Faculty Profiles - KUMAGAI, Jun

Papers - KUMAGAI, Jun

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Tuning Photoluminescence and Magnetic Properties of Ag–Ga–S and Zn–Ag–Ga–S Quantum Dots via Mn²⁺ Doping Invited Reviewed

Chang JIANG, Tomoya SAKAI, Kazutaka AKIYOSHI, Tatsuya KAMEYAMA, Jun KUMAGAI, Shota YAMADA, Hiroshi YUKAWA, Yoshinobu BABA, Taro UEMATSU, Tsukasa TORIMOTO

Electrochemistry 2025.5

Mechanism Responsible for Changes in the Luminescence Properties of Terbium (III)–Doped Layered Double Hydroxides During Carbonate/Chloride Exchange Invited Reviewed

Ryo Sasai, Kaoru Ohta, Kohei Makishima, Takuya Fujimura, Chikako Moriyoshi, Jun Kumagai, Shogo Kawaguchi

Luminescence Vol. 40 ( 4 ) page： e70174 2025.4

Radical Intermediates in Photocatalytic Activation of Carboxylic Acids: A Spin Trapping Study Reviewed

Gunik Lee, Riko Maruyama, Kexin Zou, Haifan Huang, Kin-ichi Oyama, Hisao Yoshida, Jun Kumagai

The Journal of Physical Chemistry C Vol. 129 ( 1 ) page： 402 - 414 2024.12

Selective Killing of Human Breast Cancer Cells by Plasma-Treated L-Arginine Solution Reviewed

Liyin Du, Camelia Miron, Takashi Kondo, Jun Kumagai, Masaaki Mizuno, Shinya Toyokuni, Hiroaki Kajiyama, Masaru Hori, Hiromasa Tanaka

Plasma Processes and Polymers 2024.12

Comparison of free radical formation induced by ionizing radiation , low-temperature plasma, and ultrasound Reviewed

Takashi Kondo, Jun Kumagai, Keiji Yasuda, Ken-ichi Inoue, Hiromasa Tanaka, Kenji Ishikawa, Masaru Hori

Radiation Chemistry Vol. 118 page： 3 - 11 2024.10

Rutile TiO2-Supported Pt Nanoparticle Catalysts for the Low-Temperature Oxidation of Ethane to Ethanol Reviewed

Akira Oda*, Yuya Kimura, Koyo Ichino, Yuta Yamamoto, Jun Kumagai, Gunik Lee, Kyoichi Sawabe, Atsushi Satsuma

Journal of the American Chemical Society Vol. 146 ( 29 ) page： 20122 - 20132 2024.7

Fundermentals of interactions between ionizing radiation and matter Invited

Jun Kumagai

Chemical Industry Vol. 74 ( 2 ) page： 73 - 84 2023.2

Highly Active Rutile TiO2 for Photocatalysis under Violet Light Irradiation at 405 nm Reviewed

Fumiaki Amano, Akira Yamamoto and Jun Kumagai

Catalysts Vol. 12 page： 1079-1 - 1079-12 2022.9

A π–Cu(II)−π Complex as an Extremely Active Catalyst for Enantioselective α-Halogenation of N-Acyl-3,5-dimethylpyrazoles Reviewed International coauthorship

Kazuki Nishimura, Yanzhao Wang, Yoshihiro Ogura, Jun Kumagai, and Kazuaki Ishihara

ACS Catalysis Vol. 12 page： 1012 - 1017 2022.1

Stabilization of radical active species in a MOF nanospace to exploit unique reaction pathways Reviewed International coauthorship

Harada, Yuki, Kusaka, Shinpei, Nakajo, Toshinobu, Kumagai, Jun, Kim, Cho Rong, Shim, Joo Young, Hori, Akihiro, Ma, Yunsheng, Matsuda, Ryotaro

Chemical Communications Vol. 57 page： 12115 - 12118 2021.11

Triplet Carbene with Highly Enhanced Thermal Stability in the Nanospace of a Metal–Organic Framework Reviewed

Toshinobu Nakajo, Jun Kumagai, Shinpei Kusaka, Akihiro Hori, Yuh Hijikata, Jenny Pirillo, Yunsheng Ma, and Ryotaro Matsuda

Journal of the American Chemical Society Vol. 143 ( 21 ) page： 8129 - 8136 2021.6

Perspective on the Biological Mechanisms of Radiation-induced both Bystander and Rescue effects Invited Reviewed

Genro Kashino, Jun Kumagai, Kentaro Ariyoshi, Mitsuaki Ojima

Vol. 56 ( 1 ) page： 19 - 39 2021.4

O-17-ESR Evidence for Zeolite Matrix Isolation of a Square Planar ZnO3 Ring Radical with C-2v Symmetry Reviewed

Oda, Oda, Akira; Kumagai, Jun; Sawabe, Kyoichi; Ohkubo, Takahiro ; Kuroda, Yasushige; Satsuma, Atsushi

JOURNAL OF PHYSICAL CHEMISTRY C Vol. 125 ( 9 ) page： 5136 - 5145 2021.3

A low-temperature oxyl transfer to carbon monoxide from the Zn-II-oxyl site in a zeolite catalyst Reviewed

Oda, Akira; Kumagai, Jun; Ohkubo, Takahiro; Kuroda, Yasushige

INORGANIC CHEMISTRY FRONTIERS Vol. 8 ( 2 ) page： 319 - 328 2021.1

Effects of the amount of Au nanoparticles on the visible light response of TiO<sub>2</sub> photocatalysts International journal

Yoshida, T; Misu, Y; Yamamoto, M; Tanabe, T; Kumagai, J; Ogawa, S; Yagi, S

CATALYSIS TODAY Vol. 352 page： 34 - 38 2020.8

Language：English Publishing type：Research paper (scientific journal) Publisher：Catalysis Today

