Electronic Structure of the Ferryl Intermediate in the α-Ketoglutarate Dependent Non-Heme Iron Halogenase SyrB2: Contributions to H Atom Abstraction Reactivity

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• 作者：Martin Srnec ; Shaun D. Wong ; Megan L. Matthews ; Carsten Krebs ; J. Martin Bollinger Jr. ; Edward I. Solomon
• 刊名：Journal of the American Chemical Society
• 出版年：2016
• 出版时间：April 20, 2016
• 年：2016
• 卷：138
• 期：15
• 页码：5110-5122
• 全文大小：916K
• 年卷期：0
• ISSN：1520-5126

文摘

Low temperature magnetic circular dichroism (LT MCD) spectroscopy in combination with quantum-chemical calculations are used to define the electronic structure associated with the geometric structure of the Fe^IV═O intermediate in SyrB2 that was previously determined by nuclear resonance vibrational spectroscopy. These studies elucidate key frontier molecular orbitals (FMOs) and their contribution to H atom abstraction reactivity. The VT MCD spectra of the enzymatic <i>Si> = 2 Fe^IV═O intermediate with Br^– ligation contain information-rich features that largely parallel the corresponding spectra of the <i>Si> = 2 model complex (TMG₃tren)Fe^IV═O (Srnec, M.; Wong, S. D.; England, J.; Que, L. Jr.; Solomon, E. I. <i>Proc. Natl. Acad. Sci. USAi> 2012, <i>109i>, 14326–14331). However, quantitative differences are observed that correlate with π-anisotropy and oxo donor strength that perturb FMOs and affect reactivity. Due to π-anisotropy, the Fe^IV═O active site exhibits enhanced reactivity in the direction of the substrate cavity that proceeds through a π-channel that is controlled by perpendicular orientation of the substrate C–H bond relative to the halide–Fe^IV═O plane. Also, the increased intrinsic reactivity of the SyrB2 intermediate relative to the ferryl model complex is correlated to a higher oxyl character of the Fe^IV═O at the transition states resulting from the weaker ligand field of the halogenase.