A Theoretical Study of Dioxygen Activation on the Dicopper Enzyme Model

Abstract

Abstract Dioxygen activation on the dicopper enzyme model was studied using fragment molecular orbital (FMO), Walsh-diagram, and molecular orbital overlap population (MOOP) analyses within the framework of the extended Hückel method. A dicopper peroxo model complex with a μ-η2 : η2-O2 binding mode is distorted to a corresponding dioxo complex with a Cu2(μ-O)2 diamond core along an assumed reaction coordinate describing 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 πg* orbitals of dioxygen begin with two electrons, in the early O2 binding stages two other electrons are effectively transferred from the copper d-block orbitals to O2. Qualitative calculations show that O–O bond cleavage should proceed with no cost of activation energy on the dicopper active site of actual enzyme systems.