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  • Carbon‒Carbon Bond Activation of Ketones
    Trends Chem. Pub Date : 2020-01-08
    Lin Deng; Guangbin Dong

    C−C bond activation has emerged as an increasingly useful approach for constructing complex molecular scaffolds through unusual bond-disconnection strategies. As a common versatile functional group, ketones provide an excellent handle and platform for C−C bond activation reactions. Utilizing strain-release, carbon-monoxide-extrusion, and directing-group (DG) approaches, diverse transformations of various ketones have been developed in the past few decades through cleavage of their α C−C bonds. This review highlights the development of C−C bond-activation strategies for both strained and less strained ketones with a focus on transition-metal (TM)-catalyzed approaches.

  • Encapsulating Metal Nanocatalysts within Porous Organic Hosts
    Trends Chem. Pub Date : 2020-01-08
    Xinchun Yang; Qiang Xu

    The encapsulation of metal nanoparticles (MNPs) inside porous organic hosts (POHs), such as metal-organic frameworks, covalent organic frameworks, organic molecular cages, and amorphous porous organic polymers has attracted significant attention because this procedure can generate highly catalytically active MNPs. This short review describes important recent progress in the fabrication of active MNP catalysts through confinement inside POH cavities, including various innovative synthetic strategies and catalytic applications. In particular, several representative reports of [email protected] hybrids are chosen to showcase why such POHs are so unique for confining MNPs and why the confined MNPs possess superior catalytic activity, selectivity, and stability. Finally, the challenges of employing [email protected] catalysts for future practical catalytic applications are addressed.

  • Sodium–Oxygen Batteries: Recent Developments and Remaining Challenges
    Trends Chem. Pub Date : 2020-01-03
    Hossein Yadegari; Xueliang Sun

    Sodium–oxygen (Na-O2) batteries are considered a higher-energy-efficiency alternative to the lithium–oxygen (Li-O2) system. The reversible superoxide electrochemistry governing the oxygen reduction and evolution reactions in Na-O2 cells results in a relatively lower charging overpotential. Thus, significant research attention has been directed toward Na-O2 in the hope of developing a high-energy-storage system. This review provides a brief overview of the most recent research progress in this field with special emphasis on the chemical and electrochemical reaction mechanisms. All major components of the cell including the positive and negative electrodes as well as the electrolyte are covered. Moreover, areas requiring more research attention are specified and potential directions for future research are proposed.

  • Metallo-Polyelectrolytes: Correlating Macromolecular Architectures with Properties and Applications
    Trends Chem. Pub Date : 2019-12-27
    Tianyu Zhu; Jiuyang Zhang; Chuanbing Tang

    Since the middle of the 20th century, metallopolymers have represented a standalone subfield with a beneficial combination of functionality from inorganic metal centers and processability from the organic polymeric frameworks. Metallo-polyelectrolytes are a new class of soft materials that showcase fundamentally different properties from neutral polymers due to their intrinsically ionic behaviors. This review describes recent trends in metallo-polyelectrolytes and discusses emerging properties and challenges, as well as future directions from a perspective of macromolecular architectures. The correlations between macromolecular architectures and properties are discussed from copolymer self-assembly, metallo-enzymes for biomedical applications, metallo-peptides for catalysis, crosslinked networks, and metallogels.

  • Shaping Functional Materials with DNA Frameworks
    Trends Chem. Pub Date : 2019-12-10
    Yang Yang, Rui Zhang, Chunhai Fan

    Designing and engineering materials into particular shapes and/or structural arrangements paves the way to advanced materials properties. Top-down micro/nano fabrication can achieve patterns with sub-10 nm precision; however, challenges and limitations in material versatility, dynamic arrangement, biocompatibility, and high cost still exist. Bottom-up methods, however, allow elements to grow/assemble into well-defined structures. Along with the prosperity in the field of structural DNA nanotechnology, DNA as a mature programmable polymer has been fascinating in organizing materials into complex nanostructures. In this review article, we briefly introduce key achievements of DNA nanotechnology, summarize the current progress of DNA nanostructure-based material programming and molding, and discuss the limitations and challenges of this challenging field.

