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51.
Kazuki OsakamaMasaharu Sugiura Makoto Nakajima Shunsuke Kotani 《Tetrahedron letters》2012,53(32):4199-4201
An efficient method was developed for the enantioselective reductive aldol reaction of α,β-unsaturated ketones with aldehydes in the presence of a Lewis base catalyst; conjugate reduction using a tertiary amine and trichlorosilyl triflate, followed by an aldol reaction with BINAP dioxide (BINAPO) as an organocatalyst, gave the corresponding product in high yield with high stereoselectivity. 相似文献
52.
53.
Characterization of polysaccharides having activity on the reticuloendothelial system from the rhizome of Curcuma longa 总被引:2,自引:0,他引:2
Three polysaccharides, named ukonan A, ukonan B and ukonan C, were isolated from the rhizomes of Curcuma longa L. They were homogeneous on electrophoresis and gel chromatography, and showed remarkable reticuloendothelial system-potentiating activity in a carbon clearance test. They are composed of L-arabinose: D-xylose: D-galactose: D-glucose: L-rhamnose: D-galacturonic acid in the molar ratios of 12:4:12:1:4:10 (ukonan A), 12:4:12:1:2:4 (ukonan B) and 8:3:6:14:2:3 (ukonan C), in addition to small amounts of peptide moiety. Methylation analysis, carbon-13 nuclear magnetic resonance and periodate oxidation studies indicated the structural features of ukonan B, the major one in terms of the activity. It has acidic arabino-galactan type structural units. 相似文献
54.
We have analyzed the transfer efficiency of ballistic electron emission microscopy (BEEM), taking the finite spot size of the emitted electron beam from scanning probes into account. Three-dimensional diffraction from an aperture at a surface-metal/air interface is introduced to model an effect caused by the finiteness of spot size. As a general trend, the diffraction decreases BEEM transfer efficiency. The diffraction effect increases as the spot size decreases and the air-gap distance increases. In a Au/GaAs sample, BEEM transfer efficiency markedly deteriorates down to 6% of the value derived from a conventional planar tunneling theory when a spot size of 0.2 nm, an air-gap distance of 0.6 nm, and an electron energy of 0.2 eV, measured from the bottom of the GaAs conduction band, are assumed. BEEM transfer efficiency is markedly dependent on the spot size of the emitted hot electron. This result indicates that the BEEM current depends on the spatial resolution of the scanning probe, that is, the condition of the tip apex. 相似文献
55.
56.
N Shimizu M Tomoda R Gonda M Kanari A Kubota A Kubota 《Chemical & pharmaceutical bulletin》1989,37(11):3054-3057
An acidic polysaccharide, named saposhnikovan C, was isolated from the roots and rhizomes of Saposhnikovia divaricata Schischk. It was homogeneous as judged by electrophoresis and gel chromatography, and showed remarkable reticuloendothelial system-potentiating activity in a carbon clearance test. It is composed of D-galacturonic acid:L-rhamnose:L-arabinose:D-galactose in a molar ratio of 27:7:8:8, and its molecular mass was estimated to be 132000. About 30% of the D-galacturonic acid residues exist as the methyl esters. O-Acetyl groups were identified, and the content amounted to 3.3%. Methylation analysis, carbon-13 nuclear magnetic resonance, and controlled Smith degradation studies indicated the structural features. It has a pectin-like rhamnogalacturonan backbone with branched arabinan and galactan side chains. 相似文献
57.
Komal Garg Yasuo Matsubara Mehmed Z. Ertem Anna Lewandowska‐Andralojc Shunsuke Sato David J. Szalda James T. Muckerman Etsuko Fujita 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2015,127(47):14334-14338
We prepared two geometric isomers of [Ir(tpy)(ppy)H]+, previously proposed as a key intermediate in the photochemical reduction of CO2 to CO, and characterized their notably different ground‐ and excited‐state interactions with CO2 and their hydricities using experimental and computational methods. Only one isomer, C‐trans‐[Ir(tpy)(ppy)H]+, reacts with CO2 to generate the formato complex in the ground state, consistent with its calculated hydricity. Under photocatalytic conditions in CH3CN/TEOA, a common reactive C‐trans‐[Ir(tpy)(ppy)]0 species, irrespective of the starting isomer or monodentate ligand (such as hydride or Cl), reacts with CO2 and produces CO with the same catalytic efficiency. 相似文献
58.
59.
Masashi NakamuraIsao Takahashi Shunsuke YamadaYasuo Dobashi Osamu Kitagawa 《Tetrahedron letters》2011,52(1):53-55
Intramolecular Diels-Alder reactions of various N-allyl 2-furoyl amides with different substituents on the nitrogen atom were investigated. The reaction of amides having bulky substituents proceeded at a faster rate than the analogs whose substituents were of less bulkiness. From the systematic experimental survey of the substituent effects and the energetic evaluation based on the DFT calculations at the B3LYP/6-31G(d) level, the enhanced reactivity was ascribed to the relief of steric strain upon cyclization rather than the amide rotational isomerism governed by the bulky substituents. 相似文献
60.
Alexei A. Belik Pan?e Naumov Jungeun Kim Shunsuke Tsuda 《Journal of solid state chemistry》2011,184(11):3128-3133
Low-temperature structural properties of the synthetic mineral libethenite Cu2PO4OH were investigated by single-crystal X-ray diffraction, synchrotron X-ray powder diffraction, specific heat measurements, and Raman spectroscopy. A second-order structural phase transition from the Pnnm symmetry (a=8.0553(8) Å, b=8.3750(9) Å, c=5.8818(6) Å at 180 K) to the P21/n symmetry (a=8.0545(8) Å, b=8.3622(9) Å, c=5.8755(6) Å, β=90.0012(15) at 120 K) was found at 160 K during cooling. At 120 K, the monoclinic angle is 90.0012(15) from single crystal X-ray data vs 90.083(1) from powder X-ray diffraction data. The P21/n–to–Pnnm transition may be a general feature of the adamite-type compounds, M2XO4OH. 相似文献