Oxidation Potentials of Antioxidative Flavonoids and the Radical-Scavenging Abilities

The rate of hydrogen transfer from (+)-catechin, a planar catechin derivative, or quercetin to cumylperoxyl radical was accelerated significantly in the presence of scandium triflate in oxygen-saturated propipnitrile at 203 K. This indicates that the hydrogen-transfer reaction proceeds via an initial electron transfer from (+)-catechin, planar catechin, or quercetin to cumylperoxyl radical to produce the corresponding radical cation and cumylperoxylate anion followed by proton transfer. The second-harmonic alternting current voltammograms (SHACV) were recorded for the flavonoids to estimate their one-electron oxidation potentials in acetonitrile containing 0.1 M tetrabutylammonium perchlorate at 298 K. The more negatively shifted the oxidation potential, the faster the hydrogentransfer reaction becomes. On the other hand, no effect of scandium triflate was observed on the rate of hydrogen transfer from luteolin or kaempferol, which proceeds via onestep hydrogen atom transfer rather than electron transfer.10th Annual Meeting of the Society for Free Radical Biology and Medicin