Chiral Stationary Phases For Separation Research Articles

Room temperature synthesis of a chiral covalent organic framework core-shell composite for high-performance liquid chromatography enantioseparation.

In this article, chiral covalent organic framework core-shell composite CCOF-TpPa-Py@SiO2 was facilely synthesized by induction at room temperature. The CCOF-TpPa-Py@SiO2 core-shell composite was used as a chiral stationary phase for the separation of the racemates by high-performance liquid chromatography, which exhibits good separation performance for chiral compounds including ketones, alcohols, esters, epoxides, carboxylic acids, amides, and amines. The effects of analyte injection mass on the enantioseparation were studied. The reproducibility and stability of the CCOF-TpPa-Py@SiO2 chiral column were explored. The intra-day (n=5), inter-day (n=5), and inter-column (n=3) relative standard deviations for the migration times and resolution of benzoin were 0.32%-0.54%, 0.45%-0.61%, and 1.21%-1.53%, respectively. In addition, the chiral separation ability of the CCOF-TpPa-Py@SiO2 chiral column (column A) was compared with that of the MDI-β-CD-Modified COF@SiO2 (column B) as well as a commercial chiral column (Chiralpak AD-H). The chiral recognition ability of column A is complementary to that of column B and AD-H column. The resolution mechanism of CCOF-TpPa-Py@SiO2 stationary phase towards chiral analyte was explored. Hence, the synthesis of CCOF-TpPa-Py@SiO2 core-shell composite by induction at room temperature as chiral stationary phases for chromatographic separation has important research potential and application prospects.

HPLC with chiral stationary phase for separation and kinetics study of aspartic acid epimerization in Peroxiredoxin 2 active site peptide

Amino acid epimerization, a process of converting L-amino acids to D-amino acids, will lead to modification in the protein structure and, subsequently, its biological function. This modification causes no change in protein m/z and may be overlooked during protein analysis. Aspartic Acid Epimerization (AAE) is faster than other amino acids and could be accelerated by free radicals and peroxides. In this work, a novel and site-specific HPLC method using a chiral stationary phase for determining the AAE in the active site model peptide (AP) of Peroxiredoxin 2 has been developed and validated. The developed method showed good linearity (1 – 200 μg/mL) and recoveries of the limit of quantification (LOQ), low, medium, and high concentrations were between 85% and 115%. The Kinetics of AAE in AP were studied using the developed method, and the results showed that when ascorbic acid and Cu2+ coexisted, the AP epimerized rapidly. The AAE extent increased with time and was positively correlated with hydrogen peroxide generation.

Application of Commercially Available Crown Ether Chiral Stationary Phases for Separation of Tetrapeptide Stereoisomers

Application of Commercially Available Crown Ether Chiral Stationary Phases for Separation of Tetrapeptide Stereoisomers

Recent progress of chiral stationary phases for separation of enantiomers in gas chromatography.

Chromatography techniques based on chiral stationary phases are widely used for the separation of enantiomers. In particular, gas chromatography has developed rapidly in recent years due to its merits such as fast analysis speed, lower consumption of stationary phases and analytes, higher column efficiency, making it a better choice for chiral separation in diverse industries. This article summarizes recent progress of novel chiral stationary phases based on cyclofructan derivatives and chiral porous materials including chiral metal-organic frameworks, chiral porous organic frameworks, chiral inorganic mesoporous materials, and chiral porous organic cages in gas chromatography, covering original research papers published since 2010. The chiral recognition properties and mechanisms of separation toward enantiomers are also introduced.

Further proof to the utility of polysaccharide-based chiral selectors in combination with superficially porous silica particles as effective chiral stationary phases for separation of enantiomers in high-performance liquid chromatography

The first ever report on the preparation of chiral stationary phases (CSP) based on superficially porous silica (SPS) particles for the separation of enantiomers in HPLC demonstrated clear advantages of such materials. Higher enantioselectivity at the comparable content of a chiral selector, limited dependence of plate height on the mobile phase flow rate and higher plate numbers and resolution calculated per unit time (i.e. higher speed of separation) were observed with columns made with superficially porous CSP in comparison to columns made with fully-porous silica-based CSP. However, later studies reported diverging conclusions. In this report further evidences are described supporting the findings of our first study about the superior performance of polysaccharide-based chiral selectors in combination with SPS when compared to traditional CSPs based on fully porous silica (FPS) particles.

