白藜芦醇与紫檀芪抗氧化活性差异的电化学研究

为揭示白藜芦醇(反式)与其衍生物紫檀芪的抗氧化活性差异的内在原因，对两种物质的氧化机理进行研究。采用循环伏安法考察pH值、富集时间对氧化过程的影响，采用薄层长光程紫外-可见光谱电化学方法原位监测氧化产物的形成。结果表明：紫檀芪在油性碳糊电极表面上的吸附富集作用远强于白藜芦醇；两者的初始氧化都发生在对位羟基上，通过一电子一质子传递步骤生成苯氧自由基中间体；紫檀芪自由基中间体易于耦合迅速转化为二聚体产物，而白藜芦醇自由基在碱性介质中需经历较难进行的中间双键断裂途径，转化为可溶性小分子产物。紫檀芪较强的亲脂性引起的富集作用以及氧化中间体的快速二聚化，是其具有较强抗氧化活性的重要原因。

An Electrochemical Study of the Difference in Antioxidant Activity between Resveratrol and Pterostilbene

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.