Resonance Raman spectroscopy, methane

Costas et al. have reported spectroscopic evidence for an Fe Fe complex that can be considered a structural model for the putative Fe Fe (/x-0)2 core of methane monooxygenase intermediate The synthetic complex was prepared at —80 °C in CH2CI2 by decay of a mononuclear low-spin Fe peroxo precursor. The Mossbauer spectra showed that all iron in the sample is intermediate spin (5 = 1) Fe, but the data were compatible with either a mononuclear site or a weakly coupled ( J <5cm ) symmetric dimer. Combination of the Mossbauer technique with resonance Raman and EXAFS spectroscopies provided evidence for a bis-/x-oxo bridged diiron(IV) complex. The complex of Costas et al however, is not an electronic model for intermediate Q, as the latter contains high-spin Fe sites. 

A combination of spectroscopies including Mossbauer and resonance Raman were used to identify the presence of a diiron-oxo cluster with properties similar to those identified in ribonucleotide reductase (RB2) and methane monooxygenase (MMO). These enzymes all share the ability to break unactivated carbon-hydrogen bonds with a nonheme diiron cluster cofactor. Fatty acid desaturation and methane oxidation require a two-electron reduction of the diiron cluster to initiate the oxygen activation reaction. Identification of a diiron cluster in the desaturase allowed us to propose a consensus diiron-oxo binding motif consisting of two repeats of (D/E)EXXH. 

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