAs requires RNAs containing modifications at every possible position within the oligonucleotide. Here, we present the chemo‐enzymatic RNA synthesis containing photoactivatable or 13C,15N‐labelled nucleosides. All four ribonucleotides containing ortho‐nitrophenylethyl (NPE) photocages, photoswitchable azobenzene C‐nucleotides and 13C,15N‐labelled nucleotides were incorporated position‐specifically in high yields. We applied this approach for the synthesis of light‐inducible 2′dG‐sensing riboswitch variants and detected ligand‐induced structural reorganization upon irradiation by NMR spectroscopy. This chemo‐enzymatic method opens the possibility to incorporate a wide range of modifications at any desired position of RNAs of any lengths beyond the limits of solid‐phase synthesis.
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Magnetoluminescence in a Photostable, Brightly Luminescent Organic Radical in a Rigid Environment ()
Angewandte Chemie International Edition, EarlyView.
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Modulating Photo‐ and Electroluminescence in a Stimuli‐Responsive π‐Conjugated Donor–Acceptor Molecular System ()
Abstract Functional organic materials that display reversible changes in fluorescence in response to external stimuli are of immense interest owing to their potential applications in sensors, probes, and security links. While earlier studies mainly focused on changes in photoluminescence (PL) color in response to external stimuli, stimuli‐responsive electroluminescence (EL) has not yet been explored for color‐tunable emitters in organic light‐emitting diodes (OLEDs). Here a stimuli‐responsive fluorophoric molecular system is reported that is capable of switching its emission color between green and orange in the solid state upon grinding, heating, and exposure to chemical vapor. A mechanistic study combining X‐ray diffraction analysis and quantum chemical calculations reveals that the tunable green/orange emissions originate from the fluorophore's alternating excited‐state conformers formed in the crystalline and amorphous phases. By taking advantage of this stimuli‐responsive fluorescence behavior, two‐color emissive OLEDs were produced using the same fluorophore in different solid phases.
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Porous Ionic Liquids or Liquid Metal–Organic Frameworks? ()
Abstract Porous liquids can be prepared from the dispersion metal–organic frameworks (MOFs) in ionic liquids (ILs). Porous liquids prepared from 5 % of ZIF‐8 in a phosphonium‐based ionic liquid are capable of absorbing reversibly up to 150 % more nitrogen and 100 % more methane than the pure ionic liquid.
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A 3D Organically Synthesized Porous Carbon Material for Lithium‐Ion Batteries ()
Angewandte Chemie International Edition, EarlyView.
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Carbenes and Nitrenes: Recent Developments in Fundamental Chemistry ()
Abstract Carbenes and nitrenes can exist in both singlet and triplet states, sometimes equally stable and interconverting either thermally or photochemically. Many carbene and nitrene reactions proceed via tunneling at low temperatures. Numerous singlet and triplet states have been characterized spectroscopically, and a detailed understanding of the chemical and physical properties of carbenes and nitrenes is emerging. There has been significant progress in the direct observation of carbenes, nitrenes, and many other reactive intermediates in recent years through the application of matrix photolysis and flash vacuum pyrolysis linked with matrix isolation at cryogenic temperatures. Our understanding of singlet and triplet states has improved through the interplay of spectroscopy and computations. Bistable carbenes and nitrenes as well as many examples of tunneling have been discovered and numerous rearrangements and fragmentations have been documented. The correlation of the zero‐field splitting parameter D with calculated spin densities on nitrenes and carbenes is discussed. This Minireview gives an overview of some of these developments.
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Leveraging the Knorr Pyrazole Synthesis for the Facile Generation of Thioester Surrogates for use in Native Chemical Ligation ()
Abstract Facile synthesis of C‐terminal thioesters is integral to native chemical ligation (NCL) strategies for chemical protein synthesis. We introduce a new method of mild peptide activation, which leverages solid‐phase peptide synthesis (SPPS) on an established resin linker and classical heterocyclic chemistry to convert C‐terminal peptide hydrazides into their corresponding thioesters via an acyl pyrazole intermediate. Peptide hydrazides, synthesized on established trityl chloride resins, can be activated in solution with stoichiometric acetyl acetone (acac), readily proceed to the peptide acyl pyrazoles. Acyl pyrazoles are mild acylating agents and are efficiently exchanged with an aryl thiol, which can then be directly utilized in NCL. The mild, chemoselective, and stoichiometric activating conditions allow this method to be utilized through multiple sequential ligations without intermediate purification steps.
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Low‐Coordinate Barium Boryloxides: Synthesis and Dehydrocoupling Catalysis for the Production of Borasiloxanes ()
Abstract The first soluble barium boryloxides [Ba]– OB{CH(SiMe3)2} are presented. These mono‐ or dinuclear complexes feature low coordination numbers, as low as two for [Ba(OB{CH(SiMe3)2}2)2], which is further stabilized by intra‐ and intermolecular Ba⋅⋅⋅H3C agostic interactions. Barium boryloxides and the parent [Ba{N(SiMe3)2}2⋅(thf)2] catalyze the dehydrocoupling of borinic acids with hydrosilanes, providing borasiloxanes under mild conditions.
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Acylstannanes: Cleavable and Highly Reactive Photoinitiators for Radical Photopolymerization at Wavelengths above 500 nm with Excellent Photobleaching Behavior ()
Abstract Within this work, a novel acylstannane‐based photoinitiator (PI) is presented. Tetrakis(2,4,6‐trimethylbenzoyl)stannane (1) displays outstanding properties compared to state‐of‐the‐art acylgermane‐based initiators. Most importantly, the initiator shows absorption up to 550 nm, which allows higher penetration depths, especially in highly filled photopolymers. Besides that, 1 shows extremely high photoinitiating activity towards (meth)acrylic double bonds, as well as very fast photobleaching. Furthermore, unlike many organotin compounds, 1 shows surprisingly low cytotoxicity.
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A Hierarchical Coding Strategy for Live Cell Imaging of Protein‐Specific Glycoform ()
Abstract Live cell imaging of protein‐specific glycoforms holds great promise for revolutionizing the study of glycochemistry. The imaging protocols developed thus far build upon the paired interplay of probe units, thus limiting the number of monosaccharide identification channels. A hierarchical coding (HieCo) imaging strategy, with DNA coding and decoding of protein and monosaccharides executed in fidelity to the hierarchical order of target glycoprotein, is reported herein and features expandable monosaccharide identification channels. A proof‐of‐concept protocol has been developed for MUC1‐specific imaging of terminal sialic acid (Sia) and fucose (Fuc) on MCF‐7, T47D, MDA‐MB‐231, and PANC‐1 cells, revealing distinct monosaccharide patterns for four types of cells. The protocol also permits dynamic monitoring of changes in MUC1‐specific monosaccharide patterns associated with both the alteration of cellular physiological states and the occurrence of a biologically important process.
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Pressure‐Tuneable Visible‐Range Band Gap in the Ionic Spinel Tin Nitride ()
Abstract The application of pressure allows systematic tuning of the charge density of a material cleanly, that is, without changes to the chemical composition via dopants, and exploratory high‐pressure experiments can inform the design of bulk syntheses of materials that benefit from their properties under compression. The electronic and structural response of semiconducting tin nitride Sn3N4 under compression is now reported. A continuous opening of the optical band gap was observed from 1.3 eV to 3.0 eV over a range of 100 GPa, a 540 nm blue‐shift spanning the entire visible spectrum. The pressure‐mediated band gap opening is general to this material across numerous high‐density polymorphs, implicating the predominant ionic bonding in the material as the cause. The rate of decompression to ambient conditions permits access to recoverable metastable states with varying band gaps energies, opening the possibility of pressure‐tuneable electronic properties for future applications.
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Exploiting the Synthetic Potential of Sesquiterpene Cyclases for Generating Unnatural Terpenoids ()
Abstract The substrate flexibility of eight purified sesquiterpene cyclases was evaluated using six new heteroatom‐modified farnesyl pyrophosphates, and the formation of six new heteroatom‐modified macrocyclic and tricyclic sesquiterpenoids is described. GC‐O analysis revealed that tricyclic tetrahydrofuran exhibits an ethereal, peppery, and camphor‐like olfactoric scent.
