Synthesis, structural and spectroscopic characterization and biomimetic properties of new copper, manganese, zinc complexes: Identification of possible superoxide-dismutase mimics bearing hydroxyl radical generating/scavenging abilities

A series of Cu(II), Zn(II) and Mn(II) coordination compounds has been synthesized by reaction of the corresponding metal salts and pyrazolyl-based ligands, i.e. the neutral 1-(2-(4-((2,2,2-tri(1H-pyrazol-1-yl)ethoxy)methyl)benzyloxy)-1,1-di(1H-pyrazol-1-yl)ethyl)-1H-pyrazole {p-C6H4[CH2OCH2C(pz)3]2, (L1), and the anionic hydridotris(3-phenyl-5-methylpyrazolyl)borate (L2)−, bis(pyrazolyl)acetate (L3) and bis(3,5-dimethylpyrazolyl)acetate (L4)−: the species [L1(CuCl2)2] (1), [L1(Cu(OAc)2)2] (2), [L1(Zn(OAc)2)2] (3), [(CuCl(L2)(HpzPh,Me)] (4), [Mn(L3)2]·2H2O, (5), [ZnCl(L3)(imH)]·MeOH [CuCl(L4)(imH)]·2H2O (7) have been obtained (HpzPh,Me=3-phenyl-5-methylpyrazole, imH=imidazole). Complexes 1 and 4 have been structurally characterized, also using less conventional powder diffraction methods. The superoxide scavenging activity has been characterized by indirect assays including EPR analysis. All complexes exhibit superoxide scavenging activity with IC50 in the μM range and they protect against the oxidative action of peroxynitrite in different ways. 1, 4 and 7 exert both an anti- and pro-oxidant effect depending on their concentration as evaluated by EPR and fluorescence methods. The pro-oxidative effects are absent in Zn(II) and Mn(II) complexes.