METHANE HYDROXYLATION ON A DIIRON MODEL OF SOLUBLE METHANE MANOOXYGENASE

A concerted mechanism is proposed for the conversion of methane to met hanol on intermediate Q of soluble methane monooxygenase (sMMO), the a ctive species of which is considered to involve an Fe-2(mu-O)(2) diamo nd core. A hybrid density functional theory (DFT) method is used. Meth ane is highly activated on the dinuclear iron complex through the form ation of the Q(CH4) complex, in which a four-coordinate iron plays a c entral role in the bonding interactions between intermediate Q and met hane. An H atom abstraction via a four-centered transition state and a methyl migration via a three-centered transition state successively o ccur within the complex, leading to the formation of product methanol. The reaction pathway for the methane hydroxylation on the diiron comp lex follows the mechanism for the gas-phase reaction by the bare FeOcomplex described in a previous paper (K. Yoshizawa, Y. Shiota, and T. Yamabe, Chem. Eur. J., 3, 1160 (1997)). Our mechanism for the methane hydroxylation by sMMO is against a radical mechanism which has been w idely believed to play a role in hydrocarbon hydroxylations by cytochr ome P450.