Chiral separation of enantiomers of amino acid derivatives by high-performance liquid chromatography on a norvancomycin-bonded chiral stationary phase

A novel norvancomycin-bonded chiral stationary phase (NVC-CSP) was synthesized by using the chiral selector of norvancomycin. The chiral separation of enantiomers of several dansyl-amino acids by high-performance liquid chromatography (HPLC) in the reversed-phase mode is described. The effects of some parameters, such as organic modifier concentration, column temperature, pH and flow rate of the mobile phase, on the retention and enantioselectivity were investigated. The study showed that ionic, as well as hydrophobic interactions were engaged between the analyte and macrocycle in this chromatographic system. Increasing pH of buffers usually improved the chiral resolution for dansyl--amino-n-butyric acid (Dns-But), dansyl-methionine (Dns-Met) and dansyl-threonine (Dns-Thr), but not for dansyl-glutamic acid (Dns-Glu) which contains two carboxylic groups in its molecular structure. The natural logarithms of selectivity factors (ln ) of all the investigated compounds depended linearly on the reciprocal of temperature (1/T), most processes of enantioseparation were controlled enthalpically. Interestingly, the process of enantioseparaton for dansyl-threonine was enthalpy-controlled at pH of 3.5, while at pH of 7.0, it was entropy-controlled according to thermodynamic parameters Δ_R,SΔH° and Δ_R,SΔS° afforded by Van’t Hoff plots. In order to get baseline separation for all the solutes researched, norvancomycin was also used as a chiral mobile phase additive. In combination with the NVC-CSP, remarkable increases in enanselectivity were observed for all the compounds, as the result of a “synergistic” effect.     

Synthesis and electrochemical properties of yttrium-doped LiMn<Subscript>0.98</Subscript>Y<Subscript>0.02</Subscript>O<Subscript>2</Subscript> for lithium secondary batteries

Yttrium-doped lithium manganese oxide (LiMn_0.98Y_0.02O₂) was prepared by ion exchange of lithium for sodium in NaMn_0.98Y_0.02O₂ precursors obtained by using rheological phase reaction method. This material had small particle size, which was composed of grain size of about 100 nm. Especially, LiMn_0.98Y_0.02O₂ delivered the initial discharge capacity of about 191 mA h g⁻¹ at room temperature when cycled between 2.0 and 4.4 V vs Li/Li⁺. Moreover, it showed an excellent cycling behavior, its specific capacity remained above 173 mA h g⁻¹ after 20 cycles, and the material did not transform into spinel structure during the electrochemical cycling according to the cyclic voltammograms and X-ray powder diffraction. The electrochemical results revealed that the doping of Y³⁺ improved the performance of LiMnO₂ considerably.     

TBP体系活度系数的测定和微扰理论的研究

在前人工作的基础上, 改进了液上空间气相色谱测活度系数的方法, 实验测定了TBP. 稀释剂和水形成的多个二元系、三元系和四元系的活度系数和密度. 选用的稀释剂有n-C_6H_(14)、n-C_7H_(16)、n-C_8H_(18)、C_6H_6、cy-C_6H_(12)、CCl_4和CHCl_3. 在Pierotti理论的基础上, 采用新的硬球作用表达式和径向分布函数, 并计及分子间的排斥能、色散能、取向能和诱导能, 建立了简单的活度系数模型, 并用于TBP和稀释剂体系的计算. 从二元系回归得到的分子参数较好地预测了三元系的活度系数.     

A study of a nonprimitive model for electrolyte solutions based on perturbation theory

The equation for the Helmholtz free energy for systems of small anisotropic molecules and ions is deduced by substituting the complete expression for various potential energies (including repulsive, dispersive, electrostatic, and induced energies) into the perturbation expansion. The equation is applied to pure water. The relative dielectric constant is set at unity. Based on the equal chemical potentials of equilibrated vapor and liquid phases, the molecular parameters of water are regressed from the densities of saturated vapor in the temperature range of 0 to 370°C. The ARD of regression is 1.16%. These parameters are used to predict the heat of vaporization and densities of saturated vapor and liquid phases of water in the same temperature range. The ARDs of prediction are 4.5% and 9.8%, respectively. The equation is used to correlate the osmotic coefficients of twelve 1:1 electrolyte solutions. The relative dielectric constant is set at unity. The parameters (Soft-sphere diameter and dispersive constant) of seven ions (Na⁺, K⁺, Rb⁺, Cs⁺, Cl^–, Br^–, and I^–) are obtained. The total average absolute deviation between calculated and experimental values of the osmotic coefficient is 0.041. The parameters of ions can keep constant in different systems.     