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Bis(η5:η1‐pentafulvene)niobium(V) Complexes: Efficient Synthons for Niobium Carbene and Imido Derivatives ()
Abstract Transition‐metal carbene complexes and their reactivities are a key topic of chemistry. They are an integral part of researches in catalysis, organic synthesis, coordination chemistry, and numerous other areas. In this context, we report the synthesis of a low‐valent bis(η5:η1‐(di‐p‐tolyl)‐pentafulvene)niobium chloride. Owing to the π‐η5:σ‐η1 coordination mode of the pentafulvenes and the resulting high nucleophilic character of the exocyclic carbon atom of the ligand, the bis(η5:η1‐pentafulvene)niobium complex is able to achieve the umpolung of a coordinated vinyl unit and the resulting formation of the first η5:η1 cyclic niobium Schrock carbene complex. This new synthetic route is, in comparison to classical α‐hydrogen elimination reactions or thermolysis of diazo compounds, completely unprecedented. The reactivity of the cyclic carbene function and the remaining fulvene ligand is demonstrated by double N−H bond activation of primary amines to niobium imido complexes.
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Kinetics of the Same Reaction Monitored over Nine Orders of Magnitude in Concentration: When Are Unique Subensemble and Single‐Turnover Reactivity Displayed? ()
Abstract Essentially no information is known about the behavior of individual molecular catalysts under reaction conditions. This is a result of the averaging inherent to traditional analytical techniques. Herein, a combined fluorescence microscopy and 1H NMR spectroscopy study reveals that unique (that is, non‐ensemble averaged) distributions and time‐variable kinetics from molecular ruthenium catalysts within growing polynorbornene occur and are detectable between 10−9 m and 10−6 m of substrate, surprisingly just 1000‐fold less concentrated than a typical laboratory bench‐scale reaction. The kinetic states governing single‐turnover events are determinable by overlay of the signal arising from individual monomer insertion reactions with that from polymer growth from neighboring catalysts.
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Jinlong Gong ()
Angewandte Chemie International Edition, EarlyView.
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Radical Trifluoromethoxylation of Arenes Triggered by a Visible‐Light‐Mediated N−O Bond Redox Fragmentation ()
Abstract A simple trifluoromethoxylation method enables non‐directed functionalization of C−H bonds on a range of substrates, providing access to aryl trifluoromethyl ethers. This light‐driven process is distinctly different from conventional procedures and occurs through an OCF3 radical mechanism mediated by a photoredox catalyst, which triggers an N−O bond fragmentation. The pyridinium‐based trifluoromethoxylation reagent is bench‐stable and provides access to synthetic diversity in lead compounds in an operationally simple manner.
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Fluorescence Blinking Beyond Nanoconfinement: Spatially Synchronous Intermittency of Entire Perovskite Microcrystals ()
Abstract Abrupt fluorescence intermittency or blinking is long recognized to be characteristic of single nano‐emitters. Extended quantum‐confined nanostructures also undergo spatially heterogeneous blinking; however, there is no such precedent in dimensionally unconfined (bulk) materials. Herein, we report multi‐level blinking of entire individual organo–lead bromide perovskite microcrystals (volume=0.1–3 μm3) under ambient conditions. Extremely high spatiotemporal correlation (>0.9) in intracrystal emission intensity fluctuations signifies effective communication amongst photogenerated carriers at distal locations (up to ca. 4 μm) within each crystal. Fused polycrystalline grains also exhibit this intriguing phenomenon, which is rationalized by correlated and efficient migration of carriers to a few transient nonradiative traps, the nature and population of which determine blinking propensity. Observation of spatiotemporally correlated emission intermittency in bulk semiconductor crystals opens the possibility of designing novel devices involving long‐range (mesoscopic) electronic communication.
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Innovative Strategies for Hypoxic‐Tumor Photodynamic Therapy ()
Abstract Despite its clinical promise, photodynamic therapy (PDT) suffers from a key drawback associated with its oxygen‐dependent nature, which limits its effective use against hypoxic tumors. Moreover, both PDT‐mediated oxygen consumption and microvascular damage further increase tumor hypoxia and, thus, impede therapeutic outcomes. In recent years, numerous investigations have focused on strategies for overcoming this drawback of PDT. These efforts, which are summarized in this review, have produced many innovative methods to avoid the limits of PDT associated with hypoxia.
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The Broad Aryl Acid Specificity of the Amide Bond Synthetase McbA Suggests Potential for the Biocatalytic Synthesis of Amides ()
Abstract Amide bond formation is one of the most important reactions in pharmaceutical synthetic chemistry. The development of sustainable methods for amide bond formation, including those that are catalyzed by enzymes, is therefore of significant interest. The ATP‐dependent amide bond synthetase (ABS) enzyme McbA, from Marinactinospora thermotolerans, catalyzes the formation of amides as part of the biosynthetic pathway towards the marinacarboline secondary metabolites. The reaction proceeds via an adenylate intermediate, with both adenylation and amidation steps catalyzed within one active site. In this study, McbA was applied to the synthesis of pharmaceutical‐type amides from a range of aryl carboxylic acids with partner amines provided at 1–5 molar equivalents. The structure of McbA revealed the structural determinants of aryl acid substrate tolerance and differences in conformation associated with the two half reactions catalyzed. The catalytic performance of McbA, coupled with the structure, suggest that this and other ABS enzymes may be engineered for applications in the sustainable synthesis of pharmaceutically relevant (chiral) amides.
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Building and Breaking Bonds via a Compact S‐propargyl‐cysteine to Chemically Control Enzymes and Modify Proteins ()
Analogous to reversible post‐translational protein modifications, the ability to attach and subsequently remove modifications on proteins would be valuable for protein and biological research. Although bioorthogonal functionalities have been developed to conjugate or cleave protein modifications, they are introduced into proteins on separate residues and often with bulky side chains, limiting their use to one type of control and primarily protein surface. Here we achieved dual control on one residue by genetically encoding S‐propargyl‐cysteine (SprC), which has bioorthogonal alkyne and propargyl groups in a compact structure, permitting usage in protein interior in addition to surface. We demonstrated its incorporation at the dimer interface of glutathione transferase for in vivo crosslinking via thiol‐yne click chemistry, and at the active site of human rhinovirus 3C protease for masking and then turning on enzyme activity via Pd‐cleavage of SprC into Cys. In addition, we installed biotin onto EGFP via Sonogashira coupling of SprC and then tracelessly removed it via Pd cleavage. SprC is small in size, commercially available, nontoxic, and allows for bond building and breaking on a single residue. Genetically encoded SprC will be valuable for chemically controlling proteins with an essential Cys and for reversible protein modifications.
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Boosting Hydrogen Production via Anodic Oxidation of Primary Amines over a NiSe Nanorod Electrode ()
For electrocatalytic water splitting, the sluggish anodic oxygen evolution reaction (OER) has extremely restricted the cathodic hydrogen evolution reaction (HER). Therefore, developing an alternative anodic reaction with accelerating kinetics to produce value‐added chemicals, especially coupled with HER, is of great importance. Here, a thermodynamically more favourable primary amine (‐CH2‐NH2) electrooxidation catalyzed by NiSe nanorod arrays in water is reported to replace OER for enhancing HER. The increased H2 production can be obtained at cathode, meanwhile, a variety of aromatic and aliphatic primary amines are selectively electrooxidized to nitriles with good yields at anode. Mechanistic investigations suggest that NiII/NiIII may serve as the redox active specie for the primary amines transformation. Impressively, hydrophobic nitrile products can readily escape from aqueous electrolyte/electrode interface, avoiding the deactivation of the catalyst and thus contributing to continuous gram‐scale synthesis. This work opens a facile and environmentally benign aqueous electrocatalytic way for the production of both hydrogen and nitriles at much lower potential than that of overall water splitting.
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Synthesis of Spirocyclic Ethers Via Enantioselective Copper‐Catalyzed Carboetherification of Alkenols ()
Spirocyclic ethers can be found in bioactive compounds. This copper‐catalyzed enantioselective alkene carboetherification provides 5,5‐, 5,6‐ and 6,6‐spirocyclic products containing fully substituted chiral carbons with up to 99% enantiomeric excess. This reaction features formation of two rings from acyclic substrates, 1,1‐disubstituted alkenols functionalized with arenes, alkenes or alkynes and clearly constitutes a powerful way to synthesize chiral spirocyclic ethers.
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α‐Sila‐Dipeptides: Synthesis and Characterization ()
The first two α‐sila‐dipeptides: the acyclic 1 and the cyclic 2 were synthesized, isolated and characterized by X‐ray crystallography. 1 and 2 are the first examples of a “Si for C switch” at the central α‐position of amino acids and peptides, enriching the library of acyclic‐ and cyclic‐dipeptides (diketopiperazines), including biologically active compounds.
