Series of Mn Complexes Based on <i>N</i>‐Centered Ligands and Superoxide – Reactivity in an Anhydrous Medium and SOD‐Like Activity in an Aqueous Medium Correlated to Mn^II/Mn^III Redox Potentials

Abstract

Abstract Two crystal structures are described in this article: (a) the structure of a monomeric Mn II complex with the tridentate N ‐centered N 3 ligand tris[(1‐methyl‐2‐imidazolyl)methyl]amine (TMIMA) ([Mn II (TMIMA) 2 ] 2+ ); and (b) the structure of a monomeric Mn III complex with the tridentate N ‐centered N 2 O ligand 2‐{[(1‐methyl‐2‐imidazolyl)methyl]amino}phenolate (PI – ) ([Mn III (PI) 2 ] + ) ( 5 ). The latter was isolated both in the Mn II and in the Mn III state, although only Mn III crystals were successfully grown. They are part of a series of Mn complexes prepared as SOD mimics, namely [Mn(BMPG)(H 2 O)] + ( 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)(H 2 O) 2 ] + ( 4 ) {BIG = N , N ‐bis[(1‐methyl‐2‐imidazolyl)methyl]glycinate}. The reactivity of Mn II 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 ( IC 50 with 22 μ M cytc Fe III : 1.6 ± 0.1 μ M ol 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 ). IC 50 values were converted into the corresponding kinetic constant k McCF values. A linear correlation between E a and log( k McCF ) was obtained, indicating that in this series the conversion to Mn III is probably the rate‐limiting step. This is of substantial importance for further Mn–SOD mimic design in this series. (© Wiley‐VCH Verlag GmbH &amp; Co. KGaA, 69451 Weinheim, Germany, 2005)