Quantum chemical studies on metal-oxo species related to the mechanisms of methane monooxygenase and photosynthetic oxygen evolution

During the last few years it has become possible to study enzymatic mechanisms by means of high accuracy quantum chemistry methods. In the present review, examples are given of applications of density functional theory to two mechanisms involving redox active centers. In methane monooxygenase an iron dimer complex oxidizes methane to methanol. A hydrogen abstraction mechanism is suggested involving a high-valent Fe(IV,IV) intermediate, termed Q. In Photosystem II an oxyl radical mechanism is suggested for the formation of O-2. Different models of the oxygen evolving cluster are discussed. Spin-state considerations are emphasized.