Recent Research Developments
The initial step in oxygen activation catalyzed by metalloproteins typically involves the the formation of a metal O2 adduct, often proposed to be a metal-superoxo species. For nonheme diiron enzymes, such a transient species has been proposed but not yet observed, not even for synthetic models. In a recent article published in Proc. Natl. Acad. Sci. U.S.A. (2005, 102, 5340), postdoctoral associate Xiaopeng Shan and Professor Lawrence Que, Jr. reported the successful trapping of the first example of a diiron(II,III) superoxo species in the reaction of [Fe2(μ-OH)2(6-Me3-TPA)2]2+ (6-Me3-TPA = tris(6-methyl-2-pyridylmethyl)amine) with O2 in CH2Cl2 at -80 °C prior to the formation of the previously characterized [Fe2(μ-O)(μ-1,2-O2)(6-Me3-TPA)2]2+ peroxo intermediate. This superoxo species has been characterized by resonance Raman spectroscopy to show its ν(O-O) at 1310 cm-1 with a -71 cm-1 18O isotope shift. A doublet peak pattern for the 16O18O isotopomer of this species in mixed-isotope Raman experiments strongly suggests that the superoxide ligand is bound end-on. Further studies revealed that this superoxo species, unlike the subsequent peroxide, is capable to oxidize 2,4-di-tert-butylphenol through a proton coupled electron transfer mechanism.
Next scheduled update: June 8th, 2005.
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