DEVELOPMENT AND VALIDATION OF A NEW HIGH PERFORMANCE LIQUID CHROMATOGRAPHIC METHOD FOR ENANTIOSEPARATION OF DORZOLAMIDE HYDROCHLORIDE ON A COATED CELLULOSE PHENYLCARBAMATE CHIRAL STATIONARY PHASE

A simple, accurate, precise, and sensitive method using coated cellulose phenylcarbamate chiral stationary phase for separation of dorzolamide hydrochloride (4S,6S) and its enantiomer (4R,6R) in commercial drops has been established. The mobile phase consisted of a mixture of n-hexane and 2-propanol (50:50 v/v) containing 0.1% diethylamine and used a flow rate of 1 mL min−1. The influence of temperature, flow rate, type, and concentration of organic components and diethylamine in the mobile phase on the retention and enantioselectivity was investigated. The method was validated for linearity, repeatability, accuracy, and limits of detection (LOD) and quantification (LOQ). The calibration range of quantitation for dorzolamide (4S,6S) and its enantiomer (4R,6R) was 0.5–10 µ g mL−1 and 0.2–5 µg mL−1, respectively. The LOD and LOQ were found to be 0.2 and 0.5 µ g mL−1 for dorzolamide hydrochloride (4S,6S) and 0.1 and 0.2 µg mL−1 for its enantiomer (4R,6R), respectively. Repeatability (n = 6) showed less than 0.5% relative standard deviation.

Chiral separation of amides of amino acid on a (S)‐N‐(3,5‐dinitrobenzoyl)leucine‐N‐phenyl‐N‐propylamide‐bonded silica using nonaqueous capillary electrochromatography

(S)-N-(3,5-dinitrobenzoyl)leucine-N-phenyl-N-propylamine-bonded silica was used as a chiral stationary phase for separation of a set of racemic pi-acidic and pi-basic alpha-amino acid amides in electrolyteless ACN-water eluents by CEC in the RP and polar organic (PO) modes. The effect of the amount of water in the ACN-water eluent on chiral separation was examined. As water is added to ACN, retention was shortened but resolution and selectivity deteriorated severely. Retention, enantioselectivity, and resolution factors obtained in 100% ACN were compared with those in an n-hexane-isopropanol eluent with a small amount of water by normal phase (NP) CEC. Much shorter retention times with comparable enantioselectivities were observed with 100% ACN, demonstrating the advantage of separation on (S)-N-(DNB)leucine-N-phenyl-N-propylamine-bonded silica in PO-CEC over NP-CEC.

Synthesis and characterization of new optically active polymers carrying calix[4]arene and amino acid units in the main chain and their binding properties towards toxic heavy metals

BACKGROUND: A series of novel optically active polymers containing upper rim calix[4]arene was prepared from the polycondensation reaction of calix diamine derivative 2 with two optically active diacid chlorides. RESULTS: The optically active compounds were prepared from the reaction of a pyromellitic dianhydride with two chiral amino acids. The optically active polymers were obtained in a yield of 80–86% and had an inherent viscosity of 0.20–0.26 dL g−1. The polymers were characterized using Fourier transform infrared and 1H NMR spectroscopy and elemental analysis. Studies of the complexation of the polymers towards some alkali metal and toxic transition metal cations were performed using solid–liquid sorption procedures and comparisons made with the starting monomer. CONCLUSION: It is evident from the complexation studies that the polymers investigated are good polymeric ionophores for alkali metal cations like Na+ and K+, for Ag+ and for toxic heavy metal cations such as Cu2+, Co2+, Cd2+ and Hg2+. These polymers are good candidates for use in chiral stationary phases for separation of enantiomers in ionic media, as well for removing metal ions. Copyright © 2009 Society of Chemical Industry

Enantioseparation of amino acid amides on an (S)‐N‐(3,5‐dinitrobenzoyl)leucine‐N‐phenyl‐N‐propylamide‐bonded silica in normal phase CEC

(S)-N-(3,5-Dinitrobenzoyl)leucine-N-phenyl-N-propylamide-bonded silica was used as a chiral stationary phase for separation of enantiomers of some racemic pi-acidic and pi-basic amino acid amides in normal phase capillary LC (CLC) and CEC. For generation of EOF in CEC, different amounts of water were added to n-hexane-isopropanol (IPA) eluents. Influences of added water and composition of polar modifier on retention, enantioselectivity and resolution were studied. Generally better separation was obtained in the eluents of lower water content. Shorter retention and better enantioselectivities were observed in the eluents of higher IPA content, whereas resolution became lower as IPA content was increased. Enantioselectivities were comparable but resolutions were much better in CEC than CLC.

Comparison of the performance of chiral stationary phase for separation of fluoxetine enantiomers

Separation of fluoxetine enantiomers on five chiral stationary phases (chiralcel OD-H, chiralcel OJ-H, chiralpak AD-H, cyclobond capital I, Ukrainian 2000 DM and kromasil CHI-TBB) was investigated. The optimal mobile phase compositions of fluoxetine separation on each column were hexane/isopropanol/diethyl amine (98/2/0.2, v/v/v), hexane/isopropanol/diethyl amine (99/1/0.1, v/v/v), hexane/isopropanol/diethyl amine (98/2/0.2, v/v/v), methanol/0.2% triethylamine acetic acid (TEAA) (25/75, v/v; pH 3.8) and hexane/isopropanol/diethyl amine (98/2/0.2, v/v/v), respectively. Experimental results demonstrated that baseline separation (R(S)>1.5) of fluoxetine enantiomers was obtained on chiralcel OD-H, chiralpak AD-H, and cyclobond capital I, Ukrainian 2000 DM while the best separation was obtained on the last one. The eluate orders of fluoxetine enantiomers on the columns were determined. The first eluate by chiralcel OJ-H and kromasil CHI-TBB is the S-enantiomer, while by chiralpak AD-H and cyclobond I 2000 DM is the R-enantiomer.

