45 results on '"Yoshihiko Okamoto"'
Search Results
2. Rattling Behavior in a Simple Perovskite NaWO3
- Author
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Yoshihiko Okamoto, Yuya Ikeuchi, Cédric Tassel, Taito Murakami, Craig M. Brown, Yuki Matsumoto, Hiroshi Takatsu, and Hiroshi Kageyama
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010405 organic chemistry ,Phonon ,Neutron diffraction ,Anharmonicity ,Oxide ,010402 general chemistry ,01 natural sciences ,0104 chemical sciences ,Inorganic Chemistry ,Crystallography ,chemistry.chemical_compound ,Octahedron ,Transition metal ,chemistry ,Physical and Theoretical Chemistry ,Multiplicity (chemistry) ,Perovskite (structure) - Abstract
Rattling phenomena have been observed in materials characterized by a large cage structure but not in a simple ABO3-type perovskite because the size mismatch, if it exists, can be relieved by octahedral rotations. Here, we demonstrate that a stoichiometric perovskite oxide NaWO3, prepared under high pressure, exhibits anharmonic phonon modes associated with low-energy rattling vibrations, leading to suppressed thermal conductivity. The structural analysis and the comparison with the ideal perovskite KWO3 without rattling behavior reveal that the presence of two crystallographic Na1 (2 a) and Na2 (6 b) sites in NaWO3 (space group Im3) accompanied by three in-phase WO6 octahedral (a+a+a+) rotations generates an open space Δ ∼ 0.5 A for the latter site, which is comparable with those of well-known cage compounds of clathrates and filled skutterudites. The observed rattling in NaWO3 is distinct from a quadruple perovskite AA'3B4O12 (A, A': transition metals) where the A (2 a) site with lower multiplicity is the rattler. The present finding offers a general guide to induce rattling of atoms in pristine ABO3 perovskites.
- Published
- 2019
3. Giant isotropic negative thermal expansion in Y-doped samarium monosulfides by intra-atomic charge transfer
- Author
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Yasutaka Imanaka, Yosuke Mizuno, Koshi Takenaka, Ryoichi Kaizu, Hiroyuki Suzuki, Yoshihiko Okamoto, Naoyuki Katayama, Daigo Asai, and Yasunori Yokoyama
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0301 basic medicine ,Multidisciplinary ,Materials science ,Condensed matter physics ,Magnetism ,Doping ,Isotropy ,lcsh:R ,chemistry.chemical_element ,lcsh:Medicine ,Magnetostriction ,Temperature cycling ,Article ,Thermal expansion ,Samarium ,03 medical and health sciences ,030104 developmental biology ,0302 clinical medicine ,Negative thermal expansion ,chemistry ,lcsh:Q ,lcsh:Science ,030217 neurology & neurosurgery - Abstract
Stimulated by strong demand for thermal expansion control from advanced modern industries, various giant negative thermal expansion (NTE) materials have been developed during the last decade. Nevertheless, most such materials exhibit anisotropic thermal expansion in the crystal lattice. Therefore, strains and cracks induced during repeated thermal cycling degrade their performance as thermal-expansion compensators. Here we achieved giant isotropic NTE with volume change exceeding 3%, up to 4.1%, via control of the electronic configuration in Sm atoms of SmS, (4 f)6 or (4 f)5(5d)1, by partial replacement of Sm with Y. Contrary to NTE originating from cooperative phenomena such as magnetism, the present NTE attributable to the intra-atomic phenomenon avoids the size effect of NTE and therefore provides us with fine-grained thermal-expansion compensators, which are strongly desired to control thermal expansion of microregions such as underfill of a three-dimensional integrated circuit. Volume control of lanthanide monosulfides via tuning of the 4 f electronic configuration presents avenues for novel mechanical functions of a material, such as a volume-change driven actuator by an electrical field, which has a different drive principle from those of conventional strain-driven actuators such as piezostrictive or magnetostrictive materials.
- Published
- 2019
4. Electrical and Thermal Transport Properties of the beta-Pyrochlore Oxide CsW2O6
- Author
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Kenta Niki, Koshi Takenaka, Yoshihiko Okamoto, and Rikuto Mitoka
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Condensed Matter - Materials Science ,Materials science ,Oxide ,Pyrochlore ,General Physics and Astronomy ,Materials Science (cond-mat.mtrl-sci) ,FOS: Physical sciences ,engineering.material ,chemistry.chemical_compound ,Thermal conductivity ,Thermal transport ,chemistry ,Electrical resistivity and conductivity ,Seebeck coefficient ,engineering ,Composite material - Abstract
We report the electrical resistivity, thermoelectric power, and thermal conductivity of single-crystalline and sintered samples of the 5d pyrochlore oxide CsW2O6. The electrical resistivity of the single crystal is 3 mohm cm at 295 K and gradually increases with decreasing temperature above 215 K (Phase I). The thermoelectric power of the single-crystalline and sintered samples shows a constant value of approximately -60 uV K-1 in Phase I. These results reflect that the electron conduction by W 5d electrons in Phase I is incoherent and in the hopping regime, although a band gap does not open at the Fermi level. The thermal conductivity in Phase I of both samples is considerably low, which might be due to the rattling of Cs+ ions. In Phase II below 215 K, the electrical resistivity and the absolute value of thermoelectric power of both samples strongly increase with decreasing temperature, corresponding to a transition to a semiconducting state with a band gap open at the Fermi level, while the thermal conductivity in Phase II is smaller than that in Phase I., 6 pages, 3 figures. Accepted for publication in J. Phys. Soc. Jpn
- Published
- 2020
5. Annealing effect on local structure and negative thermal expansion of antiperovskite manganese nitride fine particles
- Author
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Masaki Azuma, Masaki Ozeki, Victoria Warne-Lang, Naoyuki Katayama, Hirofumi Tsukasaki, Yoshihiko Okamoto, Koshi Takenaka, Shigeo Mori, and Yuki Sakai
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010302 applied physics ,Materials science ,Annealing (metallurgy) ,Composite number ,General Engineering ,General Physics and Astronomy ,chemistry.chemical_element ,02 engineering and technology ,Manganese ,Nitride ,021001 nanoscience & nanotechnology ,01 natural sciences ,Thermal expansion ,Grinding ,Antiperovskite ,chemistry ,Negative thermal expansion ,0103 physical sciences ,Composite material ,0210 nano-technology - Abstract
The local structure and thermal expansion properties of balled-milled manganese nitride fine particles with median diameters on the sub-micrometer scale were investigated. Negative thermal expansion (NTE) properties of the manganese nitrides are noticeably altered even with particle sizes of several micrometers. The present study indicates that the alteration of NTE properties is attributable to the structural disorder resulting from grinding. Moreover, the NTE properties were restored by annealing due to improved structural order. These achievements are expected to pave the way for the use of the giant NTE found in manganese nitrides to control thermal expansion in local regions.
- Published
- 2020
6. Structural phase transition and giant negative thermal expansion in pyrophosphate Zn2–xMgxP2O7
- Author
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Y. Kadowaki, Yasunori Yokoyama, R. Kasugai, Yoshihiko Okamoto, Koshi Takenaka, and Naoyuki Katayama
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Materials science ,Physics and Astronomy (miscellaneous) ,Transition temperature ,Doping ,Synchrotron radiation ,Thermodynamics ,Epoxy ,Pyrophosphate ,Thermal expansion ,chemistry.chemical_compound ,Negative thermal expansion ,chemistry ,visual_art ,visual_art.visual_art_medium ,Volume contraction - Abstract
By tuning the structural phase transition in Zn2–xMgxP2O7, large negative thermal expansion (NTE) was achieved at room temperature. An earlier report described that Zn2P2O7 undergoes a structural phase transition at 405 K, accompanied by volume contraction of 1.8% on heating. Results showed that as Mg doping proceeds, the transition temperature decreases. Also, the volume change becomes gradual with respect to temperature. Particularly, Zn1.6Mg0.4P2O7 has a large negative coefficient of linear thermal expansion αL of −60 ppm/K at 280–350 K. Structural analysis using synchrotron radiation revealed that this dilatometric NTE is almost identical to that of crystallographic unit cells, indicating less dominant structural effects on NTE. We also verified thermal expansion compensation capabilities of powdered Zn1.6Mg0.4P2O7 by evaluating the thermal expansion of the epoxy resin matrix composites. The present phosphates are promising for use as practical thermal expansion compensators because they are free of toxic or expensive elements and can be fabricated in air using the simple solid-state reaction method.