  • Surface Modification of TiO2 for Perovskite Solar Cells
    Trends Chem. Pub Date : 2019-12-04
    Wanpei Hu, Shangfeng Yang, Shihe Yang

    Titanium oxide (TiO2) is commonly used as an electron transport layer (ETL) of regular-structure perovskite solar cells (PSCs); however, it suffers from inherent drawbacks such as low electron mobility and a high density of trap states. Modifying the surface chemistry of TiO2 has proved facile and efficient in enhancing key electron-transport properties, thereby improving device performance. In this review, we summarize recent progress on the surface modification of TiO2 in planar PSCs. The functions of different modifiers in improving device performance are elucidated, revealing the influence of modifier chemical and electronic structure on the properties of TiO2. This offers new opportunities to exploit novel materials for modifying TiO2 toward high-efficiency PSCs.

  • Relevance of Particle Morphology for Atmospheric Aerosol Processing
    Trends Chem. Pub Date : 2019-12-03
    Claudia Marcolli, Ulrich K. Krieger

    Recent laboratory and modeling studies suggest high relevance of aerosol mixing state and particle morphology for the life cycle of atmospheric aerosols. A new article by Gorkowski and colleagues presents a framework to predict morphologies of aerosol particles based on O:C ratio for incorporation into chemical transport models.

  • Responsive and Foldable Soft Materials
    Trends Chem. Pub Date : 2019-12-03
    Jiaqi Liu, Yuchong Gao, Young-Joo Lee, Shu Yang

    Stimulus-responsive soft materials that can enable folding of a 2D sheet into a 3D object have potential significant applications, including wearable electronics, biomimetic machines, soft robotics, drug delivery, biomedical devices, and responsive buildings. The responses can be tuned by the materials chemistry, composition, and type of external stimulus; the direction and magnitude of the deformation can be varied by geometric design and incorporation of nonresponsive materials and nanofillers. In this review, we overview different types of responsive materials (e.g., responsive hydrogels, shape memory polymers, liquid crystal elastomers, and polymer composites) and some of the basic folding mechanisms. We highlight the required material properties, fabrication techniques, and structural designs for desirable folding structures.

  • Multiscale Design of Flexible Metal–Organic Frameworks
    Trends Chem. Pub Date : 2019-11-18
    Shing Bo Peh, Avishek Karmakar, Dan Zhao

    Flexible materials can adapt to external stimuli with predictable and controllable responses. The emergence of dynamic behavior in metal–organic frameworks (MOFs) is promising for the development of ‘smart’ materials for applications that leverage their porosities and tunable chemical compositions, including the storage, separation, and sensing of small molecules. The translation of molecular structural transformations to macroscopic responses requires the multiscale design of flexible MOF systems. This review summarizes the progress in this area focusing on the past 3–5 years, starting from the modular assembly of building blocks and continuing to the management of dynamics in device architectures.

  • Designer Polymers Boost Cation Exchange
    Trends Chem. Pub Date : 2019-11-09
    Peter M. Budd

    Membranes formed from polymers with rigid, contorted backbones have been explored for the separation of a variety of liquid and gaseous mixtures. Recent research reported by Helms and colleagues opens a whole new area of application, demonstrating cation-exchange membranes with exceptional performance for new batteries.

  • Organic Chemistry for Biology-Oriented Students
    Trends Chem. Pub Date : 2019-11-05
    Tien-Yau Luh, Cheng-Kung Chou

    Restructuring the syllabus of an introductory organic chemistry course to better suit the need of biology-oriented students and provide fundamental understanding of chemical principles of biochemical transformations is proposed. It is recommended that certain organic reactions less relevant to natural biological systems are replaced with biochemical reactions as illustrations.

