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排序方式: 共有1194条查询结果,搜索用时 31 毫秒
941.
Tsue H Ishibashi K Tokita S Takahashi H Matsui K Tamura R 《Chemistry (Weinheim an der Bergstrasse, Germany)》2008,14(20):6125-6134
To investigate dynamic solid-state complexation hitherto unexplored in nitrogen-bridged calixarene analogues, azacalix[6]arene hexamethyl ether has been prepared in three steps by applying a 5+1 fragment-coupling approach by using a Buchwald- Hartwig aryl amination reaction with the aid of our previously devised temporal N-silylation protocol. X-ray crystallographic analysis and NMR spectroscopic measurements have revealed that the azacalix[6]arene is well endowed with hydrogen-bonding ability, by which both the molecular and crystal structures are controlled. The azacalix[6]arene is conformationally flexible in solution on the NMR time scale, whereas it adopts a definite 1,2,3-alternate conformation with S2 symmetry in the solid state as a result of intramolecular bifurcated hydrogen-bonding interactions. In the crystal, molecules of the azacalix[6]arene are mutually interacted by intermolecular hydrogen bonds to establish one-dimensional hexane-filled nanochannel crystal architecture. Although the single crystal was broken after desolvation, the resultant polycrystalline powder material was capable of selectively adsorbing CO2 among the four main gaseous components of the atmosphere. In contrast, carbocyclic p-tert-butylcalix[6]arene hexamethyl ether, the crystal structure of which was also elucidated for the first time in the present study, gave rise to almost no uptake of CO2. Additional solid-gas adsorption experiments for another three gases, such as N2, O2, and Ar, suggested that quadrupole/induced-dipole interactions and/or hydrogen-bonding interactions played an important role in permitting the observed selective uptake of CO2 by this new azacalix[6]arene in the solid state. 相似文献
942.
We present extensive calculations of nonadiabatic couplings (NACs) between the electronically ground and excited states of molecules, using time-dependent density functional theory (TDDFT) within (modified) linear response [C. Hu et al. J. Chem. Phys. 127, 064103 (2007)]. Our approach is implemented in the pseudopotential framework, with the consideration of nonlinear core corrections. The features of either the ordinary Jahn-Teller conical intersections in X(3) (X=Li, Na, K, Cu, Ag, Au) trimers, or the elliptic Jahn-Teller conical intersections in NaH(2), have been well reproduced. In particular, anticipated results for the H-H(2) collision near the avoided crossing are obtained, showing appealing improvement over the first, real-time, TDDFT calculation. The other important type of intersections, Renner-Teller glancing intersection, has also been studied for several typical molecular systems (BH(2), AlH(2), CH(2)(+), SiH(2)(+)), giving results in reasonable agreement with the theoretical model. Despite these successes, it is found that for some systems, including both Jahn-Teller and Renner-Teller systems, the pseudopotential scheme might give inaccurate results for some NAC components on nonhydrogen atoms. By trying different construction schemes of pseudopotentials, e.g., using local pseudopotentials, the results of NACs are found scheme-dependent and show improvement for some cases. Since there is much freedom in constructing ab initio nonlocal pseudopotentials, our findings on TDDFT calculation of NACs in the pseudopotential scheme might be helpful to give clues for constructing more "realistic" pseudopotentials. 相似文献
943.