We have succeeded to prepare Au nanopareticle deposited TiO2 photocatalysts (Au/TiO2) with control of Au nanoparticle size to be around 8 nm and variation of number density using a colloid photodepostion method. The prepared Au/TiO2 exhibits activity on decomposition (oxidation) of formic acid by thermally activated and photo-activated catalytic reactions. The thermally activated catalytic decomposition gradually increases with increasing the number density of deposited Au NPs and saturated, suggesting that the decomposition occurs on Au NPs surface and/or near the interface of TiO2 and Au NPs. On the other hand, the photocatalytic decomposition is significantly improved with rather small number density deposition of Au NPs and disappeared with high number density deposition. ESR measurements of Au/TiO2 in the surrounding similar to the photocatalytic decomposition suggests that electrons excited by plasmon resonance absorption in the Au NPs transfer to TiO2 to promote the decomposition. However, high number density deposition enhances electron capture by neighboring Au NPs and reduces the photocatalytic activity. Thus there should be the optimum number density of Au NPs on TiO2 for photocatalytic decomposition of formic acid.

DOI： 10.1016/j.cattod.2019.12.035

Web of Science

Scopus

Exploiting single-electron transfer in Lewis pairs for catalytic bond-forming reactions International journal

Aramaki, Y; Imaizumi, N; Hotta, M; Kumagai, J; Ooi, T

CHEMICAL SCIENCE Vol. 11 ( 17 ) page： 4305 - 4311 2020.5

Language：English Publishing type：Research paper (scientific journal) Publisher：Chemical Science

A single-electron transfer (SET) between tris(pentafluorophenyl)borane (B(C6F5)3) andN,N-dialkylanilines is reported, which is operativeviathe formation of an electron donor-acceptor (EDA) complex involving π-orbital interactions as a key intermediate under dark conditions or visible-light irradiation depending on the structure of the aniline derivatives. This inherent SET in the Lewis pairs initiates the generation of the corresponding α-aminoalkyl radicals and their additions to electron-deficient olefins, revealing the ability of B(C6F5)3to act as an effective one-electron redox catalyst.

DOI： 10.1039/d0sc01159b

Web of Science

Scopus

PubMed

Development and verification of radio protective materials by using Tungsten fiver Invited

Taishi Tsuda, Shigefumi Imai, Jun Kumagai

Vol. 107 page： 65-68 2019.4

Fundamental study of radiosensitization targeting cancer cell environmental factors

Kashino Genro, Kumagai Jun

CANCER SCIENCE Vol. 109 page： 751-751 2018.1

Interface of Radiation Chemistry for Radia- tion Biology and Meteorology Invited Reviewed

Jun Kumagai

RADIOISOTOPES Vol. 66 page： 489-496 2017.10

Iodide Selectivity and gamma-Ray Shielding Ability of a Layered Double Hydroxide

Ryo Sasai, Eisaku Nii, Hiroaki Sato, Takuya Fujimura, Shigefumi Imai, Jun Kumagai

CHEMISTRY LETTERS Vol. 45 ( 12 ) page： 1409-1411 2016.10

Solar-UV-signature mutation prefers TCG to CCG: extrapolative consideration from UVA1-induced mutation spectra in mouse skin Reviewed

H. Ikehata, J. Kumagai, T. Ono, A. Morita

Photochem. Photobiol. Sci. Vol. 12 ( 8 ) page： 1319-27 2013.7

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

UVA1 exerts its genotoxicity on mammalian skin by producing cyclobutane pyrimidine dimers (CPDs) in DNA and preferentially inducing solar-UV-signature mutations, C T base substitution mutations at methylated CpG-associated dipyrimidine (Py-mCpG) sites, as demonstrated previously using a 364 nm laser as a UVA1 source and lacZ-transgenic mice that utilize the transgene as a mutational reporter. In the present study, we confirmed that a broadband UVA1 source induced the same mutation profiles in mouse epidermis as the UVA1 laser, generalizing the previous result from a single 364 nm to a wider wavelength range of UVA1 (340-400 nm). Combined with our previous data on the mutation spectra induced in mouse epidermis by UVB, UVA2 and solar UVR, we proved that the solar-UV-signature mutation is commonly observed in the wavelength range from UVB to UVA, and found that UVA1 induces this mutation more preferentially than the other shorter wavelength ranges. This finding indicates that the solar-UV-signature mutation-causing CPDs, which are known to prefer Py-mCpG sites, could be produced with the energy provided by the longer wavelength region of UVR, suggesting a photochemical reaction through the excitation of pyrimidine bases to energy states that can be accomplished by absorption of even low-energy UVR. On the other hand, the lower proportions of solar-UV-signature mutations observed in the mutation spectra for UVB and solar UVR indicate that the direct photochemical reaction through excited singlet state of pyrimidine bases, which can be accomplished only by high-energy UVR, is also involved in the mutation induction at those shorter wavelengths of UVR. We also found that the solar-UV signature prefers 5'-TCG-3' to 5'-CCG-3' as mutational target sites, consistent with the fact that UVA induces CPDs selectively at thymine-containing dipyrimidine sites and that solar UVR induces them preferably at Py-mCpG sites. However, the mutation spectrum in human p53 gene from non-melanoma skin cancers shows the opposite preference for 5'-CCG-3' sites. This apparent discrepancy in the site preference seems to result from the lack of 5'-TCG-3' sites mutable to missense mutations on the nontranscribed strand of human p53 gene, which should be evolutionally acquired under selective pressure from the sun.