- Published
- 2021
7. Orbital Transitions and Frustrated Magnetism in the Kagome-Type Copper Mineral Volborthite
- Author
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Hajime Ishikawa, Hiroyuki Yoshida, Zenji Hiroi, Yoshihiko Okamoto, and Jun-ichi Yamaura
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Condensed matter physics ,Spins ,010405 organic chemistry ,Chemistry ,Magnetism ,Crystal structure ,010402 general chemistry ,01 natural sciences ,0104 chemical sciences ,Magnetic field ,Inorganic Chemistry ,Atomic orbital ,Unpaired electron ,Condensed Matter::Strongly Correlated Electrons ,Physical and Theoretical Chemistry ,Spin (physics) ,Phase diagram - Abstract
Volborthite Cu3V2O7(OH)2·2H2O is a copper mineral that materializes a two-dimensional quantum magnet comprising a kagome net of spin-1/2 Cu2+ ions. We prepared single crystals of volborthite using hydrothermal conditions and investigated their crystal structures and magnetic properties. Unusual orbital "switching" and "flipping" transitions were observed: in the former type of transition (switching), the Cu 3d orbital occupied by an unpaired electron changes between the d(3z2-r2) and d(x2-y2) types, and in the latter type of transition (flipping), the d(x2-y2)-type orbitals change their directions. Their origin is ascribed to variations in the orientation of water molecules in the gap between the kagome layers and the accompanying changes of hydrogen bonding. These orbital transitions dramatically modify the magnetic interactions between Cu2+ spins, from the anisotropic kagome type to the formation of spin trimers over the kagome net. The effective spin 1/2 generated on the trimers exhibits a frustrated magnetism, resulting in a rich phase diagram in the magnetic fields. Volborthite is a unique compound showing an exceptional interplay between the orbital and spin degrees of freedom.
- Published
- 2019
8. Giant Magneto-Volume and Magneto-Caloric Effects of Frustrated Antiferromagnet Mn3GaN under Hydrostatic Pressure
- Author
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Yoshihiko Okamoto, Koshi Takenaka, Asaya Fujita, Masaki Ozeki, Takuto Sugiura, and Yoshifumi Kadowaki
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Materials science ,Condensed matter physics ,digestive, oral, and skin physiology ,Hydrostatic pressure ,General Physics and Astronomy ,Caloric theory ,chemistry.chemical_element ,Manganese ,equipment and supplies ,01 natural sciences ,010305 fluids & plasmas ,Condensed Matter::Materials Science ,Volume (thermodynamics) ,chemistry ,0103 physical sciences ,Physics::Atomic and Molecular Clusters ,Antiferromagnetism ,Condensed Matter::Strongly Correlated Electrons ,010306 general physics ,human activities ,Magneto - Abstract
Volumetric and caloric effects associated with magnetic transition have been investigated systematically for a series of manganese nitrides based on Mn3GaN. The antiferromagnetic transition tempera...
- Published
- 2021
9. Large Thermoelectric Power Factor in One-Dimensional Telluride Nb4SiTe4 and Substituted Compounds
- Author
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Yoshihiko Okamoto, Taichi Wada, Koshi Takenaka, Takumi Inohara, and Youichi Yamakawa
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010302 applied physics ,Condensed Matter - Materials Science ,Materials science ,Physics and Astronomy (miscellaneous) ,business.industry ,Band gap ,Doping ,Materials Science (cond-mat.mtrl-sci) ,FOS: Physical sciences ,02 engineering and technology ,Power factor ,021001 nanoscience & nanotechnology ,Thermoelectric materials ,01 natural sciences ,chemistry.chemical_compound ,chemistry ,Whisker ,Telluride ,0103 physical sciences ,Thermoelectric effect ,Optoelectronics ,0210 nano-technology ,business ,Solid solution - Abstract
We found that whisker crystals of Mo-doped Nb4SiTe4 show high thermoelectric performances at low temperatures, indicated by the largest power factor of 70 microW cm-1 K-2 at 230-300 K, much larger than those of Bi2Te3-based practical materials. This power factor is smaller than the maximum value in the 5d analogue Ta4SiTe4, but is comparable to that with a similar doping level. First principles calculation results suggest that the difference in thermoelectric performances between Nb and Ta compounds is caused by the much smaller band gap in Nb4SiTe4 than that in Ta4SiTe4, due to the weaker spin-orbit coupling in the former. We also demonstrated that the solid solution of Nb4SiTe4 and Ta4SiTe4 shows a large power factor, indicating that their combination is promising as a practical thermoelectric material, as in the case of Bi2Te3 and Sb2Te3. These results advance our understanding of the mechanism of high thermoelectric performances in this one-dimensional telluride system, as well as indicating the high potential of this system as a practical thermoelectric material for low temperature applications., Comment: 5 pages, 5 figures
- Published
- 2018
- Full Text
- View/download PDF
10. Large Thermoelectric Power Factor at Low Temperatures in One-Dimensional Telluride Ta4SiTe4
- Author
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Ai Yamakage, Yoshihiko Okamoto, Koshi Takenaka, Takumi Inohara, and Youichi Yamakawa
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Condensed Matter - Materials Science ,Materials science ,Thermoelectric cooling ,Physics and Astronomy (miscellaneous) ,Condensed matter physics ,Band gap ,Materials Science (cond-mat.mtrl-sci) ,FOS: Physical sciences ,02 engineering and technology ,Power factor ,021001 nanoscience & nanotechnology ,Thermoelectric materials ,01 natural sciences ,Semimetal ,chemistry.chemical_compound ,chemistry ,Electrical resistivity and conductivity ,Telluride ,Seebeck coefficient ,0103 physical sciences ,010306 general physics ,0210 nano-technology - Abstract
We report the discovery of a very large thermoelectric power over -400 microV K-1 in the whisker crystals of a one-dimensional telluride Ta4SiTe4, while maintaining a low electrical resistivity of rho = 2 mohm cm, yielding a very large power factor of P = 80 microW cm-1 K-2 at an optimum temperature of 130 K. This temperature is widely controlled from the cryogenic temperature of 50 K to room temperature by chemical doping, resulting in the largest P of 170 microW cm-1 K-2 at 220-280 K. These P values far exceed those of the Bi2Te3-Sb2Te3 alloys at around room temperature, offering an avenue for realizing the practical-level thermoelectric cooling at low temperatures. The coexistence of a one-dimensional electronic structure and a very small band gap appearing in the vicinity of the Dirac semimetals probably causes the very large power factors in Ta4SiTe4, indicating that the "one-dimensional Dirac semimetal" is a promising way to find high-performance thermoelectric materials for the low temperature applications., Comment: 5 pages, 3 figures
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- 2017
- Full Text
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11. Low Carrier Density Metal Realized in Candidate Line-Node Dirac Semimetals CaAgP and CaAgAs
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Yoshihiko Okamoto, Takumi Inohara, Ai Yamakage, Youichi Yamakawa, and Koshi Takenaka
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Condensed Matter - Materials Science ,Materials science ,Condensed matter physics ,Phosphide ,Dirac (software) ,General Physics and Astronomy ,Materials Science (cond-mat.mtrl-sci) ,FOS: Physical sciences ,Fermi energy ,Fermi surface ,02 engineering and technology ,021001 nanoscience & nanotechnology ,01 natural sciences ,Semimetal ,Arsenide ,chemistry.chemical_compound ,Condensed Matter::Materials Science ,chemistry ,0103 physical sciences ,Node (physics) ,Condensed Matter::Strongly Correlated Electrons ,010306 general physics ,0210 nano-technology ,Line (formation) - Abstract
We study polycrystalline samples of the hexagonal pnictides, CaAgP and CaAgAs, both of which are ideal candidates for line-node Dirac semimetals. The polycrystalline samples of CaAgP and CaAgAs obtained in this study are low-carrier metals, where hole carriers are dominant. By combining the hole carrier densities estimated from Hall coefficients and the electronic structures calculated by first principles calculations, both samples are found to have a ring-torus Fermi surface, derived from a ring-shaped Dirac line node. In the phosphide sample, the Fermi energy EF is located at around the end of the linear dispersion region of the electronic bands, while the EF in the arsenide sample exists in the middle of this region, suggesting that the arsenide is a more promising system for uncovering the physics of line-node Dirac semimetals., 6 pages, 5 figures
- Published
- 2016
12. Valence fluctuations and giant isotropic negative thermal expansion in Sm1–xRxS (R = Y, La, Ce, Pr, Nd)
- Author
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D. Asai, Yoshihiko Okamoto, H. S. Suzuki, Yasunori Yokoyama, Yasutaka Imanaka, Koshi Takenaka, Y. Mizuno, H. Hasegawa, and Naoyuki Katayama
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010302 applied physics ,Materials science ,Valence (chemistry) ,Physics and Astronomy (miscellaneous) ,Condensed matter physics ,Isotropy ,chemistry.chemical_element ,Crystal growth ,02 engineering and technology ,Atmospheric temperature range ,021001 nanoscience & nanotechnology ,01 natural sciences ,Thermal expansion ,Samarium ,chemistry ,Negative thermal expansion ,0103 physical sciences ,Crystallite ,0210 nano-technology - Abstract
The valence fluctuations of Sm in samarium monosulfide (SmS) are known to induce possible large isotropic negative thermal expansion (NTE), but difficulty in crystal growth prevents establishment of the NTE function. For this study, we prepared Ce-doped and Nd-doped SmS polycrystalline samples using a simpler method with much lower reaction temperature than the existing method. Typically, Sm0.80Ce0.20S exhibits giant NTE with total volume change of 2.6% in the wide temperature range from 330 K to 100 K, the lowest covered here. Achievement of giant NTE in a low-cost polycrystalline form paves the way for practical applications of this class of sulfides as a thermal-expansion compensator.
