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241.
Pei Nian Liu Fei XiaZheng Le Zhao Qing Wei WangYu Jie Ren 《Tetrahedron letters》2011,52(46):6113-6117
The vast applications of triflic acid (TfOH) in catalysis are severely limited by its corrosive and fuming properties. Immobilization of TfOH on silica gel well solves these problems and affords efficient recovery and reusability of TfOH. Two types of supported TfOH, the prepared silica gel supported TfOH and the in situ silica gel adsorbed TfOH, both exhibit good catalytic activity and reusability in the hydroamination of alkene with sulfonamide. The in situ silica gel adsorbed catalyst has been used for 5 runs with maintained reactivities and yields, which are superior to the performance of the prepared silica gel supported TfOH. For a series of alkenes and various sulfonamides, the heterogeneous hydroamination reactions catalyzed by both types of silica gel supported TfOH to afford similar moderate to excellent yields. 相似文献
242.
243.
Differentiating parts of Cinnamomum cassia using LC‐qTOF‐MS in conjunction with principal component analysis
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Pei‐Yi Chen Jhe‐Wei Yu Fen‐Ling Lu Mei‐Chih Lin Hwei‐Fang Cheng 《Biomedical chromatography : BMC》2016,30(9):1449-1457
Cinnamon bark (Rou Gui in Chinese), cinnamon twig (Gui Zhi) and shaved cinnamon bark (Gui Sin) have been widely used as spices and in traditional Chinese medicine since ancient times. On‐going issues related to quality and authenticity necessitate the development of analytical methods capable of providing an objective evaluation of samples. In this study, chemical fingerprints of cinnamon bark, cinnamon twigs and shaved cinnamon bark were established using liquid chromatography quadruple time‐of‐flight mass spectrometry in conjunction with principal component analysis (PCA). From 125 samples of cinnamon, we identified the following eight compounds and their the detection ratios: coumarin, cinnamaldehyde, cinnamyl alcohol, cinnamic acid, 2‐hydroxycinnamaldehyde, 2‐hydroxycinnamic acid, 2‐methoxycinnamaldehyde and 4‐methoxycinnamaldehyde. Of these, 4‐methoxycinnamaldehyde presented the largest variations in detection ratio, making up 64.0, 97.4 and 50.0% in cinnamon bark, cinnamon twig, and shaved cinnamon bark, respectively. The quantities of cinnamyl alcohol, coumarin and cinnamaldehyde also varied between the three parts of the plant. Chemical fingerprints of the three cinnamon samples were established using principal component analysis, the results of which indicate that cinnamon bark and shaved cinnamon bark could be easily differentiated, despite a marked similarity in outward appearance. Cinnamon twig was also shown to depart from the other clusters. The proposed method provides a fast and efficient means of identifying cinnamon herbs for quality control purposes. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
244.
We report a systematic investigation on the mixed micellization of the binary homologues of Gemini surfactant 12-s-12 series
that has a flexible polyethylene spacer. The results showed that the micellization behavior deviates from the ideality when
the difference of the spacer lengths (Δs) of two components is larger than 6. The obvious synergism between two components
occurs in the mixtures of 12-2-12/12-18-12 and 12-4-12/12-18-12. This was attributed to a relatively large difference in the
molecular shape of the two components induced by the length and the configuration of the spacer chain, which yielded better
steric compensation between two components within a mixed micelle than other mixed systems. 相似文献
245.
Haiyang Gao Xiaofang Liu Lixia Pei Qing Wu 《Journal of polymer science. Part A, Polymer chemistry》2010,48(5):1113-1121
Two bis(β‐ketoamino)copper [ArNC(CH3)CHC(CH3)O]2Cu ( 1 , Ar = 2,6‐dimethylphenyl; 2 , Ar = 2,6‐diisopropylphenyl) complexes were synthesized and characterized. Homo‐ and copolymerizations of methyl acrylate (MA) and 1‐hexene with bis(β‐ketoamino)copper(II) complexes activated with methylaluminoxane (MAO) were investigated in detail. MA was polymerized in high conversion (>72%) to produce the syndio‐rich atactic poly(methyl acrylate), but 1‐hexene was not polymerized with copper complexes/MAO. Copolymerizations of MA and 1‐hexene with 1 , 2 /MAO produced acrylate‐enriched copolymers (MA > 80%) with isolated hexenes in the backbone. The calculation of reactivity ratios showed that r(MA) is 8.47 and r(hexene) is near to 0 determined by a Fineman‐Ross method. The polymerization mechanism was discussed, and an insertion‐triggered radical mechanism was also proposed. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 1113–1121, 2010 相似文献
246.
The degradation processes of polyvinylidene fluoride (PVDF) membranes in alkaline solutions were studied using FTIR, FT-Raman, XPS and density functional theory (DFT) simulations. The activation energies for the degradation paths were calculated by LST/QST search methods. The corresponding Gibbs free energies were calculated using a continuum solvation model. The analysis of the spectra indicates the presence of C=C bonds, hydroxyl and carbonyl groups on PVDF membranes. It can be inferred, from DFT calculations, that defluorination is the energetically favorable path, followed by the formation of C=C bonds. The subsequent hydroxylation and carbonyl formation experience higher activation barriers than the formation of C=C bonds. The results indicate that the theoretical calculations are in accordance with the experimental data. 相似文献
247.
Using molecular dynamics simulations, we investigate the oscillatory behaviors of carbon nanotube oscillators containing sp3-hybridized defects formed by hydrogen chemisorption. It is found that the presence of these defects significantly affects the kinetic and potential energies of the nanotube systems, which in turn affects their oscillation periods and frequencies. We have also studied the oscillatory characteristics of the oscillators containing sp3-hybridized Stone-Wales defects. Our results show that it is possible to control the motion of the inner nanotube by introducing sp3-hybridized defects on the outer nanotube, which provides a potential way to tune the oscillatory behavior of nanotube oscillators. 相似文献
248.
249.
Back Cover: Understanding the Origins of Nucleophilic Hydride Reactivity of a Sodium Hydride–Iodide Composite (Chem. Eur. J. 21/2016)
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250.
Adomian decomposition method and Padé approximants for solving the Blaszak--Marciniak lattice
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The Adomian decomposition method (ADM) and Pade approximants are combined to solve the well-known Blaszak-Marciniak lattice, which has rich mathematical structures and many important applications in physics and mathematics. In some cases, the truncated series solution of ADM is adequate only in a small region when the exact solution is not reached. To overcome the drawback, the Pade approximants, which have the advantage in turning the polynomials approximation into a rational function, are applied to the series solution to improve the accuracy and enlarge the convergence domain. By using the ADM-Pade technique, the soliton solutions of the Blaszak-Marciniak lattice are constructed with better accuracy and better convergence than by using the ADM alone. Numerical and figurative illustrations show that it is a promising tool for solving nonlinear problems. 相似文献