Dodecyl thioglycopyranoside sulfates: novel sugar-based surfactants for enantiomeric separations by micellar electrokinetic capillary chromatography

Four novel chiral anionic surfactants having carbohydrate hydrophilic heads, sodium n-dodecyl 1-thio-beta-D-glucopyranoside 6-hydrogen sulfate (6-betaGlcD), sodium n-dodecyl 1-thio-beta-L-glucopyranoside 6-hydrogen sulfate (6-betaGlcL), sodium n-dodecyl 1-thio-beta-L-fucopyranoside 3-hydrogen sulfate (3-betaFucL), and sodium n-dodecyl 1-thio-alpha-L-rhamnopyranoside 3-hydrogen sulfate (3-alphaRhaL), were synthesized by selective sulfation of the corresponding thioglycosides. Their CMC determined by fluorescence using pyrene as a probe in water was 1.3-2.7 mM. These surfactants found to be useful as chiral selectors for enantiomeric separation by MEKC. The enantiomeric separation was optimized with respect to pH, buffer concentration, and surfactant concentration. Under the optimized conditions (50 mM phosphate buffer at pH 6.5, 30 mM surfactant, 20 kV), the enantiomeric separations of five dansylated amino acids (Dns-AAs) were achieved within approximately 20 min with the migration order of Val相似文献   

Cationic double-chained surfactant as pseudostationary phase in micellar electrokinetic capillary chromatography for drug separations

The cationic double-chained surfactant didodecyldimethylammonium bromide (DDAB) was used as pseudostationary phase (PSP) in micellar electrokinetic capillary chromatography (MEKC). Its performance on the three kinds of drugs, i.e., basic, acidic, and neutral drugs, was systematically investigated. Nicotine, cotinine, caffeine, lidocaine, and procaine were selected as the model basic drugs. Good baseline separation and high efficiency were obtained under the optimal separation condition that consisted of 50mM phosphate (pH 4.0) and 0.08 mM DDAB. Three basic phenylenediamine isomers can also be well separated with DDAB in buffer. In addition, DDAB can form cationic bilayer on the capillary wall, thus the wall adsorption of basic analytes was greatly suppressed. Compared with commonly used CTAB, the separation of basic drugs was significantly improved with a much lower amount of DDAB present in the buffer. The DDAB-involved MEKC also showed superiority to CTAB upon the separation of acidic drugs, amoxicillin and ampicillin. In the case of neutral compounds, a good separation of resorcinol, 1-naphthol and 2-naphthol was achieved with 0.1mM DDAB and 30% (v/v) acetonitrile (ACN) present in buffer. Hence, it was concluded that the double-chained cationic surfactant DDAB can be a good substitute for traditional single-chained surfactant CTAB in MEKC.     

Enantioseparation of chiral benzimidazole derivatives by electrokinetic chromatography using sulfated cyclodextrins

Baseline separation of 18 new substituted benzimidazole derivatives, potent AMP‐activated protein kinase (AMPK) activators, with one chiral center, was achieved by CD‐EKC using sulfated and highly sulfated CDs (SCDs and HS‐CDs) as chiral selectors. The influence of the type and concentration of the chiral selectors on the enantioseparations was investigated. The SCDs exhibit a very high enantioselectivity power since they allow excellent enantiomeric resolutions compared to those obtained with the neutral CDs. The enantiomers were resolved with analysis times around 6 min using 25 mM phosphate buffer at pH 2.5 containing either β‐S‐CD, HS‐β‐CD, HS‐γ‐CD (3 or 4% w/v) at 25°C, with a voltage of 20 kV. The apparent association constants of the inclusion complexes were calculated. The study of the solute structure‐enantioseparation relationships seems to show the high contribution of the interactions between the solutes phenyl ring and the CDs to the enantiorecognition process. The optimized method was briefly validated (LOD less than 1%) and the purity of enantiomers of compound 3 was determined. The enantiomer migration shows reversal order depending on the kind of CD.     

