Insight on nano-platinum-catalyzed dehydrogenation of quercetin in presence of peroxide

Abstract

Quercetin (Qu), a noted polyphenolic flavonol molecule, exhibits remarkable antioxidant properties against bioenzymes like peroxidase and tyrosinase. However, it was found that under pH = 3.5–5.5 and room temperature, Qu cannot reduce hydrogen peroxide (HP) which is a well-perceived reactive oxygen species (ROS) responsible for oxidative stress. We found that in presence of noble-metal nano-particles, such redox interactions can be accomplished. We thus synthesized homogenous PVP-coated nano-platinum particles (PNP) to catalyze the oxidation of Qu by HP. On reaction, Qu is oxidized by HP to ortho-quinone (QQ) following the first-order kinetics. The observed rate constant, ko, gradually increases and tends to saturate with increasing [HP]T where T represents the analytical concentrations of the reactant. The saturation kinetics indicates that the activities of PNP resemble to that of bioenzymes and similarly, the nano-particles host the reactants on its active surface during the redox interactions. The estimated value of the kcat reveals that the extent of catalysis of even 10−10 M PNP is nearly comparable with the rate constants of oxidation of Qu in presence of enzymes like horseradish peroxidase and tyrosinase.