Department of Chemistry, University of Rochester, Rochester, New York 14627, United States.
Department of Chemical Sciences, University of Naples Federico II, Complesso Universitario Monte S. Angelo, via Cintia 45, 80126 Naples, Italy.
Biochemistry. 2020 Mar 31;59(12):1289-1297. doi: 10.1021/acs.biochem.0c00060. Epub 2020 Mar 19.
Cobalt-mimochrome VIa (CoMC6a) is a synthetic mini-protein that catalyzes aqueous proton reduction to hydrogen (H). In buffered water, there are multiple possible proton donors, complicating the elucidation of the mechanism. We have found that the buffer p and sterics have significant effects on activity, evaluated via cyclic voltammetry (CV). Protonated buffer is proposed to act as the primary proton donor to the catalyst, specifically through the protonated amine of the buffers that were tested. At a constant pH of 6.5, catalytic H evolution in the presence of buffer acids with p values ranging from 5.8 to 11.6 was investigated, giving rise to a potential-p relationship that can be divided into two regions. For acids with p values of ≤8.7, the half-wave catalytic potential () changes as a function of p with a slope of -128 mV/p unit, and for acids with p of ≥8.7, changes as a function of p with a slope of -39 mV/p unit. In addition, a series of buffer acids were synthesized to explore the influence of steric bulk around the acidic proton on catalysis. The catalytic current in CV shows a significant decrease in the presence of the sterically hindered buffer acids compared to those of their parent compounds, also consistent with the added buffer acid acting as the primary proton donor to the catalyst and showing that acid structure in addition to p impacts activity. These results demonstrate that buffer acidity and structure are important considerations when optimizing and evaluating systems for proton-dependent catalysis in water.
钴拟色氨酸 VIa（CoMC6a）是一种合成的小型蛋白质，可催化水相质子还原为氢（H）。在缓冲水中，存在多种可能的质子供体，这使得机制的阐明变得复杂。我们发现，缓冲液 p 值和立体位阻对活性有显著影响，可以通过循环伏安法（CV）进行评估。质子化的缓冲液被认为是催化剂的主要质子供体，具体通过测试的缓冲液的质子化胺来实现。在 pH 值为 6.5 的恒定条件下，研究了在缓冲酸存在下的缓冲液 p 值范围为 5.8 至 11.6 的催化 H 演化，产生了一个可以分为两个区域的电位-关系。对于 p 值≤8.7 的酸，半波催化电位（）随 p 值的变化呈-128 mV/p 单位的斜率变化，而对于 p 值≥8.7 的酸，随 p 值的变化呈-39 mV/p 单位的斜率变化。此外，还合成了一系列缓冲酸，以探索酸性质子周围的立体位阻对催化的影响。与母体化合物相比，CV 中的催化电流在存在空间位阻较大的缓冲酸时显著降低，这也与添加的缓冲酸作为催化剂的主要质子供体一致，表明除了 p 值之外，酸的结构也会影响活性。这些结果表明，缓冲酸度和结构是优化和评估水相质子依赖催化系统时需要考虑的重要因素。
