Synthesis, Structural Evaluation and studies of Reactivity of Heteroperoxovanadates(V) and Development of Solid acid catalysts for Organic Transformations

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The thesis of aforementioned title is based on the results of studies of a few chosen aspects of peroxovanadium chemistry and heterogeneous catalysis. The text has been distributed over five chapters. The introductory chapter of the thesis presents an overview of different aspects of peroxovanadium chemistry with special reference to haloperoxidase activity and insulin mimesis, and a brief account on the importance of heterogeneous catalysis for organic transformations. The second chapter provides experimental procedures, source of reagent and solvents, and particulars of the equipment and instruments used. Chapters 3 to 5 present the newer results gathered during the Ph.D. research. Chapter 1: Introduction and Scope of the Work This Chapter highlights the importance of peroxovanadium related coordination chemistry and gives an account to their reactivity, biochemical relevance and commercial importance, especially with reference to haloperoxidase activity and insulin mimetic action of peroxovanadium compounds. Briefly speaking vanadium haloperoxidases (VHPOs) are the enzymes that catalyze the oxidation of halides by H2O2. VHPO possesses trigonal bipyramidal geometry around vanadium in the native site and a distorted tetragonal structure in the active form (peroxo-intermediate). Structural characterization has revealed that vanadate is covalently linked to the N of the imidazolyl moiety of a histidine amino acid, and further through hydrogen bonds to a variety of amino acid side chains (e.g. Arg, His, Ser, Lys) and interstitial water in the proximity of the active center. Special emphasis has been put on to the understanding of chemistry of bromoperoxidase activity because of its remifications on the synthetic applications to bromo-organic compounds having commercial importance. Quite apart from the activity highlighted above, peroxovanadium complexes are also found to be potential clinical alternatives of insulin for the treatment of diabetes. Hence, insulin-mimetic action of peroxovanadium complexes is briefly reviewed in this Chapter. Besides bio or abiomimetic catalysis, development of abio catalytic systems is yet another domain of contemporary importance. This aspect, with reference to heterogeneous catalysis and its direct bearing with Green Chemistry and Green Technology has been dully projected in this Chapter. The potential advantages of heterogeneous catalyst in organic reactions are (a) good dispersion of active sites, (b) constraints of the pores, (c) easier and safer to handle, d) easier to remove from the reaction mixture and (e) reusability. Among various heterogeneous catalysts, the importance of solid acid catalyst has been emphasized in this Chapter. The effects of supported material in reactivity of solid acid catalysts have been also discussed, highlighting the importance of alumina and titania. Solid acid catalysts are found to replace not only mineral acids but also catalyze the organic reactions. After laying the foundation as indicated above, the scope of work in the present Ph. D research have been brought out very clearly. Chapter 2: Materials and Methods The sources of chemicals and solvents, methods for quantitative chemical estimations, determination of elements and particulars of all equipment used for physico-chemical studies are provided.
Supervisor: M K Chaudhury and Gopal Das