A combined experimental and theoretical study to explore the catecholase-like activity of a hepta coordinated dinuclear Zn(II) complex

Abstract

A heptadentate N4O3 coordinating dinuclear zinc complex was synthesized and characterized by 1H NMR spectroscopy, IR spectroscopy and ESI MS spectroscopy studies. X-ray single crystal structure of the dinuclear complex revealed that both zinc atoms have pentacoordinated environment realized by the N2O2 donor set of ligand and one water molecule. The theoretical optimized structure of the dinuclear complex in solution phase was indicated a larger elongation take place in the bond distance between zinc and oxygen atom of coordinated water molecule which leads to come closer of two zinc atoms in solution phase in comparison of crystalline structure. This proximity of two zinc atoms fulfilled my aim for investigating the catalytic catecholase activity. The catecholase activity of the complex has been investigated under completely aerobic conditions in MeOH water medium at pH 8.0 against the model substrate 3,5-di-tert-butylcatechol (3,5-DTBC). Saturation kinetic studies have shown the order of conversion of substrate to product quinone. The mechanistic path of the oxidation process has been confirmed by UV–vis, CV and EPR spectral studies are made-up to be responsible for the oxidation of 3,5-DTBC. EPR experiment suggested generation of radical in the presence of 3,5-DTBC and that finding has been strengthened by cyclic voltammetric study. Thus, it proposed that the radical pathway is responsible for conversion of 3,5-DTBC to 3,5-DTBQ promoted by complex of redox-innocent ZnII ion. The ligand-centered radical generation has been further verified by density functional theory calculation.