Researchers Database

OHARA, Keishi

    Graduate School of Science and Engineering Engineering for Production and Environment Professor
Last Updated :2020/10/13

Researcher Information

Degree

  • Doctor of Science(Kyoto University)

J-Global ID

Research Interests

  • Spin-dynamics   Near-Infrared spectroscopy   EPR   Antioxidant   Free Radical   Photochemistry   Singlet Oxygen   時間分解ESR   活性酸素   生体分子   薬剤反応性   ミセル   近赤外発光   スポット計測   反応速度   化学物理   懸濁系   化学反応   スーパーオキシド   スピンプローブ   プロトン移動   天然抗酸化剤   ビタミンE   時間分解分光   

Research Areas

  • Nanotechnology/Materials / Basic physical chemistry
  • Life sciences / Pharmaceuticals - analytical and physicochemistry
  • Life sciences / Food sciences
  • Nanotechnology/Materials / Functional solid-state chemistry

Academic & Professional Experience

  • 2015/05 - Today  Ehime UniversityGraduate School of Science and EngineeringProfessor
  • 2007/04 - 2015/04  Ehime UniversityGraduate School of Science and EngineeringAssociate Professor
  • 2006/04 - 2007/03  Ehime UniversityGraduate School of Science and EngineeringSenior Assistant Professor
  • 1996/04 - 2006/03  Ehime UniversityFaculty of ScienceAssistant Professor
  • 1996/01 - 1996/04  Kyoto UniversityGraduate School of ScienceResearcher (JSPS Research Fellowships for Young Scientists)

Education

  • 1993/04 - 1996/03  Kyoto University  Graduate School of Science  Department of Chemistry
  • 1987/04 - 1989/03  Osaka University  Graduate School of Science  Inorganic and Physical Chemistry
  • 1983/04 - 1987/03  Osaka University  Faculty of Science  Department of Chemistry

Association Memberships

  • 光化学協会   SOCIETY FOR FREE RADICAL RESEARCH JAPAN   THE SOCIETY OF ELECTRON SPIN SCIENCE AND TECHNOLOGY   THE SPECTROSCOPICAL SOCIETY OF JAPAN   THE CHEMICAL SOCIETY OF JAPAN   

