A chiral porous organic polymer COP-1 used as stationary phase for HPLC enantioseparation under normal-phase and reversed-phase conditions.

A spherical chiral porous organic polymer (POPs) COP-1 is synthesized by the Friedel-Crafts alkylation reaction of Boc-3-(4-biphenyl)-L-alanine (BBLA) and 4,4'-bis(chloromethyl)-1,1'-biphenyl (BCMBP), which was used as a novel chiral stationary phase (CSPs) for mixed-mode high-performance liquid chromatography (HPLC) enantioseparation. The racemic compounds were resolved in normal-phase liquid chromatography (NPLC) using n-hexane/isopropanol as mobile phase and reversed-phase liquid chromatography (RPLC) using methanol/water as mobile phase. The COP-1-packed column exhibited excellent separation performance toward various racemic compounds including alcohols, amines, ketones, esters, epoxy compounds, organic acids, and amino acids in NPLC and RPLC modes. The effects of analyte mass and column temperature on the separation efficiency of racemic compounds were investigated. In addition, the chiral resolution ability of the COP-1-packed column not only can be complementary in RPLC/NPLC modes but also exhibit a good chiral recognition complementarity with Chiralpak AD-H column and chiral porous organic cage (POC) NC1-R column. The relative standard deviations (RSD) (n = 5) of the retention time, resolution value, and peak area by repeated separation of 1-(4-chiorophenyl)ethanol are all below 3.0%. The COP-1 column shows high column efficiency (e.g., 17,320 plates m-1 for 1-(4-chlorophenyl)ethanol on COP-1 column in NPLC), high enantioselectivity, and good reproducibility toward various racemates. This work demonstrates that chiral POPs microspheres are promising chiral materials for HPLC enantioseparation.

An Enantioselective Potentiometric Sensor for 2-Amino-1-Butanol Based on Chiral Porous Organic Cage CC3-R.

Porous organic cages (POCs) have attracted extensive attention due to their unique structures and tremendous application potential in numerous areas. In this study, an enantioselective potentiometric sensor composed of a polyvinyl chloride (PVC) membrane electrode modified with CC3-R POC material was used for the recognition of enantiomers of 2-amino-1-butanol. After optimisation, the developed sensor exhibited enantioselectivity toward S-2-amino-1-butanol ( log K S , R P o t = -0.98) with acceptable sensitivity, and a near-Nernstian response of 25.8 ± 0.3 mV/decade within a pH range of 6.0⁻9.0.

Homochiral metal-organic frameworks based on amino acid ligands for HPLC separation of enantiomers.

Natural amino acids are well known to form coordination polymers with transition metal ions. In this study, six homochiral metal-organic frameworks constructed from Zn2+ or Co2+ ions and various enantiopure amino acid (L-tyrosine, L-histidine, L-tryptophan and L-glutamic acid), namely [Zn(L-tyr)]n (L-tyrZn), [Zn4 (btc)2 (Hbtc)(L-His)2 (H2 O)4 ]·1.5H2 O, {[Zn2 (L-trp)2 (bpe)2 (H2 O)2 ]·2H2 O·2NO3 }n , [Co2 (L-Trp)(INT)2 (H2 O)2 (ClO4 )], [Co2 (sdba)((L-Trp)2 ] and [Co(L-Glu)(H2 O)·H2 O]∞ , were synthesized according to the methods previously reported in the literature. The six homochiral MOFs were explored as the chiral stationary phases for high-performance liquid chromatographic separation of enantiomers using hexane/isopropanol or hexane/dichloromethane as mobile phase. Various types of enantiomers such as alcohols, amines, ketones, ethers, organic acids, etc. can be resolved on these homochiral MOF columns. The results revealed that the enantioseletivities of homochiral MOFs based on amino acids as chiral bridging ligands used as stationary phases are practical in HPLC.

Optical resolution and mechanism using enantioselective cellulose, sodium alginate and hydroxypropyl-ß-cyclodextrin membranes.

Chiral solid membranes of cellulose, sodium alginate, and hydroxypropyl-ß-cyclodextrin were prepared for chiral dialysis separations. After optimizing the membrane material concentrations, the membrane preparation conditions and the feed concentrations, enantiomeric excesses of 89.1%, 42.6%, and 59.1% were obtained for mandelic acid on the cellulose membrane, p-hydroxy phenylglycine on the sodium alginate membrane, and p-hydroxy phenylglycine on the hydroxypropyl-ß-cyclodextrin membrane, respectively. To study the optical resolution mechanism, chiral discrimination by membrane adsorption, solid phase extraction, membrane chromatography, high-pressure liquid chromatography ultrafiltration were performed. All of the experimental results showed that the first adsorbed enantiomer was not the enantiomer that first permeated the membrane. The crystal structures of mandelic acid and p-hydroxy phenylglycine are the racematic compounds. We suggest that the chiral separation mechanism of the solid membrane is "adsorption - association - diffusion," which is able to explain the optical resolution of the enantioselective membrane. This is also the first report in which solid membranes of sodium alginate and hydroxypropyl-ß-cyclodextrin were used in the chiral separation of p-hydroxy phenylglycine.

