PMID:17500514
| Citation |
Dey, A, Jeffrey, SP, Darensbourg, M, Hodgson, KO, Hedman, B and Solomon, EI (2007) Sulfur K-edge XAS and DFT studies on NiII complexes with oxidized thiolate ligands: implications for the roles of oxidized thiolates in the active sites of Fe and Co nitrile hydratase. Inorg Chem 46:4989-96 |
|---|---|
| Abstract |
S K-edge X-ray absorption spectroscopy data on a series of NiII 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 t2 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. |
| Links |
PubMed PMC2565589 Online version:10.1021/ic070244l |
| Keywords |
Binding Sites; Cobalt; Hydro-Lyases/chemistry; Iron; Ligands; Models, Molecular; Nickel/chemistry; Organometallic Compounds/chemistry; Oxidation-Reduction; Spectrum Analysis; Sulfhydryl Compounds/chemistry; Sulfur/chemistry; X-Rays |
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