Functional site mimics of few oxidase enzymes by newly developed coordination compounds with (N, N) and (N, O) donor ligands

Abstract

Design and synthesis of transition metal complexes with polydentate ligands and commercially available ligands is a significant field of research in Chemistry. Coordination compounds in coupling between transition metals and various ligands have drawn a great deal of interest to Chemist and Biologists for their remarkable structural features, biomimicking activities, catalytic activities, optoelectronic applications, magnetic materials, semiconductors, functional composites and different biological activities. Noteworthy, metal complexes that are the synthetic analogs of various metalloenzymes create significant progress in bioinspired chemistry with fascinating mechanistic perception of the catalytic cycles. Chapter I: This introductory chapter describes the design, synthesis and application of transition metal complexes based on Schiff base and commercially available ligands. It also states the catalytic and biological activities of metal complexes and the objectives of the present work. Chapter II: This chapter consists of the synthesis, catecholase, and phosphatase activity of an oxido-and acetate-bridged tetranuclear iron (III) cluster [Fe4 III(μ-O)2(μ- OAc)6(phen)2(H2O)2] (NO3)2(H2O)3 (1), [OAc = acetate; phen = 1,10-phenanthroline. Xray structural analysis of the compound reveals that all the Fe(III) centres in 1 adopt an octahedral coordination geometry and the tetra-iron(III) core exists in an unusual asymmetric conformation. The bond valence sum (BVS) calculation recommends the existence of all iron ions in the +3 oxidation level in the crystalline state. The tetra-iron(III) cluster elegantly catalyzes the oxidation of 3,5-di-tert-butylcatechol (DTBC) viz. Catecholase-like activity with a good turnover number, kcat 9.28102 h-1 in acetonitrile medium. Spectrophotometric titration exhibits two distinct isobestic points, which unanimously proves the rarely observed enzyme-substrate binding phenomenon in solution. Electrochemical analysis recommends the production of Fe(II)-semiquinone species in the catalytic oxidation of DTBC. Furthermore, the same iron(III) cluster displays phosphoester cleavage activity towards disodium salt of p-nitrophenylphosphate (PNPP) in an aqueousmethanol medium with a rate of 7.2010-4 m-1. ESI-MS measurements of tetra-iron(III) complex in the presence of PNPP recommend the formation of organophosphorous intermediate in solution and solvent aqua molecules probably make a nucleophilic attack to phosphorous centre favouring the generation of organophosphorous intermediate.