Published Papers

  • Kosuke Oki, Masayoshi Takase, Shigeki Mori, Akitoshi Shiotari, Yoshiaki Sugimoto, Keishi Ohara, Tetsuo Okujima, Hidemitsu Uno
    Journal of the American Chemical Society 140 (33) 10430 - 10434 0002-7863 2018/08 [Peer-reviewed]
     Scientific journal 
    Copyright © 2018 American Chemical Society. A core-expanded, pyrrole-fused azacoronene analogue containing two unusual N-doped heptagons was obtained from commercially available octafluoronaphthalene and 3,4-diethylpyrrole in two steps as a heteroatom-doped nonplanar nanographene. Full fusion with the formation of the tetraazadipleiadiene framework and the longitudinally twisted structure was unambiguously confirmed by single-crystal X-ray diffraction analysis. The edge-to-edge dihedral angle along the acene moiety was 63°. This electron-rich π-system showed four reversible oxidation peaks. Despite the nonplanar structure, the Hückel aromaticity owing to a peripheral π-conjugation in the dicationic state was concluded from the bond-length alternation and nucleus-independent chemical shift (NICS) and anisotropy of the induced current density (ACID) calculations.
  • Shin-ichi Nagaoka, Yuki Bandoh, Umpei Nagashima, Keishi Ohara
    JOURNAL OF PHYSICAL CHEMISTRY A 121 (42) 8069 - 8079 1089-5639 2017/10 [Peer-reviewed]
     Scientific journal 
    Singlet-oxygen (O-1(2)) quenching, free-radical scavenging, and excited-state intramolecular proton-transfer (ESIPT) activities of hydroxyflavones, anthocyanidins, and 1-hydroxyanthraquinones were studied by means of laser, stopped-flow, and steady-state spectroscopies. In hydroxyflavones and anthocyanidins, the O-1(2) quenching activity positively correlates to the free radical scavenging activity. The reason for this correlation can be understood by considering that an early step of each reaction involves electron transfer from the unfused phenyl ring (B-ring), which is singly bonded to the bicyclic chromen or chromenylium moiety (A- and C-rings). Substitution of an electron-donating OH group at B-ring enhances the electron transfer leading to activation of the O-1(2) quenching and free-radical scavenging. In 3-hydroxyflavones, the OH substitution at B-ring reduces the activity of ESIPT within C-ring, which can be explained in terms of the nodal-plane model. As a result, the 102 quenching and free-radical scavenging activities negatively correlate to the ESIPT activity. A catechol structure at B-ring is another factor that enhances the free-radical scavenging in hydroxyflavones. In contrast to these hydroxyflavones, 1-hydroxyanthraquinones having an electron-donating OH substituent adjacent to the O-H-O = C moiety susceptible to ESIPT do not show a simple correlation between their O-1(2) quenching and ESIPT activities, because the OH substitution modulates these reactions.
  • Yamamoto Ryoma, Yamamoto Takashi, Ohara Keishi, Naito Toshio
    MAGNETOCHEMISTRY 3 (2) 2312-7481 2017/06 [Peer-reviewed]
  • Noma Hiroki, Ohara Keishi, Naito Toshio
    INORGANICS 4 (2) 2304-6740 2016/06 [Peer-reviewed]
  • Tetsuo Okujima, Chie Ando, Saurabh Agrawal, Hiroki Matsumoto, Shigeki Mori, Keishi Ohara, Ichiro Hisaki, Takahiro Nakae, Masayoshi Takase, Hidemitsu Uno, Nagao Kobayashi
    JOURNAL OF THE AMERICAN CHEMICAL SOCIETY 138 (24) 7540 - 7543 0002-7863 2016/06 [Peer-reviewed]
     Scientific journal 
    An acenaphthylene-fused cyclo[10]pyrrole 1b was selectively synthesized via an oxidative coupling reaction of the corresponding 2,2'-bipyrrole with the appropriate dianion template, croconate anion. The structure of 1b as the isolated largest cyclo[n]pyrrole was elucidated by X-ray crystallographic analysis. The absorption spectrum exhibited a markedly red-shifted, intensified L band at 1982 nm, which was interpreted by application of Michl's perimeter and Gouterman's 4-orbital models, supported by magnetic circular dichroism (MCD) data and theoretical calculations.
  • Shin-ichi Nagaoka, Hikaru Endo, Keishi Ohara, Umpei Nagashima
    JOURNAL OF PHYSICAL CHEMISTRY B 119 (6) 2525 - 2532 1520-6106 2015/02 [Peer-reviewed]
     Scientific journal 
    Excited-state intramolecular proton-transfer (ESIPT) and singlet-oxygen (O-1(2)) quenching activities of intramolecularly hydrogen-bonded 1-(acylamino)anthraquinones have been studied by means of static and laser spectroscopies. The ESIPT shows a substituent effect, which can be explained in terms of the nodal-plane model. The ESIPT activity positively and linearly correlates with their O-1(2) quenching activity. The reason for this correlation can be understood by considering ESIPT-induced distortion of their ground-state potential surface and their encounter complex formation with O-1(2). Intramolecularly hydrogen-bonded hydroxyanthraquinones found in aloe also show a similar positive and linear correlation, which can be understood in the same way.
  • Hiroki Noma, Keishi Ohara, Toshio Naito
    CHEMISTRY LETTERS 43 (8) 1230 - 1232 0366-7022 2014/08 [Peer-reviewed]
     Scientific journal 
    [Cu(dmit)(2)](2-) formally consists of a magnetic Cu2+ ion (S = 1/2) and closed-shell pi-conjugated dmit(2-) ligands. However, it has been determined by electron spin resonance and molecular orbital calculations that the majority (91-100%) of the spin delocalizes over the ligands in the ground state, while the spin significantly (40-90%) localizes on Cu under UV irradiation. Considering the results of X-ray structural analyses under UV irradiation, the spin distribution varies depending on the wavelengths irradiated and retaining the square-planar coordination geometries.
  • Toshio Naito, Tomoaki Karasudani, Naoki Nagayama, Keishi Ohara, Kensuke Konishi, Shigeki Mori, Takahiro Takano, Yukihiro Takahashi, Tamotsu Inabe, Shota Kinose, Sadafumi Nishihara, Katsuya Inoue
    EUROPEAN JOURNAL OF INORGANIC CHEMISTRY (24) 4000 - 4009 1434-1948 2014/08 [Peer-reviewed]
     Scientific journal 
    The simple molecular salt NMQ[Ni(dmit)(2)] (NMQ = N-methylquinolinium, dmit = 1,3-dithiol-2-thione-4,5-dithiolate) functions as a diamagnetic insulator with an activation energy E-a(dark) of 0.20 eV. However, at 300 K, it exhibits ca. 40 times higher conductivity (sigma(UV)) under UV irradiation [(375 +/- 5) nm, 15.7 mW cm(-2)] than it does under dark conditions (sigma(dark)). The ratio sigma(UV)/sigma(dark) rapidly increases with decreasing temperature and reaches ca. 880 at 200 K. From the temperature dependence of sigma(UV), the activation energy under irradiation E-a(UV) is 0.12 eV. These observations cannot be explained as the result of sample heating during UV irradiation. Rather, the X-ray photoelectron spectra of the sulfur and nickel atoms, the calculated band structure, and the UV/Vis spectra of the salt can all be explained consistently as follows: charge transfer between the Ni(dmit)(2) moieties upon exposure to 375 nm UV light induces melting of the charge-ordered state and produces the unusually large photoconductivity of NMQ[Ni(dmit)(2)].
  • Tetsuo Okujima, Yoichi Shida, Keishi Ohara, Yuya Tomimori, Motoyoshi Nishioka, Shigeki Mori, Takahiro Nakae, Hidemitsu Uno
    JOURNAL OF PORPHYRINS AND PHTHALOCYANINES 18 (8-9) 752 - 761 1088-4246 2014/08 [Peer-reviewed]
     Scientific journal 
    A series of O-chelated BODIPYs fused with aromatic rings such as benzene and acenaphthylene at beta,beta-positions was synthesized as a near-infrared dye. The photophysical properties were examined by UV-vis-NIR absorption and fluorescence measurement. Acenaphthylene-fused O-BODIPYs showed a intense absorption at 750-840 nm with the epsilon of 10(5) M-1.cm(-1). and a fluorescene emission at 770-850 nm with the high Phi value of 0.06-0.43.
  • Tomoko Saiki, Shigeld Mori, Keishi Ohara, Toshio Naito
    CHEMISTRY LETTERS 43 (7) 1119 - 1121 0366-7022 2014/07 [Peer-reviewed]
     Scientific journal 
    beta-DiCC[Ni(dmit)(2)] (dmit: 1,3-dithiole-2-thione-4,5-dithiolato and DiCC: 3,3'-dihexyloxacarbocyanine) is a charge-transfer salt with redox activity. When voltages are applied, it brings about a reversible, hysteretic, solid-state-electrolytic reaction exhibiting a capacitor-like electric response. Based on the electron spin resonance spectra, the resistivity behavior, and the tight-binding band calculation, it is indicated that one can finely and reversibly control the redox equilibrium between DiCC(+) and [Ni(dmit)(2)](-) molecules by applying voltages.
  • Yoshimi Sueishi, Masashi Hori, Misa Ishikawa, Keiko Matsu-Ura, Erisa Kamogawa, Yusaku Honda, Masakazu Kita, Keishi Ohara
    JOURNAL OF CLINICAL BIOCHEMISTRY AND NUTRITION 54 (2) 67 - 74 0912-0009 2014/03 [Peer-reviewed]
     Scientific journal 
    Scavenging rate constants of eight hydrophilic antioxidants, including caffeic acid, chlorogenic acid, genistein, glutathione, N-acetylcysteine, rutin, trolox, and uric acid against multiple ROS, namely superoxide anion, hydroxyl radical, singlet oxygen, and alkoxyl radical were determined with the electron spin resonance method. Direct flash photolysis measurement of the second-order rate constant in the reaction of alkoxyl radical plus the spin trap 5,5-dimethyl-pyrroline N-oxide made it possible to evaluate scavenging rate constants in antioxidants. The magnitudes of scavenging rate constants were notably dependent on the character of each ROS and the overall rate constants were highest in hydroxyl radical scavenging and the lowest in superoxide anion. The highest scavenging rate constant against superoxide anion was obtained by chlorogenic acid (2.9 x 10(5) M-1 s(-1)) and the lowest was by N-acetylcysteine (5.0 x 10(2) M-1 s(-1)) For singlet oxygen, the highest was by glutathione (9.4 x 10(8) M-1 s(-1)) and the lowest was by uric acid (2.3 x 10(6) M-1 s(-1)). All other numbers are listed and illustrated. Redox potential measurements of the antioxidants indicated that the antioxidants are likely to react with superoxide anion and singlet oxygen through electron transfer processes.
  • Hisako Sato, Kenji Tamura, Keishi Ohara, Shin-ichi Nagaoka
    NEW JOURNAL OF CHEMISTRY 38 (1) 132 - 139 1144-0546 2014/01 [Peer-reviewed]
     Scientific journal 
    Mono- and multi-layered films comprised of amphiphilic cationic iridium(III) complexes hybridized with the exfoliated nanosheets of synthetic saponite were prepared by the modified Langmuir-Blodgett method. Three iridium(III) complexes with different emission maxima (lambda(max)) were used as incorporated complexes: [Ir(dfppy)(2)(dc9bpy)](+) (lambda(max) = 500 nm) (dfppyH = 2-(4',6'-difluorophenyOpyridine; dc9bpy = 4,4'-dinonY1-2,2'-bipyridine) [Ir(ppy)(2)(dc9bpy)](+) (lambda(max) = 550 nm) (ppyH = 2-phenylpyridine) and [Ir(piq)(2)(dc9bpy)](+) (lambda(max) = 590 nm) (piqH = 1-phenylisoquinoline) for blue, yellow and red emissions, respectively. Six triple-layered films with different layer sequences were fabricated by layer-by-layer deposition onto quartz substrates. Stationary emission spectra were recorded on the prepared films under vacuum and at various oxygen pressures Notably the change in the spectral shape at surrounding oxygen pressure depended remarkably on the layer sequence. Quenching by oxygen molecules was analyzed by applying a two-site model to the Stern-Volmer plots. The present nanometer-thick films were regarded as a benchmark for an optical device emitting different visible lights in response to oxygen pressure.
  • Tetsuo Okujima, Chie Ando, John Mack, Shigeki Mori, Ichiro Hisaki, Takahiro Nakae, Hiroko Yamada, Keishi Ohara, Nagao Kobayashi, Hidemitsu Uno
    CHEMISTRY-A EUROPEAN JOURNAL 19 (41) 13970 - 13978 0947-6539 2013/10 [Peer-reviewed]
     Scientific journal 
    An acenaphthylene-fused cyclo[8]pyrrole was synthesized by using an oxidative coupling reaction of the corresponding 2,2-bipyrrole. Two conformational isomers 1a and 1b were isolated, and their molecular structures were elucidated by X-ray crystallographic studies. The less-polar and lower-symmetry 1b isomer can be converted into the 1a isomer through a thermal ring flip. Application of the perimeter model developed by Michl to magnetic circular dichroism spectroscopic data and theoretical calculations demonstrate that there is a marked redshift of the near-IR absorption maxima relative to cyclo[8]isoindole because there is a significant stabilization of the LUMO due to the differing effects of a fused ring expansion with acenaphthylene and benzene moieties on the frontier molecular orbitals.
  • Keishi Ohara, Kohji Doi, Yuka Niizaki, Shin-ichi Nagaoka
    JOURNAL OF PHOTOCHEMISTRY AND PHOTOBIOLOGY A-CHEMISTRY 249 (1) 1 - 8 1010-6030 2012/12 [Peer-reviewed]
     Scientific journal 
    A kinetic study on singlet oxygen (O-1(2)) quenching by 4-hydroxycinnamic acid derivatives (ferulic acid (FA) and caffeic acid (CA)) has been performed by measuring time-evolutions of O-1(2) phosphorescence at 1274 nm in ethanol, in an ethanol/acetone mixed solvent and in an ethanol/H2O mixed solvent under acidic, neutral and basic conditions. In organic solvents, the estimated second-order rate constants of O-1(2) quenching (k(Q)) were distributed between 10(5) and 10(6) M-1 s(-1): for example, in ethanol, 2.2 x 10(5) M-1 s(-1) for FA and 5.2 x 10(5) M-1 s(-1) for CA. On the other hand, the k(Q) values in ethanol/H2O solutions were enlarged from those in organic solvents, and varied largely with pH from 10(6) to over 10(8) M-1 s(-1). In the case of FA, the O-1(2) quenching activity decreased in the order of FA(2-) (at pH > 10)>> FA(-) (pH 5-9) > FA (pH < 4). The result suggests that deprotonation due to the acid-base equilibrium affects the O-1(2) quenching activity. For both of FA and CA, the phenolate anion under basic conditions (pH 10-12) showed the largest activity probably because of occurrence of the favored chemical quenching through the electron transfer from the phenolate anion to O-1(2). These behaviors would affect several antioxidant assays in vivo and in vitro targeting O-1(2). (C) 2012 Elsevier B.V. All rights reserved.
  • Kazuya Morimoto, Takahiro Nakae, Keishi Ohara, Kenji Tamura, Shin-ichi Nagaoka, Hisako Sato
    NEW JOURNAL OF CHEMISTRY 36 (12) 2467 - 2471 1144-0546 2012/12 [Peer-reviewed]
     Scientific journal 
    Langmuir-Blodgett (LB) films were prepared by hybridizing a floating monolayer of an amphiphilic cationic iridium(m) complex with clay particles in a subphase. Two kinds of iridium(III) complexes were used: [Ir(dfppy)(2)(dc9bpy)](+) (denoted by DFPPY: dfppyH = 2-(4',6'-difluoro-phenyl)pyridine; dc9bpy = 4,4'-dinonyl-2,2'-bipyridine) with the maximum emission wavelength (lambda(max)) at 500 nm and [Ir(ppy)(2)(dc9bpy)](+) (denoted by PPY: ppyH = 2-phenylpyridine) with lambda(max) at 550 nm. Stationary emission spectra were recorded on the following films under vacuum: {DFPPY or PPY/clay}(n) (n = 1-3), {DFPPY/clay/PPY/clay} and {PPY/clay/DFPPY/clay}. The intensity of emission from {PPY/clay}(n) or {DFPPY/clay}(n) increased nearly in proportion to the layer number (n). Both DFPPY and PPY emitted simultaneously from {DFPPY/clay/PPY/clay}, indicating the low contribution of energy transfer. Contrarily PPY emitted exclusively from {PPY/clay/DFPPY/clay} as a result of the efficient quenching of excited DFPPY in the lower layer by PPY in the upper layer. The introduction of oxygen gas resulted in the decrease of emission for all films. Notably {DFPPY/clay/PPY/clay} exhibited a dual emitting character under an oxygen atmosphere, that is, the broad emission maximum was observed around 530 nm at lower oxygen pressure (0 < P-O2 < 4 kPa), while the emission peak shifted to 550 nm at higher oxygen pressure (P-O2 > 4 kPa).
  • Toshio Naito, Tomoaki Karasudani, Keishi Ohara, Takahiro Takano, Yukihiro Takahashi, Tamotsu Inabe, Ko Furukawa, Toshikazu Nakamura
