The reaction between superoxide anion and quercetin was studied. The signals of two intermediates, an o-benzosemiquinone type anion radical and an unidentified radical were obtained by ESR spectroscopy. The UV dynamic spectra and the anal. of products show that the reaction between superoxide anion and quercetin takes place at various reactive sites of the quercetin mol. Protocatechuic acid and depside may be formed from the opening of the heterocyclic ring and polymers may be formed by several paths. The similarity in the mechanism of the reaction of quercetin with superoxide anion and the oxidation of quercetin in alkaline medium is discussed.

Key words: KINETIC ANALYSIS, ULTRAVIOLET SPECTROPHOTOMETRY, ELECTRON SPIN RESONANCE, SUPEROXIDE, QUERCETIN