Faculty Profiles - KUMAGAI, Jun

Papers - KUMAGAI, Jun

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Absence of recombination of neighboring H atoms in highly purified solid parahydrogen: Electron spin resonance, electron-nuclear double resonance, and electron spin echo studies Reviewed

T. Kumada, M. Sakakibara, T. Nagasaka, H. Fukuta, J. Kumagai, T. Miyazaki

J. Chem. Phys. Vol. 116 ( 3 ) page： 1109-1119 2002.1

Language：English Publishing type：Research paper (scientific journal)

Diffusion and recombination of H atoms were studied in solid hydrogen containing ortho-H(2) molecules at relative concentration X(o)=0.001 -->0.75 using electron spin resonance (ESR), electron-nuclear double resonance (ENDOR), and electron spin echo (ESE) methods at around 4 K. When the rate-determining step for recombination is assumed to be the diffusion of H atoms, the rate constant for recombination at X(o)greater than or equal to0.1 is consistent with the diffusion coefficient estimated from the analysis of ENDOR spectra and longitudinal spin relaxation behaviors. The recombination rate constant at X(o)<0.1, however, is too slow to be explained using the diffusion coefficient estimated from longitudinal spin relaxation and forbidden spin-flip satellite transition studies. This result suggests that, even if one H atom finds another H in its immediate neighborhood, these H atoms do not react to form a H(2) molecule at X(o)<<0.1. The absence of recombination of H atoms is due to lack of the energy dispersion path required for the recombination of diatomic molecules. Since the absence of recombination becomes less significant at higher X(o), ortho-H(2) molecules are found to play an important role in the energy dispersion which accompanies the recombination reaction

DOI： 10.1063/1.1426410

An ESR and ESEEM study of long-lived radicals which cause mutation in irradiated mammalian cells Reviewed

J. Kumagai, T. Miyazaki, S. Kodama, M. Watanabe

Int. Congress Series Vol. 1236 page： 351-354 2002

突然変異やガン化を誘発する長寿命タンパク質ラジカル　〜電子スピン共鳴法・電子スピンエコー法による解析〜 Invited

熊谷　純

放射線生物研究 Vol. 37 page： 85-103 2002

A role of long-lived radicals in radiation mutagenesis and its suppression by epigallocatechin gallate Reviewed

Vol. 1236 page： 355-358 2002

High-resolution electron spin resonance spectroscopy of ethyl radicals in solid parahydrogen Reviewed

T. Kumada, J. Kumagai, T. Miyazaki

J. Chem. Phys. Vol. 114 ( 22 ) page： 10024-10030 2001.6

Language：English Publishing type：Research paper (scientific journal)

High-resolution electron spin resonance (ESR) spectrum of ethyl radicals isolated in solid parahydrogen (> 99.5 mol %) has been measured in the temperature range between 3.1 and 6.7 K. This study was carried out by UV photolysis of ethyl iodide doped in solid parahydrogen. Although ESR linewidth of the spectrum is broadened due to anisotropic terms of hyperfine interactions, the linewidth measured in parahydrogen remains comparable to that of the isotropic spectrum measured in liquid ethane [R. W. Fessenden, J. Chem. Phys. 37, 747 (1962)]. Small splittings were found in the resolved ESR signals and assigned as ethyl radicals with A(A',A') and E(E',E') symmetries, respectively. The ratio in the ESR intensities is not proportional to that of the degeneracy of each symmetry but varies as a function of temperature. We measured the signal intensities as a function of temperature and determined the rotational energy level splitting of methyl groups between the lowest with the A(A('),A(')) symmetry and the second-lowest with the E(E-',E-') symmetry in solid parahydrogen to be 5.3 +/-0.7 K. The level splitting is close to that measured by infrared-absorption study in gas phase and theoretical calculation, whereas the splitting measured in conventional matrices have been much smaller. Intermolecular interaction between guest radicals and surroundings in solid parahydrogen are found to be much smaller than those in other conventional matrices giving less shifted spectral parameters.

