Electrochemical Monitoring of the Superoxide Anion Radical with Quercetin and Metallo-Quercetin Complexes

Abstract

Excess production of reactive oxygen species (ROS), such as the superoxide anion radical (O2˙–) can contribute to oxidative stress, and subsequently the onset of some pathological diseases. The free radical, O2˙–, is naturally generated in the body via a single electron reduction of molecular oxygen.1-3 Phenolic compounds such as flavonoids have strong antioxidant properties against ROS, including O2˙–.1,3 Due to their ability to donate an electron to the ROS, antioxidants actively act as free radical scavengers, which allows for prevention of cell damage and related health issues induced by ROS production.1 In addition to antioxidant properties, flavonoids such as quercetin (QCR) also play a role as metal ion chelators, by which their coordination with biologically relevant metal ions results in the formation of metallo-flavonoid complexes.2 Metal ions are known to regulate ROS activity via Fenton reactions, which may also influence the antioxidant activity and capacity of the flavonoid upon complexation. The role of metal ions and metallo-flavonoid complexes as antioxidants towards O2˙– is not fully understood. Herein, cyclic voltammetry (CV) was employed for electrochemical generation of the O2˙–/O2 redox couple.4 The anodic and cathodic peaks associated with the redox couple were monitored prior and post interaction with QCR and its metallo-QCR complexes. Overall, CV data show a decrease in anodic and cathodic peak currents, demonstrating varying extents of antioxidant activity and O2 reactivity with the antioxidants.