  • Flow Photochemistry: Shine Some Light on Those Tubes!
    Trends Chem. Pub Date : 2019-11-01
    Carlo Sambiagio, Timothy Noël

    Continuous-flow chemistry has recently attracted significant interest from chemists in both academia and industry working in different disciplines and from different backgrounds. Flow methods are now being used in reaction discovery/methodology, in scale-up and production, and for rapid screening and optimization. Photochemical processes are currently an important research field in the scientific community and the recent exploitation of flow methods for these methodologies has made clear the advantages of flow chemistry and its importance in modern chemistry and technology worldwide. This review highlights the most important features of continuous-flow technology applied to photochemical processes and provides a general perspective on this rapidly evolving research field.

  • Emerging Applications of Supramolecular Peptide Assemblies
    Trends Chem. Pub Date : 2019-10-31
    Beom Jin Kim, Dongsik Yang, Bing Xu

    Supramolecular peptide assemblies not only provide molecular insight into understanding and mimicking the fundamental features of the self-assembly of biological molecules, but also promise many important applications. This review discusses representative examples of supramolecular assemblies of peptides or peptide derivatives and highlights the emerging applications of these materials, including tissue engineering, molecular imaging, and cancer therapeutics. These results underscore the tremendous promise of supramolecular peptide assemblies as an emerging interdisciplinary research branch at the interface of chemistry and biological science.

  • A Leap towards Stable Li-Metal Anode Interphases
    Trends Chem. Pub Date : 2019-10-25
    Chen-Zi Zhao, Qiang Zhang

    Electrochemical interphases dominate the performance of reactive Li-metal anodes, which possess high theoretical specific capacity and low electrochemical potential. A new article by Bao and colleagues describes an artificial interfacial layer to overcome common sources of instability through the use of a dynamic, electrolyte-blocking, and single-ion-conducting dynamic polymer network.

  • Amphidynamic Crystals Key to Artificial Molecular Machines
    Trends Chem. Pub Date : 2019-09-05
    Indranil Roy, J. Fraser Stoddart

    Amphidynamic crystals have close links to molecular machines, which have considerable potential for developing smart materials. A recently published article in Matter (Colin-Molina et al.) reports an amphidynamic supramolecular rotor that displays a remarkable thermosalient effect when undergoing a phase transition, concomitant with a substantial structural reconfiguration resulting in crystal motility.

  • Modularity: Adding New Dimensions to Total Synthesis
    Trends Chem. Pub Date : 2019-06-21
    Alexander W. Sun, Sebastian Lackner, Brian M. Stoltz

    As the field of synthetic chemistry seeks to tackle new frontiers, total synthesis is primed to address significant medical challenges such as the rise of antibiotic resistance and cancer. One emerging frontier focuses on increasingly concerted efforts to utilize modular total synthesis as a strategy to generate analogs of natural product targets for biological studies, with the ultimate goal of new therapeutic development. This new frontier is enabled by a confluence of human ingenuity in synthetic design, newly developed reactions that facilitate advances in total synthesis strategies, and emerging technologies. In this review, we highlight the evolving trend of modular total synthesis, including new reactions and automated technologies. This trend should lead to an increasingly important source of new medicines to improve human health.

  • Extrapolating the Fragment-Based Approach to Inorganic Drug Discovery
    Trends Chem. Pub Date : 2019-05-30
    Lucinda K. Batchelor, Paul J. Dyson

    The fragment-based approach is a well-established strategy for organic drug discovery. Recent studies have shown that this approach also has considerable potential in medicinal inorganic chemistry, and yet the approach has not been formally described. Here, we describe selected compounds that form (or have potential to form) intra- or inter-DNA–DNA, DNA–protein, and protein–protein crosslinks. Such dual interactions provide a powerful way to generate metal-based drugs with superior efficacies to those currently used. We demonstrate that the fragment-based approach represents an ideal way to design these bioactive compounds. In this review, we point out the limitations of current examples and delineate key components that might lead to more effective compounds (i.e., compounds that are more selective and have stronger binding affinities for specific biomolecular targets).

