Sulfur K-Edge XAS and DFT Calculations on Nitrile Hydratase: Geometric and Electronic Structure of the Non-heme Iron Active Site

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• 作者：Abhishek Dey ; Marina Chow ; Kayoko Taniguchi ; Priscilla Lugo-Mas ; Steven Davin ; Mizuo Maeda ; Julie A. Kovacs ; Masafumi Odaka ; Keith O. Hodgson ; Britt Hedman ; and Edward I. Solomon
• 刊名：Journal of the American Chemical Society
• 出版年：2006
• 出版时间：January 18, 2006
• 年：2006
• 卷：128
• 期：2
• 页码：533 - 541
• 全文大小：629K
• 年卷期：v.128,no.2(January 18, 2006)
• ISSN：1520-5126

文摘

The geometric and electronic structure of the active site of the non-heme iron enzyme nitrilehydratase (NHase) is studied using sulfur K-edge XAS and DFT calculations. Using thiolate (RS^-)-, sulfenate(RSO^-)-, and sulfinate (RSO₂^-)-ligated model complexes to provide benchmark spectral parameters, theresults show that the S K-edge XAS is sensitive to the oxidation state of S-containing ligands and that thespectrum of the RSO^- species changes upon protonation as the S-O bond is elongated (by ~0.1 Å).These signature features are used to identify the three cysteine residues coordinated to the low-spin Fe^IIIin the active site of NHase as CysS^-, CysSOH, and CysSO₂^- both in the NO-bound inactive form and inthe photolyzed active form. These results are correlated to geometry-optimized DFT calculations. The pre-edge region of the X-ray absorption spectrum is sensitive to the Z_eff of the Fe and reveals that the Fe in[FeNO]⁶ NHase species has a Z_eff very similar to that of its photolyzed Fe^III counterpart. DFT calculationsreveal that this results from the strong back-bonding into the * antibonding orbital of NO, which shiftssignificant charge from the formally t₂⁶ low-spin metal to the coordinated NO.