Biomimetic oxidation of catechol employing complexes formed in situ with heterocyclic ligands and different copper(II) salts

Abstract

In the present work, catecholase activity is presented. The complexes were prepared by condensation of the organic ligand pyrazolyl L 1 –L 4 and copper(II) ion in situ. The pyrazolyl compounds L 1 –L 4 used in this study are: L 1 is (3,5-dimethyl-pyrazol-1-ylmethyl)-(4-methyl-pyridin-2-yl)-pyrazol-1-ylmethyl-amine; L 2 is 1-{4-[(3,5-dimethyl-pyrazol-1-ylmethyl)-pyrazol-1-ylmethyl-amino]-phenyl}-ethanone; L 3 is 1-{4-[(3,5-dimethyl-pyrazol-1-ylmethyl)-[1,2,4]triazol-1-ylmethyl-amino]-phenyl}-ethanone, and L 4 is 2-[(3,5-dimethyl-pyrazol-1-ylmethyl)-[1,2,4]triazol-1-ylmethyl-amino]-6-methyl-pyrimidin-4-ol, and copper ions salts Cu(II) are (Cu(CH3COO)2, CuCl2, Cu(NO3)2 and CuSO4). In order to determine factors influencing the catecholase activity of these complexes, the effect of ligand nature, ligand concentration, nature of solvent and nature of counter anion has been studied. The best activity of catechol oxidation is given by the combination formed by one equivalent of ligand L 2 and one equivalent of Cu(CH3COO)2 in methanol solvent which is equal to 9.09 µmol L−1 min−1. The Michaelis–Menten model is applied for the best combination, to obtain the kinetic parameters, and we proposed the mechanism for oxidation reaction of catecholase.