Kinetic and thermodynamic parameters of copper-dioxygen interaction with different oxygen binding modes

Kinetic and thermodynamic parameters for metal ion-O-2 interaction have been obtained for a variety of copper(I) complexes with different binding modes for dioxygen. In general, favorable binding enthalpies of up to 80 kJ mol(-1) are compensated by strongly negative reaction entropies up to -220 J K-1 mol(-1), restricting the range of overall stabilities. Sequential formation of superoxo and peroxo complexes, as well as concomitant formation of eta(1):eta(1) and eta(2):eta 2 mu-peroxo complexes has been established by low-temperature stopped-flow experiments. In several cases, pseudoreversible binding of dioxygen is followed by an irreversible oxidation of the organic ligand. A recent result is the identification of a rapid equilibrium between an eta(2):eta(2) mu-peroxo complex and the isomeric bis-mu-oxo compound with broken O-O bond which maybe fundamental to several O-2 dependent redox enzymes.