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排序方式: 共有649条查询结果,搜索用时 171 毫秒
641.
Shindoh N Kitaura K Takemoto Y Takasu K 《Journal of the American Chemical Society》2011,133(22):8470-8473
The torquoselectivity of the 4π electrocyclic ring-opening reaction of 2-azetines can be controlled by the Br?nsted acidity of the catalyst and the polarity of the solvent. DFT calculations provided insight into the mechanism of this remarkable switch. Anti and syn stereoisomers of α,β-unsaturated amidines were selectively synthesized from ynamides and aldimines in the presence of Tf(2)NH and CSA, respectively. 相似文献
642.
Suzuki T Yamaguchi H Hashimoto A Nozaki K Doi M Inazumi N Ikeda N Kawata S Kojima M Takagi HD 《Inorganic chemistry》2011,50(9):3981-3987
The tetrafluoroborate salt of bis{8-(diphenylphosphino)quinoline}copper(I), [Cu(Ph(2)Pqn)(2)]BF(4), afforded orange prismatic (2O) or yellow columnar (2Y) crystals, dependent on the solvent and concentration of the recrystallization solution used. X-ray analysis revealed that crystals of 2O and 2Y had the same composition and exhibited different crystal systems: 2O was triclinic, with space group P ?1 and Z = 2, and 2Y was monoclinic with space group P2(1)/c and Z = 4. In these crystals, the tetrahedral copper(I) complex exhibited a strong "rocking distortion" toward a trigonal pyramidal coordination geometry (by a slide translation of one of the unsymmetrical bidentate chelating ligands along the tetrahedral edge). In addition, both the 2O and 2Y complexes showed a "flattening distortion", meaning that the dihedral angle between the two chelate planes were off-perpendicular and oriented toward opposite directions, which resulted in a pair of distortion isomers: syn clinal (sc: 2O) and anti clinal (ac: 2Y). (31)P CP-MAS NMR spectroscopy indicated that 2O and 2Y could be distinguished. Both isomers exhibited inequivalent P atoms, but a larger difference in chemical shift was observed in 2Y. TD-DFT calculations reproduced the difference in spectra between the orange- and yellow-colored complexes, which originated from metal-to-ligand charge-transfer transitions. 相似文献
643.
Naoki Nanashima Kayo Horie Maiko Kitajima Shizuka Takamagi Kasumi Mikami Naoya In Toshiko Tomisawa 《Molecules (Basel, Switzerland)》2021,26(13)
Blackcurrant extract (BCE) ameliorates dyslipidemia in menopausal model animals and in elderly women at a risk of dyslipidemia. However, it is unknown whether the daily intake of BCE can prevent lipid abnormalities in healthy individuals. Lipids are essential for the body, but they also cause arteriosclerosis. In this noncomparative pilot study, we examined the effects of BCE administered for 29 days on serum lipids in young healthy women. Blood samples were collected before and on days 4 and 29 after BCE intake, and 20 lipoprotein fractions in the serum were separated using a gel-permeation high-performance liquid chromatography method to measure the triacylglycerol and cholesterol levels in lipoproteins. There were no effects on lipids on day 4 of BCE intake, but the total cholesterol level decreased on day 29. Furthermore, the levels of total very-low-density lipoprotein (VLDL) cholesterol, small VLDL cholesterol, and large low-density lipoprotein cholesterol were significantly decreased. These results suggest that the daily intake of BCE has a hypocholesterolemic effect in healthy women, and that it is effective in preventing atherosclerosis. 相似文献
644.
Shingo Kanehira Kiyotaka Miura Kazuyuki Hirao Naoya Shibata Yuichi Ikuhara 《Applied Physics A: Materials Science & Processing》2008,92(4):913-916
We show a unique technique to form dense dislocations locally inside a MgO single crystal with a rock-salt type structure
using femtosecond (fs) laser irradiation. Cross-shaped patterns of micrometer size, originating from densely introduced dislocations,
are formed spontaneously around the focal point. We controlled the three-dimensional propagation of the dislocations by adjusting
the pulse energy of the fs laser and NA of objective lens. The technique may open up a new field of dislocation technology
for optical applications. 相似文献
645.
