| 1. |
T Takeuchi, K Yoshizawa, Y Shiota, O Nakamura, H Kageyama, T Yamabe, Orbital interaction and vibrational mode analyses for phase transitions of BaTiO3, JOURNAL OF MATERIALS CHEMISTRY, 10.1039/a607475h, Vol.7, No.6, pp.969-975, 1997.06, The phase transitions of ATiO(3)-type perovskite structures, mainly those of barium titanate (BaTiO3), aro studied theoretically in terms of orbital interactions and vibrational modes. Vibrational analyses for fundamental TiO6 clusters, up to Ti8O36, are performed with a hybrid (Hartree-Fock/density functional) method. Important structural distortions from the high symmetry cubic phase are rationalized by a second-order perturbational treatment of quantum chemistry. The orbital symmetry argument based on group theory indicates that the transition density around frontier molecular orbitals plays an important role in the motions of ions at the transition temperatures. Our orbital interaction and vibrational mode analyses of the phase transitions are consistent with the soft mode theory of Cochran.. |
| 2. |
K Yoshizawa, Y Shiota, T Yamabe, Methane-methanol conversion by MnO+, FeO+, and CoO+: A theoretical study of catalytic selectivity, JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 10.1021/ja971723u, Vol.120, No.3, pp.564-572, 1998.01, The entire reaction pathway for the gas-phase methane-methanol conversion by late transition-metal-oxide ions, MnO+, FeO+, and CoO+, is studied using an ab initio hybrid (Hartree-Fock/density-functional) method. For these oxo complexes, the methane-methanol conversion is proposed to proceed via two transition states (TSs) in such a way MO+ + CH4 --> OM+(CH4) --> [TS1] --> HO-M+-CH3 --> [TS3] --> M+(CH3OH) --> M+ + CH3OH, where M is Mn, Fe, and Co. A crossing between high-spin and low-spin potential energy surfaces occurs both at the entrance channel and at the exit channel for FeO+ and CoO+, but it occurs only once near TS2 for MnO+. The activation energy from OMn+(CH4) to HO-Mn+-CH3 via TS1 is calculated to be 9.4 kcal/mol, being much smaller than 22.1 and 30.9 kcal/mol for FeO+ and CoO+, respectively. This agrees with the experimentally reported efficiencies for the reactions. The excellent agreement between theory and experiment indicates that HO-M+-CH3 plays a central role as an intermediate in the reaction between MO+ and methane and that the reaction efficiency is most likely to be determined by the activation energy from OM+(CH4) to HO-M+-CH3 via TS1. We discuss in terms of qualitative orbital interactions why MnO+ (d(4) oxo complex) is most effective for methane C-H bond activation. The activation energy from HO-M+-CH3 to M+(CH3OH) via TS2 is computed to be 24.6, 28.6, and 35.9 kcal/mol for CoO+, FeO+, and MnO+, respectively. This result explains an experimental result that the methanol-branching ratio in the reaction between MO+ and methane is 100% in CoO+, 41% in FeO+, and < 1% in MnO+. We demonstrate that both the barrier heights of TS1 and TS2 would determine general catalytic selectivity for the methane-methanol conversion by the MO+ complexes.. |
| 3. |
K Yoshizawa, T Kamachi, Y Shiota, A theoretical study of the dynamical aspects of alkane hydroxylation by compound I of cytochrome p450, JOURNAL OF INORGANIC BIOCHEMISTRY, Vol.86, No.1, p.488, 2001.08. |
| 4. |
Y Shiota, K Yoshizawa, A theoretical study of the mononuclear non-hem iron complex of phenylalanine hydroxylase (PAH), JOURNAL OF INORGANIC BIOCHEMISTRY, Vol.96, No.1, p.228, 2003.07. |
| 5. |
K. Yoshizawa, Y. Shiota, G. Juhasz, Role of tyrosine residue in methane activation by pMMO, JOURNAL OF BIOLOGICAL INORGANIC CHEMISTRY, Vol.19, p.S216, 2014.03. |
| 6. |
大環状アニオン性配位子を有する鉄錯体の高酸化状態における電子構造. |
| 7. |
酸化還元活性な配位子を有する鉄錯体の高酸化状態における電子構造. |
| 8. |
銅2核錯体によるC‐H結合活性化に関する理論的研究. |
| 9. |
Theoretical study of methane activation catalyzed by transition metal-oxo species Yoshihito SHIOTA (Institute for materials chemistry and engineering, Kyushu University, Motooka, Nishi-ku, Fukuoka 819-0395, Japan)
Reaction pathways and energetics for the conversion of methane to methanol by the bare FeO+ ion, the FeO+ species over Fe-ZSM-5, and the dicopper species of pMMO are discussed using density-functional-theory calculations. Computed reaction pathway is a non-radical mechanism to form a hydroxo intermediate, HO–M+–CH3, via H-atom abstraction with a four-centered transition state, which occurs at a coordinatively unsaturated metal center. A detailed analysis of the potential energy surfaces shows that crossing between high-spin and low-spin potential energy surfaces occurs twice in the entrance channel and in the exit channel in FeO+.
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