It is conventionally assumed that the growth of monodisperse colloidal nanocrystals requires a temporally discrete nucleation followed by monomer attachment onto the existing nuclei. However, recent studies have reported violations of this classical growth model, and have suggested that inter-particle interactions are also involved during the growth. Mechanisms of nanocrystal growth still remain controversial. Using in situ transmission electron microscopy, we show that platinum nanocrystals can grow either by monomer attachment from solution onto the existing particles or by coalescence between the particles. Surprisingly, an initially broad size distribution of the nanocrystals can spontaneously narrow. We suggest that nanocrystals take different pathways of growth based on their size- and morphology-dependent internal energies. These observations are expected to be highly relevant for other nanocrystal systems.

Observation of Single Colloidal Platinum Nanocrystal Growth Trajectories

The chemistry of vanadium has seen remarkable activity in the past 50 years. In the present review, reactions catalyzed by homogeneous and supported vanadium complexes from 2008 to 2018 are summarized and discussed. Particular attention is given to mechanistic and kinetics studies of vanadium-catalyzed reactions including oxidations of alkanes, alkenes, arenes, alcohols, aldehydes, ketones, and sulfur species, as well as oxidative C–C and C–O bond cleavage, carbon–carbon bond formation, deoxydehydration, haloperoxidase, cyanation, hydrogenation, dehydrogenation, ring-opening metathesis polymerization, and oxo/imido heterometathesis. Additionally, insights into heterogeneous vanadium catalysis are provided when parallels can be drawn from the homogeneous literature.

Catalytic Applications of Vanadium: A Mechanistic Perspective.

Covalent inhibition is a rapidly growing discipline within drug discovery. Many historical covalent inhibitors were discovered by serendipity, with such a mechanism of action often regarded as undesirable due to potential toxicity issues. Recent progress has seen a major shift in this outlook, as covalent inhibition shows promise for targets where previous efforts to identify non-covalent small molecule inhibitors have failed. Targeted covalent inhibitors (TCIs) can offer drug discovery scientists the ability to increase the potency and/or selectivity of small molecule inhibitors, by attachment of reactive functional groups designed to covalently bind to specific sites in a target. In this tutorial review we introduce the broader concept of covalent inhibition, discuss the potential benefits and challenges of such an approach, and provide an overview of the current status of the field. We also describe some strategies and computational tools to enable successful covalent drug discovery.

Structure-based design of targeted covalent inhibitors.

Structure-based virtual screening (VS) is a widely used approach that employs the knowledge of the three-dimensional structure of the target of interest in the design of new lead compounds from large-scale molecular docking experiments. Through the prediction of the binding mode and affinity of a small molecule within the binding site of the target of interest, it is possible to understand important properties related to the binding process. Empirical scoring functions are widely used for pose and affinity prediction. Although pose prediction is performed with satisfactory accuracy, the correct prediction of binding affinity is still a challenging task and crucial for the success of structure-based VS experiments. There are several efforts in distinct fronts to develop even more sophisticated and accurate models for filtering and ranking large libraries of compounds. This paper will cover some recent successful applications and methodological advances, including strategies to explore the ligand entropy and solvent effects, training with sophisticated machine-learning techniques, and the use of quantum mechanics. Particular emphasis will be given to the discussion of critical aspects and further directions for the development of more accurate empirical scoring functions.

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Empirical Scoring Functions for Structure-Based Virtual Screening: Applications, Critical Aspects, and Challenges.

Catching CO oxidation Details of the transition state that forms as carbon monoxide (CO) adsorbed on a ruthenium surface is oxidized to CO2 have been revealed by ultrafast excitation and probe methods. Öström et al. initiated the reaction between CO and adsorbed oxygen atoms with laser pulses that rapidly heated the surface and then probed the changes in electronic structure with oxygen x-ray absorption spectroscopy. They observed transition-state configurations that are consistent with density functional theory and a quantum oscillator model. Science, this issue p. 978 Ultrafast x-ray spectroscopy reveals electronic changes that occur during the oxidation of carbon monoxide on a ruthenium surface. Femtosecond x-ray laser pulses are used to probe the carbon monoxide (CO) oxidation reaction on ruthenium (Ru) initiated by an optical laser pulse. On a time scale of a few hundred femtoseconds, the optical laser pulse excites motions of CO and oxygen (O) on the surface, allowing the reactants to collide, and, with a transient close to a picosecond (ps), new electronic states appear in the O K-edge x-ray absorption spectrum. Density functional theory calculations indicate that these result from changes in the adsorption site and bond formation between CO and O with a distribution of OC–O bond lengths close to the transition state (TS). After 1 ps, 10% of the CO populate the TS region, which is consistent with predictions based on a quantum oscillator model.