    ADVANCED MATERIALS 24 (46) 6153 - 6157 0935-9648 2012/12 [Peer-reviewed]
     Scientific journal 
    An organic insulating crystal reversibly becomes a magnetic conductor under UV irradiation. The rapid and qualitative change in the physical properties is wavelength selective and explained by charge transfer between donor and photochemically active acceptor molecules. The photochemical redox reaction in the crystal produces a partially filled band and localized spins simultaneously.
  • Toshio Naito, Tomoaki Karasudani, Shigeki Mori, Keishi Ohara, Kensuke Konishi, Takahiro Takano, Yukihiro Takahashi, Tamotsu Inabe, Sadafumi Nishihara, Katsuya Inoue
    JOURNAL OF THE AMERICAN CHEMICAL SOCIETY 134 (45) 18656 - 18666 0002-7863 2012/11 [Peer-reviewed]
     Scientific journal 
    UV irradiation reversibly switches a new insulating and nonmagnetic molecular crystal, BPY[Ni(dmit)(2)](2) (BPY = N,N'-ethylene-2,2'-bipyridinium; Ni(dmit)(2) = bis(1,3-dithiole-2-thione-4,5-dithiolato)nickelate(III)), into a magnetic conductor. This is possible because the bipyridyl derivative cations (BPY2+) trigger a photochemical redox reaction in the crystal to produce a change of similar to 10% in the filling of the Ni(dmit)(2) valence band, leaving localized spins on the BPY themselves. In the dark, almost all of the BPY molecules are closed shell cations, and most of the Ni(dmit)(2). radical anions form spin singlet pairs; thus, this material is a diamagnetic semiconductor. Under UV irradiation, a photocurrent is observed, which enhances the conductivity by 1 order of magnitude Electron-spin resonance. measurements indicate that the 'UV:. irradiation reversibly generates. carriers and localized spins on the Ni(dmit)(2). and the BPY, respectively: This high photoconductivity can be explained by charge transfer (CT) transitions between Ni(dmit)(2) and BPY in the UV region. In other words, the photoconduction and "photomagnetism" can be described as reversible optical control of the electronic states between an ionic salt (BPY2+/[Ni(dmit)(2)](-), nonmagnetic insulator) and a CT complex (BPY2(1-delta)+/[Ni(dmit)(2)]((1-delta)-) (delta approximate to 0.1), magnetic conductor) in the solid state.
  • Shin Ichi Nagaoka, Keishi Ohara, Miki Takei, Mari Nakamura, Mariko Mishima, Umpei Nagashima
    Journal of Photochemistry and Photobiology A: Chemistry 240 75  1010-6030 2012/07 [Peer-reviewed]
     Scientific journal
  • Shin Ichi Nagaoka, Akiko Fujii, Megumi Hino, Mai Takemoto, Misaki Yasuda, Mariko Mishima, Keishi Ohara, Akane Masumoto, Hidemitsu Uno, Umpei Nagashima
    Journal of Physical Chemistry B 116 2338  1520-6106 2012/02 [Peer-reviewed]
     Scientific journal
  • Shin-ichi Nagaoka, Keishi Ohara, Miki Takei, Mari Nakamura, Mariko Mishima, Umpei Nagashima
    JOURNAL OF PHOTOCHEMISTRY AND PHOTOBIOLOGY A-CHEMISTRY 225 (1) 106 - 112 1010-6030 2011/12 [Peer-reviewed]
     Scientific journal 
    The UV protection and singlet-oxygen ((1)O(2)) quenching activity of intramolecularly hydrogen-bonded hydroxyanthraquinone derivatives found in aloe have been studied by means of laser spectroscopy. The UV protective activity provided by excited-state intramolecular proton-transfer (ESIFT) in these molecules correlates with their (1)O(2) quenching activity, and the UV protective molecules have high (1)O(2)-quenching function. The reason for this correlation can be understood by considering ESIPT-induced distortion of ground-state potential surfaces in encounter complexes with (1)O(2). (C) 2011 Elsevier B.V. All rights reserved.
  • Tetsuo Okujima, Guangnan Jin, Naoki Matsumoto, John MacK, Shigeki Mori, Keishi Ohara, Daiki Kuzuhara, Chie Ando, Noboru Ono, Hiroko Yamada, Hidemitsu Uno, Nagao Kobayashi
    Angewandte Chemie - International Edition 50 5699 - 5703 1433-7851 2011/06 [Peer-reviewed]
     Scientific journal 
    Retro: Cyclo[8]isoindole, which has a saddle-shaped geometry (see picture, 2), was synthesized by oxidative coupling of a bicyclo[2.2.2]octadiene(BCOD)- fused 2,2′-bipyrrole followed by a retro-Diels-Alder reaction of BCOD-fused cyclo[8]pyrrole (1). Key trends in the optical spectra of ring-annelated cyclo[8]pyrroles are identified based on magnetic circular dichroism spectra and theorectical calculations. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
  • Keishi Ohara, Akihiro Ikeda, Shin-ichi Nagaoka
    JOURNAL OF PHOTOCHEMISTRY AND PHOTOBIOLOGY A-CHEMISTRY 218 (1) 93 - 100 1010-6030 2011/02 [Peer-reviewed]
     Scientific journal 
    The quenching kinetics of superoxide (O(2)(-center dot)) in water/oil (w/o) interface region of Aerosol OT reversed micelle has been investigated with a transient absorption method. Photodecomposition of alpha-tocopherol by 266 nm laser light in the presence of O(2) produced O(2)(-center dot) together with the tocopheroxyl radical (Toc(center dot)). The subsequent reaction between Toc(center dot) and O(2)(-center dot) occurred in the time region of 1-150 mu s after the photoexcitation. There. O(2)(-center dot) kinetics could be traced by monitoring the Toc(center dot) absorption. In an Aerosol OT reversed micelle solution containing vitamin C (VC), VC would be located in water droplets inside the reversed micelle and would react with both Toc(center dot) and O(2)(-center dot) at the w/o interface around the reversed micelle. The Toc(center dot) decay in the time region of 1-150 mu s was accelerated by addition of VC, suggesting that the O(2)(-center dot) quenching by VC progressed as well as the Tor quenching by VC. From a numerical simulation with treating the simultaneous rate equations for Toc(center dot) concentration by Runge-Kutta method, the rate constant for the O(2)(-center dot) quenching by VC could be estimated to be 6.9 x 10(7) M(-1) s(-1). This value is much larger than the corresponding value reported in homogeneous water solution, suggesting that the O(2)(-center dot) quenching by VC indeed occurred at the w/o interface of the reversed micelle. (C) 2010 Elsevier B.V. All rights reserved.
  • Hisako Sato, Kenji Tamura, Keishi Ohara, Shin-ichi Nagaoka, Akihiko Yamagishi
    NEW JOURNAL OF CHEMISTRY 35 (2) 394 - 399 1144-0546 2011 [Peer-reviewed]
     Scientific journal 
    The Langmuir-Blodgett films were prepared by hybridizing the clay minerals (synthetic saponite, synthetic hectorite and sodium montmorillonite)with the floating film of a cationic Ir(III) complex, [Ir(ppy)(2)(dc18bpy)](+) (ppy = 2-phenylpyridine; dc18bpy = 4,4'-dioctadecyl-2,2'-bipyridine). When the single-layered hybrid LB film was irradiated at 430 nm, it emitted light in the visible region, whose intensity responded reversibly to the pressure change of oxygen.
  • Hiroko Yamada, Kei Ohkubo, Daiki Kuzuhara, Tetsuro Takahashi, Atula S. D. Sandanayaka, Tetsuo Okujima, Keishi Ohara, Osamu Ito, Hidemitsu Uno, Noboru Ono, Shunichi Fukuzumi
    JOURNAL OF PHYSICAL CHEMISTRY B 114 (45) 14717 - 14728 1520-6106 2010/11 [Peer-reviewed]
     Scientific journal 
    Free base and zinc porphyrins are linked with fullerene (C(60)) through beta,beta`-pyrrolic positions rather than meso-positions by Diels-Alder reaction of monoanthraporphyrins (H(2)P-mA and ZnP-mA) and C(60) to afford a pi-expanded free base porphyrin-fullerene dyad (H(2)P-C(60)) and its zinc porphyrin-fullerene dyad (ZnP-C(60)) in 86 and 51% yield, respectively The X-ray crystallographic analysis of ZnP-C(60) showed two comma-shaped swirls-like structure in a unit cell The intramolecular center-to-center and edge-to-edge distances between the porphyrin and fullerene moieties were 11 5 and 2 5 angstrom, respectively The porphyrins and fullerenes were packed in layer-by-layer structure and the porphyrins lied down in parallel The Intermolecular center-to-center distances between the neighboring fullerenes were 10 252, 10028, and 10 129 angstrom, which were less than typical van der Waals distance and the pi-pi interaction spread two-dimensionally The energy of the charge-separated (CS) state of ZnP-C(60) (1 11 eV) determined by differential-pulse voltammetry measurements in benzonitrile is significantly lower than those of zinc porphyrin-C(60) dyads linked at meso positions because of the low oxidation potential of the a-expanded ZnP moiety The CS energy of ZnP-C(60) in a nonpolar solvent such as toluene (1 40 V) is lower than the triplet excited state of C(60) ((3)C(60)*), enabling us to attain a longed lived triplet CS state (8 1 mu s) in toluene, detected by nanosecond laser flash photolysis experiments The distance between unpaired electrons in the triplet CS state was determined by the EPR spectrum to be 9 1 angstrom, which agreed with the distance between a zinc atom of the porphyrin and a carbon edge of C(60) in the crystal structure of ZnP-C(60) The rate constants of photoinduced electron transfer and back electron transfer of H(2)P-C(60) and ZnP-C(60), which were determined by femtosecond and nanosecond laser flash photolysis measurements, were analyzed in light of the Marcus theory of electron transfer
  • Keishi Ohara, Ryotaro Mitsumori, Mitsuharu Takebe, Daiki Kuzuhara, Hiroko Yamada, Shin-ichi Nagaoka
    JOURNAL OF PHOTOCHEMISTRY AND PHOTOBIOLOGY A-CHEMISTRY 215 (1) 52 - 58 1010-6030 2010/09 [Peer-reviewed]
     Scientific journal 
    A synthesized vitamin K model compound, NQ-6 (2-hexyloxy-1,4-naphthoquinone) showed weak fluorescence around 440 nm in ethanol. Addition of antioxidants such as vitamin E to a NQ-6 solution suppressed the NQ-6 emission quantitatively. A kinetic study on the quenching of the NQ-6 emission by hydrogen-donor type antioxidants (three tocopherol analogues, catechin, and 2,6-di-tert-butyl-4-methylphenol) in ethanol was performed. The quenching rate constant obtained from the Stern-Volmer plots for the steady-state fluorescence intensity was consistent with the second-order rate constant of each antioxidant for the free-radical scavenging. The NQ-6 emission is thought to be the delayed fluorescence caused by the thermal population to the excited singlet state from the triplet state. Thus, the fluorescence quenching occurred through a hydrogen atom transfer reaction from an antioxidant to NQ-6 in the excited triplet state ((3)NQ-6*). The second-order rate constant for the reaction between (3)NQ-6* and a-tocopherol was estimated to be 1.2 x 10(10) M(-1) s(-1) from the quenching parameter and the (3)NQ-6* lifetime in ethanol (1.2 mu s) measured with the transient absorption. From the high reactivity of (3)NQ-6* to the antioxidants and the amphiphilic property of NQ-6 as a vitamin K model, NQ-6 is applicable to the quantitative antioxidant assay as a new fluorescence probe. (C) 2010 Elsevier B.V. All rights reserved.
  • Keishi Ohara, Takashi Origuchi, Shin-ichi Nagaoka
    BULLETIN OF THE CHEMICAL SOCIETY OF JAPAN 83 (3) 246 - 253 0009-2673 2010/03 [Peer-reviewed]
     Scientific journal 
    The singlet oxygen (O-1(2)) behavior in emulsions dispersing natural vitamin E (VE) (alpha-, beta-, gamma-, and delta-tocopherols) was investigated by measuring time-profiles of O-1(2) phosphorescence. The O-1(2) rise and decay dynamics noticeably reflected the existence of VE oil-droplets. The decay rate constant (k(d)) in the a-tocopherol emulsion decreased with increase of VE concentration ([VE]), and became roughly constant in [VE] > 5 x 10(-4)M. This k(d) behavior correlated to the oil-droplet diameter measured by dynamic light scattering. The droplet diameter increased rapidly from 270 to 430 nm with increase of [VE], and reached the limit for dispersing in [VE] >= 5 x 10(-4) M. This result means that the O-1(2) surroundings became more hydrophobic with increase of droplet size. On the other hand, in the emulsions dispersing tocopherols other than alpha-tocopherol, the k(d) values were roughly constant, indicating that the oil-droplets did not contribute to O-1(2) quenching. The droplet diameter in the delta-tocopherol emulsion was around 212-243 nm and was much smaller than that in the alpha-tocopherol emulsion. The peculiar results observed in the alpha-tocopherol emulsion should be due to the large hydrophobicity of alpha-tocopherol which has two methyl-groups neighboring the OH group.
  • Keishi Ohara, Ayumi Shimizu, Yuki Wada, Shin-ichi Nagaoka
    JOURNAL OF PHOTOCHEMISTRY AND PHOTOBIOLOGY A-CHEMISTRY 210 (2-3) 173 - 180 1010-6030 2010/02 [Peer-reviewed]
     Scientific journal 
    In order to investigate effect of the inhomogeneous dispersion system on photogeneration and decay dynamics of the tocopheroxyl radical (Toc(center dot)), transient absorption and steady-state and time-resolved EPR measurements on photolysis of vitamin E (VE) were carried out. Tocopherol (TocH) is photo-decomposed through electron-detachment in the excited state and the subsequent proton releasing, which produce Toc(center dot) and the solvated electron (e(solv)(-)). The decay of Toc(center dot) is explained by (i) a rapid decay within 2 mu s by recombination between Toc(center dot) and e(solv)(-), (ii) a second-order decay observed in the range of 5-150 mu s by reaction between Toc(center dot) and the superoxide anion radical (O(2)(center dot-)), and (iii) a slow decay in >10 ms by bimolecular self-quenching of Toc(center dot). The Toc(center dot) decay in the VE emulsion was very different from that in the homogeneous solution. In the emulsion, the Toc(center dot) yield was small, the contribution of the reaction with O(2)(center dot-) was rather small, and the decay due to the bimolecular reaction of Toc(center dot) was much accelerated. In the emulsion, Toc(center dot) could not be detected by steady-state EPR, although it could in ethanol. These differences should be caused by the oil-droplet formation in the emulsion. From these results, we can expect that the photostability of the VE emulsion is superior to that of the VE homogeneous solutions. (C) 2010 Elsevier By. All rights reserved.
  • Keishi Ohara, Kaori Kikuchi, Takashi Origuchi, Shin-ichi Nagaoka
    JOURNAL OF PHOTOCHEMISTRY AND PHOTOBIOLOGY B-BIOLOGY 97 (3) 132 - 137 1011-1344 2009/12 [Peer-reviewed]
     Scientific journal 
    Singlet oxygen ((1)O(2)) quenching by trolox C (TC, 6-hydroxy-2,5,7,8-tetramethylchroman-2-carboxylic acid), which is a water-soluble vitamin E analogue, in ethanol-water solutions and in aqueous SDS and CTAC micelles was studied by measuring the time-profiles of (1)O(2) phosphorescence at 1274 nm. The second-order rate-constant for (1)O(2) quenching by TC was determined in the ethanol-water solution to be 1.03 x 10(8), 6.22 x 10(7) and 6.23 x 10(7) M(-1) s(-1) at pH 2.0, 7.0, and 8.4, respectively. These values mean that the non-dissociated form of TC under acidic conditions has superior activity to the mono-anion form. In aqueous micelle systems, the decay rate of (1)O(2) at first decreased and then increased with increase of the concentration of TC. This behavior is explained in terms of the (1)O(2) quenching by TC in the bulk phase and in terms of shifting the environment surrounding (1)O(2) to lipophilic by dissolving TC in the hydrophobic region inside the micelle. The present investigation on (1)O(2) emission dynamics in inhomogeneous solutions made it possible to detect a little change in the solutions, which affects the environment around (1)O(2) , such as the micelle formation and dissolving solute in the micelle. (C) 2009 Elsevier B.V. All rights reserved.
  • Nagaoka Shin-ichi, Ouchi Aya, Kakiuchi Takuhiro, Ohara Keishi, Mukai Kazuo
    Vitamins 日本ビタミン学会 83 (9) 521 - 527 0006-386X 2009/09 
