Copper‐flavonoid complexes in acidic solutions

Abstract

Summary. Amperometric titration was used to detect complexing of cupric ions by flavonoids in solutions more acid than pH 4.5. Strongest complexing ability was shown by the 3‐hydroxy‐4‐carbonyl system although the 5‐hydroxy‐4‐carbonyl system also complexed with copper in acid solution. the o‐diphenolic grouping did not form complexes under the conditions used. Complexing ability was enhanced by the presence of hydroxyl groups in conjugation with the carbonyl group. Quercetin was the only flavonoid tested capable of complexing copper at pH 2.3. the significance of these results to the antioxidant action of flavonoids in fruit juices is discussed.