Theoretical study of the biologically important dioxo diiron diamond core structures

Density functional theory calculations were used to investigate synthetic complexes with diiron dioxo diamond cores and models for intermediates in the catalytic cycle of methane monooxygenase (MMO). The synthetic complexes share an antiferromagnetically coupled diiron dioxo/hydroxo diamond core structure with the oxidized and reduced intermediates (H-ox and H-red, respectively) of MMO. The DFT (B3P86) calculations on model complexes of the synthetic models, with ferromagnetic coupling, reproduce the crystal structure data to within 0.05 angstrom and 5 degrees for the diamond core parameters. The crystal structures of H-ox extracted from two different bacteria (Bath and OB3b) indicate that H-ox has either two bridging hydroxy ligands or one hydroxy and one water bridge. The B3P86 calculations strongly suggest that both bridging ligands in H-ox are hydroxy groups. The carboxylate shift established in the crystal structures of H-red was calculated to be a minimum at the BP86 level of theory.