Chiral Resolution Ability Research Articles

Polymers Bearing Covalently Linked Chiral Proline-Based Pendants: Induction of a Highly Stable Helical Sense that Mimics Double-Stranded Helical Morphology and Their Chiral Resolution Ability

Polymers Bearing Covalently Linked Chiral Proline-Based Pendants: Induction of a Highly Stable Helical Sense that Mimics Double-Stranded Helical Morphology and Their Chiral Resolution Ability

Preparation of porous organic cage and its use as chiral stationary phase for capillary electrochromatography

Porous organic cages (POCs) are a unique type of microporous materials composed of discrete molecules with internal cavities that are accessible to various compounds. In this study, a prismatic chiral POC with good thermochemical stability was synthesized by condensing (1R,2R)-diaminocyclohexane and 3,3',5,5'-teturonic-4,4'-biphenediol via the Schiff base reaction and characterized by proton nuclear magnetic resonance spectroscopy, infrared (IR) spectroscopy, thermogravimetric analysis (TGA), and scanning electron microscopy. The IR spectrum of the POC revealed a strong characteristic absorption peak at 1635 cm-1, indicating that it formed imine bonds (C=N). The absorption peak at 3425 cm-1 was attributed to the stretching vibrations of -OH, the absorption peaks at 2925 and 2858 cm-1 were attributed to the stretching vibrations of N=C-H and C-H, and the absorption peaks at 1446 and 1383 cm-1 were attributed to the stretching vibrations of C=C-H and C=C in the benzene ring. High-resolution mass spectral analysis of the POC showed a molecular ion peak at m/z 1363.7228, indicating its successful synthesis. TGA was performed from 25 to 800 ℃ at a rate of 10 ℃/min, and the results of this analysis showed that the POC was stable up to approximately 300 ℃. The POC was dissolved in dichloromethane and uniformly coated on the inner wall of a quartz capillary via the dynamic coating method to prepare a capillary electrochromatographic column. The experimental results revealed that the chiral electrochromatographic column could not only resolve ofloxacin, Troger's base, 2-amino-1-butanol, and 1-phenyl-1-amyl alcohol but also separate the isomers of o-, m-, and p-toluidine and o-, m-, and p-chloroaniline, indicating its good chiral separation ability. Investigation of the optimal separation conditions for ofloxacin, Troger's base, 2-amino-1-butanol, and 1-phenyl-1-amyl alcohol revealed that the voltage, buffer solution concentration, and pH significantly affected their separation degree. In particular, the optimal separation voltage for ofloxacin, Troger's base, and 2-amino-1-butanol was 15 kV, while that for 1-phenyl-1-amyl alcohol was 17 kV. The optimal buffer concentration and pH for ofloxacin, Troger's base, 2-amino-1-butanol, and 1-phenyl-1-amyl alcohol were 0.100 mol/L and 7.5. Under optimal chromatographic conditions, the resolution values for ofloxacin, Troger's base, 2-amino-1-butanol, and 1-phenyl-1-pentanol were 1.80, 3.33, 1.69, and 1.18, respectively. The results collectively demonstrate that the prepared POC may serve as a good chiral stationary phase for capillary electrochromatography with a certain chiral resolution ability and has good application prospects in chromatographic separation.

In situ growth preparation of a new chiral covalent triazine framework core-shell microspheres used for HPLC enantioseparation.

Themanufacturing of chiral covalent triazine framework core-shell microspheres CC-MP CCTF@SiO2 composite is reportedas stationary phase for HPLC enantioseparation. The CC-MP CCTF@SiO2 core-shell microspheres were prepared by immobilizing chiral COF CC-MP CCTF constructed using cyanuric chloride and (S)-2-methylpiperazine on the surface of activated SiO2 through an in-situ growth approach. Various racemates as analytes were separated on the CC-MP CCTF@SiO2-packed column. The experimental results indicate that 19 pairs of enantiomers were well separated on the CC-MP CCTF@SiO2-packed column, including alcohols, phenols, amines, ketones, and organic acids. Among them, there are 17 pairs of enantiomers that can achieve baseline separation with good peak shapes. Their resolution values on this chiral column are between 0.4 and 5.61. The influences of analyte mass, column temperature, and composition of the mobile phase on the resolution of enantiomers were studied. In addition, the chiral resolution ability of CC-MP CCTF@SiO2-packed column was compared with the commercial chiral chromatographic columns (Chiralpak AD-H and Chiralcel OD-H columns) and some CCOF@SiO2 chiral columns (β-CD-COF@SiO2, CTpBD@SiO2, and MDI-β-CD-modified COF@SiO2). The CC-MP CCTF@SiO2-packed column exhibited some unique advantages and can complement these chiral columns in chiral separations. The research results show that the CC-MP CCTF@SiO2 chiral column offered high column efficiency (e.g., 17680 plates m-1 for ethyl mandelate), low column backpressure (5-9 bar), high enantioselectivity, and excellent chiral resolution ability for HPLC enantioseparation with good stability and reproducibility. The relative standard deviations (RSD) (n = 5) of the retention time, and peak areas by repeated separation of ethyl mandelate are 0.23% and 0.67%, respectively. It demonstrates that the CC-MP CCTF@SiO2 core-shell microsphere composite has great potential in enantiomeric separation by HPLC.

