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961.
Rosaria Villano Maria Rosaria Acocella Antonio Massa Laura Palombi Arrigo Scettri 《Tetrahedron: Asymmetry》2006,17(24):3332-3334
Chiral δ-hydroxy-β-ketoesters are easily available through the enantioselective vinylogous aldol reaction of Chan’s diene promoted by a SiCl4/chiral phosphoramide catalytic system. The procedure is conveniently exploited for a very rapid approach to (+)-kavain, a natural bio-active -pyrone compound. 相似文献
962.
The reductive radical cyclisation of δ- and ?-epoxynitrile-2-azetidinones has been achieved using titanocene monochloride. The reaction was regioselective and afforded bicyclic β-lactams and tricyclic β-lactams containing an aryl group fused to a seven-membered ring. 相似文献
963.
Vassil St. Georgiev Grace A. Bennett Lesley A. Radov Dietgard K. Kamp Laura A. Trusso 《Journal of heterocyclic chemistry》1986,23(5):1359-1362
The synthesis of a series of 2-substituted 2,3-dihydro-5H-thiazolo[2,3-b]quinazoline derivatives is described. Some of the title compounds exerted antiinflammatory and immunomodulating activities in laboratory animal models. 相似文献
964.
Some properties of LiChrolut-EN resins as normal-phase sorbent have been studied. Retention factors using pentane as solvent range from less than 2 (ethyl esters) to more than 56 (fatty acids and vanillin). All retention factors were smaller than 2 with dichloromethane. The efficiency of the bed was between 4 and 13 plates per cm. A method for the fast fractionation of wine flavor extracts has been further developed. Wine (75 ml) is extracted on a 0.5 g LiChrolut-EN bed. Volatile compounds are recovered in 5 ml of dichloromethane and the extract is further concentrated to 0.1 ml. Recoveries of the extraction procedure are above 85% for all compounds less polar than isoamyl alcohol. This extract is fractionated on a bed (5.0 cm height, 0.6 cm internal diameter) packed with 0.55 g of LiChrolut-EN resins. A first fraction is collected by the elution with 4 ml of pentane. A second one with 6 ml of a mixture pentane/dichloromethane (9:1) and a final fraction with 4 ml of dichloromethane. The first fraction is enriched in ethyl esters and some other non-polar compounds. The second fraction concentrates the alcohols and some volatile phenols, while the third is enriched in fatty acids, vanillin derivatives and some lactones. The recovery in the fractionation is complete. The profile obtained in the fractionation is very stable, and becomes distorted only when the column is loaded with an extract containing 80 mg of major volatiles (coming from more than 150 ml of wine). The fractionation of extracts from different wines showed that the performance of the process does not depend on the composition of the extract. Twenty-seven out of 32 studied compounds eluted reproducibly mainly in one fraction. The results suggest that the method can be applied as an aid for qualitative or quantitative analysis to any kind of organic extract as an alternative to liquid chromatography on silica-gel. 相似文献
965.
Águeda Sonseca Sandra Camarero‐Espinosa Laura Peponi Christoph Weder E. Johan Foster José M. Kenny Enrique Giménez 《Journal of polymer science. Part A, Polymer chemistry》2014,52(21):3123-3133
Polyesters based on polyols and sebacic acid, known as poly(polyol sebacate)s (PPS), are attracting considerable attention, as their properties are potentially useful in the context of soft‐tissue engineering applications. To overcome the drawback that PPSs generally display rather low strength and stiffness, we have pursued the preparation of nanocomposites based poly(mannitol sebacate) (PMS), a prominent example of this materials family, with cellulose nanocrystals (CNCs). Nanocomposites were achieved in a two‐step process. A soluble, low‐molecular‐weight PMS pre‐polymer was formed via the polycondensation reaction between sebacic acid and D‐mannitol. Nanocomposites with different CNC content were prepared by solution‐casting and curing under vacuum using two different profiles designed to prepare materials with low and high degree of crosslinking. The as‐prepared nanocomposites have higher stiffness and toughness than the neat PMS matrix while maintaining a high elongation at break. A highly crosslinked nanocomposite with a CNC content of 5 wt % displays a sixfold increase in Young's modulus and a fivefold improvement in toughness. Nanocomposites also exhibit a shape memory effect with a switch temperature in the range of 15 to 45 °C; in particular the materials with a thermal transition in the upper part of this range are potentially useful for biomedical applications. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 3123–3133 相似文献
966.
967.
Laura Trapiella-Alfonso Fanny d’Orlyé Anne Varenne 《Analytical and bioanalytical chemistry》2016,408(11):2669-2675
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970.
Ana M. Tarditi Noelia Barroso Agustín E. Galetti Luis A. Arrúa Laura Cornaglia María C. Abello 《Surface and interface analysis : SIA》2014,46(8):521-529
The surface properties of Ni/MgAl2O4 catalysts doped with Ce or Pr were analyzed by XPS after treatment in an inert and reductive atmosphere at 400 °C. The Ce‐promoted solids presented the Ce3+/Ce4+ couple on the surface even after treatment in a reductive atmosphere, H2(5%)/Ar. The promotion effect of Ce on these solids could be associated with their participation on the carbon deposition‐removal mechanism. Pr‐doped catalysts showed a very high concentration of Pr3+ under a reductive atmosphere and the redox behavior associated with the carbon removal could be partially inhibited or become slower. The size of the Ni0 particles after both an inert and a reductive atmosphere was estimated by XPS intensity ratio using the model proposed by Davis. The results obtained from the Davis model showed that an important increase occurred in Ni particle size after treatment in H2(5%)/Ar for the Pr‐promoted solids. The metal sintering under reductive atmosphere could be the reason for the higher loss of activity of the Pr‐doped solids under reforming conditions. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献