Chapter 13: Theoretical Studies of O–O and H–H Bond Formation in Enzymes

In this review, computational studies of water oxidation and reversible H–H bond formation in enzymes are described. These types of studies, using density functional theory, have been performed the past 10–15 years with a gradually increased understanding of these processes. For water oxidation in photosystem II, a mechanism has been reached with good agreement for all observations made, including structural ones. The O–O bond is suggested to be formed between a terminal oxygen radical in the center of the OEC and a bridging oxo-ligand. For H–H bond cleavage in NiFe-hydrogenase and H₂ bond cleavage in FeFe-hydrogenases, a similar level of understanding has been obtained. For both these systems, unusually low oxidation states, Ni(i) and Fe(i), respectively, play important roles.