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Enomoto, Akiko,Itoh, Ken,Harada, Takanori,Yamamoto, Masayuki The Korean Society of Toxicology Korea Environment 2001 Toxicological Research Vol.17 No.-
Xenobiotics and their reactive intermediates bind to cellular macromolecules and/or generate oxidative stress. which provoke deleterious effects on the cell function. Induction of xenobiotic-biotrans-forming enzymes and antioxidant molecules is an important defense mechanism against such insults. A group of genes involved in the defense mechanism. e.g. genes encoding glutathione S-transferases. NAD(P)H: quinone oxidoreductase, UDP-glucuronosyltransferase (UDP-GT) and ${\gamma}$-glutamylcysteine synthetase (GGCS). have a common regulatory sequence, Antioxidant or Electrophile Responsive Element (ARE/EpRE). Recently. Nrf2. discovered as a homologue of erythroid transcription factor p45 NF-E2, was shown to bind ARE/EpRE and induce the expression of these defense genes. Mice that lack Nrf2 show low basal levels of expression and/or impaired induction of these genes. which makes the animals highly sensitive to xenobiotic toxicity. Indeed. we show here that nrf2-deficient mice had a higher mortality than did the wild-type mice when exposed to acetaminophen (APAP). Detailed analyses of APAP hepatotoxicity in the nrf2 knockout mice indicate that a large amount of reactive APAP metabolites was generated in the livers due to the impaired basal expression of two detoxifying enzyme genes, UDP-GT (Ugt1a6) and GGCS. while the cytochrome P450 content was unchanged. Thus. the studies using the nrf2 knockout mice clearly demonstrate significance of the expression of Nrf2-regulated enzymes in protection against xenobiotic toxicity.
Magnetic Frustration Effects in the New Colossal Magnetoresistance Oxide NaCr2O4
Hikaru Takeda,Yasuhiro Shimizu,Masayuki Itoh,Hiroya Sakurai,Eiji Takayama-Muromachi 한국물리학회 2013 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.62 No.12
We have investigated the magnetic properties of the new colossal magnetoresistance oxideNaCr2O4 with the calcium-ferrite-type structure by using 23Na, 53Cr nuclear magnetic resonance(NMR) and magnetization measurements. This chromate is found to show an antiferromagneticorder with the spin moments slightly canted from the b axis at temperatures below TN=125 K. The spin structure may be governed by the competition between double-exchange ferromagneticand superexchange antiferromagnetic interactions in the double chains. The origin of the largemagnetoresistance is discussed for several scenarios such as phase separation, rearrangement of thespin structure induced by the magnetic field, and domain walls.
In-plane Anisotropy of the Magnetic and the Electric Properties of the Fe Pnictide Ba(Fe1−xCox)2As2
Yoshiaki Kobayashi,Akihiro Ichikawa,Masayuki Toyoda,Masayuki Itoh,Masatoshi Sato 한국물리학회 2013 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.63 No.3
The anisotropy of the electronic and the magnetic properties within the FeAs planes of Co(2%)-doped BaFe2As2 has been investigated by using 75As nuclear magnetic resonance (NMR) measurementson the As (As0) sites with all four nearest neighbor sites occupied by Fe. Even in thetetragonal phase at temperatures above 100 K, two sets of NMR spectra with twofold symmetry ofin-plane Knight shifts and electronic nuclear quadrupole frequencies are observed. They originatefrom two domains with their symmetry axes lying at right angles to each other. The anisotropies ofthe electronic and the magnetic properties become pronounced at 140 K, below which an in-planeanisotropy is reported to appear in electrical resistivity under a pressure along one of Fe-Fe directions. 75As NMR measurements have also been carried out for the As (As1) sites surrounded byone Co and three Fe. From the data, we conclude that the spin susceptibility of As1 is ~1/3 thatof As0 and that the antiferromagnetic spin fluctuation of As1 is fairly suppressed as compared withthat of As0. We discuss these behaviors of the FeAs layer in connection with the impurity-inducedlocal orbital order model proposed by theoretical studies.
Phase Separation of Antiferromagnetism and Superconductivity in RbxFe2−ySe2 Observed by Using Rb NMR
Yoshiaki Kobayashi,Shunsuke Saiki,Shouhei Kototani,Masayuki Itoh,Masatoshi Sato 한국물리학회 2013 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.63 No.3
We have carried out 87Rb NMR measurements on single crystals with and without the superconducting(SC) transition to clarify whether the SC and the antiferromagnetic (AFM) states aremicroscopically coexistent or just phase-separated in the Rb-intercalated iron-selenide RbxFe2−ySe2. The 87Rb NMR spectra observed at temperature below 300 K for these crystals are clearly separableinto two parts with different structures and widths. The broader spectrum can be explainedby the presence of a region with an AFM spin structure proposed by neutron scattering studies. The narrower spectrum in the crystal with the SC transition can be understood from the temperaturedependences of the spectral frequency-position and shape to stem from the SC region withTc = 30.8 K. Thus, we can clearly conclude that the superconductivity and the antiferromagnetismin the present system are phase-separated. Also, the crystal without the SC transition has twophase-separated regions with respective magnetic transitions at 500 and 50 K.
Magnetism and Superconductivity in RbxFe2−ySe2
Kazuki Ohishi,Masatoshi Sato,Shouhei Kototani,Shunsuke Saiki,Yoshiaki Kobayashi,Masayuki Itoh 한국물리학회 2013 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.62 No.12
We have performed zero-field muon spin relaxation measurements in single-crystalline samplesof superconducting (SC) RbxFe2−ySe2 (Tc = 29 K) and non-SC RbxFe2−ySe2 in order to elucidatewhether there is difference in the magnetic states between SC and non-SC systems. In the SCsample, no temperature dependence of the muon spin polarization was observed at temperaturesbelow 40 K while a decrease in the spin polarization was observed in the non-SC sample withdecreasing temperature. This suggests that a new magnetically ordered state seems to develop inthe non-SC sample.