DOI： 10.1039/c3pp25444e

Suppressive effect of ascorbic acid on the mutagenesis induced by the bystander effect through mitochondrial function Reviewed

G. Kashino, Y. Tamari, J. Kumagai, K. Tano, M. Watanabe

Free Radic. Res. Vol. 47 ( 6-7 ) page： 474-479 2013.7

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

We focused on suppressive effect of ascorbic acid (AsA) on changes in mitochondrial function and mutagenesis by the radiation-induced bystander eff ect (RIBE). In mammalian cell lines, medium transfer assay was performed and conditioned medium including secreted factors after X-irradiation were examined to detect the RIBE. We found that the membrane potential and increased levels of superoxide radical (O-2(-)) in mitochondria were modulated in cells treated with conditioned medium from irradiated cells. The result of the present study also demonstrated that increases in reactive oxygen species (ROS) levels led to the induction of gene mutations. Interestingly, the modulations in mitochondria, in addition to mutation inductions by RIBE, were completely suppressed by treatment with AsA in cells treated with conditioned medium. These results suggest that mutagenesis, which may have resulted from secreted factors involving the RIBE, may be induced by ROS that are localized in mitochondria and may be relieved by AsA.

DOI： 10.3109/10715762.2013.791025

Reaction Mechanism of Aromatic Ring Amination of Benzene and Substituted Benzenes by Aqueous Ammonia over Platinum-Loaded Titanium Oxide Photocatalyst Reviewed

H. Yuzawa, J. Kumagai, H. Yoshida

J. Phys. Chem. C Vol. 117 ( 21 ) page： 11047-11058 2013.5

A heterogeneous palladium catalyst hybridised with a titanium dioxide photocatalyst for direct C-C bond formation between an aromatic ring and acetonitrile Reviewed

H. Yoshida, Y. Fujimura, H. Yuzawa, J. Kumagai, T. Yoshida

Chem. Commun. Vol. 49 ( 36 ) page： 3793-3795 2013.3

Electrical properties of lead-free ferroelectric Mn-Doped K0.5Na0.5NbO3-CaZrO3 thin films prepared by chemical solution deposition Reviewed

T. Matsuda, W. Sakamoto, B.Y. Lee, T. Iijima, J. Kumagai, M. Moriya, T. Yogo

Vol. 51 ( 9 ) page： 09LA03 2012.9

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

Lead-free ferroelectric K0.5Na0.5NbO3-CaZrO3 thin films were prepared by chemical solution deposition. Chemically optimized K0.5Na0.5NbO3-CaZrO3 precursor thin films crystallized in the perovskite single phase on Pt/TiOx/SiO2/Si substrates at 650 degrees C. The K0.5Na0.5NbO3-CaZrO3 thin films showed poor ferroelectric polarizations due to the insufficient insulating resistance. The leakage current of the K0.5Na0.5NbO3-CaZrO3 films, especially in the high-applied-field region, was markedly reduced by 1 mol % Mn doping for the Nb site. Also, the ferroelectric properties of the K0.5Na0.5NbO3-CaZrO3 thin films depended on CaZrO3 concentration. 1 mol % Mn-doped K0.5Na0.5NbO3-CaZrO3 thin films exhibited slim and small ferroelectric polarization-electric field (P-E) hysteresis loops at room temperature with an increase in CaZrO3 amount. Furthermore, these films showed a typical field-induced displacement curve with a small hysteresis, and the estimated effective d(33) values were 32 pm/V for the 1 mol % Mn-doped 0.95K(0.5)Na(0.5)NbO(3)-0.05CaZrO(3) thin films and 21 pm/V for the 1 mol % Mn-doped 0.9K(0.5)Na(0.5)NbO(3)-0.1CaZrO(3) thin films.

DOI： 10.1143/JJAP.51.09LA03

The Bystander Effect is a Novel Mechanisms of UVA-Induced Melanogenesis Reviewed

H. Nishiura, J. Kumagai, G. Kashino, T. Okada, K. Tano, M. Watanabe

Vol. 88 ( 2 ) page： 389-397 2012.3

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

We successfully identified the bystander effect in B16 murine melanoma cells exposed to UVA irradiation. The effect was identified based on melanogenesis following the medium transfer of the B16 cells, which had been cultured for 24 h after being exposed to UVA irradiation, to nonirradiated cells (bystander cells). Our confirmation study of the functional mechanism of bystander cells confirmed the reduced levels of mitochondrial membrane potential 14 h after the medium transfer. In addition, we observed increased levels of intracellular oxidation after 912 h, and the generation of melanin radicals, including long-lived radicals, 24 h after medium transfer. Further analysis of bystander factors revealed that the administration of EGTA treatment at the time of medium transfer led to an inhibition of melanogenesis and to neutralization of the mitochondrial membrane potential level, as well as to the restoration of intracellular oxidation levels to those of controls. The results demonstrated that the UVA irradiation bystander effect in B16 cells, as indicated by melanogenesis, was induced by the increase in intracellular oxidation due to the mitochondrial activity of calcium ions, which were among the bystander factors involved in the increase.

DOI： 10.1111/j.1751-1097.2011.01046.x

放射線誘導長寿命ラジカルが DNA 損傷を起源としない発がん経路の引き金 Invited Reviewed

渡邉正己, 菓子野元郎, 熊谷　純

放射線化学 Vol. 93 page： 15-22 2012.3

Negative and positive ion trapping by isotopic molecules in cryocrystals in case of solid parahydrogen containing electrons and H6+ radical cations Reviewed

Y. Shimizu, M. Inagaki, T. Kumada, J. Kumagai

Vol. 132 ( 24 ) page： 244503 2010.6

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

We performed electron spin resonance studies of trapped electrons and H-6(+) radical cations produced by radiolysis of solid parahydrogen (p-H-2), p-H-2-ortho-D-2 (o-D-2), and p-H-2-HD mixtures. Yields of trapped electrons, H-6(+) radical cations, and its isotopic analogs H6-nD(n)(+) (4 >= n >= 1) increased with increasing o-D-2 and HD concentrations in solid p-H-2. Electrons were found trapped near an o-D-2 or an HD in solid p-H-2 due to the long-range charge-induced dipole and quadrupole interactions between electrons and isotopic hydrogen molecules. H-6(+) radical cations diffuse in solid p-H-2 by repetition of H-6(+)+H-2 -> H-2+H-6(+) and are trapped by ortho-D-2 or HD to form H6-nDn+ (4 >= n >= 1) as isotope condensation reactions. Decay behaviors of these cations by the repetition, isotope condensation, and geminate recombination between electrons and H6-nDn+ (4 >= n >= 0) were reproduced by determining the corresponding reaction rate constants k(1), k(2), and k(3). Values of 0.045 and 0.0015 L mol(-1) min(-1) were obtained for k1 (H-6(+)+D-2 -> H-2+H4D2+) and k(2) (H4D2++D-2 -> H-2+H(2)D4+), respectively, and the value was quasinull for k(3) (H(2)D4++D-2 -> H-2+D6+). These rate constants suggest that hole mobility drastically decreased in the repetition reaction when H-6(+) radical cations acting as hole carriers formed H4D2+ or H(2)D4+. HD and D-2 molecules, therefore, act as electron and hole acceptors in irradiated solid p-H-2-o-D-2 and p-H-2-HD mixtures.