DOI： 10.1063/1.1370080

ESR, ENDOR and ESEEM spectroscopy study on local structure and motion of reactants: highly selective tunneling radical abstraction in neopentane-ethane mixture Reviewed

Jun Kumagai, Yoshiteru Itagaki, Masanobu Ishizuka, Takayuki Kumada, Anders Lund, Tetsuo Miyazaki

J. Phys. Chem. A Vol. 105 ( 14 ) page： 3652-3657 2001.4

Authorship：Lead author Language：English Publishing type：Research paper (scientific journal)

Local structures and motions of radical reactants in highly selective tunneling abstraction reaction in neopentane-ethane mixture are investigated with CW-ESR, ENDOR, and ESEEM spectroscopy at different temperatures. H atoms produced by the radiolysis of neo-C5H12 in the neo-C5H12-C2H6 (2 mol %) mixtures above 40 K react selectively with the solute C2H6 to give ethyl radicals. The selective reaction is suppressed below 30 K. The local structures of neopentane matrix around neopentyl and ethyl radicals are approximately the same in the temperature range from 4.4 to 45 K. Although neopentyl radicals are rigidly trapped below 100 K, ethyl radicals in neopentane matrix begin to librate even at 6 K and increase the degree of motion up to 30 K, Finally, the librating motion of the ethyl radicals in neopentane matrix is vigorous above 40 K. The ethane molecule can take more favorable orientation for the hydrogen abstraction reaction by H atoms than rigid neopentane molecules by the vigorous libration motion, resulting in the selective reaction with H atoms.

DOI： 10.1021/jp003396+

Controlling factors of tunneling reactions in solid hydrogen at very low temperature Reviewed

Tetsuo Miyazaki, Jun Kumagai, Takayuki Kumada

Radiat. Phys. Chem. Vol. 60 ( 4-5 ) page： 381-387 2001.3

Language：English Publishing type：Research paper (scientific journal)

The recent studies on tunneling reactions: of our group are;auto-reviewed. The local structure around reactants, the new temperature effect. and the impurity effect are pointed out as important controlling factors of tunneling reactions in the solid phase. The distances between H(D) atoms and H-2(HD. D,) molecules in solid hydrogen and solid argon M ere estimated by ESR, electron nuclear double resonance (ENDOR), and electron spin echo (ESE). The temperature effects on tunneling reaction were observed in a reaction D + HD --> D-2 + H in solid HD. A mechanism of a vacancy-assisted tunneling reaction has been proposed to account for the temperature effect. The strange temperature dependence of a tunneling electron-transfer-reaction H-2(-) + H-2 + H-2(-) was explained in terms elf the phonon-scattering effect and the impurity effect on the tunneling reaction. The rate constant fur a tunneling reaction H + p-H-2 --> p-H-2 + H in solid para-H-2 (p-H-2) decreases with the increase in the concentration of ortho-H-2 (o-H-2). The results were explained by the model that the orientational defects: by o-H-2 molecules affect the tunneling reaction H + p-H-2. A tunneling reaction at very low temperature gives a surprising example in control of a reaction that a small amount of energy as such 2 cal mol(-1) can affect the rate of a reaction. The tunneling reaction in the solid phase. which can be considered as a multidimensional tunneling phenomenon. is affected significantly by the condition surrounding reactants.

DOI： 10.1016/S0969-806X(00)00413-8

Resonance effect on the tunneling reaction: H+H₂ -> H₂+H in solid hydrogen Reviewed

T. Kumada, S. Mori, T. Nagasaka, J. Kumagai, T. Miyazaki

J. Low Temp. Phys. Vol. 122 ( 3-4 ) page： 265-277 2001.2

Language：English Publishing type：Research paper (scientific journal)

The tunneling abstraction reaction: H + H-2 --> H-2 + H in gamma -irradiated solid hydrogen has been studied using electron spin resonance (ESR) and electron-nuclear double resonance (ENDOR) spectroscopy and gas-chromatography. The rate constant for the tunneling reaction in solid hydrogen was found to decrease with the increase in the concentration of ortho-H-2 molecules in solid hydrogen. We concluded that the decrease in the rate constant is clue to the energy level mismatching between reactant species of H + H-2 trapped and product species of H-2 + H trapped in the reverse induced by inhomogeneous intermolecular interactions between ortho-H-2 molecules in solid hydrogen. This result indicates that resonance effects play an important role in tunneling reactions in solids.

