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111.
Katsuhiko?Kamio Yoshifumi?Kusumoto Masashi?Sakai Katumitu?HayakawaEmail author 《Colloid and polymer science》2003,281(7):608-613
The conformation of the sodium salt of poly(l-glutamic acid) (P(Glu)) in solutions of the cationic bipolar amphiphile 1, 20-isosanediylbis(alkylammonium chloride) (C 20(RA) 2) with different alkyl head groups as a function of amphiphile concentration was investigated using circular dichroism (CD). RA included methylammonium (MA), ethylammonium (EA), propylammonium (PA), butylammonium (BA), and pentylammonium (PeA) cationic groups. The CD spectrum of each C 20(RA) 2 had a double minima corresponding to the a-helix of P(Glu), which was replaced by CD spectra with a single minimum at wavelengths larger than 222 nm as concentration increased. These changes in the CD spectrum were ascribed to the conformational change from random coil to a-helix and to aggregates of helices. In C 20(EA) 2 solutions, a step-like change in the CD intensity was observed at 222 nm as a function of the ratio of C 20(RA) 2 to P(Glu). At the step, the CD spectrum of the complete a-helix was observed. At 10–35 °C, an a-helix was induced in P(Glu) in the order: C 20(EA) 2>C 20(MA) 2>C 20(PA) 2>C 20(BA) 2>C 20(PeA) 2. This order was ascribed to the best fit of ethylammonium to the P(Glu) side chain. 相似文献
112.
The reaction of zirconium n-propoxide in glycol at 300°C yielded microcrystalline tetragonal zirconia (ZrO2). The crystallite size of the product depended on the carbon number of the glycol and increased in the following order (carbon
number of glycol): 2<6<4, which suggested that the heterolytic cleavage of O-C bond of gylcoxide formed by transesterification
is the prime factor for the formation of the product. In toluene, zirconium isopropoxide also gave tetragonal zirconia at
300°C, and zirconium tert-butoxide decomposed at 200°C yielding amorphous zirconia, while zirconium n-propoxide was stable at 300°C. These results suggest that the reaction in toluene depends on the structure of the alkyl group
of the alkoxides. Thus-obtained tetragonal zirconias maintained large surface areas (90–160 m2/g) even after calcination at 500°C. 相似文献
113.
Oku K Watanabe H Kubota M Fukuda S Kurimoto M Tsujisaka Y Komori M Inoue Y Sakurai M 《Journal of the American Chemical Society》2003,125(42):12739-12748
Trehalose is a disaccharide that attracts much attention as a stress protectant. In this study, we investigated the mechanism of the antioxidant function of trehalose. The spin-lattice relaxation times (T(1)) of (1)H and (13)C NMR spectra were measured to investigate the interaction between trehalose and unsaturated fatty acid (UFA). We selected several kinds of UFA that differ in the number of double bonds and in their configurations (cis or trans). Several other disaccharides (sucrose, maltose, neotrehalose, maltitol, and sorbitol) were also analyzed by NMR. The T(1) values for the (1)H and (13)C signals assigned to the olefin double bonds in UFA decrease with increasing concentration of trehalose and the changes reaches plateaus at integer ratios of trehalose to UFA. The characteristic T(1) change is observed only for the combination of trehalose and UFA with cis double bond(s). On the other hand, from the (13)C-T(1) measurements for trehalose, the T(1) values of the C-3 (C-3') and C-6' (C-6) are found to change remarkably by addition of UFA. (1)H[bond](1)H NOESY measurements provide direct evidence for complexation of trehalose with linoleic acid. These results indicate that one trehalose molecule stoichiometrically interacts with one cis-olefin double bond of UFA. Computer modeling study indicates that trehalose forms a stable complex with an olefin double bond through OH...pi and CH...O types of hydrogen bonding. Furthermore, a significant increase in the activation energy is found for hydrogen abstraction reaction from the methylene group located between the double bonds that are both interacting with the trehalose molecules. Therefore, trehalose has a significant depression effect on the oxidation of UFA through the weak interaction with the double bond(s). This is the first study to elucidate the antioxidant function of trehalose. 相似文献
114.
Itoh T Nagata K Yokoya M Miyazaki M Kameoka K Nakamura S Ohsawa A 《Chemical & pharmaceutical bulletin》2003,51(8):951-955
Chiral 1-substituted isoquinoline derivatives, which were obtained by the reaction using alanine derivatives as chiral auxiliaries, were transformed to (S)-2,3,9,10,11-pentamethoxyhomoprotoberberine (7) and a synthetic intermediate for O-methylkreysigine (9) in good yields and high stereoselectivity. The corresponding chiral allyl derivative of isoquinoline was transformed to a pyrrolidinoisoquinoline (16) in a highly enantioselective manner. 相似文献
115.
