engleski

Laser flash photolysis study of the photochemistry of resveratrol in acetonitrile

Resveratrol (trans-3, 5, 4'-trihydroxystilbene), a natural compound has attracted considerable interest because of its biological activities against a collection of diseases. The cancer chemoprevention effects of resveratrol has been related to its antioxidant activity, because free radical mediated peroxidation of membrane lipids and ensuing oxidative damage are assumed to play a causative role in cancer. However, it is somewhat surprising that spectral and kinetic data of the transient and mechanism of resveratrol reaction with most relevant radical species are scarce, particularly with alkoxyl radicals which are well known mediators in lipid peroxidation process. The chain-breaking ability of polyphenols is referred to the ease of the donation of the phenolic H-atom to the attacking free radical. At the same time, H-atom abstraction is probably the best known chemical reaction of aromatic carbonyl triplets which are particularly interesting in biological systems since their excited states can be produced in vivo. It was pointed out that triplet carbonyls with n*character behave like alkoxyl radicals and can thus initiate several chain reactions, including lipid peroxidation. The present study uses an efficient generation of tert-butoxyl radicals (t-BuO●) to provide spectroscopic and kinetic data regarding the reactivity of resveratrol toward t-BuO●. The rate constant was determined under pseudo-first order conditions in acetonitrile solutions at room temperature. The t-BuO● radicals were generated directly by homolytic photodecomposition of di-tert-butyl peroxide using laser flash photolysis. The rate constant was determined by measuring the phenoxyl radical formation rate at 390 nm as function of resveratrol concentration in acetonitrile. The rate constant was determined to be 6.5 × 108 M−1 s−1. In view of the fact that n* triplets present many similarities with alkoxyl radicals in their hydrogen abstraction reactions, a comparison between the kinetics of t-BuO● radicals and the benzophenone triplet state in respect of their reactions with resveratrol will be presented.

resveratrol; alkoxyl radicals; benzophenone; laser flash photolysis

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