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首页> 外文期刊>Inorganic Chemistry: A Research Journal that Includes Bioinorganic, Catalytic, Organometallic, Solid-State, and Synthetic Chemistry and Reaction Dynamics >Sulfur K-edge XAS and DFT studies on Ni-II complexes with oxidized thiolate ligands: Implications for the roles of oxidized thiolates in the active sites of Fe and Co nitrile hydratase
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Sulfur K-edge XAS and DFT studies on Ni-II complexes with oxidized thiolate ligands: Implications for the roles of oxidized thiolates in the active sites of Fe and Co nitrile hydratase

机译：具有氧化硫醇盐配体的Ni-II配合物的硫K-edge XAS和DFT研究：氧化硫醇盐在Fe和Co腈水合酶活性位点中的作用

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S K-edge X-ray absorption spectroscopy data on a series of Ni-II complexes with thiolate (RS-) and oxidized thiolate (RSO2-) ligands are used to quantify Ni-S bond covalency and its change upon ligand oxidation. Analyses of these results using geometry-optimized density functional theory (DFT) calculations suggest that the Ni-S sigma bonds do not weaken on ligand oxidation. Molecular orbital analysis indicates that these oxidized thiolate ligands use filled high-lying S-O pi* orbitals for strong sigma donation. However, the RSO2- ligands are poor pi donors, as the orbital required for pi interaction is used in the S-O sigma-bond formation. The oxidation of the thiolate reduces the repulsion between electrons in the filled Ni t(2) orbital and the thiolate out-of-plane pi-donor orbital leading to shorter Ni-S bond length relative to that of the thiolate donor. The insights obtained from these results are relevant to the active sites of Fe- and Co-type nitrile hydratases (Nhase) that also have oxidized thiolate ligands. DFT calculations on models of the active site indicate that whereas the oxidation of these thiolates has a major effect in the axial ligand-binding affinity of the Fe-type Nhase (where there is both sigma and pi donation from the S ligands), it has only a limited effect on the sixth-ligand-binding affinity of the Co-type Nhases (where there is only sigma donation). These oxidized residues may also play a role in substrate binding and proton shuttling at the active site.
机译：一系列具有硫醇盐（RS-）和氧化硫醇盐（RSO2-）配体的Ni-II配合物的S K边缘X射线吸收光谱数据用于量化Ni-S键的共价键及其在配体氧化后的变化。使用几何优化密度泛函理论（DFT）计算对这些结果进行的分析表明，Ni-S sigma键不会在配体氧化时减弱。分子轨道分析表明，这些氧化的硫醇盐配体使用填充的高位S-O pi *轨道进行强σ捐赠。但是，RSO2-配体是较差的pi供体，因为pi相互作用所需的轨道用于S-Oσ键形成。硫醇盐的氧化减少了填充的Ni t（2）轨道中的电子与硫醇盐平面外pi-供体轨道之间的排斥，从而导致相对于硫醇盐供体的Ni-S键长度较短。从这些结果中获得的见解与也具有氧化的硫醇盐配体的Fe型和Co型腈水合酶（Nhase）的活性位点有关。根据活性位点模型进行的DFT计算表明，尽管这些硫醇盐的氧化对Fe型Nhase的轴向配体结合亲和力（其中S配体同时提供σ和pi）具有重大影响，但它具有仅对Co型Nhases的第六个配体结合亲和力（只有sigma捐赠）产生有限的影响。这些氧化的残基还可能在底物结合和质子在活性位点穿梭中起作用。

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