  • MXenes: An Introduction of Their Synthesis, Select Properties, and Applications
    Trends Chem. Pub Date : 2019-05-30
    Louisiane Verger, Varun Natu, Michael Carey, Michel W. Barsoum

    Two dimensional (2D) materials have attracted significant attention in the past decade for their high application potential to address some of society’s most pressing issues such as energy storage and the scarcity of potable water. One of the latest, and relatively large, family of 2D materials is transition-metal carbides and nitrides, called MXenes. Since the initial synthesis of Ti3C2 in hydrofluoric acid in 2011, almost 30 other new compositions and at least eight different synthesis pathways have been reported. In this review, we overview the structure, synthesis, and chemistry of MXenes, with examples of their properties and potential applications that partially explain why these materials have become so popular.

  • Recent Advances in the Green, Sustainable Synthesis of Semiconducting Polymers
    Trends Chem. Pub Date : 2019-09-03
    Samantha Phan, Christine K. Luscombe

    There is a significant need for economic and environmentally sustainable chemistry in both academia and industry. The field of organic electronics is also rapidly growing due to substantial interest in semiconducting polymers. A major limitation associated with semiconducting polymers is their synthesis, which often requires many synthetic steps and relies on stoichiometric amounts of toxic metallic reagents. For a technology to be sustainable, both the economic and environmental costs must be feasible. Recently, significant effort has been expended towards synthesizing semiconducting polymers with greener biomass-derived solvents, more sustainable catalysts, and under energy-efficient reaction conditions. This review highlights key efforts in synthesizing environmentally benign, scalable, and high-performing semiconducting polymers.

  • Next-Generation Cathode Materials for Non-aqueous Potassium-Ion Batteries
    Trends Chem. Pub Date : 2019-05-21
    Haegyeom Kim, Huiwen Ji, Jingyang Wang, Gerbrand Ceder

    Potassium-ion batteries have recently attracted considerable attention as cost-effective alternatives to lithium-ion batteries for large-scale energy storage. However, a major obstacle to the practical application of this emerging technology is the lack of suitable cathode materials that are capable of delivering high gravimetric/volumetric energy, stable cycle life, and high rate capability. In this review article, we review the recent progress in cathodes development for potassium-ion batteries. These materials are categorized into four types: layered oxides, Prussian blue analogs, poly-anion, and organic compounds. Based on our critical review of the reported literature, we identify poly-anion compounds as a class of promising candidates among all types and provide suggestions for future optimization.

  • Lithium-Anode Protection in Lithium–Sulfur Batteries
    Trends Chem. Pub Date : 2019-07-09
    Chong Yan, Xue-Qiang Zhang, Jia-Qi Huang, Quanbing Liu, Qiang Zhang

    Lithium–sulfur (Li–S) batteries show significant promise as next-generation energy-storage devices due to their high energy density (2600 Wh kg-1). However, the severe shuttling of polysulfide intermediates and low Coulombic efficiency during operation induce rapid capacity loss, hindering their practical applications. Although sulfur coin cells can reach 1000 cycles, sulfur pouch cells reach only dozens of cycles before the lithium-metal anode is damaged by the electrolyte and/or polysulfides. Therefore, lithium-metal protection is an important issue in realizing long lifespans of Li–S pouch cells. In this review, we highlight recent progress on lithium-metal protection, including altering the solvation structure of lithium ions in the liquid electrolyte, designing an artificial solid electrolyte interphase (SEI), employing solid-state electrolytes, and adopting micro/nanostructured hosts.

