New bioinspired alkoxo-bridged Mn2-complexes with catalase activity. Influence of bridging ligands and vacant coordination sites on catalysis

SIGNORELLA, S. R.; LEDESMA, G. N.; DRUSIN, S. I.; SCHULZ LANG, E.

Manchester

Conferencia; First European Inorganic Chemistry Conference; 2011

Comité Organizador del First EuCheMS Inorganic Chemistry Conference (RSC)

Manganese catalases (MnCAT) catalyze disproportionation of H2O2 into H2O and O2 by using a Mn2(m-O2CR)(m-O/OH/H2O)2 structural unit that cycles between the MnII2 and MnIII2 oxidation states. The use of inorganic complexes to model MnCAT is a powerful strategy that can help delineate the functional roles of the ligands and structural motif that play a key role in the catalytic mechanism; two aspects essential for the rational design of antioxidants with potential use as catalytic scavengers of peroxide for preventing oxidative stress injuries. Crystal structures of the isolated enzymes revealed that one of the Mn subsites is coordinated to a terminal water molecule, which is likely to serve as the initial substrate binding site during catalysis. Therefore, this structural feature of the enzyme has to be considered for the design of biomimetic catalysts. With this in mind, we have obtained new hexadentate asymmetric dinucleating ligands derived from 1,3-diaminopropan-2-ol which provide an alkoxo oxygen for the endogenous bridging of two metal ions, and two arms with differentiated chelating donor sets: {[(2-hydroxy-5-X-benzyl)(2-pyridylmethyl)amino][(benzyl)(2-hydroxy-X-benzyl)amino]}propan-2-ol. Upon reaction with Mn(OAc)3, these ligands afford complexes with the Mn2(m-O2CR)2(m-OR) core and an accessible coordination site on one Mn of the pair, occupied by one exogenous solvent molecule to facilitate the initial binding to the substrate. These complexes catalyze H2O2 dismutation with turnover rates influenced by solvent and acidity of the medium, and modulate the redox potential of the metal centre to employ MnII/MnIII levels during catalysis. In order to highlight the structural features that are key to control the CAT activity, kinetic and spectroscopic (EPR, ESI-MS, UV-vis) results will be discussed and compared to those of other symmetric alkoxo-bridged1,2 and asymmetric phenoxo-bridged3 Mn2-complexes.