Separation of some chiral flavonoids by microbial cyclosophoraoses and their sulfated derivatives in micellar electrokinetic chromatography

Neutral cyclosophoraoses (Cys) and highly sulfated cyclosophoraoses (HS-Cys) were successfully applied as chiral selectors with SDS for the separation of some chiral flavonoids in MEKC. HS-Cys were synthesized by the chemical modification of a family of neutral Cys isolated from a soil microorganism, Rhizobium meliloti 2011. Chiral catechin was separated with a resolution (R(s)) of 0.754 by neutral Cys and SDS. In the case of isosakuranetin and neohesperidin, resolution (R(s)) values of 1.483 and 1.306 were obtained with HS-Cys and SDS, respectively.     

Analysis of nucleic acid derivatives by micellar electrokinetic capillary chromatography

The use of micellar electrokinetic capillary chromatography (MECC) for the analysis of the major nucleobases, nucleosides, and nucleotides, and their chemically modified derivatives, has been developed and refined. The dimensions of the separating capillaries, the composition of the buffering systems, and the conditions used for electrophoresis were investigated in order to obtain the best performance. Particular emphasis was placed on the identification of the physiological constituents of nucleic acids and their chemically modified analogs: in vitro studies on calf thymus DNA exposed to genotoxic agents have demonstrated that adducted bases and nucleolides can be identified by MECC.     

A comparison of ionic liquids to molecular organic solvents as additives for chiral separations in micellar electrokinetic chromatography

In this study, we report the effects of adding ionic liquids (ILs), as compared to adding conventional molecular organic solvents (MOSs), to aqueous buffer solutions containing molecular micelles in the separation of chiral analyte mixtures in micellar EKC (MEKC). The molecular micelle used in this study was polysodium oleyl-L-leucylvalinate (poly-L-SOLV). The ILs were 1-alkyl-3-methylimidazolium tetrafluoroborate, where the alkyl group was ethyl, butyl, hexyl, or octyl. These ILs were chosen due to their hydrophobicity, good solvating, and electrolyte properties. Thus, it was expected that these ILs would have favorable interactions with chiral analytes and not adversely affect the background current. Common CE buffers, mixed with a molecular micelle, and an IL or a MOS, were used for these chiral separations. The buffers containing an IL in the concentration range of 0.02-0.1 v/v were found to support a reasonable current when an electric field strength of 500 V/cm was applied across the capillary. However, a current break down was observed for the buffers containing more than 60% v/v MOS on application of the above-mentioned electric field. The chiral resolution and selectivity of the analytes were dependent on the concentration and type of IL or MOS used.     

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.     

Chiral separation of raltitrexed by cyclodextrin-modified micellar electrokinetic chromatography

A rapid and effective method was developed for the chiral separation of raltitrexed (RD) enantiomers by carboxymethyl-beta-cyclodextrin (CM-β-CD)-modified micellar electrokinetic chromatography (MEKC). Optimization of conditions including the type and concentration of the chiral selector, concentration of sodium dodecyl sulfate (SDS), pH and concentration of the background electrolyte (BGE), capillary temperature, and applied voltage was investigated. The enantiomers of raltitrexed could be separated with satisfactory resolution and linear response by using 75 mM Tris-phosphate at pH 8.0 containing 30 mM SDS and 8 mM CM-β-CD as buffer system. Furthermore, the usefulness of this method was demonstrated in a purity test of a real synthetic drug sample. Figure Chiral separation of raltitrexed by CM-β-CD MEKC was optimized and applied to test the purity of a synthetic drug sample     

Effect of hydrophobic chain length of the chiral surfactant on enantiomeric separations by electrokinetic chromatography: Comparison between micellar and vesicular pseudo-stationary phases

