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31.
The Mannich-type reaction of imines with (1-methoxy-2-methylpropenyloxy)trimethylsilane and aza-Diels-Alder reaction of imines with Danishefsky's diene can be carried out in scCO2 in the presence of lithium heptadecafluorooctanesulfonate which offer a way to synthesize β-amino carbonyl compounds and nitrogen-containing six-membered ring compounds under environmentally benign conditions. 相似文献
32.
We carried out detailed calculations for photorefractive wave-mixing switches based on one of three crystals with high electro-optic coefficients, namely, BaTiO3, Strontium Barium Niobate (SBN (0.75)), and Potasium Sodium Strontium Barium Niobate (KNSBN). A comparison of results for the three crystals shows that a 0_-cut BaTiO3 crystal is suitable for a longitudinal switch and requires a voltage of about 80 for a 2-mm-thick crystal to induce sufficient phase mismatch. The electrodes must be transparent for the incident and diffracted beams. A 45_-cut SBN (0.75) crystal, however, is suitable for a lateral switch and requires a voltage of about 150 for a 1-mm-wide crystal. The electrodes do not need to be transparent. 相似文献
33.
Yu‐Hsiang Hu Chuh‐Yung Chen Chen‐Chien Wang Yao‐Hui Huang Shao‐Ping Wang 《Journal of polymer science. Part A, Polymer chemistry》2004,42(19):4976-4993
The bulk polymerization of styrene initiated by ?‐caprolactam (CL) and n‐dodecyl mercaptan (RSH) has been explored. This novel polymerization system shows living characteristics. For example, the molecular weight of the resulting polymers increases with conversion, and the system has the ability to form diblock copolymers and so forth. The polymer chain end contains thiol and lactam structures, which we have investigated with Fourier transform infrared, 1H NMR, and 13C NMR techniques. Electron spin resonance spectra and theoretical calculations by the Hartree–Fock methods have been used to examine the mechanism. The results reveal that the initial polymerization starts from thiol via a chain‐transfer reaction, and the propagation proceeds by the insertion of a monomer between the terminal group and the intermediate structure of lactam. Finally, the polymerization kinetics have been examined. The polymerization rate varies linearly with the concentration of CL and RSH, and this confirms the mechanism. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 4976–4993, 2004 相似文献
34.
Chin‐Ping Yang Sheng‐Huei Hsiao Che‐Yu Tsai Guey‐Sheng Liou 《Journal of polymer science. Part A, Polymer chemistry》2004,42(10):2416-2431
Two series of fluorinated polyimides were prepared from 2,2′‐bis(4‐amino‐2‐trifluoromethylphenoxy)biphenyl ( 2 ) and 2,2′‐bis(4‐amino‐2‐trifluoromethylphenoxy)‐1,1′‐binaphthyl ( 4 ) with various aromatic dianhydrides via a conventional, two‐step procedure that included a ring‐opening polyaddition to give poly(amic acid)s, followed by chemical or thermal cyclodehydration. The inherent viscosities of the polyimides ranged from 0.54 to 0.73 and 0.19 to 0.36 dL/g, respectively. All the fluorinated polyimides were soluble in many polar organic solvents, such as N,N‐dimethylacetamide and N‐methylpyrrolidone, and afforded transparent and light‐colored films via solution‐casting. These polyimides showed glass‐transition temperatures in the ranges of 222–280 and 257–351 °C by DSC, softening temperatures in the range of 264–301 °C by thermomechanical analysis, and a decomposition temperature for 10% weight loss above 520 °C both in nitrogen and air atmospheres. The polyimides had low moisture absorptions of 0.23–0.58%, low dielectric constants of 2.84–3.61 at 10 kHz, and an ultraviolet–visible absorption cutoff wavelength at 351–434 nm. Copolyimides derived from the same dianhydrides with an equimolar mixture of 4,4′‐oxydianiline and diamine 2 or 4 were also prepared and characterized. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 2416–2431, 2004 相似文献
35.
