Catechol oxidase activity of dicopper complexes with N-donor ligands

Abstract

The catecholase activity of two dicopper(II) complexes [Cu 2(L 1)(CF 3SO 3) 2(H 2O) 4](CF 3SO 3) 2 ( 1) and [Cu 2(L 2O)](CF 3SO 3)](CF 3SO 3) 2 ( 2) containing the ligands 1,3-bis{ N, N-bis(2-[2-pyridyl]ethyl)}aminopropane (L 1) and 1,3-bis{ N, N-bis(2-[2-pyridyl]ethyl)}amino-2-hydroxypropane (L 2OH) was studied as functional as well as structural models for the type 3 copper enzyme, catechol oxidase. The X-ray structure of 1 in solid form shows a CuCu distance of 7.840 Å, while in 2 the CuCu distance is only 3.699 Å. Complex 1 can have flexible conformations in solution while the other is being fixed by the bridging alkoxo group. The catalytic activity of the complexes 1 and 2 on the oxidation of 3,5-di- tert-butylcatechol was determined spectrophotometrically by monitoring the increase of the 3,5-di- tert-butyl- o-benzoquinone characteristic absorption at 400 nm over time in methanol saturated with O 2 at 25 °C. The complexes were able to oxidize 3,5-di- tert-butylcatechol to the corresponding o-quinone and hydrogen peroxide. A kinetic treatment of the data based on steady-state treatment and Michaelis–Menten approach was applied. Mechanisms for the catalytic reactions are proposed, which show that with complex 1 copper(I) dioxygen chemistry determines the kinetic scenario, while with complex 2 the reaction follows a Michaelis–Menten type kinetics.