Two novel amino acid based surfactants sodium N-(4-n-decyloxybenzoyl)-l-valinate (SDeBV) and sodium N-(4-n-octyloxybenzoyl)-l-valinate (SOBV) have been synthesized and used as chiral selectors for enantiomeric separations by micellar electrokinetic chromatography (MEKC). The aggregation behavior of the surfactants was studied in buffered aqueous solution using surface tension and fluorescence probe techniques. The microenvironment of the aggregates was studied using pyrene, and 1,6-diphenyl-1,3,5-hexatriene (DPH) as probe molecules. Results of these studies indicate that these two surfactants form micelles in buffered aqueous solution. Successful enentioseparation has been achieved for 1,1′-bi-2-naphthol (BOH), 1,1′-binaphthyl-2,2′-diylhydrogenphosphate (BNP), 2,8-dimethyl-6H-5,11-methanodibenzo[b,f] [1,5]diazocine (Tröger's base, TB), and benzoin (BZN) using the two chiral selectors SDeBV and SOBV. The separations were optimized with respect to surfactant concentration, pH, and buffer concentration. The results are discussed in light of the aggregation behavior of the surfactants. A comparison of the results of this study has been made with the data from literature to investigate the effect of self-assembly morphology on enantiomeric separations.     

Advances in chiral separations of small peptides by capillary electrophoresis and chromatography

Many chemical and biological processes are controlled by the stereochemistry of small polypeptides (di‐, tri‐, tetra‐, penta‐, hexapeptides, etc). The biological importance of peptide stereoisomers is of great value. Therefore, the chiral resolution of peptides is an important issue in biological and medicinal sciences and drug industries. The chiral resolutions of peptide racemates have been discussed with the use of capillary electrophoresis and chromatographic techniques. The various chiral selectors used were polysaccharides, cyclodextrins, Pirkle types, macrocyclic antibiotics, crown ethers, imprinted polymers, etc. The stereochemistry of dipeptides is also discussed. Besides, efforts are made to explain the chiral recognition mechanisms, which will be helpful in understanding existing and developing new stereoselective analyses. Future perspectives of enantiomeric resolution are also predicted. Finally, the review concludes with the demand of enantiomeric resolution of all naturally occurring and synthetic peptides.     

Enantioseparation of esbiothrin by cyclodextrin‐modified microemulsion and micellar electrokinetic chromatography

A comparison between chiral cyclodextrin‐modified microemulsion electrokinetic chromatography (CD‐MEEKC) and cyclodextrin‐modified micellar electrokinetic chromatography (CD‐MEKC) for the enantiomeric separation of esbiothrin was carried out. For both methods, the separation conditions were optimized by varying CD types and concentration, running buffer pH and compositions, organic modifiers, and temperature. The optimal CD‐MEEKC conditions were 0.8% n‐heptane, 2.3% SDS, 6.6% n‐butanol, 90.3% 10 mM sodium tetraborate containing 3% (w/v, the ratio of CD mass to microemulsion volume) methyl‐β‐cyclodextrin, pH 10, 25°C. The optimized CD‐MEKC conditions were 3.3% SDS, 96.7% 10 mM sodium tetraborate containing 5% (w/v) β‐CD, pH 10, 25°C. The difference in physicochemical properties of the buffer and CDs resulted in different optimal CD type. The competitive distribution between the microemulsion (or micelle) and chiral CD contributed to the chiral separation. Both methods provided excellent separation (R_s ～? 3) with similar migration time (ca. 15 min). CD‐MEEKC provided higher separation efficiencies (>300000) than CD‐MEKC (>200000). The LODs for CD‐MEEKC and CD‐MEKC were 4.7 μg/mL and 3.2 μg/mL, respectively. The RSDs of migration time and peak area for CD‐MEEKC were slightly higher than for CD‐MEKC. Both the demonstrated CD‐MEEKC and CD‐MEKC methods provided high efficiencies, low LODs, and reproducible enantioseparations of esbiothrin.     

Separation of anabolic steroids by micellar electrokinetic capillary chromatography

Summary The separation of seven analogous anabolic steroids was studied by micellar electrokinetic capillary chromatography (MECC). The retention order was found to be dependent on polarity. All of these steroids were well separated by the addition of organic modifiers to the separation buffer. Of the organic modifiers tested, 1-propanol gave the best separation, better than methanol or acetonitrile.     

The separation of herbicides by micellar electrokinetic capillary chromatography

Summary A method for the separation of a number of herbicides consisting of chlorophenoxy acids by micellar electrokinetic capillary chromatography (MECC) was developed. Sodium dodecyl sulphate (SDS), Brij 35, cetyltrimethylammonium bromide (CTAB) and methanol were introduced into the buffers to investigate their effects on the separation of the herbicides. SDS combined with Brij 35 as the micellar agent was found to provide the best overall separation of these components.     