  • Rational Design of Bimetallic Nanocatalysts for Tandem Transformations
    Trends Chem. Pub Date : 2019-10-18
    Ivo F. Teixeira, Pedro H.C. Camargo

    Tandem reactions consist of a sequence of two or more distinct transformations that can be achieved in a single synthetic step. A new article by Sun and colleagues demonstrates how the catalytic properties of bimetallic nanoparticles can be rationally optimized to enable the one-pot synthesis of polybenzoxazole (PBO).

  • Mechanisms of Nickel-Catalyzed Cross-Coupling Reactions
    Trends Chem. Pub Date : 2019-09-13
    Justin B. Diccianni, Tianning Diao

    Advances in nickel-catalyzed cross-coupling reactions have expanded the chemical space of accessible structures and enabled new synthetic disconnections. The unique properties of Ni catalysts facilitate the activation of traditionally inert substrates, tolerate alkyl coupling partners that undergo decomposition via β-hydride (β-H) elimination with Pd, and enable stereoconvergent cross-couplings. The radical pathways accessed by Ni catalysts have been merged with photoredox and electrochemical catalysis to achieve new reactivity. The growing utility of Ni catalysis is, in no small part, due to advances in our fundamental understanding of the properties of Ni catalysts and the mechanisms by which the reactions occur. This review highlights recent important contributions to the field with an emphasis on studies that have afforded mechanistic insight.

  • Building Brain-Inspired Logic Circuits from Dynamically Switchable Transition-Metal Oxides
    Trends Chem. Pub Date : 2019-09-13
    Justin L. Andrews, David A. Santos, M. Meyyappan, R. Stanley Williams, Sarbajit Banerjee

    Processing, storing, and transmitting information accounts for ~10% of global energy use; projections suggest that computational energy demands will be 10× higher than the projected global energy supply by 2040. Realizing solid-state analogs of neural circuitry, using ‘neuromorphic’ materials, holds promise for enabling a new energy-efficient computing paradigm. The metal–insulator transitions (MITs) of electron-correlated transition-metal oxides provide an attractive vector for achieving large conductance switching with minimal energy dissipation. Here, we review current understanding of the mechanisms underpinning electronic instabilities, discuss methods for modulation of spiking behavior through tuning of atomistic and electronic structure, and highlight the need for establishing deterministic and independent control of transformation characteristics such as switching magnitude, energy thresholds, heat dissipation, hysteresis, and dynamics of relaxation.

  • Bio-orthogonal Click Chemistry for In Vivo Bioimaging
    Trends Chem. Pub Date : 2019-09-09
    Kenry, Bin Liu

    The rapid advancement of bio-orthogonal click chemistry in the past decade has enabled the study and precise manipulation of biological processes within living organisms. The capability to induce fast and selective chemical reactions between two exogenous complementary moieties in living systems, with negligible perturbation to their native activities, have rendered bio-orthogonal click chemistry highly promising for a multitude of bioapplications. This review provides an overview of recent developments in bio-orthogonal click chemistry for bioimaging in living organisms. Bio-orthogonal click reactions commonly performed in in vivo systems and their in vivo biological labeling and imaging applications, particularly for the visualization of biomolecular processes, therapeutic cells, tumors, and bacteria, are discussed. Potential future directions of this exciting area are also presented.

  • Engineering Charge-Transfer States for Efficient, Low-Energy-Loss Organic Photovoltaics
    Trends Chem. Pub Date : 2019-09-05
    Xiao Liu, Barry P. Rand, Stephen R. Forrest

    Charge transfer (CT) between donors and acceptors following photoexcitation of organic photovoltaics (OPVs) gives rise to bound electron–hole pairs across the donor–acceptor interface, known as CT states. While these states are essential to charge separation, they are also a source of energy loss. As a result of reduced overlap between electron and hole wavefunctions, CT states are influenced by details of the film morphology and molecular structure. Here, we describe several important strategies for tuning the energy level and dynamics of the CT state and approaches that can enhance their dissociation efficiency into free charges. Furthermore, we provide an overview of recent physical insights into the key parameters that significantly reduce the Frenkel-to-CT energy offset and recombination energy losses while preserving a high charge-generation yield. Our analysis leads to critical morphological and molecular design strategies for achieving efficient, low-energy-loss OPVs.

