A low-spin alkylperoxo-iron(III) complex with weak Fe-O and O-O bonds: Implications for the mechanism of superoxide reductase

Divya Krishnamurthy, Gary D. Kasper, Frances Namuswe, William D. Kerber, Amy A Narducci Sarjeant, Pierre Moenne-Loccoz, David P. Goldberg

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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 °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.

Original languageEnglish (US)
Pages (from-to)14222-14223
Number of pages2
JournalJournal of the American Chemical Society
Volume128
Issue number44
DOIs
StatePublished - Nov 8 2006

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Paramagnetic resonance
Iron
Raman Spectrum Analysis
Raman spectroscopy
Catalytic Domain
Substitution reactions
Enzymes
Temperature
Oxidoreductases
superoxide reductase

ASJC Scopus subject areas

  • Chemistry(all)

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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.

In: Journal of the American Chemical Society, Vol. 128, No. 44, 08.11.2006, p. 14222-14223.

Research output: Contribution to journalArticle

Krishnamurthy, Divya ; Kasper, Gary D. ; Namuswe, Frances ; Kerber, William D. ; Sarjeant, Amy A Narducci ; Moenne-Loccoz, Pierre ; Goldberg, David P. / A low-spin alkylperoxo-iron(III) complex with weak Fe-O and O-O bonds : Implications for the mechanism of superoxide reductase. In: Journal of the American Chemical Society. 2006 ; Vol. 128, No. 44. pp. 14222-14223.
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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 °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.",
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AU - Krishnamurthy, Divya

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AU - Namuswe, Frances

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AB - 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.

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