Y. Noda S. Shimono M. Baba J. Yamauchi Y. Uchida N. Ikuma R. Tamura 《Applied magnetic resonance》2008,33(3):251-267
By electron paramagnetic resonance spectroscopy we investigated the molecular orientation in a surface-stabilized liquid crystal
(LC) cell, which includes a racemic (±) or an enantiomerically enriched (S,S) paramagnetic LC, (2S,5S)-2,5-dimethyl-2-tridecyloxyphenyl-5-[4-(4-tridecyloxy-benzenecarbonyloxy)phenyl]pyrrolidine-1-oxy (2), whose spin source is fixed inside the rigid core. For both the smectic C (SmC) phase of (±)-2 and the chiral smectic C (SmC*) phase of (S,S)-2 in a surface-stabilized LC cell (antiparallel configuration, thickness of 4 μm), the profile of the observed g-value as a function of the angle between the applied magnetic field and the cell plane could be explained by the orientation
model, where, with some disordering, the molecules align uniformly with the direction which tilts from the normal line of
the smectic layer being orthogonal to the rubbing direction on the cell surface. We divided the effect from the disordering
into two parts, one of which is concerning the direction of the molecular long axis and the other is concerning the rotation
around the molecular long axis. As a result of the analysis, the SmC* phase gave quite lower ordering concerning the direction of the molecular long axis and a little lower ordering concerning
the rotation around the molecular long axis than the SmC phase at the same temperature (80 °C). The obtained lower ordering
in the SmC* phase is probably due to the chirality that would result in the formation of a helical superstructure in a bulky state.
Authors' address: Yohei Noda, Laboratory of Electron Spin Chemistry, Department of Chemistry, Graduate School of Science,
Kyoto University, 606-8502 Kyoto, Japan 相似文献
944.
Chandrasekar Balachandran Kenta Yokoi Kana Naito Jebiti Haribabu Yuichi Tamura Masakazu Umezawa Koji Tsuchiya Toshitada Yoshihara Seiji Tobita Shin Aoki 《Molecules (Basel, Switzerland)》2021,26(22)
In our previous paper, we reported that amphiphilic Ir complex–peptide hybrids (IPHs) containing basic peptides such as KK(K)GG (K: lysine, G: glycine) (e.g., ASb-2) exhibited potent anticancer activity against Jurkat cells, with the dead cells showing a strong green emission. Our initial mechanistic studies of this cell death suggest that IPHs would bind to the calcium (Ca2+)–calmodulin (CaM) complex and induce an overload of intracellular Ca2+, resulting in the induction of non-apoptotic programmed cell death. In this work, we conduct a detailed mechanistic study of cell death induced by ASb-2, a typical example of IPHs, and describe how ASb-2 induces paraptotic programmed cell death in a manner similar to that of celastrol, a naturally occurring triterpenoid that is known to function as a paraptosis inducer in cancer cells. It is suggested that ASb-2 (50 µM) induces ER stress and decreases the mitochondrial membrane potential (ΔΨm), thus triggering intracellular signaling pathways and resulting in cytoplasmic vacuolization in Jurkat cells (which is a typical phenomenon of paraptosis), while the change in ΔΨm values is negligibly induced by celastrol and curcumin. Other experimental data imply that both ASb-2 and celastrol induce paraptotic cell death in Jurkat cells, but this induction occurs via different signaling pathways. 相似文献
945.
Shinji Tanaka Yumiko Nakajima Atsuko Ogawa Takashi Kuragano Yoshihiro Kon Masanori Tamura Kazuhiko Sato Christophe Copret 《Chemical science》2022,13(16):4490
Polymer-supported catalysts have been of great interest in organic syntheses, but have suffered from the difficulty in obtaining direct structural information regarding the catalyst species embedded in the polymer due to the limitations of most analytical methods. Here, we show that dynamic nuclear polarization (DNP)-enhanced solid-state NMR is ideally positioned to characterize the ubiquitous cross-linked polystyrene (PS)-supported catalysts, thus enabling molecular-level understanding and rational development. Ammonium-based catalysts, which show excellent catalytic activity and reusability for the transesterification of methyl esters with glycidol, giving glycidyl esters in high yields, were successfully characterized by DNP 15N NMR spectroscopy at 15N natural abundance. DNP 15N NMR shows in particular that the decomposition of quaternary alkylammonium moieties to tertiary amines was completely suppressed during the catalytic reaction. Furthermore, the dilute ring-opened product derived from glycidol and NO3− was directly characterized by DNP 15N CPMAS and 1H–15N and 1H–13C HETCOR NMR using a 15N enriched (NO3) sample, supporting the view that the transesterification mechanism involves an alkoxide anion derived from an epoxide and NO3−. In addition, the detailed analysis of a used catalyst indicated that the adsorption of products on the cationic center is the major deactivation step in this catalysis.We demonstrated that DNP-enhanced NMR spectroscopy enables the direct and detailed characterization of polymer-supported alkylammonium catalysts. 相似文献
946.