    Recent studies on the kinetics of the regeneration reactions of vitamin E in solutions by means of stopped-flow spectroscopy confirmed that the quantum effect often plays an important role. Vitamin E may inhibit the autooxidation of lipids in cellular membranes by taking advantage of proton tunneling. It is interesting that the microscopic quantum-mechanical tunneling effect manifests itself in a macroscopic vital function. Although this finding is in conflict with our intuition at first glance, living cells might, in reality, know quantum mechanics very well and use them effectively.
  • Bilkish Rahman, Hiroki Akutsu, Jun-ichi Yamada, Keishi Ohara, Shin'ichi Nakatsuji
    SYNTHETIC METALS 159 (12) 1123 - 1130 0379-6779 2009/06 [Peer-reviewed]
     Scientific journal 
    Series of radical salts derived from a 2,4,6-triphenylpyridinium (TPP) carrying TEMPO-substituent and transition metal complexes were prepared by the anion exchange of the TPP-TEMPO tetrafluoroborate with [n-Bu(4)N][Ni(dmit)(2)], [n-Bu(4)N](2)[Pd(dmit)(2)], [n-Bu(4)N(2)][Pt(dmit)(2)], [n-Bu(4)N][Ni(mnt)(2)], or [n-Bu(4)N](2)[Ni(mnt)(2)] to give crystals with different structural features. While weak antiferromagnetic interactions of the Curie-Weiss behavior of S = 1/2 spin are predominantly observed in the salts of Pd(dmit)(2), Pt(dmit)(2) and Ni(mnt)(2), the magnetic behavior of 1:1 Ni(dmit)(2) salt can be explained by the additional contribution from the spins on Ni(dmit)(2) anions (chi - chi(TEMPO)), obeying the 2D Heisenberg model. A couple of the oxidized salts, [TPP][Ni(dmit)(2)] as well as [TPP](2)[Pd(dmit)(2)], exhibit semi-conducting properties with relatively high room temperature conductivities. (C) 2009 Elsevier B.V. All rights reserved.
  • Keishi Ohara, Yoko Ichimura, Shin-ichi Nagaoka
    BULLETIN OF THE CHEMICAL SOCIETY OF JAPAN 82 (6) 689 - 691 0009-2673 2009/06 [Peer-reviewed]
     Scientific journal 
    The second-order rate constants (k(Q)) of singlet-oxygen quenching by caffeic acid and related phenols were measured in ethanol and toluene. Caffeic acid derivatives deactivate singlet-oxygen largely by physical quenching at k(Q) = 10(6) - 10(7) M-1 s(-1) through the charge-transfer transition state.
  • Kazuo Mukai, Aya Ouchi, Akiko Mitarai, Keishi Ohara, Chihiro Matsuoka
    BULLETIN OF THE CHEMICAL SOCIETY OF JAPAN 82 (4) 494 - 503 0009-2673 2009/04 [Peer-reviewed]
     Scientific journal 
    In order to understand the dynamics of antioxidant actions of vitamin E (alpha-, beta-, gamma-, and delta-tocopherols, TocH) in biological systems, kinetic study of the formation and decay reactions of vitamin E radicals (alpha-, beta-, gamma-, and delta-tocopheroxyls, Toc center dot) has been performed in organic solvents, using stopped-flow spectrophotometry. By mixing alpha-, beta-, gamma-, and delta-TocH with aryloxyl radical (ArO center dot) in ethanol, the peaks of the UV-vis absorption due to alpha-, beta-, gamma-, and delta-Toc center dot radical appeared rapidly at ca. 430-340 nm, showed maxima, and then decayed gradually. The second-order rate constants (k(f) and 2k(d)) for the formation and decay (that is, bimolecular disproportionation) reactions of alpha-Toc center dot were determined by comparing the observed curves with the simulation ones obtained by the numerical calculation of differential equations related to the above reactions. From the results, the wavelengths of absorption maxima (lambda(i)(max)) and molar extinction coefficients (epsilon(i)) (i = 1-4) of the optical spectra were determined for alpha-Toc center dot radical. Notable solvent effects have been observed for the reaction rates (k(f) and 2k(d)) and absorption spectra (lambda(i)(max) and epsilon(i)) of alpha-Toc center dot radical. The scheme of the formation and decay reactions of alpha-, beta-, gamma-, and delta-Toc center dot radicals has been discussed based on the results obtained.
  • Takuhiro Kakiuchi, Kazuo Mukai, Keishi Ohara, Shin-ichi Nagaoka
    BULLETIN OF THE CHEMICAL SOCIETY OF JAPAN 82 (2) 216 - 218 0009-2673 2009/02 [Peer-reviewed]
     Scientific journal 
    A study of the kinetics of the proton-transfer reaction in flavonoid in ethanol solution by means of stopped-flow spectroscopy indicated that proton tunneling plays an important role in the antioxidant reaction.
  • Keishi Ohara, Yoshimi Hashimoto, Chiaki Hamada, Shin-ichi Nagaoka
    JOURNAL OF PHOTOCHEMISTRY AND PHOTOBIOLOGY A-CHEMISTRY 200 (2-3) 239 - 245 1010-6030 2008/12 [Peer-reviewed]
     Scientific journal 
    The photochemical reactions of vitamin K (VK) with antioxidant vitamins (vitamin E (VE) and vitamin C (VC)) in aqueous hexadecyltrimethylammonium chloride (CTAC), sodium dodecyl sulfate (SDS), and Triton X-100 micelle systems, and in an aerosol OT (AOT) reversed micelle system were investigated by a time-resolved EPR (TR-EPR). The photolysis of VK with VE in the aqueous micelle solutions gave the TR-EPR spectra having strong intensity and net emissive polarization, suggesting that the excited triplet state of VK ((3)VK(center dot)) was rapidly quenched by VE coexisting inside the micelle. On the other hand. the photolysis of VK with VC in the aqueous SDS and CTAC micelle systems gave the spectra having weak intensity, showing that the reaction between (3)VK(center dot) and VC was inefficient in these micelle systems, probably because (3)VK(center dot) scarcely diffused Out from the micelle. The photolysis of VK with VC in the AOT reversed micelle solution gave the spin-correlated radical pair CIDEP spectrum. The result suggests that the long-lived radical pair was generated from the reaction between (3)VK(center dot) and VC in the water/oil interface region of the AOT micelle, although one of the reactants dissolved in the oil phase and another did in the separated water phase. (C) 2008 Elsevier B.V. All rights reserved.
  • Keishi Ohara, Takashi Origuchi, Kanako Kawanishi, Shin-ichi Nagaoka
    Bulletin of the Chemical Society of Japan 81 (3) 345 - 347 0009-2673 2008/12 [Peer-reviewed]
     Scientific journal 
    The decay rate constant of the phosphorescence of singlet oxygen ( 1O2) was measured in a vitamin E (VE) emulsion system by single-photon counting. The results suggest that the 1O2 emission mainly occurs around the oil droplets of VE rather than in the bulk solution.
  • Kazuo Mukai, Aiko Tokunaga, Shingo Itoh, Yu Kanesaki, Aya Ouchi, Keishi Ohara, Shin-ichi Nagaoka, Kouichi Abe
    BIOFACTORS 32 (1-4) 49 - 58 0951-6433 2008 [Peer-reviewed]
     Scientific journal 
    Detailed kinetic studies have been performed for the reaction of aroxyl (ArO center dot) radical with vitamin E (alpha-, beta-, gamma-, delta-tocopherol, TocH), ubiquinol-10, and related antioxidants in micellar solution, using a stopped-flow spectrophotometer. The second-order reaction rates (k(s)) obtained increased in the order of hydroquinone < tocol <delta-T6cH < ubiquinol-0 <gamma-TocH similar to beta-TocH < ubiquinol-10 <alpha-TocH at pH 4 similar to 9. The antioxidants which have lower oxidation potentials (E(p)) showed higher reactivities. The reaction rates obtained in micellar solution were pH dependent because of the dissociation of OH groups in the antioxidants. For instance, by comparing the k(s) values with the mole fraction of each molecular form of ubiquinol-10, the reaction rate k(s1) (1.21 x 10(5) M(-1)s(-1)) for undissociated form, k(s2) (1.04 x 10(6) M(-1) s(-1)) for monoanion and k(s3) (0 M(-1)s(-1)) for dianion, and the pK(a1) and PK(a2) values (11.4 and 12.7) were determined. It was found that the relative ratio of K(s) values (100:21:20:2.9) of alpha-, beta-, gamma-, delta-tocopherols in micellar dispersion has good correlation with the relative biological activities for rat fetal resorption, rat haemolysis, and chicken muscle dystrophy. The relative antioxidant activities of alpha-tocopherol and ubiquinol-10 have been discussed on the basis of the products of the k(s) values and their concentrations in serum and several tissues (heart, muscle, liver, kidney, and brain).
  • Shin-ichi Nagaoka, Akiko Fujii, Megumi Hino, Mai Takemoto, Misaki Yasuda, Mariko Mishima, Keishi Ohara, Akane Masumoto, Hidemitsu Uno, Umpei Nagashima
    JOURNAL OF PHYSICAL CHEMISTRY B 111 (45) 13116 - 13123 1520-6106 2007/11 [Peer-reviewed]
     Scientific journal 
    The UV protection and singlet oxygen quenching of aloesaponarin I have been studied by means of laser spectroscopy. The excited-state intramolecular proton transfer that provides the UV protection takes place along only one of the molecule's two intramolecular hydrogen bonds, and this can be understood by considering the nodal pattern of the wave function. The functional groups participating in the excited-state intramolecular proton transfer also play important roles in the singlet oxygen quenching. Aloesaponarin I has a quenching rate constant larger than that of vitamin E and has a long duration of action due to its resistance to UV degradation and chemical attacks by singlet oxygen and free radicals.
  • Shin-ichi Nagaoka, Takuhiro Kakiuchi, Keishi Ohara, Kazuo Mukai
    CHEMISTRY AND PHYSICS OF LIPIDS 146 (1) 26 - 32 0009-3084 2007/03 [Peer-reviewed]
     Scientific journal 
    The rate constant and activation energy of the regeneration reaction of natural vitamin E by vitamin C were determined with a double-mixing stopped-flow spectrophotometer. The formation of vitamin C radical was observed in the absorption spectrum. The kinetic effect of methyl substitution on the aromatic ring of vitamin E radical indicates that partial charge-transfer plays a role in the reaction. Since a substantial deuterium kinetic isotope effect was not found, the tunneling effect may not play an important role under the present experimental conditions. (c) 2007 Elsevier Ireland Ltd. All rights reserved.
  • Kazuo Mukai, Aiko Tokunaga, Shingo Itoh, Yu Kanesaki, Keishi Ohara, Shin-ichi Nagaoka, Kouichi Abe
    JOURNAL OF PHYSICAL CHEMISTRY B 111 (3) 652 - 662 1520-6106 2007/01 [Peer-reviewed]
     Scientific journal 
    The reaction rates (k(s)) of vitamin E (alpha-, beta-, gamma-, delta-tocopherols, TocH), ubiquinol-10, and related antioxidants (tocol, ubiquinol-0, and hydroquinone) with aroxyl (ArO center dot) radical have been measured in micellar solution by stopped-flow spectrophotometer. The k(s) values increased in the order of hydroquinone < tocol < delta-TocH < ubiquinol-0 < gamma-TocH approximate to beta-TocH < ubiquinol-10 < alpha-TocH at pH 4 similar to 8. The antioxidants which have lower oxidation potentials showed higher reactivities. The k(s) values of alpha-, beta-, gamma-, delta-tocopherol, and tocol remained constant between pH 4 and 10, and decreased rapidly at pH 11 similar to 12 by increasing pH value. From the pH dependence of k(s) values, the pK(a) values (= 13.1 similar to 12.6) have been determined for these tocopherols. The k(s) values of ubiquinol-10 also remained constant between pH 4 and 9, and increased rapidly at pH 9.5. Ubiquinol-10 is dibasic acid and can exist in three different molecular forms, depending on the pH value. By comparing the k(s) values with the mole fraction of each molecular form of ubiquinol-10, the reaction rate k(s1) (= 1.21 x 10(5) M(-1)s(-1)) for the undissociated form, k(s2) (= 1.04 x 10(6) M(-1)s(-1)) for monoanion and k(s3) (= 0 M (-1)s (-1)) for dianion, and the pK(a1) and pK(a2) values (= 11.4 and 12.7) were determined. The k(s2) value is 8.6 times as large as the k(s1) value. Similar analyses were performed for ubiquinol-0 and hydroquinone. It was found that the relative ratio of k(s) values (100:21:20:2.9) of alpha-, beta-, gamma-, delta-tocopherols in micellar dispersion has good correlation with the relative biopotency ratios for rat fetal resorption, rat hemeolysis, and chicken muscle dystrophy. The relative antioxidant activities of alpha-tocopherol and ubiquinol-10 have been discussed based on the k(s) values obtained and their concentrations in serum and several tissues (heart, muscle, liver, kidney, and brain).
  • Keishi Ohara, Yoko Ichimura, Kumi Tsukamoto, Mayumi Ogata, Shin-ichi Nagaoka, Kazuo Mukai
    BULLETIN OF THE CHEMICAL SOCIETY OF JAPAN 79 (10) 1501 - 1508 0009-2673 2006/10 [Peer-reviewed]
     Scientific journal 
    A kinetic study involving 4-hydroxycinnamic acid derivatives (HCAs) was performed in order to clarify the mechanism for free radical-scavenging and vitamin E-regenerating. The second-order rate constants of the radical-scavenging reaction (k(s)) observed for caffeic acid derivatives are larger than those for ferulic acid derivatives. The result may be explained by i) the lower oxidation potential coming from the existence of the more electron-donating hydroxy group comparing with methoxy group, and ii) the stabilization effect of the corresponding radicals produced in the radical-scavenging reaction through intramolecular hydrogen bonding. The radical-scavenging activity of HCAs in ethanol mainly occurs via the hydrogen atom transfer from the phenolic OH-protons. The pH dependence of k(s) for ferulic acid in the aqueous Triton X-100 micelle solutions suggests the importance of the phenolic OH proton on the radical-scavenging reaction. On the other hand, the pH dependence of k(s) for caffeic acid and chlorogenic acid suggests the occurrence of intramolecular hydrogen bonding and an electron-transfer process in the radical-scavenging reaction.
  • Keishi Ohara, Debora M. Martino, Hans van Willigen
    JOURNAL OF PHOTOCHEMISTRY AND PHOTOBIOLOGY A-CHEMISTRY 181 (2-3) 325 - 332 1010-6030 2006/07 [Peer-reviewed]
     Scientific journal 
    The anomalous net absorptive CIDEP spectra observed in the photoinduced hydrogen abstraction reaction of chromone (CR) and chromone2-carboxylic acid (CRCA) from 2-propanol with addition of hydrochloric acid (HCl) were investigated with FT-EPR. In neat 2-propanol, the spectra of the ketyl and 2-hydroxypropan-2-yl (2-HP) radicals display E-*/A (low-field side emission and high-field side absorption, the asterisk denoting excess net polarization) or E/A type polarization, which is explained by the STO mixing radical pair mechanism and minor contributions of the triplet mechanism (TM). The addition of HCl to these systems gives the net absorptive CIDEP spectra, while the triplet states of CR and CRCA should have emissive polarizations. The analysis of the time developments of the EPR signals indicates that the radical generation rate increases with the increase of the HCl concentration, while the signal intensity of radicals does not increase. The net absorptive polarization might be explained by non-reactive quenching of the triplet by the spin-sublevel dependent back charge-transfer process in the intermediate exciplex. (c) 2005 Elsevier B.V. All rights reserved.
  • K Ohara, A Fujii, Y Ichimura, K Sato, K Mukai
    BULLETIN OF THE CHEMICAL SOCIETY OF JAPAN 79 (3) 421 - 426 0009-2673 2006/03 [Peer-reviewed]
     Scientific journal 
    A kinetic study was performed for edaravone (3-methyl-1-phenyl-2-pyrazolin-5-one) in order to clarify the mechanism of its free-radical-scavenging and vitamin E-regenerating actions. The second-order rate constants for the radical-scavenging reaction of edaravone were measured in several organic solvents and in a water/methanol mixed solvent at various pH. The keto-enol tautomerism and the acid-base dissociation equilibrium of edaravone produce keto, enol, and anion forms in solutions, and their contributions and activities varied depending on the properties of the solutions. From the results of NMR and kinetic studies, it has been clarified that the keto-enol tautomerism of edaravone actually exists, and the keto form has larger radical-scavenging activity than the enol form. Furthermore, the pH dependence of the rate constants suggests that the anion form produced by the acid-base dissociation equilibrium of edaravone has the highest radical-scavenging activity in the keto, enol, and anion forms.