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Highly Regioselective Domino Benzannulation Reaction of Buta‐1,3‐diynes to Construct Irregular Nanographenes ()
The properties of nanographenes can be tuned by changing their shapes, therefore the development of new methods that are suitable for the synthesis of various nanographenes is highly desirable. Herein, we describe an intramolecular InCl₃‐AgNTf₂‐catalyzed regioselective domino benzannulation reaction of buta‐1,3‐diynes to build irregular nanographenes. Different nanographene compounds were easily obtained in moderate to high yields through careful design of the precursor compounds. This new domino reaction was successfully applied to a four‐fold alkyne benzannulation of dimethoxy‐1,1'‐binaphthalene derivatives to arrive at novel chiral butterfly ligand precursors. The regioselectivity of the benzannulation reaction was unambiguously confirmed by the X‐ray crystallography. Moreover, this new method enables us to synthesize different nanographene isomers and study their optical properties as a function of shape.
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H2 Oxidation Electrocatalysis Enabled by Metal‐to‐Metal Hydrogen Atom Transfer: A Homolytic Approach to a Heterolytic Reaction ()
H2 is used on a huge scale industrially, and has received increased attention for chemical energy storage. Oxidation of H2 in a fuel cell converts the chemical energy of the H‐H bond into electricity. Electrocatalytic oxidation of H2 by molecular catalysts typically requires one metal to perform multiple chemical steps: bind H2, heterolytically cleave H2, and then undergo two oxidation and two deprotonation steps. We discovered the electrocatalytic oxidation of H2 by a cooperative system using Cp*Cr(CO)3H and [Fe(diphosphine)(CO)3]+. A key step of the proposed mechanism is a rarely observed metal‐to‐metal hydrogen atom transfer from the Cr‐H complex to the Fe, forming an Fe‐H complex that is deprotonated and then oxidized electrochemically. This "division of chemical labor" features Cr interacting with H2, while Fe interfaces with the electrode. Neither metal is required to heterolytically cleave H2, so this system thereby provides a very unusual example of a homolytic reaction being a key step in a molecular electrocatalytic process.
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Palladium‐Catalysed Reductive [5+1] Cycloaddition of 3‐Acetoxy‐1,4‐enynes with CO: Access to Phenols Enabled by Hydrosilanes ()
A new palladium‐catalysed reductive [5+1] cycloaddition of 3‐acetoxy‐1,4‐enynes with CO enabled by hydrosilanes is developed for producing valuable functionalized phenols. This methodology employs hydrosilanes as the external functional reagents to fulfil the [5+1] carbonylative benzannulation, and is featured as a conceptually and mechanistically novel carbonylative cycloaddition route to construct substituted phenols through the formation of four new chemical bonds with excellent functional group tolerance.
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Unique Supramolecular Liquid Crystal Phases with Different Two‐Dimensional Crystal Layers ()
We report here a series of tetrablock‐mimic azobenzene‐containing fullerene dyads that form phase segregated two‐dimensional (2D) crystal constructed supramolecular liquid crystals (LCs). The unique double‐, triple‐ and quadruple‐layer packing structure of fullerenes in 2D crystals leads to different smectic supramolecular LC phases, and novel LC phase transitions are observed due to the change of fullerene packing layer number in 2D crystals. Interestingly, by combining the LC properties with 2D crystals, these materials show excellent electron mobility in the order of 10^‐3 cm^2V^‐1s^‐1, despite their relatively low fullerene content. Our results provide a novel method to manipulate 2D crystal layer thickness, with promising applications in optoelectronic devices.
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Highly Flexible and Efficient All‐Polymer Solar Cells with High‐Viscosity Processing Polymer Additive toward Potential of Stretchable Devices ()
Considering the potential applications of all‐polymer solar cells (all‐PSCs) as wearable power generators, it is urgent to develop photoactive layers that possess intrinsic mechanical endurance while maintaining a high power‐conversion efficiency (PCE). We herein demonstrate a strategy to simultaneously control the intercalation behavior and nanocrystallite size in the polymer‐polymer blend by using a newly developed high‐viscosity polymeric additive, poly(dimethylsiloxane‐co‐methyl phenethylsiloxane) (PDPS), into the TQ‐F:N2200 all‐PSC matrix. A mechanically robust blend film, 10PDPS with a great toughness of 9.67 MJ m−3 and elongation at a break of 50.92% was obtained, affording negligible loss of the initial PCE (~7.0%) in conventional devices. This allows to fabricate highly flexible all‐PSCs with a satisfactory PCE of 5.60% while retaining 90% of its efficiency after 100 bending cycles at a bending radius of 3 mm. Our results provide a feasible route for producing high‐performance ductile all‐PSCs, which can potentially be used to realize stretchable all‐PSCs as a linchpin of next‐generation electronics.
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All‐Inorganic Perovskite CsSnBr3 as a Thermally Stable, Free‐Carrier Semiconductor ()
Hybrid organic‐inorganic perovskites, especially methylammonium lead triiodide (MAPbI3), are intensely studied for their optoelectronic properties. The organic MA+ cation is held responsible for the superior performance of MAPbI3 but also its instability toward moisture and heat. To explore compositions beyond MAPbI3, we performed experiments and calculations on two isomorphous perovskites CsSnBr3 and MASnBr3. CsSnBr3 is slightly smaller than MASnBr3 in cell dimension, but outperforms MASnBr3 in bandgap energy, charge‐carrier reduced effective mass, and optical dielectric constant all by ~19%. These merits accumulate to drastically cut the exciton binding energy from 33 meV for MASnBr3 to 19.6 meV for CsSnBr3, making CsSnBr3 a black, free‐carrier semiconductor. CsSnBr3 also exhibits distinctly higher stability toward moisture and heat than its organic counterparts. These advantages suggest ecofriendly applications for CsSnBr3, such as tandem solar cells and direct X‐ray detectors.
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Copper‐Catalyzed Remote C(sp3)‐H Arylation of Carboxamides and Sulfonamides ()
We report herein an unprecedented copper‐catalyzed remote C(sp3)‐H arylation protocol. Stirring a trifluorotoluene solution of N‐fluorocarboxamides or N‐fluorosulfonamides and arylboronic acids in the presence of a catalytic amount of copper(II) trifluoroacetylacetonate, 2,2'‐bipyridine and sodium tert‐butoxide afforded the λ and δ‐C(sp3)‐H arylated carboxamides and sulfonamides, respectively, in good to high yields. Mechanistic studies indicated that the reaction might proceed through a sequence of amidyl radical generation, 1,5‐hydrogen atom transfer (HAT) followed by Cu‐catalyzed cross coupling of the resulting carbon radical with arylboronic acids.
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Self‐assembly of an Anion Binding Cryptand for the Selective Encapsulation, Sequestration and Precipitation of Phosphate from Aqueous Systems. ()
The self‐assembled trimetallic species [L2Cu3]6+ contains a cavity that acts as a host to many different anions and using X‐ray crystallography, ESI‐MS and UV‐Vis we show that these anions are encapsulated both in the solid‐state and aqueous systems. Upon encapsulation the anions Brˉ, Iˉ, CO32ˉ, SiF62ˉ, IO63ˉ, VO43ˉ, WO42ˉ, CrO42ˉ, SO42ˉ, AsO43ˉ and PO43ˉ are all precipitated from solution and can be removed by filtration. Furthermore, the cavity can be tuned to be selective to either phosphate or sulfate anions by variation of the pH. Phosphate anions can be removed from water, even in the presence of other common anions, reducing the concentration from 1000 to < 0.1 ppm and recovering ~99% of the phosphate anion.
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Nickel‐Catalyzed Amide Bond Formation from Methyl Esters ()
Despite being one of the most important and frequently run chemical reactions, the synthesis of amide bonds is accomplished primarily by wasteful methods that proceed by stoichiometric activation of one of the starting materials. We report a nickel‐catalyzed procedure that can enable diverse amides to be synthesized from abundant methyl ester starting materials, producing only volatile alcohol as a stoichiometric waste product. In contrast to acid‐ and base‐mediated amidations, the reaction is proposed to proceed by a neutral cross coupling‐type mechanism, opening up new opportunities for direct, efficient, chemoselective synthesis.
