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Photophysical and photochemical properties of resveratrol

Plant-derived compound resveratrol (ArOH, trans- 3, 5, 4'-trihydroxystilbene) possesses a variety of biological effects including antioxidant properties. The antioxidant activity is referred to the ease of the donation of the phenolic H-atom to the attacking free radical with the formation of phenoxyl radical (ArO•) either by HAT, SPLET or ET-PT mechanisms. In order to investigate the addition of radicals to the resveratrol double bond as one more possible mechanism of resveratrol antioxidative activity, thiyl radicals (RS•) are chosen because they are responsible for cis-trans isomerisation of lipids through addition reactions and there is lack of studies of the reaction of RS• radicals with resveratrol. Some photophysical properties of resveratrol need to be determined in order to investigate the above reactions. ArOH transient radical cation (ArOH•+) was generated by resonant biphotonic excitation in ACN by 50 mJ 355 nm or 15 mJ 266 nm Nd:YAG laser pulses. ArOH•+ absorption peak was found at 500 nm with lifetime of 5 μs and leads to a long lived ArO• with a peak at 390 nm. Extinction coefficient of ArOH•+ is determined to be 33 400 M-1 cm-1 in ACN. Since ArOH•+ was not observed in H2O due to its fast deprotonation, only ArO• with peak at 410 nm, deprotonation rate constant of ArOH•+ in ACN by addition of 0.25 – 1 % of H2O is determined to be 1.3 ´ 108 M-1 s-1. Extinction coefficients of ArO• in H2O as well as in ACN were determined to be 15 200M-1 cm-1 and 14 600 M-1 cm-1, respectively.

resveratrol; resveratrol radical cation; absorption coefficient

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