Catechol oxidase activity of dicopper complexes with N-donor ligands

The catecholase activity of two dicopper(II) complexes [Cu-2(L-1)(CF3SO3)(2)(H2O)(4)](CF3SO3)(2) (1) and [Cu-2((LO)-O-2)](CF3SO3)](CF3SO3)(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 ((LOH)-O-2) 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 Angstrom, while in 2 the Cu-Cu distance is only 3.699 Angstrom. 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 degreesC. 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(l) dioxygen chemistry determines the kinetic scenario, while with complex 2 the reaction follows a Michaelis-Menten type kinetics. (C) 2003 Elsevier B.V. All rights reserved.