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Cobalt‐Catalyzed Enantioselective Synthesis of Chiral gem‐Bisborylalkanes ()
We report an asymmetric synthesis of enantio‐enriched gem‐bisborylalkanes via enantioselective diborylation of 1,1‐disubstituted alkenes catalyzed by Co(acac)2/(R)‐DM‐segphos. A range of activated and unactivate alkenes underwent this asymmetric diborylation in the presence of cyclooctene as a hydrogen acceptor, affording the corresponding gem‐bisborylalkanes with high enantioselectivity. The synthetic utilities of these chiral organoboronate compounds were exemplified through several stereospecific derivatizations and the synthesis of sesquiterpenes and sesquiterpenoids natural products.
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Enantioselective Total Synthesis of (+)‐Plumisclerin A ()
The first and enantioselective total synthesis of (+)‐plumisclerin A, a novel unique complex cytotoxic marine diterpenoid, has been accomplished. Around the central cyclopentane anchorage, a sequential ring‐formation protocol was adopted to generate the characteristic tricycle[4.3.1.0/1,5]decane and trans‐fused dihyrdopyran moiety. Scalable enantioselective La(III)‐catalyzed Michael reaction, palladium(0)‐catalyzed carbonylation and SmI2‐mediated radical conjugate addition were successfully applied in the synthesis, affording multiple grams of the complex and rigid B/C/D‐ring system having six continuous stereogenic centers and two all‐carbon quaternary centers. The trans‐fused dihyrdopyran moiety with an exo side‐chain was furnished in final stage through sequential redox transformations from a lactone precursor, which overcome the largish steric strain of the dense multiring system. The reported total synthesis also confirms the absolute chemistries of natural (+)‐plumisclerin A.
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Autocatalytic Synthesis of Bifluoride Ionic Liquids via SuFEx Click Chemistry ()
Ionic liquids with bifluoride anions possess properties such as high conductivity, wide electrochemical windows and low viscosity, which make them attractive materials for various electrochemical devices. However, due to the lack of reliable synthetic routes, bifluoride‐based ionic liquids have seldom been explored. Herein, an autocatalytic strategy for the HF‐free synthesis of bifluoride‐based sulfonamide ionic liquids via the sulfur(VI) fluoride exchange (SuFEx) reaction was reported. This reaction requires no chromatographic purification and yields are quantitative. Their thermophysical properties (i.e. phase transition behavior and decomposition temperature), and electrochemical stability were studied. The products with alkyl, aryl and perfluoroalkyl side chains exhibited extraordinary wide electrochemical windows (up to 6.0 V) with reproducible results among multiple replicate measurements.
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Customizable Lipid Nanoparticle Materials for the Delivery of siRNAs and mRNAs ()
RNAs are a promising class of therapeutics given their ability to regulate protein concentrations at the cellular level. Developing safe and effective strategies to deliver RNAs remains important for realizing their full clinical potential. Here, we develop lipid nanoparticle formulations that can deliver short interfering RNAs (for gene silencing) or messenger RNAs (for gene upregulation). Specifically, we study how the tail length, tail geometry, and linker spacing in diketopiperazine lipid materials influences LNP potency with siRNAs and mRNAs. Eight lipid materials are synthesized, and 16 total formulations are screened for activity in vitro; the lead material is evaluated with mRNA for in vivo use and demonstrates luciferase protein expression in the spleen. In undertaking this approach, not only do we develop synthetic routes to delivery materials, but we also reveal structural criteria that could be useful for developing next‐generation delivery materials for RNA therapeutics.
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Operando X‐Ray Absorption Spectroscopy Shows Fe Oxidation is Concurrent with Oxygen Evolution in Cobalt‐Iron (Oxy)hydroxide Electrocatalysts ()
Iron cations are essential for the high activity of nickel and cobalt‐based (oxy)hydroxides for the oxygen evolution reaction, but the role of iron in the catalytic mechanism remains under active investigation. Here we use operando X‐ray absorption spectroscopy and density functional theory calculations to demonstrate partial Fe oxidation and a shortening of the Fe‐O bond length during oxygen evolution on Co(Fe)OxHy. Cobalt oxidation during oxygen evolution is only observed in the absence of iron. These results demonstrate a different mechanism for water oxidation in the presence and absence of iron and support the hypothesis that oxidized iron species are involved in water‐oxidation catalysis on Co(Fe)OxHy.
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Conjugated Polymer Nanoparticles Appending Photo‐Responsive Units for Controlled Drug Delivery, Release and Imaging ()
Carriers that can afford tunable physical and structural changes are envisioned to address critical issues in controlled drug delivery applications. Herein, we report photo‐responsive conjugated polymer nanoparticles (CPNs) functionalized with donor‐acceptor Stenhouse adduct (DASA) and folic acid units for controlled drug delivery, release and imaging. Upon visible light (λ = 550 nm) irradiation, CPNs undergo structure, color, and polarity changes simultaneously that swell and open‐up CPNs to release encapsulated drugs into the medium and cells. The backbone of CPN favours fluorescence resonance energy transfer (FRET) to DASA units boosting the fluorescence tracing performance. Notably, drug loaded CPNs exhibit excellent biocompatibility in dark implicating perfect control of light trigger for synchronized structural opening of CPNs for relatively sustainable drug release. We demonstrated the delivery of both hydrophilic and hydrophobic drugs with good loading efficiency. This strategy enables remotely controlled drug delivery and release with visible light irradiation, which sets an example for designing controlled delivery vehicles for non‐invasive therapeutics.
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Lead‐Free Solar Cells based on Tin Halide Perovskite Films with High Coverage and Improved Aggregation ()
Two simple methods to improve tin halide perovskite film structure are introduced, aimed at increasing the power conversion efficiency of lead free perovskite solar cells. First, a hot antisolvent treatment (HAT) was found to increase the film coverage and prevent electric shunting in the photovoltaic device. Second, it was discovered that annealing under a low partial pressure of dimethyl sulfoxide vapor increased the average crystallite size. The topographical and electrical qualities of the perovskite films are substantively improved as a result of the combined treatments, facilitating the fabrication of Sn‐based perovskite solar cell devices with power conversion efficiencies of over 7%.
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Asymmetric anion‐pillared metal‐organic framework as multisite‐adsorbent enables simultaneous removal of propyne and propadiene from propylene ()
The implement of one‐step removal of multi‐component gases based on single material will significantly improve the efficiency of separation processes but still remains challenging, due to the difficulty to precisely fabricate the porous materials with multiple binding sites that are tailored for the different guest molecules. Here, we report a novel niobium oxide‐fluoride anion‐pillared interpenetrated material ZU‐62 (also termed as NbOFFIVE‐2‐Cu‐i, NbOFFIVE = NbOF52‐) featuring asymmetric O/F node coordination for the simultaneous removal of trace propyne and propadiene from the propylene, industrial processes relevant for the production of polymer‐grade propylene. The narrow‐distributed nanospace (aperture of Site I: 6.75 Å, Site II: 6.94 Å, and Site III: 7.20 Å) derived from the special coordination geometry within ZU‐62 customized the corresponding energy favorable binding sites for the propyne and propadiene that enable the recorded propadiene uptake (1.74 mmol g‐1) as well as the excellent propyne uptake (1.87 mmol g‐1) under ultra‐low pressure (5000 ppm). The multisite classified capture mechanism was revealed by modeling studies.
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Auto‐regulated Protein Assembly on a Supramolecular Scaffold ()
Controlled protein assembly provides a means to regulate function. Supramolecular building blocks, including rigid macrocycles, have proven to be versatile triggers of protein assembly. Here, we show that sulfonato‐calix[8]arene (sclx8) mediates the formation of cytochrome c tetramers in solution. This tetramer spontaneously disassembles at ≥ 2 equivalents of sclx8 providing a remarkable example of "auto‐regulation". Using X‐ray crystallography we characterize in detail the sclx8 binding sites on cytochrome c. Crystal structures at different protein‐ligand ratios reveal varying degrees (up to ~35 %) of protein surface coverage by the calixarene and suggest a mechanism for oligomer disassembly. The solution structure of the oligomer was characterized by small angle X‐ray scattering. Overall, the data indicate calixarene‐controlled protein assembly and disassembly without the requirement for a competitive inhibitor, and point to protein encapsulation by a flexible macrocycle.
