engleski

Elementary radical reactions of the antioxidant action of resveratrol

Resveratrol (trans-3, 5, 4'-trihydroxystilbene), a plant-derived compound, has attracted much attention during the last years due to the simplicity of its structure and its low toxicity in vivo systems. The cancer chemoprevention effects of resveratrol might be traced back to its antioxidant activity, because free radical mediated peroxidation of membrane lipids and oxidative damage are assumed to play a causative role in cancer. The relation of radical-scavenging activity of resveratrol and its analogues to their structure has been studied.1, 2 However, spectral and kinetic data of the reaction and mechanism of resveratrol with the most relevant radical species are scarce, particularly with alkoxyl and thiyl radicals which are biologically very important. Alkoxyl radicals are well known mediators in lipid peroxidation process and propagators of the chain free radical reactions in lipids, while thiyl radicals protect lipids against degradation. The present study aims to achieve an efficient generation of alkoxyl and thiyl radicals and to provide spectroscopic and kinetic data regarding the reactivity of resveratrol towards each of the generated radicals. The t-butoxyl radicals were generated directly from t-butylperoxide by peroxide bond cleavage using Nd:YAG laser at 355 nm.2, 3 The rate constant for the reaction of t-butoxyl radicals with resveratrol was studied under pseudo-first order conditions. The rate constant was determined by measuring the phenoxyl radical formation rate at about 390 nm as function of resveratrol concentration. The rate constant of the reaction of t-butoxyl radicals with resveratrol in acetonitrile was determined to be 6.5 × 108 M-1 s-1. Thiyl radicals could be generated indirectly by using a photosentizer benzophenone4 after the 347 nm ruby laser pulse. The existing set-up and the procedure of resolving the transient spectra allowed us to obtain the optimum concentration profiles of transient species formed under chosen conditions.

Resveratrol; Alkoxyl radicals; Thiyl radicals; Rate constant

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