Imidazolate-bridged dicopper(II) and copper(II)-zinc(II) complexes of macrocyclic ligand with methylimidazol pendants: Model study of copper(II)-zinc(II) superoxide dismutase

Two new homo- and hetero-dinuclear complexes, [Cu2L(im)](ClO4)(3)center dot 4H(2)O (1) and [CuZnL(im)] (ClO4)(3)center dot 4H(2)O (2) (where Im=1H-1midazole and L=3,6, 9, 16, 19, 22-hexaaza-6, 19-bis(1H-imidazol-4-ylmethyl)tricycle[22,2,2,2(11,14)]triaconta-1, 11, 13, 24, 27, 29-hexaene) were synthesized and characterized as model compounds for the active site of copper(11)-zinc(II) superoxide dismutase (Cu2Zn2-SOD). X-ray crystal structure analysis revealed that the metal centers in both complexes exhibit distorted trigonal-bipyramid coordination geometry and the Cu center dot center dot center dot Cu and Cu center dot center dot center dot Zn distances are both 6.02 angstrom. Magnetic and ESR spectral measurements of 1 showed antiferromagnetic exchange interactions between the imidazolate-bridged Cu(II) ions. The ESR spectrum of 2 displays typical signals of mononuclear Cu(II) complex, demonstrating the formation of heterodinuclear complex 2 rather than a mixture of homodinuclear Cu(II)/Zn(II) complexes. pH-dependent ESR and UV-visible spectral measurements manifest that the imidazolate exists as a bridging ligand from pH 6 to 11 for both complexes. The IC50 values of 1.96 and 1.57 mu M [per Cu(II) ion] for 1 and 2 suggest that they are good models for the Cu2Zn2-SOD. (C) 2009 Elsevier Inc. All rights reserved.