Stereoelectronic factors that control the activity of biomimetic antioxidants

DAIER, V. A.; PALOPOLI, C. M.; BIAVA, H. D.; MORENO, D. M.; DE GAUDIO, M.; SIGNORELLA, S. R.

BIOCELL

Año: 2008 vol. 32 p. 57 - 57

0327-9545

Catalases (CAT) and superoxide dismutases (SOD) constitute the main line of defense of living organisms for controlling O2·- y O2=. However, exogenously administered SOD/CAT has been tested with limited success, especially because of immunogenic responses. This led to an interest in developing synthetic SOD/ CAT mimics with more favorable pharmaceutical properties. We examined the CAT/SOD activities of MnL1-2 and [Mn2L3-5(m-OAc)(m-OMe)] complexes, using 1,3-bis(5-SO3-salicyliden amino)propan-2-ol (H3L1), 1,4-bis(salicylidenamino)butan-2-ol (H3L2), 1,3-bis[(2-hydroxy-5-X-benzyl-2-methylpyridyl)amino] propan-2-ol (H3L3), 1,5-bis(5-SO3-salicylidenamino)pentan-3-ol (H3L4) and 1,5-bis[(2-hydroxy-5-X-benzyl-2-methylpyridyl) amino]pentan-3-ol (H3L5), where X = phenyl substituent. The catalase activity was determined 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. These studies reveal that (i) for MnL1-2 complexes, the ability of the ligand to act as an intramolecular base to assist electron transfer is a key factor in the SOD activity; (ii) in [MnL1-2]2 and [Mn2L3,5(m-OAc)(m-OMe)], where the metal coordination sphere is saturated by non-labile ligands, peroxide binds Mn as a terminal ligand; (iii) [Mn2L4(m-OAc)(m-OMe)] with two substitution-labile sites, employs MnIII-m-O2-MnIII and [MnIV=O]2 species for CAT activity.