Abstract: The oxidation mechanisms of trans-resveratrol and its derivative pterostilbene were studied to better understand the difference in antioxidant activity between the stilbene compounds. The effects of pH and accumulation time were examined by cyclic voltammetry, and the formation of oxidation products was in situ by thin layer UV-Vis spectroelectrochemistry. It was observed that adsorptive accumulation of pterostilbene on the oleaginous surface of the carbon paste working electrode was much stronger than that of resveratrol. The initial oxidation of both the stilbenes occurred at the p-hydroxyl group via one electron one proton transfer, forming phenoxy free radicals. The radical intermediates of pterostilbene might couple immediately to yield dimers at the electrode surface, while those of resveratrol, especially in the alkaline media, had to undergo the oxidative cleavage of the center double bond to produce soluble small molecules. Lipophilicity of pterostilbene superior to resveratrol might be the important reason for its higher antioxidant activity, since lipophilicity increases the adsorptive accumulation as well as accelerates the dimerization of the oxidized radical intermediates.

Key words: antioxidant activity, resveratrol, pterostilbene, cyclic voltammetry, in situ spectroelectrochemistry