Reactivity of flavonoids toward superoxide radical: An electrochemical approach

Abstract

The reactivities of a set of 18 diverse flavonoids against electrochemically generated superoxide anion radical were studied by monitoring changes in O2/O2·− cyclic voltammetry response upon addition of increasing concentrations of flavonoids. In the presence of flavonoids, the O2·- anodic peak current decreased, while the cathodic peak of O2 remained almost unchanged. Concomitantly with an O2·- anodic peak current decrease, a new irreversible cathodic pre-peak before the O2 reduction peak appeared on the CVs of O2/O2·− upon adding flavonoids. This phenomenon is described in detail for the first time on the basis of experimental measurements and model calculations. Based on the changes in O2/O2·− cyclic voltammetry response upon adding flavonoids, we could draw conclusions about the mechanism of superoxide radical scavenging by flavonoids. The superoxide radical scavenging activities of flavonoids, determined by measuring the anodic current decay of the radical in the presence of increasing concentrations of flavonoids, were expressed in terms of EC60 values, i.e. the concentration of flavonoid needed to consume 40% of a superoxide radical. All of the studied flavonoids showed a more or less pronounced superoxide radical scavenging activity, depending on their structural features. The structure-activity relationship was discussed. Superoxide radical scavenging activities of flavonoids correlated well with their electrochemical oxidation potentials, implying that the scavenging activity of flavonoids is mainly governed by their redox properties.