  • K Mukai, D Shiba, K Yoshida, K Mukai, H Hisatou, K Ohara, Y Hosokoshi, N Azuma
    BULLETIN OF THE CHEMICAL SOCIETY OF JAPAN 78 (12) 2114 - 2123 0009-2673 2005/12 [Peer-reviewed]
     Scientific journal 
    Four kinds of 1:1 salts of 3-(4- and 3-alkyl-pyridinium)-1,5-diphenylverdazyl (alkyl = ethyl and methyl) radical cations with the Ni(dmit)(2) anion ([p-EtPyDV](+)[Ni(dmit)(2)](-) (1), [m-EtPyDV](+)[Ni(dmit)(2)](-) (2), [p-MePyDV](+)[Ni(dmit)(2)](-) (3), and [m-MePyDV](+)[Ni(dmit)(2)](-) (4)) have been prepared. The magnetic properties of salts 1-4 were discussed based on the results obtained by magnetic susceptibility and ESR measurements of 1-4 and the crystal structure analysis of 1. The results of the crystal structure analysis of salt 1 indicate the dimer formation in Ni(dmit)(2) anion molecules, and the dimers are sandwiched between two verdazyl cations [p-EtPyDV](+), indicating the formation of a magnetic linear tetramer in 1. The magnetic susceptibility data for salt 1 have been fitted to a four-spin linear tetramer model using an end exchange interaction of 2J(1)/k(B) = -780 K and a central interaction of 2J(2)/k(B) = -200 K. The conductivity (sigma) of salts 1, 2, 3, and 4 at room temperature was sigma = 2.3 x 10(-5), 1.8 X 10(-4), 1.4 x 10(-5), and 5.4 x 10(-6) S cm(-1) with an activation energy of E-A = 0.28, 0.52, 0.21, and 0.33 eV, respectively. The 1: 1 salts 1-4 are new molecular paramagnetic semiconductors.
  • K Mukai, D Shiba, K Mukai, K Yoshida, H Hisatou, K Ohara, Y Hosokoshi, N Azuma
    POLYHEDRON 24 (16-17) 2513 - 2521 0277-5387 2005/11 [Peer-reviewed]
     Scientific journal 
    Five kinds of (1:1) and (1:3) salts of 3-(4- and 3-alkyl-pyridinium)-1,5-diphenylverdazyl (alkyl = ethyl and methyl) radical cations with Ni(dmit)(2) anion ([p-EtPyDV](+)[Ni(dmit)(2)](3)(-) (1), [m-EtPyDV](+)[Ni(dmit)(2)](-) (2), [p-MePyDV](+)[Ni(dmit)(2)](-) (3), [m-MePyDV](+)[Ni(dmit)(2)](-) (4), and [p-MePyDV](+)[Ni(dmit)(2)](3)(-) (5)) (dmit = 1,3-dithiol-2-thione-4,5-dithiolate) have been prepared, and the magnetic susceptibilities (chi(M)'s) have been measured between 1.8 and 300 K. The chi(M) of salt 1 can be well explained by a four-spin linear tetramer model ([p-EtPyDV](+)-[Ni(dmit)(2)](-)-[Ni(dmit)(2)](-)-[p-EtPyDV](+)) with an end exchange interaction 2J(1)/k(B) = -780 K and a central interaction 2J(2)/k(B) = -200 K. The formation or magnetic tetramer in salt 1 has been ascertained by the crystal structure analysis of 1. The chi(M) of salt 2 was explained by the SUM of the contributions from: (i) a dimer system (2J/k(B) = -320 K) due to Ni(dmit)(2) anions and (ii) the one-dimensional (1D) Heisenberg ferromagnetic linear-chain system (2J k(B) = +2.5 K) due to verdazyl cations. The chi(M) of salt 3 is similar to that of salt 1, suggesting a formation of magnetic tetramer in salt 3. The chi(M) of salt 4 shows a broad maximum at T-max = 100 +/- 2 K, and can be explained by a 1D Heisenberg antiferromagnetic alternating-chain model with 2J(1)/k(B) = -165 K (alternation parameter alpha = J(2)/J(1) = 0.6). The conductivity (sigma) of salts 1, 2, 3 and 4 at 293 K was sigma = 2.3 x 10(-5), 1.1 x 10(-3), 1.4 x 10(-5) and 5.4 x 10(-6) S cm(-1) with an activation energy of E-A = 0.28, 0.52, 0.21 and 0.33 eV, respectively. The (1:3) salt 5 (sigma = 1.0 S cm(-1), E-A = 0.048 eV) showed three to five orders of magnitude higher conductivity than those of the (1:1) salts 1-4 at room temperature. All the (1:1) and (1:3) salts 1-5 are new molecular paramagnetic semiconductors. (c) 2005 Elsevier Ltd. All rights reserved.
  • H Yamada, Y Yamashita, M Kikuchi, H Watanabe, T Okujima, H Uno, T Ogawa, K Ohara, N Ono
    CHEMISTRY-A EUROPEAN JOURNAL 11 (21) 6212 - 6220 0947-6539 2005/10 [Peer-reviewed]
     Scientific journal 
    A novel alpha-diketone precursor of pentacene, 6,13-dihydro-6,13-ethanopentacene-15,16-dione, was prepared and converted successfully to pentacene in 74% yield by photolysis of the precursor in toluene: Irradiation of the diketone solution in toluene with light of 460 nm under an Ar atmosphere caused the solution to change from yellow to fluorescent orange-pink within a few minutes, after which, purple precipitates appeared. After 35 min, the solution changed to colorless and the purple precipitates were filtered to give pentacene in 74% yield. By contrast, in the presence of oxygen, the color of the solution changed from yellow to pale yellow., and only 6,13-endoperoxide of pentacene was quantitatively obtained. The rate of the reaction upon photolysis was measured by observing the decay of n-pi* absorption of the precursor at 460 nm, and was found to be similar in both the presence and absence of oxygen. Therefore, the photoreaction of the alpha-diketone precursor seemed to occur via the singlet excited state. Because the T-T absorption of pentacene was observed upon photolysis of the precursor in the nanosecond transient absorption measurement under an Ar atmosphere, the excited triplet state of the pentacene generated singlet oxygen by sensitization, and it reacted with the ground-state pentacene to give the 6,13-endoperoxide. The alpha-diketone deposited on glass was also converted successfully to pentacene film by photoirradiation. In addition, diketone precursors of a mixture of 2,8- and 2,9-di-bromopentacene and 2,6-trianthrylene were also prepared and their photoconversion was performed.
  • K Mukai, S Nagai, K Ohara
    FREE RADICAL BIOLOGY AND MEDICINE 39 (6) 752 - 761 0891-5849 2005/09 [Peer-reviewed]
     Scientific journal 
    A kinetic study of the quenching reaction of singlet oxygen (O-1(2)) with catechins (catechin (CA), epicatechin (EC), epigallocatechin (EGC), epicatechin gallate (ECG), epigallocatechin gallate (EGCG)) and related compounds (5-methoxyresorcinol (MR), 4-methylcatechol (MC), and n-propyl gallate (PG)) was performed in ethanol at 35 degrees C. MR, MC, and PG are considered to be a model of resorcinol (A)-, catechol (B)-, and gallate (G)-rings in catechins, respectively. The overall rate constants, k(Q) ( k(q) + k(r) physical quenching + chemical reaction), for the reaction of catechins with 10, increased in the order of PG < MR < MC < CA < EC < EGC < ECG < EGCG. In a comparison of the rate constants, the relationship between quenching rates and chemical structures is discussed. The catechins which have lower peak oxidation potentials, E-P, show higher reactivities. It was observed that the chemical reaction (k(r)) is almost negligible in the quenching reaction Of O-1(2) by catechins. The kQ values of EGCG (1.47 x 10(8) M-1 s(-1)) and ECG (7.81 X 10(7)) were found to be larger than those of lipids (1.3 x 10(5-)1.9 X 10(5) M-1 s(-1)), amino acids (< 3.7 x 10(7)), and DNA (5.1 x 10). Further, these values are similar to those (1.15 x 10(8)-2.06 x 10(8) M-1 s(-1)) of alpha- and gamma-tocopherol, ubiquinol-10, and gamma-tocopherol hydroquitione (plastoquinol model). The result suggests that catechins may contribute to the protection of oxidative damage in biological systems, by quenching O-1(2). (c) 2005 Elsevier Inc. All rights reserved.
  • K Mukai, S Mitani, K Ohara, SI Nagaoka
    FREE RADICAL BIOLOGY AND MEDICINE 38 (9) 1243 - 1256 0891-5849 2005/05 [Peer-reviewed]
     Scientific journal 
    The reaction rates (k(r)) of 5,7-diisopropyl-tocopheroxyl radical (Toc(center dot)) with catechins (epicatechin (EC), epicatechin gallate (ECG), epigallocatechin (EGC), epigoallocatechin gallate (EGCG)) and related compounds (methyl gallate (MG), 4-methyleatechol (MC), and 5-Foethoxyresorcinol (MR)) have been measured by stopped-flow spectrophotorneter. The k(r), values increased in the order of MR << MG < EC < MC similar to ECG < FGC < EGCG in ethanol and 2-propanol/H2O (5/1, v/v) solutions, indicating that the reactivity of the OH groups in catechins increased in the order of resorcinol A-ring << gallate G-ring < catechol B-ring < pyrogallol B-ring. The catechins which have lower oxidation potentials show higher reactivities. The rate constants for catechins in micellar solution showed notable pH dependence with one or two peaks around pH 9-11, because of the dissociation of various phenolic hydroxyl protons in catechins. The Structure-activity relationship in the free-radical-scaveril-ing reaction by catechins has been clarified by the detailed analyses of the pH dependence of kr values. The reaction rates increased remarkably with increasing the anionic character of catechins, that is, the electron-donating capacity of catechins. The mono anion form at catechol B-and resorcinol A-rings and dianion form at pyrogallol B-and gallate G-rings show the highest activity for free-radical-scavenging. It was found that catechins (EC, ECG, EGC, and EGCG) have activity similar to or higher than that of vitamin C in vitamin E regeneration at pH 7-12 in micellar solution. (c) 2005 Elsevier Inc. All rights reserved.
  • K Ohara, W Mizukami, A Tokunaga, S Nagaoka, H Uno, K Mukai
    BULLETIN OF THE CHEMICAL SOCIETY OF JAPAN 78 (4) 615 - 621 0009-2673 2005/04 [Peer-reviewed]
     Scientific journal 
    A kinetic Study was performed for the free-radical scavenging actions of curcumin and half-curcumin, which has a half-structure of curcumin, in order to clarify the mechanism of free-radical-scavenging in curcumin. The second-order rate constants for radical-scavenging reactions of curcumin and half-curcumin were measured by a stopped-flow spectrophotometer in several organic solvents (methanol, ethanol, acetonitrile, chloroform, and benzene) and in aqueous Triton X-100 (5.0 wt %) micelle solutions at various pH. The difference in the rate constant and solvent dependence between curcumin and half-curcumin suggests that the enol structure with the intramolecular hydrogen-bond Of Curcumin strongly enhances the radical-scavenging activity. Furthermore, notable pH dependences were observed for the rate constants of curcumin and half-curcumin in micelle solutions, suggesting that the acid-base dissociation equilibrium of phenol-protons in curcumin and half-curcumin affects their radical-scavenging activities.
  • S Nagai, K Ohara, K Mukai
    JOURNAL OF PHYSICAL CHEMISTRY B 109 (9) 4234 - 4240 1520-6106 2005/03 [Peer-reviewed]
     Scientific journal 
    The quenching rate of singlet oxygen (O-1(2)) by seven kinds of flavonoids (flavone, flavonol, chrysin, apigenin, rutin, quercetin, and myricetin) with 2,3-double bonds has been measured spectrophotometrically in ethanol at 35 degreesC. The overall rate constants k(Q) (=k(q) + k(r), physical quenching + chemical reaction) increased as the number of OH groups substituted to the flavone skeleton (that is, the total electron-donating capacity of flavonoids) increases. The existence of catechol or pyrogallol structure in the B-ring is essential for the O-1(2) quenching of flavonoids. Log k(Q) was found to correlate with their peak oxidation potentials, E-P; the flavonoids that have smaller E-P values show higher reactivities. Similarly, log k(Q) values of flavonoids correlate with the energy level of the highest occupied molecular orbital (E-HOMO), calculated by the PM3 MO method, and the longest wavelength pipi* excitation energy (E-ex). The contribution of the chemical reaction (k(r)) was found to be negligible in these flavonoids. The k(Q) values of rutin, quercetin, and myricetin [(1.21similar to5.12) x 10(8) M-1 s(-1)] were found to be larger than those of lipids [(0.9similar to6.4) x 10(4) M-1 s(-1)], amino acids (< 3.7 x 10(7) M-1 s(-1)),and DNA (5.1 x 10(5) M-1 s(-1)). The result suggests that these flavonoids may contribute to the protection of oxidative damage in foods and plants, by quenching O-1(2).
  • Y Teki, M Kimura, S Narimatsu, K Ohara, K Mukai
    BULLETIN OF THE CHEMICAL SOCIETY OF JAPAN 77 (1) 95 - 99 0009-2673 2004/01 [Peer-reviewed]
     Scientific journal 
    The excited high-spin quartet (S = 3/2) state of the intramolecular triplet-radical pair between the excited triplet state of pyrene and a dangling verdazyl radical was reported. A novel verdazyl radical with the pyrene moiety was designed and synthesized. The time-resolved ESR spectrum and a DFT calculation show the photo-induced ferromagnetic spin alignment between the excited triplet state of the pyrene moiety and the dangling verdazyl radical. This is the first observation of the high-spin (S > 1) excited state of the pi-conjugated pyrene-radical pair.
  • K Mukai, N Senba, T Hatanaka, H Minakuchi, K Ohara, M Taniguchi, Y Misaki, Y Hosokoshi, K Inoue, N Azuma
    INORGANIC CHEMISTRY 43 (2) 566 - 576 0020-1669 2004/01 [Peer-reviewed]
     Scientific journal 
    Four kinds of 1:1 and 1:3 salts of 3-[4-(trimethylammonio)phenyl]-1,5-diphenyl-6-oxoverdazyI radical cation ([1](+)) and its mono- and dimethyl derivatives ([2](+) and [3](+)) with Ni(dmit)(2) anions (d(mit) = 1,3-dithiol-2-thione-4,5-dithiolate) ([1](+)[Ni(dmit)(2)](-) (4), [2](+)[Ni(dmit)(2)](-) (5), [3](+)[Ni(dmit)(2)](-) (6), and [1](+)[Ni(dmit)(2)](3)(-) (7)) have been prepared, and the magnetic susceptibilities (chi(M)) have been measured between 1.8 and 300 K. The chi(M) values of salts 5 and 7 can be well reproduced by the sum of the contributions from (i) a Curie-Weiss system with a Curie constant of 0.376 (K emu)/mol and negative Weiss constants (Theta) of -0.4 and -1.7 K and (ii) a dimer system with strong negative exchange interactions of 2J/k(B) = -354 and -258 K, respectively. The dimer formations in Ni(dmit)(2) anions have been ascertained by the crystal structure analyses of salts 4-6. In salts 4 and 6, Ni(dmit)(2) dimer molecules are sandwiched between two verdazyl cations, indicating the formation of a linear tetramer in 4 and 6. The magnetic susceptibility data for salts 4 and 6 have been fitted to a linear tetramer model using an end exchange interaction of 2J(1)/k(B) = -600 K and a central interaction of 2J(2)/k(B) = -280 K for 4 and 2J(1)/k(B) = -30 K and 2J(2)/k(B) = -580 K for 6, respectively. The results of the temperature dependence of the 9(T) value in salts 4-6 obtained by ESR measurement also support the above analyses. The 1:1 salts 4-6 are insulators. On the other hand, the conductivity of the 1:3 salt 7 at 20 degreesC was sigma = 0.10 S cm(-1) with an activation energy E-A = 0.099 eV, showing the semiconductor property. Salt 7 is a new molecular paramagnetic semiconductor.
  • K Ohara, R Watanabe, Y Mizuta, S Nagaoka, K Mukai
    JOURNAL OF PHYSICAL CHEMISTRY B 107 (41) 11527 - 11533 1520-6106 2003/10 [Peer-reviewed]
     Scientific journal 
    The photoinitiated reaction between vitamin C and xanthone in sodium lauryl sulfate (SDS), hexadecyltrimethylammonium chloride (CTAC), and Triton X-100 micelle solutions at various pH was investigated by time-resolved electron paramagnetic resonance (TR-EPR). The TR-EPR spectra were explained by superimpositions of the xanthone ketyl and the vitamin C radicals, showing that a fast hydrogen abstraction reaction of the excited xanthone from vitamin C progresses around the water-oil interface region of the micelles. The EPR signal intensity of the vitamin C radical showed the notable pH dependence, which seems to be attributable to the acid-base dissociation equilibrium of vitamin C. The results suggested that the present reaction is controlled by the transportation of the excited xanthone and vitamin C to the reaction-progressing region, which is the surface or inside of the micelle, and by the difference of the reactivity between the dissociation forms of vitamin C.
  • Yoshinori Nishioku, Keishi Ohara, Kazuo Mukai, Shin-ichi Nagaoka
    Journal of Physical Chemistry B 105 (21) 5032 - 5038 1089-5647 2002/05 [Peer-reviewed]
     Scientific journal 
