The contribution of tunnelling to high values of kinetic isotope effect in aliphatic hydroxylation by a cytochrome P-450 model

High values of kinetic isotope effect (KIE), up to 21.9 ± 1.9 at 20 °C, are obtained in cyclohexane oxidation by an iron tetramesitylporphyrin (TMPFeCl)–hypochlorite system; their very sharp dependence on temperature suggests tunnelling contribution to the C–H bond cleavage step.