CONICET | Buscador de Institutos y Recursos Humanos

Manganese is known to be an essential element in many biological systems, and its oxidation-reduction chemistry is especially important to the electron-transfer reactions of mitochondrial superoxide dismutase, bacterial catalases and photosystem II in green plant photosynthesis.1 Catalases (CAT) and superoxide dismutases (SOD) efficiently catalyse disproportionation of intracellular O2= and O2·- and provide a vital biological defense against these toxic oxygen metabolites through a mechanism involving cyclic oxidation and reduction of the metal cofactor. In MnSOD the active site contains one penta-coordinated Mn ion in a N3O2 environment,2-3 whereas MnCAT catalyze the disproportionation of H2O2 by using a bis(m-oxo(hydroxo)-m-carboxylate dimanganese structural unit as the active site.4-5 Owing to their potential application as therapeutic agents against oxidative stress various mononuclear Mn complexes have been selected for pharmaceutical uses as O2·- scavengers,6-8 and a number of dinuclear manganese-based complexes has been investigated as low molecular weight catalytic scavengers of H2O2.9-14 Particularly attractive are complexes exhibiting combined CAT and SOD activity because they offer a possible therapeutic advantage arising from their multiple mechanism of action.15-16 Among these complexes are those of the Mn-salen17 series (salen = 1,2-bis(salicylidenamino)ethane)) that have been tested as catalytic antioxidants in preclinical trials. It is known that the flexibility of the ligand, the metal environment and the coordination geometry affect the electronic properties of the metal centre and, hence, the catalytic activity of the resulting complex. Here, we report the synthesis, structure, properties and combined SOD and CAT activity of two novel manganese complexes [Mn(salbutO)N3] and [Mn(salbutO)SCN] obtained with the asymmetric Schiff base ligand 1,4-bis(salicylidenamino)butan-2-ol (H3salbutO) as a means to evaluate the effect of the length and symmetry of the aliphatic unit on the properties and activity of Mn complexes.