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The protected ceramide: N‐((2S,3S,4R)‐3,4‐bis(benzyloxy)‐1‐hydroxyoctadecan‐2‐yl)tetracosanamide, was attempted to introduce a triflate as a leaving group followed by a nucleophilic substitution with azido group in one‐pot manner. Unexpectedly, the oxazole ring formed via a thermodynamically favored intramolecular cyclization was opened to generate the original ceramide by triflic acid. In addition, the residual acid promoted a formylation of the primary hydroxy group in DMF. 相似文献
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Bartosz Mozgawa Dr. Filip Zasada Dr. Monika Fedyna Prof. Kinga Góra-Marek Dr. Edyta Tabor Dr. Kinga Mlekodaj Dr. Jiří Dědeček Prof. Zhen Zhao Dr. Piotr Pietrzyk Prof. Zbigniew Sojka 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(68):17159-17180
NH3 temperature-programmed desorption (NH3-TPD) is frequently used for probing the nature of the active sites in CuSSZ-13 zeolite for selective catalytic reduction (SCR) of NOx. Herein, we propose an interpretation of NH3-TPD results, which takes into account the temperature-induced dynamics of NH3 interaction with the active centers. It is based on a comprehensive DFT/GGA+D and first-principles thermodynamic (FPT) modeling of NH3 adsorption on single Cu2+, Cu+, [CuOH]+ centers, dimeric [Cu-O-Cu]2+, [Cu-O22−-Cu]2 species, segregated CuO nanocrystals and Brønsted acid sites (BAS). Theoretical TPD profiles are compared with the experimental data measured for samples of various Si/Al ratios and distribution of Al within the zeolite framework. Copper reduction, its relocation, followed by the intrazeolite olation/oxolation processes, which are concomitant with NH3 desorption, were revealed by electron paramagnetic resonance (EPR) and IR. DFT/FPT results show that the peaks in the desorption profiles cannot be assigned univocally to the particular Cu and BAS centers, since the observed low-, medium- and high-temperature desorption bands have contributions coming from several species, which dynamically change their speciation and redox states during NH3-TPD experiment. Thus, a rigorous interpretation of the NH3-TPD profiles of CuSSZ-13 in terms of the strength and concentration of the active centers of a particular type is problematic. Nonetheless, useful connections for molecular interpretation of TPD profiles can be established between the individual component peaks and the corresponding ensembles of the adsorption centers. 相似文献
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The quantum field theory of stimulated Raman scattering is formulated. It is shown to give the correct classical limit. Ilowever, the quantum growth rate is bigger. An additional physical process of creation of two plasmons from two photons is intrinsically predicted by the theory. 相似文献
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In this report,the stable corona discharge region of multi-wire proportional cham-ber(MWPC)has been measured.In this region we observed double peak pheno- menon in Fe55 pulse amplitude distribution,and establish the fact that,once cornadischarge region is present in MWPC,the spatial resolution power for light partic-les will be lost. 相似文献
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ZHAO ZHEN-LAN XU YUAN-BIAO GUO YING-HUAN LO SHI-HUA HUANG ZHONG-WIANG YANG RUI-YING 《中国物理C(英文版)》1982,6(1):111-112
In present paper, a non-classical method of obtaining the decay constant andhalf-life of 99mTc was introduced. The results were compared with that obtained bythe classical method of the least square analysis. The half-life by non-classioal me-thod is 6.006±0.004 hours, that by classical method is 6.009±0.005 hours. 相似文献
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无损残余应力测量及其新技术 总被引:1,自引:0,他引:1
简述及比较了主要的残余应力无损测量技术,重点为磁力法,并介绍一台新的磁力仪MAPS,且对MAPS及传统磁力仪作了比较,同时以X射线及中子衍射得到的结果验证了MAPS的可靠性,也介绍了文献上较少见的火车钢轨残余应力分布图。 相似文献
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