New functional models for catechol oxidases

The new dinuclear copper(II) complexes [Cu-2(L1)(mu-OAc)](ClO4)(2). CH3CN ( 1), [Cu-2(L2)(CH3CN)(2)](ClO4)(4). C2H5OH (2), [Cu-2(L3)(2)(CH3CN)(2)](PF6) (2) (3) and [Cu-2(L4)(2)](PF6)(2). CH2Cl2 (4) were prepared with the ligand s N,N,N',N'-tetrakis((N-2-hydroxy-ethyl)-2-benzimidazolylmethyl)-2-hydroxy- 1,3-diaminopropane HL1, N,N,N',N'-tetrakis (2-methylimidazolyl)-2-hydroxy-1 ,3-diaminopropane HL2, (2-pyridylmethyl)(1-hydroxypropyl)amine HL3 and (2-h ydroxybenzyl)(N,N-dimethylpropyl)amine HL4. All complexes were characterize d by X-ray structure determination, revealing dinuclear cations and perchlo rate or hexafluorophosphate counter ions. In the complex cations the two co pper(II) atoms show different coordination spheres with N4O, N3O2 or N2O2 d onor sets and different bridging systems. The Cu ... Cu distances vary from 2.918(2) to 4.756(2) Angstrom. The catalytic performance of the oxidation of 3,5-di-tert-butylcatechol to quinone was studied using UV-Vis absorption spectra methods. Complex 3 exhibits the highest activity with a turnover n umber of 32 h(-1) while the other compounds show lower rates of oxidation. A kinetic treatment on the basis of the Michaelis-Menten model was applied. (C) 2000 Elsevier Science S.A. All rights reserved.