title: Investigation of metal-dithiolate fold angle effects: implications for molybdenum and tungsten enzymes.
abstract: Gas-phase photoelectron spectroscopy and density functional theory have been used to investigate the interactions between the sulfur pi-orbitals of arene dithiolates and high-valent transition metals as minimum molecular models of the active site features of pyranopterin MoW enzymes. The compounds (Tp*)MoO(bdt) (compound 1), Cp(2)Mo(bdt) (compound 2), and Cp(2)Ti(bdt) (compound 3) [where Tp* is hydrotris(3,5-dimethyl-1-pyrazolyl)borate, bdt is 1,2-benzenedithiolate, and Cp is eta(5)- cyclopentadienyl] provide access to three different electronic configurations of the metal, formally d(1), d(2), and d(0), respectively. The gas-phase photoelectron spectra show that ionizations from occupied metal and sulfur based valence orbitals are more clearly observed in compounds 2 and 3 than in compound 1. The observed ionization energies and characters compare very well with those calculated by density functional theory. A "dithiolate-folding-effect" involving an interaction of the metal in-plane and sulfur-pi orbitals is proposed to be a factor in the electron transfer reactions that regenerate the active sites of molybdenum and tungsten enzymes.
authors.affiliation: Department of Chemistry, University of Arizona, Tucson, AZ 85721, USA.
authors.forename: Hemant K
authors.initials: HK
authors.lastname: Joshi
authors.forename: J Jon A
authors.initials: JJ
authors.lastname: Cooney
authors.forename: Frank E
authors.initials: FE
authors.lastname: Inscore
authors.forename: Nadine E
authors.initials: NE
authors.lastname: Gruhn
authors.forename: Dennis L
authors.initials: DL
authors.lastname: Lichtenberger
authors.forename: John H
authors.initials: JH
authors.lastname: Enemark
mesh_terms: D042931:Aldehyde Oxidase; D000445:Aldehyde Oxidoreductases / Q000737:chemistry / Q000378:metabolism; D001665:Binding Sites; D004798:Enzymes / Q000737:chemistry / Q000378:metabolism*; D007506:Iron-Sulfur Proteins; D007700:Kinetics; D008958:Models, Molecular; D008982:Molybdenum / Q000737:chemistry* / Q000378:metabolism; D010084:Oxidation-Reduction; D010088:Oxidoreductases / Q000737:chemistry / Q000378:metabolism; D050862:Oxidoreductases Acting on Sulfur Group Donors / Q000737:chemistry / Q000378:metabolism; D017510:Protein Folding; D013438:Sulfhydryl Compounds / Q000737:chemistry* / Q000378:metabolism; D014414:Tungsten / Q000737:chemistry* / Q000378:metabolism; D014968:Xanthine Dehydrogenase / Q000737:chemistry / Q000378:metabolism
chemical_list: D004798:Enzymes; D007506:Iron-Sulfur Proteins; D013438:Sulfhydryl Compounds; D008982:Molybdenum; D010088:Oxidoreductases; D014968:Xanthine Dehydrogenase; D000445:Aldehyde Oxidoreductases; D042931:Aldehyde Oxidase; D050862:Oxidoreductases Acting on Sulfur Group Donors; C045664:dimethyl sulfoxide reductase; D014414:Tungsten