OHARA, Keishi

Graduate School of Science and Engineering Engineering for Production and Environment
Last Updated :2018/05/25

Researcher Profile and Settings


  •   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


  • Doctor of Science

Academic & Professional Experience

  •   2015 05 ,  - 現在, Ehime University, Graduate School of Science and Engineering, Professor
  •   2007 04 ,  - 2015 04 , Ehime University, Graduate School of Science and Engineering, Associate Professor
  •   2006 04 ,  - 2007 03 , Ehime University, Graduate School of Science and Engineering, Senior Assistant Professor
  •   1996 04 ,  - 2006 03 , Ehime University, Faculty of Science, Assistant Professor
  •   1996 01 ,  - 1996 04 , Kyoto University, Graduate School of Science, Researcher (JSPS Research Fellowships for Young Scientists)

Association Memberships


Committee Memberships

  •   2004 04  - 現在, Spectroscopical Society of Japan, Organizer of Ehime Block

Research Activities

Research Areas

  • Basic chemistry, Basic chemistry
  • Pharmacy, Physical pharmacy
  • Agricultural chemistry, Food science
  • Applied Chemistry, Functional materials chemistry

Research Interests

    Photochemistry, Singlet Oxygen, Free Radical, Antioxidant, EPR, Near-Infrared spectroscopy, Spin-dynamics

Published Papers


Books etc

Research Grants & Projects

  • Antioxidant activity evaluation of trace sample by the spot measurement of singlet oxygen luminescence lifetime
    Ministry of Education, Culture, Sports, Science and Technology, Grants-in-Aid for Scientific Research(基盤研究(C)), 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.
  • Kinetics and Spin-Dynamics in Quenching Reactive Oxygen Species with Natural Antioxidants in Dispersion / Emulsion Systems
    Ministry of Education, Culture, Sports, Science and Technology, Grants-in-Aid for Scientific Research(基盤研究(C)), Keishi OHARA
  • Development of Superconducting Ferromagnet Based on New Verdazyl Radical Complex
    Ministry of Education, Culture, Sports, Science and Technology, Grants-in-Aid for Scientific Research(基盤研究(C)), Kazuo MUKAI, 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.
  • Spin Dynamics of the Anti-Aging Actions by NaturalAntioxidants
    Ministry of Education, Culture, Sports, Science and Technology, Grants-in-Aid for Scientific Research(特定領域研究), Kazuo MUKAI, 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.
  • Antioxidant Activity of Natural Antioxidants versus Reactive Oxygen Species in Emulsion Systems and Its Spin-Dynamics
    Ministry of Education, Culture, Sports, Science and Technology, Grants-in-Aid for Scientific Research(基盤研究(C)), 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.
  • Mechanism of Excited-State Proton-Transfer- From Near-Infrared to Soft X-ray -
    Ministry of Education, Culture, Sports, Science and Technology, Grants-in-Aid for Scientific Research(基盤研究(C)), Shin-ichi NAGAOKA
  • CIDEP Spin-probe for Singlet Oxygen Dynamics around Micelles and Biomembranes
    Ministry of Education, Culture, Sports, Science and Technology, Grant-in-Aid for Young Scientists (A), Keishi OHARA
  • Natural Antioxidants : Their Activities and Action Mechanism
    Ministry of Education, Culture, Sports, Science and Technology, Grants-in-Aid for Scientific Research(基盤研究(B)), Kazuo MUKAI, 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.
  • A Study of Excited -State-Proton-Transfer Reaction
    Ministry of Education, Culture, Sports, Science and Technology, Grants-in-Aid for Scientific Research(基盤研究(C)), Shin-ichi NAGAOKA, 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.
  • Syntheses of New Verdazyl Radicals and Mechanism of Appearance of Genuine Organic Ferromagnetism and Weak Ferromagnetism
    Ministry of Education, Culture, Sports, Science and Technology, Grants-in-Aid for Scientific Research(基盤研究(B)), Kazuo MUKAI, 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).
  • FT-ESR Study of Initial Process of Phtochemical Reactions
    Ministry of Education, Culture, Sports, Science and Technology, Grants-in-Aid for Scientific Research(国際学術研究), Noboru HIROTA, 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.

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