  • Brownian Dynamics Simulations of Biological Molecules
    Trends Chem. Pub Date : 2019-08-28
    Gary A. Huber, J. Andrew McCammon

    Brownian dynamics (BD) is a technique for carrying out computer simulations of physical systems that are driven by thermal fluctuations. Biological systems at the macromolecular and cellular level, while falling in the gap between well-established atomic-level models and continuum models, are especially suitable for such simulations. We present a brief history, examples of important biological processes that are driven by thermal motion, and those that have been profitably studied by BD. We also present some of the challenges facing developers of algorithms and software, especially in the attempt to simulate larger systems more accurately and for longer times.

  • Ultrafast Photophysics of 2D Semiconductors and Related Heterostructures
    Trends Chem. Pub Date : 2019-08-28
    Stefano Dal Conte, Chiara Trovatello, Christoph Gadermaier, Giulio Cerullo

    Atomically thin transition-metal dichalcogenides (TMDs) exhibit strong light–matter interaction and pronounced excitonic behavior. Understanding the nonequilibrium dynamical processes of photoexcited carriers in such materials is a key step in view of their technological applications. Here, we review the ultrafast photophysics of 2D TMDs and related heterostructures (HSs) measured by femtosecond optical spectroscopy. First, we provide a general introduction on the physics of the materials and a brief explanation of the ultrafast optical techniques. Then we discuss the physical processes governing their nonequilibrium optical response, with a particular emphasis on the intervalley scattering dynamics, and the charge-transfer processes in 2D HSs. We conclude by discussing open issues and perspectives for future experiments.

  • From DNA Tiles to Functional DNA Materials
    Trends Chem. Pub Date : 2019-08-23
    Amelie Heuer-Jungemann, Tim Liedl

    Over the past few decades, DNA has turned into one of the most widely used molecular linkers and a versatile building block for the self-assembly of DNA nanostructures. Such complexes, composed of only a few oligonucleotides (e.g., DNA tiles) or assembled from hundreds of synthetic and natural scaffolding strands (e.g., DNA origami), are being increasingly assembled into higher-order architectures such as lattices and crystals. A wide variety of assembly methods and techniques (e.g., solution-phase and substrate-assisted sticky-ended cohesion or blunt-end stacking) have emerged and are constantly being refined. This review provides a summary of the methods and building blocks for the assembly of 2D and 3D DNA lattices and crystals, and discusses some of their potential applications in materials science.

  • Universal Chemical Synthesis and Discovery with ‘The Chemputer’
    Trends Chem. Pub Date : 2019-08-15
    Piotr S. Gromski, Jarosław M. Granda, Leroy Cronin

    There is a growing drive in the chemistry community to exploit rapidly growing robotic technologies along with artificial intelligence-based approaches. Applying this to chemistry requires a holistic approach to chemical synthesis design and execution. Here, we outline a universal approach to this problem beginning with an abstract representation of the practice of chemical synthesis that then informs the programming and automation required for its practical realization. Using this foundation to construct closed-loop robotic chemical search engines, we can generate new discoveries that may be verified, optimized, and repeated entirely automatically. These robots can perform chemical reactions and analyses much faster than can be done manually. As such, this leads to a road map whereby molecules can be discovered, optimized, and made on demand from a digital code.

  • Emerging Strategies for C–H Silylation
    Trends Chem. Pub Date : 2019-08-07
    Sven C. Richter, Martin Oestreich

    Silicon-containing molecules are of great academic and industrial interest with widespread applications in several research areas such as materials science, medicinal chemistry, and complex-molecule synthesis. C–Si bond formation by direct C–H functionalization is a modern synthetic approach toward highly valuable compounds that offers a superior step and atom economy in contrast to conventional procedures involving at least one prefunctionalized reaction partner. In this review, we summarize the different strategies for C–H silylation. Organized by their reaction mechanism, a representative selection of recent methodologies is introduced and compared with regard to their substrate scope, functional-group tolerance, and regioselectivity.