THE Py SCALE OF SOLVENT POLARITIES. SOLVENT EFFECTS ON THE VIBRONIC FINE STRUCTURE OF PYRENE FLUORESCENCE and EMPIRICAL CORRELATIONS WITH ET and Y VALUES

Abstract— Pyrene fluorescence spectra have been run in 62 solvents of widely differing solvent polarity. As has been noted previously, the intensity ratio of the first (the 0–0 band) and third bands in vibronic fine structure of these spectra are very sensitive to solvent polarity. These I ₁/ I ₃ values, however, are not sensitive to hydrogen bonding aspects of solvent-solute interactions. Correlations are reported with Winstein's Y values and with Dimrotb's E _T values. On this basis the I ₁/ I ₃ values for pyrene fluorescence are suggested as the basis for a new empirical scale of solvent polarity, called the Py scale, which offers certain conveniences over other scales of solvent polarity.     

A novel hexairon cluster with one disulfide and two Ph2PCS3− ligands

The title compound, hexadecacarbonylbis{μ₃‐[(diphenylphosphanyl)methanediidyl]sulfanido}‐μ₄‐disulfido(2−)‐hexairon(4 Fe—Fe), [Fe₆(C₁₃H₁₀PS)₂(S₂)(CO)₁₆], contains two inversion‐related [Fe₃(Ph₂PCS)(CO)₈] subclusters linked by an equatorial disulfide bond [S—S = 2.1490 (9) Å]. Each Ph₂PCS³⁻ ligand is coordinated to a triiron core in a μ₃‐κP:κ²C:κ²S fashion.     

N-heterocyclic carbene-catalyzed regio- and stereoselective hydrothiolation reaction of alkynes

N-heterocyclic carbenes (NHCs) have been utilized as Brønsted base to catalyze the hydrothiolation reaction between alkynes and thiols to produce the vinyl sulfides stereoselectively.     

The efficient in‐situ reduction and cyclization reaction of aromatic aldehyde, 1,3‐cyclopentanedione (tetronic acid), and nitro‐compound under SnCl2·2H2O‐THF medium

An efficient in‐situ reduction and cyclization reaction for the synthesis of pyrazolo[4,3‐f]quinoline, pyrazolo[3,4‐f]quinoline, and pyrazolo[3,2‐f]quinoline derivatives directly form 5‐nitroindazole, 6‐nitroindazole and 5‐nitroindole in the presence of SnCl₂·2H₂O was reported. Compared to traditional synthetic methods, this approach has the advantages of stable reagents, easy obtaining raw material, and high yields. In this research, SnCl₂·2H₂O is the efficient reducing agent for the in‐situ reduction and cyclization reaction of nitro‐compound. In addition, this process provided an alternative approach for the synthesis of target compounds.     

Analysis of a meshless solver for high Reynolds number flow

In this paper, the extension of an upwind least‐square based meshless solver to high Reynolds number flow is explored, and the properties of the meshless solver are analyzed both theoretically and numerically. Existing works have verified the meshless solver mostly with inviscid flows and low Reynolds number flows, and in this work, we are interested in the behavior of the meshless solver for high Reynolds number flow, especially in the near‐wall region. With both theoretical and numerical analysis, the effects of two parameters on the meshless solver are identified. The first one is the misalignment effect caused by the significantly skewed supporting points, and it is found that the meshless solver still yields accurate prediction. It is a very interesting property and is opposite to the median‐dual control volume based vertex‐centered finite volume method, which is known to give degraded result with stretched triangular/tetrahedral cells in the near‐wall region. The second parameter is the curvature, and according to theoretical analysis, it is found in the region with both large aspect ratio and curvature, and the streamwise residual is less affected; however, the wall‐normal counterpart suffers from accuracy degradation. In this paper, an improved method that uses a meshless solver for the streamwise residual and finite difference for wall‐normal residual is developed. This method is proved to be less sensitive to the curvature and provides improved accuracy. This work presents an understanding of the meshless solver for high Reynolds number flow computation, and the analysis in this paper is verified with a series of numerical experiments. Copyright © 2012 John Wiley & Sons, Ltd.