DOI： 10.1063/1.3432780

照射培地移動による放射線バイスタンダー効果を遅発性長寿命ラジカルから探る Reviewed

熊谷　純、菓子野元郎

放射線化学 Vol. 89 page： 20-24 2010.3

Improvement in Ferroelectric Properties of Chemically Synthesized Lead-Free Piezoelectric (K,Na)(Nb,Ta)O3 Thin Films by Mn Doping Reviewed

N. Kondo,W . Sakamoto, B.Y. Lee, T. Iijima, J. Kumagai, M. Moriya T. Yogo

Jpn. J. Appl. Phys. Vol. 49 page： 09MA04 2010

*固体パラ水素中の H6+同位体イオンと捕捉電子の放射線化学 Invited Reviewed

清水裕太、熊谷　純

放射線化学 Vol. 87 page： 23-33 2009.3

Electron spin resonance spectroscopy of molecules in large precessional motion: A case of H6+ and H4D2+ in solid parahydrogen Reviewed

Yuta Shimizu, Takayuki Kumada, Jun Kumagai

J. Mag. Reson. Vol. 194 ( 1 ) page： 76–80 2008.9

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

We have measured electron spin resonance (ESR) spectra of H-6(+) and H4D2+ tons produced in gamma-ray irradiated solid parahydrogen. Anisotropic hyperfine-coupling constants for H-6(+) and H4D2+ determined by the analysis of ESR lines at 4.2 K were -0.06 and -0.12 mT, respectively, which were opposite in sign to and much smaller than theoretical results of 1.17-1.25 mT. Although no change was observed in H-6(+), the constant for H4D2- increased to be 1.17 mT at 1.7 K, which is very close to the theoretical value. We concluded that H-6(-) both at 4.2 and 1.7 K and H4D2+ at 4.2 K should be in a large precessional motion with the angle of 57-59 degrees, but the precession of H4D2+ is stopped at 1.7 K.

DOI： 10.1016/j.jmr.2008.05.024

*放射線照射後に細胞中で生じてくる遅発性長寿命ラジカルと遅延放射線生物影響 Invited

熊谷　純

電子スピンサイエンス Vol. 6 ( 11 ) page： 109-115 2008.9

H atom, e(-), and H(6)(+) ions produced in irradiated solid hydrogens: An electron spin resonance study Reviewed

T. Kumada, Y. Shimizu, T. Ushida, J. Kumagai

Radiat. Phys. Chem. Vol. 77 ( 10-12 ) page： 1318-1322 2008

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

We carried out electron spin resonance (ESR) study of irradiated solid H(2) and para-H(2). H-atom, e(-), and H(6)(+) lines were observed. The H-atom radicals diffuse in solid H2 by the tunneling chemical reaction H+H(2) -> H(2)+H below 4 K, and by the thermally activated process above 5 K. These decay via H-H recombination. Yield of trapped electrons e- produced by the radiolysis of solid para-H2 increases with increase in the concentration of added isotopic hydrogen, HD or D(2). These decay via geminate recombination with positive ions with a half-life of 8 h at 4 K. H(6)(+) ion is an ionic hydrogen radical whose spectrum has firstly been observed in irradiated solid para-H(2). H(6)(+) ions diffuse in solid H2 by sequence of H(6)(+)+H(2) -> H(2)+H(6)(+) reactions, and terminate by the isotope-exchange reaction H(6)(+)+HD -> H(5)D(+)+H(2) or H(6)(+)D(2) -> H(4)D(2)(+)+H(2). Unlike H(6)(+), isotopically substituted H(5)D(+) and H(4)D(2)(+) cannot diffuse in solid para-H(2). Rate-determining step of their decay is charge recombination with e(-).

DOI： 10.1016/j.radphyschem.2008.05.026

放射線照射後に細胞中で生じてくる遅発性長寿命ラジカルと遅延放射線生物影響 Invited

熊谷　純

電子スピンサイエンス Vol. 6 page： 109-115 2008

Electron spin resonance study on H6+, H5D+, H4D2+, and H2D4+ in solid parahydrogen Reviewed

Jun Kumagai, Hiroki Inagaki, Susumu Kariya, Takahiro Ushida, Yuta Shimizu, Takayuki Kumada

J. Chem. Phys. Vol. 127 ( 2 ) page： 024505 2007.7

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

We carried out an electron spin resonance (ESR) study on hydrogen ion radicals produced by radiolysis of solid para-H-2. In addition to quartet ESR lines proposed to be H-2(+)-core H-6(+) (D-2d) ions in solid para-H-2 [T. Kumada , Phys. Chem. Chem. Phys. 7, 776 (2005)], we newly observed totally more than 50 resolved lines in gamma-ray irradiated solid para-H-2-ortho-D-2 (1 mol %) and para-H-2-HD (1 mol %) mixtures. We assigned these lines to be isotope substituents of H-2(+)-core H-6(+) ions such as H5D+, H4D2+, and H2D4+ throughout the comparison of their ESR parameters with theoretical results. These results provide a conclusive evidence that H-2(+)-core H-6(+) ions are generated in irradiated solid hydrogens. Analysis of the EPR spectrum and ab initio calculations predicts D-2d symmetry of the H-6(+) ions, whereas a lowering symmetry (D-2d -> C-2v) induced by asymmetric nuclear wave function is observed in H5D+ and H4D2+. We also observed isotope-substitution reactions such as H-6(+)+D-2 -> H4D2++H-2 and H-6(+)+HD -> H5D++H-2, which are analogous to the well-known isotope-condensation reactions of H-3(+) in dark nebula, H-3(+)+HD -> HD2++H-2 and HD2++HD -> D-3(+)+H-2.