β-Cyclodextrin-hexamethylene diisocyanate copolymer-coated zirconia for separation of racemic 2,4-dinitrophenyl amino acids in reversed-phase liquid chromatography

We report use of β-cyclodextrin (CD)-hexamethylene diisocyanate (HMDI) copolymer(CDPU)-coated zirconia (CDPUZ) as a chiral stationary phase for separation of enantiomers of a set of 2,4-dinitrophenyl (DNP) amino acids in reversed-phase liquid chromatography. The effects of polymer loading on zirconia and HMDI/CD molar ratio in the preparation of CDPU on retention and selectivity in the separation of DNP-amino acids in were examined to find optimum polymer loading and HMDI/CD ratio. It was observed that 8% loading of the CDPU prepared with the HMDI/CD molar ratio of 4 gave the best separation of the amino acids investigated. Retention and chiral selectivity of CDPUZ were also compared to those for previously reported carboxymethyl-β-CD-coated zirconia (CMCDZ). CDPUZ gave better chiral separation than CMCDZ for the DNP-amino acids.

Separation of racemic 2,4-dinitrophenyl amino acids on zirconia-immobilized quinine carbamate in reversed-phase liquid chromatography.

Zirconia is known to be one of the best chromatographic support materials due to its excellent chemical, thermal, and mechanical stability. A quinine carbamate-coated zirconia was prepared as a chiral stationary phase for separation of enantiomers of DNP-amino acids in reversed-phase liquid chromatography. Retention and enantioselectivity of this phase were compared to those for quinine carbamate bonded onto silica. Most amino acids studied were separated on the quinine carbamate-zirconia CSP although retention was longer and chiral selectivity was somewhat lower than on the corresponding silica CSP. Increased retention and decreased selectivity are probably due to strong non-enantioselective Lewis acid-base interactions between the amino acid molecule and the residual Lewis acid sites on the zirconia surface.

Separation of enantiomers on bovine serum albumin coated zirconia in reversed-phase liquid chromatography

Zirconia is known to be one of the best materials for the chromatographic support due to its excellent chemical, thermal and mechanical stability. In this work we report preparation and use of bovine serum albumin (BSA)-immobilized zirconia as a chiral stationary phase for separation of some enantiomers in reversed-phase liquid chromatography. The BSA-zirconia showed good enantioselectivity for some of the enantiomers studied and could be used for RPLC separations in mobile phases of alkaline pH.

Open tubular capillary electrochromatography with adsorbed stationary phase

A novel preparation method of stationary phase was presented for open tubular capillary electrochromatography (OTCEC). The adsorbed stationary phases were prepared easily by rinse the capillary with a buffer containing cationic surfactant such as cetyltrimethylammonium bromide (CTAB) or basic protein such as lysozyme. After a surfactant bilayer or a protein layer was adsorbed on the capillary wall, the capillary was rinsed again with a running buffer containing no CTAB or protein. The CTAB bilayer was used as a stationary phase for separation of neutral solutes. Five alkyl substituted benzenes were baseline separated within 6 min with theoretical plate number of 223 000/m for benzene and 181 000/m for toluene. The adsorbed lysozyme layer was used as chiral stationary phase for separation of enantiomers. Four amino acids and the drug of mephenytoin were separated within 5 min with a resolution from 1.74 to 2.05.

L-N-(3,5-Dimethoxybenzoyl)isoleucine chiral stationary phase for separation of enantiomers by HPLC

L-N-(3,5-dimethoxyoxybenzoyl)isoleucine, ionically bonded to γ-aminopropyl silica, has been tested as a chiral stationary phase for the separation of racemates by HPLC. The phase shows good selectivity towards different types of racemates and in particular for those having an electron-poor aromatic group in their molecule. The separation of benzoin racemate can be achieved on the developed chiral phase with an α value of 1.10.

Synthesis and characterization of chiral stationary phases from amino acids and small peptides for liquid chromatography fractionations of a racemic alcohol

A series of amino acid and dipeptide bonded phases have been prepared and the performances of these chiral stationary phases for separation of R,S-2,2,2-trifluoro-1-(9-anthryl)ethanol have been examined. The elution order in n-hexane, that contained a small percentage of a polar solvent, was shown to reverse when a d-configuration containing stationary phase was substituted for l-configuration on the surface of silica. Eluents, which contained different polar solvents (2-propanol and methylene chloride) in percentages that gave approximately the same retention times, gave different separation factors. Increases in the percentages of the polar solvents in the eluents decreased the retention times; however, for a given solvent, the separation factors remained constant. In addition, the effects of removing the butyloxycarbonyl (BOC) group from the immobilized valine and substituting a benzyloxycarbonyl group resulted in a decrease with the separation factor. Bonding of second l-valine to the BOC- l-valine stationary phase gave an improved α value whereas additions of other amino acids usually decreased the separation factor, even when the acid had the same chirality.