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551.
Fujiwara N Môri N Uwatoko Y Matsumoto T Motoyama N Uchida S 《Physical review letters》2003,90(13):137001
Pressure-induced superconductivity in a spin-ladder cuprate Sr2Ca12Cu24O41 has not been studied on a microscopic level thus far although the superconductivity was already discovered in 1996. We have improved the high-pressure technique using a large high-quality crystal, and succeeded in studying the superconductivity using 63Cu nuclear magnetic resonance. We found that the anomalous metallic state reflecting the spin-ladder structure is realized and the superconductivity possesses an s-wave-like character in the meaning that a finite gap exists in the quasiparticle excitation: At a pressure of 3.5 GPa, we observed two excitation modes in the normal state from the relaxation rate T-11. One gives rise to an activation-type component in T-11, and the other T-linear component linking directly with the superconductivity. This gapless mode likely arises from free motion of holon-spinon bound states appearing by hole doping, and the pairing of them likely causes the superconductivity. 相似文献
552.
Takehiko Nishio Norikazu Okuda Choji Kashima 《Journal of heterocyclic chemistry》1988,25(5):1437-1438
2-Substituted tetrahydro- and cyclopentathiophenes 2 were produced in high yields by treatment of the semi-cyclic trisubstituted 1,4-diketones 1 such as 2-phenacylcyclohexan-1-one, 2-acetonylcyclohexan-1-one, and 2-phenacylcyclopentan-1-one, with Lawesson's reagent. 相似文献
553.
The locus of the photodimerization reaction of 9-methylanthracene in the crystal was examined by high-resolution solid-state
NMR techniques. Examination of the
spectra of the products showed that only the trans dimer is formed by the solid state photodimerization, while both trans and cis dimers are formed by the photodimerization in benzene solution. The
T1 relaxation curves for the monomer and the dimer at various exposure times were separately observed via well-resolved
peaks. The two T1 curves exhibit characteristic features for relaxation of a weakly coupled two-spin system. By analyzing the T1 curves, the spin diffusion rates between the monomer and the dimer and the fraction of the dimer were obtained for various exposure times. From the result, the maximum domain size of the minor component during the photodimerization process was estimated to be ca. 0.3 μm. The heterogeneous domain structure generated by the photodimerization indicates that the reaction takes place at defects of the crystal in the monomer. 相似文献
554.
555.
The ionic and electronic conduction in α'-NaxV2O5 prepared by the solid state reaction has been investigated. The electronic conductivity is nearly equal to the total conductivity and depends on the V4+ ion concentration. The Na+ ion conductivity was measured by a dc technique. The building up and decaying curves obtained at the transient polarization phenomena were analyzed by using a certain approximation for the steady state in order to save experimental time. The typical ionic conductivities were relatively low, namely 3×10?6 and 2×10?1 S cm?1 at 300°C for the samples of x=1.0 and 0.8, respectively which seemed to be dependent on the number of vacant Na+ ion sites. 相似文献
556.
Tertiary amides, ureas, and amines undergo direct intermolecular addition to aldehydes under the Et3B/air conditions, thereby providing a unique and simple means for the radical sp3 C-H transformation of nitrogen-containing molecules. 相似文献
557.
558.
Nishiyama Y Kaneda M Asaoka S Saito R Mori T Wada T Inoue Y 《The journal of physical chemistry. A》2007,111(51):13432-13440
Enantiodifferentiating anti-Markovnikov photoaddition of alcohol (methanol, ethanol, 2-propanol, and tert-butanol) to aromatic alkene (1,1-diphenylpropene and 1,1-diphenyl-1-butene), sensitized by optically active alkyl and saccharide naphthalene(di)carboxylates, was investigated in supercritical carbon dioxide at varying pressures to elucidate the effects of clustering on photosensitization and enantiodifferentiation behavior, in particular on the product's enantiomeric excess (ee). For all the alkene/alcohol/chiral sensitizer combinations examined, a sudden change in the product's ee was consistently observed near the critical density, which is attributable to the critical pressure dependence of clustering around the intervening exciplex intermediate. 相似文献
559.
Yutaka Takahashi Masamichi Nakakoshi Satoshi Sakurai Yoshitake Akiyama Hiroto Suematsu Hiroaki Utsumi Takehiko Kitamori 《Analytical sciences》2007,23(4):395-400
The development of an NMR interface microchip and its applications to the real-time monitoring of chemical reactions are described. The microchip device was named "MICCS" (MIcro Channeled Cell for Synthesis monitoring), and the method using it was named "MICCS-NMR". MICCS was inserted into a 5 mm Phi NMR sample tube. Thus standard solution NMR probes without any modifications can be used in MICCS-NMR measurements. A gap between MICCS and the sample tube was filled with a deuterated solvent for an NMR lock. The reaction temperature and reaction time in MICCS can be easily changed by adjusting the temperature of the NMR probe and changing the flow rates, respectively. The effectiveness of the MICCS-NMR was verified in the real-time monitoring of the Wittig reaction. Preliminary data on the direct detection of intermediates of the Grignard reaction is also reported. Besides real-time monitoring of chemical reactions, MICCS-NMR would be useful as a qualitative detection method for microchip-based synthesis. 相似文献
560.
A convergent asymmetric total synthesis of (+)-danicalipin A is accomplished, in which two chlorinated fragments are stereoselectively joined by 1,3-dipolar coupling, leading to the confirmation of the absolute configuration of the natural product. 相似文献