Chiral recognition by enantioselective liquid chromatography: Mechanisms and modern chiral stationary phases

An overview of the state-of-the-art in LC enantiomer separation is presented. This tutorial review is mainly focused on mechanisms of chiral recognition and enantiomer distinction of popular chiral selectors and corresponding chiral stationary phases including discussions of thermodynamics, additivity principle of binding increments, site-selective thermodynamics, extrathermodynamic approaches, methods employed for the investigation of dominating intermolecular interactions and complex structures such as spectroscopic methods (IR, NMR), X-ray diffraction and computational methods. Modern chiral stationary phases are discussed with particular focus on those that are commercially available and broadly used. It is attempted to provide the reader with vivid images of molecular recognition mechanisms of selected chiral selector–selectand pairs on basis of solid-state X-ray crystal structures and simulated computer models, respectively. Such snapshot images illustrated in this communication unfortunately cannot account for the molecular dynamics of the real world, but are supposed to be helpful for the understanding. The exploding number of papers about applications of various chiral stationary phases in numerous fields of enantiomer separations is not covered systematically.     

Author Index to Volume 33

A new compound floatation agent for graphite is described. It is very effective on the floatation of cryptocrystalline graphite. The structure and composition of the new floatation agent are studied by using Raman and infrared spectra.     

基于移动学习平台的物理化学混合教学模式探索与实践

移动学习以移动性、及时性、交互性、随时随地性等优势改变着学习方式。将基于网络教学平台的移动学习引入到物理化学的教学中，尝试形成“线上+线下”“课内+课外”的混合教学模式。实践表明：基于移动学习平台的混合教学模式调动了学生的积极性和自主性，提高了教学质量，增强了人才素质，受到了学生的普遍好评。     

基于多Agent的无线传感器网络分层融合框架研究

客户端/服务器（C/S）模式和移动代理（MA）模式是无线传感器网络中的两种最主要的计算模式,MA计算模式可以弥补C/S计算模式能量消耗大、延时长等方面的不足。为了更好的降低能量消耗和缩短网络中数据融合时间,提出一种基于多Agent的无线传感器网络分层融合框架。将无线传感器网络监测区域分层若干个区域,将每个小的监测区域分为簇头―sink和簇头―簇成员节点两层,由sink节点根据用户需求向每个监测区域派遣移动Agent并完成数据采集和数据融合。这种模式可以有效地缩短网络中数据融合时间和降低能量消耗。     

手性流动相添加剂法拆分氧氟沙星对映体的热力学研究

采用配位体金属离子交换剂作为手性流动相添加剂,以L-苯丙氨酸和硫酸铜溶液为手性配体流动相,考察了293~313K温度范围内,氧氟沙星对映体在C18高效液相色谱柱上拆分的热力学性质。结果表明,在实验范围内,随着温度的升高,对映体的保留时间、分离度和选择性因子均减少;用lnk′对1/T作图,得Van’t Hoff曲线具有良好的线性关系,相关系数R0.999。计算了氧氟沙星对映体在色谱柱分离的焓变、焓变差值和熵变差值等热力学参数。在实验温度范围内,氧氟沙星对映体满足︱△S,R△H0︱︱T△S,R△S0︱,说明手性拆分过程为焓控过程。     

Performance of new prototype packed columns for very high pressure liquid chromatography

