Kinetics and Mechanisms of Cu^I/O₂ Reactions

Abstract

Copper proteins are found in each class of enzymes engaged in the interaction with dioxygen. Typical examples are lacease¹ as an electron transfer oxidase, tyrosinase² as an oxygenase and hemocyanin as an oxygen carrier³. Direct interaction of O₂ with the reduced enzyme is essential in every case. Unstable dioxygen adducts have long been postulated in enzymatic and low-molecular reaction schemes. They were, however, not really backed by direct experimental observation with the single exceptions of hemocyanin and later tyrosinase⁴. The situation has dramatically changed with the identification and characterization, first by spectroscopic methods, of pseudoreversible dioxygen adducts or peroxo complexes to low-molecular Cu^I compounds by Karlin and coworkers^5,6. Many speculations have been put to an end upon the structural X-ray characterization of a trans-p-peroxo bridged dicopper(II) complex⁷ [Cu(L]₂O ²⁺₂ (L = tris[(2-pyriaVl)methyl]amine) and a μ-η²:η² peroxo complex [Cu(L’)]₂ O₂ ⁸ (L’ = hydrodotns(3,5-diiopropyl-1-pyrazolyl)borate). Most recently, the η²:η²bmdingmode also has been reported tor oxyhemocyanin⁹.