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101.
Proline-derived N-sulfonylcarboxamides efficiently catalyze the asymmetric Mannich reaction of cyclic ketones with N-(p-methoxyphenyl)-protected iminoglyoxylate. Both classical organic solvents and ionic liquids were used as the reaction media. With cyclohexanone, the reaction proceeded with high enantioselectivity (99% ee). Enamine intermediates were investigated by DFT calculations. 相似文献
102.
Liquid explosives pose a threat to security on airplanes and other public places, since they can easily be concealed as benign
liquids. A detector, able to quickly identify liquids, would increase the possibility to detect such threats and speed up
security checks. As a step towards a long-term goal to develop a liquid explosive detector, we have constructed an experimental
setup based on a low-cost 1.1 T permanent magnet with huge static magnetic field gradient of 4.8 T/m, which allows us to measure
proton relaxation times T
1 and T
2 and the self-diffusion coefficient D in liquid samples in a thin slice excited by radio-frequency pulses. We have developed a simple model in order to explain
diffusion-enhanced non-exponential magnetization recovery in inversion recovery T
1 experiment in this setup. Measuring a wide variety of liquid samples, we have demonstrated that it is possible to discriminate
between the liquids based solely on these parameters. We discuss further improvements to the detection method, among those
the choice of magnetic field, based on the fast field-cycling measurements. 相似文献
103.
Toma Galaon Dan-Florin Anghel Victor David Hassan Y. Aboul-Enein 《Chromatographia》2013,76(23-24):1623-1630
Non-linear van’t Hoff plots were observed for several benzodiazepines over the usual temperature interval used in RP-LC (10–60 °C), when acetonitrile was added in the mobile phase. Such deviation from linearity was not observed when methanol or isopropanol was added to the mobile phase. Polynomial regressions were applied to fit the experimental data when acetonitrile was used as organic additive in mobile phase. The second-order polynoms may allow finding out the maximum retention depending on temperature, which can be within or out of the normal temperature range used in RP mechanism. A thermodynamic model deriving from the partition of two or more tautomers of the same analyte was proposed to explain this deviation from linearity of van’t Hoff plots. 相似文献
104.
Abstract This paper deals with the spectroelectrochemical characterization of the RuIII/II and N0+/0 oxidation states of the trans-[Ru(NO)(dmgH)2Cl] complex (dmgH = dimethylglyoximate ion). The cyclic voltammograms of the complex in acetonitrile solution exhibited a reversible wave at -0.09 V versus SHE, and two less intense waves at 1.19 and 1.41 V. Visible-UV spectra were recorded at -0.4 and 1.5 V, however, the absorption bands collapsed into a single tail, providing little information on the redox states involved. In contrast, in the FTIR measurements at -0.4 V, the v(NO) peak shifted from 1878 to 1855cm?1, without changing the vibrational peaks of the dmgH ligand, indicating an electrochemical process involving the NO+/0 redox couple. At 1.5 V, the changes in the vibrational peaks of the NO and dig lagans indicated a redox process associated with the RuIII/II redox'couple. The existence of an open and a cyclic hydrogen bridged configuration was proposed, in order to explain the occurrence of two electrochemical waves at positive potentials. 相似文献
105.
The aim of this paper was to obtain the quantitative estimation of the W0/WT (initial electric energy/atmospheric parameter of a surrounding medium) ratio for CG lightnings initiated with a stepped leader process. The results of analytical and numerical models show that the W0/WT ratio for CG lightnings spans the range of approximately two orders of magnitude 20 ≤ W0/WT ≤ 2000. The results also suggest that CG lightnings differ significantly from small-scale discharges in the laboratories: the thundercloud CG lightnings occur at considerably lower initial electric energy, higher atmospheric parameter of the surrounding medium or a combination of both. 相似文献
106.
Conversion of Pomacea lineate shells into hydroxyapatite (HA) bioceramic materials was investigated by their in vitro treatment with phosphate solutions, at room temperature. Confocal Raman microscopy revealed that the conversion proceeds at distinct rates through the nacreous or periostracum sides of the shell. The conversion can be accelerated using powdered samples, yielding biocompatible materials of great interest in biomedicine. 相似文献
107.
For a connected finite graph G and a subset V0 of its vertex set, a distance-residual subgraph is a subgraph induced on the set of vertices at the maximal distance from V0. Some properties and examples of distance-residual subgraphs of vertex-transitive, edge-transitive, bipartite and semisymmetric graphs are presented. The relations between the distance-residual subgraphs of product graphs and their factors are explored. 相似文献
108.
109.
Seventeen organocatalyts were tested for their ability to catalyst the addition of thiophenols to chalcones in [bmim]PF6. The products were isolated in high yield after a short reaction time, but no stereoselectivity was observed. The reactions also proceeded (without any stereoselectivity) in four other ionic liquids. In contrast, 16% and 26% ee were observed when L-proline and cinchonine, respectively, were used as the catalysts in CH2Cl2. Addition of thiophenols is also catalysed by HCl, as well as D-mandelic and L-tartaric acids. Addition of thiophenols to chalcones also occurred in neat ionic liquids, without any additional catalyst, but the rate of the reaction depended considerably on the structure of ionic liquid. The scope of the non-catalysed reaction in ionic liquids was tested by the reactions of 5 different thiols and 3 different alpha-enones. 相似文献
110.
Toma Albu 《Journal of Number Theory》2003,99(1):222-224
This note presents corrections and additions to my paper (J. Number Theory 41 (1992) 322-358). 相似文献