title: Electronic Structure of the Ferryl Intermediate in the α-Ketoglutarate Dependent Non-Heme Iron Halogenase SyrB2: Contributions to H Atom Abstraction Reactivity.
abstract: 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 S = 2 Fe(IV)═O intermediate with Br(-) ligation contain information-rich features that largely parallel the corresponding spectra of the S = 2 model complex (TMG3tren)Fe(IV)═O (Srnec, M.; Wong, S. D.; England, J; Que, L; 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 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.
authors.affiliation: Department of Chemistry, Stanford University , Stanford, California 94305-5080, United States .|J. Heyrovský Institute of Physical Chemistry, The Czech Academy of Sciences , Dolejškova 2155/3, 182 23 Prague 8, Czech Republic.
authors.forename: Martin
authors.initials: M
authors.lastname: Srnec
authors.affiliation: Department of Chemistry, Stanford University , Stanford, California 94305-5080, United States .
authors.forename: Shaun D
authors.initials: SD
authors.lastname: Wong
authors.affiliation: Department of Chemistry, Pennsylvania State University , University Park, Pennsylvania 16802, United States.
authors.forename: Megan L
authors.initials: ML
authors.lastname: Matthews
authors.affiliation: Department of Chemistry, Pennsylvania State University , University Park, Pennsylvania 16802, United States.
authors.forename: Carsten
authors.initials: C
authors.lastname: Krebs
authors.affiliation: Department of Chemistry, Pennsylvania State University , University Park, Pennsylvania 16802, United States.
authors.forename: J Martin
authors.initials: JM
authors.lastname: Bollinger
authors.affiliation: Department of Chemistry, Stanford University , Stanford, California 94305-5080, United States .
authors.forename: Edward I
authors.initials: EI
authors.lastname: Solomon
mesh_terms: D001426:Bacterial Proteins / Q000737:chemistry / Q000378:metabolism; D002942:Circular Dichroism; D005977:Glutarates / Q000737:chemistry* / Q000378:metabolism; D006859:Hydrogen / Q000737:chemistry*; D058085:Iron Compounds / Q000737:chemistry* / Q000378:metabolism; D008958:Models, Molecular; D019159:Nonheme Iron Proteins / Q000737:chemistry* / Q000378:metabolism; D010088:Oxidoreductases / Q000737:chemistry* / Q000378:metabolism; D011789:Quantum Theory; D013912:Threonine / Q000737:chemistry / Q000378:metabolism
chemical_list: D001426:Bacterial Proteins; D005977:Glutarates; D058085:Iron Compounds; D019159:Nonheme Iron Proteins; C032677:syringomycin; D013912:Threonine; D006859:Hydrogen; D010088:Oxidoreductases