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排序方式: 共有268条查询结果,搜索用时 46 毫秒
1.
Takuji Sato 《Proceedings of the American Mathematical Society》2003,131(9):2903-2909
We obtain a non-Kähler almost Hermitian manifold of constant holomorphic sectional curvature by changing the almost complex structure in a Kähler manifold of constant holomorphic sectional curvature.
2.
Takuji Hirose Kumiko Naito Megumi Nakahara Hiroaki Shitara Yoshio Aoki Hiroyuki Nohira Bruce W. Baldwin 《Journal of inclusion phenomena and macrocyclic chemistry》2002,43(1-2):87-93
Two Kemp's acid diamides were synthesized and applied to chiral amine recognition using 1H NMR analysis. One derivative based on 1-(1-naphthyl)ethylamine had good chiral recognition of six amines and was useful to determine the optical purity for three amines, i.e., methylbenzylamine, 1-(1-naphthyl)ethylamine and 1- henylpropylamine,however, the cyclohexylethylamine derivative showed little discrimination for the amines studied. Together with the results for alkylamines, it was shown that aromatic structure was important for aromatic shielding anisotropy and –– interactions between host and guest. The structure of the 1-(1-naphthyl)ethylamine derivative in solution was also considered based on 1H NMR data and computer simulation. 相似文献
3.
Takeshi Ishijima Yoshiki Mizumori Kenji Kikuchi Atsushi Suzuki Takuji Okaya 《Colloid and polymer science》2005,283(7):799-804
Polymerization of vinyl acetate (VAc) in various fatty acids (carbon numbers 4–18) was carried out. Chain transfer constants to the acids were determined to be 20–35×10–4, from which the constant to a methylene group was obtained to be 0.73×10–4. Viscometry in aqueous solution of derived poly (vinyl alcohol) (PVA) showed the usual behavior in terms of Huggins constant obtained by the Schulz–Blaschkes equation for PVAs derived from fatty acid systems lower than hexadecanoic acid. PVA derived from octadecanoic acid system showed abnormality, indicating association of alkyl groups. Contact angles on surfaces of PVAs cast from aqueous solutions were measured. While those of PVA derived from lower acid systems were 62°, those of PVAs derived from higher aids were higher and increased to 92° with increase in carbon number to octadecanoic acid. Alkyl groups in the PVAs were estimated to appear on the surfaces. Surface tension of aqueous solution of the PVA derived from octadecanoic acid showed high surface activity, and depended on pH of the solution, indicating the presence and cleavage of lactone ring at the combined portion between PVA and the acid. 相似文献
4.
Yamamoto T Mukai SR Endo A Nakaiwa M Tamon H 《Journal of colloid and interface science》2003,264(2):532-537
Growth of colloidal particles formed during the sol-gel transition of a resorcinol-formaldehyde (RF) solution was simulated based on the population balance equation by using the discrete-sectional model (DSM). During the early stage of the sol-gel transition, the transient change of sizes of colloidal particles estimated by this method agreed well with the previous experimental observation by dynamic light scattering (DLS), which confirmed the influence of the catalyst concentration of a starting RF solution on the growth rate of the particles. From the size distribution of colloidal particles predicted at the gelation time, the surface area of a RF hydrogel after the completion of the sol-gel transition was estimated, which coincided with the BET surface area of a RF aerogel because the porous structure of a hydrogel was maintained and few micropores were formed during supercritical drying. 相似文献
5.
Murakami K Irie K Ohigashi H Hara H Nagao M Shimizu T Shirasawa T 《Journal of the American Chemical Society》2005,127(43):15168-15174
Amyloid fibrils mainly consist of 40-mer and 42-mer peptides (Abeta40, Abeta42). Abeta42 is believed to play a crucial role in the pathogenesis of Alzheimer's disease because its aggregative ability and neurotoxicity are considerably greater than those of Abeta40. The neurotoxicity of Abeta peptides involving the generation of free radicals is closely related to the S-oxidized radical cation of Met-35. However, the cation's origin and mechanism of stabilization remain unclear. Recently, structural models of fibrillar Abeta42 and Abeta40 based on systematic proline replacement have been proposed by our group [Morimoto, A.; et al. J. Biol. Chem. 2004, 279, 52781] and Wetzel's group [Williams, A. D.; et al. J. Mol. Biol. 2004, 335, 833], respectively. A major difference between these models is that our model of Abeta42 has a C-terminal beta-sheet region. Our biophysical study on Abeta42 using electron spin resonance (ESR) suggests that the S-oxidized radical cation of Met-35 could be generated by the reduction of the tyrosyl radical at Tyr-10 through a turn structure at positions 22 and 23, and stabilized by a C-terminal carboxylate anion through an intramolecular beta-sheet at positions 35-37 and 40-42 to form a C-terminal core that would lead to aggregation. A time-course analysis of the generation of radicals using ESR suggests that stabilization of the radicals by aggregation might be a main reason for the long-lasting oxidative stress of Abeta42. In contrast, the S-oxidized radical cation of Abeta40 is too short-lived to induce potent neurotoxicity because no such stabilization of radicals occurs in Abeta40. 相似文献
6.
