High-field EPR investigations of (MnMnIV)-Mn-II and (MnMnIII)-Mn-II states of dimanganese catalase and related model systems

摘要

Multi-frequency EPR experiments at 9, 34 and 94 GHz are reported on the antiferromagnetically coupled mixed valence (MnMnIII)-Mn-II complex of manganese catalase and on several dinuclear manganese model systems. They are compared with similar experiments obtained earlier for the (MnMnIV)-Mn-III states. It is demonstrated how accurate information on the G- and Mn-55 hyperfine tensors can be derived from this approach. Furthermore, the effect of oxidation state, planarity of the manganese-oxygen core and the type of ligands bridging the manganese ions on the magnetic resonance parameters and the related electronic structure is investigated. 'Broken-symmetry' density functional calculations on two (MnMnIV)-Mn-III complexes, including the superoxidized state of the catalase, are presented. The agreement between calculated and experimental EPR parameters and complex geometries is remarkably good. Implications of these results for the structure and function of the dimanganese catalase are discussed. Copyright (c) 2005 John Wiley & Sons, Ltd.