Satavisha Kayal Jun Kikuchi Naoya Shinagawa Shigenobu Umemiya Masahiro Terada 《Chemical science》2022,13(33):9607
A highly efficient kinetic resolution (KR) of racemic tertiary allylic alcohols was achieved through an intramolecular allylic substitution reaction using a co-catalyst system composed of chiral bisphosphoric acid and silver carbonate. This reaction afforded enantioenriched diene monoepoxides along with the recovery of tertiary allylic alcohols in a highly enantioselective manner, realizing an extremely high s-factor in most cases. The present method provides a new access to enantioenriched tertiary allylic alcohols, multifunctional compounds that are applicable for further synthetic manipulations.A highly efficient KR of racemic tertiary allylic alcohols was developed through the intramolecular SN2′ reaction using the chiral bisphosphoric acid/silver carbonate co-catalyst system, affording cis-epoxides and recovered alcohols in a high s-factor. 相似文献
646.
Polymerization of ethylene and propene were conducted with bis(cyclopentadienylzirconium dichloride) (Cp2ZrCl2) and ethylenebis(1-indenyl)zirconium dichloride (Et(Ind)2ZrCl2) combined with trialkylaluminium compounds using heteropolyacids as the counter-anions, giving linear polyethylene and isotactic polypropene, respectively. No polymer was obtained when using Cp2Zr(CH3)2 instead of Cp2ZrCl2. The mechanism of the formation of active species is briefly discussed on the basis of these results. 相似文献
647.
Naoya Ieda Masato Sawada Runa Oguchi Masato Itoh Seina Hirakata Daisuke Saitoh Akito Nakao Mitsuyasu Kawaguchi Prof. Kazunobu Sawamoto Prof. Toshitada Yoshihara Prof. Yasuo Mori Prof. Hidehiko Nakagawa 《Angewandte Chemie (International ed. in English)》2023,62(20):e202217585
We present an optochemical O2 scavenging system that enables precise spatiotemporal control of the level of hypoxia in living cells simply by adjusting the light intensity in the illuminated region. The system employs rhodamine containing a selenium or tellurium atom as an optochemical oxygen scavenger that rapidly consumes O2 by photochemical reaction with glutathione as a coreductant upon visible light irradiation (560–590 nm) and has a rapid response time, within a few minutes. The glutathione-consuming quantum yields of the system were calculated as about 5 %. The spatiotemporal O2 consuming in cultured cells was visualized with a hypoxia-responsive fluorescence probe, MAR. Phosphorescence lifetime imaging was applied to confirmed that different light intensities could generate different levels of hypoxia. To illustrate the potential utility of this system for hypoxia research, we show that it can spatiotemporally control calcium ion (Ca2+) influx into HEK293T cells expressing the hypoxia-responsive Ca2+ channel TRPA1. 相似文献
648.
Naoya Ogata 《Macromolecular Symposia》1994,77(1):167-175
Poly(L-glutamate) having amphiphilic side chains was designed as membrane materials for optical resolution of α -amino acids. Solvent- cast films of the poly(L-glutamate) had a self-ordered structure containing α-helix of the poly(L-glutamate). Optical resolutions of various amino acids were carried out through the thin membranes of the amphiphilic poly(L-glutamate). Racemic mixtures of Tryptophan were completely separated through the membrane. Mechanism of the optical resolutions was investigated in terms of molecular recognitions of racemic Tryptophan by the ordered structure of the mambrane. 相似文献
649.
Lihua Lin Pongpen Kaewdee Vikas Nandal Ryota Shoji Hiroyuki Matsuzaki Kazuhiko Seki Mamiko Nakabayashi Naoya Shibata Xiaoping Tao Xizhuang Liang Yiwen Ma Takashi Hisatomi Tsuyoshi Takata Prof. Kazunari Domen 《Angewandte Chemie (International ed. in English)》2023,62(42):e202310607
Photocatalytic water splitting is an ideal means of producing hydrogen in a sustainable manner, and developing highly efficient photocatalysts is a vital aspect of realizing this process. The photocatalyst Y2Ti2O5S2 (YTOS) is capable of absorbing at wavelengths up to 650 nm and exhibits outstanding thermal and chemical durability compared with other oxysulfides. However, the photocatalytic performance of YTOS synthesized using the conventional solid-state reaction (SSR) process is limited owing to the large particle sizes and structural defects associated with this synthetic method. Herein, we report the synthesis of YTOS particles by a flux-assisted technique. The enhanced mass transfer efficiency in the flux significantly reduced the preparation time compared with the SSR method. In addition, the resulting YTOS showed improved photocatalytic H2 and O2 evolution activity when loaded with Rh and Co3O4 co-catalysts, respectively. These improvements are attributed to the reduced particle size and enhanced crystallinity of the material as well as the slower decay of photogenerated carriers on a nanosecond to sub-microsecond time range. Further optimization of this flux-assisted method together with suitable surface modification is expected to produce high-quality YTOS crystals with superior photocatalytic activity. 相似文献