DOI： 10.1063/1.2748046

固体パラ水素中に生成したH6+のESR分光研究 Reviewed

熊田高之、牛田考洋、清水裕太、熊谷　純

電子スピンサイエンス Vol. 5 page： 134-139 2007

ESR study of H₆⁺ and H₄D₂⁺ produced in irradiated solid hydrogens Reviewed

T. Kumada, T. Takayanagi, J. Kumagai

J. Mol. Struc. Vol. 786 ( 2-3 ) page： 130-133 2006.4

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

We reinvestigated the quartet ESR lines with g-valueg=2.002 and hyperfine coupling constant A approximate to 20 mT produced in gamma-ray irradiated solid pH, in order to determine to which the lines should be assigned, H-2(-) or H-6(+). We newly found further splitting of each of the quartet lines into quintet ones in irradiated solid p-H-2 containing o-D-2 at 1 mol%. ESR parameters of these new lines were found to be consistent with those of H4D2+ calculated. This result supports the assignment to H-6(+) rather than H-2(-).

DOI： 10.1016/j.molstruc.2005.08.036

Is the ESR spectrum attributable to H2- or H2+(H2)2? Precise measurement of the g-value and anisotropic hyperfine structure in gamma-irradiated solid parahydrogen Reviewed

Jun Kumagai, Masatsugu Hanabusa, Hiroki Inagaki and Susumu Kariya

Phys. Chem. Chem. Phys. Vol. 6 ( 17 ) page： 4363-4368 2004.6

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

Four ESR lines, found by Miyazaki et al. in 1995 in irradiated solid parahydrogen (ca. 92% para-purity) at 4.2 K, assigned as "H-2(-),'' were precisely re-measured with highly pure solid parahydrogen (>99.9%) and compared with calculated g-value and hyperfine coupling constants of H-2(+)(H-2)(2). The g-value of I,M-I=0,0 feature, reported previously as 2.0033 or 2.0023, was found to be incorrect and has now been corrected to 2.002120+/-0.000012. This corrected value is clearly smaller than that of free electron. We also found that the remaining three lines corresponding to I, M-I=1,0; 1, +1; and 1, -1 features have axially symmetric hyperfine anisotropic structure i.e., A(parallel to)=20.318 and A(perpendicular to)=20.502 mT. This anisotropy corresponds to the rotation of the species in solid parahydrogen. Although the experimental g-value and isotropic hyperfine coupling constants are in good agreement with those of H-2(+)(H-2)(2) estimated by ab initio calculation, it is still difficult to explain why H-2(+)(H-2)(2) clusters turned into ESR inactive species by addition of 0.1similar to1% D-2 in the present system. In this regard, we still maintain that the species in solid parahydrogen are H-2(-).

DOI： 10.1039/b402756f

Long-lived mutagenic radicals induced in mammalian cells by ionizing radiation are mainly localized to proteins Reviewed

J. Kumagai, K. Masui, Y. Itagaki, M. Shiotani, S. Kodama, M. Watanabe, T. Miyazaki

Radiat. Res. Vol. 160 ( 1 ) page： 95-102 2003.7

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

We have provided evidence that long-lived radicals, produced by ionizing radiation, are highly mutagenic and transforming in mammalian cells. Long-lived radicals are scavenged effectively by vitamin C or by epigallocatechin-3-O-gallate (EGCG). Long-lived radicals are not involved in lethality or in the induction of chromosome aberrations. We now report the results of experiments that define the relative amounts of long-lived radicals in DNA and proteins and identify the major protein radicals as sulfinyl radicals (R-CH2-S-O-.). To make these assignments, yields of long-lived radicals in gamma-irradiated salmon sperm DNA and albumin were compared by ESR. ESR spectra of long-lived radicals produced in irradiated Syrian hamster embryo (SHE) cells were analyzed precisely and compared with ESR parameters obtained by density functional theory calculations. Long-lived radicals yields of 99.8% were produced in proteins. We also identified a new type of long-lived radical as H-added phenylalanine radicals. While our evidence does not rule out the possibility of important biological consequences of the low-level long-lived radicals created by radiation, it implicates radicals in proteins as playing a key role in genetic effects of ionizing radiation. We suggest that these novel radicals, wherever they reside, need to be considered in explanations of biological sequela of radiation.

DOI： 10.1667/RR3015

Active sites and active oxygen species for photocatalytic epoxidation of propene by molecular oxygen over TiO₂-SiO₂ binary oxides Reviewed

C. Murata, H. Yoshida, J. Kumagai, T. Hattori

J. Phys. Chem. B Vol. 107 ( 18 ) page： 4364-4373 2003.5

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

TiO2-SiO2 binary oxides of low Ti content promoted photocatalytic epoxidation of propene by molecular oxygen. By catalytic runs and UV spectra, it was revealed that the isolated tetrahedral Ti species on the TiO2-SiO2 samples are active for the photoepoxidation of propene, while the aggregated titanium oxide species are active mainly for the side reactions. By ESR and stoichiometric reaction tests of radical species, the following mechanism was proposed. Over the isolated tetrahedral Ti species, a [Ti3+-O-L(-)]* radical pair is formed by UV irradiation. The Ti3+ moiety reacts with O-2 to form O-2(-), which could not activate propene by itself. The O-L(-) moiety, a hole center on lattice oxygen, reacts with O-2 to form O-3(-), and the O-3(-) reacts with propene to yield PO. It is first suggested that the O-3(-) is the electrophilic oxygen species effective for the epoxidation of propene. When the O-L(-) moiety reacts with propene, acrolein or ethanal is produced through H abstraction or CC bond fission. The lower selectivity of the aggregated titanium oxide species was attributed to the lower stability of the O-3(-) and high activity for the consecutive reaction of PO.