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- 2019
13. Extended operating temperature window of giant negative thermal expansion in Sn-doped Ca2RuO4
- Author
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Yoshihiko Okamoto, Masaki Azuma, Koshi Takenaka, Takumi Nishikubo, N. Inoue, Y. Mizuno, Yuki Sakai, and Naoyuki Katayama
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Materials science ,Physics and Astronomy (miscellaneous) ,Condensed matter physics ,Doping ,Sintering ,chemistry.chemical_element ,02 engineering and technology ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,Thermal expansion ,0104 chemical sciences ,Crystal ,chemistry ,Negative thermal expansion ,Operating temperature ,0210 nano-technology ,Tin ,Anisotropy - Abstract
Colossal negative thermal expansion (NTE) recently discovered in layered ruthenate Ca2RuO4 is achieved by microstructural effects because of the crystal grains showing highly anisotropic thermal distortion and the pores in the sintered body. To improve the NTE properties, we have investigated element-substitution effects. We discovered that Sn doping expanded the operating-temperature window toward higher temperatures up to 700 K and improved the temperature linearity of NTE without decreasing the total volume change related to NTE. We discuss changes in NTE properties caused by Sn doping in terms of the electronic states and the structural transformation.
- Published
- 2018
14. ChemInform Abstract: Orbital Arrangements and Magnetic Interactions in the Quasi-One-Dimensional Cuprates ACuMoO4(OH) (A: Na, K)
- Author
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Kazuhiro Nawa, Zenji Hiroi, Takeshi Yajima, and Yoshihiko Okamoto
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Slow heating ,Aqueous solution ,Chemistry ,Physical chemistry ,Quasi one dimensional ,Cuprate ,General Medicine ,Alkali metal ,Autoclave - Abstract
Single crystals of the new compound KCuMoO4(OH) are hydrothermally synthesized from aqueous solutions of Cu(NO3)2 and K2MoO4 (autoclave, 433 K followed by slow heating to 493 K in 240 h).
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- 2015
15. Orbital Arrangements and Magnetic Interactions in the Quasi-One-Dimensional Cuprates ACuMoO4(OH) (A = Na, K)
- Author
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Takeshi Yajima, Yoshihiko Okamoto, Kazuhiro Nawa, and Zenji Hiroi
- Subjects
Condensed matter physics ,Strongly Correlated Electrons (cond-mat.str-el) ,Chemistry ,FOS: Physical sciences ,Crystal structure ,Ion ,Inorganic Chemistry ,Condensed Matter - Strongly Correlated Electrons ,Crystallography ,Atomic orbital ,Octahedron ,Ferromagnetism ,Superexchange ,Condensed Matter::Superconductivity ,Antiferromagnetism ,Cuprate ,Condensed Matter::Strongly Correlated Electrons ,Physical and Theoretical Chemistry - Abstract
A new spin-1/2 quasi-one-dimensional antiferromagnet KCuMoO_4(OH) is prepared by the hydrothermal method. The crystal structures of KCuMoO_4(OH) and the already-known Na-analogue, NaCuMoO_4(OH), are isotypic, comprising chains of Cu^{2+} ions in edge-sharing CuO_4(OH)_2 octahedra. Despite the structural similarity, their magnetic properties are quite different because of the different arrangements of d_{x2-y2} orbitals carrying spins. For NaCuMoO_4(OH), d_{x2-y2} orbitals are linked by superexchange couplings via two bridging oxide ions, which gives a ferromagnetic nearest-neighbor interaction J_1 of -51 K and an antiferromagnetic next-nearest-neighbor interaction J_2 of 36 K in the chain. In contrast, a staggered d_{x2-y2} orbital arrangement in KCuMoO_4(OH) results in superexchange couplings via only one bridging oxide ion, which makes J_1 antiferromagnetic as large as 238 K and J_2 negligible. This comparison between the two isotypic compounds demonstrates an important role of orbital arrangements in determining the magnetic properties of cuprates., Comment: 7 pages, 5 figures published to Inorg. Chem. (2015)
- Published
- 2015
16. Spin dynamics of S = 1/2 kagome lattice antiferromagnets observed by high-field ESR
- Author
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Takahiro Sakurai, Weimin Zhang, Yoshihiko Okamoto, Zenji Hiroi, Susumu Okubo, Masashi Fujisawa, Hitoshi Ohta, and Hiroyuki Yoshida
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Condensed matter physics ,Chemistry ,media_common.quotation_subject ,Frustration ,Crystal structure ,Condensed Matter Physics ,Electronic, Optical and Magnetic Materials ,Magnetic field ,law.invention ,Paramagnetism ,law ,Antiferromagnetism ,Quantum spin liquid ,Electron paramagnetic resonance ,Excitation ,media_common - Abstract
Due to the existence of strong spin frustration in a system, the spin dynamics of S= 1/2 kagome lattice antiferromagnet at low temperature has attracted much interest. High-field ESR has been measured on its model substances, Cu 3 V 2 O 7 (OH) 2 · 2H 2 O (volborthite) and BaCu 3 V 2 O 3 (OH) 2 (vesignieite), down to 1.8 K using pulsed magnetic fields up to 16 T. The measurements are performed for 160 and 315 GHz using polycrystalline samples. Although both samples showed the g-shift and the change of linewidth at low temperature, volborthite showed a small gap excitation of the order of 40 GHz (1.9 K) while vesignieite showed a paramagnetic behavior down to 1.9 K. Observed difference will be discussed in connection with the crystal structure, and the possible spin liquid state in vesignieite will be discussed.
- Published
- 2010
17. Growth and moiré superstructure of palladium films on Ni(111) studied by STM
- Author
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Yoshihiko Okamoto, Nagahiro Saito, S. Terada, Toshiaki Ohta, and Toshihiko Yokoyama
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Superstructure ,Chemistry ,chemistry.chemical_element ,Surfaces and Interfaces ,Substrate (electronics) ,Condensed Matter Physics ,Surfaces, Coatings and Films ,Overlayer ,law.invention ,Crystallography ,Nickel ,Vacuum deposition ,Transition metal ,law ,Materials Chemistry ,Scanning tunneling microscope ,Palladium - Abstract
The growth mechanism of ultrathin palladium films deposited on Ni(111) at 300 K was studied by scanning tunneling microscopy (STM) in ultrahigh vacuum. It was revealed that nearly ideal two-dimensional palladium films grow on Ni(111) up to the first three layers. Wide-area STM images clarified that palladium islands grow initially from the step edges of the substrate, indicating the existence of a significant barrier for diffusion across the step edges. Hexagonal moire superstructures were clearly observed in the overlayer images. The periodicity of the moire patterns was determined to be 33±3 A, which corresponds to 12 palladium atoms and 13 nickel atoms. Based on the STM images, a structure model for the palladium overlayer on Ni(111) is proposed.
