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

Abstract

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 η 1: η 1 and η 2: η 2 μ-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 η 2: η 2 μ-peroxo complex and the isomeric bis-μ-oxo compound with broken OO bond which may be fundamental to several O 2 dependent redox enzymes.