Functional superoxide dismutase mimics.: Structural characterization and magnetic exchange interactions of copper(II)-N-substituted sulfonamide dimer complexes

Dinuclear copper(II) complexes with N-substituted sulfonamide ligands as superoxide dismutase (SOD) mimics have been investigated. The new N-(thiazol-2-yl)toluenesulfonamide (Htz-tol) and N-(thiazol-2-yl)naphthalenesulfonamide (Htz-naf) ligands have been prepared and structurally characterized. The complexes derived from these ligands, [Cu-2(tz-tol)(4)] (1) and [Cu-2(tz-naf)(4)] (2), have been synthesized, and their crystal structure, magnetic properties, and EPR spectra were studied in detail. In both compounds the metal centers are bridged by four nonlinear triatomic NCN groups. The coordination geometry of the coppers in the dinuclear entity of 1 and 2 is distorted square planar with two N-thiazole and two N-sulfonamido atoms. Magnetic susceptibility data show a strong antiferromagnetic coupling, with -2J = 121.3 cm(-1) for compound 1 and -2J = 104.3 cm(-1) for compound 2. The EPR spectra of the polycrystalline samples of compounds 1 and 2 have been measured at the X- and Q-band frequencies at different temperatures. Above 20 K the spectra are characteristic of S = 1 species with zero-field splitting parameter D = 0.230 cm(-1) for compound 1 and 0.229 cm(-1) for compound 2. The EPR parameters are discussed in terms of the known binuclear structures. The complexes exhibit high SOD activity, as shown by the low IC50 values obtained with the xanthine/xanthine oxidase/NBT assay: 0.13 muM for compound 1; 0.17 muM for compound 2.