Based on the complexation between proteins and Cu(II) coupled with the time-resolved chemiluminescence (CL) technique, a highly sensitive and quantitative assay for measuring proteins in solution is described. The complexes of proteins with Cu(II) have a strongly catalytic effect on the luminol-H2O2 CL reaction. Because the CL emission produced by the complexes is much more long-lived than that by Cu(II), the CL signals originating from proteins can be easily identified and measured with a time-resolved technique. On this basis, bovine albumin fraction V (BAF V) can be quantitatively determined in the range of 0.01 - 5.0 microg/ml with a detection limit of 5.8 ng/ml. The results show that the proposed assay exhibits a small variation in the response values for the same amount of different proteins, as compared to the Lowry as well as Bradford assays. The CL assay has also been studied for the detection of immobilized proteins. 相似文献
36.
Seiichi Nishizawa Tomoyuki Kamaishi Tomoyuki Yokobori Ryo Kato Ying-Yu Cui Takeshi Shioya Norio Teramae 《Analytical sciences》2004,20(11):1559-1565
Facilitated SO4(2-) transfers by hydrogen bond-forming ionophores are investigated across the nitrobenzene (NB)-water interface by using polarography with a dropping electrolyte electrode. Bis-thiourea 1, alpha,alpha'-bis(N'-p-nitrophenylthioureylene)-m-xylene, is found to significantly facilitate the transfer of the highly hydrophilic SO4(2-) whereas its counterpart, N-(p-nitrophenyl)-N'-propylthiourea (ionophore 2), cannot. In contrast to the predominant formation of a 1:1 complex with SO4(2-) in the bulk NB phase, the SO4(2-) transfer assisted by 1 is indeed based on the formation of a 1:2 complex between SO4(2-) and ionophore, even under the condition of [SO4(2-)]aq > [1]org. Such an exclusive formation of the 1:2 (SO4(2-) to ionophore) complex at the NB-water interface is not observed with structurally similar bis-thiourea 3, alpha,alpha'-bis(N'-phenylthioureylene)-m-xylene, where p-nitrophenyl moietes of bis-thiourea 1 are simply replaced by phenyl groups. The facilitated transfer of SO4(2-) with bis-thiourea 1 is further compared to that of HPO4(2-) and H2PO4- across the NB-water interface, which was previously shown to be assisted by 1 through the formation of the 1:1 and 2:1 (anion to ionophore) complexes, respectively. On the basis of these examinations, unique binding behaviors of hydrogen bond-forming ionophores at the NB-water interface are discussed, with a view towards development of ionophore-based anion-selective chemical sensors. 相似文献
37.
Ri Cheng XUAN* Wei Xiao HU Zhong Yu YANG Ya Ping LU College of Pharmaceutical Sciences Zhejiang University of Technology Hangzhou 《中国化学快报》2004,(2)
2-Chloro-5-methylpyridine is an important intermediate for the preparation of biological active compounds, especially insecticides1, e.g. imidacloprid2, and is usually manufac- tured from 3-methylpyridine N-oxide. However, the manufacturing process also forms the by-products: 3-methylpyridine and its isomer 2-chloro-3-methylpyridine3. The pro- perties of the isomers are similar, it is difficult to separate by ordinary methods, such as distillation. Scheme 1 79.4%13.6%5.2%NClCH3NCH3ClNC… 相似文献
38.
DongXiangLI WanGuoHOU ShuPingLI MingTuHAO GaoYongZHANG 《中国化学快报》2004,15(2):224-227
The relation of the isoelectric point (IEP) and the point of zero net charge (PZNC) of the hydrotalcite-like compounds was discussed. It was found that the IEP does not equal to the PZNC and the IEP is higher than the PZNC. The structural positive charges existing in the HTlc,which cause the difference between the IEP and the PZNC. The effects of the structural positive charges of the HTlc on its IEP and PZNC are the same as the specific adsorption of metal cations. 相似文献
39.
德国夏洛滕堡物理技术研究所(The Physikallisch-Technische Reichanstalt,简称PTR)是世界上第一个国家级的物理技术研究所,它开创了科学研究和技术研究相结合,服务于工业和国家经济之先河。文章从PTR建立的历史背景、早期研究工作和所产生的影响等方面作较为全面的讨论。 相似文献
40.