ja6b01151_si_001.pdf (2.88 MB)
Electronic Structure of the Ferryl Intermediate in the α‑Ketoglutarate Dependent Non-Heme Iron Halogenase SyrB2: Contributions to H Atom Abstraction Reactivity
journal contribution
posted on 2016-03-29, 00:00 authored by Martin Srnec, Shaun D. Wong, Megan L. Matthews, Carsten Krebs, J. Martin Bollinger, Edward I. SolomonLow
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 FeIVO 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 S = 2 FeIVO intermediate with Br– ligation contain information-rich features that largely
parallel the corresponding spectra of the S = 2 model
complex (TMG3tren)FeIVO (Srnec, M.;
Wong, S. D.; England, J.; Que, L. Jr.; Solomon, E. I. Proc. Natl.
Acad. Sci. USA 2012, 109, 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 FeIVO
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–FeIVO 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 FeIVO at the transition states resulting from the weaker
ligand field of the halogenase.