  • The Structure and Function of DNA G-Quadruplexes
    Trends Chem. Pub Date : 2019-07-31
    Jochen Spiegel, Santosh Adhikari, Shankar Balasubramanian

    Guanine-rich DNA sequences can fold into four-stranded, noncanonical secondary structures called G-quadruplexes (G4s). G4s were initially considered a structural curiosity, but recent evidence suggests their involvement in key genome functions such as transcription, replication, genome stability, and epigenetic regulation, together with numerous connections to cancer biology. Collectively, these advances have stimulated research probing G4 mechanisms and consequent opportunities for therapeutic intervention. Here, we provide a perspective on the structure and function of G4s with an emphasis on key molecules and methodological advances that enable the study of G4 structures in human cells. We also critically examine recent mechanistic insights into G4 biology and protein interaction partners and highlight opportunities for drug discovery.

  • Chemo-Mechanical Challenges in Solid-State Batteries
    Trends Chem. Pub Date : 2019-07-26
    John A. Lewis, Jared Tippens, Francisco Javier Quintero Cortes, Matthew T. McDowell

    Solid-state batteries (SSBs) could exhibit improved safety and energy density compared with traditional lithium-ion systems, but fundamental challenges exist in integrating solid-state electrolytes with electrode materials. In particular, the (electro)chemical evolution of electrode materials and interfaces can often be linked to mechanical degradation due to the all-solid nature of these systems. This review presents recent progress in understanding the coupling between chemistry and mechanics in solid-state batteries, with a focus on three important phenomena: (i) lithium filament growth through solid-state electrolytes, (ii) structural and mechanical evolution at chemically unstable interfaces, and (iii) chemo-mechanical effects within solid-state composite electrodes. Building on recent progress, overcoming chemo-mechanical challenges in solid-state batteries will require new in situ characterization methods and efforts to control evolution of interfaces.

  • Recent Developments in Cyclopropane Cycloaddition Reactions
    Trends Chem. Pub Date : 2019-07-19
    Jiaxin Liu, Ruixing Liu, Yin Wei, Min Shi

    In organic synthesis, the synthetic methodology of using cyclopropanes for cycloadditions has witnessed significant progress over the past several years. A series of cyclopropane-related cycloaddition reactions via organic or metal-catalyzed/mediated pathways has been exploited in constructing cyclic frameworks such as polycycles, bridged-ring carbocycles, and heterocycles. Moreover, this synthetic chemistry has also recently blossomed in the pursuit of highly efficient asymmetric cycloadditions, C–H bond-activated cycloadditions, photoredox catalysis-cooperated cycloadditions, and several other unique reaction processes. Although numerous cyclopropane-based cycloaddition reactions have been reported, the newly explored cycloadditions have not yet been reviewed. Herein, we present recent progress in cyclopropane-related cycloadditions over the past 6 years.

  • Emerging Photocatalysts for Hydrogen Evolution
    Trends Chem. Pub Date : 2019-07-15
    Shuang Cao, Lingyu Piao, Xiaobo Chen

    Hydrogen evolution via solar-driven photocatalytic water splitting (PWS) is considered an important strategy for facilitating clean global energy and overcoming the severe environmental challenges facing our society. As a result, many photocatalysts have been developed over the past several years. In this review, we outline the most recent advances in hydrogen evolution photocatalysts over the past 2 years. In particular, we introduce hydrogen production methods, main and cocatalysts for hydrogen evolution through water splitting, the underlying photocatalytic mechanisms, and current challenges and future potential advances for this exciting field.

