Theoretical Evidence of Electrophilic Superoxides in Models of Oxyhemocyanin/Oxytyrosinase Active Sites. Influence of the Ligand's Arrangement

Abstract

The most widely accepted mechanism for the molecular dioxygen bioactivation by dicopper monooxidases, or their biomimetic models, in arene oxidation relies on a direct electrophilic oxygen transfer from an intermediate μ-η2:η2 peroxo dicopper complex into a substrate C−H bond. However, the electrophilic character of the activated form of dioxygen in such complexes has never been established. Extended Huckel calculations on a set of (Cu+(Im-H)3)2−O2 complexes, taken as model of oxyhemocyanin and oxytyrosinase active sites, are reported for both eclipsed and staggered arrangements of the imidazole ligands. The results obtained indicate such two conformations to be isoenergetic. In both situations, the molecular electrostatic potential maps show two striking features: (i) the plane perpendicular to the O−O bond and containing the two metal ions exhibit, as previously shown for the staggered situation, two nucleophilic potential wells; (ii) two strongly positive regions extend from the oxygens along the O−O ...