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

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Title: Insights into the P-to-Q conversion in the catalytic cycle of methane monooxygenase from a synthetic model system.
Authors: Genqiang Xue1, Fiedler, Adam T.1, Martinho, Marlene2, Münck, Eckard2 emunck@cmu.edu, Que Jr, Lawrence1 larryque@umn.edu
Source: Proceedings of the National Academy of Sciences of the United States of America. 12/30/2008, Vol. 105 Issue 52, p20615-20620. 6p. 4 Diagrams, 1 Chart, 5 Graphs.
Subjects: Methane, Monooxygenases, Oxygenases, Organic compounds, Physical & theoretical chemistry
Abstract: 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(lll) intermediate P gives rise to the diiron(IV) intermediate Q with an Fe2(µ-O)2 diamond core, which oxidizes methane to methanol. As a model for this conversion, (µ-oxo)-diiron(lll) 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 ESl-MS at m/z 1,399, corresponding to the {[Fe2O3L2H](OTf)2}+ ion in which 1 oxygen atom derives from 1 and the other two originate from H2O2. 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-FeIV = O core for 2. Protonation of 2 results in the loss of H2O 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(lll) unit can transform into an [FeIV2(µ-O)2] core. [ABSTRACT FROM AUTHOR]
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Abstract: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(lll) intermediate P gives rise to the diiron(IV) intermediate Q with an Fe2(µ-O)2 diamond core, which oxidizes methane to methanol. As a model for this conversion, (µ-oxo)-diiron(lll) 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 ESl-MS at m/z 1,399, corresponding to the {[Fe2O3L2H](OTf)2}+ ion in which 1 oxygen atom derives from 1 and the other two originate from H2O2. 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-FeIV = O core for 2. Protonation of 2 results in the loss of H2O 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(lll) unit can transform into an [FeIV2(µ-O)2] core. [ABSTRACT FROM AUTHOR]
ISSN:00278424
DOI:10.1073/pnas.0808512105