Catecholase activity of mononuclear copper(II) complexes of tridentate 3N ligands in aqueous and aqueous micellar media: Influence of stereoelectronic factors on catalytic activity

Abstract

A series of mononuclear copper(II) complexes of the type [Cu(L)Cl2] 1–6, where L is a tridentate 3 N ligand such as N-methyl-N′-(pyrid-2-ylmethyl)ethylenediamine (L1), N-ethyl-N′-(pyrid-2-ylmethyl)ethylenediamine (L2), N-phenyl-N′-(pyrid-2-ylmethyl)ethylenediamine (L3), N,N-dimethyl-N′-(pyrid-2-ylmethyl)ethylenediamine (L4), N,N-diethyl-N′-(pyrid-2-ylmethyl)-ethylenediamine (L5) and N-methyl-N′-(pyridin-2-ylmethyl)benzene-1,2-diamine (L6), has been isolated and studied as functional models for catechol oxidase enzymes in different aqueous micellar media. The X-ray crystal structures of 2 and 5 contain a CuN3Cl2 chromophore with a trigonal bipyramidal based coordination geometry. Interestingly, all the complexes form cationic [Cu(L)(DBC)(H2O)]+ adduct species in which DBC2− acts as a monodentate ligand, and the adduct species interacts strongly with anionic SDS micelles. The rates of the oxygenase reaction follow the trend SDS > TX-100 ∼ water > CTAB, revealing that the rate of the reaction in micellar media are higher than those in aqueous solution and that the nature of biomimetic microenvironments of the micellized copper(II) catalyst and also the ligand stereoelectronic factors like donor atom basicity and steric bulk of ligand N-alkyl substituents, determine the catecholase-like activity.