    The models of vitamin K and vitamin E linked molecule, (1-(1,4-naphthoquinone-2-oxy)-6-(hydroxy-2,5,7,8-tetramethylchroman-2-carbonylox y)-hexane), was synthesized as a model of vitamin K and vitamin E which coexist in biological membranes. The time-resolved EPR (TR-EPR) spectra of this molecule could be assigned to vitamin K and E radicals and showed that the excited triplet state of thh vitamin K moiety was rapidly quenched by abstraction of hydrogen from the vitamin E moiety. The broad and emissive CIDEP spectra observed in ethanol suggested that the intramolecular interaction between vitamin K and vitamin E radicals was strong there. The relatively resolved spectra observed in a TX-100 micelle system, on the other hand, indicated that the interaction between these radicals was very weak. These results suggest that the vitamin K and E radicals existed around the water-oil interface of the micelle independently. The absence of a deuterium effect in our experiments showed that tunneling does not contribute significantly to the quenching reaction.
  • N Azuma, N Senba, K Okuda, K Ohara, Y Hosokoshi, K Inoue, K Mukai
    MOLECULAR CRYSTALS AND LIQUID CRYSTALS 376 341 - 346 1058-725X 2002 [Peer-reviewed]
     Scientific journal 
    Three kinds of (1:1) salts of TCNQF(4) anion with 3-(4trimethylaminophenyl)-1,5-diphenyl-6-oxo-verdazyl radical cation [1(+)] and its mono-methyl [2(+)] and di-methyl [3(+)] derivatives have been prepared, and magnetic property and crystal structure of the salts have been studied. The salts were found to be new genuine organic magnetic compounds consisting of open-shell verdazyl radical cation and electron acceptor TCNQF(4) anion.
  • K Ohara, K Mukai
    CHEMICAL PHYSICS LETTERS 317 (6) 619 - 623 0009-2614 2000/02 [Peer-reviewed]
     Scientific journal 
    The addition effect of hydrochloric acid (HCl) on the photoreduction of chromone-2-carboxylic acid (CRCA) is studied by time-resolved EPR, The EPR lines of CRCA ketyl radical show an enhanced absorption in the presence of HCl, while without HCl these show an emissive character. On the other hand, the lines of the CRCA alkyl type radical show an emissive character whether HCl is included or not. The simultaneous reactions of the closely-lying two excited tripler states (T-1 and T-2) of CRCA may induce the above anomalous CIDEP behavior. (C) 2000 Elsevier Science B.V. All rights reserved.
  • S Nagaoka, M Inoue, C Nishioka, Y Nishioku, S Tsunoda, C Ohguchi, K Ohara, K Mukai, U Nagashima
    JOURNAL OF PHYSICAL CHEMISTRY B 104 (4) 856 - 862 1089-5647 2000/02 [Peer-reviewed]
     Scientific journal 
    Studies of the kinetics of the proton- or hydrogen-transfer reactions concerning vitamin E in solutions and in micellar dispersions by means of stopped-flow and absorption spectroscopy indicated that proton tunneling plays an important role in the antioxidant and regeneration reactions that are advantageous in vivo but not as a part of the harmful prooxidant action.
  • K Ohara, S Nagaoka, K Mukai
    BULLETIN OF THE CHEMICAL SOCIETY OF JAPAN 73 (1) 37 - 42 0009-2673 2000/01 [Peer-reviewed]
     Scientific journal 
    The photosensitized reaction of maleimide (MI) with xanthone (Xn) in 2-propanol was investigated by the time-resolved EPR method. The emissive CIDEP spectrum observed in neat 2-propanol is predominantly assigned to two kinds of MI alkyl-type radicals. On the other hand, the absorptive spectrum of the MI anion radical has been newly observed in 2-propanol including hydrochloric acid. The addition effect of hydrochloric acid indicates the existence of two mechanisms for the photosensitization of MI by Xn. One is a typical triplet-triplet energy transfer followed by hydrogen abstraction by the triplet state of MI from the solvent. The other is an electron-transfer process to MI from the Xn ketyl radical produced primarily by a fast reaction of the triplet Xn with HCl. The spin-polarization transfer mechanism based on these photosensitization processes can successfully explain the present CIDEP results. The effect of water and the sensitizer dependence on the above reaction were also investigated.
  • K Mukai, K Suzuki, K Ohara, JB Jamali, N Achiwa
    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 68 (9) 3078 - 3085 0031-9015 1999/09 [Peer-reviewed]
     Scientific journal 
    The magnetic susceptiblities, ESR and powder X-ray patterns of verdazyl radical alloy, (p-CDpOV)(1-x)(p-BDpOV)(x) (x = 0-1), were measured to study the doping effects of magnetic impurities for the quasi-1D Heisenberg ferromagnet (p-CDpOV) and antiferromagnet (p-BDpOV) with S = 1/2, which have similar van der Waals radius to each other. The susceptibility curves systematically change with impurity concentration x. The most noticeable point is that the impurity effect is rather mild on the 1D ferromagnetic Heisenberg system. The characteristic feature of 1D ferromagnet still survives even in the heavily doped sample with x = 0.50. The positive Weiss constant (theta) and the ferromagnetic intrachain exchange interaction (2J(intrachain)) remain constant between x = 0 and 0.50. The results indicate that the p-BDpOV radical functions as an ideal dopant for the 1D ferromagnet; p-CDpOV. This is the first report of the effects of magnetic impurities on the quasi-1D ferromagnetic chain system.
  • K Ohara, N Hirota, DM Martino, H van Willigen
    JOURNAL OF PHYSICAL CHEMISTRY A 102 (28) 5433 - 5439 1089-5639 1998/07 [Peer-reviewed]
     Scientific journal 
    CIDEP spectra from free radicals produced by the photolysis of xanthone (Xn) in 2-propanol were investigated with FT-EPR. The spectra were assigned to the 2-hydroxypropan-2-yl (2HP) and xanthone ketyl (XnH) radicals. In pure 2-propanol and 2-propanol containing 10% H2O, the spectra display low field emission/ high field absorption with net emission (E*/A) type polarization. The observed CIDEP pattern is mainly due to the S-To radical pair mechanism (RPM) with minor contributions from the triplet mechanism (TM) and radical triplet pair mechanism (RPM). Upon addition of HCl, the polarization changes to net absorption. The rise time of the absorptive signals is determined by the response time of the spectrometer (similar to 3 x 10(-8) s). Transient optical absorption measurements show that the triplet state of xanthone ((3)Xn*) is quenched by HCl, and the change in spin polarization produced by HCl addition is attributed to this quenching process. The dependence of the CIDEP pattern and triplet xanthone lifetime on HCl concentration shows that both involve a diffusion-controlled process. The main 3Xn(*) quenching process was found to be nonreactive, but it is proposed that its spin selectivity produces spin polarization in the products of the hydrogen abstraction reaction that runs in parallel with this quenching process.
  • NAGAOKA Shin-ichi, NISHIOKU Yoshinori, OHARA Keishi, MUKAI Kazuo
    X-RAYS The Crystallographic Society of Japan 40 (1) 119-123,133-133 - 123 0369-4585 1998/02 
    Since a vitamin E radical produced by the antioxidant reaction of vitamin E causes damage to vital functions, ubiquinol and vitamin C regenerate a vitamin E molecule from a vitamin E radical <I>in vivo</I>. The kinetic studies of the regeneration reactions have been carried out in solutions by means of stopped-flow spectroscopy. Substantial deuterium kinetic-isotope-effects on the second-order rate constants have been observed in both the reactions of ubiquinol and vitamin C. Furthermore, a deviation from a linear relationship in the Arrhenius plot has been observed in the reaction of ubiquinol. These results suggest that the tunneling effect plays an important role in the regeneration reactions in various tissues and mitochondria.
  • T Koga, K Ohara, K Kuwata, H Murai
    JOURNAL OF PHYSICAL CHEMISTRY A 101 (43) 8021 - 8025 1089-5639 1997/10 [Peer-reviewed]
     Scientific journal 
    The hydrochloric-acid-addition effect on the photochemical reaction of xanthone in alcohol is studied by a time-resolved ESR technique. The CIDEP spectra of the transient radicals peculiarly reveal an enhanced absorption by the addition of hydrochloric acid, while the ordinary triplet mechanism of xanthone is known to be emissive. The spin-polarization inversion phenomenon is explained by the triplet mechanism induced by the excitation of a ground-state weak charge-transfer complex of xanthone and HCl.
  • K Ohara, Y Miura, M Terazima, N Hirota
    JOURNAL OF PHYSICAL CHEMISTRY A 101 (4) 605 - 611 1089-5639 1997/01 [Peer-reviewed]
     Scientific journal 
    The magnetic field dependence of the chemically induced dynamic electron polarization (CIDEP) spectra of spin-correlated radical pairs (SCRPs) was studied by time-resolved EPR at three different external magnetic fields, i.e., X band (9.2 GHz, 330 mT), S band (3.0 GHz, 100 mT), and L band (1.5 GHz, 50 mT). The CIDEP spectra were obtained by the photolysis of three systems, xanthone and 2,6-di-tert-butylphenol (2,6-DBP) in a sodium dodecyl sulfate (SDS) micelle solution, zinc tetrakis(4-sulfonatophenyl)porphyrin (ZnTPPS) and p-benzoquinone (p-BQ) in a cetyltrimethylammonium chloride (CTAC) micelle solution, and acetone in 2-propanol, at low temperatures. In the two micelle systems, the SCRP spectra scarcely depend on the external magnetic field, and the decay times do not change much on going from the X band to the L band. These observations are discussed in terms of the cage escape rate and the spin-lattice relaxation rate. The strong magnetic field dependence found for the net emissive polarization in the CIDEP spectra of the xanthone and 2,6-DBP system is ascribed to the magnetic field dependence of the triplet mechanism (TM). On the other hand, the intensity of the SCRP spectrum in the acetone system drastically decreases with decreasing the magnetic field. This observation is rationalized on the basis of the restricted motions of the SCRPs in the 2-propanol solution at low temperatures.
  • K Ohara, N Hirota
    BULLETIN OF THE CHEMICAL SOCIETY OF JAPAN 69 (6) 1517 - 1526 0009-2673 1996/06 [Peer-reviewed]
     Scientific journal 
    The Chemically Induced Dynamic Electron Polarization (CIDEP) mechanisms in the hydrogen abstraction reactions of excited azaaromatic compounds; quinoxaline, phenazine, and quinoline are investigated in detail. It is shown that several polarization mechanisms are involved and the observed CIDEP spectra vary strongly depending on various factors such as the concentration, the temperature, the delay time, and the excitation light intensity. The net emissive spin polarization is ascribed mainly to the radical-triplet pair mechanism (RTPM), which is strongly dependent on the concentrations of the radical and triplet molecules. It is shown that the triplet molecules are long-lived and the condition to produce the RTPM polarization is satisfied. The observed time evolutions of the transient EPR signals are qualitatively explained on the basis of the rate equations, which include the RTPM polarization and the relaxation.
  • K Ohara, N Hirota, CA Steren, H vanWilligen
    JOURNAL OF PHYSICAL CHEMISTRY 100 (8) 3070 - 3074 0022-3654 1996/02 [Peer-reviewed]
     Scientific journal 
    The secondary quenching reactions of the 2-hydroxypropan-2-yl radical produced by photolysis of pyrazine, quinoxaline, and p-benzoquinone in 2-propanol were investigated with time-resolved EPR. The quenching rate constants are 6.6 x 10(6), 1.2 x 10(8), and similar to 10(8) M(-1) s(-1) for pyrazine, quinoxaline, and p-benzoquinone, respectively. The time profiles of the transient EPR signals of pyrazinyl and 2-hydroxypropan-2-yl radicals were measured by FT-EPR and analyzed in detail in terms of a reaction scheme involving the primary hydrogen abstraction reaction and the subsequent quenching reaction. It is found that half of the signal intensity of the pyrazinyl radical arises from polarization transfer accompanying 2-hydroxypropan-2-yl quenching by pyrazine.
  • K Ohara, M Terazima, N Hirota
    JOURNAL OF PHYSICAL CHEMISTRY 99 (51) 17814 - 17821 0022-3654 1995/12 [Peer-reviewed]
     Scientific journal 
    A CIDEP study on the triplet mechanism (TM) was carried out on three systems, zinc tetraphenylporphyrin (TPP) and p-benzoquinone (p-BQ) in alcohols, pyrazine/2-propanol, and maleic anhydride/2-propanol, in three different microwave frequency regions, i.e. X-(9.5 GHz), S-(3.0 GHz), and L-(1.5 GHz) bands. The CIDEP spectra involving TM contributions drastically change depending on the microwave (MW) frequency or the magnetic field. Tn the ZnTPP and p-BQ systems the TM contribution increases with a decrease of the MW frequency, whereas in the other two systems the TM contribution increases with an increase of the MW frequency. The results can be explained by the frequency dependence of the initial spin polarization produced by the TM which is strongly influenced by the rotational correlation time, the zero field splitting, and the reaction rate of the triplet molecule. The experimental results are compared with the predictions of the Atkins-Evans theory. Reasonable agreements between the experimental results and the theoretical predictions are obtained.
  • K OHARA, JN HIROTA, CA STEREN, H VANWILLIGEN
    CHEMICAL PHYSICS LETTERS 232 (1-2) 169 - 175 0009-2614 1995/01 [Peer-reviewed]
     Scientific journal 
    The results of an FT-EPR study of the CIDEP of 2-propanolyl radical produced by the photochemical reaction of acetone with triethylamine are reported. The time profiles of the signals are explained satisfactorily on the basis of a hydrogen abstraction reaction involving the acetone singlet and/or triplet excited states depending upon the amine concentration and CIDEP mechanisms involving singlet and/or triplet geminate pairs and triplet F pairs together with spin-lattice relaxation.
  • M TERAZIMA, Y MIURA, K OHARA, N HIROTA
    CHEMICAL PHYSICS LETTERS 224 (1-2) 95 - 100 0009-2614 1994/07 [Peer-reviewed]
     Scientific journal 
    Chemically induced dynamic electron polarization (CIDEP) in an acetone/2-propanol system is investigated in the L band microwave frequency region at various temperatures. The polarization due to the ST- mechanism is analyzed in terms of the mixing of hyperfine-independent (ST-M-i) and hyperfine-dependent (ST-M-d) mechanisms. At higher temperature, ST-M-d dominates over ST-M-i in the ST-M polarization, while the relative contribution of ST-M-i increases with decreasing temperature. A mechanism of ST-M-d is discussed based on the radical diffusion in solution and a possible contribution of the ST+M polarization in the CIDEP spectrum is discussed.
  • K OHARA, H MURAI, K KUWATA
    BULLETIN OF THE CHEMICAL SOCIETY OF JAPAN 65 (6) 1672 - 1678 0009-2673 1992/06 [Peer-reviewed]
     Scientific journal 
    A triplet photosensitization reaction of maleic anhydride with alcohols and the subsequent secondary reaction were studied by a time-resolved ESR method. The hydrogen abstraction reaction of the C=C bond site of maleic anhydride in the excited triplet state was examined and discussed as the primary step. The adduct radical formed in the secondary reaction between maleic anhydride and alcohol radicals showed a characteristic E/A-shaped hyperfine line(s). This phenomenon can be explained by the CIDEP ''memory transfer'' of the multiplet (E/A) spin polarization of the alcohol radicals to the adduct radical. The spin-lattice relaxation times of the excited triplet state of xanthone as the sensitizer in 2-propanol and cyclohexanol were also estimated.
  • T TAKEMURA, K OHARA, H MURAI, K KUWATA
    CHEMISTRY LETTERS 19 (9) 1635 - 1638 0366-7022 1990/09 [Peer-reviewed]
     Scientific journal
  • K OHARA, H MURAI, K KUWATA
    BULLETIN OF THE CHEMICAL SOCIETY OF JAPAN 62 (8) 2435 - 2440 0009-2673 1989/08 [Peer-reviewed]
     Scientific journal

