Phases For Separation Of Enantiomers Research Articles

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.

ChemInform Abstract: Separation of Enantiomeric Amino Acid Derivatives on Axially Chiral 1, 1′-Binaphthyl-2,2′-bis(N-decylcarboxamide) as a Stationary Phase for Capillary Gas Chromatography.

Axially chiral 1,1′-binaphthyl-2,2′-bis(N-decylcarboxamide) was utilized as a chiral stationary phase for capillary gas chromatograpic separation of enantiomers. This stationary phase showed efficient differentiation for amino acid derivatives allowing complete separation of eleven N-trifluoroacetyl amino acid isopropyl esters.

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.

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.

Design, Preparation and Application of a New π-Basic Chiral Stationary Phase for the Liquid Chromatographic Separation of Enantiomers

A new reciprocal π-basic chiral stationary phase (CSP) was designed based on the reciprocity conception of chiral recognition and prepared starting from (S)-leucine. The CSP thus prepared was applied in resolving various π-acidic N-(3,5-dinitrobenzoyl)-α-amino amides and esters and found to be very effective. Especially, N-(3,5-dinitrobenzoyl)-α-amino N,N-dialkyl amides were resolved very well on the new reciprocal CSP. From the chromatographic resolution results and based on the reciprocity conception of chiral recognition with the aid of Corey/Pauling/Koltan (CPK) molecular model studies, a chiral recognition mechanism which utilizes n-n interaction and simultaneously two hydrogen bonding interactions between the CSP and the analyte has been proposed. The CSP prepared in this study was also successful in resolving 3,5-dinitrophenylcarbamate derivatives of 2-hydroxycarboxylic acid esters.

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.

Preparation and evaluation of new chiral stationary phases for high-performance liquid chromatographic separation of enantiomers : Comparison of enantiomeric and diastereomeric phases based on (α)-1-napththylethylamine for the resolution of derivatives of amino acid enantiomers

Three new chiral stationary phases [two diastereomeric phases based on R-phenylglycyl- R/S-(α)-1-napththylethylamide and one enantiomeric phase based on glycycl- S-(α)_-1-napththylethylamide] have been prepared and evaluated. There were marginal differences betwen the phases for the separation of enantiomers of 3,5-dinitrobenzoyl amino acid esters when used in conjunction with isopropanol—hexane mobile phases. However, there were marked differences when dichloromethane—hexane mobile phases were used. With the latter mobile phase the R/R chiral support did not separate any of the derivatives into their enantiomers and the R/S chiral support gave larger separation factors than the enantiomeric ( S) phase. The R/S chiral support gave comparable separation factors with either dichloromethane or isopropanol containing mobile phases. The R/R chiral phase gave the largest separation fctor for the enantiomers of the N-α-3,5-dinitro benzoyl derivative of ethyl-α-amino-2-imidazolepropionate (isohistidine ethyl ester).