Effect of the basic medium on the catalase activity of phenoxo-bridged diMn(III) complexes with terminal carboxylato ligands

DISETTI, M. E.; SIGNORELLA, S.; SOLÍS, V.; LESCANO, L.; PALOPOLI, C.; GÓMEZ, G.

Florianópolis

Conferencia; 18th International Conference on Biological Inorganic Chemistry; 2017

Universidad de Santa Catarina

Inspired in the Mn2(-O2CR)(-OH/H2O/O) active site of manganese catalases (MnCAT), many diMn complexes have been tested as MnCAT mimics with potential use as catalytic scavengers of H2O2 for preventing oxidative stress damage. In protic media, the proton coupled disproportionation of H2O2 catalyzed by the diMn unit is strongly affected by pH, which in turn affects the lability of the ligands, key features of CAT activity.2 In this work, we have evaluated the effect of base on the CAT activity of a phenoxo-bridged diMn complex [Mn2L(OH)2]Na, formed by reaction of Mn(ClO4)2 with the sodium salt of 5-methyl-2-hydroxy-1,3-xylene--diamine-N,N,N?,N?-tetraacetato (Na4L), in methanol. The reaction exhibits second-order kinetics, with k = 305 M-1 min-1, and turnovers as high as 1000 mol H2O2/mol catalyst, with partial loss of activity. EPR spectra taken during catalysis show the Mn2II reduced form of the catalyst is the major species. Upon addition of 10 equiv. of base, the catalytic activity of the complex is threefold enhanced. Addition of higher amounts of base does not cause any further significant increase, suggesting that the effect of the base is tostabilize the Mn2 III oxidized catalyst, preventing ligand protonation and metal dissociation. In buffered solutions, metal dissociation is inhibited but clusters of higher nuclearity form.