Insights into the P-to-Q conversion in the catalytic cycle of methane monooxygenase from a synthetic model system

Genqiang Xue, Adam T. Fiedler, Marlène Martinho, Eckard Münck, Lawrence Que

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For the catalytic cycle of soluble methane monooxygenase (sMMO), it has been proposed that cleavage of the O-O bond in the (μ-peroxo)diiron(III) intermediate P gives rise to the diiron(IV) intermediate Q with an Fe 2(μ-O)2 diamond core, which oxidizes methane to methanol. As a model for this conversion, (μ-oxo)-diiron(III) complex 1 ([FeIII2(μ-O)(μ-O2H3)(L) 2]3+, L = tris(3,5-dimethyl-4-methoxypyridyl-2-methyl) amine) has been treated consecutively with one eq of H2O2 and one eq of HClO4 to form 3 ([FeIV2(μ-O) 2(L)2]4+). In the course of this reaction a new species, 2, can be observed before the protonation step; 2 gives rise to a cationic peak cluster by ESI-MS at m/z 1,399, corresponding to the {[Fe 2O3L2H](OTf)2}+ ion in which 1 oxygen atom derives from 1 and the other two originate from H 2O2. Mössbauer studies of 2 reveal the presence of two distinct, exchange coupled iron(IV) centers, and EXAFS fits indicate a short Fe-O bond at 1.66 Å and an Fe-Fe distance of 3.32 Å. Taken together, the spectroscopic data point to an HO-FeIV-O-Fe IV = O core for 2. Protonation of 2 results in the loss of H 2O and the formation of 3. Isotope labeling experiments show that the [FeIV2(μ-O)2] core of 3 can incorporate both oxygen atoms from H2O2. The reactions described here serve as the only biomimetic precedent for the conversion of intermediates P to Q in the sMMO reaction cycle and shed light on how a peroxodiiron(III) unit can transform into an [FeIV2(μ-O)2] core.

Original languageEnglish (US)
Pages (from-to)20615-20620
Number of pages6
JournalProceedings of the National Academy of Sciences of the United States of America
Issue number52
StatePublished - Dec 30 2008


  • Diiron(IV)
  • Iron-oxo
  • Mössbauer spectroscopy
  • Nonheme
  • Oxygen activation


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