Yoshiaki Hidaka Hiromitsu Masaoka Hidekazu Oshita Takuji Nakamura Koji Tanaka Hiroyuki Kawano 《国际化学动力学杂志》1992,24(10):871-885
The thermal decomposition of vinylacetylene (C4H4) was studied behind reflected shock waves using both a single-pulse method (reaction time between 0.8 and 3.3 ms) and a time-resolved UV-absorption method (230 nm). The studies were done over the temperature range of 1170–1690 K at the total pressure range of 1.3–2.3 atm. The mechanism was used to interpret both the early and late stages of vinylacetylene decomposition at the high temperatures. It was confirmed that C4H4 dissociation proceeded through the following three channels. The rate constant expression of reaction (1) was determined as k1 = 6.3 × 1013 exp(?87.1 kcal/RT) s?1. The rate constants of the succeeding reactions (chain reaction, C4H4 + H → i-C4H3 + H2 and C4H4 + H → C2H2 + C2H3 and decomposition reactions of free radicals, i-C4H3 + M → C4H2 + H + M) were confirmed or estimated. © John Wiley & Sons, Inc. 相似文献
7.
To make clear the reason of unsuitability of poly(vinyl alcohol) (PVA) protective colloid for the emulsion polymerization
of conjugated monomers, a model experiment of emulsion polymerization of methyl methacrylate (MMA) was carried out with ammonium
persulfate (APS) or azobis(isobutyronitrile) (AIBN) initiators, where a small amount of MMA (1/100th of the concentration
compared with ordinary emulsion polymerization) was employed. This corresponds to the initial stage of the emulsion polymerization.
Grafting of MMA onto PVA took place remarkably irrespective of the kind of the initiators. Formation of homo-poly(MMA) was
observed to a small extent. The formation of new emulsion particles smaller than 100 nm continued to increase to almost the
end of the polymerization. PVA molecules in the grafted polymer are supposed to act as stabilizers of newly formed particles.
From kinetic treatment using the experimental data, the important issues were derived as follows. Firstly, the sulfate anion
radical from APS is much more reactive than the isobutyronitrile radical from AIBN in terms of hydrogen abstraction from PVA.
Secondly, high grafting ability of the latter initiator system, notwithstanding the much lower reactivity in the hydrogen
abstraction compared with the APS system, is attributed to the relative reactivity of the primary radicals, i.e., hydrogen
abstraction reaction from PVA to initiation reaction with MMA. The much slower rate of addition of the isobutyronitrile radical
to the monomer compared with that of hydrogen abstraction from PVA facilitates the grafting, although the rate constant of
hydrogen abstraction is far smaller than that with the sulfate anion radical by 10−4 times.
Received: 26 April 2001 Accepted: 6 September 2001 相似文献
8.
Ayako Torikai Teruyuki Hattori Takuji Eguchi 《Journal of polymer science. Part A, Polymer chemistry》1995,33(11):1867-1871
Polymethylmethacrylate (PMMA) containing benzophenone (BP) was photo-irradiated with monochromatic radiation of wavelength 260–360 nm using the Okazaki Large Spec-trograph (OLS). On irradiation of PMMA films containing BP in air, the sensitized main-chain scission and photocrosslinking of PMMA took place simultaneously. These reactions are dependent on irradiation wavelength. The threshold wavelength for both reactions is found to be ca. 380 nm. The number of main-chain scission and amount of gel increased with the increase of BP concentration in PMMA. Photosensitized main-chain scission favors the irradiation of radiation at ca. 280 nm and photocrosslinking takes place efficiently with the exposure of 340 nm radiation. A possible mechanism for photosensitized reaction is proposed. © 1995 John Wiley & Sons, Inc. 相似文献
9.
The synthesis of 11‐methyl‐6H‐pyrido[4,3‐b]carbazole‐1(2H)‐one (5), which can be important for the synthesis of other pyridocarbazole alkaloids and especially 1‐substituted ellipticines, is described. Construction of the tetracyclic structure was achieved by a new route and two important precursor compounds (4a and 4b) for the synthesis of pyridocarbazole alkaloids and also many new tetrahydrocar‐bazole derivatives (7, 8, 9, 10, 11, 12, 13) were synthesized. 相似文献
10.
Diphenyl sulphoxide (DPSO) reacts with an equimolar amount of potassium (K) in tetrahydrofuran (THF) at ?78° to form a reddish-black solution, giving an electron spin resonance (ESR) signal only below ?70°. The signal is attributed to a very labile DPSO anion radical. The solution of DPSO-K (1/1) reaction products reacts further with another molecular amount of K at this temperature to give no ESR signal. The DPSO-K (1/1) reaction products initiates the polymerization of acrylonitrile (AN), but not the polymerizations of methyl methacrylate (MMA), styrene (St) or isoprene (IP). The active species of the solution initiating the polymerization of AN is assumed to be potassium benzene sulphenate from analyses of the solution and the infra-red spectrum of AN oligomers obtained using the complex. The DPSO-K (1/2) reaction products solution initiates the polymerization of MMA, St and IP as well as AN. The active species initiating the polymerization of MMA, St or IP is assumed to be phenylpotassium. 相似文献