- Published
- 1999
18. Thiophene adsorption on Pd(111) and Pd(100) surfaces studied by total-reflection S K-edge X-ray absorption fine-structure spectroscopy
- Author
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Toshiaki Ohta, Akihito Imanishi, S. Terada, Yoshinori Kitajima, Manabu Kiguchi, Yoshihiko Okamoto, Toshihiko Yokoyama, and M. Sakano
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Valence (chemistry) ,Extended X-ray absorption fine structure ,Stereochemistry ,Surfaces and Interfaces ,Condensed Matter Physics ,Surfaces, Coatings and Films ,X-ray absorption fine structure ,chemistry.chemical_compound ,Crystallography ,chemistry ,K-edge ,Chemisorption ,Materials Chemistry ,Thiophene ,Molecule ,Spectroscopy - Abstract
The total-reflection grazing-incidence technique has been applied to measure the S K-edge soft X-ray absorption fine structure spectra of submonolayer thiophene on Pd(111) and Pd(100) surfaces. The total-reflection mode allows us to obtain reliable spectra with a much higher signal-to-background ratio compared to that given by the conventional non-total reflection method. Similar surface structures of adsorbed thiophene are consequently determined on both surfaces. Thiophene molecules are found to lie flat accompanied by slightly elongated S–C bonds due to the charge transfer of 1.1–1.2 electrons from the Pd valence bands to the thiophene π* orbital. The S atom in the thiophene adsorbate is located at an intermediate position between bridge and atop sites. The displacement is estimated to be 0.61±0.05 A away from the bridge site towards the atop one. The structural and electronic properties of adsorbed thiophene on Pd(111) and Pd(100) are discussed in comparison with the previous results on Ni(100) and Cu(100).
- Published
- 1998
19. Structural studies on copper(II) complex containing (Z)-2-(2-Aminothiazol-4-yl)-N-(2-hydroxyethyl)-2-(hydroxyimino) acetamide, A model compound for a cephalosporin antibiotic cefdinir
- Author
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Yayoi Shihahara, Yoshihiko Okamoto, Marie T. Mooney, Shinnichiro Suzuki, Kyoko Yamamoto, Mamoru Fujioka, Shuhei Deguchi, Toshiji Tada, and Tsutomu Yasuda
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Aqueous solution ,Inorganic chemistry ,chemistry.chemical_element ,Biochemistry ,Copper ,Inorganic Chemistry ,Trigonal bipyramidal molecular geometry ,chemistry.chemical_compound ,Crystallography ,chemistry ,Molecule ,Titration ,Thiazole ,Acetamide ,Monoclinic crystal system - Abstract
(Z)-2-(2-aminothiazol-4-yl)-N-(2-hydroxyethyl)-2-(hydroxyimino)acetamide (HL) has been employed as a model compound for an orally active cephalosporin antibiotic, Cefdinir (CFDN). A binuclear copper(II) complex Cu2L4 (1) has been obtained from an aqueous solution containing CuCl2 and HL, and its structure determined by means of X-ray crystallography: monoclinic, P2/c, a = 11.954(3) A, b = 10.661(3) A, c = 16.969(7) A, β = 108.13(3)°, Z = 2. The molecular structure of 1 is a dimeric copper(II) complex consisting of two copper(II) complex units CuL2, where the two molecules of L (La and Lb) are coordinated to the copper atom through their thiazole and oximate nitrogen atoms. La is also coordinated to the copper atom of the other CuL2 unit through the oximate oxygen atom, namely, the two complex units are bound to each other by forming a pair of oximate NO bridges of the two La molecules. The coordination environment of the copper atom is a distorted trigonal bipyramid. In addition, based on the molecular structure, the coordination property of CFDN to copper(II) in water has been clarified by means of spectrophotometry and titration. Both copper(II) (0.05 mM)-HL (0.1 mM) and copper(II) (0.05 mM)-CFDN (0.1 mM) aqueous solutions gave broad d-d bands at ca. 720 nm above pH 6, corresponding to that observed in the diffuse reflectance spectrum of the crystals of 1. The results indicate that CFDN also forms a binuclear copper(II) complex, Cu2(CFDN)4, corresponding to Cu2L4 as the main species in water above pH 7. Stability constants are as follows: log β110 = 11.12, log β240 = 41.13 for copper(II)-L complexes. The theoretical species distribution diagram as a function of pH for the copper(II) (0.05 mM)-HL (0.1 mM) system shows that Cu2L4 exists as the main species above pH 7. The titration results are consistent with the spectral data. The spectral and titration studies indicate that not only HL, but also CFDN forms a binuclear complex Cu2(CFDN)4 corresponding to Cu2L4 as the main species under the neutral and basic conditions. In addition, the stability constants of CFDN complexes should be as large as those of CuL complexes, although titrations for copper(II)-CFDN systems could not be carried out due to precipitation of copper(II)-CFDN complexes.
- Published
- 1997
20. Degradation Kinetics and Isomerization of Cefdinir, a New Oral Cephalosporin, in Aqueous Solution. 1
- Author
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Yoshihiro Namiki, Junichi Matsushita, Mamoru Fujioka, Yoshihiko Okamoto, Kuniko Kiriyama, and Tsutomu Yasuda
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Cefdinir ,Aqueous solution ,Chemistry ,Hydrolysis ,Kinetics ,Molecular Conformation ,Administration, Oral ,Pharmaceutical Science ,Hydrogen-Ion Concentration ,Cephalosporins ,Solutions ,medicine ,Degradation (geology) ,Organic chemistry ,Epimer ,Isomerization ,Antibacterial agent ,medicine.drug - Abstract
Hydrolytic degradation products of cefdinir were studied in acidic (pH 1), neutral (pH 6), and basic (pH 9) solutions. Seven major degradation products were isolated by preparative and/or high-performance liquid chromatography and characterized by UV, IR, 1H-NMR, and mass spectra. To clarify degradation pathways in each pH solution, kinetic and product analyses during hydrolysis of cefdinir were carried out along with the followup reaction of representative degradation products. Cefdinir was shown to degrade via two major degradation routes: beta-lactam ring-opening and pH-dependent isomerizations (lactonization, epimerization at C-6 or C-7, syn-anti isomerization of N-oxime function).
- Published
- 1996
21. Degradation Kinetics and Isomerization of Cefdinir, a New Oral Cephalosporin, in Aqueous Solution. 2. Hydrolytic Degradation Pathway and Mechanism for β-Lactam Ring Opened Lactones
- Author
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Yoshihiro Namiki, Tsutomu Yasuda, Junichi Matsushita, Mamoru Fujioka, Yoshihiko Okamoto, and Kuniko Kiriyama
- Subjects
chemistry.chemical_classification ,Cefdinir ,Chemistry ,Hydrolysis ,Diastereomer ,Administration, Oral ,Pharmaceutical Science ,Stereoisomerism ,Combinatorial chemistry ,Cephalosporins ,Solutions ,chemistry.chemical_compound ,Deprotonation ,medicine ,Lactam ,Organic chemistry ,Enantiomer ,Isomerization ,Lactone ,medicine.drug - Abstract
Hydrolysis of cefdinir leads to pH-dependent isomerizations and beta-lactam ring-opening. Lactam ring opened gamma-lactones were produced as a mixture of four diastereoisomers based on the lactone methyl, and C-6 isomerizations in acidic to neutral solutions. Cefdinir and its 7-epimer were hydrolyzed to clarify the pathway leading to these lactones and the mechanism of C-6 epimerization with the aid of chiral separation techniques. Chiral separation using a bovine serum albumin column was employed to detect the beta-lactam ring opened products of cefdinir and its 7-epimer; the C-6 and C-7 isomerization was thereby observed; however, it was found to be pH-dependent at pH > or = 9. Optical activity detection applied to the lactones produced from cefdinir and its 7-epimer demonstrated that the corresponding peaks of these lactones were enantiomeric pairs. In addition, the smallest rate constant at pH 4 was observed for C-6 epimerization of the lactones, and it was found to proceed without deprotonation at C-6 by 1H-NMR spectroscopy. From the results of these studies, a plausible mechanism for C-6 epimerization has been proposed. Additionally, it was confirmed that two degradation pathways were involved during hydrolysis of cefdinir to the lactone.
- Published
- 1996
22. Method development for the determination of cefdinir and its related substances by high-performance liquid chromatography
- Author
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Tsutomu Yasuda, Kohji Itoh, Yoshihiro Namiki, Junichi Matsushita, Yoshihiko Okamoto, and Mamoru Fujioka
- Subjects
Quality Control ,Cefdinir ,Chromatography ,Chemistry ,Clinical Biochemistry ,Reproducibility of Results ,Pharmaceutical Science ,Hydrogen-Ion Concentration ,High-performance liquid chromatography ,Method development ,Cephalosporins ,Analytical Chemistry ,Solutions ,Drug Stability ,Calibration ,Drug Discovery ,medicine ,Indicators and Reagents ,Hplc method ,Quantitative analysis (chemistry) ,Chromatography, High Pressure Liquid ,Spectroscopy ,Antibacterial agent ,medicine.drug - Abstract
The validation of the HPLC method used for the determination of cefdinir and its related substances is described. The developed method was specific and stability-indicating and provided a linear response with concentration. The system and method precision, expressed as relative standard deviations, were not greater than 1%, and the reproducibilities within and between laboratories were acceptable for the assay method. The procedure can quantitate related substances greater than approximately 0.05% of the principal cefdinir peak.