Books etc

  • ビタミンE研究の進歩XIII
    ビタミンE研究会 2009
  • Kinetic Study of Vitamin E Regeneration Reaction with Catechins (EC, EGC, ECG, and EGCG) in Homogeneous and Micellar Solution
    Kazuo Mukai, Shuji Mitani, Souichi Nagai, Keishi Ohara (Contributor, Proceedings of the 3rd China-Japan International Conference on Vitamins', Guilin, China, 2004)
    2004
  • ビタミンE研究の進歩Ⅹ
    ビタミンE研究会 2002
  • ビタミンE研究の進歩Ⅹ
    ビタミンE研究会 2002
  • ビタミンE研究の進歩Ⅸ
    (Contributor, 時間分解ESR法によるビタミンE類の一重項酸素消光速度の測定(pp1-6), 時間分解ESR法による光酸化開始に対するビタミンE類の抗酸化機構の研究(pp7-12))
    ビタミンE研究会 2000
  • CIDEP studies of photochemical reactions at different microwave frequencies, ST0M and ST-M.
    Keishi Ohara, Noboru Hirota (Contributor, Modern Applications of EPR/ESR: From Biophysics to Materials Science, Proceedings of the Asia-Pacific EPR/ESR Symposium, 1st, Kowloon, Hong Kong, Jan. 20-24, 1997, p114-122)
    Springer-Verlag, Singapore 1998

Works

  • 生物・分子機能性化学における近赤外発光の新展開
    2004

MISC

Research Grants & Projects

  • Japan Society for the Promotion of Science (JSPS):Grants-in-Aid for Scientific Research (Scientific Research (C))
    Date (from‐to) : 2014/04 -2017 
    Author : Keishi OHARA
  • Ministry of Education, Culture, Sports, Science and Technology:Grants-in-Aid for Scientific Research(基盤研究(C))
    Date (from‐to) : 2010 -2013 
    Author : Keishi OHARA
     
    In order to evaluate antioxidant activities of trace amount of natural materials, a method of measuring lifetimes of singlet oxygen near-infrared luminescence using a fiber-spot probe (0.4 mm) was developed. Time-evolutions of singlet oxygen luminescence were successfully obtained from measurements of less than 0.1 mL of solutions and also hydrogel samples by the spot method. The quenching rate constants for trace amount of samples such as 0.05 mg of carotenoid isomers, and also that of the quencher in hydro-gel samples were determined. The relationship between singlet oxygen quenching activity and chemical structure for the lipophilic constituents of spices such as capsaicin were investigated in the cyclodextrin aqueous solution. However, in the spot measurements, the photo-damages often occurred in test materials and/or photosensitizers in the accumulation time (10 min). The shorter accumulation time (< 1 min) is hopeful for applying the spot-scan method to the antioxidant assay.
  • 飲料・食品のための簡便・短時間で計測可能な抗酸化力評価法の開発
    科学技術振興機構(JST):研究成果最適展開支援プログラム(A-STEP)FSステージ探索タイプ
    Date (from‐to) : 2011/08 -2012/03 
    Author : 小原 敬士
     
    飲料サンプル用の標準抗酸化力評価キットの作成と高感度・短時間で試料を測定する計測法の最適化を実施し、含有成分の抗酸化力の簡便迅速な標準評価手法を新たに開発し提案することを目標とする。
  • Ministry of Education, Culture, Sports, Science and Technology:Grants-in-Aid for Scientific Research(基盤研究(C))
    Date (from‐to) : 2007 -2008 
    Author : Keishi OHARA
     
    飲料・食品・化粧品・医薬品などで注目されている分散・懸濁系での天然抗酸化剤による活性酸素種消去ダイナミクスの詳細を明らかにするため、油水分散エマルジョン, 水油分散の逆ミセル系の油水界面で起こる抗酸化反応を過渡吸収法及び一重項酸素(1O_2)近赤外発光寿命法などの時間分解計測を用いて研究した。スーパーオキシドラジカルや1O_2 が天然抗酸化剤により油水界面近傍で消去されるダイナミクスを直接観測することに成功し、反応速度定数が求められた。
  • Ministry of Education, Culture, Sports, Science and Technology:Grants-in-Aid for Scientific Research(基盤研究(C))
    Date (from‐to) : 2007 -2008 
    Author : Shin-ichi NAGAOKA, Keishi OHARA
     
    励起状態における水素結合に沿ったプロトン移動は、正確な測定と定量的理論解析に適している。今回我々は、プロトン移動が重要な役割を示す生理活性物質に我々が提唱している理論モデルを適用できることを見いだした。また、さらに長波長領域の励起状態である一重項酸素消去における分子内水素結合を含む生体関連分子が示す役割を研究すると共に、逆に短波長領域である軟X 線領域にも研究のウイングを広げた。
  • Ministry of Education, Culture, Sports, Science and Technology:Grants-in-Aid for Scientific Research(特定領域研究)
    Date (from‐to) : 2003 -2006 
    Author : Kazuo MUKAI, Kunihiko TAJIMA, Keishi OHARA, Shin-ichi NAGAOKA, Masaki MITO
     
    Human aging is induced by the reaction of lipid, protein, and nucleic acid with active oxygens and free radicals. Natural antioxidants such as vitamin E (α-, β-, γ-, δ-tocopherol, TocH), ubiquinol, vitamin C, polyphenols (flavones, catechins) etc., which exist in biological systems, scavenge active oxygens and free radicals quickly, and protect the aging. In the present work, the kinetic studies of i) free-radical-scavenging action, ii) tocopherol-regeneration action, and iii) singlet-oxygen-quenching action with the above natural antioxidants were performed, and several interesting results were obtained.1) The aroxyl-radical-scavenging rates (k_s) of vitamin E (α-, β-, γ-, δ-TocH) and ubiquinol were measured in micellar solutions by varying pH, using stopped-flow spectrophotometer. It has been clarified that ubiquinol shows higher and lower free-radical-scavenging activity than a-tocopherol in mitochondria of several tissues (heart, muscle, liver and brain) and in serum, respectively.2) Quenching rates (K_Q) of singlet oxygen (^1O_2) by 7 kinds of flavone derivatives and 4 kinds of catechins have been measured The K_Q values of several kinds of flavones and catechins were found to be larger than those of lipids, amino acids, and DNA. Further, these values are similar to those of a-and y-tocopherol, ubiquinol-10, and plastoquinol model, suggesting that these polyphenols may contribute to the protection of oxidative damage in biological systems, by quenching ^1O_2.3) In order to understand the dynamics of antioxidant actions of vitamin E (α-,β-, γ-, δ-TocH) in biological systems, kinetic study of the formation and decay reactions of vitamin E radicals (α-, β-, γ-, δ-tocopheroxyls, Toc) has been performed in organic solvents, using stopped-flow spectrophotometer. The second-order rate constants (k_f and 2k_d) for the formation and decay reactions of Toc were determined by comparing the observed curves with the simulation ones obtained by the numerical calculation of differential equations related to the above reactions. The k_f values decreased in the order of α-> β-~γ-> δ-TocH, and the 2kd values increased in the order of α-< β-< γ-< δ-Toc in ethanol. The wavelengths of absorption maxima (λmax^1) and molar extinction coefficients (ε_1) of the optical spectra (for example, i = 1~4 for α-Toc.) were determined for these radicals. The scheme of the decay reactions of α-, β-, γ-, δ-Toc radicals has been discussed based on the results obtained.4)The rate constant and activation energy of the regeneration reaction of natural vitamin E by vitamin C were determined with a double-mixingstopped-flow spectrophotometer. The kinetic effect ofmethyl substitution on the aromatic ring of vitamin E radical indicates that partial charge-transfer plays a role in the reaction Since a substantial deuterium kinetic isotope effect was not found, the tunneling effect may not play an important role under the present experimental conditions.
  • Ministry of Education, Culture, Sports, Science and Technology:Grants-in-Aid for Scientific Research(基盤研究(C))
    Date (from‐to) : 2004/04 -2005 
    Author : Keishi OHARA
     
    In the present study, a kinetic investigation was progressed on the antioxidant reactions versus reactive oxygen species for natural antioxidants, such as vitamin E and catechins, in the emulsion phase by using time-resolved methods based on the fluorescence or ESR detection.1.The second-order rate constant for the scavenging reaction of the model free-radical in vitamin E (VE) emulsion systems was firstly obtained by using the fluorescence-detected stopped-flow method. The result indicates that the rate constants in emulsion systems are different from that in the homogeneous solution. This kinetic approach could also be applicable to the scavenging reaction of other radicals, such as galvinoxyl and DPPH, in emulsion systems.2.For investigating the dynamics of singlet oxygen (^1O_2) in the emulsion systems, the emission (at 1275 nm) from ^1O_2 was measured directly by using a time-resolved near-infrared fluorescence spectrophotometer. In the VE emulsion system, the life-time of ^1O_2 increases with an increase of the concentration of VE, while the VE usually shows 10^7 - 10^8 M^<-1>s^<-1> as the ^1O_2 quenching rate constant in homogeneous solutions. The result suggests that the ^1O_2 dynamics occurs mainly near the oil-droplet of VE in this system.3 The investigation on the spin-dynamics for the short-lived intermediate radials generated by the laser excitation of natural vitamin E and hydroperoxide is progressed by using the time-resolved ESR and transient absorption methods.The results of the present study give the time-resolved tools for investigating the kinetics and the spin-dynamics of the free-radicals and ^1O_2 in emulsion phase, which is a model of biological systems, colloids, food, and drinks. The obtained information for emulsion systems will clarify the unique dynamics in inhomogeneous systems.
  • Ministry of Education, Culture, Sports, Science and Technology:Grants-in-Aid for Scientific Research(基盤研究(C))
    Date (from‐to) : 2003 -2004 
    Author : Kazuo MUKAI, Keishi OHARA
     
