Synthesis, characterization and antioxidant activity of water soluble MnIII complexes of sulphonato-substituted Schiff base ligands

MORENO DIEGO; DAIER VERÓNICA; PALOPOLI CLAUDIA; TUCHAGUES JEAN PIERRE; SIGNORELLA SANDRA

JOURNAL OF INORGANIC BIOCHEMISTRY

ELSEVIER SCIENCE INC

Año: 2010 vol. 104 p. 496 - 502

0162-0134

Two new MnIII complexes Na[Mn(5-SO3-salpnOH)(H2O)] Á 5H2O (1) and Na[Mn(5-SO3-salpn)(MeOH)] Á 4H2O (2) (5-SO3-salpnOH = 1,3-bis(5-sulphonatosalicylidenamino)propan-2-ol, 5-SO3-salpn = 1,3-bis(5- sulphonatosalicylidenamino)propane) have been prepared and characterized. Electrospray ionization- mass spectrometry, UV–visible and 1H NMR spectroscopic studies showed that the two complexes exist in solution as monoanions [Mn(5-SO3-salpn(OH))(solvent)2]À, with the ligand bound to MnIII through the two phenolato-O and two imino-N atoms located in the equatorial plane. The E1/2 of the MnIII/MnII couple (À47.11 (1) and À77.80 mV (2) vs. Ag/AgCl) allows these complexes to efficiently catalyze the dismuta- tion of OÅÀ , with catalytic rate constants 2.4  106 (1) and 3.6  106 (2) MÀ1 sÀ1, and IC50 values of 1.14 (1) 2 and 0.77 (2) lM, obtained through the nitro blue tetrazolium photoreduction inhibition superoxide dis- mutase assay, in aqueous solution of pH 7.8. The two complexes are also able to disproportionate up to 250 equivalents of H2O2 in aqueous solution of pH 8.0, with initial turnover rates of 178 (1) and 25.2 (2) mM H2O2 minÀ1 mMÀ1 catalystÀ1. Their dual superoxide dismutase/catalase activity renders these com- pounds particularly attractive as catalytic antioxidants.