- Published
- 1996
23. Synthesis and Superconducting Properties of a Hexagonal Phosphide ScRhP
- Author
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Youichi Yamakawa, Koshi Takenaka, Takumi Inohara, and Yoshihiko Okamoto
- Subjects
Superconductivity ,Materials science ,Condensed matter physics ,Phosphide ,Transition temperature ,Condensed Matter - Superconductivity ,FOS: Physical sciences ,General Physics and Astronomy ,Fermi energy ,02 engineering and technology ,021001 nanoscience & nanotechnology ,01 natural sciences ,Heat capacity ,Superconductivity (cond-mat.supr-con) ,symbols.namesake ,Magnetization ,chemistry.chemical_compound ,chemistry ,Electrical resistivity and conductivity ,0103 physical sciences ,symbols ,010306 general physics ,0210 nano-technology ,Debye model - Abstract
We report the synthesis and superconducting properties of the ternary phosphide ScRhP. The crystal structure of ScRhP is determined to be the ordered Fe2P type with the hexagonal P-62m space group by powder X-ray diffraction experiments. Resistivity, magnetization, and heat capacity data indicate that ScRhP is a bulk superconductor with a transition temperature Tc of 2 K. This Tc is lower than that of its 5d analogue, ScIrP (Tc = 3.4 K), although ScRhP is found to have larger electronic density of states at the Fermi energy and a higher Debye temperature than those of ScIrP., 6 pages, 6 figures
- Published
- 2016
24. Interaction of Cefdinir with Iron in Aqueous Solution
- Author
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Tsutomu Yasuda, Shuhei Deguchi, Yoshihiko Okamoto, Marie T. Mooney, Mamoru Fujioka, and Toshiji Tada
- Subjects
Aqueous solution ,Chemistry ,Metal ions in aqueous solution ,Potentiometric titration ,Inorganic chemistry ,General Chemistry ,General Medicine ,Oxime ,Cefdinir ,Bioavailability ,chemistry.chemical_compound ,Stability constants of complexes ,Drug Discovery ,medicine ,medicine.drug ,Antibacterial agent - Abstract
Cefdinir (CFDN) is an orally active, semisynthetic cephalosporin antibiotic and its structure is characterized by an oxyimino side chain which is able to form complexes with various metal ions. We observed that bioavailability of CFDN in dogs was reduced when it was co-administered with iron(II) salts. To assess possible effects of extraneous iron such as iron supplements on the bioavailability of CFDN, stability constants of the complexes formed between CFDN and iron(II) and iron(III) have been determined in aqueous solution by potentiometric and spectrophotometric titration methods. The stability constants were as follows : log β110=7.53, log β120=14.44, log β130=18.33 for the iron(II) complexes and log β110=10.43, log β120=20.40 and log β130=27.54 for the iron(III) complexes. Theoretical species distribution diagrams as a function of pH for solutions of metal (M) (0.1 mM) and ligand (L) (0.3 mM) showed that M1L1H0 and M1L2H0 existed as major species for the iron(II) system and M1L2H0 and M1L3H0 were main species for the iron(III) system under neutral conditions. From these results it is believed that complex formation in the digestive tract is involved in the reduction of the bioavailability of CFDN in dogs. In addition, spectrophotometric studies indicated that iron(II) coordinated to CFDN via the thiazole-ring and deprotonated oxime nitrogen atoms and iron(III) coordinated via the amide and deprotonated oxime oxygen atoms.
- Published
- 1995
25. Large Diamagnetism of AV2Al20 (A = Y and La)
- Author
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Jun-ichi Yamaura, Takahiro Hirose, Zenji Hiroi, Atsushi Onosaka, and Yoshihiko Okamoto
- Subjects
Condensed Matter - Materials Science ,Materials science ,Strongly Correlated Electrons (cond-mat.str-el) ,General Physics and Astronomy ,chemistry.chemical_element ,Materials Science (cond-mat.mtrl-sci) ,FOS: Physical sciences ,Unit volume ,Bismuth ,Crystal ,Crystallography ,Condensed Matter - Strongly Correlated Electrons ,Lattice constant ,chemistry ,Diamagnetism ,Electronic band structure - Abstract
We find anomalously large diamagnetic responses in the cage compounds AV2Al20 where A = Y and La, not A = Al0.3, Sc0.4, and Lu, despite the apparent similarities in crystal and electronic structures among these compounds. The magnetic susceptibilities of the Y and La compounds become -1.94 and -7.44 x 10-4 cm3 mol-1 at 10 K, respectively, the latter of which corresponds to approximately one-quarter of that of bismuth, a well-known diamagnetic material, in terms of unit volume. The origin is not clear but may be related to a specific evolution in the band structure, as the diamagnetic response increases with increasing lattice constant., 5 pages, 4 figures, 1 table; to pe published in J. Phys. Soc. Jpn
- Published
- 2012
26. ChemInform Abstract: A Novel Crystal Polymorph of Volborthite, Cu3V2O7(OH)2·2H2O
- Author
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Jun-ichi Yamaura, Zenji Hiroi, Hiroyuki Yoshida, Gøran J. Nilsen, Hajime Ishikawa, and Yoshihiko Okamoto
- Subjects
Crystal ,Crystallography ,Chemistry ,General Medicine ,Autoclave - Abstract
A new polymorph of the title compound is hydrothermally synthesized from a solution of CuO and V2O5 in 1% aq, HNO3 (autoclave, 443 K, 10 d).
- Published
- 2012
27. Blockade of TRPM8 activity reduces the invasion potential of oral squamous carcinoma cell lines
- Author
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Tsuyako Ohkubo, Yoshihiko Okamoto, Jun Yamazaki, and Tetsuro Ikebe
- Subjects
Cancer Research ,Patch-Clamp Techniques ,TRPM Cation Channels ,Antineoplastic Agents ,Pyrimidinones ,Biology ,Real-Time Polymerase Chain Reaction ,Membrane Potentials ,Transient receptor potential channel ,chemistry.chemical_compound ,Cell Movement ,Cell Line, Tumor ,TRPM8 ,Humans ,Anilides ,Neoplasm Invasiveness ,Calcium Signaling ,RNA, Messenger ,Cell Proliferation ,Oncogene ,Reverse Transcriptase Polymerase Chain Reaction ,Icilin ,Cell cycle ,Immunohistochemistry ,Tongue Neoplasms ,Squamous carcinoma ,Menthol ,stomatognathic diseases ,Matrix Metalloproteinase 9 ,Oncology ,chemistry ,Cancer cell ,Immunology ,Carcinoma, Squamous Cell ,Cancer research ,Intracellular - Abstract
Several members of the transient receptor potential (TRP)-channel family are expressed in cancer cells. One, cold/menthol-sensitive TRPM8, is reportedly an important player in carcinogenesis in human prostate cancer, although its involvement in oral squamous cell carcinoma (SCC) remains unclear. The present immunohistochemistry and RT-PCR results revealed intense TRPM8 expression in two SCC cell lines, HSC3 and HSC4, derived from the human tongue. Menthol, icilin, and a more specific TRPM8 agonist (WS-12) induced non-specific cation currents, with Ca2+ permeability being greater than that of Na+ or K+. The novel TRPM8 antagonist RQ-00203078 (RQ) profoundly reduced such agonist-induced cation currents. Intracellular Ca2+ imaging revealed that menthol induced both intracellular Ca2+ release and store-operated Ca2+ entry, with RQ inhibiting each effect. To assess the possible pathophysiological role of TRPM8 in oral SCC, we performed motility and invasion assays, and gelatin zymography. Menthol augmented the migration and invasion abilities of both HSC3 and HSC4 cells by potentiating MMP-9 activity. RQ suppressed all of these effects. These results may aid understanding of the pathophysiological implications of TRPM8 channels in the oral SCC cells, support TRP proteins as valuable targets for pharmaceutical intervention, and inform the targeting of oral SCC in which the prognosis is poor.