Novel inorganic mesoporous material with chiral nematic structure derived from nanocrystalline cellulose for high-resolution gas chromatographic separations.

Chiral nematic mesoporous silica (CNMS) has attracted widespread attention due to some unique features, such as its nematic structure, chirality, large pore size, high temperature resistance, low cost, and ease of preparation. We first reported the use of CNMS as a stationary phase for capillary gas chromatography (GC). The CNMS-coated capillary column not only gives good selectivity for the separation of linear alkanes, aromatic hydrocarbons, polycyclic aromatic hydrocarbons (PAHs), and isomers but also offers excellent enantioselectivity for chiral compounds. Compared with enantioseparations on commercial ß-DEX 120 and Chirasil-l-Val columns, a CNMS-coated capillary column offers excellent enantioselectivity, chiral recognition complementarity, and the separation of analytes within short elution times. It can also be potentially applied in high-temperature GC at more than 350 °C. This work indicates that CNMS could soon become very attractive for separations.

Porous metal membranes for solid-phase extraction of polycyclic aromatic hydrocarbons.

Solid-phase extraction (SPE) is one of the most important techniques for sample preparation, purification, concentration and cleanup. Membranes made from synthetic organic polymers, cellulose, or glass fibers are used for sample pretreatment. In this work, we report that a porous metal membrane, the metal filter in HPLC, was used as a novel kind of solid-phase extraction adsorbent material. To evaluate the performance of the porous metal membrane for the SPE, naphthalene, fluorene, anthracene, phenanthrene, fluoranthene, pyrene, chrysene, perylene and benzo(a)pyrene were selected as analytes. Several parameters that affected the extraction efficiency such as the extraction time, the concentration of NaCl, the extraction temperature and the agitation speed were optimized. The experimental result indicates that the porous metal membrane possesses high adsorption ability to the tested polycyclic aromatic hydrocarbons (PAHs). Under the optimum conditions, the detection limits of the developed method were in the range of 0.03-0.082 µg L(-1) (S/N = 5), and excellent linear correlations between peak area and concentration of PAHs were found over the range of 0.1-60 µg L(-1). The precisions (RSD) for five replicate extractions of the PAHs from sample solutions were in the range of 2.6-5.0%. The recoveries of the PAHs from tap water and river water samples spiked with 9 PAHs (20 µg L(-1) of each individual PAH) ranged from 83.0% to 112.5%. The porous metal membrane is durable, simple, inexpensive, reproducible and has a high adsorption ability for use in SPE of PAHs.

Chiral separation of D,L-mandelic acid through cellulose membranes.

This work reports the chiral separation of D,L-mandelic acid with cellulose membranes. Cellulose was chosen as membrane material because it possesses multichiral carbon atoms in its molecular structure unit. The flux and permselective properties of membrane using aqueous solutions of D,L-mandelic acid as feed solution was studied. The top surface and cross-section morphology of the resulting membrane were examined by scanning electron microscopy. When the membrane was prepared with 8.1 wt % cellulose and 8.1 wt % LiCl in the DMA casting solution, and the operating pressure and feed concentration of racemate were 0.0125 MPa and 0.5 mg/ml, respectively, over 90% of enantiomeric excess could be obtained. This is the first report that the cellulose membrane is used for isolating the optical isomers of D,L-mandelic acid. Chirality, 2011.

Highly selective separation of enantiomers using a chiral porous organic cage.

Porous solids composed of shape-persistent organic cage molecules have attracted considerable attention due to their important applications such as molecular separation, heterogeneous catalysis, and gas storage. In this study, an imine-linked porous organic cage (POC) CC10 diluted with a polysiloxane OV-1701 was explored as a novel stationary phase for high-resolution gas chromatography (GC). A wide variety of enantiomers belonging to different classes of organic compounds have been resolved on the coated capillary column, including chiral alcohols, esters, ketones, ethers, halohydrocarbons, epoxides, and organic acids. The fabricated column complements to commercial ß-DEX 120 column and our recently reported CC3-R column for separating enantiomers, which indicates that the excellent chiral recognition ability of CC10 is not only interesting academically, but also has potential for practical application. In addition, CC10 also exhibits good selectivity for the separation of n-alkanes, n-alcohols, Grob mixture, and positional isomers. This work also indicates that this type of chiral POCs will become a new class of chiral selector in the near future.