Evaluation of newly synthesized and commercially available charged cyclomaltooligosaccharides (cyclodextrins) for capillary electrokinetic chromatography

Negatively charged cyclodextrins: Synthesis and applications in chiral analysis-A review

The negatively charged cyclodextrins (CDs) play an important role in chiral analysis due to the additional electrostatic effect beyond the host-guest inclusion, especially in enantioanalysis of positively charged and electrically neutral analytes. This review presents recent advances in application of anionic CDs for enantioanalysis during the past five years. Firstly, the synthesis approaches of random substitution and single isomers of anionic CDs are briefly discussed. The main part focuses on the chiral analysis using anionic CDs in various analytical techniques, including capillary electrophoresis, high-performance liquid chromatography, capillary electrochromatography, counter current chromatography, nuclear magnetic resonance, etc. Particular attention is given to the capillary electrophoresis application since charged CDs could be used as a carrier of enantiomers by virtue of their self-mobility and offer an easy adjustment of the enantiomer migration order. Finally, future opportunities are also discussed in the conclusion of this review.

Simultaneous determination of dihydroxybenzene and phenylenediamine positional isomers using capillary zone electrophoresis coupled with amperometric detection

In general capillary zone electrophoresis (CZE) separation models, o-, m-, and p-phenylenediamine isomers can be separated in a weak acidic running buffer for their pK(a) values being 4.52, 5.64, 6.04, respectively, while o-, m-, and p-dihydroxybenzene isomers can be separated in a weak basic buffer for their pK(a) values being 9.40, 9.40 and 10.04, respectively. So, it is hard to find a suitable running buffer at a fixed pH in normal CZE for simultaneous separation of these two groups of positional isomers. In this paper, a novel method based on alternately running two different pH buffers in CZE coupled with amperometric detection (CZE-AD) was designed to simultaneously determine these two groups of positional isomers. It is found that when two different pH running buffers were employed alternately under appropriate order and time, the six analytes could be separated perfectly in less than 20 min and the detection limits were as low as 10(-7) mol/L. Furthermore, the effects of working electrode potential, pH and concentration of running buffer, separation voltage and injection time on CZE-AD were investigated. Experimental results demonstrated that the introduced method was practical to simultaneously determine two groups of positional isomers with different pK(a) and had some advantages of high sensitivity, good repeatability and small sample requirement.

Analysis of carbohydrates and glycoconjugates by matrix-assisted laser desorption/ionization mass spectrometry: An update for 2003-2004

This review is the third update of the original review, published in 1999, on the application of matrix-assisted laser desorption/ionization (MALDI) mass spectrometry to the analysis of carbohydrates and glycoconjugates and brings the topic to the end of 2004. Both fundamental studies and applications are covered. The main topics include methodological developments, matrices, fragmentation of carbohydrates and applications to large polymeric carbohydrates from plants, glycans from glycoproteins and those from various glycolipids. Other topics include the use of MALDI MS to study enzymes related to carbohydrate biosynthesis and degradation, its use in industrial processes, particularly biopharmaceuticals and its use to monitor products of chemical synthesis where glycodendrimers and carbohydrate-protein complexes are highlighted.

Surface-enhanced Raman spectroscopy substrates created via electron beam lithography and nanotransfer printing

The development of quantitative, highly sensitive surface-enhanced Raman spectroscopy (SERS) substrates requires control over size, shape, and position of metal nanoparticles. Despite the fact that SERS has gained the reputation as an information-rich spectroscopy for detection of many classes of analytes, in some isolated instances down to the single molecule detection limit, its future development depends critically on techniques for nanofabrication. Herein, an unconventional nanofabrication approach is used to produce efficient SERS substrates. Metallic nanopatterns of silver disks are transferred from a stamp onto poly(dimethysiloxane) (PDMS) to create nanocomposite substrates with regular periodic morphologies. The stamp with periodic arrays of square, triangular, and elliptical pillars is created via electron beam lithography (EBL) of ma-N 2403 resist. A modified cyclodextrin is thermally evaporated onto the stamp to overcome the adhesive nature of the EBL resist and to function as a releasing layer. Subsequently, Ag is physically vapor deposited onto the stamp at a controlled rate and thickness and used directly for nanotransfer printing (nTP). Stamps, substrates, and the efficiency of the nTP process were explored by scanning electron microscopy. Transferred Ag nanodisk-PDMS substrates are studied by SERS using Rhodamine 6G as the probe analyte. There are observed optimal conditions involving both Ag and cyclodextrin thickness. The SERS response of metallic nanodisks of various shapes and sizes on the original stamp is compared to the corresponding nTP created substrates with similar trends observed. Limits of detection for crystal violet and Mitoxantrone are approximately 10(-8) and 10(-9) M, respectively. As an innovative feature of this approach, we demonstrate that physical manipulation of the PDMS post-nTP can be used to alter morphology, e.g., to change internanodisk spacing. Additionally, stamps are shown to be reusable after the nTP process, adding the potential to scale-up regular morphology substrates by a stamp-and-repeat methodology.