  • Towards High-Efficiency Synthesis of Xenonucleic Acids
    Trends Chem. Pub Date : 2019-07-06
    Benjamin D. Fairbanks, Heidi R. Culver, Sudheendran Mavila, Christopher N. Bowman

    Beyond their central role in storing and transmitting genetic information, nucleic acids are renowned for their high-specificity, high-affinity hybridization. In the past several decades, scientists have become increasingly interested in emulating this unique property of nucleic acids using synthetic mimics. Many creative strategies for the synthesis of xenonucleic acids (XNAs) have been developed, with the field ultimately striving for high-efficiency, scalable routes to achieving sequence-controlled XNA synthesis. Emerging strategies in both biology (e.g., directed evolution) and chemistry (e.g., dynamic covalent reactions) are leading to new breakthroughs in XNA synthesis that will make applications of nucleic acids, such as gene therapy, agricultural disease management, and electronics, more accessible.

  • Carbon Nanodots for Capacitor Electrodes
    Trends Chem. Pub Date : 2019-06-13
    Chenxiang Wang, Volker Strauss, Richard B. Kaner

    Carbon nanodots (CNDs) and graphene/carbon quantum dots (GQDs/CQDs) have emerged as useful components for the fabrication of electrodes in electric double-layer capacitors (EDLCs). In this review, we highlight the emerging trend of employing CNDs and their relatives as active components in EDLCs. We discuss recent progress in converting CNDs with intrinsically low electrical conductivity into conductive electrode materials. Specifically, we highlight advances in improving specific surface area (SSA) and rate capability, as well as employing abundant active sites on CNDs to increase electrode specific capacitance based on conductive carbon, metal compounds, and/or conductive polymers.

  • Lanthanide Photonics: Shaping the Nanoworld
    Trends Chem. Pub Date : 2019-06-11
    Jean-Claude G. Bünzli

    Lanthanide luminescent materials have gradually become indispensable in a wealth of applications, including phosphors for lighting and displays, security inks and tags, lasers, optical fibers, night vision, photocatalysis, bioprobes, nanoscopy, and light-activated drug delivery. In this short review, we describe the basic properties of lanthanide luminescence, highlight major current applications, and discuss the growing trend of embedding luminescent lanthanide ions into nanostructures, which not only enhances their emissive properties but also, and quite importantly, unlocks a whole (nano)world of new applications.

  • Electrochemical Reduction of CO2 Catalyzed by Metal Nanocatalysts
    Trends Chem. Pub Date : 2019-06-06
    Zhouyang Yin, G. Tayhas R. Palmore, Shouheng Sun

    The electrochemical CO2 reduction reaction (CO2RR) catalyzed by metal nanostructures has been studied extensively in recent years. This research has led to a better understanding of the reaction as it occurs on nanomaterial surfaces to achieve efficient conversion of CO2 to specific carbon products. This review focuses on metallic nanocatalysts designed and prepared to catalyze the electrochemical CO2RR. It also summarizes new strategies developed to further enhance catalysis at the atomic scale that lead to more efficient conversion of CO2. Active and selective conversion of CO2 to hydrocarbons is an important step toward a society based on renewable energy.

  • Rylene Diimide Electron Acceptors for Organic Solar Cells
    Trends Chem. Pub Date : 2019-05-31
    Jiayu Wang, Xiaowei Zhan

    Rylene diimide-based n-type organic semiconductors possess several advantages over traditional materials, such as structural diversity, facile chemical modification, and tunable optical and electronic properties. Rylene diimides are widely used as electron acceptors in organic solar cells (OSCs), with power conversion efficiencies of >11%. Recent studies have revealed that several rylene diimide acceptors show unique properties, such as efficient charge separation under negligible driving force and triplet excitons. This review summarizes the structural evolution of rylene diimide acceptors associated with an efficiency enhancement from 1% to 10%, aiming to extract effective design strategies and propose future perspectives and opportunities.

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上海纽约大学William Glover