| Research Abstract |
Chemical Functions of Novel Amino Acid Derived Redox-Active Cofactors: One of our longstanding research activities involves synthesis and characterization of newly found organic cofactors such as pyrroloquinolinequinone (PQQ) of bacterial alcohol dehydrogenases, tryptophan tryptophylquinone (TTQ) and cysteine tryptophylquinone (CTQ) of amine dehydrogenases, and tyrosine-cysteine cofactor (Tyr-Cys) of galactose oxidase. The main efforts of this study have been directed toward exploration of redox functions and the reaction mechanism as well as the post-translational modification pathways of CTQ and Tyr-Cys cofactors. In addition, great deals of efforts have been focused on the examination of metal ion effects on the redox reactivity of the organic cofactors. As the results, we have found that the redox activity and stability of the Tyr-Cys cofactor model compounds are largely controlled by the interaction with transition-metal ions, providing siginificantly important insights into the m
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echanism of enzymatic redox reactions. Model compounds of CTQ cofactor have also been developed in order to examine the chemical properties and functions of the organic cofactor
Redox Properties and Functions of Organic Radical Complexes: Our main attention has focused on the development of model compounds of biologically relevant organic radicals such as phenoxyl radicals and semiquinone radicals. Electronic structures and redox reactivity of the organic radicals as well as the structure, physicochemical properties, and catalytic activities of their metal complexes have been investigated to shed light on biological functions of such species in RNR (ribonucleotide reductase), PSII (photosystem II), prostaglandin synthase, and so on. For example, phenolate and phenoxyl radical complexes of a series of alkaline earth metal ions as well as the monovalent and divalent cations have been prepared using 2,4-di-tert-butylphenol connected to aza-crown ethers, 2,4-di-tert-butyl-6-(1,4,7,10-tetraoxa-13-aza-cyclopentadec-13-ylmethyl) phenol and 2,4-di-tert-buty1-6-(1,4,7,10,13-pentaoxa-16-aza-cyclooctadec-16-ylmethyl) phenol. This was done to examine the effects of the cations on the structure, physicochemical properties and redox reactivity of the phenolate and phenoxyl radical complexes Less
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