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Enzymatic Amide Tailoring Expedites Unusual Retro‐Aldol‐Type Amino Acid Conversion to Form Antifungal Cyclopeptide ()
Aspirochlorine is an unusual antifungal cyclopeptide produced by Aspergillus oryzae, an important mold used for food fermentation. Whereas its structure suggested that a non‐ribosomal peptide synthetase assembles the cyclopeptide from phenylalanine and glycine building blocks, labeling studies indicated that one Phe moiety is transformed into Gly after peptide formation. By means of genetic engineering, heterologous expression, biotransformations, and in vitro assays we dissected and reconstituted four crucial steps in aspirochlorine biosynthesis that involve two cytochrome P450 monooxygenases, (AclL and AclO), a methyltransferase (AclU), and a halogenase (AclH). We found that the installation of the N‐methoxylation of the peptide bond sets the stage for a retro‐aldol reaction that leads to the Phe‐to‐Gly conversion. The substrate scopes of the dedicated enzymes as well as bioassays revealed that the peptide editing has evolved to optimize the antifungal action of the natural product.
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Vibrational coupling between organic and inorganic sub‐lattices of hybrid perovskites ()
The interplay of electronic and nuclear degrees of freedom in semiconductor hybrid organic‐inorganic perovskites determines many of their fundamental photophysical properties. For instance, charge carriers are dressed with phonons, i.e., form polarons, and combination modes composed of strongly mixed localized vibrations and delocalized phonons can provide pathways for electronic energy relaxation and dissipation. Mixing of the different types of nuclear motion in vibrational combination modes requires their strong coupling. Here we report the direct measurement of coupling between the high‐frequency N‐H stretch modes of the organic methylammonium and formamidinium ions and low‐frequency Pb‐I phonon modes of the inorganic sub‐lattice in hybrid organic‐inorganic perovskites. The results reveal direct and substantial coupling between the non‐covalently interacting organic and inorganic sub‐lattices.
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Total Synthesis of Asperchalasines A, D, E and H ()
The first total syntheses of cytochalasan dimers asperchalasines A, D, E and H have been accomplished. The key steps of the synthesis include a highly stereoselective intermolecular Diels‐Alder reaction and a HWE macrocyclization to establish the key monomer aspochalasin B and an intermolecular Diels‐Alder reaction followed by a biomimetic oxidative heterodimerization via 5+2 cycloaddition to furnish asperchalasine A. The synthetic efforts provide insight into the biosynthetic pathway of cytochalasan dimers and enables the further study of their biological properties.
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Low Temperature Thermal Rate Constants for the Water Formation Reaction H2 +OH from Rigorous Quantum Dynamics Calculations ()
Thermal rate constants for the prototypical water‐forming H2 +OH→H+H2 O reaction are calculated for temperatures between 150K and 600K using rigorous quantum dynamics calculations including all degrees of freedom. Results are reported for a recent, highly accurate neural network potential (NN1) [J. Chem. Phys. 138, 154301 (2013)] and compared to results obtained on a previous, semi‐empirical potential (SE) [Chem. Phys. Lett. 21, 73 (1980)]. Rate constants computed on both potentials significantly differ in their temperature dependence and differences of over an order of magnitude in the rates are found. The rate constants computed for the NN1 potential compare very well to experimental work. Furthermore, the influence of overall rotation is discussed for the title reaction. While previous close‐coupling simulations were limited to thermal rate constants above room temperature, we report rate constants as low as 250 K due to a better choice of the dividing surface. Good comparison between close‐coupling and J‐shifting calculations is found for the NN1 potential. Moreover, microcanonical rates are obtained for both the NN1 and SE PES. The high‐level results reported here provide an accurate benchmark for the development of approximate methods for the calculation of thermal as well as microcanonical rate constants.
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Semiconducting Polymer Nanobiocatalysts for Photoactivation of Intracellular redox ()
Regulation of biochemical reactions in living systems presents a precise way to understand the related biology and discover new therapeutic targets. Despite the critical role of intracellular redox, its in‐situ activation using light has not been achieved in living cells. Herein, an organic semiconducting polymer nanobiocatalyst (SPNB) composed of a semiconducting polymer core conjugated with microsomal cytochrome P450 (CYP) is developed for photoactivation of intracellular redox. The core serves as the light‐harvesting unit to initiate photoinduced electron transfer (PET) and facilitate the regeneration of dihydronicotinamide adenine dinucleotide phosphate (NADPH), while CYP is the catalytic center for intracellular redox. Under light irradiation, the semiconducting core can efficiently catalyze the generation of NADPH with the turnover frequency (TOF) 75‐times higher than the reported nanosystems, ensuring the supply of the cofactor for intracellular redox. SPNB‐mediated intracellular redox thus can be efficiently activated by light in living cells to convert the model substrate, and also to trigger the bioactivation of anticancer drug. This study provides an organic nanobiocatalytic system that allows light to remotely control intracellular redox in living systems, which are promising for in‐vivo activation of prodrugs.
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Rationally Designed Fluorescence *OH Probe with High Sensitivity and Selectivity for Monitoring the Generation of *OH in Iron Autoxidation without Addition of H2O2 ()
Herein, we report the first sensitive fluorescence *OH probe (1) that is capable of monitoring the generation of trace *OH in the iron autoxidation. The probe 1 was designed by utilizing both the unique aromatic hydroxylation and the electrophilicity of *OH, and prepared by incorporating a strong electron‐donating methoxy group into a cyanine fluorochrome to enhance the trapping ability for *OH. Reaction of 1 with *OH leads to a larger π‐conjugation formation and near‐infrared fluorescence off‐on response. The capability of probe 1 has been demonstrated by imaging *OH generated in living cells under iron autoxidation as well as various stimuli, which reveals that the basal level of *OH in RAW 264.7 cells is lower than that in HeLa cells. The superior analytical performance of probe 1 makes it useful for detecting trace *OH in some critical physiological and pathological processes associated with iron autoxidation.
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Stereoselective Solid‐State Synthesis of Substituted Cyclobutanes Assisted by Pseudorotaxane‐like MOFs ()
Regioselective photodimerization of trans‐4‐styrylpyridine (4‐spy) derivatives is performed using pseudorotaxane‐like Zn‐based metal organic frameworks MOFs as templates. The formation of rctt‐HT (head‐to‐tail) dimers is achieved by confining pairs of coordinated 4‐spy derivative ligands within hexagonal windows and then irradiating them with UV light. It is also possible to achieve a photodimerization reaction where two different substituted 4‐spy ligands are included in such a MOF material. The ether bond formation is employed to protect the sensitive ‐OH group of HO‐spy and the methyl group of CH3O‐spy is subsequently removed after the formation of cyclobutane derivative in the CH3O‐Spy‐based MOF. Introducing substituents at the 2‐ or 3‐position of the phenyl group of 4‐spy does not significantly affect the rate of the dimerization process except in the case of the strongly electron‐withdrawing nitro group where the rate is significantly decreased. These results are in striking contrast to the mixtures of photoproducts and low yields obtained by untemplated photodimerization in organic solvents.
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The Open Circuit Voltage in Biofuel Cells: Nernstian Shift in Pseudocapacitive Electrodes ()
In the development of biofuel cells, great effort is dedicated to achieve outstanding figures of merit, such as pursuing high stability, maximum power output, and a large open circuit voltage. Biofuel cells that make use of immobilized redox mediators such as e.g. redox polymers with integrated enzymes, show an experimentally substan¬tially larger open circuit voltage as compared with the thermodyna¬mically expected value. We demonstrate that this is the result of a Nernstian shift of the electrode potential when catalytic conversion takes place in the absence or at very low current flow. Although this phenomenon is widely present in literature, a comprehensive under¬standing of the potential shift and the high open circuit voltages has not been discussed in detail and hence it is only accepted as an inherent property of the investigated systems. Moreover, additional experimental evidence confirms that the immobilization of redox cen¬ters on the electrode surface permits the assembled biofuel cell to deliver a higher power output due to charge storage upon catalytic conversion. Our findings have direct implication in the design and evaluation of (bio)fuel cells that make use of pseudocapacitive elements.
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Beyond Friedel and Crafts: Innate Alkylation of C‐H Bonds in Arenes ()
Alkylated arenes are ubiquitous molecules and building blocks commonly utilized in most areas of science where there is a need for small organic molecules. Despite its apparent simplicity, the regioselective alkylation of arenes is still a challenging transformation in a lot of cases. Classical methods for the introduction of alkyl groups on arenes, which include the venerable Friedel‐Crafts reaction, radical additions, metallation or pre‐functionalization of the arene, as well as alternatives such as the directed alkylation of C‐H bonds, still suffer from severe limitations in terms of scope, efficiency and selectivity. This can be addressed by exploiting the innate reactivity of some (hetero)arenes, in which electronic and steric properties, governed (or not) by the presence of one (or multiple) heteroatom(s) ensure high levels of regioselectivity. These innate alkylations of C‐H bonds in (hetero)arenes will be overviewed, in a comprehensive manner, in this review article.
