Department of Chemistry, University of California, Irvine , Irvine, California 92697, United States.
Department of Chemistry, University of California, Berkeley , Berkeley, California 94720, United States.
J Am Chem Soc. 2018 Feb 28;140(8):2739-2742. doi: 10.1021/jacs.7b13052. Epub 2018 Feb 13.
Artificial metalloproteins (ArMs) containing CoO cubane active sites were constructed via biotin-streptavidin technology. Stabilized by hydrogen bonds (H-bonds), terminal and cofacial Co-OH moieties are observed crystallographically in a series of immobilized cubane sites. Solution electrochemistry provided correlations of oxidation potential and pH. For variants containing Ser and Phe adjacent to the metallocofactor, 1e/1H chemistry predominates until pH 8, above which the oxidation becomes pH-independent. Installation of Tyr proximal to the CoO active site provided a single H-bond to one of a set of cofacial Co-OH groups. With this variant, multi-e/multi-H chemistry is observed, along with a change in mechanism at pH 9.5 that is consistent with Tyr deprotonation. With structural similarities to both the oxygen-evolving complex of photosystem II (H-bonded Tyr) and to thin film water oxidation catalysts (CoO core), these findings bridge synthetic and biological systems for water oxidation, highlighting the importance of secondary sphere interactions in mediating multi-e/multi-H reactivity.
通过生物素-链霉亲和素技术构建了含有 CoO 立方烷活性位点的人工金属蛋白（ArMs）。在一系列固定化立方烷位点中，通过氢键（H 键）稳定，观察到末端和面对面的 Co-OH 部分在晶体中存在。溶液电化学提供了氧化电位和 pH 值的相关性。对于含有与金属配合物相邻的 Ser 和 Phe 的变体，1e/1H 化学占主导地位，直到 pH 8，高于该 pH 值，氧化成为与 pH 无关。将 Tyr 安装在 CoO 活性位点的近端，为一组面对面的 Co-OH 基团之一提供了一个氢键。对于这种变体，观察到多电子/多质子化学，以及在 pH 9.5 时发生的与 Tyr 去质子化一致的机制变化。由于与光合作用系统 II 的放氧复合物（氢键结合的 Tyr）和薄膜水氧化催化剂（CoO 核）具有相似的结构，这些发现为水氧化的合成和生物系统架起了桥梁，突出了次级球相互作用在介导多电子/多质子反应性中的重要性。
