Tuning the redox properties and CAT/SOD activity of water soluble manganese andi ron complexes

SIGNORELLA, SANDRA; PALOPOLI CLAUDIA; DAIER, VERÓNICA; LEDESMA, GABRIELA; BELLU, SEBASTIAN

ANGRA DOS REI

Congreso; XV Brazilian Meeting on Inorganic Chemistry and II Latin American Meeting on biological Chemistry; 2010

Manganese catalases (MnCAT) and superoxide dismutases (MnSOD) deplete O2·- and O2= in cells through a ping-pong mechanism involving cyclic oxidation and reduction of the metal cofactor. To disproportionate O2·- and O2= efficiently, the reduction potential of MnSOD and MnCAT is fine-tuned to values much lower than that of the Mn3+(ac)/Mn2+(ac) couple. A number of di- and mononuclear manganese-based complexes has been investigated as low molecular weight catalytic scavengers of H2O2 and O2·-, respectively.1,2 However, only a few studies have been performed on the ability of the ligand to control the redox potential, a physical property that makes the metal ion to act as catalytic center, and are still fewer those that have explored the divergence between Mn and Fe redox potentials in bioinorganic models despite their high biological relevance.3,4 In this context, we have synthesized and evaluated the redox potential and catalytic activity of water soluble mono- and dinuclear Mn complexes with the ligands: 1,3-bis(5-SO3-salicylidenamino)propan-2-ol, 1,3-bis(5-SO3-salicylidenamino)propane and 1,5-bis(5-SO3-salicylidenamino)pentan-3-ol, and their Fe counterparts. The redox potentials were determined by cyclic, linear and square-wave voltammetry. The catalase activity was evaluated by measuring the oxygen concentration of H2O2 + catalyst mixtures with a Clark-type oxygen electrode. The SOD activity was assayed by measuring the inhibition of the photoreduction of nitro blue tetrazolium in the presence of the catalyst.   Our results show that although DE(Mn/Fe) is small (~ 100 mV, for both the mono- and dinuclear complexes), Mn complexes are much more efficient to catalyze O2= and O2·- disproportionation than the Fe analogues, and that kinetic, more than thermodynamic, factors should be responsible for the observed different activity.