Our earlier studies have shown that the compounds diphenyltin dichloride (DPhT) and triphenyltin chloride (TPhT) in the presence of UVC radiation enhanced the degree of phosphatidylcholine liposome membrane oxidation (J. Agric. Food Chem. 2005, 53, 76-83). The prooxidative behavior of the compounds has now been confirmed with the electron paramagnetic resonance method, which proved the possibility that the studied compounds can exist in free radical forms. The present work investigates the possibility of the protective action of quercetin on phosphatidylcholine liposome membranes exposed to the prooxidative action of DPhT and TPhT induced by UV radiation (lambda = 253.7 nm). The concentrations of quercetin and its equimolar mixtures with DPhT and TPhT were determined (and compared with well-known antioxidants as standards-trolox and butylated hydroxytoluene, also in the presence of phenyltins) as those that induce 50% inhibition in oxidation of liposomes radiated with UV. They are 5.1 +/- 0.10, 2.9 +/- 0.12, and 1.9 +/- 0.08 microM (differences between the values are statistically significant), constituting the following sequence of antioxidative activity: quercetin:TPhT > quercetin:DPhT > quercetin. This relation is confirmed by the results on the antiradical ability of quercetin and its mixtures with DPhT and TPhT toward the free radical 1,1-diphenyl-2-pricrylhydrazil. Similar sequences obtained in both studies suggest a possible mechanism of the antiradical action of the mixtures as free radical scavengers. We suggested that (i) quercetin's ability, documented by spectrophotometric, infrared attenuated total reflectance spectroscopy, (1)H NMR, and molecular modeling methods, to form complexes with phenyltins indicates a possible way of protection against the peroxidation caused by the free radical forms of phenyltins and (ii) the differentiation in the action of the quercetin/TPhT and quercetin/DPhT associates (statisticaly significant) may result from a different localization in the liposome membrane, which is indicated by the results of the fluorimetric studies.
The work investigates the possibility of the protective action of kaempferol on phosphatidylcholine liposome membranes exposed to the pro-oxidative action of diphenyltin dichloride (DPhT) and triphenyltin chloride (TPhT) induced by UV radiation (lambda = 253.7 nm). The concentrations of kaempferol and its equimolar mixtures with DPhT and TPhT were determined so that they induce 50% inhibition in oxidation of liposomes irradiated with UV. They are 11.6, 10.0, and 4.5 microM/L, which constitute the following sequence of antioxidative activity: kaempferol/triphenyltin > kaempferol/diphenyltin > kaempferol. This relationship is confirmed by the results on the antiradical ability of kaempferol and its mixtures with DPhT and TPhT toward the free radical 2,2-diphenyl-1-picrylhydrazyl. Similar sequences obtained in both studies suggest a possible mechanism of the antiradical action of the mixtures as free radical scavengers. Kaempferol's ability, then documented, to form complexes with phenyltins indicates (a) a possible way to liquidate the peroxidation caused by the free radical forms of phenyltins and (b) the stabilizing role of chelating in the antioxidative action of the kaempferol/phenyltins. The differentiation in the action of the compounds studied may, among others, result from different localizations in the liposome membrane, which is indicated by the results of the fluorometric studies.
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