ESR study of the flavonoid effect on the metal ion breakdown of lipid peroxidation system

Abstract

The formation of alkoxyl radical during metal ion breakdown of hydroperoxide-enriched methyl linoleate of sunflower oil has been established by a combination of spin trapping and electron spin resonance (ESR) spectroscopy. The influence of different concentrations (10-100 μmol dm-3) of myricetin, quercetin, morin, kaempferol, rutin, fisetin, diosmetin, apigenin, luteolin, and naringenin, respectively, on the formation and transformation of alkoxyl radical was evaluated. Results demonstrated that the antioxidative activity depends on the structure and concentration of applied flavonoids and it decreases in the following order: flavonol > flavone > flavanone. The formation of relatively stable free radicals for these flavonoid derivatives was studied. Under experimental conditions employed, the generation of stable free radicals has been evidenced for myricetin, quercetin, rutin, and luteolin and their hyperfine coupling constants were determined. The 2,3-double bond in conjugation with 4-oxo function and the additional presence of both 3- and 5-hydroxyl groups as well as o-dihydroxyl groups in the B-ring are very important for antioxidant activity of the investigated flavonoids and aroxyl radical stabilisation.