DOI： 10.1023/A:1004840631947

Electron spin echo study of long-lived radicals which cause mutation in gamma-ray irradiated mammalian cells. Reviewed

Jun Kumagai, Takayuki Kumada, Masami Watanabe, Tetsuo Miyazaki

Spctrochimica Acta. A. Vol. 56 ( 13 ) page： 2509-2516 2000.11

Authorship：Lead author Language：English Publishing type：Research paper (scientific journal)

Long-lived radicals, produced by gamma -ray irradiation of mammalian cells at room temperature, cause mutation and morphological transformation in the cells. The local environment near the long-lived radicals in irradiated cells was investigated here by the analysis of electron spin echo envelope modulation (ESEEM) spectra. The number of hydrogen (deuterium) atoms surrounding the long-lived radical, which may correspond to the number of water molecules, was estimated roughly as one or two. It is postulated that the long-lived radicals are generated in the interior of biopolymers. The radicals are not produced by the reaction of OH radicals, but mainly by the decomposition of biopolymer which absorbed directly the energy of the ionizing radiation

DOI： 10.1016/S1386-1425(00)00360-7

Decay dynamics of H atoms in solid hydrogen at 4.2 and 2.2 K. Controlling factor of tunneling reaction H + para-H2 Reviewed

T. Miyazaki, S. Mori, T. Nagasaka, J. KUmagai, Y. Aratono, T. Kumada

J. Phys. Chem. A. Vol. 104 ( 42 ) page： 9403-9407 2000.10

Language：English Publishing type：Research paper (scientific journal)

H atoms produced by the gamma -ray irradiation of solid para-H-2 (p-H-2) and solid normal-H-2 (n-H-2) decay gradually when the irradiated sample is stored at 4.2 K. ortho-H-2 (o-H-2) molecules at the sites nearest an H atom in solid n-H-2 convert to p-H-2 molecules by interacting with the H atom. H atoms in solid H-2 decay by the process of tunneling diffusion H + p-H-2 --> p-H-2 + H and finally recombine with other I-I atoms. The rate constants for the tunneling reaction were obtained from the decay rates of H atoms in solid H-2 at various concentrations of o-H-2 When solid n-H-2 is stored for 10 h at 4.2 K after gamma -ray irradiation, a number of o-H-2 molecules change into p-H-2 molecules by a catalytic chain reaction induced by mobile H atoms. The G value of the o-H-2 yields from H atoms amounts to 1-2.6 x 10(4). The rate constant for the tunneling reaction ii + p-H-2 --> p-H-2 + H decreases drastically with increasing numbers of o-H-2 molecules, which exist as orientational defects in solid p-H-2. It was concluded that a very small amount of energy (ca. 2 cal mol(-1)) affects the tunneling reaction at very low temperatures.

DOI： 10.1021/jp000440c

An ENDOR study of H atoms in HD solid at 4.2 K Reviewed

J. Kumagai, T. Noda, T. Miyazaki

Chem. Phys. Lett. Vol. 321 ( 1-2 ) page： 8-12 2000.4

Authorship：Lead author Language：English Publishing type：Research paper (scientific journal)

An ENDOR spectrum of H atoms in the gamma-ray irradiated HD solid was measured at 4.2 K for elucidating the local environment of HD molecules surrounding ii atoms. The analysis of the ENDOR spectrum indicates that the H atoms are not trapped in substitutional but in pseudo octahedral interstitial sites of HD solid. It is postulated that an H atom, produced by the gamma-irradiation, initially enters the octahedral interstitial site, and then the HD molecules at the first nearest site from the Ii atom are pushed back by zero-point vibration of the ii atom.

