Enantiomer separation by CEC——Enantiomer separation by packed-capillary electrochromatography

Three chiral compounds were successfully separated in a short time with two enantiomer separation models on packed-capillary electrochromatography (CEC). (i) 75 μm I.D. capillaries were packed with 5 μm β-cyclodextrin (β-CD) chiral stationary phase (CSP). Effects of voltage, pH and concentration of organic modifier on electroosmotic flow (EOF) and chiral separations were investigated systematically. Enantiomers of a neutral compound (benzoin) and a neutral drug (mephenytoin) were separated within a short time with high efficiency. Efficiency of 32 000 theoretical plates per meter and resolution (R_s) of 1.42 were achieved for enantiomers of benzoin using a βCD packed column with 6.2 cm packed length. Efficiency of 45 000 theoretical plates per meter and R_s of 3.40 were obtained for enantiomers of mephenytoin. Especially, the enantiomer separation of mephenytion was performed in just 3.4 min with R_s of 2.60. (ⅱ) 75 μm I.D. capillary was packed with octadecylsilica particles (ODS). Chiral separat     

Optical resolution of racemic stilbenediamine using N*-chiralortho-palladated matrix

Optical resolution of racemic stilbenediamine (Stien) was performed by recrystallization of its diastereomeric adducts withortho-palladated(S)-N-isopropyl-α-methylbenzylamine. The less soluble (S _C R _N′,SS) diastereomer was stuided by X-ray diffraction analysis. It was established that the crystal of this diastereomer consists of dimers formedvia association of two molecules of the mononuclear cationic complex with an additional molecule of free diamine of the same absolute configuration. The association occurs through a system of hydrogen bonds and weak agostic interactions. The association occurs through a system of hydrogen bonds and weak agostic interactions. Based on the X-ray diffraction data, the procedure was improved for the resolution of stilbenediamine due to the more profitable use of theortho-palladated reagent. The Stien/Pd ratio in the diastereomer isolated was inceased up to 3∶2. The conformational features of the complex are discussed on the basis of¹H NMR spectroscopy data. The preliminary results were reported previously, see Ref. 1. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 184–195, January, 1999.     

Use of immobilized amyloglucosidase as chiral selector in chromatography. Control of enantioselective retention and resolution in liquid chromatography

Summary Several mobile phase parameters were investigated for controlling enantioselective retention and resolution on a chiral stationary phase made in-house. The chiral selector was the enzyme amyloglucosidase, which was immobilized onto a silica support via reductive amination. The influences of the mobile phase pH, concentration and type of uncharged organic modifier, ionic strength and column temperature on enantios-electivity were studied. The analysis time for resolving enantiomers could be adjusted with only a minor decrease in enantioselectivity by using a high ionic strength mobile phase buffer. This indicated a retention mechanism involving ion-exchange interactions. It was further confirmed by the decreasing enantioselectivity of amines when using a mobile phase pH below the isoelectric point of the native protein. Interesting effects were observed when the organic modifier concentration was increased and also when the column temperature was raised. Both retention and enantioselectivity increased with increasing concentration of 2-propanol in the mobile phase. Examples are given where both enantioselectivity and retention increased with increasing column temperature. Thermodynamic studies were performed to calculate the entropy and enthalpy constants. The results showed that, depending on mobile phase composition, the enantioselective retention may be caused by differences in entropy or enthalpy.     

Solving triangular algebraic systems by means of simultaneous iterations

Our aim in this paper is to extend a variant of the Weierstrass method for the simultaneous computation of the solutions of a triangular algebraic system of equations. The appropriate tools are the symmetric functions of the roots of a polynomial. Using these symmetric functions we give another equivalent formulation for the search of all the roots of a triangular algebraic system. Using the latter formulation our method consists in solving a more simple system (where partial degrees of all the equations do not exceed 1) by Newton’s method. The quadratic convergence of our method is an immediate consequence of Newton’s method and need not be proved explicitly. This revised version was published online in June 2006 with corrections to the Cover Date.     

