Yasutaka Nagai

Local structure analyses of Ce0.5Zr0.5O2 mixed oxides by XAFS.

Three types of CeO2-ZrO2 with the same composition (Ce/Zr = 1) were prepared by different methods, exhibited the different oxygen storage/release capacity (OSC). To investigate the relationship between the OSC and the local structure, the Ce and Zr K-edges XAFS spectra for these samples were measured. The features of Fourier transforms of these samples were different from each other. This suggested that the OSC was remarkably exerted by the local structure around Ce and Zr. The quantitative curve-fitting analysis of EXAFS was applied, and it was concluded that homogeneous Ce(0.5)Zr(0.5)O2 solid solution at atomic level exhibited the highest OSC among these CeO2-ZrO2 with the same composition (Ce/Zr = 1).

Extradiol oxygenation of 3,5-di-tert-butylcatechol with O2by iron chlorides in tetrahydrofuran–water as a model reaction for catechol-2,3-dioxygenases

Selective extradiol oxygenation of 3,5-di-tert-bytylcatechol 1 with O2catalysed by Fe2+ is achieved in THF in the presence of water; the different selectivity obtained by FeCl2 and FeCl3 in THF–H2O and THF–pyridine supports the explanation of the intra- and extra-diol oxygenations by Fe3+ and Fe2+, respectively, as proposed in the enyzmatic systems.

X-ray crystallographic and absorption spectroscopic analyses of structures of catecholato (pyridine)iron chloride complexes in relevance to functional model complexes for catechol 1,2-dioxygenases

Abstract Catecholatoiron complexes were isolated in the crystalline or non-crystalline form from the reaction solution of catechols with FeCl 3 in the presence of pyridine in THF; they form a functional model system for catechol dioxygenases. Two types of complex were obtained, depending on substituent on catechol and pyridine: [FeCl (catechol)(pyridine)](pyridine) and [FeCl 2 (catechol)] − ·2[pyridine·H] + . An X-ray quality single crystal was obtained with the 3.5-di-tert-butycatecholato(2,6-lutidine)iron chloride complex: it is monoclinic, space group C2 m , with cell dimensions a = 11.947(3), b = 16.122(3), c = 14.725(2) A , β = 100.38(2)°, and Z = 2. The [Fe 2 (catechol) 2 Cl 4 ] 2− anion forms a dinuclear complex with two crystallographically equivalent iron centers, each metal ion of which is in a five-coordinated distorted square-pyramidal geometry with two chloride anions and two oxygen atoms of two bridging catechol molecules. Extended X-ray absorption fine structure (EXAFS) and X-ray absorption near edge structure (XANES) studies have revealed that the other isolated complexes are also dimeric in the solid state and become monomeric in the THF solution. The presence of Feue5f8Cl bonding and its conversion to Fe-pyridine in solution are shown by the Br K-edge EXAFS analysis of the analogous bromide complex.

Activation of chelated catecholatoiron species for catalytic oxygenation of catechols by catecholdioxygenase-model iron complexes

Reactivity of the isolated catecholatoiron complex with O2 and the spectroscopic observation of the reversible catecholate ligand exchange reveal that a stable chelated catecholate species may be activated to be reactive with O2 in the catalytic system.