DOI： 10.1016/S0009-2614(00)00327-4

Strong resistance of Arabidopsis thaliana and Raphanus sativus seeds for ionizing radiation as studied by ESR, ENDOR, ESE spectroscopy and germination measurement: Effect of long-lived and super-long-lived radicals. Reviewed

J. Kumagai, H. Katoh, T. Kumada, A. Tanaka, S. Tano, T. Miyazaki

Radiat. Phys. Chem. Vol. 57 ( 1 ) page： 75-83 2000.1

Authorship：Lead author Language：English Publishing type：Research paper (scientific journal)

Resistance of seeds for ionizing radiation effects on Arabidopsis thaliana and Raphanus sativus seeds were investigated by ESR, ENDOR, ESE spectroscopy and germination measurement. Two types of free radicals, such as long-lived (LL) and super-long-lived (SL) radicals, were produced by the gamma-irradiation in the seeds. More than 90% of the 1 kGy-irradiated-seeds can germinate probably by decreasing the LL radicals by absorbing water. 10 kGy-irradiated-seeds cannot germinate at all probably due to the existence of significant amounts of the SL radicals even after absorbing water.

DOI： 10.1016/S0969-806X(99)00306-0

長寿命ラジカルの生物効果　～イネのUVB照射効果～ Invited

熊谷　純、宮崎哲郎

IGEシリーズ Vol. 27 page： 3-12 2000

Trapping sites of hydrogen atoms in solid HD and D2 : An electron spin echo study Reviewed

T. Kumada, T. Noda, J. Kumagai, Y. Aratono, T. Miyazaki

J. Chem. Phys. Vol. 111 ( 24 ) page： 10974-10978 1999.12

Language：English Publishing type：Research paper (scientific journal)

Trapping sites of H and D atoms in solid HD and D-2 have been determined using electron spin echo (ESE) spectroscopy. It was found that all the H and D atoms are trapped in substitutional sites and that the H atoms push back surrounding HD(D-2) molecules to produce local lattice distortion around the atoms, whereas the D atoms do not. It is expected that the local lattice distortion is produced by zero-point motion of the H atoms whose amplitude is larger than that of host HD(D-2) molecules and that the isotope effect is due to difference in the amplitude between the H and D atoms. The lattice distortion around the H atoms may induce the increase in rate constant for the tunneling reaction D+DH --> D-2+H with the increase in temperature in solid HD reported in Chem. Phys. Lett. 261, 463 (1996).

DOI： 10.1063/1.480461

Differences in the sensitivity to UVB radiation of two cultivars of rice (Oryza sativa L.) based on observation of long-lived radicals Reviewed

J. Kumagai, H. Katoh, T. Miyazaki, J. Hidema, T. Kumagai

J. Radiat. Res. Vol. 40 ( 4 ) page： 303-310 1999.12

Authorship：Lead author Language：English Publishing type：Research paper (scientific journal)

Free radicals with a long lifetime were observed in the leaves of two rice cultivars (Oryza sativa L,.), Sasanishiki (UVB resistant) and Norin-1 (UVB sensitive), by electron spin resonance spectroscopy. The leaves of both cultivars grown with visible light show very similar ESR spectra composed of radical 1 (R1) and radical 2 (R2), which may be attributable to P-700 cation radicals in the reaction center of photosystem I, and tyrosine cation radicals in the reaction center of photosystem II, respectively. The ESR spectrum composed of R1 and R2 radicals in the leaves of Sasanishiki grown under visible light with supplemental UVB was similar to that in the plant grown without supplemental UVB. On the other hand, the amount of R2 radicals in the leaves of Norin-1 grown under visible light with supplemental UVB was significantly smaller than that in the plant grown without supplemental UVB. It is suggested that the loss of R2 radicals in Norin-1 upon UVB irradiation is related to the instability of the plant.