Lead zirconate titanate cantilever for noncontact atomic force microscopy

Noncontact atomic force microscopy with frequency modulation detection is a promising technique for surface observation with true atomic resolution. The piezoelectric material itself can be an actuator and sensor of the oscillating probe simultaneously, without the need for additional electro-mechanical transducers or other measurement systems. A vertical resolution of 0.01 nm rms has been achieved using a microfabricated cantilever with lead zirconate titanate thin film in noncontact mode frequency modulation detection. The cantilever also has a sharpened pyramidal stylus with a radius of about 10 nm for noncontact atomic force microscopy.     

双层飞行时间探测器(TOF)的性能研究

利用BC408塑料闪烁体直接耦合R2490–05高抗磁光电倍增管,组成双层飞行时间探测器.通过2GeV的π–束流测量,结果表明其本征时间分辨(标准偏差)≤50ps.利用该探测单元组成的飞行时间探测器系统,以其时间性能、结构、技术成熟和价格的优势,可以应用到τ–c工厂的带电粒子鉴别系统上.     

5.6 Cellulose acetate in separation technology

Cellulose acetate has been utilized in a variety of separation and purification processes. In membrane separation, cellulosics, in particular cellulose acetate, have played important roles. Hemodialysis and desalination are the established fields where acetate membranes have been applied. Recently, a new application, that is the purification of drinking water, is growing. The history of cellulosic membranes, preparation of acetate membranes, and applications will be reviewed. Cellulose acetate is also useful in chromatography and related separation technologies. These application will also be reviewed and the relationship between the superstructure of cellulose triacetate and its adsorptive behavior is briefly mentioned.     

高效高分辨率大面积透射光栅谱仪特性的理论分析

为提高透射光栅谱仪对激光等离子体Ｘ光源的收集效率的光谱分辨同铲高分辨率大面积航向光栅光谱仪。该谱仪由轮胎镜、无支撑高线密度光栅和软Ｘ光ＣＣＤ相机组成。应用部分相干光衍射理论,研究了该谱仪成偈面上的光强分布和光谱分辩率,在１．４～１２ｎｍ的摄谱范围内光 人发辨率为０．０５ｎｍ,与实验符合得很好。由于其高效率,该谱仪尤其适用于超短飞秒脉冲激光产生等离子体的实验研究。     

核心素养视域下化学学科知识的教学困境及消解策略

目前教育正在迈入核心素养的时代。核心素养为本的知识教学引发了很多教师的不适。需要对课堂教学与知识教学、核心素养和知识教学等关系进行梳理和理解。结合“金属钠及其化合物”内容,阐述了化学教学中存在的知识教学困境主要包括:知识点选择困境、包含知识的情境选择困境和训练反馈练习选择困境。提出教学困境的消解策略有:选择具有培养学生关键能力和必备品格的核心知识;创造出有利于知识学习的教学情境;充分发挥知识学习过程的引领作用和构建以促进学生意义启迪旨趣的知识教学。     

Crystallographic shear defect in molybdenum oxides: Structure and TEM of molybdenum sub‐oxides Mo18O52 and Mo8O23

Molybdenum trioxide and molybdenum sub‐oxides are of great interests in catalysis due to their utilities as model system to elucidate the correlations between the structure and the catalytic performance. The suboxides are usually an intermediate phase during catalytic reaction in which the lattice oxygen is involved. We show the identification of the two common molybdenum sub‐oxides Mo₁₈O₅₂ and Mo₈O₂₃, derived from MoO₃ by crystallographic shearing (CS), by means of electron diffraction and High‐Resolution Transmission Electron Microscopy (HRTEM) in combination with image simulation. The coincidence of simulated electron diffraction patterns and high‐resolution images with the experimental ones indicates the feasibility of CS structure determination by these techniques.