| Co-Investigator(Kenkyū-buntansha) |
SAKIYAMA Hiroshi Kyushu University, Faculty os Science, 理学部, 助手 (20253396)
MATSUMOTO Naohide Kyushu University, Faculty os Science, 理学部, 助教授 (80145284)
LATOUR Jean-maro Center d'Etudes Nucleaires de Grenoble, 主任研究員
FENTON David e The University of Sheffield, Department of Chemistry, 化学科, 教授
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| Research Abstract |
1. Model Studies on Manganese Catalase.
mu-Phenoxobis (mu-carboxylato) dimanganese (II) core complexes, relevant to a mu-oxobis (mu-carboxylato) dimanganese core supposed for biological manganese catalase (Mn-CAT), have been derived from phenol-based dinucleating ligands and used for model studies on Mn-CAT.They showed a CAT-like activity to decompose H_2O_2 in DMF solution. From detailed studies using these and related complexes, the following important findings were obtained.
(1) Based on FAB masspectrometry using isotopic H_2^<18>O_2 and visible spectroscopy showing a characeristic absorption at 530 nm with vibration modes separated by 730 cm^<-1>, an active intermediate {Mn (IV) (=O)}_2 was first detected along with a less reactive intermediate {Mn (II) Mn (IV) (=O)}. On the basis of kinetic considerations, the catalytic cycle by {Mn (IV) (=O)}_2/{Mn (III) (OH)}_2 was proposed.
(2) The mu-phenoxobis (mu-carboxylato) dimangenese (II) core structure of the complexes was carefully examin
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ed and it is found the complexes of Cs symmetry give the active cis-{Mn (IV) (=O)}_2 whereas the complexes of C_2 symmetry give the less active {Mn (II) Mn (IV) (=O)}.
(3) Dinuclear Mn complexes comprised of elecutronically non-equivalent Mn ions were examined in CAT-like activity. In this case a side eraction through a radical mechanism occurs, giving rise to a reduction in the O_2 yield. The result clearly demonstrates the significance of an equivalent pair of Mn ions in Mn-CAT.
(4) Based on studies on CAT-like activity of macrocyclic Mn_2 complexes, the involvement of Mn (III) species was proved. Thus, the cycle of {Mn (IV) (=O)} 2/{Mn (III) (OH)}_2 in the H_2O_2 disproportionation was demonstrated.
2. Model Studies on Multi-copper Enzymes
A bioinorganic approach was made to the active site of multi-copper enzymes containing type I,type II and type III coppers. An assembly complex comprised of one dinuclear Cu_2 (II,II) and two mononuclear Cu (II) units, {Cu (II) -Cu_2 (II,II)-Cu (II)}, was prepared by the use of a dinucleating ligand derived from the [1 : 2] condensation of 2,6-diformyl-4-methylphenol and tetraethylenepentamine. Electrochemical reduction at the mononuclear center was performed to provide {Cu (I) -Cu_2 (II,II) -Cu (I)}, which caused an intramolecular electron transfer to give {Cu (II) -Cu_2 (I,I) -Cu (II)}. This is the first evidence for the electron transfer supposed for ascorbate oxidase, one of multicopper enzymes. Less
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