    The development of organic ferromagnet and superconductor has attracted much attention in the field of material science, and many studies have been performed with great success in recent years. On the other hand, the examples of magnetic superconductors, where the superconducting state and antiferromagnetic or ferromagnetic order coexist in a system are very limited, because of the difficulty in molecular design of the complexes. Especially, the examples of the magnetic superconductor consisting of purely organic compounds have not been reported.In the present work, in order to obtain the organic magnetic conductors, first, we prepared several kinds of iodide salts of verdazyl radical cations (for example, 3-(4- and 3-methylpyridinium)-1,5-diphenylverdazyl radical cations ([p-MePyDV]^+ and [m-MePyDV]^+). These iodide salts were reacted with Li^+[TCNQ]^-, Li^+[Me_2-TCNQ]^-, and [n-Bu_4N]^+[Ni(dmit)_2]^- salts, giving the (1:1) salts of verdazyl cations with TCNQ, Me_2-TCNQ, and Ni(dmit)_2 anions. Several kinds of (1:2) and (1:3) salts of verdazyl cations with TCNQ, Me_2-TCNQ, and Ni(dmit)_2 anions were prepared by the oxidation of the (1:1) salts. Further, the magnetic and electric properties, and crystal structures of these radical salts have been studied. It has been clarified that the eight kinds of salts are new molecular magnetic semiconductors.
  • 文部科学省:科学研究費補助金(特定領域研究(B))
    Date (from‐to) : 1999 -2001 
    Author : 向井 和男, 小原 敬士, 東 長雄
     
    純有機反強磁性超伝導体或いは純有機強磁性伝導体を得るために、次のような種々の合成と、測定を試みた。1)分子内に正の電荷を有する種々の新規フェルダジルラジカルを合成し、TCNQ、Me_2TCNQ、Cl_2TCNQ、DDQ等の電子受容体との(1:1)及び(1:2)塩を作成した。その磁化率、ESR、伝導度の測定と、結晶構造解析結果から、4種の(1:2)TCNQ塩が純有機磁気半導体であることを見出した。低温での比熱測定を行ない、反強磁性への転移を見出すことを試みた。しかしながら、TCNQ分子間のスピン間反強磁性相互作用が大きいため、低温でその磁性が消えてしまい、反強磁性転移を見出すに至らなかった。現在、分子間の相互作用を小さくするため、Me_2TCNQやCl_2TCNQとの塩について詳細な研究を進めている。2)1)と同様、分子内に正の電荷を有するフェルダジルラジカルとNi(dmit)_2等の塩を合成した。(1:3)塩は何れも磁気半導体としての性質を示した。今後、加圧下での伝導度の測定を行い、超伝導への転移を見出すことを試みる。3)分子内に負の電荷を有する種々の新規フェルダジルラジカルを合成し、TTF、BEDT-TTF、BETS、等の電子供与体との塩を作成し、磁気伝導体の開発を試みている。現在までに、カルボキシル基を有する数種のラジカルの合成に成功している。
  • Ministry of Education, Culture, Sports, Science and Technology:Grants-in-Aid for Scientific Research(基盤研究(B))
    Date (from‐to) : 1999 -2000 
    Author : Kazuo MUKAI, Keish OHARA, Shin-ichi NAGAOKA
     
    In the present work, we measured the rate constants of the reaction of peroxyl, tocopheroxyl, and aroxyl free radicals with natural antioxidants, such as catechins, caffeic acids and related compounds in homogeneous and micellar solutions, by using oxygen absorption method, stopped-flow spectrophotometer, and time-resolved ESR method. We have succeeded in obtaining the following interesting results :l) Detailed kinetic studies have been performed for the reaction of aroxyl (ArO ・) and 5,7-diisopropyltocopheroxyl (Toc ・ ) radicals with catechin, epicatechin, and related antioxidants in homogeneous and micellar solutions. The structure-activity relationship in the scavenging reaction of free radicals by catechin and epicatechin in solution was discussed. It has been found that catechin and epicatechin have high activity in vitamin E regeneration.2) The antioxidant activity of curcumin (1,7-bis(4-hydroxy-3-methoxyphenyl)-1,6-heptadiene-3,5-dione) was determined by inhibition of controlled initiation of styrene oxidation. Synthetic nonphenolic curcumins exhibited no antioxidant activity, therefore, curcumin is a classical phenolic chain-breaking antioxidant, donating H atoms from the phenolic groups not the CH_2 group as has been suggested (Jovanovic et al. J.Am. Chem. Soc., 121, 9677 (1999)).3) Studies of the kinetics of the proton- or hydrogen-transfer reactions concerning vitamin E in solutions and in micellar dispersions by means of stopped-flow and absorption spectroscopy indicated that proton tunneling plays an important role in the antioxidant and regeneration reactions that are advantageous in vivo but not as a part of the harmful prooxidant action.
  • Ministry of Education, Culture, Sports, Science and Technology:Grant-in-Aid for Young Scientists (A)
    Date (from‐to) : 1999 -2000 
    Author : Keishi OHARA
     
    本研究は、ミセル・脂質二分子膜に導入されたCIDEPスピンプローブを用いて局所場での一重項酸素の寿命を時間分解ESRにより測定することにより、その動態を検討することを目的とする。本年度は本課題を実施するにあたり、以下のことを行った。(1)CIDEPスピンプローブとなるアルキル鎖及びペプチド鎖を持ったニトロキシドラジカル4種を設計・合成し、これがミセル中に取り込まれることを蛍光法及びESR法により確認した。3種の表面電荷の異なるミセル系において、油溶性のキサントン及び水溶性のTPPS(ポルフィリン誘導体)を用い、ミセル内外に存在するこれらの分子の励起状態とスピンプローブのミセルの水・油界面での相互作用について、時間分解ESR法により検討した。その結果、アルキル鎖によりミセルの疎水性部分に保持されたプローブは水相の励起分子との相互作用が小さく、アルキル鎖のないラジカル単体では比較的強い相互作用が観測されたことから、アルキル鎖のないラジカルがミセル内から水相に拡散している様子が示された。これらの結果から、合成した分子は不均一系のプローブとして有効に機能することがわかった。現在、脂質二分子膜モデルとなるフォスファチジルコリンを用いた系で検討を行っている。(2)水相で発生させた一重項酸素とプローブの相互作用について検討したが、一重項酸素の低収率と感度不足のため充分な信号強度が得られなかった。また、局所的に一重項酸素を発生させる試みとして、光により励起状態となる分子を持つミセル・ペプチド分子の合成を試みたが、中間体の副反応や低収率のため現在まで合成に至っていない。現在も引き続きこれらの検討を行っている。(3)ミセル系でのビタミンE及びビタミンCの挙動を励起分子としてキサントンを用いた系で検討し、分子の可溶化位置と反応速度のミセル,pHの依存性を時間分解ESR法で検討した。得られた顕著なミセル、pH依存性から、これらの抗酸化剤の界面での挙動が明かとなった。スピンプローブとこれらの抗酸化剤をミセル系に導入した系で時間分解ESRを測定することにより、界面での抗酸化反応機構について検討中である。
  • Ministry of Education, Culture, Sports, Science and Technology:Grants-in-Aid for Scientific Research(基盤研究(C))
    Date (from‐to) : 1997 -1998 
    Author : Shin-ichi NAGAOKA, Keishi OHARA, Kazuo MUKAI
     
    Proton transfer is a very simple chemical process readily accessible to both accurate measurement and quantitative theoretical analysis. We have constructed a simple theoretical model of the excited-state-proton-transfer, a model based on the nodal pattern of the wave function. In this project we have studied the application of our nodal-plane model to the following three problems.1. The substituent effect and the electronic-state dependence in the excited-state-intramolecular-proton-transfer (ESIPT) of o-hydroxybenzladehydes.2. The substituent-position effect in ESIPT of 2-(o-hydroxyaryl)benzazoles : Although both 2-(2-hydroxy- 3-aryl)benzazole and 2-(1-hydroxy- 2-aryl)benzazole consist of an aryl moiety, a benzazol-2-yl group, and an Oil group, their emission properties are very different.3. The substituent and solvent effects in ESIPT of aminoanthraquinones : The singlet-triplet energy-gap of the proton-transferred form is much less than that in the normal form.The experimental results obtained on the above three problems strongly support our nodal-plane model.Furthermore, we synthesized a bridged molecule of vitamin E and quinones, and studied the radical scavenging reaction of vitamin E.It is interesting that the microscopic electron behavior could manifest itself in the macroscopic vital-function.Although our nodal-plane model is a qualitative one, it allows us to recognize the important features of ESIPT immediately and provides useful information about the reaction mechanisms. Our nodal-plane model is applicable to photochemical reactions in various excited states of various molecules. Many chemists have cited it, and the usefulness of our explanation is recognized by many researchers.
  • Ministry of Education, Culture, Sports, Science and Technology:Grants-in-Aid for Scientific Research(基盤研究(B))
    Date (from‐to) : 1996 -1998 
    Author : Kazuo MUKAI, Keisi OHARA
     
    In the present work, about 50 kinds of new organic verdazyl radical crystals have been prepared. From the results of the measurements of magnetic susceptibility, ac magnetic susceptibility, heat capacity arid ESR and the X-ray analyses, we have succeeded in obtaining the following compounds having interesting magnetic properties.1) Finding of three kinds of new organic ferromagnet (p-CDTV, p-CDpOV and p-MeDpOV) and the mechanism of appearance of ferromagnetism.2) Finding of two kinds of new organic weak ferromagnet (TOV and p-CyDpTV).3) Doping effect of nonmagnetic impurities on weak ferromagnet, TOV.4) Finding of two kinds of new organic antiferromagnet (p-NTV and p-BDpTV).5) Finding of a new spin-Peierls transition compound (p-CyDOV) and study of its magnetic phase diagram.6) The study of doping effect of magnetic and nonmagnetic impurities on the spin-Peierls transition of p-CyDOV radical crystal.7) Finding of a new verdazyl spin frustration compound, p-FPDV.8) Magnetism of molecular complexes between verdazyl radical and electron acceptor (TCNQ and TCNQF_4).9) The study of doping effect of magnetic impurities on quasi-one dimensional Heisenberg organic ferromagnet (p-CDpOV) and antiferromagnet (p-BDpOV).
  • Ministry of Education, Culture, Sports, Science and Technology:Grants-in-Aid for Scientific Research(国際学術研究)
    Date (from‐to) : 1996 -1996 
    Author : Noboru HIROTA, Keishi OHARA, Kouichi NAKAGAWA, Masahide TERAZIMA, WILLIGEN Han, WILLIGEN, Hans Van, Hans von WILLIGEN
     
    At the international symposium on spin and magnetic field effects held in Novosibirsk in August, 1996 Hirota, van Willigen and Ohara discussed the detailed plan of the cooperative work. It was decided that the initial processes of photochemical reactions of xanthone of which a number of unsolved problems exist should be studied by FT-EPR method. Following this discussion, Ohara went to Boston in September to make FT-EPR measurements. In this work he obtained the following results.1) Emissive polarization found in xanthone/2-propanol is mainly determined by the hydrogen abstraction of xanthone and its mechanism is radical pair mechanism (RPM).2) The rise of the absorptive polarization observed in xanthone/2-propanol +HィイD22ィエD2O +HCl is very rapid determined by the time -resolution of the spectrometer and the mechanism is likely to be triplet mechanism (TM). However, the intensity of the polarization is very weak.In November, Hirota made further measurement in Boston and examined the effect of the concentration of HCl on the polarization. It was found that inversion of the polarization of the hydroxypropyl radical from E to A takes place at a relatively low concentration of HCl. Moreover, it was found that the polarization of the xanthone ketyl radical showed an inversion from A to E. It was though that additional transient absorption experiments are needed to clarify the initial processes in the photochemistry of xanthone and work along this line was tried in Kyoto with Prof. van Willigen. However, this work has not been completed yet, and further work will be continued.In addition to the above work Nakagawa made FT-EPR work on the hydrated electron in the SDS micelle produced by the photoionization of phenothiazine and its derivatives. He obtained detailed information about the phase of the CIDEP signal of the hydrated electron, dynamics of disappearance and quenching of the CIDEP signal of the hydrated electron.

Committee Membership

  • 2004/04 - Today   Spectroscopical Society of Japan   Organizer of Ehime Block   Spectroscopical Society of Japan

愛媛大学教員活動実績

教育活動(B)

担当授業科目(B01)

  • 2019, the first semester, under graduate, 分子分光学
  • 2019, the first semester, under graduate, 卒業研究Ⅰ
  • 2019, the first semester, under graduate, 化学Ⅰ
  • 2019, the first semester, under graduate, 化学実験Ⅱ
  • 2019, the first semester, under graduate, 化学実験Ⅲ
  • 2019, the first semester, master course, 化学物質管理の基礎知識
  • 2019, the first semester, master course, 化学物質管理の基礎知識
  • 2019, the first semester, doctor course, 物質機能科学特論Ⅲ
  • 2019, the first semester, under graduate, 化学実験Ⅱ
  • 2019, the first semester, under graduate, 化学実験Ⅲ


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