Catalase mimics of a manganese(II) complex: The effect of axial ligands and pH

• DOI: 10.1016/j.molcata.2007.11.005
• Publication Date: 2007-11-14T12:12:14Z
• Authors: József Kaizer; Tamás Csay; Péter Kővári; Gábor Speier; László Párkányi
• Keywords: Imidazole; Enzyme Kinetics

Abstract The mononuclear [Mn(indH)Cl 2 ](CH 3 OH) (indH: 1,3-bis(2′-pyridylimino)-isoindoline) complex has been prepared and characterized by various techniques such as elemental analysis, IR, UV–vis, ESR spectroscopy and X-ray diffraction. The title compound in the presence of a base such as 1-methylimidazole, imidazole or pyridine is efficient catalyst for the disproportionation of H 2 O 2 in CH 3 CN. Among the various nitrogenous bases investigated in this study imidazole and substituted imidazoles with strong π-donating ability show better co-catalytic effect. In case of aqueous solution the complex [Mn(indH)Cl 2 ](CH 3 OH) shows much higher catalytic activity, and the initial rate of the disproportionation of H 2 O 2 increases with increasing pH and goes through a maximum, which was found at pH ∼ 9.6. In this pH value the reaction shows first-order dependence on the catalyst, and saturation kinetics on [H 2 O 2 ] with V max = 8.1 × 10 −3 Ms −1 , K M = 489 mM, k cat = 38 ± 2 s −1 and k 2 ( k cat / K M ) = 79 ± 4 M −1 s −1 .