8 research outputs found

    Isocyanate-free approaches to polyurea dispersions and coatings

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    Studies in chemistry

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    Thermal rearrangements of some hydroxamic acid derivatives

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    An historical survey of the thermolyses of hydroxamic acids and O-acylated hydroxamic acids is presented, and thermal rearrangements which proceed by [l,3 ]-sigmatropic and free radical shifts are reviewed, together with the phenomenon of chemically induced dynamic nuclear polarisation (CIDNP). N-Methyl hydroxamic acids are found to undergo, on distillation, a novel thermal rearrangement to the isomeric N-methyl-O-acylhydroxylamines, the thermodynamically less stable product. The rearrangement is shown to occur, at least in part, via an intermolecular mechanism involving formation of N-methylhydroxylamine and N-methyl-N,0-diacylhydroxylamine. Various O-thiocarbamoylated N-methyl hydroxamic acids are found to undergo, in solution, a thermal [l,3 ] rearrangement to the isomeric hydrosulphamine derivatives. This rearrangement, which is accompanied by appreciable fragmentation to the corres­ponding N-methyl amide, is shown to proceed largely via a pathway involving caged free radical pairs

    Single Atom Catalysts for Efficient Electroreduction of Carbon Dioxide and Carbon Monoxide

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    Electrochemical reduction of CO2 (CO2RR), powered by renewable electricity, is a promising approach to convert CO2 into valuable chemicals and fuels, mitigating strong dependence on traditional fossil fuels and addressing the environmental issues. However, CO2RR suffers from sluggish kinetics, the side-reaction of hydrogen evolution reaction (HER) and high overpotential. Single atom catalysts (SACs) can overcome these problems and achieved excellent CO2RR performances, attributed to their well-defined active sites, strong atom-support interaction, and maximum metal utilization. Up to date, achievements have been made for CO2RR in strong alkaline electrolytes, especially for the production of high value C2+ species. However, CO2RR is unstable under alkaline conditions, due to the interaction between CO2 and OH-, which results in carbonate formation. There also exists a large energy penalty for CO2 regeneration from the generated carbonate. To address this problem, an alternative route is carrying out CO2RR in two steps: CO2-to-CO and then CO-to-C2+. Compared with CO2RR, electrochemical reduction of CO (CORR) can operate stably and achieve high selectivity to C2+ species. In this case, efficient catalysts with high activity and selectivity to C2+ species from CORR are required. This thesis focuses on designing efficient SACs for CO2RR and CORR, which exhibited high activity, selectivity and stability. Besides, their catalytic mechanism is explored, laying foundations for future developments of SACs for CO2RR. Firstly, we developed a facile synthetic strategy for fabricating metal-nitrogen-carbon nanotube (M-N-CNT, M=Ni, Co, Cu, Fe, Mn, Zn, Pt, or Ru) SACs at scale (> 1 g) by direct pyrolysis of metal cations, phenonathroline and CNT at high temperature. The pyrolysis leads to forming coordinated Ni-N active sites anchored on CNT. The prepared Ni-N-CNT catalyst with a remarkable Ni loading of 2 wt% determined by inductively coupled plasma optical emission spectrometry (ICP) exhibits the highest activity for CO2-to-CO conversion with a high faradaic efficiency of 94% and excellent stability. Aberration-corrected high-angle annular dark-field transmission electron microscopy (HAADF-STEM), X-ray photoelectron spectroscopy and X-ray absorption spectroscopy confirm the presence of isolated Ni single atoms in Ni-N-CNT, which act as the active centers for CO2 electroreduction while the CNT support offers fast pathways for electron and mass transports. This work laid foundations for practical applications of SACs in CO2 electroreduction and beyond. Secondly, nanoconfined ionic liquids are introduced into porous atomically dispersed nickel-nitrogen-carbon (Ni-N-C) catalysts to enrich local CO2 concentration and increase the CO2RR reaction kinetics. A series of high-CO2-solubility ionic liquids (ILs) were impregnated into the pores of the columnar Ni-N-C catalyst to alter the CO2-Ni sites interactions and create a solid/liquid interface with high CO2 concentration. The optimal Ni-N-C/[Bmim][PF6] composite outperforms the Ni-N-C catalyst for pure CO2 electroreduction with a maximum CO Faradaic efficiency (FECO) of 99.6% and 2.7-fold larger CO partial current density (jCO). The high solubility of CO2 in ILs compared to aqueous electrolyte enables direct electrolysis of CO2 at low concentrations. When fed with 5-10 % (v/v) CO2, the Ni-N-C/[Bmim][PF6] composite exhibited up to 1.5-fold higher FECO and a 68% increase of jCO, in comparison to Ni-N-C, and robust stability over 30 h. Thirdly, a Cu-Au alloy catalyst with abundant atomic Cu-Au interfaces was developed to drive efficient CORR for acetate production. The unique geometric and electronic structure of atomic Cu-Au interfaces affords improved acetate activity and selectivity, surpassing the metallic Cu nanoparticles and CuAu bulk alloys. A high Faradaic efficiency of 39% was achieved with a large partial current density of 217 mA cm-2 for acetate production in alkaline flow cells. Density functional theory calculation reveals that the introduced Au atoms into Cu support promotes C-C coupling and improve acetate formation by weakening the binding strength of *CO+*CO on catalyst surface. Fourthly, atomically dispersed Cu-Au alloy was functionalized with aromatic heterocycle such as thiadiazole derivate (N2SN) to improve the conversion of CO into C2+ species e.g. acetate as the main product. Theoretical calculation predicted that the N2SN molecule doping contributed to lower energy barrier for C-C coupling, improved activity and selectivity to CORR, and suppressed HER, as compared with the unmodified sample. The N2SN functional groups with electron withdrawing property could alternate the oxidization state of copper, as confirmed by XPS and XAS, thus orienting the CORR pathway to C2+/acetate. In situ Raman revealed that the N2SN treated sample exhibited stronger signal of *CO intermediate for further dimerization and the C-C-O intermediate related to acetate formation. As a result, we achieve high Faradaic efficiency (FEC2+, 78.8%) and maximum partial current density (jC2+, 422.82 mA cm-2) for C2+ formation, as well as that (57.42%, 307.92 mA cm-2) for acetate production in alkaline flow cell. Besides, the optimal FEC2+ (89%), jC2+ (397 mA cm-2), and energy efficiency for C2+ species (24%) were obtained in MEA. This thesis develops new strategies for SACs, including fabricating Ni SAC at gram-scale, introducing nanoconfined ILs into Ni SACs, structure control of atomic Cu-Au interfaces, and functionalizing atomic Cu-Au alloy with molecule doping, which demonstrate great potential of SACs for CO2RR and CORR

