| Abstract
| - The antioxidant activities of a series of commonly consumed and biogenetically related plant phenolics,namely, anthocyanidins, anthocyanins, and catechins, in a liposomal model system have beeninvestigated. The antioxidant efficacies of the compounds were evaluated on their abilities to inhibitthe fluorescence intensity decay of an extrinsic probe, 3-[p-(6-phenyl)-1,3,5-hexatrienyl]phenylpropionicacid, caused by free radicals generated during metal ion-induced peroxidation. Distinct structure−activity relationships were revealed for the antioxidant abilities of these structurally related compounds.Whereas antioxidant activity increased with an increasing number of hydroxyl substituents presenton the B-ring for anthocyanidins, the converse was observed for catechins. However, substitution bymethoxyl groups diminished the antioxidant activity of the anthocyanidins. Substitution at position 3of ring C played a major role in determining the antioxidant activity of these classes of compounds.The anthocyanidins, which possess a hydroxyl group at position 3, demonstrated potent antioxidantactivities. For the cyanidins, an increasing number of glycosyl units at position 3 resulted in decreasedantioxidant activity. Similarly, the substitution of a galloyl group at position 3 of the flavonoid moietyresulted in significantly decreased antioxidant activity for the catechins. Among catechins, cis−transisomerism, epimerization, and racemization did not play a role in overall antioxidant activity. Theantioxidant activities of test compounds (at 40 μM concentrations) were compared to the commercialantioxidants tert-butylhydroquinone, butylated hydroxytoluene, butylated hydroxyanisole, and vitaminE (all at 10 μM concentrations). Keywords: Fluorescence spectroscopy; lipid peroxidation; antioxidants; catechins; anthocyanidins;anthocyanins; SAR
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