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排序方式: 共有5102条查询结果,搜索用时 13 毫秒
91.
Dirk Mehlhorn Dr. Rustem Valiullin Prof. Jörg Kärger Kristin Schumann Dr. Alfons Brandt Dr. Baldur Unger 《化学,工程师,技术》2011,83(12):2251-2259
The pulsed field gradient (PFG) NMR technique is applied for exploring the diffusion behavior of guest molecules in binderless NaX beads in comparison with the zeolite powder employed for their production. With both probe molecules applied (water, n‐hexane), the diffusivities in the powder and the beads are found to essentially coincide as long as the diffusion path lengths are sufficiently small in comparison with the extension of the individual particles (crystallites) of the powder. With increasing diffusion path lengths, characteristic deviations become observable that can be attributed to the differences in long‐range mass transfer through the intercrystalline void volume of the bed of crystallites and within the individual beads of the binderless molecular sieve, respectively. With these studies, PFG NMR demonstrates its potentials for simultaneously recording mass transfer phenomena in both the micro‐ and macropores of commercially produced binderless molecular sieves. 相似文献
92.
Satoshi Murakami Kazuhiro Satou Taturo Kijima Masataka Watanabe Taeko Izumi 《European Journal of Lipid Science and Technology》2011,113(4):450-458
The enantiopure of (R)‐(?) MαNPA was allowed to react with racemic 18‐(tert‐butyldimethylsilyloxy)‐5‐octadecayne‐7‐ol which was derived from dodecane‐1,12‐diol, yielding diastereomeric esters mixture. These racemic esters were easily separated by HPLC on silica‐gel. The absolute configurations of the first‐eluted diastereomeric esters from the separated esters were determined using 1H NMR anisotropy method. Analysis on 1H NMR spectra and HPLC elution time of the synthesized esters and those of MαNP ester derived from natural methyl‐12‐hydroxystealate showed that the absolute configuration of natural 12‐hydroxystearic acid was R form, and the enantiomeric excess was over 99%. 相似文献
93.
Thermochromic changes of 10,12‐pentacosadiynoic acid (PCDA) were investigated in combination with four aromatic compounds, benzene, furan, thiophene, and cyclopentadiene, with subsequent exposure to UV radiation. Using Raman spectroscopy and solid‐state Fluorometry, no differences were observed between benzene, furan, or thiophene from the PCDA itself, with respect to the blue to red color change, which took place from 80°C to 100°C. However, the addition of cyclopentadiene exhibited the color change at a significantly higher temperature, ranging from 180°C to 200°C. Lack of new products formed during the initial mixing period was ruled out by analysis using solid‐state NMR MAS and differential scanning calorimetry (DSC), with only monomer peaks at 69.61°C for the PCDA and 72.37°C for PCDA in combination with cyclopentadiene, as recorded by the DSC. It is believed that a chemical bond between PCDA and cyclopentadiene is formed after polymerization from catalysis by the UV radiation. Solid‐state NMR MAS revealed a chemical shift peak of 131.55 ppm for the PCDA and a much larger peak at 130.84 ppm for the PCDA and cyclopentadiene. The DSC exhibited melting point peaks at 193.26°C and 194.88°C for PCDA and PCDA with cyclopentadiene, respectively. Because the color change involves C C bond rotation of side groups, stressing π‐bond overlap, the cyclopentadiene bond is thought to prevent rotation by steric hindrance until a higher temperature or melting occurs at the DSC stated temperature of 194.88°C. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011 相似文献
94.
95.
Cover Feature: Characterisation of the Carboxypeptidase G2 Catalytic Site and Design of New Inhibitors for Cancer Therapy (ChemBioChem 18/2018) 下载免费PDF全文
96.