DOI： 10.1269/jrr.40.303

Observation of electron bubbles in para-H2-D2 (HD) mixtures by high-resolution ESR spectroscopy Reviewed

T. Kumada, S. Mori, J. Kumagai, Y. Aratono, T. Miyazaki

J. Phys. Chem. A Vol. 103 ( 45 ) page： 8966-8968 1999.11

Language：English Publishing type：Research paper (scientific journal)

A sharp singlet signal assigned to electron bubbles was observed in gamma-irradiated solid para-H-2-D-2 (HD) mixtures by use of high-resolution ESR spectroscopy. The signal was not observed in pure para-H-2 but in the mixtures. This result indicates that the D-2 and HD molecules play an important role in the formation of the electron bubbles in para-H-2. The electron bubbles decay with a half-lifetime of about 2 h, and the decay rate constant at 4.2 K is very close to that at 2.2 K. This result shows that the electron bubbles migrate in the p-H-2 sample via quantum mechanical tunneling.

DOI： 10.1021/jp991650w

Hydrogen radical anions and electron bubbles in solid hydrogen Reviewed

T. Ichikawa, H. Tachikawa, T. Kumada, J. Kumagai, T. Miyazaki

Chem. Phys. Lett. Vol. 307 ( 3-4 ) page： 283-286 1999.7

Relation between the helicity and the ESR g-anisotropy of δ-conjugated quantum wires Reviewed

T. Ichikawa, M. Sumita, J. Kumagai

Chem. Phys. Lett. Vol. 307 ( 1-2 ) page： 81-88 1999.6

Suppression of the Anderson localization of charge carriers on polysilane quantum wire Reviewed

T. Ichikawa, Y. Yamada, J. Kumagai, M. Fujiki

Chem. Phys. Lett. Vol. 306 ( 5-6 ) page： 275-279 1999.6

Language：English Publishing type：Research paper (scientific journal)

Comparison of the ESR and electronic absorption spectra of the radical ions of poly(cyclohexylmethylsilane) and poly(n-decyl-(s)-2-methylbutylsilane) has shown that the Anderson localization of charge carriers on part of the Si-Si polymer skeleton can be suppressed by replacing the pendant groups with bulky ones. Replacement reduces the flexibility of the polymer skeleton and therefore the dispersion of the resonance energies of the charge carriers between adjacent Si atoms, which suppresses the localization of the charge carriers arising from irregularity of the periodic potential field on the skeleton.

DOI： 10.1016/S0009-2614(99)00487-X

Optical and electronic properties of polysilane radical anions Reviewed

T. Ichikawa, H. Koizumi, J. Kumagai

J. Phys. Chem. B Vol. 103 ( 19 ) page： 3812-3817 1999.5

Language：English Publishing type：Research paper (scientific journal)

Analyses of the electronic absorption spectra and their polarization spectra of the radical anions of permethylated hexa- and octasilane and poly(cyclohexylmethylsilane) in the mixed solvents of nonpolar methylcyclohexane and polar 2-methyltetrahydrofuran at 77 K have revealed that the orbitals of the excess electrons in the radical anions are antibonding pseudo-pi composed of Si 3p(y) atomic orbitals bisecting the Si-Si-Si planes. The near-IR and UV bands of the radical anions are assigned as being due to the excitation of an electron from the SOMO pseudo-pi(3p(y)) to pseudo-pi(3p(y)) and from the HOMO pseudo-pi(3p(x)) to antibonding-sigma(3s), respectively. The near-IR band of the polysilane radical anion shows strong solvatochromic shift, which arises from the localization of the excess electron on a part of the main chain. Localization of the excess electron is proposed to be due to Anderson localization which is induced by the fluctuation of pseudo-pi conjugation arising from the irregularity of the torsional angles of the Si-Si bonds.

DOI： 10.1021/jp9834715

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Papers - KUMAGAI, Jun