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31.
Kazuhiro Haraguchi Kiju Konno Kaori Yamada Yasuyuki Kitagawa Kazuo T. Nakamura Hiromichi Tanaka 《Tetrahedron》2010,66(25):4587-8669
Stereoselectivity in N-iodosuccimide (NIS)-mediated electrophilic glycosidation was examined by employing 2,4-bis-O-(trimethylsilyl)thymine and three different silyl-protected erythro-furanoid glycals 12, 16, and 18. As a result, it was found that 3,5-O-(di-t-butylsilylene)-protected 18 gave only the β-anomer (21). The remarkable stereoselectivity observed by employing 18 is discussed on the basis of its X-ray crystallographic analysis. 1-Substituted glycals gave the corresponding β-anomer, again exclusively, to provide access to 1′-branched 2′-deoxynucleosides. 相似文献
32.
Hiromichi Fujioka 《Tetrahedron letters》2010,51(15):1945-2017
The first asymmetric total syntheses of the (+)- and (−)-cryptocaryones are described. Removal of the acetal unit of the enone acetal 5, which was obtained in our previous study from the cyclohexadiene acetal 3, afforded the enone acetal 8 in a one-pot procedure. The acylation of 8 with cinnamoyl chloride and subsequent hydrolysis of the resulting acetal gave the lactol 11. Its oxidation with NIS and tetra-n-butylammonium iodide (TBAI) finally furnished the natural (+)-cryptocaryone 2. The same procedure from ent-3 afforded the unnatural one 1. 相似文献
33.
Weber F Rosenkranz S Castellan JP Osborn R Hott R Heid R Bohnen KP Egami T Said AH Reznik D 《Physical review letters》2011,107(10):107403
We report inelastic x-ray scattering measurements of the temperature dependence of phonon dispersion in the prototypical charge-density-wave (CDW) compound 2H-NbSe2. Surprisingly, acoustic phonons soften to zero frequency and become overdamped over an extended region around the CDW wave vector. This extended phonon collapse is dramatically different from the sharp cusp in the phonon dispersion expected from Fermi surface nesting. Instead, our experiments, combined with ab initio calculations, show that it is the wave vector dependence of the electron-phonon coupling that drives the CDW formation in 2H-NbSe2 and determines its periodicity. This mechanism explains the so far enigmatic behavior of CDW in 2H-NbSe2 and may provide a new approach to other strongly correlated systems where electron-phonon coupling is important. 相似文献
34.
The European Physical Journal E - 相似文献
35.
In the present work, a review of the metallic (M) and semiconducting (S) separation of single‐wall carbon nanotubes (SWCNTs) using polysaccharide gels is presented. First, the progress of the M/S separation is described, including the following: the discovery of high‐yield separation using agarose gel electrophoresis, the separation of SWCNTs without an electric field, such as through the use of the freeze and squeeze method, the development of continuous separation using column chromatography, and the single‐chirality separation of SWCNTs using a multicolumn with dextran‐based gel. Next, the separation mechanism using gel is discussed, in which separation is achieved by selective adsorption of S‐SWCNTs by gel with a specific combination of surfactant and gel. Lastly, future directions for the separation of SWCNTs and for the use of the separated SWCNTs are discussed.
36.
Aragonite twinning in gastropod nacre 总被引:1,自引:0,他引:1
Hiroki Mukai Kazuko Saruwatari Hiromichi Nagasawa Toshihiro Kogure 《Journal of Crystal Growth》2010,312(20):3014-3019
Aragonite twinning in gastropod nacre has been investigated using scanning electron microscopy (SEM), electron back-scattered diffraction (EBSD), and transmission electron microscopy (TEM) with the focused ion beam (FIB) sample preparation technique. At the growth front of nacre, Haliotis discus hannai and Omphalius rusticus form a “stack-of-coins” structures, which consist of pseudo-hexagonal and elliptical aragonite tablets, respectively. SEM, EBSD, and TEM analyses revealed that these tablets are monolithic single crystal and almost free of the {1 1 0} twins that are common in aragonite of biotic or abiotic origin. The longest diagonal of the hexagon and the longer axis of the ellipse are parallel to the a-axis of aragonite. The crystal orientation of each tablet in a stack, measured by TEM-Kikuchi pattern analysis, is almost the same but there is occasionally {1 1 0} twin-like relationship between adjacent tablets along the stacking. On the other hand, the fibrous aragonite layer formed prior to the nacreous structure is composed of polycrystalline aragonite with high density of {1 1 0} twins. TEM observation suggests that the interlamellar organic sheet prevents the inheritance of the twins, by selecting only single domain of the twins, through the mineral bridge. 相似文献
37.
Hiromichi Aono Hiroki Ebara Ryota Senba Takashi Naohara Tsunehiro Maehara Hideyuki Hirazawa Yuji Watanabe 《Journal of magnetism and magnetic materials》2012
Nano-sized magnetic Y3Fe5O12 ferrite having a high heat generation ability in an AC magnetic field was prepared by bead milling. A commercial powder sample (non-milled sample) of ca. 2.9 μm in particle size did not show any temperature enhancement in the AC magnetic field. The heat generation ability in the AC magnetic field improved with a decrease in the average crystallite size for the bead-milled Y3Fe5O12 ferrites. The highest heat ability in the AC magnetic field was for the fine Y3Fe5O12 powder with a 15-nm crystallite size (the samples were milled for 4 h using 0.1 mm? beads). The heat generation ability of the excessively milled Y3Fe5O12 samples decreased. The main reason for the high heat generation property of the milled samples was ascribed to an increase in the Néel relaxation of the superparamagnetic material. The heat generation ability was not influenced by the concentration of the ferrite powder. For the samples milled for 4 h using 0.1 mm? beads, the heat generation ability (W g−1) was estimated using a 3.58×10−4 fH2 frequency (f/kHz) and the magnetic field (H/kA m−1), which is the highest reported value of superparamagnetic materials. 相似文献
38.
A facile preparation of 3-acyl-substituted isoxazolines, benzisoxazoles, and isoxazoles from the corresponding 3-carboxylate esters is described. The process, involving reaction of the ester derivative of 3-carboxylic acid substituted heterocycles with Grignard or alkynyl lithium reagents, leads to direct generation of the corresponding 3-acyl heterocycle. The presence of α-imino ester moieties in the heterocyclic substrates for the reactions is thought to be a key feature governing the nature of these transformations. The synthetic utility of the new methodology is demonstrated by its application in a two-step route for the preparation of novel linked bis-heterocycles. 相似文献
39.
40.
Palladium nanoparticles stabilized by a polyion complex composed of poly{4-chloromethylstyrene-co-(4-vinylbenzyl) tributylammonium chloride} and poly(acrylic acid) were easily recovered by filtration after pH treatment. The polyion complex stabilized palladium nanoparticles have high catalytic activity for the Suzuki and Heck reactions in water. 相似文献