Energetics for the oxygen rebound mechanism of alkane hydroxylation by theiron-ore species of cytochrome p450

Density-functional-theory calculational results on the reaction pathway for alkane hydroxylation by a compound I model of cytochrome P450 are discusse d. Our calculations demonstrate that the transition state for the H-atom ab straction of ethane involves a linear (Fe)O . . .H . . .C array and that th e resultant carbon radical is bound to the iron-hydroxo species. This compt ational result is partly consistent with the oxygen rebound mechanism in th at the direct H-atom abstraction by the iron-ore species takes place in the initial stages of the reaction pathway. However, the iron-hydroxo species cannot be viewed as a stable reaction intermediate in view of the energy di agram. Our results may not be consistent with the model of a free radical s pecies with a finite lifetime and barrier to displacement of the OH group f rom the iron center that is commonly assumed and typically stated for the o xygen rebound mechanism.