Real‐time monitoring by proton relaxometry of radical polymerization reactions of acrylamide in aqueous solution 下载免费PDF全文
Elton Jorge da Rocha Rodrigues Roberto Pinto Cucinelli Neto Pedro José Oliveira Sebastião Maria Inês Bruno Tavares 《Polymer International》2018,67(6):675-683
The potential of time‐domain nuclear magnetic resonance (TD‐NMR) for the real‐time monitoring of solution radical polymerizations is demonstrated. A model system composed of a redox‐pair initiator system, acrylamide as monomer and water as solvent was investigated. A second‐generation continuous wave free precession technique was employed to measure the longitudinal relaxation time constant (T1) of the samples throughout the polymerization reactions. This parameter was shown to be sensitive to the reactant feed free‐radical enhancement of the water molecule relaxation time, making it a good probe to monitor monomer conversion in real time in an automated, non‐destructive fashion. It was found that the T1 value was better than the transverse relaxation time constant (T2) for describing the evolution of the polymerization reactions, due to its greater sensitivity to paramagnetic effects. The TD‐NMR signal variation observed was linked to the formation, propagation and termination steps of the radical polymerization kinetics scheme. These first results may contribute to the application of real‐time monitoring of radical polymerization reactions employing low‐cost and robust TD‐NMR spectrometers. © 2018 Society of Chemical Industry 相似文献
97.
Hainan Bai Jiulin Hu Xiaoguang Li Yusen Duan Feng Shao Takahiro Kozawa Makio Naito Jingxian Zhang 《Ceramics International》2018,44(6):6558-6563
Concerning the safety problems of conventional Li-ion batteries with liquid electrolytes, it is crucial to develop reliable solid-state electrolytes with high ionic conductivity. Li1+xAlxTi2?x(PO4)3 (LATP, x = 0.3) is regarded as one of the most promising solid electrolytes due to its high ionic conductivity and excellent chemical stability to humidity.Herein, a new strategy is proposed for improving the sintering behavior and enhancing the ionic conductivity of LATP by using LiBO2 as the sintering aid via liquid phase sintering. The as-prepared sample LATP with homogeneous microstructure and high relative density of 97.1% was successfully synthesized, yielding high total ionic conductivity of 3.5 × 10?4 S cm?1 and low activation energy of 0.39 eV at room temperature. It was found that the addition of LiBO2 could effectively enhance the densification and increase the ionic conductivity of LATP electrolyte, proving an effective way to synthesis LATP ceramics by a simple and reliable route. 相似文献
98.
This work reports a low-cost and versatile electronic device designed to trigger NMR acquisitions from the cardiac cycle of an isolated perfused heart, or to perform electrical stimulation of the heart. The triggering is synchronised with the pressure curve of the perfused heart. The cardiac pacing is achieved from pulses of the NMR system, or by an internal pulse generator, in order to be operated separately from the NMR instrument. 相似文献
99.
A Decade of Oxothiomolybdenum Wheels: Synthesis,Behavior in Solution,and Electrocatalytic Properties
Jean-François Lemonnier Sylvain Duval Sébastien Floquet Emmanuel Cadot 《Israel journal of chemistry》2011,51(2):290-302
The last decade has see the development of sulfur-containing polyoxometalates (POTMs) as a subclass of the polyoxometalate family. The structural and physico-chemical properties of this emerging class of compounds is dominating by the striking coordination properties of the [Mo2O2S2(OH2)6]2+ oxothio cation, used as a building block. The cyclic topology of this arrangement corresponds to the main feature of the {Mo2O2S2}-based compounds, able to develop cycle-based chemistry. The control of the linear oligomerization of the {Mo2O2S2} core is achieved by the presence of the anionic component, which acts as a template. Here, we report on recent examples which illustrate how the use of various template ions such as halide, sulfate, polyphosphate, and polycarboxylate anions allows to tune the nuclearity of the inorganic host from {Mo8} to {Mo18}. A special focus on behavior in solution is given, highlighting the dynamic and fluxional character of these host–guest systems. The Diffusion Ordered Spectroscopy (DOSY) 1H NMR, carried out on a large series of cycle-based and capsule-like compounds, demonstrates that such a method can be applied for the speciation of POM anions in solution. Finally, electrocatalytic behavior of the {Mo2O2S2}-based compounds is presented. Preliminary results show that the electrocatalytic reduction of protons into hydrogen (HER) could constitute one of the most relevant applications for this class of molecular compounds. 相似文献
100.
研究了辽河、胜利焦化蜡油的组成,考察了硫、氮、残炭在焦化蜡油中的分布,采用改进的B-L法、n-d-M法计算了辽河、胜利焦化蜡油的结构参数,并与大庆焦化蜡油文献数据进行了比较,讨论了焦化蜡油中氮对掺炼的影响。 相似文献