Abstract: Electronic properties of superoxide dismutase(SOD) mimetics, the water-insoluble imidazolate-bridged dinuclear Cu(Ⅱ) complex, {[Cu(L)(H₂O)(β-CD)]₂(im)}³⁺, where L is 4-(4’-tert-butyl)benzyl-diethylenetriamine, β-CD is β-cyclodextrin and im is imidazolate, and its guanidinium-containing derivatives were studied with semi-expire PM3 and ab initio DFT/B3LYP methods. The analysis of charge distribution and bond characters for all studied systems were performed by using the Natural Bond Orbital(NBO) theory. The present calculated results show that the combination of the central Cu ion in the complex with water molecule is weak. It is possibly occurred that the water molecule is substituted by the superoxide radical anion in the catalytic reaction. β-Cyclodextrin linked to the guanidine causes more positive charge localizing at the central Cu cation of {[Cu(L)(H₂O)(β-GCD)]₂(im)}³⁺, which is favorable to catalyze the dismutation reaction. The combination of Cu ion in the complexes with the ligand N atom linked to two pentagons is much weaker than other ligands N atoms around the central Cu ion of these complexes. The structures of spin quimtuplet state of {[Cu(L)(OOH)(β-CD)]₂(im)}³⁺ and {[Cu(L)(OOH)(β-GCD)]₂(im)}⁵⁺ are more stable than those of spin singlet states of these complexes. Additionally, the imidazolate-bridge localized at the middle of two central Cu ions in these complexes is helpful to stabilize these mimetic complexes.

Key words: MP3 and DFT/B3LYP method, SOD mimetics, NBO theory, Guanidine