Investigation of β-CD-derivatized erythromycin as chiral selector in CE

A novel water-soluble beta-CD-derivatized erythromycin (EM) was synthesized and used as an effective chiral selector for the resolution of chiral compounds in CZE. The purpose of substitution at the primary hydroxyl site of beta-CD with 1-oxygen-2,3-epoxypropane is to produce a compound having functions of both beta-CD and EM. beta-CD-derivatized EM exhibited excellent enantioselectivities compared with single beta-CD and EM for chiral separation in CE. We also investigated the influence of pH and concentration of BGE, concentration of chiral selector, applied potential, and organic modifier on chiral compounds' separation.

Advances in chiral separation using capillary electromigration techniques

This review gives an overview of recent developments in CZE, EKC, and CEC covering the literature since the year 2004. Since there appeared a special issue on applications, this review focuses on the progress in electromigration techniques and new methodological developments. New techniques, new chiral selectors as well as new chiral stationary phases for CEC are discussed.

Recent advances in pharmaceutical applications of chiral capillary electrophoresis

This review article summarizes developments and applications of chiral capillary electrophoresis (CE) in the pharmaceutical field published from January 2004 to June 2005. Due to the tremendous number of publications, this article is aimed to focus on major developments in chiral separations and some selected applications rather than to provide a descriptive overview of all published papers. Valuable information is also collected from several excellent reviews published during this period. Developments are classified according to CE modes, namely capillary zone electrophoresis (CZE), micellar electrokinetic capillary chromatography (MEKC), microemulsion electrokinetic chromatography (MEEKC). In the CZE section, different types of chiral selectors including cyclodextrins, oligo- and polysaccharides, crown ethers, macrocyclic antibiotics, ligand exchange systems and proteins are described. Nonaqueous capillary electrophoresis is also included in this section. Coupling CE to MS is discussed in a separate part, followed by a summary of selected pharmaceutical applications of enantioselective CE. Finally, some conclusions are drawn and prospects of CE in chiral analysis are also drafted.

Capillary zone electrophoretic chiral discrimination using 6-O-(2-hydroxy-3-trimethylammoniopropyl)-β-cyclodextrin as a chiral selector

A charged highly water-soluble CD derivative, 6-O-(2-hydroxy-3-trimethylammoniopropyl)-beta-CD (herein noted as 6-HPTMA-beta-CD) was synthesized and successfully used as a chiral selector for enantiomeric separation of some acidic compounds by CZE in an uncoated capillary. Substitution with 2-hydroxy-3-trimethylammoniopropyl groups at the primary hydroxyl group of the CD was aimed at influencing the magnitude and selectivity of analyte-CD interactions. The behavior of 6-HPTMA-beta-CD was compared with that of the commercially available quaternary ammonium-beta-CD (QA-beta-CD) under the same separating conditions. The experiments were carried out using a BGE consisting of 50 mM phosphate in the pH range of 4-6 by adding a relatively low concentration of chiral selector (less than 10 mM). The effects of the concentration of CD and the pH of the electrolyte on the resolution of these compounds were studied.

Recent advances in chiral separation principles in capillary electrophoresis and capillary electrochromatography

This review summarizes recent developments in chiral separation in capillary zone electrophoresis (CZE), electrokinetic chromatography (EKC), and capillary electrochromatography (CEC) covering literature published since the year 2000. New chiral selectors and innovative approaches for CE and CEC are introduced. Recent progress in column technology for CEC is highlighted and the development of new chiral stationary phases is discussed. This review is not dedicated to list applications but will focus on new developments.

Evaluation of newly synthesized derivative of cyclodextrin for the capillary electrophoretic separation

A highly water-soluble new cyclodextrin (CD) derivative 2-O-acetonyl-2-O-hydroxypropyl-beta-CD (2-AHP-beta-CD) was synthesized and tested as an effective chiral selector for the capillary zone electrophoretic resolution (Rs) of several basic and acidic analytes. The primary purpose of the research was to explore the capability of the 2-AHP-beta-CD as chiral selectors on comparison with the neutral CDs such as beta-CD, DM-beta-CD and HP-beta-CD. Substitution with 2-O-acetonyl-2-O-hydroxypropyl group at the secondary hydroxyl sites of the CD is aimed at influencing the magnitude and selectivity of analyte-CD interactions. The chiral resolution was strongly influenced by the concentration of the CDs and buffer pH. 2-AHP-beta-CD showed the best enantiomer resolution properties among the tested compounds, while the other CDs showed inferior or no performances at all.