DOI： 10.1021/jp0277006

Test for antioxidant ability by scavenging long-lived mutagenic radicals in mammalian cells and by blood test with intentional radicals: an application of gallic acid Reviewed

J. Kumagai, T. Kawaura, T. Miyazaki, M. Prost, E. Prost, M. Watanabe, J. Q. Leclercq

Radiat. Phys. Chem. Vol. 66 ( 1 ) page： 17-25 2003.1

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

Antioxidant ability of gallic acid (GA) are determined both by electron spin resonance measurement of long-lived radicals produced in gamma-ray irradiated Syrian golden hamster embryo cells with GA and by hemolysis measurement with GA when blood cells are submitted to radicals. Scavenging properties of GA are determined by the reaction rate constant with long-lived mutagenic radicals in the cells while the blood test allows to analyze the global effects of this compound: radical scavenger + metal ion chelator + regeneration of intra- and extra-cellular antioxidant.

DOI： 10.1016/S0969-806X(02)00288-8

磁気共鳴法を用いた照射生体中の長寿命ラジカルの観測と生物効果との関連性の解明 Invited Reviewed

熊谷　純

放射線化学 Vol. 75 page： 3-11 2003

Long-lived radicals produced by gamma-irradiation or vital activity in plants, animals, cells, and protein solution: their observation and inhomogeneous decay dynamics Reviewed

T. Miyazaki, A. Morikawa, J. Kumagai, M. Ikehata, T. Koana, S. Kikuchi

Radiat. Phys. Chem. Vol. 65 ( 2 ) page： 151-157 2002.9

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

Long-lived radicals produced by gamma-irradiation or vital activity in plants, animals, cells, and protein (albumin) solution were studied by electron spin resonance spectroscopy. Long-lived radicals produced by vital activity exist in biological systems, such as plants, animals, and cells, in the range of 0.1-20 nmol g(-1). Since vital organs keep the radicals at a constant concentration, the radicals are probably related to life conservation. Long-lived radicals are also produced by gamma-irradiation of cells or protein solution. The radicals decay after death of living things or after gamma-irradiation. We found that the decay dynamics in all biological systems can be expressed by the same kinetic equation of an inhomogeneous reaction

DOI： 10.1016/S0969-806X(02)00198-6

Suppression and enhancement of tunneling ion recombination of electron bubbles in solid para-hydrogen-ortho-hydrogen mixtures at 4.2 K: controlling factors of tunneling reaction Reviewed

T. Miyazaki, H. Fukuta, M. Hanabusa, T. Kumada, J. Kumagai

Chem. Phys. Lett. Vol. 360 ( 1-2 ) page： 8-12 2002.7

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

The decay of electron bubbles due to a tunneling ion recombination was studied by ESR in gamma-ray irradiated solid para-hydrogen (p-H-2)-ortho-hydrogen (o-H-2) mixtures at 4.2 K. In the range of 10-75% o-H-2 (region I), the decay rates of the electron bubbles increase with decreasing o-H-2 concentration. The decay rate constant shows the maximum around 10% o-H-2. Then, the decay rates decrease with decreasing o-H-2 concentration below 10% o-H-2 (region II). The results were interpreted by two different rate-determining steps: a tunneling process in region I and an energy-dissipation process in region II. (C) 2002 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0009-2614(02)00823-0

Scavenging of long-lived radicals by (-)-epigallocatechin-3-O-gallate and simultaneous suppression of mutation in irradiated mammalian cells Reviewed

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

Vol. 64 ( 4 ) page： 293-297 2002.7

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

Effect of (-)-epigallocatechin-3-O-gallate (EGCg) on scavenging long-lived radicals and its biological significance were investigated using electron-spin-resonance spectroscopy and mutation assay in cultured human embryo cells. EGCg scavenged long-lived radicals in irradiated golden hamster embryo cells and albumin solution, and simultaneously reduced mutation frequency in the irradiated human embryo cells. These results indicate that long-lived radials are involved in the induction of mutation by radiation.

DOI： 10.1016/S0969-806X(01)00501-1

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

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

Vol. 1236 page： 355-358 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

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

Decay of H₂-anions in solid parahydrogen via two-stage quantum tunneling diffusion processes Reviewed

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

J. Low Temp. Phys. Vol. 114 ( 5-6 ) page： 413-429 1999.5

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

Decay mechanism of H-2(-) anions in X(gamma)-irradiated solid para-H-2 (p-H-2) has been studied using high-resolution ESR spectroscopy in the temperature range between 1.3-6.6 K. The results are summarized as follows. First, the decay rate constant of the H-2(-) anions is not proportional to initial yields of reactive species such as cations and H atoms but proportional to the concentration of less-reactive species of HD molecules in p-H-2. This result shows that the decay of the H-2(-) anion is due to the reaction neither with cations nor H atoms but the HD molecules originally contained in the p-H-2 sample at natural abundance. Second, the decay rate constant of the H-2(-) anions increases proportionally with the increase in temperature below 3 K and decreases with the increase in temperature between 3-5 K, although it increases exponentially with the increase in temperature above 5 K. This result indicates that the decay rate constant of the H-2(-) anions is controlled by the rate constant for the diffusion of the H-2(-) anions via one-phonon assisted quantum tunneling below 3 K, two-photon scattered or assisted quantum tunneling between 3-5 K, and thermally-activated process above 5 K.