Vacuum-assisted thermal bonding of β-cyclodextrin and its derivatives as chiral stationary phases for high-performance liquid chromatography

In this work, the vacuum-assisted thermal bonding method was proposed for the covalent coupling of β-cyclodextrin (β-CD) (CD-CSP), hexamethylene diisocyanate cross-linked β-CD (HDI-CSP) and 3, 5-dimethylphenyl isocyanate modified β-CD (DMPI-CSP) onto the isocyanate silane modified silica gel. Under vacuum conditions, the side reaction due to the water residue from the organic solvent, air, reaction vessels and silica gel could be avoided, and the optimal temperature and time of vacuum-assisted thermal bonding method were determined as 160°C and 3 h. These three CSPs were characterized by FT-IR, TGA, elemental analysis and the nitrogen adsorption-desorption isotherms. The surface coverage of CD-CSP and HDI-CSP on silica gel was determined as ∼0.2 μmol m−2, respectively. The chromatographic performances of these three CSPs were systematically evaluated by separating 7 flavanones, 9 triazoles and 6 chiral alcohols enantiomers under the reversed-phase condition. It was found that the chiral resolution ability of CD-CSP, HDI-CSP and DMPI-CSP was complementary to each other. Among them, CD-CSP could separate all 7 flavanones enantiomers with the resolution of 1.09–2.48. HDI-CSP had a good separation performance for triazoles enantiomers with one chiral center. DMPI-CSP showed excellent separation performance for chiral alcohol enantiomers, among which the resolution of trans-1, 3-diphenyl-2-propen-1-ol reached 12.01. Generally, the vacuum-assisted thermal bonding had been demonstrated as a direct and efficient method for the preparation of chiral stationary phases of β-CD and its derivatives.

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.

Superficial chiral etching on an achiral metal-organic framework for high-performance liquid chromatography enantioseparations.

Chiral metal-organic frameworks have shown great potential in enantioselective separation and asymmetric catalysis due to their diverse and adjustable structures with abundant chiral recognition sites. Herein, a new chiral post-synthetic modification was used for preparing an achiral@chiral metal-organic frameworks core-shell composite [Cu3 (Btc)2 ]@[Cu2 ((+)-Cam)2 Dabco] by a superficial chiral etching method. The [Cu3 (Btc)2 ]@[Cu2 ((+)-Cam)2 Dabco] composite was utilized as a novel chiral stationary phase for HPLC enantioseparation. Various racemates were separated on the [Cu3 (Btc)2 ]@[Cu2 ((+)-Cam)2 Dabco]-packed column (column A). It exhibited good chiral resolving ability toward many different kinds of racemates, especially chiral drugs. Among them, the highest resolution value for 1,2-diphenyl-1,2-ethanediol reaches 2.70. The relative standard deviations of retention time and peak area for repeated separation of 1,2-diphenyl-1,2-ethanol were 0.45% and 0.81%, respectively. Compared with the resolution ability of [Cu2 ((+)-Cam)2 Dabco]-packed column (column B), column A shows higher column efficiency and better separation performance than those of column B. The results indicated that the [Cu3 (Btc)2 ]@[Cu2 ((+)-Cam)2 Dabco] as a stationary phase can greatly improve the column efficiency and chiral resolution ability of chiral metal-organic frameworks, which demonstrated that the superficial chiral etching as an economic and efficient strategy opens up a new way for the application of metal-organic frameworks.