Degradingdehydroabietylisothiocyanate as a chiral derivatizing reagent for enantiomeric separations by capillary electrophoresis

Abietic acid is a naturally occurring enantiomeric diterpenic acid. Its absolute optical purity and very stable stereochemistry structure makes it an excellent starting material for preparing chiral derivatizing reagents for chromatographic or electrophoretic applications. This paper describes the synthesis and evaluation of a novel chiral derivatization reagent, i.e., degradingdehydroabietylisothiocyanate (DDHAIC) derived from dehydroabietic acid. Its applicability for the enantioseparation of racemic amino acids by CE was demonstrated. DDHAIC reacted readily with amino acids at an elevated temperature (70 degrees C). The resulting derivatives were highly stable and separable by MEKC. Separation of amino acid-DDHAIC diastereomers was achieved with a running buffer consisting of 50 mM Na(2)HPO(4) (pH 9.0), 18 mM SDS, and 25% v/v ACN. Under the conditions selected, diastereomers formed from ten pairs of tested amino acid enantiomers including D/L-Asn, D/L-Met, D/L-Leu, D/L-Phe, D/L-Trp, D/L-Ser, D/L-Val, D/L-Ala, D/L-Thr, and R/S-vigabatrin were well resolved. The resolution values were in the range of 0.95-8.9.     

胶束扫集毛细管电动色谱法测定药物中3种邻苯二甲酸酯

采用胶束扫集毛细管电动色谱技术,建立了测定药物中邻苯二甲酸二甲酯(DMP)、邻苯二甲酸二乙酯(DZP)和邻苯二甲酸二丁酯(DBP)的方法。电泳缓冲体系含80 mmol/L SDS,20 mmol/L NaH2PO4(pH 2.20),5%甲醇(V/V),分离电压-18 kV,重力进样80s×15.0cm,检测波长225 nm,使用Φ50μm×62.0 cm石英毛细管,有效长度50.0 cm。讨论了磷酸盐浓度、有机改善剂、SDS浓度、分离电压、进样时间等因素的影响,并考察了胶束扫集法对DMP、DEP和DBP的富集能力。在优化条件下,线性关系良好,相关系数大于0.9986,DMP、DEP和DBP的线性范围分别为1.25～240,1.04～200和1.56～200 mg/L,检出限分别为0.26,0.26和0.39 mg/L。方法应用于肠溶片中DMP、DEP和DBP的测定,回收率在93.3%～108%之间,RSD≤5.2%。每次样品测定可在10 min内完成。     

Determination of amino acid ratios in natural products by micellar electrokinetic chromatography

Summary Separation of dansyl and di-dansyl derivatives of amino acids present in natural products (corn seed flour, wheat flour fraction gliadine) is described. Problems with coelution of derivatization by-products and reagent with some dansyl amino acids (DNS-AA) were solved. A preconcentration step after derivatization of real sample is described. DNS-AA peak areas for different varieties of corn seed flour were compared. Di-dansyl histidine is not separated from di-dansyl lysine and didansyl tyrosine. Additional separation mechanisms have to be introduced to achieve separation of these three species.     

Determination of polyphenol components in herbal medicines by micellar electrokinetic capillary chromatography with Tween 20

A simple and convenient method of micellar electrokinetic capillary chromatography (MEKC) using polyoxyethylene sorbitan monolaurate (Tween 20) to form single micelle and methanol as a buffer additive was introduced for the simultaneous determination of five polyphenols, including scopoletin, rutin, esculetin, chlorogenic acid and caffeic acid. A running buffer solution of pH 9.3, 20 mmol/L sodium tetraborate containing 64 mmol/L Tween 20 and 9% (v/v) methanol was adopted in the separation. Because rutin and esculetin were difficult to be separated by capillary zone electrophoresis (CZE) and SDS-based MEKC, Tween 20-based MEKC was adopted and the polyphenols were separated satisfactorily. The proposed method was used to determine the polyphenol components in the herbal medicine of Cortex fraxini. The separation mechanism of Tween 20-based MEKC for the polyphenols was discussed preliminarily.