Mono-, di- and tri-nuclear manganese(II) complexes derived from a quinquedentate ligand: Superoxide dismutase and catalase mimetic studies

In this study, three manganese complexes [Mn(H2L)Cl-2]center dot MeOH, [Mn-3(L)(2)(OAc)(2)(MeOH)(2)]center dot 2MeOH and [Mn2Ca(L)(2)(OAc)(2)(MeOH)(2)]center dot 2MeOH derived from a quinquedentate Schiff base ligand (H2L) were synthesised and characterised by the spectroscopic and analytic methods. Molecular structures of the complexes were determined by single crystal X-ray diffraction studies. In mononuclear complex [Mn(H2L)Cl-2]center dot MeOH, the Mn(II) ions are seven-coordinate pentagonal bipyramidal geometry with two chloride ions at the axial positions. The trinuclear complex [Mn-3(L)(2)(OAc)(2)(MeOH)(2)]center dot 2MeOH consists of two mononuclear units linked by a central Mn(II) ion. The calcium containing complex [Mn2Ca(L)(2)(OAc)(2)(MeOH)(2)]center dot 2MeOH contains two mononuclear units bridged by a six-coordinate Ca(II) ion. The superoxide dismutase (SOD activities of the structurally complexes were evaluated and the mononuclear complex [Mn(H2L)Cl-2]center dot MeOH showed the greatest SOD activity with an IC50 value of 0.95 mu M which gives a calculated k(cat) value of 1.67 x 10(6) M (1) s (1). Finally, the ability of the complexes to disproportionate H2O2 in the presence of base was tested by measuring the rate of oxygen evolution at room temperature. The trinuclear [Mn-3(L)(2)(OAc)(2)(MeOH)(2)]center dot 2MeOH complex is the most efficient complex catalase mimic of the tested complexes with the fastest rate 5.33 ml/s. (C) 2015 Elsevier B.V. All rights reserved.