Manoj V M, Mohan H, Aravind U K, Aravindakumar C T
School of Chemical Sciences, Mahatma Gandhi University, Kottayam 686560, Kerala, India.
Free Radic Biol Med. 2006 Oct 15;41(8):1240-6. doi: 10.1016/j.freeradbiomed.2006.06.025. Epub 2006 Jul 11.
One-electron reduction of S-nitrosothiols (RSNO) has been studied using radiolytically produced reducing entity, the hydrated electron (e(aq)(-)), in aqueous medium. Both kinetics of the reaction and the mechanistic aspects of the decomposition of S-nitroso derivatives of glutathione, L-cysteine, N-acetyl-L-cysteine, N-acetyl-D,L-penicillamine, N-acetylcysteamine, L-cysteine methyl ester, and D,L-penicillamine have been investigated at neutral and acidic pH. The second-order rate constants of the reaction of e(aq)(-) with RSNOs were determined using a pulse radiolysis technique and were found to be diffusion controlled (10(10) dm(3) mol(-1) s(-1)) at neutral pH. The product analysis using HPLC, fluorimetry, and MS revealed the formation of thiol and nitric oxide as the major end products. It is therefore proposed that one-electron reduction of RSNO leads to the liberation of NO. There is no intermediacy of a thiyl radical as in the case of oxidation reactions of RSNOs. The radical anion of RSNO (RSN()O(-)) is proposed as a possible intermediate. The overall reaction could be written as RSNO + e(aq)(-) --H+--> RSH + ()NO.
在水介质中，利用辐射产生的还原实体——水合电子（e(aq)(-)），对亚硝基硫醇（RSNO）的单电子还原反应进行了研究。在中性和酸性pH条件下，研究了谷胱甘肽、L-半胱氨酸、N-乙酰-L-半胱氨酸、N-乙酰-D,L-青霉胺、N-乙酰半胱胺、L-半胱氨酸甲酯和D,L-青霉胺的亚硝基衍生物分解反应的动力学和机理。采用脉冲辐解技术测定了e(aq)(-)与RSNO反应的二级速率常数，发现在中性pH条件下该反应受扩散控制（10(10) dm(3) mol(-1) s(-1)）。利用高效液相色谱、荧光分析法和质谱进行的产物分析表明，硫醇和一氧化氮是主要的最终产物。因此，有人提出RSNO的单电子还原反应会导致NO的释放。与RSNO的氧化反应不同，该反应不存在硫自由基中间体。有人提出RSNO的自由基阴离子（RSN()O(-)）可能是一种中间体。总的反应式可写为RSNO + e(aq)(-) --H+--> RSH + ()NO。
