title: A low-spin alkylperoxo-iron(III) complex with weak Fe-O and O-O bonds: implications for the mechanism of superoxide reductase.
abstract: The synthesis of a mononuclear, five-coordinate ferrous complex [([15]aneN4)FeII(SPh)](BF4) (1) is reported. This complex is a new model of the reduced active site of the enzyme superoxide reductase (SOR), which is comprised of a [(NHis)4(Scys)FeII] center. Complex 1 reacts with alkylhydroperoxides (tBuOOH, cumenylOOH) at low temperature to give a metastable, dark red intermediate (2a: R = tBu; 2b: R = cumenyl) that has been characterized by UV-vis, EPR, and resonance Raman spectroscopy. The UV-vis spectrum (-80 degrees C) reveals a 526 nm absorbance (epsilon = 2150 M-1 cm-1) for 2a and a 527 nm absorbance (epsilon = 1650 M-1 cm-1) for 2b, indicative of alkylperoxo-to-iron(III) LMCT transitions, and the EPR data (77 K) show that both intermediates are low-spin iron(III) complexes (g = 2.20 and 1.97). Definitive identification of the Fe(III)-OOR species comes from RR spectra, which give nu(Fe-O) = 612 (2a) and 615 (2b) cm-1, and nu(O-O) = 803 (2a) and 795 (2b) cm-1. The assignments for 2a were confirmed by 18O substitution (tBu18O18OH), resulting in a 28 cm-1 downshift for nu(Fe-18O), and a 46 cm-1 downshift for nu(18O-18O). These data show that 2a and 2b are low-spin FeIII-OOR species with weak Fe-O bonds and suggest that a low-spin intermediate may occur in SOR, as opposed to previous proposals invoking high-spin intermediates.
authors.affiliation: Department of Chemistry, Johns Hopkins University, Baltimore, Maryland 21218, USA.
authors.forename: Divya
authors.initials: D
authors.lastname: Krishnamurthy
authors.forename: Gary D
authors.initials: GD
authors.lastname: Kasper
authors.forename: Frances
authors.initials: F
authors.lastname: Namuswe
authors.forename: William D
authors.initials: WD
authors.lastname: Kerber
authors.forename: Amy A
authors.initials: AA
authors.lastname: Narducci Sarjeant
authors.forename: Pierre
authors.initials: P
authors.lastname: Moënne-Loccoz
authors.forename: David P
authors.initials: DP
authors.lastname: Goldberg
mesh_terms: D000473:Alkanes / Q000737:chemistry*; D001665:Binding Sites; D002412:Cations; D007501:Iron / Q000737:chemistry*; D015394:Molecular Structure; D009942:Organometallic Compounds / Q000737:chemistry*; D010084:Oxidation-Reduction; D010088:Oxidoreductases / Q000737:chemistry / Q000378:metabolism; D010100:Oxygen / Q000737:chemistry*; D010545:Peroxides / Q000737:chemistry*; D013056:Spectrophotometry, Ultraviolet; D013059:Spectrum Analysis, Raman
chemical_list: D000473:Alkanes; D002412:Cations; D009942:Organometallic Compounds; D010545:Peroxides; D007501:Iron; D010088:Oxidoreductases; C121849:superoxide reductase; D010100:Oxygen