DOI： 10.1023/A:1021850103903

突然変異や癌化を引き起こす長寿命ラジカルを電子スピンエコー法から探る Invited Reviewed

熊谷　純

放射線化学 Vol. 67 page： 20-25 1999

An ENDOR spectrum of H atoms in solid H2 Reviewed

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

Chem. Phys. Lett. Vol. 288 ( 5-6 ) page： 755-759 1998.5

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

An ENDOR spectrum of H atoms produced in the gamma-ray irradiated solid H-2 was measured at 4.2 K in order to elucidate the structure of the local environment of the H atoms in solid H-2. We found that the H atoms were not trapped in interstitial sites but in substitutional sites of the solid, and almost all the ortho-H(2 )molecules at the first nearest sites from the H atoms converted into para-H-2 molecules. This result shows that the ortho-para conversion is induced by electron spins of the H atoms

DOI： 10.1016/S0009-2614(98)00296-6

Temperature Effect on Selective Tunneling Abstraction Reaction by H Atoms in Neopentane-Alkane Mixtures 4-100K Reviewed

J. Kumagai, T. Kumada, N. KItagawa, N. Morishita, T. MIyazaki

J. Phys. Chem. A Vol. 102 ( 17 ) page： 2842-2846 1998.4

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

When H atoms are produced by the photolysis of HI or the radiolysis of neo-C5H12 in the neo-C5H12-i-C4H10(2 mol %) mixtures above 40 K, the H atoms react selectively with the solute i-C4H10. The selective reaction is suppressed below 30 K. The reactions have been studied by electron spin resonance and electron spin echo measurements at 4-100 K. The drastic temperature effect on the reaction by H atoms suggests that the H atoms concerned are not hot atoms, but thermal atoms. The thermal H atoms react with the solute alkane by quantum tunneling at low temperature. Temperature effects on the ESR spectra and the spin-lattice relaxation times of the solvent neo-C5H11 radicals and the solute t-C4H9 radicals indicate that local motions of the solute i-C4H10 molecules take place above 40 K, while motions of the solvent neo-C5H12 molecules are severely restricted even at 100 K. It is concluded that the local motions of the solute i-C4H10 assist the tunneling abstraction reaction by H atoms, resulting in the selective reaction with the solute above 40 K.

DOI： 10.1021/jp9801020

Structure of Conduction Electrons on Polysilanes As Studied by Electron Spin-Echo Envelope Modulation Analysis Reviewed

T. Ichikawa, H. Koizumi, J. Kumagai

J. Phys. Chem. B Vol. 101 ( 50 ) page： 10698-10703 1997.12

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

The orbital structures of conduction electrons on permethylated oligosilane, Si-8(CH3)(18), and poly(cyclohexylmethylsilane) have been determined by analyzing the electron spin-echo envelope modulation signals of the radical anions of these silanes in a deuterated rigid matrix at 77 K. The conduction electron on permethylated oligosilane is delocalized over the entire main chain, whereas that on poly(cyclohexylmethylsilane) is localized on a part of the main chain composed of about six Si atoms, Quantum-chemical calculations suggest that Anderson localization due to fluctuation of sigma conjugation by conformational disorder of the main chain is responsible for the localization of both the conduction electron and the hole.

DOI： 10.1021/jp972068f

Stabilization of Hydrogen Radical Anions in Solid Hydrogen Reviewed

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

J. Phys. Chem. A Vol. 101 ( 40 ) page： 7315-7317 1997.10

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

The electron spin resonance g-factor of H-2(-) in gamma-irradiated crystalline H-2 was found to be not 2.003 but 2.0023, A novel model has been proposed for explaining the formation and stabilization of Hz-in crystalline H-2. The model assumes H-2(-) to be located at the center of a cavity that has previously been occupied by a trapped electron. The excess electron of H-2(-) is forced to be attached on one H-2 in the cavity due to strong repulsive interactions between the excess electron and H-2 molecules surrounding the cavity. A quantum mechanical calculation shows that an electron trapped in the vacancy of crystalline Hz automatically converts to H-2(-) by drawing one of the surrounding H-2 molecules into the center of the vacancy.

DOI： 10.1021/jp971923s

Direct observation of radical formation by charge recombination

T. Ichikawa, K. Kagei, J. Kumagai, H. Koizumi, H. Yoshida, J. Kubo

Radiat. Phys. Chem. Vol. 49 ( 4 ) page： 433-436 1997.4

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

Formation of the 2,3,4-trihydronaphtyl radical from the radical cation of tetralin by charge recombination has been studied by electronic absorption spectroscopy. Illumination of the gamma-irradiated glassy alkane solution of tetralin with visible light at 77 K causes electron ejection from the radical anion of tetralin, and the ejected electron recombines with the radical cation to generate the excited tetralin, which then converts to the neutral 2,3,4-trihydronaphtyl radical. The quantum yield of the formation of the neutral radical is approximately the same as that for UV-excited tetralin, which suggests that highly excited states of tetralin are not important for the formation of the neutral radical. The highly excited tetralin molecules generated by charge recombination relax to the first excited state without any chemical reaction, and the scission of a C-H bond takes place under the first excited state.

DOI： 10.1016/S0969-806X(96)00164-8

Electronic Structure of Charge Carriers in a Polysilane Quantum Wire Reviewed

J. Kumagai, H. Yoshida, T. Ichikawa

Nucleonica Vol. 42 page： 465 1997

Interchain Migration of Electrons and Holes in Polysilanes Reviewed

J. Kumagai, H. Tachikawa, H. Yoshida, T. Ichikawa

J. Phys. Chem. Vol. 100 ( 42 ) page： 16777-16778 1996.10

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

The measurements of the ESR and optical absorption spectra of polysilane radical ions revealed that the hole in the radical cation is delocalized onto the side chains, whereas the excess electron in the radical anion is confined within the silicon main chain. This observation suggests that the side chains hinder the interchain hopping of the charge for the anion but not the cation. Therefore the hole is the primary charge carrier in polysilanes.