- Published
- 2012
28. Distorted Kagome Lattice Generated by a Unique Orbital Arrangement in the Copper Mineral KCu3As2O7(OH)3
- Author
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Yoshihiko Okamoto, Zenji Hiroi, Gøran J. Nilsen, and Hajime Ishikawa
- Subjects
Condensed Matter - Materials Science ,Materials science ,Condensed matter physics ,Geometrical frustration ,General Physics and Astronomy ,chemistry.chemical_element ,Materials Science (cond-mat.mtrl-sci) ,FOS: Physical sciences ,Copper ,Magnetic susceptibility ,Heat capacity ,Atomic orbital ,chemistry ,Ferromagnetism ,Antiferromagnetism ,Condensed Matter::Strongly Correlated Electrons ,Crystallite - Abstract
We study polycrystalline samples of KCu3As2O7(OH)3, a new candidate spin-1/2 kagome antiferromagnet, by magnetic susceptibility and heat capacity measurements above 2 K. The unique arrangement of the 3z2 - r2 and x2 - y2 orbitals on the Cu2+ kagome net is noted and compared to the orbital patterns found in other kagome minerals. It is suggested that this orbital arrangement gives rise to one antiferromagnetic and two ferromagnetic interactions on isosceles triangles forming a highly distorted kagome lattice. KCu3As2O7(OH)3 is found to show an antiferromagnetic long-range order at T_N = 7.2 K. Remarkably, a spin entropy is more gradually released upon cooling below T_N compared with a conventional magnetic long-range order, which may originate from the geometrical frustration still present in this highly distorted kagome lattice., Comment: 5 pages, 4 figures
- Published
- 2012
- Full Text
- View/download PDF
29. A novel crystal polymorph of volborthite, Cu3V2O7(OH)2 2H2O
- Author
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Jun-ichi Yamaura, Yoshihiko Okamoto, Hajime Ishikawa, Hiroyuki Yoshida, Gøran J. Nilsen, and Zenji Hiroi
- Subjects
Crystal ,Condensed Matter - Materials Science ,Crystallography ,Spins ,Chemistry ,Materials Science (cond-mat.mtrl-sci) ,FOS: Physical sciences ,General Medicine ,Crystal structure ,Single crystal ,General Biochemistry, Genetics and Molecular Biology ,Monoclinic crystal system - Abstract
A new polymorph of volborthite [tricopper(II) divanadium(V) heptaoxide dihydroxide dihydrate], Cu3V2O7(OH)2 2H2O, has been discovered in a single crystal prepared by hydrothermal synthesis. X-ray analysis reveals that the monoclinic structure has the space group C2/c at room temperature, which is different from that of the previously reported C2/m structure. Both structures have Cu3O6(OH)2 layers composed of edge-sharing CuO4(OH)2 octahedra, with V2O7 pillars and water molecules between the layers. The Cu atoms occupy two and three independent crystallographic sites in the C2/m and C2/c structures, respectively, likely giving rise to different magnetic interactions between CuII spins in the kagome lattices embedded in the Cu3O6(OH)2 layers., Comment: 7pages, 2figures
- Published
- 2012
- Full Text
- View/download PDF
30. Crystal Chemistry and Magnetic Properties of Manganese Zinc Alloy 'YMn2Zn20' Comprising a Mn Pyrochlore Lattice
- Author
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Takeshi Shimizu, Zenji Hiroi, Jun-ichi Yamaura, and Yoshihiko Okamoto
- Subjects
Materials science ,Crystal chemistry ,Magnetism ,Geometrical frustration ,Inorganic chemistry ,Pyrochlore ,chemistry.chemical_element ,FOS: Physical sciences ,Manganese ,Crystal structure ,engineering.material ,Inorganic Chemistry ,Condensed Matter::Materials Science ,Materials Chemistry ,Physical and Theoretical Chemistry ,Chemical composition ,Condensed Matter - Materials Science ,Magnetic moment ,Materials Science (cond-mat.mtrl-sci) ,Condensed Matter Physics ,Electronic, Optical and Magnetic Materials ,Crystallography ,chemistry ,Ceramics and Composites ,engineering ,Condensed Matter::Strongly Correlated Electrons - Abstract
The chemical composition, crystal structure, and magnetic properties of a manganese zinc alloy with an ideal composition of YMn2Zn20, which comprises a pyrochlore lattice made of Mn atoms, are reported. The compound is stable only when In or Al is partially substituted for Zn. We have determined the actual chemical formula as YMn2+dZn20-x-dMx, with M = In or Al, and have identified the characteristic preferences with which the incorporated M and excess Mn atoms occupy the three crystallographic sites for Zn atoms. The Mn atoms in the pyrochlore lattice possess small magnetic moments that interact with each other antiferromagnetically but exhibit no long-range order above 0.4 K, probably owing to the geometrical frustration of the pyrochlore lattice. As a result, the effective mass of the conduction electrons is considerably enhanced, as observed in the related pyrochlore-lattice compounds (Y,Sc)Mn2 and LiV2O4. However, the presence of excess Mn atoms with large localized magnetic moments comparable to spin 5/2 tends to mask the inherent magnetism of the pyrochlore Mn atoms. It is suggested that "YMn2Zn18In2" with neither excess Mn atoms nor site disorder would be an ideal compound for further study., Comment: 19 pages, 18 figures, accepted for publication in J. Solid State Chem
- Published
- 2012
- Full Text
- View/download PDF
31. Superconductivity and Rattling under High Pressure in the beta-Pyrochlore Oxide RbOs2O6
- Author
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Yoshihiko Okamoto, Jun-ichi Yamaura, Zenji Hiroi, Nao Takeshita, and Hiroki Ogusu
- Subjects
Superconductivity ,Materials science ,Condensed Matter - Superconductivity ,Pyrochlore ,Analytical chemistry ,Oxide ,General Physics and Astronomy ,FOS: Physical sciences ,engineering.material ,Ion ,Superconductivity (cond-mat.supr-con) ,chemistry.chemical_compound ,chemistry ,Electrical resistivity and conductivity ,High pressure ,engineering ,Single crystal ,Ambient pressure - Abstract
Rattling-induced superconductivity in the beta-pyrochlore oxide RbOs2O6 is investigated under high pressures up to 6 GPa. Resistivity measurements in a high-quality single crystal show that the superconducting transition temperature Tc increases gradually from 6.3 K at ambient pressure to 8.8 K at 3.5 GPa, surprisingly remains almost constant at 8.8 \pm 0.1 K in a wide pressure range between 3.5 (Po) and 4.8 GPa, and suddenly drops to 6.3 K at Ps = 4.9 GPa, followed by a gradual decrease with further pressure increase. Two anomalies in the temperature dependence of the normal-state resistivity are observed at Po < P < Ps and P > Ps, revealing the presence of two high-pressure phases corresponding to the changes in Tc. The rattling of the Rb ion inside a cage made of Os and O atoms may be slightly and seriously modified in these high-pressure phases that probably have cages of reduced symmetry, respectively, so that electron-rattler interactions that govern the superconducting and transport properties of beta-RbOs2O6 are significantly affected., arXiv admin note: text overlap with arXiv:1009.0355
- Published
- 2011
- Full Text
- View/download PDF
32. Studies on Structures of Urinary Metabolites of Quinotolast, a New Oral Anti-allergics
- Author
-
Satoshi Kitamura, Yoshihiko Okamoto, Noriaki Kihara, Tsutomu Yasuda, and Akihiro Sato
- Subjects
Male ,Pharmacology ,Chromatography ,Urinary system ,Tetrazoles ,Pharmaceutical Science ,Urine ,Rats ,chemistry.chemical_compound ,Dogs ,Glucosides ,chemistry ,Glucoside ,Animals ,Humans ,Tetrazole ,QUINOTOLAST ,Glucuronide ,Chromatography, High Pressure Liquid ,Quinolizines ,Conjugate - Abstract
Metabolites of quinotolast in the human, rat and dog urine were isolated chromatographically and their structures were determined spectroscopically. para-Hydroxy substitution to the phenoxyl function of quinotolast, and glucoside or glucuronide conjugate to its tetrazole ring were observed.
- Published
- 1993
33. [Untitled]
- Author
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Yoshihiko Okamoto, Satoshi Kitamura, Toshiji Tada, and Tsutomu Yasuda
- Subjects
Pharmacology ,Tetrahydrate ,Stereochemistry ,Vapor pressure ,Sodium ,Organic Chemistry ,Vapour pressure of water ,Pharmaceutical Science ,chemistry.chemical_element ,Quinolizine ,chemistry.chemical_compound ,Reaction rate constant ,chemistry ,Molecular Medicine ,Pharmacology (medical) ,Thermal analysis ,Hydrate ,Biotechnology ,Nuclear chemistry - Abstract
Two hydrates (tetrahydrate, I, and monohydrate, II) of a new antiallergic, sodium 5-(4-oxo-phenoxy-4H-quinolizine-3-carbox-amide)-tetrazolate (FR71021), were prepared and characterized by means of infrared spectrometry, thermal analysis, and power X-ray diffraction spectrometry. While I was confirmed to dehydrate readily resulting in an anhydrate form (noncrystalline form) below its critical relative humidity for dehydration, I was also transformed into II under humid conditions. The transformation kinetics from I to II were investigated under varying temperature and humidity conditions by a powder X-ray diffraction technique. The transformation mechanism followed a zero-order reaction, and the apparent transformation rate constant (k) could be described as a function of water vapor pressure (P), temperature (T), and the interaction orders between water vapor pressure and the samples (s) :k = A · exp(−Ea/ RT) ·Ps, where Ea is the activation energy and R is the gas constant.
