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S3 State Models of Nature’s Water Oxidizing Complex: Analysis of Bonding and Magnetic Exchange Pathways, Assessment of Experimental Electron Paramagnetic Resonance Data, and Implications for the Water Oxidation Mechanism
The Journal of Physical Chemistry B ( IF 3.3 ) Pub Date : 2021-08-31 , DOI: 10.1021/acs.jpcb.1c04459
Thomas A Corry 1 , Patrick J O'Malley 1
Affiliation  

Broken symmetry density functional theory (BS-DFT) calculations on large models of Nature’s water oxidizing complex (WOC) are used to investigate the electronic structure and associated magnetic interactions of this key intermediate state. The electronic origins of the ferromagnetic and antiferromagnetic couplings between neighboring Mn ions are investigated and illustrated by using corresponding orbital transformations. Protonation of the O4 and/or O6 atoms leads to large variation in the distribution of spin around the complex with associated changes in its magnetic resonance properties. Models for Sr2+ exchange and methanol addition indicate minor perturbations reflected in slightly altered spin projection coefficients for the Mn1 and Mn2 ions. These are shown to account for the observed changes observed experimentally via electron paramagnetic resonance methods and suggest a reinterpretation of the experimental findings. By comparison with experimental determinations, we show that the spin projections and resulting calculated 55Mn hyperfine couplings support the open cubane form of an oxo (O5)–hydroxo (O6) cluster in all cases with no need to invoke a closed cubane intermediate. The implications of these findings for the water oxidation mechanism are discussed.

中文翻译:

自然界水氧化复合物的 S3 状态模型:键合和磁交换途径分析、实验电子顺磁共振数据评估以及对水氧化机制的影响

使用对自然水氧化复合物 (WOC) 大型模型的破坏对称密度泛函理论 (BS-DFT) 计算来研究该关键中间态的电子结构和相关磁相互作用。通过使用相应的轨道变换研究和说明了相邻 Mn 离子之间铁磁和反铁磁耦合的电子起源。O4 和/或 O6 原子的质子化导致复合物周围的自旋分布发生很大变化,并伴随着其磁共振特性的相关变化。Sr 2+交换和甲醇添加的模型表明轻微扰动反映在 Mn 1和 Mn 2 的自旋投影系数略有变化离子。这些被证明可以解释通过电子顺磁共振方法实验观察到的变化,并建议对实验结果进行重新解释。通过与实验测定的比较,我们表明自旋投影和由此产生的计算出的55 Mn 超精细耦合在所有情况下都支持氧 (O5)-羟基 (O6) 簇的开立方形式,而无需调用封闭立方烷中间体。讨论了这些发现对水氧化机制的影响。
更新日期:2021-09-16
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