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"Probing the Transition State Region in Catalytic CO Oxidation on Ru" data files

Monometallic catalysts, in particular those containing noble metals, are frequently used in heterogeneous catalysis, but they are expensive, rare and the ability to tailor their structures and properties remains limited. Traditionally, alloy catalysts have been used instead that feature enhanced electronic and chemical properties at a reduced cost. Furthermore, the introduction of single metal atoms anchored onto supports provided another effective strategy to increase both the atomic efficiency and the chance of tailoring the properties. Most recently, single-atom alloy catalysts have been developed in which one metal is atomically dispersed throughout the catalyst via alloy bonding; such catalysts combine the traditional advantages of alloy catalysts with the new feature of tailoring properties achievable with single atom catalysts. This review will first outline the atomic scale structural analysis on single-atom alloys using microscopy and spectroscopy tools, such as high-angle annular dark field imaging-scanning transmission electron microscopy and extended X-ray absorption fine structure spectroscopy. Next, progress in research to understand the electronic properties of single-atom alloys using X-ray spectroscopy techniques and quantum calculations will be presented. The catalytic activities of single-atom alloys in a few representative reactions will be further discussed to demonstrate their structure–property relationships. Finally, future perspectives for single-atom alloy catalysts from the structural, electronic and reactivity aspects will be proposed.

Single-atom alloy catalysts: structural analysis, electronic properties and catalytic activities

Modeling covalent-modifier drugs.

Single-atom catalysts (SACs) have recently emerged as an exciting system in heterogeneous catalysis showing outstanding performance in many catalytic reactions. Single-atom catalytic sites alone are not stable and thus require stabilization from substrates. Crystalline porous materials such as zeolites and metal-organic frameworks (MOFs) are excellent substrates for SACs, offering high stability with the potential to further enhance their performance due to synergistic effects. This review features recent work on the structure, electronic, and catalytic properties of zeolite and MOF-protected SACs, offering atomic-scale views from the "inside" thanks to the subatomic resolution of synchrotron X-ray absorption spectroscopy (XAS). The extended X-ray absorption fine structure and associated methods will be shown to be powerful tools in identifying the single-atom site and can provide details into the coordination environment and bonding disorder of SACs. The X-ray absorption near-edge structure will be demonstrated as a valuable method in probing the electronic properties of SACs by analyzing the white line intensity, absorption edge shift, and pre-/postedge features. Emphasis is also placed on in situ/operando XAS using state-of-the-art equipment, which can unveil the changes in structure and properties of SACs during the dynamic catalytic processes in a highly sensitive and time-resolved manner.

Single-Atom Catalysts Supported by Crystalline Porous Materials: Views from the Inside.

TiO2 is one of the most widely used photocatalysts and photothermocatalysts. Tailoring their structure and electronic properties is crucial for the design of high-performance TiO2 catalysts. Herein, we report a strategy to significantly enhance the performance of TiO2 in the photothermocatalytic reduction of CO2 by doping high crystalline nano-TiO2 with tungsten. A variety of tungsten doping concentrations ranging from 2% to 10% were tested and they all showed enhanced catalytic activities. The 4% W-doped TiO2 exhibited the highest activity, which was 3.5 times greater than that of the undoped TiO2 reference. Structural characterization of these W-doped TiO2 catalysts indicated that W was successfully doped into the TiO2 lattice at relatively low dopant concentration. Synchrotron X-ray absorption spectroscopy at both the W L3- and Ti K-edges was further used to provide insight into the local structure and bonding properties of the catalysts. It was found that the replacement of Ti with W led to the formation of Ti vacancies in order to maintain the charge neutrality. Consequently, dangling oxygen and oxygen vacancies were produced that acted as catalytically active sites for the CO2 reduction. As the W doping concentration increased from 2% to 4%, more such active sites were generated which thus resulted in the enhancement of the catalytic activity. When the W doping concentration was further increased to 10%, the extra W species that cannot replace the Ti in the lattice aggregated to form WO3. Due to the lower conduction band of WO3, the catalytic O sites were deactivated and CO2 reduction was inhibited. This work presents a useful strategy for the development of highly efficient catalysts for CO2 reduction as well as new insights into the catalytic mechanism in cation-doped TiO2 photothermocatalysis.

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W-Doped TiO2 for photothermocatalytic CO2 reduction

CO oxidation is one of the most studied reactions in heterogeneous catalysis. It is present in air cleaning and automotive emission control. It also participates in the removal of CO from streams o...

Andrew G. Walsh

Papers

Single-atom alloy catalysts: structural analysis, electronic properties and catalytic activities

Modeling covalent-modifier drugs.

Single-Atom Catalysts Supported by Crystalline Porous Materials: Views from the Inside.

W-Doped TiO2 for photothermocatalytic CO2 reduction

Synergism of Iron and Platinum Species for Low-Temperature CO Oxidation: from Two-Dimensional Surface to Nanoparticle and Single-Atom Catalysts.