Synthesis, characterization and catecholase-mimetic activity of mononuclear copper(II) aspirinate complexes

Abstract

Four mononuclear copper(II) complexes have been prepared by allowing copper(II) aspirinate to react with benzimidazole, 2-methylbenzimidazole, metronidazole or 2-methyl-5nitrobenzimidazoIe Iigands. Elemental analyses, UV-Vis, IR, EPR and magnet moment data are consistent with mononuclear square planar complexes that contain two aspirinate Iigands and two N-containing ligands to give a CuOrN, chromophore. The benzimidazole, 2-methylbenzimidazole and metronidazole complexes catalyze the oxidation of catechol to o-quinone. This reaction was monitored spectrophotometrically by following the increase in intensity of the o-quinone band at 390 nm with time. Enzyme-mimetic activity of these copper complexes was determined and expressed as micromoles of substrate per mg catalyst per min. The activities were found to be 0.314 for the benzimidazole complex, 0.0998 for the 2-methylbenzimidazole complex, and 0.129 for the metronidazole complex. In the case of the 2-methyl-5-nitrobenzimidazoIe complex the initial formation of o-quinone is very rapid; however, after 2-3 min the catalyst is poisoned and the concentration of o-quinone drops slightly and remains constant.