- Published
- 1992
34. Determination of cefixime and its metabolises by high-performance capillary electrophoresis
- Author
-
Atsushi Taga, Susumu Honda, Shigetaka Koda, Kazuaki Kakehi, and Yoshihiko Okamoto
- Subjects
Electrophoresis ,Cefotaxime ,Chromatography ,Chemistry ,Metabolite ,Organic Chemistry ,Phosphate buffered saline ,Anti-Infective Agents, Urinary ,General Medicine ,Urine ,Biochemistry ,Analytical Chemistry ,chemistry.chemical_compound ,Capillary electrophoresis ,Cefixime ,medicine ,Humans ,medicine.drug ,Cephalosporin Antibiotic - Abstract
Cefixime (CX), an oral cephalosporin antibiotic, and its metabolites in human digestive organs were separated by various modes of high-performance capillary electrophoresis. The zone electrophoresis mode in phosphate buffer (pH 6.8) containing 3-[(3-cholamidopropyl)dimethylammonio]-1-propanesulphonate gave the best separation, permitting the complete resolution of CX and all of five metabolites. On the other hand, the plain zone electrophoresis mode in phosphate buffer (pH 6.8) offered a simple procedure for the direct determination of urinary CX concentration using intact urine samples.
- Published
- 1992
35. Evidence for oxygen holes due tod−prehybridization in thermoelectricSr1−xRh2O4
- Author
-
T. Baba, H. Takagi, Masaharu Matsunami, M. Taguchi, Shik Shin, Ritsuko Eguchi, Yoshihiko Okamoto, Yukiaki Ishida, A. Chainani, Yasunori Senba, and Hiromichi Ohashi
- Subjects
Physics ,Condensed matter physics ,Binding energy ,chemistry.chemical_element ,Charge (physics) ,Condensed Matter Physics ,Oxygen ,Electronic, Optical and Magnetic Materials ,chemistry ,Vacancy defect ,Thermoelectric effect ,Strongly correlated material ,Absorption (logic) ,Texture (crystalline) - Abstract
Soft-x-ray photoemission and absorption spectroscopies are employed to investigate the electronic structures of ${\text{Sr}}_{1\ensuremath{-}x}{\text{Rh}}_{2}{\text{O}}_{4}$. Similar to the layered cobaltates such as ${\text{Na}}_{1\ensuremath{-}x}{\text{CoO}}_{2}$, a valence-band satellite feature (VBS) occurs at higher binding energy to the $\text{O}\text{ }2p$ band. We find that the VBS resonates at the $\text{O}\text{ }1s$ edge. Additionally, core absorption shows clear $x$ dependence in the $\text{O}\text{ }1s$ edge rather than in the $\text{Rh}\text{ }3p$ edge. These results indicate that the holes in the initial state mainly have $\text{O}\text{ }2p$ character presumably due to $d\text{\ensuremath{-}}p$ rehybridizations affected by ${\text{Sr}}^{2+}$ vacancy potentials. The resultant inhomogeneous charge texture may have impact on the thermoelectric transport properties at low $x$.
- Published
- 2009
36. Band Jahn-Teller Instability and Formation of Valence Bond Solid in a Mixed-Valent Spinel OxideLiRh2O4
- Author
-
Akira Sekiyama, Masaya Uchida, Takeshi Waki, Ryotaro Arita, Seiji Niitaka, Hidenori Takagi, Yoshitaka Nakatsu, Masashi Takigawa, Shigemasa Suga, and Yoshihiko Okamoto
- Subjects
Materials science ,Condensed matter physics ,Band gap ,Jahn–Teller effect ,Spinel ,Oxide ,General Physics and Astronomy ,engineering.material ,Condensed Matter::Materials Science ,chemistry.chemical_compound ,Paramagnetism ,Crystallography ,chemistry ,Seebeck coefficient ,engineering ,Condensed Matter::Strongly Correlated Electrons ,Valence bond theory ,Valence electron - Abstract
We have synthesized a new spinel oxide ${\mathrm{LiRh}}_{2}{\mathrm{O}}_{4}$ with a mixed-valent configuration of ${\mathrm{Rh}}^{3+}$ and ${\mathrm{Rh}}^{4+}$. At room temperature, it is a paramagnetic metal, but on cooling, a metal-insulator transition occurs and a valence bond solid state is formed below 170 K. We argue that the formation of valence bond solid is promoted by a band Jahn-Teller transition at 230 K and the resultant confinement of ${t}_{2g}$ holes within the $xy$ band. The band Jahn-Teller instability is also responsible for the observed enhanced thermoelectric power in the orbital-disordered phase above 230 K.
- Published
- 2008
37. X-ray Crystallographic Characterization of two Polymorphs of 8-(2-Methoxycarbonylamino-6-methylbenzyloxy)-2-methyl-3-(2-propynyl)-imidazo[1, 2-a]pyridine
- Author
-
Shigetaka Koda, Satoshi Kitamura, Akira Miyamae, Yoshihiko Okamoto, and Yukiyoshi Morimoto
- Subjects
Differential Thermal Analysis ,Spectrophotometry, Infrared ,Bicyclic molecule ,Pyridines ,Chemistry ,Stereochemistry ,Hydrogen bond ,Propynyl ,Imidazoles ,Molecular Conformation ,Pharmaceutical Science ,Hydrogen Bonding ,Crystal structure ,Crystallography ,chemistry.chemical_compound ,X-Ray Diffraction ,Polymorphism (materials science) ,Intramolecular force ,X-ray crystallography ,Crystallization ,Monoclinic crystal system - Abstract
Structural characterization of two polymorphs (Forms A and B) of 8-(2-methoxycarbonylamino-6-methylbenzyloxy)-2-methyl-3-(2-p ropynyl)-imidazo [1,2-a]pyridine (1) was accomplished by X-ray crystallographic analysis. Form A crystallized in the monoclinic space group C2/c, with a = 42.936 (14), b = 4.356 (1), c = 21.536 (6) A, beta = 109.92 (4) degrees, z = 8, and dcal = 1.275 g/cm3. Form B crystallized in the monoclinic space group P2(1)/c, with a = 4.367 (1), b = 38.214 (3), c = 11.253 (1) A, beta = 95.47 (2) degrees, z = 4, and dcal = 1.292 g/cm3. Some subtle conformational differences between the polymorphs were observed. Although the Form B crystal has a somewhat more compactly packed structure than Form A, this compactness is thought to be disadvantageous to conformational features and to the crystal structure of Form B. The intramolecular hydrogen bonding force between N(1) and NH(22) atoms of Form B is weaker than that of Form A, and the stacking force between the imidazopyridine rings of Form B may also be weaker than that of Form A. Thus, Form A is considered to be a more stable structure than Form B. In DSC analysis, Form B transformed to Form A. Based on these results, phase transformation from Form B to A occurs during a transient fluid state.
- Published
- 1990
38. Spin-Liquid State in theS=1/2Hyperkagome AntiferromagnetNa4Ir3O8
- Author
-
Minoru Nohara, Hiroko Aruga-Katori, Hidenori Takagi, and Yoshihiko Okamoto
- Subjects
Physics ,Condensed matter physics ,Spinel ,Oxide ,General Physics and Astronomy ,engineering.material ,Magnetic field ,Magnetization ,chemistry.chemical_compound ,chemistry ,Lattice (order) ,engineering ,Antiferromagnetism ,Condensed Matter::Strongly Correlated Electrons ,Quantum spin liquid ,Ground state - Abstract
A spinel related oxide, Na(4)Ir(3)O(8), was found to have a three dimensional network of corner shared Ir(4+) (t(2g)(5)) triangles. This gives rise to an antiferromagnetically coupled S = 1/2 spin system formed on a geometrically frustrated hyperkagome lattice. Magnetization M and magnetic specific heat C(m) data showed the absence of long range magnetic ordering at least down to 2 K. The large C(m) at low temperatures is independent of applied magnetic field up to 12 T, in striking parallel to the behavior seen in triangular and kagome antiferromagnets reported to have a spin-liquid ground state. These results strongly suggest that the ground state of Na(4)Ir(3)O(8) is a three dimensional manifestation of a spin liquid.