The reduced heights equivalent to a theoretical plate (HETP) of naphtho[2,3-a]pyrene were measured at room temperature on two sets of new prototype columns designed to be used in very high pressure liquid chromatography (VHPLC). The mobile phase used was pure acetonitrile. The columns are 50, 100, and 150 mm long. Those of the first set are 2.1 mm I.D., those of the second set, 3.0 mm I.D. The performance of these new columns were compared to those of the first generation of VHPLC columns, commercially available in 2.1 mm I.D. The prototype and commercial columns behave similarly at low reduced linear velocities (ν<5$\nu <5$), when the heat effects are negligible. At high flow rates, the shorter prototype columns have a twice better efficiency and less steep C-branches than the commercial columns. In contrast, the C-branch of the 150 mm long prototype columns are slightly steeper than those of the commercial columns. The important contribution to the reduced HETP that is due to the heat effects at high flow rates can in part be accounted for by a band broadening model governed by a flow mechanism with the shortest prototype columns. The sole heat effects cannot, however, explain the mediocre reduced HETPs of the 2.1 and 3.0 I.D. 150 mm long prototype columns. It seems that radial heterogeneity of the flow rate of the long prototype columns is significantly larger than that of the short columns. The contribution of the packing heterogeneity adds up to that of the heat effects to yield a poor column efficiency when sub-2μm$\text{sub-}2\mu \text{m}$ are packed into thin, long column tubes.     

Analytical model for minority games with evolutionary learning

In a recent work [D. Campos, J.E. Llebot, V. Méndez, Theor. Popul. Biol. 74 (2009) 16] we have introduced a biological version of the Evolutionary Minority Game that tries to reproduce the intraspecific competition for limited resources in an ecosystem. In comparison with the complex decision-making mechanisms used in standard Minority Games, only two extremely simple strategies (juveniles and adults) are accessible to the agents. Complexity is introduced instead through an evolutionary learning rule that allows younger agents to learn taking better decisions. We find that this game shows many of the typical properties found for Evolutionary Minority Games, like self-segregation behavior or the existence of an oscillation phase for a certain range of the parameter values. However, an analytical treatment becomes much easier in our case, taking advantage of the simple strategies considered. Using a model consisting of a simple dynamical system, the phase diagram of the game (which differentiates three phases: adults crowd, juveniles crowd and oscillations) is reproduced.     

HPLC with polysaccharide chiral stationary phase in polar‐organic phase mode: Application to the asymmetric epoxidation of allylic alcohols

A simple and rapid HPLC method using a polysaccharide‐based chiral stationary phase (Chiralpak AD‐H) in polar‐organic phase mode has been developed for direct resolution of glycidyl nitrobenzoate (GNB) and 2‐methyl glycidyl nitrobenzoate (MGNB) enantiomers. ACN and methanol were used as mobile phase and the effects of the addition of ethanol and 2‐propanol as organic modifier in the mobile phase, flow rate and the column temperature were tested. The optimized conditions were: methanol/ethanol (80:20) at a flow rate of 0.9 mL/min and 40°C. Analysis time was ?13 min and the chiral resolution was ?2. The method was validated and resulted to be selective, precise and accurate. The method was found to be linear in 2–300 μg/mL range (R² >0.999) with an LOD nearly 0.5 μg/mL for four enantiomers. GNB and MGNB enantiomers were obtained by asymmetric epoxidation of allyl alcohol and 2‐methyl allyl alcohol, respectively, using chiral titanium–tartrate complexes as catalyst and dichloromethane as solvent after in situ derivatization of the intermediate glycidols derivatives. The quite simple and rapid validated method was applied successfully for direct determination of the enantiomeric excess (?90%) and yield obtained in real samples of asymmetric epoxidation of allylic alcohols without further purification, workup or solvent removal. The method provides a useful and value‐added tool for controlling the enantiomeric purity of the synthesized epoxides.     

进化博弈视角下移动服务商合作行为分析

基于进化博弈复制动态分析方法,建立移动服务商群体进化博弈模型,并对移动服务商合作行为进行分析。首先,扩展一般的进化博弈模型为成本分摊与收益共享的群体博弈模型,然后,探讨了服务商收益与惩罚力度不同大小关系下进化稳定策略。博弈分析结果表明,移动服务商群体进化博弈模型中,收益、成本与惩罚大小和群体初始比例等将直接影响博弈结果。合理的惩罚参数设置,能有效的规范服务商进化行为。