Models for Diiron-Oxo Proteins: The Peroxide Adduct of Fe2(HPTB)(OH)(NO3)4

Bridget A. Brennan, Qiuhao Chen, Carlos Juarez-Garcia, Anne E. True, Lawrence Que, Charles J. O’Connor

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Abstract

The complex of Fe(NO3)3 and N,N,N′,N′-tetrakis(2-benzimidazolylmethyl)-2-hydroxy-1,3-diaminopropane (HPTB) is reformulated as [Fe2(HPTB)(μ-OH)(NO3)2](NO3)2 on the basis of 1H NMR, EXAFS, X-ray diffraction, and conductivity data. This complex reacts with hydrogen peroxide to form a 1:1 adduct with a new charge-transfer band at 600 nm (є = 1500 M-1 cm-1). Resonance Raman studies show two resonance-enhanced vibrations, vFe-o at 476 cm-1 and vo-o, which appears as a Fermi doublet centered at 895 cm-1; these features shift to 457 and 854 cm-1, respectively, with the use of H218O2 but are not affected by D2O. 1H NMR measurements indicate that the antiferromagnetic coupling is increased from -J = 20 cm-1 to ca. 70 cm-1 upon formation of the peroxide adduct, suggesting the introduction of a new coupling pathway. The 57Fe Mössbauer spectrum of the peroxide complex reveals a quadrupole doublet (δ - 0.54 mm/s, ΔEQ = 0.84 mm/s) distinct from that of the precursor complex (δ = 0.49 mm/s, ΔEQ = 0.66 mm/s), indicating that the two irons are affected similarly by peroxide binding. Conductivity measurements in CH3CN show that the adduct is a 1:1 electrolyte. Taken together, the physical data suggest the formulation [Fe2(HPTB)(μ-η11-O2)-NO3)2](NO3) for the peroxide complex. Such dinuclear iron peroxide complexes may be relevant to putative intermediates in the oxygenation of the reduced forms of ribonucleotide reductase and methane monooxygenase.

Original languageEnglish (US)
Pages (from-to)1937-1943
Number of pages7
JournalInorganic chemistry
Volume30
Issue number8
DOIs
StatePublished - Apr 1 1991

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