A THEORETICAL-STUDY OF DIOXYGEN ACTIVATION ON THE DICOPPER ENZYME MODEL

Dioxygen activation on the dicopper enzyme model was studied using fra gment molecular orbital (FMO), Walsh-diagram, and molecular orbital ov erlap population (MOOP) analyses within the framework of the extended Huckel method. A dicopper peroxo model complex with a mu-eta(2):eta(2) -O-2 binding mode is distorted to a corresponding dioxo complex with a Cu-2(mu-O)(2) diamond core along an assumed reaction coordinate descr ibing O-O bond cleavage. FMO and Walsh-diagram analyses have clarified the bonding and orbital interactions between the dicopper active site and dioxygen. While the pi(g) orbitals of dioxygen begin with two el ectrons, in the early O-2 binding stages two other electrons are effec tively transferred from the copper d-block orbitals to O-2. Qualitativ e calculations show that O-O bond cleavage should proceed with no cost of activation energy on the dicopper active site of actual enzyme sys tems.