title: Influence of sequential thiolate oxidation on a nitrile hydratase mimic probed by multiedge X-ray absorption spectroscopy.
abstract: Nitrile hydratases (NHases) are Fe(III)- and Co(III)-containing hydrolytic enzymes that convert nitriles into amides. The metal-center is contained within an N(2)S(3) coordination motif with two post-translationally modified cysteinates contained in a cis arrangement, which have been converted into a sulfinate (R-SO(2)(-)) and a sulfenate (R-SO(-)) group. Herein, we utilize Ru L-edge and ligand (N-, S-, and P-) K-edge X-ray absorption spectroscopies to probe the influence that these modifications have on the electronic structure of a series of sequentially oxidized thiolate-coordinated Ru(II) complexes ((bmmp-TASN)RuPPh(3), (bmmp-O(2)-TASN)RuPPh(3), and (bmmp-O(3)-TASN)RuPPh(3)). Included is the use of N K-edge spectroscopy, which was used for the first time to extract N-metal covalency parameters. We find that upon oxygenation of the bis-thiolate compound (bmmp-TASN)RuPPh(3) to the sulfenato species (bmmp-O(2)-TASN)RuPPh(3) and then to the mixed sulfenato/sulfinato speices (bmmp-O(3)-TASN)RuPPh(3) the complexes become progressively more ionic, and hence the Ru(II) center becomes a harder Lewis acid. These findings are reinforced by hybrid DFT calculations (B(38HF)P86) using a large quadruple-ζ basis set. The biological implications of these findings in relation to the NHase catalytic cycle are discussed in terms of the creation of a harder Lewis acid, which aids in nitrile hydrolysis.
authors.affiliation: Department of Chemistry, University of Nevada, Reno, Nevada 89557, USA. shearer@unr.edu
authors.forename: Jason
authors.initials: J
authors.lastname: Shearer
authors.forename: Paige E
authors.initials: PE
authors.lastname: Callan
authors.forename: César A
authors.initials: CA
authors.lastname: Masitas
authors.forename: Craig A
authors.initials: CA
authors.lastname: Grapperhaus
mesh_terms: D040761:Biomimetic Materials / Q000737:chemistry*; D056831:Coordination Complexes / Q000737:chemistry*; D006836:Hydro-Lyases / Q000737:chemistry*; D008958:Models, Molecular; D010084:Oxidation-Reduction; D012428:Ruthenium / Q000737:chemistry*; D013438:Sulfhydryl Compounds / Q000737:chemistry*; D056928:X-Ray Absorption Spectroscopy
chemical_list: D056831:Coordination Complexes; D013438:Sulfhydryl Compounds; D012428:Ruthenium; D006836:Hydro-Lyases; C048831:nitrile hydratase