Institut für Anorganische Chemie, Eberhard Karls Universität Tübingen, Auf der Morgenstelle 18, 72076 Tübingen, Germany.
Lehrstuhl für Theoretische Chemie, Ruhr-Universität Bochum, 44780 Bochum, Germany.
Inorg Chem. 2020 Dec 7;59(23):17234-17243. doi: 10.1021/acs.inorgchem.0c02467. Epub 2020 Nov 17.
Sulfur-bridged bimetallic 2M-2S type structures are essential cofactors that participate in biological long-range electron transport and metabolism. Metal-sulfur bond covalency is a decisive property for inner sphere (through-bond) type electron transfer that dominates in buried or hydrophobic protein environments. This work reports on a combined experimental and computational study of the effect of ligand charge on the electronic structure of a 2Ni-2S model site that adopts the biologically relevant = / redox state. Starting out from an isostructural dinickel(1.5+)-dithiophenolate platform with sulfur-bridged tetrahedral Ni sites, η:η-μ-coordination of the = / [2Ni-2S] core to either a neutral π-system or strongly σ-donating cyclohexadienido renders its electronic structure substantially different. Density functional theory analysis corroborates pulse and continuous wave electron paramagnetic resonance data that associate co-ligand charge with the significant change in the mechanism and size of electron-P nuclear spin hyperfine coupling to a phosphine reporter ligand at each nickel center. An increasing level of charge donation attenuates direct and through-bridge electronic coupling of the metal sites, resulting in a stronger electronic coupling of the 2Ni-2S core to its terminal phosphine donors. Drawing a connection to biological 2M-2S sites, our 2Ni-2S system indicates that a fine balance of intracore and core-protein electronic coupling is key to biological function for which the degree of charge donation by peripheral donors appears to be a significant parameter.
硫桥双金属 2M-2S 型结构是参与生物长程电子传递和代谢的必需辅因子。金属-硫键的共价性是内球（键间）型电子转移的决定性性质，这种转移在埋置或疏水环境中的蛋白质中占主导地位。本工作报道了一项实验和计算相结合的研究，研究了配体电荷对采用生物学相关 = / 氧化还原态的 2Ni-2S 模型位点电子结构的影响。从具有硫桥四面体 Ni 位的同构二镍（1.5+）-二噻吩酚配体平台出发， = / [2Ni-2S] 核的 η:η-μ-配位到中性 π-体系或强 σ-供体环己二烯基，使其电子结构发生显著变化。密度泛函理论分析证实了脉冲和连续波电子顺磁共振数据，表明共配体电荷与电子-P 核自旋超精细耦合机制和大小在每个镍中心与膦报告配体的变化有关。电荷供体水平的增加会减弱金属位点的直接和桥间电子耦合，从而增强 2Ni-2S 核与其末端膦供体的电子耦合。将我们的 2Ni-2S 系统与生物 2M-2S 位点联系起来，表明核心内和核心-蛋白质电子耦合的精细平衡是生物功能的关键，而外围供体的电荷供体程度似乎是一个重要参数。