DOI： 10.1021/jp961004m

Radical ions of oligosilane and polysilane Reviewed

J. Kumagai, T. Ichikawa, H. Yoshida

Radiat. Phys. Chem. Vol. 47 ( 3 ) page： 497-499 1996.5

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

In order to elucidate electronic properties of polysilane Si-Si skeleton, the radical ions generated by gamma-irradiation of polycyclohexylmethylsilane and polymethylphenylsilane were studied by ESR and optical absorption methods. The ion radicals of permethyloligosilanes (Si-4 similar to Si-8) have also been studied for comparison. The observed results suggest that the unpaired electron is localized on a limited region of Si-Si skeleton in the polymers and it is delocalized on the whole Si-Si skeleton of the oligomers.

DOI： 10.1016/0969-806X(95)00147-P

Effect of ionizing radiation on polysilane Reviewed

J. Kumagai, K. Oyama, H. Yoshida, T. Ichikawa

Radiat. Phys. Chem. Vol. 47 ( 4 ) page： 631-636 1996.4

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

ESR and gel permeation chromatographic measurements of poly(diethylsilane) and poly(cyclohexylmethylsilane) gamma-irradiated at temperatures between 77 K and 300 K were carried out to elucidate the mechanism of radiation-induced degradation of polysilanes. Radical species observed after the irradiation are not silyl-type radicals generated by the cleavage of the Si-Si bond but alkyl radicals generated by the scission of the C-H bond. The G value of the main-chain scission depends strongly on the irradiation temperature and dose. It is proposed that sigma-conjugation along the main chain allows the migration of the radiation energy to the weakest bond in the main chain where the direct scission of the bond is induced.

DOI： 10.1016/0969-806X(95)00066-7

Formation and isomerization mechanisms of M⁺CO₂^-(M=Li, Na)ion-pair complexes. An Abinitio MO and RPKM study Reviewed

H. Tachikawa, Y. Takatori, A. Ohtake, J. Kumagai, H. Yoshida

Theochem. Vol. 342 page： 1-7 1995.10

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

Structures and electronic states of the M(+)CO(2)(-) (M = Li and Na) ion-pairs have been investigated by means of ab initio MO calculations. The potential energy surfaces (PESs) for the ion-pair formation reaction (M + CO2 --> M(+)CO(2)(-)) show that the ground state MCO(2) complex has a van der Waals (vdW) character (M . CO2) at the entrance region in the reaction and an ionic one (M(+)CO(2)(-)) at short M-C distances and that the activation barrier is found at the intermediate region between the vdW and ion-pair states. The wavefunctions of the ion-pair for the low-lying excited states are obtained by the multireference single and double excitation configuration interaction (MR-SD-CI) method. The first and second electronic excitations are characterized by charge-transfer transition from CO2- to Na+ and local excitation within the CO2- moiety in M(+)CO(2)(-) respectively. In order to elucidate the isomerization mechanism of the Li+CO2- ion-pair from C-s to C-2v structures, which was observed by Kafafi et al. (J. Am. Chem. Sec., 105 (1983) 3886), the Rice-Ramsperger-Kassel and Marcus (RRKM) theory is applied to calculate the microcanonical reaction rate along the reaction coordinate. The calculations strongly support their experimental results in which the reaction Li+CO2-(C-s) --> Li+CO2- (C-2v) occurs preferentially on IR irradiation.

Electronic Structure of Oligosilane and Polysilane Radical Cations as Studied by Electron Spin Resonance and Electronic Absorption Spectroscopy Reviewed

J. Kumagai, H. Yoshida, T. Ichikawa

J. Phys. Chem. Vol. 99 ( 20 ) page： 7965-7969 1995.5

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

The electron spin resonance (ESR) and the electronic absorption spectra of oligosilane (Si(n)R(n+1)R(n+1)', n = 2 similar to 6) radical cations in a cryogenic solid of a Freon mixture have been compared with those of poly(cyclohexylmethylsilane) and poly(methylphenylsilane) radical cations for elucidating the structure of the SOMO orbital of the radical cations or the HOMO orbitals of the neutral polysilanes, The absorption and ESR spectra of the polymer radical cations are similar to each other and also similar to those of the oligosilane radical cations, which suggests that the unpaired electron of the polymer radical cations is not delocalized all over the Si-Si main chain. The absorption spectra of the polysilane radical cations are composed of a UV and near IR bands which correspond to SOMO --> LUMO and SOMO - 1 --> SOMO, respectively. The oligosilane and the polysilane radical cations show broad isotropic ESR spectra due to hyperfine interactions with side-chain protons. Analysis of the ESR spectra shows that the unpaired electron of the polysilane radical cation is confined to only a part of the polymer chain composed of six Si atoms.

DOI： 10.1021/j100020a019

Electronec Structure of Oligosilane and Polysilane Radical Anions As Studied by Electron Spin Resonance and Electronic Absorption Spectroscopy Reviewed

J. Kumagai, H. Yoshida, H. Koizumi, T. Ichikawa

J. Phys. Chem. Vol. 98 ( 50 ) page： 13117-13122 1994.12

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

The electron spin resonance (ESR) and the electronic absorption spectra of poly(cyclohexylmethylsilane) and poly(methylphenylsilane) radical anions in a cryogenic 2-methyltetrahydrofuran solid have been compared with those of permethyloligosilanes [Si-n(CH3)(2n+2), n = 4-6] for elucidating the electronic structure of polysilane radical anions. The spectra of the polysilane radical anions are very similar to each other and also to those of the oligosilane radical anions in which an unpaired electron occupies not an antibonding sigma(not asymptotic to)(sp) orbital but a pseudo-pi(p) orbital composed of antibonding Si-Si and antibonding Si-C orbitals. The polysilane radical anions show axially symmetric ESR spectra with g(perpendicular to) = 2.0023 and g(parallel to) = 2.0064 and the electronic absorption spectra composed of UV and near-IR bands. Analysis of the ESR and the absorption spectra shows that the unpaired electron of the polysilane radical anions is not delocalized all over the polymer chain but is confined in only a part of the polymer chain, probably around the elongated Si-Si bond of a branched polymer chain.

DOI： 10.1021/j100101a005

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