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Beyond Friedel and Crafts: Directed Alkylation of C‐H Bonds in Arenes ()
The alkylation of arenes is one of the most fundamental transformations in chemical synthesis leading to privileged scaffolds in many areas of science. Classical methods for the introduction of alkyl groups to arenes are mostly based on the Friedel‐Crafts reaction, radical additions, metallation or pre‐functionalization of the arene: these methods however suffer from limitations in scope, efficiency and selectivity. Moreover, they are based on the innate reactivity of the starting arene, favoring the alkylation at a certain position and rendering the introduction of alkyl chains at other positions much more challenging. This can be addressed by the use of a directing group facilitating, in the presence of a metal catalyst, the regioselective alkylation of a C‐H bond. These directed alkylations of C‐H bonds in arenes are overviewed, in a comprehensive manner, in this review article.
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Light‐driven enzymatic decarboxylation of fatty acids ()
Photoenzymatic decarboxylation of fatty acids into alkanes is proposed as alternative approach for biodiesel synthesis. Using a recently discovered photodecarboxylase from Chlorella variabilis NC64A (CvFAP) we demonstrate the irreversible preparation of alkanes from fatty acids and triglycerides. Several fatty acids and their triglycerides are converted by CvFAP upon illumination with blue light in near‐quantitative yield and exclusive selectivity. Already in this proof‐of‐concept study very promising turnover numbers of up to 8000 were achieved.
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Perfluorinated Covalent Triazine Framework for High‐selectivity Electroconversion CO2 into CH4 ()
Developing cost‐effective electrocatalysts for high‐selectivity CO2 electroreduction remains a daunting challenge. We here report a perfluroinated covalent triazine framework (CTF) electrocatalyst that holds an impressive high selectivity towards CO2 electroreduction conversion into CH4 with faradaic efficiency of 99.3% in aqueous electrolyte. Systematic characterization and electrochemical study, coupling with density functional theory calculations, demonstrate that co‐covalent of nitrogen and fluorine in CTF provides a unique pathway that is inaccessible with the individual components for CO2 electroreduction, contributing to the catalytic sites with high selectivity for CO2 conversion into CH4.
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FLP‐Catalyzed Transfer Hydrogenation of Silyl Enol Ethers ()
Herein we report the first catalytic transfer hydrogenation of silyl enol ethers. This metal free approach employs tris(pentafluorophenyl)borane and 2,2,6,6‐tetramethylpiperidine (TMP) as a commercially available FLP catalyst system and naturally occurring γ‐terpinene as a dihydrogen surrogate. A variety of silyl enol ethers undergo efficient hydrogenation, with the reduced products isolated in excellent yields (29 examples, 82% average yield).
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Spatially separating the conformers of a dipeptide ()
Atomic‐resolution‐imaging approaches for single molecules, such as coherent x‐ray diffraction at free‐electron lasers, require the delivery of high‐density beams of identical molecules. However, even very cold beams of biomolecules typically have multiple conformational states populated. We demonstrate the production of very cold (Trot ∼ 2.3 K) molecular beams of intact dipeptide molecules, which we then spatially separate into the individual populated conformational states. This is achieved using the combination of supersonic expansion laser‐desorption vaporization with electrostatic deflection in strong inhomogeneous fields. This represents the first demonstration of a conformer‐separated and rotationally‐cold molecular beam of a peptide, which enables the investigation of conformer‐specific chemistry using inherently non‐conformer specific techniques. It furthermore represents a milestone toward direct structural imaging of individual biological molecules with atomic resolution using ultrafast diffractive‐imaging methods.
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Catalytic Enantioselective [10+4]‐Cycloadditions ()
The first peri‐ and stereoselective [10+4]‐cycloaddition between catalytically generated amino isobenzofulvenes and electron‐deficient dienes is described. The highly stereoselective catalytic [10+4]‐cycloaddition exhibits a broad scope with high yields reflecting a robust higher‐order cycloaddition. Experimental and computational investigations support a kinetic distribution of intermediate rotamers dictating the enantioselectivity, which relies heavily on additive effects.
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Smart Transformation of POSS Shell Controlled by Thiolate Silver(I) Nanocluster Core in Cluster@Clusters Dendrimers ()
Using thiol group modified polyhedral oligomeric silsesquioxane (POSS) as protected ligand, novel atom‐precise multi‐heteorocluster‐based dendrimers Ag₁₂@POSS₆ (1a and 1b) have been assembled for the first time. Through the reactive ‐SH groups, six POSS shell ligands stabilize the central 12‐core silver(I) cluster by diverse Ag‐S interactions. When such Ag₁₂@POSS₆ complex was stimulated by different solvents (acetone or tetrahydrofuran), the core Ag₁₂ silver(I) cluster underwent reversible structural transformation between flattened cubo‐octahedral (in 1a) and normal cubo‐octahedral (in 1b) configuration, concomitant shell POSS clusters rearranging from pseudo‐octahedral to quasi‐octahedral mode. Also, it is different for the hydrophobicity of 1a compared to 1b in the film matrix. Such Ag₁₂@POSS₆ complex opens a new path to the design and synthesis of atom‐precise metal cluster@silica clusters dendrimers, and the unique structure of such mutiple‐heteoroclusters would endow future diverse promising properties and applications.
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Development of a Minimal Photosystem for Hydrogen Production in Inorganic Chemical Cells ()
Inorganic chemical cells (iCHELLs) are compartment structures consisting of polyoxometalates (POMs) and cations, offering structured and confined reaction spaces bounded by membranes. We have constructed a system capable of efficient anisotropic and hierarchical photo‐induced electron transfer across the iCHELL membrane. Mimicking photosynthesis, our system uses proton gradients between the compartment and the bulk to drive efficient conversion of light into chemical energy, producing hydrogen upon irradiation. This illustrates the power of the iCHELL approach for catalysis, where the structure, compartmentalisation and variation in possible components could be utilised to approach a wide range of reactions.
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Rh‐Catalyzed [4 + 2 + 1] Cycloaddition of in situ Generated Ene/Yne‐Ene‐Allenes and CO ()
We report here the first Rh‐catalyzed [4+2+1] cycloaddition of in situ generated ene/yne‐ene‐allenes and CO to synthesize challenging seven‐membered carbocycles fused with five‐membered rings. This reaction is designed based on the 1,3‐acyloxy migration of ene/yne‐ene‐propargyl esters to ene/yne‐ene‐allenes, followed by oxidative cyclization, CO insertion and reductive elimination to form the final [4+2+1] cycloadducts. The possible competing [4+1], [4+2] and [2+2+1] cycloadditions were disfavored, making the present reaction as an efficient way to access functionalized 5/7 rings.
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Colorimetric Carbonyl Sulfide (COS)/Hydrogen Sulfide (H2S) Donation from γ‐Ketothiocarbamate Donor Motifs ()
Hydrogen sulfide (H2S) is a biologically‐active molecule that exhibits protective effects in a variety of physiological and pathological processes. Although a number of H2S‐related biological effects have been discovered by using H2S donors, knowing how much H2S has been released from donors under different conditions remains a significant challenge. Aligned with this need, we report here a series of γ‐ketothiocarbamate (γ‐KetoTCM) compounds that provide the first examples of colorimetric H2S donors and enable direct quantification of H2S release. These compounds are activated through a pH‐dependent deprotonation/β‐elimination sequence to release carbonyl sulfide (COS), which is quickly converted to H2S by carbonic anhydrase. The p‐nitroaniline released upon donor activation provides an optical readout, which we demonstrate correlates directly with COS/H2S release. We also establish that γ‐KetoTCM‐1 releases COS/H2S in live cells and reduces LPS‐induced NO generation, which is consistent with anti‐inflammatory activity. Taken together, γ‐KetoTCM compounds provide a promising new platform for H2S donation and readily enable colorimetric measurement of H2S donation.
