213918-87-7Relevant academic research and scientific papers
Modeling the diiron centers of non-heme iron enzymes. Preparation of sterically hindered diiron(II) tetracarboxylate complexes and their reactions with dioxygen
LeCloux, Daniel D.,Barrios, Amy M.,Mizoguchi, Tadashi J.,Lippard, Stephen J.
, p. 9001 - 9014 (2007/10/03)
A series of diiron(II) complexes, [Fe2(μ-L)(μ-O2CR)(O2CR)(N)2], where L is a dinucleating bis(carboxylate) ligand based on m-xylylenediamine bis(Kemp's triacid imide) and N is a pyridine- or imidazole-derived ligand, were prepared as models for the carboxylate-bridged non-heme diiron cores of the O2-activating enzymes, soluble methane monooxygenase hydroxylase (MMOH), and the R2 subunit of ribonucleotide reductase (RNR-R2). X-ray crystallographic studies revealed differences in the coordination geometry of the bridging monocarboxylate ligand, which shifts from monodentate to syn,syn-bidentate bonding modes. The extent of this carboxylate shift depends on both the steric bulk of the monocarboxylate and the basicity of the ancillary N-donor ligands. Exposure of these diiron(II) complexes to O2 at - 77 °C in nonpolar solvents (CH2Cl2, THF, toluene) yielded deep blue solutions (λ(max) ? 580 nm, ε ? 1200 M-1 cm-1), consistent with the generation of diiron(III) peroxo species. This reaction was irreversible, and its stoichiometry was determined by manometry to be 1:1 in diiron(II) complex and O2. The diiron(III) peroxo complexes exhibited oxygen isotope-sensitive resonance Raman bands at ~ 860 cm-1, which are assigned to the O-O stretching frequency of a μ-1,2-peroxodiiron(III) core. 57Fe Mossbauer spectroscopy confirmed the assignment of the diiron(III) oxidation level and indicated that the two iron sites have inequivalent environments (δ1 ? 0.47 mm s-1, ΔE(Q1) ? 0.88 mm s-1; δ2 ? 0.63 mm s-1, ΔE(Q2) ? 1.20 mm s-1). Kinetics experiments provided rate constants for the reaction and revealed it to be first order in both diiron(II) complex and O2. The factors controlling the rate of formation of the blue species and its stability are discussed.
