Tuning the O–O bond formation pathways of molecular water oxidation catalysts on electrode surfaces via second coordination sphere engineering

A molecular [Ru(bda)]-type(bda = 2,2’-bipyridine-6,6’-dicarboxylate) water oxidation catalyst with 4-vinylpyridine as the axial ligand(Complex 1) was immobilized or co-immobilized with 1-(trifluoromethyl)-4-vinylbenzene(3 F) or styrene(St) blocking units on the surface of glassy carbon(GC) electrodes by electrochemical polymerization, in order to prepare the corresponding poly-1@GC, poly-1+P3 F@GC, and poly-1+PSt@GC functional electrodes. Kinetic measurements of the electrode surface reaction revealed that [Ru(bda)] triggers the O–O bond formation via(1) the radical coupling interaction between the two metallo-oxyl radicals(I2 M) in the homo-coupling polymer(poly-1), and(2) the water nucleophilic attack(WNA) pathway in poly-1+P3 F and poly-1+PSt copolymers. The comparison of the three electrodes revealed that the second coordination sphere of the water oxidation catalysts plays vital roles in stabilizing their reaction intermediates, tuning the O–O bond formation pathways and improving the water oxidation reaction kinetics without changing the first coordination structures.

具有非共价相互作用的金属酶模拟物

金属酶催化的高效性和选择性来源于第一配位环境金属催化中心和第二配位环境非共价相互作用力的协同作用。针对金属催化中心构效关系的研究已有大量报道,相比之下,有关非共价相互作用的研究尚不够充分。金属酶的非共价作用力,包括氢键、静电相互作用、范德华力和疏水相互作用等产生于第二配位环境中的氨基酸残基。阐述第二配位环境中氨基酸残基作用的首要障碍来自于复杂并难以界定的分子内和分子间的相互作用网络。制备包含非共价相互作用的金属酶模拟物是攻克这一难题行之有效的方法,它不但有利于理解非共价相互作用和金属离子之间的协同作用,而且有助于发展可应用于工业、医药、生物技术等领域的仿生催化剂。本文按照非共价弱相互作用的类型,对近期报道的典型案例进行综述。文中阐述了基于简单多齿配体,如联吡啶、三联吡啶、环胺、卟啉等,和基于超分子配体,如功能化的环糊精和杯芳烃等的金属酶模型物。在讨论模型物之前,本文对天然金属酶中的非共价相互作用简略探讨。