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Selective boryl‐anion migration in a vinyl sp2‐sp3 diborane induced by soft borane Lewis acids ()
A novel intramolecular 1,2‐boryl anion migration from boron to carbon has been achieved by selective activation of the π‐system in [(vinyl)B2Pin2)]‐ using "soft" BR3 electrophiles (BR3 = BPh3 or 9‐Aryl‐BBN). The soft character is key to ensure 1,2‐migration proceeds instead of oxygen coordination / B‐O activation. The BR3 induced‐1,2‐boryl anion migration represents a triple borylation of a vinyl Grignard reagent using only B2Pin2 and BR3 and forms differentially protected 1,1,2‐triborylated alkanes. Notably, by increasing the steric bulk on the beta position of the vinyl Grignard used to activate B2Pin2, 1,2‐boryl‐anion migration can be suppressed in favor of intermolecular {BPin}‐ transfer to BPh3, which represents a simple way to access unsymmetrical sp2‐sp3 diboranes.
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Alkali Lithosilicates ‐ Renaissance of a Reputable Substance Class with Surprising Luminescence Properties ()
In this communication, we report on a hitherto unknown synthetic access to alkali lithosilicates, a substance class first described by Hoppe in the eighties of the last century. With the synthesis and characterization of NaK7[Li3SiO4]8, we were able to discover a new representative, expanding the family of known alkali lithosilicates. Astonishingly, NaK7[Li3SiO4]8 and the already established alkali lithosilicates Na[Li3SiO4] as well as K[Li3SiO4] display unforeseen luminescence properties, when doped with Eu2+. Na[Li3SiO4]:Eu2+ exhibits an ultra‐narrow blue, K[Li3SiO4]:Eu2+ a broadband, and NaK7[Li3SiO4]8:Eu2+ a yellow‐green double emission upon excitation with near‐UV to blue light. Consequently, all of the investigated substances of this class of compounds are highly interesting phosphors for application in phosphor converted LEDs.
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Hydrogenation of CO2‐Derived Carbonates and Polycarbonates to Methanol and Diols via Metal Ligand Cooperative Manganese Catalysis ()
The first example of base‐metal catalysed hydrogenation of the CO2‐derived‐carbonates to alcohols is presented. The well‐defined complex operates at low catalyst loading (as low as 0.5 mol %) and under mild conditions. The method provides a practical route to convert CO2 to methanol with the co‐production of the value‐added vicinal diols. Besides, the successful development the recycling of polycarbonates with the simultaneous formation of valuable diols and methanol has been achieved. Experimental and computational studies indicate a metal ligand cooperative catalysis mechanism.
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Sequential Transformation of Zr(IV)‐MOFs into Heterobimetallic MOFs Bearing Magnetic Anisotropic Co(II) Centers ()
Heterometallic metal‐organic frameworks (MOFs) allow the precise placement of various metals at atomic precision within a porous framework. This new level of control by MOFs promises fascinating advances in basic science and application. However, the rational design and synthesis of heterometallic MOFs remain a challenge due to the complexity of the heterometallic systems. Herein, we show that bimetallic MOFs with MX2(INA)4 moieties (INA = isonicotinate; M = Co2+ or Fe2+; X = OH‐, Cl‐, Br‐, I‐, NCS‐, or NCSe‐) can be generated by the sequential modification of a Zr‐based MOF. This multi‐step modification not only replaced the linear organic linker with a square planar MX2(INA)4 unit, but also altered the symmetry, unit cell, and topology of the parent structure. Single‐crystal to single‐crystal transformation is realized so that snapshots for transition process were captured by successive single‐crystal X‐ray diffraction. Furthermore, the installation of Co(NCS)2(INA)4 endows field‐induced slow magnetic relaxation property to the diamagnetic Zr‐MOF.
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A Dimeric Mn‐Catalyzed Completely Selective Hydroarylation of 1,3‐Diynes for the Modular Synthesis of (Z)‐Enynes Library ()
The transition‐metal‐catalyzed selective hydroarylation of unsymmetrical alkynes represents the state‐of‐art in organic chemistry, which still mainly relies on the use of precious late transition‐metal catalysts. In this communication, we have developed an unprecedented Mn(I)‐catalyzed hydroarylation of unsymmetrical 1,3‐diyne alcohols with commercially available arylboronic acids in a predictive selectivity. This method well addresses the challenges in regio‐, stereo‐ and chemoselectivity. It offers a general, convenient and practical strategy for the modular synthesis of multisubstituted (Z)‐configurated conjugated enynes. This protocol is distinguished by its simple operation, complete selectivity, excellent functional group compatibility and gram‐scale capacity. A dimeric Mn(I) species, Mn2(CO)8Br2, was proven to be a much more efficient catalyst precursor than Mn(CO)5Br.
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RNA Structure and Cellular Applications of Fluorogenic Light‐Up Aptamers ()
Cellular functions of RNA are no longer limited to their role as blueprints for protein synthesis. Especially noncoding RNA, such as, snRNAs, lncRNAs, miRNAs, play important roles. With increasing numbers of RNAs being identified, it is well known that the transcriptome outnumbers the proteome by far. This emphasizes the great importance of functional RNA characterization and the need to further develop the toolbox for these investigations, of which many are still in their infancy. Fluorescent Light‐up APtamers (FLAPs) are RNA sequences that can bind nontoxic, cell‐permeable, small‐molecule fluorogens and enhance their fluorescence over many orders of magnitude upon binding. FLAPs can be encoded on DNA level using standard molecular biology tools and are subsequently transcribed into RNA by the cellular machinery, so that they can be used as fluorescent RNA‐tags (FLAP‐tags). Here, we give a brief overview of utilized fluorogens and their binding RNA aptamers with a special focus on published crystal structures. A summary of current and future cellular FLAP applications with an emphasis on the study of RNA‐RNA and RNA‐protein interactions using split‐FLAP and Förster resonance energy transfer (FRET) systems is given.
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Regioselective Metal‐ and Reagent‐Free Arylation of Benzothiophenes by Dehydrogenative Electrosynthesis ()
A novel strategy for the efficient synthesis of biaryls consisting of a benzothiophene and phenol moiety is reported. These heterobiaryls are of utmost interest for pharmaceutical, biological, and high‐performance optoelectronic applications. By a metal‐ and reagent‐free, sustainable, electrosynthetic and highly efficient method, 2‐(hydroxyphenyl)‐ or 3‐(hydroxyphenyl)benzo[b]thiophenes are regioselectively obtained. The described one‐step synthesis is easy to conduct, scalable and inherently safe. The products are afforded in high yields up to 88% and exquisite selectivity. The protocol also features a broad scope and tolerates a large variety of functional groups.
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Pack die Sonne in den Tank: Zur Weiterentwicklung nachhaltiger Energiesysteme ()
Der Umbau von Energiesystemen hin zu nachhaltigen Lösungen schreitet seit einigen Jahren voran. Damit kann seine Wirkung im Klimaschutz durch Projektionen abgeschätzt werden. Dies geschieht hier für die Region der Europäischen Union. Das Resultat wird mit den Zielen des Pariser Klimavertrages verglichen. Es zeigt sich, dass zusätzliche qualitativ andersartige Maßnahmen ergriffen werden müssen.
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Modular Redesign of a Cationic Lytic Peptide to Promote the Endosomal Escape of Biomacromolecules ()
Endocytosis is an important route for the intracellular delivery of biomacromolecules, wherein their inefficient endosomal escape into the cytosol remains a major barrier. Based on the understanding that endosomal membranes are negatively charged, we focused on the potential of cationic lytic peptides for developing endosomolysis agents to release such entrapped molecules. As such, a venom peptide, Mastoparan X, was employed and redesigned to serve as a delivery tool. Appending a tri‐glutamate unit to the N‐terminus attenuates the cytotoxicity of Mastoparan X by ~40 fold, while introduction of a Ni(II)‐dipicolylamine complex enhances cellular uptake of the peptide by ~17 fold. Using the optimized peptide, various fluorescently labeled macromolecules were successfully delivered to the cytosol, enabling live‐cell imaging of acetylated histones.
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High‐Capacity Upconversion Wavelength and Lifetime Binary Encoding for Multiplexed Biodetection ()
Optical multiplexing benefits on‐site detection, and plays an important role in fields ranging from advanced biological assays to security. However, conventional codes based on fluorescent color and intensity are limited to spectral overlap and background interference, thus restricting the number of distinguishable identities. Herein, we present a new multiplexing concept by manipulating the luminescence emission color and decay lifetimes of upconversion nanoparticles (τλ‐UCNPs) separately for the first time through decently designing of the core/multi‐layered structure and controlled energy relay method. More importantly, the lifetime tunability induced variation of emission intensity can also be compensated by manipulating the thickness of the absorption layer. This new color/lifetime binary strategy exhibits exponentially scalable encoding capacity (>105) based on the τλ‐UCNPs loaded porous polystyrene microspheres, with 3 orders higher than that of conventional color/intensity ways. Our encoding stratagy thus enables the multiplexed detection of human papilloma virus (HPV) subtypes in patient sample and robust anti‐counterfeiting. This work opens new opportunities for optical multiplexing with luminescent materials.
