Enantioseparation Of Aromatic Dipeptides Using Carboxymethyl-β-Cyclodextrin Polymer As Chiral Selector By Capillary Electrophoresis

ABSTRACT

Chiral separation of peptides is of interest because of the different biological activity of enantiomers. In this report, several underivatized dipeptides with benzene moieties were optically resolved by employing carboxymethyl-β-cyclodextrin polymer(CM-β-CD polymer) as chiral selector. The effects of different cyclodextrin types, selector concentration, buffer pH, and organic additive were examined. Selector concentration and buffer pH played significant roles in resolution. Enantioseparation was found to be negatively influenced by adding the organic additive into running buffer and even completely lost at the organic additive content of 16%. It was also noted that the dipeptides with short chain in the vicinity of the second chiral carbon atom showed better chiral resolution by using CM-β-CD polymer than by using either carboxyethyl-β-CD or succinylated-β-CD. Simultaneous chiral separation of a mixture of DL-Ala-DL-Phe and DL-Leu-DL-Phe was also obtained using 27 mg/ml CM-β-CD polymer in the running buffer at pH5.12.     

(R)‐N,N,N‐Trimethyl‐2‐Aminobutanol‐Bis(Trifluoromethane‐Sulfon)Imidate Chiral Ionic Liquid Used as Chiral Selector in HPCE,HPLC, and CGC

Abstract

In this work, the (R)‐N,N,N‐trimethyl‐2‐aminobutanol‐bis(trifluoromethanesulfon)imidate chiral ionic liquid was first used in chromatography and exhibited a excellent chiral recognition ability in high performance capillary electrophoresis (HPCE), high performance liquid chromatography (HPLC), and capillary gas chromatography (CGC), which also showed for the first time that chrial ionic liquid was an effective chiral selector in HPCE and HPLC. The compounds that have been separated using this chiral ionic liquid at least included alcohol, amine, acid, and amino acid, et al. enantiomers. As the chiral ionic liquid can be easily synthesized from relatively inexpensive materials, it should have a great potentiality for chiral separation in chromatographic science.     

Doubly tethered tertiary amide linked and ionically bonded diproline chiral stationary phases

Oligoproline chiral stationary phase (CSP) is a new class peptide chiral stationary phase. Many proline chiral stationary phases with different proline chain lengths and linkers have been prepared and evaluated. However, the doubly tethered and ionic type linkers have not been adequately investigated. In this study, covalently and ionically bonded chiral stationary phases with doubly tethered linker were prepared and characterized. The new covalently bonded doubly tethered diproline CSP was applied successfully to resolve various enantiomers of acidic, basic, and neutral compounds with phenyl, naphthyl, anthryl, or similarly sized groups. The enantiorecognition performances of singly and doubly tethered diproline CSPs were comparable. Variation of the type and content of organic modifiers in hexane or heptane mobile phase showed that the branch alcohols such as 2‐propanol and 2‐butanol, 1,2‐dichloroethane, methyl tert‐butyl ether, and ethyl acetate in the mobile phase enhanced chiral separation. End‐capping on doubly tethered diproline CSP did not always improve the separation factor and resolution. Due to the rigid structure of the double tether, the enantioseparation ability of ionically bonded diproline CSP was well expressed to some analytes.     

Evaluation of the enantioselectivity of glycogen-based dual chiral selector systems towards basic drugs in capillary electrophoresis

Several chiral reagents including cyclodextrins (CDs) and derivatives, crown ethers, proteins, chiral surfactants and polymers have been involved in dual selector systems for enantioseparation of a series of chiral compounds by capillary electrophoresis (CE). In comparison to the chiral reagents above-mentioned, there is no report concerning the use of polysaccharides in dual chiral CE system. In this paper we first investigate the enantioselectivity of polysaccharide-based dual selector systems towards some chiral drugs. During our recent work, glycogen belonging to the class of branched polysaccharides has been used as a novel chiral selector in CE. In this study, three glycogen-based dual chiral CE systems have been established for enantiomeric separations of several racemic basic drugs consisting of duloxetine, cetirizine, citalopram, sulconazole, laudanosine, amlodipine, propranolol, atenolol and nefopam. These three dual systems combined glycogen (neutral polysaccharide) with chondroitin sulfate A (CSA, ionic polysaccharide), β-CD and HP-β-CD, respectively. It was found that the dual system of glycogen/CSA exhibited good enantioselective properties toward the tested drugs. More importantly, compared to the single selector systems, synergistic effect was observed when glycogen was used with CSA for most of the analytes. This indicated the enhancement of enantioseparation observed for these analytes in glycogen/CSA system might be due to some favorable interaction effects between glycogen and CSA. Moreover, in order to evaluate the stereoselectivity of glycogen/CSA, the influences of buffer pH and selector concentration on enantioseparation of the studied drugs were also investigated.     

电磁波在周期性结构星型波导中的传输特性

提出一种新型波导结构,在二维周期性结构平板介质中引入两条线缺陷形成星型波导,在波导中加入介电常数不同的介质点阵形成缺陷,采用时域有限差分法(FDTD)对该结构的导波特性进行数值模拟。计算结果表明,该星型结构波导的透射频谱比入射波频谱的带宽更窄,说明此结构具有窄带滤波作用。当改变该星型波导中缺陷结构介电常数取值时,透射过该波导的电磁波中心频率随缺陷介质介电常数的增大而减小,呈良好的线性关系。当改变中心介质柱直径时,透射电磁波的中心频率随缺陷介质柱直径的增大而减小。这种周期性结构星型波导可作为一种窄带滤波和选频器件。     

随机二阶多值周期问题解的存在性

本文研究了随机二阶多值周期问题解的存在性,在非常一般的假定下建立了凸和非凸问题解的存在性定理,并给出了在随机周期反馈控制系统中的应用．     

Recent developments in chiral analysis of β‐blocker drugs by capillary electromigration techniques

The latest developments in chiral analysis of β‐blocker drugs by capillary electromigration techniques are reviewed in this article. Following the previous review by Aturki et al. [Electrophoresis 2011, 32, 2602–2628], this review includes the papers published during the period from January 2011 to December 2013. During this time, some novel chiral selectors were reported and applied to improve the enantioseparation of β‐blocker drugs and structurally related compounds. These chiral selectors include CDs and their derivatives, macrocyclic antibiotics, tartrate complexs, the monolithic molecularly imprinted polymer, and the polymeric surfactants. In addition, this article summarizes the methodological improvements for enhancing sensitivity in chiral analysis of β‐blockers and structurally related compounds by CE. The involved authors described the use of online sample preconcentration techniques to increase the detection sensitivity in the enantiomeric analysis of a broad range of samples.     

属性相关选择和AdaBoost算法在入侵检测中的应用

入侵事件的识别是入侵检测系统的关键,入侵事件的识别是一个网络数据的分类问题。通过基于相关的属性选择算法,选择出相关度高的属性子集,去除冗余度高的属性,在选择的属性子集上,使用AdaBoost算法对网络数据分类,识别入侵事件。实验结果表明,在选用的实验数据上,基于相关的属性选择算法和AdaBoost算法结合使用,提高了分类正确率和入侵事件的检出率,降低了入侵事件的误报率。     

双四选一数据选择器74HC153的级联分析及研究

将多片双四选一数据选择器74HC153级联,再附加2线—4线译码器74HC139构成不同的数据选择器,能够灵活、有效地扩大数据选择器的使用范围。不同的74HC153进行级联时,任何时候只允许一个数据选择器工作,数据选择器的输出状态由地址输入端决定。