Abstract:

As one of flavonols with a 3-OH group in their chemical structures, quercetin (3,5,7,3',4'-pentahydroxyflavone) shows much stronger antioxidant activity than its corresponding flavone luteolin (5,7,3',4'-tetrahydroxyflavone) does. In the present study, cyclic voltammetry and in situ UV-Vis spectroelectrochemical method were used to investigate the electro-oxidation processes of both flavonoids for discovering the reaction mechanism by which 3-OH group promotes the antioxidant activity. The results indicateed that both compounds are oxidized to the corresponding o-quinones via 2e–/2H+ reactions, and only the quercetin o-quinone can be further isomerized to the more stable united conjugated structure in the presence of 3-OH group. This subsequent chemical transformation drives the loss process of electron and gives an additional contribution to the antioxidant activity of quercetin.

Key words: antioxidant activity, spectroelectrochemistry, UV-Vis spectrum, quercetin, luteolin