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Insights into mechanochemical reactions at targetable and stable, sub‐ambient temperatures ()
We provide early insights into the effects of stable and verifiable, low‐temperature conditions on mechanochemical reactions. These are made possible by modifications made to a SPEX 8000M Mixer/mill allowing dial‐able and reliable, fine control of low‐temperature mechanochemical reactions. Our initial insights into these unique conditions were obtained using the reduction of 4‐tert‐butylcyclohexanone as a model system. The diastereomeric product distribution bore a strong dependence on the selected temperature of the jar. Comparison of the same reduction in methanol at room temperature shows similar stereoselectivity trends between the two methodologies. When temperature is varied, both cases demonstrate that decreasing temperature tends to favor increases in selectivity, although the effect is more prominently pronounced in the solvent‐free mechanochemical conditions. These results indicate that the cooled jar provides a heatsink to help mitigate the effects of the exothermic character of the reaction. Stereoselectivity also showed a dependence on operating frequency, although the nature of this dependence remains unclear. Applications of our reactor extend far beyond what is presented here, including exciting opportunities such as discovering new reactions and studying kinetics at constant temperatures. Just as our previous development of high‐temperature mechanochemistry increased the scope and understanding of mechanochemical reactions, so too does this development serve as the next step in the evolution of mechanochemistry.
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Supramolecular Metallopolymers: From Linear Materials to Infinite Networks ()
The fields of coordination polymers (CPs) and supramolecular metallopolymers (SMPs) have been extensively studied for decades. Spectacular recent advances in both fields have created new compounds that lie at the interface between these two classes of organic‐inorganic hybrid materials. At this interface, materials based on molecular weaving, supramolecular clusters, and metal‐organic framework‐polymer hybrids have emerged. This minireview provides a perspective on the intellectual emergence and connection between different supramolecular constructs and the state of the art with respect to this new materials interface.
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Supramolecular Assemblies with Near‐Infrared Emission Two‐Stage Mediated by Cucurbituril and Amphiphilic Calixarene for Lysosome‐Targeted Cell Imaging ()
Organelle‐targeted cell imaging still remains a key challenge in supramolecular chemistry in recent years. Herein, we report a two‐stage mediated near‐infrared (NIR) emissive supramolecular assembly for lysosome‐targeted cell imaging. In this system, 4,4'‐anthracene‐9,10‐diylbis(ethene‐2,1‐diyl))bis(1‐ethylpyridin‐1‐ium) bromide (ENDT) has been synthesized as an organic dye with weak fluorescence emission at 625nm. When ENDT complexes with cucurbit[8]uril (CB[8]), this binary supramolecular complex assembles into nanorods and achieve a near‐infrared fluorescence emission (655 nm) and fluorescence enhancement as the first stage. Additionally, such supramolecular complex interacts with lower‐rim dodecyl‐modified sulfonatocalix[4]arene (SC4AD) to form nanoparticles for further fluorescence enhancement as the second stage. Therefore, the emission of ENDT dye has achieved a near‐infrared emission and enhancement by two‐stage mediation of cucurbituril and amphiphilic calixarene. Furthermore, due to co‐staining experiment with LysoTracker Blue, such nanoparticles can be proved to apply in NIR lysosome‐targeted cell imaging.
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Intermetalloid Clusters: Molecules and Solids in a Dialogue ()
Atom‐precise, ligand‐stabilized metalloid clusters have emerged as outstanding model systems to study fundamental structure and bonding situations of compositionally related extended solid phases. However, this fascinating field of research is still largely restricted to homometallic and pseudo‐heterometallic systems of closely related d‐block metals. In this article, we will highlight our own, and others', efforts to project the structural and compositional diversity of intermetallics with dissimilar d‐ and p‐block metal combinations, particularly the Zintl and Hume‐Rothery phases, onto the molecular level in order to bridge the still gaping chasm between heterometallic molecular coordination chemistry and solid state intermetallics. Herein, fundamental synthetic approaches, as well as structural and electronic properties of thus accessible "molecular alloys" will be addressed, and placed against their exceptional position as intermediates on the way to nanomaterials.
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Stereospecific β‐L‐Rhamnopyranosylations Using Organoboron Reagents via SNi‐Type Mechanism ()
Stereospecific β‐L‐rhamnopyranosylations were conducted using a 1,2‐anhydro‐L‐rhamnopyranose donor and mono‐ol or diol acceptors in the presence of a glycosyl‐acceptor‐derived borinic or boronic ester. Reactions proceeded smoothly to provide the corresponding β‐L‐rhamnopyranosides (β‐L‐Rhap) with complete stereoselectivity in moderate to high yields without any further additives under mild conditions. Mechanistic studies of the borinic ester‐mediated glycosylation using 13C kinetic isotope effect (KIE) measurements and DFT calculations were consistent with a concerted SNi mechanism with an exploded transition state. In addition, the present glycosylation method was applied successfully to the synthesis of a trisaccharide, α‐L‐Rhap‐(1,2)‐β‐L‐Rhap‐(1,4)‐Glcp derived from Streptococcus pneumoniae serotypes 7B, 7C, and 7D.
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Fluorescence Probes of ALKBH2 Measure DNA Alkylation Repair and Drug Resistance Responses ()
The DNA repair enzyme ALKBH2 is implicated in both tumorigenesis as well as resistance to chemotherapy in certain cancers. It is currently under study as a potential diagnostic marker and has been proposed as a therapeutic target. To date, however, there exist no direct methods for measuring the repair activity of ALKBH2 in vitro or in biological samples. Here we report a highly specific, fluorogenic probe design based on an oligonucleotide scaffold that reports directly on ALKBH2 activity both in vitro and in cell lysates. Importantly, the probe enables the monitoring of cellular regulation of ALKBH2 activity in response to treatment with the chemotherapy drug temozolomide through a simple fluorescence assay, which has only previously been observed through indirect means such as qPCR and Western blots. Furthermore, the probe provides a viable high throughput assay for drug discovery.
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Ammonia storage via reversible host‐guest site exchange in a robust metal‐organic framework ()
MFM‐300(Al) shows reversible uptake of NH3 (15.7 mmol g‐1 at 273 K and 1.0 bar) over 50 cycles with an exceptional packing density of 0.62 g cm‐3 at 293 K. In situ neutron powder diffraction and synchrotron FTIR micro‐spectroscopy on ND3@MFM‐300(Al) confirms reversible H/D site exchange between the adsorbent and adsorbate, representing a new type of adsorption interaction.
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Photo‐Organocatalytic Enantioselective Radical Cascade Reactions of Unactivated Olefins ()
Radical cascade processes are invaluable for their ability to rapidly construct complex chiral molecules from simple substrates. However, implementing catalytic asymmetric variants is difficult. Herein we report a visible‐light‐mediated organocatalytic strategy that exploits the excited‐state reactivity of chiral iminium ions to trigger radical cascade reactions with high enantioselectivity. By combining two sequential radical‐based bond‐forming events, the method converts unactivated olefins and α,β‐unsaturated aldehydes into chiral adducts in a single step. The implementation of an asymmetric three‐component radical cascade further demonstrates the complexity‐generating power of this photochemical strategy
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A carboxylate to amide substitution tunes fold switching in a protein domain ()
Metamorphic proteins are biomolecules prone to adopt alternative conformations. Because of this feature, they represent ideal systems to investigate the general rules allowing primary structure to dictate protein topology. Here we performed a comparative molecular dynamics study on the denatured states of two proteins sharing nearly identical amino acid sequence (88%) but different topology, namely an all‐α‐helical bundle protein named GA88, and an α+β‐protein, named GB88. The analysis allowed us to successfully design, and to validate experimentally, a site‐directed mutant that promotes at least in part the fold switch from GB88 to GA88. The mutated position, in which a glutamic acid was replaced by a glutamine, does not make any intramolecular interactions in the native state of GA88, such that its stabilization can be explained by considering the effects on the denatured state. The results represent a direct demonstration of the role of the denatured state in sculpting native structure.
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