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991.
Massimo Del Bubba Leonardo Checchini Luciano Lepri 《Analytical and bioanalytical chemistry》2013,405(2-3):533-554
The current state of chiral separations by thin-layer chromatography using chiral stationary phases is reviewed. Both stationary phases essentially constituted by the chiral selector and those obtained by the impregnation of achiral plates with appropriate chiral selectors are described. Particular attention is paid to commercial and non-commercial cellulose and cellulose-derivative plates, as well as commercially available Chiralplate?, which are currently the most widely used. Some of the most important results obtained to date are reported and discussed; the examples provided illustrate the very wide range of structurally different solutes that can be readily resolved into their enantiomers by planar chromatographic methods. Special attention is paid to the discussion of the retention and resolution factors that influence chiral discrimination. The quantitative analysis of enantiomers is also discussed, especially from the point of view of determination of enantiomeric purity. 相似文献
992.
993.
994.
Raffaella Puliti Carlo A. Mattia Alessia De Fazio Maria R. Ghiara Lelio Mazzarella 《Acta Crystallographica. Section C, Structural Chemistry》2001,57(12):1447-1449
The title compound, (3R,4S,8R,9S)-cinchoninium (2R,3R)-tartrate tetrahydrate, C19H23N2O+·C4H5O6−·4H2O, is a hydrated salt of cinchonine. In the cinchoninium cation, the geometry around the quinuclidinic N atom is typical of a protonated N atom, and the bond lengths and angles in the tartrate moiety clearly indicate the mono-ionized form. The relative orientation of the quinoline and quinuclidine systems is that most frequently observed in structures of cinchona salts and corresponds to one of the energy minima calculated for this type of molecule in the gas phase. An extended network of intermolecular hydrogen bonds spreads parallel to the bc plane separating apolar layers. 相似文献
995.
Ruth Meléndrez Alberto Alarcón Gloria Del Angel Ricardo Gómez 《Reaction Kinetics and Catalysis Letters》2000,70(1):113-118
o-Xylene and carvone hydrogenation on supported Pd on exchanged Y-zeolites was done. A controlled selectivity of hydrogen stereoaddition (cis- and trans-) in o-xylene and a large control of the multiple hydrogen addition in carvone were obtained. These effects were achieved by controlling the exchanged Y zeolites acidity. 相似文献
996.
Tjark H. Meyer Ramesh C. Samanta Antonio Del Vecchio Lutz Ackermann 《Chemical science》2021,12(8):2890
Manganaelectro-catalyzed azidation of otherwise inert C(sp3)–H bonds was accomplished using most user-friendly sodium azide as the nitrogen-source. The operationally simple, resource-economic C–H azidation strategy was characterized by mild reaction conditions, no directing group, traceless electrons as the sole redox-reagent, Earth-abundant manganese as the catalyst, high functional-group compatibility and high chemoselectivity, setting the stage for late-stage azidation of bioactive compounds. Detailed mechanistic studies by experiment, spectrophotometry and cyclic voltammetry provided strong support for metal-catalyzed aliphatic radical formation, along with subsequent azidyl radical transfer within a manganese(iii/iv) manifold.The merger of manganese-catalyzed C–H functionalization with electrosynthesis enabled C(sp3)–H azidation devoid of chemical oxidants or photochemical irradiation. Detailed mechanistic studies are supportive of a manganese(iii/iv) electrocatalysis. 相似文献
997.
Belén García Jesús S. Pérez Del Río Jaume Llibre 《Rendiconti del Circolo Matematico di Palermo》2006,55(3):420-440
In this work we classify the phase portraits of all quadratic polynomial differential systems having a polynomial first integral.
IfH(x, y) is a polynomial of degreen+1 then the differential systemx′=−∂H/∂y,y′=∂H/∂x is called a Hamiltonian system of degreen. We also prove that all the phase portraits that we obtain in this paper are realizable by Hamiltonian systems of degree
2. 相似文献
998.
We give sufficient conditions on Banach spaces X and Y so that their projective tensor product X ⊗π
Y, their injective tensor product X ⊗ɛ
Y, or the dual (X ⊗π
Y)* contain complemented copies of ℓp. 相似文献
999.
Pt-Sn was supported on titania and silica, and the resulting interactions between the components in prepared samples and the resulting interactions between the components before and after treatment with hydrogen were characterized by Mössbauer spectroscopy, X-ray diffraction, Rietveld refinement, high-resolution transmission electron microscopy (HRTEM) and catalytic tests data. Results show the presence of Pt and SnO2 after calcinations, and Pt3Sn, PtSn and PtSn3 after reduction. Rietveld analysis shows that some Ti4+ are replaced by Sn4+ atoms in the titania structure. Finally, HRTEM and the practically absence of activity observed confirms that metallic platinum is encapsulated. 相似文献
1000.
In this paper, we investigate the convergence of empirical processes for a class of interacting particle numerical schemes arising in biology, genetic algorithms and advanced signal processing. The Glivenko–Cantelli and Donsker theorems presented in this work extend the corresponding statements in the classical theory and apply to a class of genetic type particle numerical schemes of the nonlinear filtering equation. 相似文献