    IN SILICO METHODS FOR DRUG DESIGN AND DISCOVERY

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    Computer-aided drug design (CADD) methodologies are playing an ever-increasing role in drug discovery that are critical in the cost-effective identification of promising drug candidates. These computational methods are relevant in limiting the use of animal models in pharmacological research, for aiding the rational design of novel and safe drug candidates, and for repositioning marketed drugs, supporting medicinal chemists and pharmacologists during the drug discovery trajectory.Within this field of research, we launched a Research Topic in Frontiers in Chemistry in March 2019 entitled “In silico Methods for Drug Design and Discovery,” which involved two sections of the journal: Medicinal and Pharmaceutical Chemistry and Theoretical and Computational Chemistry. For the reasons mentioned, this Research Topic attracted the attention of scientists and received a large number of submitted manuscripts. Among them 27 Original Research articles, five Review articles, and two Perspective articles have been published within the Research Topic. The Original Research articles cover most of the topics in CADD, reporting advanced in silico methods in drug discovery, while the Review articles offer a point of view of some computer-driven techniques applied to drug research. Finally, the Perspective articles provide a vision of specific computational approaches with an outlook in the modern era of CADD

    Development and applications of electrically-driven separation methods.

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    The use of non-aqueous media in CE was investigated primarily in an attempt to identify alternative mobile phases for application in CEC. Several solvents were found to support a rapid EOF even without the presence of a supporting electrolyte. These initial experiments led to the development of a separation involving an active pharmaceutical ingredient (Cimetidine) and a series of related materials. The latter displayed alternative selectivity relative to a comparable aqueous-based separation and offered a number of advantages. However, the underlying fundamental principles that govern separations in non-aqueous media were not well understood and method development was somewhat of a "black art". Further studies were therefore undertaken in order to gain an understanding of the mechanisms that influence separations in non-aqueous media. Under certain conditions the mode of separation appeared to be based on some form of interaction with the background electrolyte and the choice of a suitable EOF marker was not straightforward. HPLC separations of EPA priority pollutant phthalate esters were developed to assess the ease by which they could be transferred to CEC and determine any advantages offered by the electrically-driven technique. The practicalities of fabricating columns for CEC separations are critically discussed along with the unsuitability of some of the stationary phases employed. Attempts to utilise non-aqueous media in CEC separations are also described. A series of "real" applications were undertaken to assess the practicality of various electrically-driven separation techniques. The latter comprised a series of alkyltin compounds, the pesticide pirimicarb and its related metabolites and the determination of ethylenediammine (EDA). No meaningful separations were achieved with alkyltin compounds. However, the use of NMF as a non-aqueous mobile phase for CEC was demonstrated. Investigations involving EDA also did not lead to a successful separation. However, issues with the proposed derivatisation schemes were uncovered. The separations involving pirimicarb clearly demonstrated the enhanced scope available for method development offered by the various modes of CE that are available. Only partial separations were possible using CE in both aqueous and non-aqueous media. However, complete resolution of the 4 structurally similar materials was achieved using MEKC
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