Amphidinolide Y, a novel 17-membered macrolide from dinoflagellate Amphidinium sp.: plausible biogenetic precursor of amphidinolide X 总被引:1,自引:0,他引:1
Tsuda M Izui N Shimbo K Sato M Fukushi E Kawabata J Kobayashi J 《The Journal of organic chemistry》2003,68(23):9109-9112
A novel cytotoxic 17-membered macrolide, amphidinolide Y (1), has been isolated from a marine dinoflagellate Amphidinium sp., and it was elucidated to exist as a 9:1 equilibrium mixture of 6-keto- and 6(9)-hemiacetal forms (1a and 1b, respectively) on the basis of 2D NMR data and chemical means. The feeding experiments with (13)C-labeled acetates suggested that amphidinolide Y (1) may be a biogenetic precursor of 16-membered macrodiolide, amphidinolide X (2). 相似文献
116.
Masashi Hamaguchi Kazuma TakahashiTakumi Oshima Hatsue Tamura 《Tetrahedron letters》2003,44(23):4339-4342
Reactions of tricarbonyl compounds with vinyl diazo compounds 2 were carried out. Reaction of 1,2,3-indanetrione with 2a,b,c gave the spiroindan-1,3-dione-2,2′-benzodihydrooxepin 7a,b,c, but not normal products oxirane and dihydrofuran derivatives expected from intermediate vinyl carbonyl ylides 4. Formation of 7 requires isomerization of vinyl carbonyl ylides 4 bearing a (Z)-cyanostyryl group to unstable (E)-form 5 and subsequent cyclization to oxepin 6 followed by a 1,5-hydrogen shift. However, reaction of 2 with six-membered cyclic tricarbonyl compounds 1,2,3-trioxo-2,3-dihydrophenalene 11 and dimethylalloxane 13 gave the dioxole 12 and the dihydrofuran 14, respectively, typical products expected from vinyl carbonyl ylides. 相似文献
117.
Assembly of Na3V2(PO4)3 Nanoparticles Confined in a One‐Dimensional Carbon Sheath for Enhanced Sodium‐Ion Cathode Properties 下载免费PDF全文
Dr. Satoshi Kajiyama Dr. Jun Kikkawa Junichi Hoshino Dr. Masashi Okubo Dr. Eiji Hosono 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(39):12636-12640
Structural and morphological control is an effective approach for improvement of electrochemical properties in rechargeable batteries. One‐dimensionally assembled structure composed of NASICON‐type Na3V2(PO4)3 nanoparticles were fabricated through an electrospinning method to meet the requirements for the development of efficient electrode materials in Na‐ion batteries. High‐temperature treatment of electrospun precursor fibers under an argon flow provides a nonwoven fabric of nanowires comprising crystallographically oriented nanoparticles of NASICON‐type Na3V2(PO4)3 within a carbon sheath. The mesostructure comprising NASICON‐type Na3V2(PO4)3 and carbon give a short sodium‐ion transport pass and an efficient electron conduction pass. Electrochemical properties of NASICON‐type Na3V2(PO4)3 are improved on the basis of one‐dimensional nanostructures designed in the present study. 相似文献
118.
Dual Catalysis with Copper and Rhenium for Trifluoromethylation of Propargylic Alcohols: Efficient Synthesis of α‐Trifluoromethylated Enones 下载免费PDF全文
Dr. Hiromichi Egami Takafumi Ide Masashi Fujita Toshifumi Tojo Prof.Dr. Yoshitaka Hamashima Prof.Dr. Mikiko Sodeoka 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(38):12061-12065
Trifluoromethylation of propargylic alcohols to provide (Z)‐α‐trifluoromethylated enones and β‐unsubstituted α‐trifluoromethylated enones proceeded with high yield and selectivity in the presence of CuI/Re2O7. The Z isomer was formed under kinetic control, though it is less stable than the E isomer in terms of steric repulsion. 相似文献
119.
Direct Asymmetric Mannich‐Type Reaction of α‐Isocyanoacetates with Ketimines using Cinchona Alkaloid/Copper(II) Catalysts 下载免费PDF全文
Masashi Hayashi Masaru Iwanaga Noriyuki Shiomi Dr. Daisuke Nakane Prof. Dr. Hideki Masuda Prof. Dr. Shuichi Nakamura 《Angewandte Chemie (International ed. in English)》2014,53(32):8411-8415
The enantioselective direct Mannich‐type reaction of ketimines with α‐isocyanoacetates has been developed. Excellent yields and enantioselectivity were observed for the reaction of various ketimines and α‐isocyanoacetates using cinchona alkaloid/Cu(OTf)2 and a base. Both enantiomers of the products could be obtained by using pseudoenantiomeric chiral catalysts. This process offers an efficient route for the synthesis of α,β‐diamino acids. 相似文献
120.
Ryota Inoue Masashi Hasegawa Tohru Nishinaga Kenji Yoza Yasuhiro Mazaki 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2015,127(9):2772-2776
A series of thiacalix[n]dithiothiophenes (n=4–10) was prepared by a facile method and X‐ray analysis was used to determine the molecular structures of square‐ (4‐mer) and pentagonal‐shaped macrocycles (5‐mer). In the cyclic voltammograms, reversible multielectron redox processes, which are due to electronic delocalization, were observed at low oxidation potentials. The cyclic 4‐mer acted as a “Janus‐head” cavitand for two C60 molecules, whereas the 5‐ and 6‐mer formed stable 1:1 complexes with C60 . 相似文献