HAN Yun-Cheng Nobuyuki Chiga Yu Fujii Kenta Putatsukawa Osamu Hashimoto Kentaro Hirose Takatsugu Ishikawa Hiroki Kanda Masashi Kaneta Daisuke Kawama Yue Ma Kazushige Maeda Tomofumi Maruta Nayuta Maruyama Akihiko Matsumura Youhei Miyagi Koji Miwa Satoshi N. Nakamura Hajime Shimizu Koutarou Shirotori Koutaku Suzuki Tadaaki Tamae Hirokazu Tamura Kyo Tsukada WANG Tie-Shan Hirohito Yamazaki 《中国物理C(英文版)》2010,34(1)
The energy of tagged photons, which were provided from the internal photon tagging system of the Laboratory of Nuclear Science, Tohoku University, has been calibrated using the d(γ,π-pp) reaction. Charged pions and protons in the final state were detected with the Neutral Kaon Spectrometer (NKS2). Photon energies were obtained from the reaction of d(γ,π-pp). The derived photon energy was consistent with the design of the tagger system and the previous measurement using electron-positron pair production. The consistency demonstrates the performance of NKS2 and the capability of the photon energy calibration using d(γ,π-pp). 相似文献
947.
T. Kaneko K. Tamura S. Kimura H. Kudo 《Journal of Radioanalytical and Nuclear Chemistry》1999,240(1):53-57
The complex formation of LaCl3 with dipivaloylmethane (dpm) was investigated in a view of the applicability to a rapid chemistry. It was found that the
complex formation of lanthanum chloride with dpm in a gas phase was recognized and a volatile LaCl2 (dpm) which was formed by substitution of a chloride atom in LaCl3 by dpm molecule was mainly produced. A temperature dependence of LaCl2 (dpm) formation was examined and the activation energy of the reaction was deduced. 相似文献
948.
T. Asano M. Tamura S. Yoshizawa K. Tomoda S. Noda 《Physica E: Low-dimensional Systems and Nanostructures》2000,7(3-4)
An all-optical modulation of interband-resonant light (near-infrared signal light: 800 nm) by intersubband-resonant light (mid-infrared control light: 4–7 μm) in n-doped AlGaAs/GaAs multiple quantum wells is investigated by two-color femtosecond pump–probe experiments at room temperature. The modulation of the near-infrared signal light with an ultrafast recovery as short as 1 ps is successfully observed when the quantum wells are pumped by the mid-infrared control light pulse (4 fJ/μm2). The dependence of the modulation depth on the wavelength of the control light is also measured, which is shown to be consistent with the intersubband absorption spectrum of the quantum wells. The results indicate that the utilization of the intersubband transition is promising for the ultrafast all-optical modulation and switching. 相似文献
949.
This paper deals with the mass operator representing multiple-scattering effects in the theory of wave scattering from a slightly random surface. By means of the stochastic-functional approach, a recurrence equation for the mass operator is obtained in the form of an iterative integral. However, its solution oscillates in a non-physical manner against the number of iterations. Next, the recurrence equation may be regarded as a nonlinear integral equation, when the number of iterations goes to infinity. An analytical solution of the nonlinear integral equation is presented for a special case in which the roughness spectrum is the Dirac delta function. Then, the nonlinear integral equation is solved numerically for the Gaussian roughness spectrum by iteration, starting from such an analytical solution. It is shown that only a few iterations are required to obtain the mass operator, even when the correlation distance is small. Effects of the mass operators on the coherent reflection coefficient and the incoherent scattering cross section are calculated and shown in figures. 相似文献
950.