Electrochemical behavior of superoxide anion radical towards quinones: a mechanistic approach

Abstract

Among the reactive oxygen species, the superoxide anion radical (O 2 ·− ) has a fundamental role in several biological functions. Consequently, its interaction with several chemical moieties is equally important both from a biological and chemical point of view. Considering this importance, the present study demonstrates the electrochemical generation of O 2 ·− followed by its interaction with four different quinones. The fate of electrochemically generated O 2 ·− was probed in the presence of a quinone while monitoring the changes in the shape of its voltammogram. The nature of interaction was interpreted in terms of electrochemical mechanism and the interaction moiety was identified both from voltammetric and computational data (Mullikan charges). The chemical coupled reactions of the quinones with O 2 ·− were identified as hydrogen atom transfer, protonation and electron transfer in different cases. The strength of interaction was quantified in terms of association constant (Kao) and IC50 values for antiradical activity of quinones and compared with standards of vitamin C and quercetin. The kinetics of the interaction reaction was quantitated having second-order rate constant values 0.1 to 3.0 × 103 M−1 s−1.