- Published
- 2007
39. High-pressure resistivity measurements on the β-pyrochlore oxide KOs2O6
- Author
-
Jun-ichi Yamaura, Yoshihiko Okamoto, Hiroki Ogusu, Nao Takeshita, and Zenji Hiroi
- Subjects
Superconductivity ,Materials science ,Drop (liquid) ,Analytical chemistry ,Oxide ,Pyrochlore ,Energy Engineering and Power Technology ,engineering.material ,Condensed Matter Physics ,Electronic, Optical and Magnetic Materials ,chemistry.chemical_compound ,stomatognathic system ,chemistry ,Electrical resistivity and conductivity ,High pressure ,engineering ,Electrical and Electronic Engineering ,Single crystal ,Ambient pressure - Abstract
High-pressure resistivity measurements are performed on a high-quality single crystal of the β -pyrochlore oxide KOs2O6 in the pressure range of 1.0 to 5.0 GPa. The superconducting transition temperature T c increases slightly from 9.6 K at ambient pressure to 9.8 K at 1.0 GPa, decreases gradually with increasing pressure, and suddenly drops from 6.5 K to 3.2 K across P s = 3.6 GPa . The drop of T c at P s is likely to be related to a change in the rattling vibration associated with a symmetry-breaking structural transition.
- Published
- 2010
40. The spin dynamics in distorted kagome lattices: a comparative Raman study
- Author
-
Hiroyuki Yoshida, Zenji Hiroi, Peter Lemmens, Yoshihiko Okamoto, and Dirk Wulferding
- Subjects
Condensed matter physics ,Spin dynamics ,Phonon ,Chemistry ,Crystal structure ,Condensed Matter Physics ,symbols.namesake ,Lattice (order) ,symbols ,Condensed Matter::Strongly Correlated Electrons ,General Materials Science ,Anisotropy ,Raman spectroscopy ,Fluctuation spectrum ,Raman scattering - Abstract
Despite the conceptional importance of realizing spin liquids in solid states only few compounds are known. On the other hand the effect of lattice distortions and anisotropies on the magnetic exchange topology and the fluctuation spectrum is an interesting problem. We compare the excitation spectra of the two s = 1/2 kagome lattice compounds, volborthite and vesignieite, using Raman scattering. We demonstrate that even small modifications of the crystal structure may have a huge effect on the phonon spectrum and low-temperature properties.
- Published
- 2012
41. Structural studies on an iron(III) complex containing (Z)-2-(2-aminothiazol-4-yl)-N-(2-hydroxyethyl)-2-(hydroxyimino)acetamide, a model compound for a cephalosporin antibiotic Cefdinir
- Author
-
Kazuya Yamaguchi, Yoshihiko Okamoto, Mamoru Fujioka, Shinnichiro Suzuki, Nobuhumi Nakamura, Tsutomu Yasuda, and Shuhei Deguchi
- Subjects
chemistry.chemical_compound ,Crystallography ,chemistry ,Stereochemistry ,Amide ,Atom ,Mössbauer spectroscopy ,Molecule ,General Chemistry ,Ring (chemistry) ,Thiazole ,Acetamide ,Monoclinic crystal system - Abstract
(Z)-2-(2-Aminothiazol-4-yl)-N-(2-hydroxyethyl)-2-(hydroxyimino)acetamide (HL) has been employed as a model compound for a cephalosporin antibiotic, Cefdinir. A trinuclear iron(III) complex [Fe3L6]Cl[OH]21 has been obtained from a methanol solution containing HL and FeCl3 and its structure determined by X-ray crystallography: monoclinic, space group P21/n, a= 15.559(1), b= 19.295(2), c= 10.963(1)A, β= 101.29(1)°, Z= 2. The molecular structure contains a linear Fe(1)–Fe(2)–Fe(1′) arrangement, the central atom Fe(2) being an inversion centre. Atom Fe(1) is co-ordinated to three molecules of L through the thiazole and oximate nitrogen atoms to form Fe(1)L3, and Fe(2) to six oximate oxygen atoms of the two Fe(1)L3 units. The two Fe(1)L3 units are bridged by the central iron atom Fe(2). The Mossbauer spectrum of 1 gave an apparent doublet signal consisting of two doublets, A and B, assigned to Fe(1) and Fe(2), respectively. The isomer shifts δ of these doublets are the same (0.26 mm s–1), and are typical for high-spin iron(III). In addition, the reflectance spectrum did not show any intervalence bands. These spectral data indicate that the three iron atoms are high-spin iron(III). The compound co-ordinates to iron(III)via the thiazole ring nitrogen atom and the oximate nitrogen atom (2N mode) in methanol which is different from that in water, where L prefers to co-ordinate to an iron(III) through the oximate oxygen atom and the amide oxygen atom (2O mode).
- Published
- 1996
42. Mobility Anisotropy of Electrons in Inversion Layers on Oxidized Silicon Surfaces
- Author
-
Yoshihiko Okamoto, Hisashi Hara, Yoshiyuki Takeishi, and Tai Sato
- Subjects
Azimuth ,Materials science ,Silicon ,chemistry ,Condensed matter physics ,Scattering ,Electric field ,Perpendicular ,chemistry.chemical_element ,Inversion (meteorology) ,Electron ,Anisotropy - Abstract
Measurements of the field-effect mobility of electrons in $n$-type inversion layers of Si as functions of the crystalline orientation of the surface and of the azimuthal direction of the current path within the layers are reported. Significant mobility anisotropy observed over a range of strong electric fields perpendicular to the surface at temperatures from 77 to 320 \ifmmode^\circ\else\textdegree\fi{}K contrasts substantially with that in the case of $p$-type inversion layers reported previously. The anisotropy at room temperature can be successfully interpreted in terms of the effective-mass anisotropy calculated on the basis of Stern and Howard's formula for the two-dimensional carriers. For a full understanding of the experimental results, particularly at low temperatures, theoretical investigations including the anisotropy of the relaxation time are required, but have not been explored enough. Extensive data on the dependences of the mobility on the electric field and temperature as well as bulk-acceptor concentration are presented and discussed in the light of existing scattering theories. Some hole-mobility data are included for comparison.
- Published
- 1971
43. The Synthesis and Properties of N-Acylimino-3, 4-dihydroisoquinolinium Betaines
- Author
-
Jun-ichi Minamikawa, Yasumitsu Tamura, Yasuyoshi Miki, Masazumi Ikeda, and Yoshihiko Okamoto
- Subjects
Betaine ,Pharmacology ,Chemistry ,Chemical Phenomena ,Quinolinium Compounds ,Pharmaceutical Science - Published
- 1973
44. Studies of oligosaccharides. XIV. Structure-activity relationship of variations in the sugar moiety of digitoxin
- Author
-
Kiyoshi Takiura, Hidetaka Yuki, Hitoshi Takai, Susumu Honda, and Yoshihiko Okamoto
- Subjects
Digitoxin ,Guinea Pigs ,Fractionation ,Lethal Dose 50 ,chemistry.chemical_compound ,Mice ,Structure-Activity Relationship ,Glucosides ,Drug Discovery ,medicine ,Structure–activity relationship ,Monosaccharide ,Organic chemistry ,Animals ,chemistry.chemical_classification ,Chromatography ,Glycoside ,Heart ,General Chemistry ,General Medicine ,Digitoxigenin ,chemistry ,Lipophilicity ,Toxicity ,medicine.drug - Abstract
Digitoxigenin oligosaccharides of the 1, 6-β-linked D-glucose series and 1, 4-β-linked D-digitoxose series were obtained by the Konigs-Knorr condensation of digitoxigenin with gentio oligosaccharides and by the partial hydrolysis of digitoxin, followed by chromatographic fractionation of products, respectively. Cardiac activity as well as toxicity increased and decreased with the increasing number of unit monosaccharides for glycosides of the D-glucose and the D-digitoxose series, respectively. There was observed a parallelism between the activity as well as toxicity and the lipophilicity of these glycosides.
- Published
- 1974
45. ChemInform Abstract: THE SYNTHESIS AND PROPERTIES OF N-ACYLIMINO-3,4-DIHYDROISOQUINOLINIUM BETAINES
- Author
-
Yasuyoshi Miki, Yoshihiko Okamoto, Jun-ichi Minamikawa, Yasumitsu Tamura, and Masazumi Ikeda
- Subjects
Chemistry ,Organic chemistry ,General Medicine - Published
- 1973
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