Decomposition of reactive oxygen species by copper(II) bis(1-pyrazolyl)methane complexes

Two bis(1-pyrazolyl)alkane ligands, bis(3,5-dimethyl-1-pyrazolyl)methane and bis(4-iodo-3,5-dimethyl-1-pyrazolyl)methane, and their copper(II) complexes, bis(3,5-dimethyl-1-pyrazolyl)methanedinitratocopper(II) CuL₁(NO₃)₂] and bis(4-iodo-3,5-dimethyl-1-pyrazolyl)methanedinitratocopper(II) CuL₂(NO₃)₂]·2H₂O, were prepared. Physiochemical properties of the copper(II) complexes were studied by spectroscopic (UV–vis, IR, EPR) techniques and cyclic voltammetry. Spectroscopic analysis revealed a 1:1 stoichiometry of ligand:copper(II) ion and a bindentate coordination mode for the nitrate ions in both of the complexes. According to experimental and theoretical ab initio data, the copper(II) ion is located in an octahedral hexacoordinated environment. Both complexes were able to catalyze the dismutation of superoxide anion () (pH 7.5) and decomposition of H₂O₂ (pH 7.5) and peroxynitrite (pH 10.9). In addition, both complexes exhibited superoxide dismutase (SOD) like activity toward extracellular and intracellular reactive oxygen species produced by activated human neutrophils in whole blood. Thus, these complexes represent useful SOD mimetics with a broad range of antioxidant activity toward a variety of reactive oxidants.