Mechanism of the methane {r{underscore}arrow} methanol conversion reaction catalyzed by methane monooxygenase: A density functional study
Journal Article
·
· Journal of the American Chemical Society
The hybrid density functional (DFT) method B3LYP was used to study the mechanism of the methane hydroxylation reaction catalyzed by a non-heme diiron enzyme, methane monooxygenase (MMO). The key reactive compound Q of MMO was modeled by (NH{sub 2})(H{sub 2})Fe({micro}-O){sub 2}({eta}{sup 2}-HCOO){sub 2}Fe(NH{sub 2})(H{sub 2}O), (1). The reaction is shown to take place via a bound-radical mechanism and an intricate change of the electronic structure of the Fe core is associated with the reaction process. Starting with (1), which has a diamond-core structure with two Fe{sup IV} atoms, L{sub 4}Fe{sup IV}({micro}-O){sub 2}Fe{sup IV}L{sub 4}, the reaction with methane goes over the rate-determining H-abstraction transition state to reach a bound-radical intermediate, L{sub 4}Fe{sup IV}({micro}-O)({micro}-OH({center{underscore}dot}{center{underscore}dot}{center{underscore}dot}CH{sub 2}))Fe{sup III}L{sub 4}, which has a bridged hydroxyl ligand interacting weakly with a methyl radical and is in an Fe{sup III}-Fe{sup IV} mixed valence state. This short-lived intermediate easily rearranges intramolecularly through a low barrier at transition state for addition of the methyl radical to the hydroxyl ligand to give the methanol complex, L{sub 4}Fe{sup III}(OHCH{sub 3})({micro}-O)Fe{sup III}L{sub 4}, which has an Fe{sup III}-Fe{sup III} core. The barrier of the rate-determining step, methane H-abstraction, was calculated to be 19 kcal/mol. The overall CH{sub 4} oxidation reaction to form the methanol complex, (1) + CH{sub 4}{r{underscore}arrow} L{sub 4}Fe{sup III}(OHCH{sub 3})-({micro}-O)Fe{sup III}L{sub 4}, was found to be exothermic by 39 kcal/mol.
- Research Organization:
- Emory Univ., Atlanta, GA (US)
- OSTI ID:
- 20000103
- Journal Information:
- Journal of the American Chemical Society, Journal Name: Journal of the American Chemical Society Journal Issue: 31 Vol. 121; ISSN JACSAT; ISSN 0002-7863
- Country of Publication:
- United States
- Language:
- English
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