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941.
T. Kasai H. Nakajima T. Fujii I. Terasaki T. Watanabe H. Shibata A. Matsuda 《Physica C: Superconductivity and its Applications》2009,469(15-20):1016-1019
We report on the density of states measurements of Bi2212 (Bi2+xSrxCaCu2O8+δ) near the superconductivity-insulator transition using a low temperature scanning tunneling microscope. We prepared highly underdoped Bi rich Bi2212 single crystals (Tc 32 K). The energy gap distribution did not provide an energy scale proportional to Tc. Averaged tunnel spectra with various doping levels were scaled into a single line if energy was normalized by their respective gap values. This indicated there was no crossover energy, which separates a pseudogap and a superconducting gap. 相似文献
942.
The hydrophobic effect in the reaction of a homoallyl alcohol with an aldehyde (Yadav's reaction system) under aqueous conditions in the presence of an acidic surfactant was studied indicating the presence of the alkyl‐substituent effect, although not a dramatic one. The DBSA‐promoted reaction proceeds relatively faster when both the homoallyl alcohol and the aldehyde carry a cycloalkyl group (DBSA=4‐dodecylbenzenesulfonic acid). In contrast, the reaction of the substrates having an unbranched alkyl group is relatively more favorable in SDS/HCl than in DBSA (SDS=sodium dodecyl sulfate). 相似文献
943.
Hidehisa Hagiwara Dr. Takanori Inoue Prof. Dr. Kenji Kaneko Prof. Dr. Tatsumi Ishihara Prof. Dr. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2009,15(46):12862-12870
The mechanism of photocatalytic splitting of H2O into H2 and O2 on Pt/KTa(Zr)O3 modified with various porphyrinoids was investigated. The photocatalytic activity of KTaO3 catalysts is improved by dye modification. Cyanocobalamin (vitamin B12) is the most effective for improving water‐splitting activity, and the formation rates of H2 and O2 achieved values of 575 and 280 μmol gcat.?1 h?1, respectively. X‐ray photoelectron spectroscopy spectra of KTa(Zr)O3 photocatalysts showed that Pt loaded onto dye‐modified KTaO3 was slightly oxidized and had low catalytic activity for the H2 oxidation reaction. Photoluminescence (PL) spectra of KTaO3 catalysts suggested that excitation energy was transferred between KTaO3, tetraphenylporphyrinatochromium(III) (Cr–TPP), and the Pt cocatalyst. The wavelength dependence of the activity of dye‐modified KTa(Zr)O3 photocatalysts indicated that excitation of both KTa(Zr)O3 and the dye was essential for achieving increased photocatalytic activity. This result suggests that two‐step excitation occurred in the dye‐modified KTa(Zr)O3 photocatalysts. Because the lifetime of the charge‐separated state increased, this study reveals that modification with porphyrinoids is effective for increasing water‐splitting activity. 相似文献
944.
In order to obtain detailed insights into the physicochemical mechanism of DNA damage induction, “in situ” measurement of electron paramagnetic resonance (EPR) signal from DNA constituent nucleobases, guanine and adenine, has been performed in a vacuum using monochromatic synchrotron soft X-rays. We found that short-lived unpaired electron species arise only during irradiation to the evaporated thin film on a surface. The EPR spectrum of the short-lived species significantly depends on the photon energy irradiated, and the spin concentration obtained from the EPR spectra shows a similar fine structure to the X-ray photoabsorption spectra (X-ray absorption near edge structure; XANES). For the adenine sample, the spin concentration alters strikingly by water absorption on the sample surface. Trapping of photo- or Auger electrons into a newly generated potential in the nucleobases as the consequence of photoelectric effect is suggested as mechanisms of the induction of the short-lived species. 相似文献
945.
Haiying Fu Yosuke Katsumura Mingzhang Lin Yusa Muroya Kuniki Hata Kentaro Fujii Akinari Yokoya Yoshihiko Hatano 《Radiation Physics and Chemistry》2009,78(12):1192-1197
Two histidine-containing natural dipeptides, carnosine and anserine (β-alanyl-1-methyl-l-histidine), have been examined for their antioxidant and radioprotective abilities. Pulse radiolysis studies indicated the antioxidative properties of carnosine and anserine aqueous solutions at different pH. The rate constants for the reaction OH radical with carnosine at neutral pH were determined to be 5.3×109 M−1 s−1 at 300 nm, and 4.1×109 M−1 s−1 at 400 nm, respectively. Carnosine and anserine also protected plasmid pUC18 DNA from X-ray radiation-induced strand breaks as evidenced from the studies by agarose gel electrophoresis. Carnosine showed higher protective efficiency under the experimental conditions. Our data demonstrated that carnosine and anserine may play an important role in the maintenance of the antioxidant system. 相似文献
946.
To reveal the chemical changes induced in DNA by irradiation with ionizing radiation, we have investigated the spectral change in the X-ray absorption near edge structure (XANES) of DNA resulting from exposure to monochromatic soft X-rays. We used a thin film of calf thymus DNA as a sample and observed nitrogen K-shell and oxygen K-shell XANES spectra. The typical monochromatic soft X-ray energies used for the irradiation (395, 408, 528, and 538 eV) were obtained from a soft X-ray beamline (BL23SU, SPring-8). These energies correspond to those just below or just above the nitrogen and oxygen K-shell ionization energy, respectively. The obtained XANES spectra show significant changes by irradiation. Particularly a new π* resonance peak in oxygen XANES spectra evidently appeared by the irradiation above oxygen K-shell ionization potential. These results suggest that carbonyl groups, presumably a propenal group (OC–CC), may be produced in the sample by oxygen ionization. Thus characteristic damage induced by induction in the DNA molecule would be predicted following exposure to monochromatized synchrotron soft X-rays. 相似文献
947.
