Series of Mn Complexes Based on N-Centered Ligands and Superoxide - Reactivity in an Anhydrous Medium and SOD-Like Activity in an Aqueous Medium Correlated to MnII/MnIII Redox Potentials
Résumé
Two crystal structures are described in this article: (a) the structure of a monomeric MnII complex with the tridentate N-centered N3 ligand tris[(1-methyl-2-imidazolyl)methyl]amine (TMIMA) ([MnII(TMIMA)2]2+); and (b) the structure of a monomeric MnIII complex with the tridentate N-centered N2O ligand 2-[(1-methyl-2-imidazolyl)methyl]aminophenolate (PI-)2 ([MnIII(PI)2]+) (5). The latter was isolated both in the MnII and in the MnIII state, although only MnIII crystals were successfully grown. They are part of a series of Mn complexes prepared as SOD mimics, namely [Mn(BMPG)(H2O)]+ (2) BMPG = N,N-bis[(6-methyl-2-pyridyl)methyl]glycinate, [Mn(IPG)(MeOH)]+ (3) IPG = N-[(1-methyl-2-imidazolyl)methyl]-N-(2-pyridylmethyl)glycinate, [Mn(BIG)(H2O)2]+ (4) BIG = N,N-bis[(1-methyl-2-imidazolyl)methyl]glycinate. The reactivity of MnII complexes 1 and 2 in an anhydrous medium is described and compared to that of complexes 3 and 4, the data for which was previously published. The cyclic voltammograms of the whole complex series were recorded in an aqueous medium (collidine buffer). Their SOD-like activities were estimated by the McCord-Fridovich test (IC50 with 22 μM cytc FeIII: 1.6 ± 0.1 μMol L-1 for 1, 1.2 ± 0.5 μmol L-1 for 2, 3.0 ± 0.2 μmol L-1 for 3, 3.7 ± 0.6 μmol L-1 for 4, 0.8 ± 0.1 μmol L-1 for 5). IC50 values were converted into the corresponding kinetic constant kMcCF values. A linear correlation between Ea and log(kMcCF) was obtained, indicating that in this series the conversion to MnIII is probably the rate-limiting step. This is of substantial importance for further Mn-SOD mimic design in this series. (\textcopyright Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)
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