916148-26-0Relevant academic research and scientific papers
Rational tuning of the thiolate donor in model complexes of superoxide reductase: Direct evidence for a trans influence in FeIII-OOR complexes
Namuswe, Frances,Kasper, Gary D.,Narducci Sarjeant, Amy A.,Hayashi, Takahiro,Krest, Courtney M.,Green, Michael T.,Moenne-Loccoz, Pierre,Goldberg, David P.
, p. 14189 - 14200 (2009/03/11)
Iron peroxide species have been identified as important intermediates in a number of nonheme iron as well as heme-containing enzymes, yet there are only a few examples of such species either synthetic or biological that have been well characterized. We describe the synthesis and structural characterization of a new series of five-coordinate (N4S(thiolate))FeII complexes that react with tert-butyl hydroperoxide (tBuOOH) or cumenyl hydroperoxide (CmOOH) to give metastable alkylperoxo-iron(III) species (N4S(thiolate)FeIII-OOR) at low temperature. These complexes were designed specifically to mimic the nonheme iron active site of superoxide reductase, which contains a five-coordinate iron(II) center bound by one Cys and four His residues in the active form of the protein. The structures of the FeII complexes are analyzed by X-ray crystallography, and their electrochemical properties are assessed by cyclic voltammetry. For the FeIII-OOR species, low-temperature UV-vis spectra reveal intense peaks between 500-550 nm that are typical of peroxide to iron(III) ligand-to-metal charge-transfer (LMCT) transitions, and EPR spectroscopy shows that these alkylperoxo species are all low-spin iron(III) complexes. Identification of the vibrational modes of the FeIII-OOR unit comes from resonance Raman (RR) spectroscopy, which shows ν(Fe-O) modes between 600-635 cm-1 and ν(O-O) bands near 800 cm-1. These Fe-O stretching frequencies are significantly lower than those found in other low-spin FeIII-OOR complexes. Trends in the data conclusively show that this weakening of the Fe-O bond arises from a trans influence of the thiolate donor, and density functional theory (DFT) calculations support these findings. These results suggest a role for the cysteine ligand in SOR, and are discussed in light of the recent assessments of the function of the cysteine ligand in this enzyme.
A low-spin alkylperoxo-iron(III) complex with weak Fe-O and O-O bonds: Implications for the mechanism of superoxide reductase
Krishnamurthy, Divya,Kasper, Gary D.,Namuswe, Frances,Kerber, William D.,Sarjeant, Amy A. Narducci,Moenne-Loccoz, Pierre,Goldberg, David P.
, p. 14222 - 14223 (2008/02/09)
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 °C) reveals a 526 nm absorbance (ε = 2150 M-1 cm-1) for 2a and a 527 nm absorbance (ε = 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 ν(Fe-O) = 612 (2a) and 615 (2b) cm-1, and ν(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 ν(Fe-18O), and a 46 cm-1 downshift for ν(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. Copyright