Taiga Fujii Hiromu Kashida Dr. Hiroyuki Asanuma Prof. Dr. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2009,15(39):10092-10102
To test the molecular exciton theory for heterodimeric chromophores, various heterodimers and clusters, in which two different dyes were stacked alternately, were prepared by hybridizing two oligodeoxyribonucleotides (ODNs), each of which tethered a different dye on D ‐threoninol at the center of the strand. NMR analyses revealed that two different dyes from each strand were stacked antiparallel to each other in the duplex, and were located adjacent to the 5′‐side of a natural nucleobase. The spectroscopic behavior of these heterodimers was systematically examined as a function of the difference in the wavelength of the dye absorption maxima (Δλmax). We found that the absorption spectrum of the heterodimer was significantly different from that of the simple sum of each monomeric dye in the single strand. When azobenzene and Methyl Red, which have λmax at 336 and 480 nm, respectively, in the single strand (Δλmax=144 nm), were assembled on ODNs, the band derived from azobenzene exhibited a small hyperchromism, whereas the band from Methyl Red showed hypochromism and both bands shifted to a longer wavelength (bathochromism). These hyper‐ and hypochromisms were further enhanced in a heterodimer derived from 4′‐methylthioazobenzene and Methyl Red, which had a much smaller Δλmax (82 nm; λmax=398 and 480 nm in the single‐strand, respectively). With a combination of 4′‐dimethylamino‐2‐nitroazobenzene and Methyl Red, which had an even smaller Δλmax (33 nm), a single sharp absorption band that was apparently different from the sum of the single‐stranded spectra was observed. These changes in the intensity of the absorption band could be explained by the molecular exciton theory, which has been mainly applied to the spectral behavior of H‐ and/or J‐aggregates composed of homo dyes. However, the bathochromic band shifts observed at shorter wavelengths did not agree with the hypsochromism predicted by the theory. Thus, these data experimentally verify the molecular exciton theory of heterodimerization. This coherent coupling among the heterodimers could also partly explain the bathochromicity and hypochromicity that were observed when the dyes were intercalated into the duplex. 相似文献
948.
Yongdong Su Hirofumi Fujii Ekaterina A. Burakova Boris P. Chelobanov Masayuki Fujii Dmitry A. Stetsenko Vyacheslav V. Filichev 《化学:亚洲杂志》2019,14(8):1212-1220
The effect of phosphate group modifications on formation and properties of G‐quadruplexes (G4s) has not been investigated in detail. Here, we evaluated the structural, thermodynamic and kinetic properties of the parallel G‐quadruplexes formed by oligodeoxynucleotides d(G4T), d(TG4T) and d(TG5T), in which all phosphates were replaced with N‐methanesulfonyl (mesyl) phosphoramidate or phosphoryl guanidine groups resulting in either negatively charged or neutral DNA sequences, respectively. We established that all modified sequences were able to form G‐quadruplexes of parallel topology; however, the presence of modifications led to a decrease in thermal stability relative to unmodified G4s. In contrast to negatively charged G4s, assembly of neutral G4 DNA species was faster in the presence of sodium ions than potassium ions, and was independent of the salt concentration used. Formation of mixed G4s composed of both native and neutral G‐rich strands has been detected using native gel electrophoresis, size‐exclusion chromatography and ESI‐MS. In summary, our results indicate that the phosphate modifications studied are compatible with G‐quadruplex formation, which could be used for the design of biologically active compounds. 相似文献
949.
Mikio Fujii Taiki Kuramochi Yuhi Nakakuki Rina Hatazawa Kiju Konno Tatsuo Munakata Yasuaki Hirai 《Tetrahedron letters》2019,60(10):721-725
Gentianine is a metabolite of gentiopicroside and swertiamarin. Several biological activities have been reported for gentianine, such as antiinflammatory and antidiabetic activity, and hypotensive effect. Gentiopicroside is found in 0.9–9.8% content in Gentian root or Gentian scabra root, and Swertiamarin is contained in Swertia herb in 2–10%. These natural products can be potential starting materials for the synthesis of gentianine. This study describes the β-glucosidase-catalyzed hydrolysis of gentiopicroside and swertiamarin in the presence of hydroxylamine to afford gentianine N-oxide, which can be a synthetic precursor of gentianine derivatives. Enzymatic hydrolysis of swertiamarin selectively afforded gentianine N-oxide in 81% yield, whereas gentiopicroside afforded gentianine N-oxide and gentianol N-oxide. Plausible reaction pathways leading to gentianine, gentianol, and their N-oxides were also investigated. 相似文献
950.
Midori Kanda Ko Urushibara Soyoung Park Shinya Fujii Hyuma Masu Kosuke Katagiri Isao Azumaya Hiroyuki Kagechika Aya Tanatani 《Tetrahedron》2019,75(19):2771-2777
N,N′-Bis(ortho-substituted phenyl)squaramides afforded chiral crystals, in which squaramide molecules are arranged in one-handed helical networks, upon simple recrystallization. Three types of crystals with different helices were obtained, depending on the substituents or recrystallization solvent. Folded-type intermolecular hydrogen-bonding interactions of squaramides play a key role in forming the helical networks. 相似文献