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Title: Mechanism of the methane {r{underscore}arrow} methanol conversion reaction catalyzed by methane monooxygenase: A density functional study

Abstract

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 tomore » 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.« less

Authors:
; ; ;
Publication Date:
Research Org.:
Emory Univ., Atlanta, GA (US)
OSTI Identifier:
20000103
Resource Type:
Journal Article
Journal Name:
Journal of the American Chemical Society
Additional Journal Information:
Journal Volume: 121; Journal Issue: 31; Other Information: PBD: 11 Aug 1999; Journal ID: ISSN 0002-7863
Country of Publication:
United States
Language:
English
Subject:
03 NATURAL GAS; 09 BIOMASS FUELS; METHANE; METHANOL; OXIDATION; BIOSYNTHESIS; CHEMICAL REACTION KINETICS; ENZYMES; CATALYSIS; IRON COMPOUNDS; MATHEMATICAL MODELS

Citation Formats

Basch, H., Mogi, K., Musaev, D.G., and Morokuma, K. Mechanism of the methane {r{underscore}arrow} methanol conversion reaction catalyzed by methane monooxygenase: A density functional study. United States: N. p., 1999. Web. doi:10.1021/ja9906296.
Basch, H., Mogi, K., Musaev, D.G., & Morokuma, K. Mechanism of the methane {r{underscore}arrow} methanol conversion reaction catalyzed by methane monooxygenase: A density functional study. United States. doi:10.1021/ja9906296.
Basch, H., Mogi, K., Musaev, D.G., and Morokuma, K. Wed . "Mechanism of the methane {r{underscore}arrow} methanol conversion reaction catalyzed by methane monooxygenase: A density functional study". United States. doi:10.1021/ja9906296.
@article{osti_20000103,
title = {Mechanism of the methane {r{underscore}arrow} methanol conversion reaction catalyzed by methane monooxygenase: A density functional study},
author = {Basch, H. and Mogi, K. and Musaev, D.G. and Morokuma, K.},
abstractNote = {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.},
doi = {10.1021/ja9906296},
journal = {Journal of the American Chemical Society},
issn = {0002-7863},
number = 31,
volume = 121,
place = {United States},
year = {1999},
month = {8}
}