Chemistry Department, Virginia Commonwealth University, Richmond, VA 23284, USA.
Phys Chem Chem Phys. 2018 Jul 4;20(26):17666-17675. doi: 10.1039/c8cp01415a.
Glutathione (GSH), whose thiol group dictates its redox chemistry, is oxidized to the thiyl radical (GS˙), which rapidly dimerizes to GSSG. Previously, we found that the oxidation rate of GSH by IrCl62- depends on the base (B) concentration and the pKa of its conjugate acid BH+, so that collateral to a stepwise mechanism, the concerted pathway GSH + IrCl62- + B = GS˙ + IrCl63- + BH+ was proposed as the rate determining step. Herein, this investigation is extended to include oxidant-base pairs that render exothermic and endothermic conditions of ΔG°' for electron transfer (ET) and proton transfer (PT). Experiments were conducted by the reaction of GSH with an electrogenerated oxidant M+ and using digital simulations to infer the mechanism. Data analysis shows that despite parallel mechanisms, the concerted one seems to predominate for the oxidant-base pair that renders the most isoenergetic coupled state, whereby a PT with is capable of producing an ET with , as a result of the Nernstian shift of with pKa. In contrast, the stepwise PT-ET appears to dominate when GS- grows in stability as becomes more negative. Understanding the interplay between ET and PT will help in the design of catalysts for energy harvesting processes that rely on proton-coupled electron transfer.
谷胱甘肽（GSH）的巯基决定了其氧化还原化学性质，会被氧化为硫自由基（GS˙），后者迅速二聚形成 GSSG。此前，我们发现 IrCl62-氧化 GSH 的速率取决于碱基（B）的浓度及其共轭酸 BH+的 pKa，因此除了逐步机制外，协同途径 GSH + IrCl62- + B = GS˙ + IrCl63- + BH+被提出为速控步骤。在此，我们将这一研究扩展到包括那些会产生放热和吸热条件的氧化剂-碱基对，以用于电子转移（ET）和质子转移（PT）。通过 GSH 与电生成氧化剂 M+的反应进行实验，并通过数字模拟来推断机制。数据分析表明，尽管存在平行机制，但对于产生最等能耦合态的氧化剂-碱基对，协同机制似乎占主导地位，其中具有的 PT 能够产生具有的 ET，这是由于 Nernst 位移使与 pKa 相关联。相比之下，当 GS-变得更加稳定时，PT-ET 似乎占据主导地位，变得更加负。了解 ET 和 PT 之间的相互作用将有助于设计依赖于质子耦合电子转移的能量收集过程的催化剂。
