SO4●－自由基氧化酪氨酸反应中的溶剂效应

研究了水-乙腈混合溶液中SO4●－自由基氧化酪氨酸的反应.实验结果表明，SO4●－自由基氧化酪氨酸的反应机制不因乙腈的加入而改变，但所产生的瞬态粒子的动力学行为受到较大影响.随介质中乙腈体积分数的增加，SO4●－的衰变速率减慢而酪氨酸中性自由基（TyrO●）的衰变速率加快.我们认为这两种自由基所呈现出来的相反的溶剂效应是由于其所带电荷的不同.随介质中乙腈体积分数的增加，SO4●－氧化酪氨酸的反应速率减慢.这一实验结果意味着，在有机溶剂存在的情况下TyrO●/ TyrOH的氧化还原电势可能发生了变化，从而旁证了关于TyrO●/ TyrOH的氧化还原电势因酪氨酸从游离状态变到肽或蛋白质中而发生变化的推测.

Solvent Effects on the Oxidation of TyrOH by SO·4- Radical

This work presents the study on the oxidation of TyrOH by SO4●－ in water/ACN mixed media. Investigations show that the reaction mechanism between TyrOH and SO4●－ does not change by the addition of ACN, whereas the kinetic behavior of the transient species produced is significantly affected. The decay of SO4●－ decelerates with increasing volume fraction of ACN in mixed media whereas the decay of TyrO● accelerates. We suggest that the contrary effects of the solvent on the decay of both SO4●－ and TyrO● are due to their different charges. The deceleration of the oxidation of TyrOH by SO4●－ with the increase of ACN fraction may demonstrate that in the presence of organic solvents the redox potential of TyrO●/TyrOH is altered, which provides support for the suggestion that the redox potential of TyrO●/ TyrOH might be altered with their inclusion into peptides and proteins.