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71.
Highly substituted 4,4'-biimidazoles were synthesized, in good to excellent yields, through a multicomponent imidazole ring synthesis by using imidazol-4-yl-ethane-1,2-diones as starting materials. The obtained compounds were preliminarily tested as chromogenic and fluorescent sensors for heavy metals. 相似文献
72.
A comparison of the extraction of clove buds with supercritical carbon dioxide and superheated water
A. A. Clifford Annamaria Basile Salim H. R. Al-Saidi 《Fresenius' Journal of Analytical Chemistry》1999,364(7):635-637
Supercritical carbon dioxide and superheated water (subcritical water above 100 °C under pressure) have both been used to
extract the buds of cloves (Syzygium aromaticum). The yields of eugenol and eugenyl acetate obtained by these methods and also by steam distillation and liquid solvent (Soxhlet)
extraction are similar, but the yields of caryophyllene were lower for the methods using water.
Received: 23 December 1998 / Revised: 26 March 1999 / Accepted: 31 March 1999 相似文献
73.
[reaction: see text] alpha,beta-Unsaturated acetals afford, in the presence of the LIC-KOR superbase, 1-alkoxybuta-1,3-dienes. These substrates cross couple with aryl derivatives in the presence of Pd catalyst (Heck conditions) in a regio- and stereoselective mode. With dialkyl acetals, the reaction affords arylated dienes; on the other hand, in the case of 1,3-dioxane derivatives, the final outcome of the process formally corresponds to the direct gamma-arylation reaction of the starting alpha,beta-unsaturated material. 相似文献
74.
Groom CA Halasz A Paquet L Thiboutot S Ampleman G Hawari J 《Journal of chromatography. A》2005,1072(1):73-82
An Agilent 3DCE capillary electrophoresis system using sulfobutylether-beta-cyclodextrin (SB-beta-CD)-ammonium acetate separation buffer pH 6.9 was coupled to a Bruker Esquire 3000+ quadrupole ion trap mass detector via a commercially available electrospray ionization interface with acetonitrile sheath flow. The CE-MS system was applied in negative ionization mode for the resolution and detection of nitroaromatic and polar cyclic or caged nitramine energetic materials including TNT [2,4,6-trinitrotoluene, formula mass (FW) 227.13], TNB (1,3,5-trinitrobenzene, FW 213.12), RDX (hexahydro-1,3,5-trinitro-1,3,5-triazine, FW 222.26) HMX (octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine, FW 296.16), and CL-20 (2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane, FW 438.19). The CE-MS system conformed to the high-performance liquid chromatography with ultraviolet absorbance detection (HPLC-UV) and HPLC-MS reference methods for the identification of energetic contaminants and their degradation products in soil and marine sediment samples. 相似文献
75.
Polyolefins that bear a chiral side chain (typically an isobutyl group) experience a so-called macromolecular amplification of chirality: the chiral side-chain induces a slight preference for either tg or tg- main chain conformation. This slight conformational bias is amplified cooperatively along the chain, and results in preferred chirality of the main chain helical conformations. As a result, these polymers display a liquid-crystal (LC) phase both in solution and, in the melt as a transient phase on the way to crystallization. The existence of two processes (melt-LC and LC-crystal transitions) results in unconventional behaviors that were first analyzed by Pino and collaborators back in 1975. These polymers also offer a means to test the structural consequences of recently introduced crystallization schemes. These schemes postulate the formation of a transient liquid-crystal phase as a general scheme for polymer crystallization. 相似文献
76.
Annamaria Canino Berardino Sciunzi Alessandro Trombetta 《NoDEA : Nonlinear Differential Equations and Applications》2016,23(2):8
We consider quasilinear elliptic equations involving the p-Laplacian and singular nonlinearities. We prove comparison principles and we deduce some uniqueness results. 相似文献
77.
Blangetti M Deagostino A Prandi C Zavattaro C Venturello P 《Chemical communications (Cambridge, England)》2008,(14):1689-1691
A new approach to the synthesis of pyrimidines and cyclopentenones is described. The method exploits the reactivity of alpha,beta-unsaturated acetals with aromatic nitriles in the presence of the Schlosser's superbase LIC-KOR. 相似文献
78.
79.
Annamaria Barbagallo Giovanni Scilla 《Journal of Mathematical Analysis and Applications》2018,457(2):1118-1134
A class of stochastic weighted variational inequalities in non-pivot Hilbert spaces is proposed. Existence and continuity results are proved. These theoretical results play a prominent role in order to introduce a new weighted transportation model with uncertainty. Moreover, they allow to establish the equivalence between the random weighted equilibrium principle and a suitable stochastic weighted variational inequality. At the end, a numerical model is discussed. 相似文献