Model for type 2 Cu(II) oxidase: structure reactivity correlation studies on some mononuclear Cu(X-Salmeen)Im complexes, where X = H, Cl and Im = Imidazole: molecular association, electronic spectra and ascorbic oxidation

The compounds [Cu(Salmeen)(Im)(H2O)](ClO4) (1) and [Cu(Cl-Salmeen)(Im)(ClO4)] (2), where Salmeen = N,N-dimethyethyl-enesalicylidenamine, were synthesized and characterized. The Copper(II) metal in both complexes [Cu(Salmeen)Im(H2O)](ClO4) (1) and [Cu(Cl-Salmeen)(Im)(ClO4)] (2) possesses square pyramidal geometry, fulfilling the four corners of the square base with the Salmeen moiety and imidazole ligand, while the water and perchlorate anions occupy the axial position of the respective complexes. The weak inter and intra-dimeric H-bonding interactions mediated through heterocyclic nitrogens of imidazole, perchlorate anions and pi-pi stacking interactions between the aromatic rings and imidazole rings form an interesting supramolecular association. The electronic spectral studies indicate that the existence of weak apical coordination by water and perchlorate ions found in the solid state, is replaced by strong coordinating solvents such as DMSO in solution and thereby the opening of an active site for catalytic reaction is demonstrated with the reduction by the ascorbate dianion (Asc(2-)) as a model for type-2 Cu(II) ascorbate oxidase. The self-assembled molecular association that favors the electron transfer redox process is demonstrated using UV-Vis electronic spectral studies. (C) 2004 Elsevier Ltd. All rights reserved.