A chiral metal-organic cage [Fe4L6](ClO4)8 used for capillary gas chromatographic separations

Metal-organic cages (MOCs), as a promising class of crystalline porous materials with well-defined cavities, have attracted wide attention due to their multifarious potential applications in gas storage, host-guest chemistry, molecular recognition, separation, catalysis, sensing, and drug delivery and so on. Herein, we report that a chiral MOC [Fe4L6](ClO4)8 coated capillary column was fabricated for high-resolution gas chromatographic separation of various analytes, including n-alkanes, n-alcohols, positional isomers, aromatic hydrocarbon mixture, especially for racemic compounds. A series of racemic compounds such as alcohols, epoxides, aldehydes, ketones, ethers, esters, alkenes, sulfoxides and amino acid derivatives could be well separated on the [Fe4L6](ClO4)8 coated capillary column with high enantioselectivity and good reproducibility. Comparing the chiral resolution ability of the MOC [Fe4L6](ClO4)8 coated column with the commercial β-DEX 120 column and the porous organic cage (POC) CC10 coated column, the chiral MOC column can be complementary to the two different types of columns. The results show that the chiral MOC [Fe4L6](ClO4)8 exhibited excellent separation performance toward a wide range of organic compounds, which will be very attractive as a new chiral separation media and has potential application prospects in separation science.

Chiral metal-organic framework [Co2(d-cam)2(TMDPy)]@SiO2 core-shell microspheres for HPLC separation

Chiral metal-organic frameworks (MOFs), an emerging class of chiral porous materials, possess many excellent characteristics such as uniform and adjustable cavities, abundant chiral active sites and excellent chemical stability, which make them a promising candidate as new chiral stationary phases (CSPs) for usage in HPLC. Up to now, there are some homochiral MOFs that have been applied as CSPs for HPLC enantioseparations. Nevertheless, the irregular morphology of most prepared MOF crystals with wide size distribution often cause high column backpressure and low column efficiency for MOF packed columns, which is the main impediment for the practical applications of chiral MOFs in chiral separation. In this article, we adopted an in-situ growth method to prepare monodisperse homochiral MOF [Co2(d-cam)2(TMDPy)]@SiO2 core-shell composites as chiral selector for HPLC enantioseparation. The fabricated [Co2(d-cam)2(TMDPy)]@SiO2 column (column A) exhibited excellent chiral resolution ability toward various racemates. In addition, some positional isomers can be well separated on column A. Compared with the resolution ability of [Co2(d-cam)2(TMDPy)] packed column (column B), the column A shows higher column efficiency (e.g., 17,000 plates/m for trans-stilbene oxide) and lower background pressure (column pressure = 27 bar) than those of column B. The results indicated that the monodisperse chiral MOF [Co2(d-cam)2(TMDPy)]@SiO2 core-shell composites as CSP greatly improve the column efficiency and chiral resolution ability of the chiral MOF columns, providing a promising platform for chiral MOFs widely used in chiral separation.

Click preparation and application of chiral stationary phase based on intrinsic recognition ability of cyclodextrin

Most of the studies on cyclodextrin (CD)-based chiral stationary phase (CSP) have focused on the functional derivatization of CD or the bridging arms to introduce more interaction sites and thus improve the chiral resolution ability. At present, there are only a few reports on CSP that can reflect the intrinsic recognition ability of natural CD. In this study, a mono(6-mercapto-6-deoxy)-β-CD CSP (CSP1) with a clear and controllable structure was synthesized by the "thiol-ene" click reaction. CSP1 retained the intrinsic structure of natural CD to the maximum extent, and the bridge arm had no recognition site. The results of 13C solid-state nuclear magnetic resonance (SSNMR) and Fourier transform infrared (FTIR) analyses confirmed the successful preparation of CSP1. Elemental analysis results showed that compared with double-bond functionalized silica, the percentages of C, H, and N in CSP1 increased, and the calculated CD loading of CSP1 was 0.82 μmol/m2. Reversed-phase high performance liquid chromatography was performed for the chiral resolution of more than 50 chiral enantiomers, including isoxazoline, chiral lactide, chiral ketone, flavone, and dansyl amino acid. This fully demonstrated the intrinsic chiral recognition ability of natural CD, and the results showed that the intrinsic recognition ability of cyclodextrin was more conducive to the separation of Ph-Ph samples containing two hydrophobic benzene ring groups in the isoxazoline samples. For the Ph-Py and Ph-OPr samples, the separation effect was not satisfactory. The separation results for the Ph-Py samples were not ideal because the outer hydroxyl group of cyclodextrin could form a hydrogen bond with the pyridine nitrogen, thus hindering the inclusion and the separation effect. This eventually led to poor separation of the enantiomers. While the pyrrolidone group in the Ph-OPr sample could also form a good inclusion complex with cyclodextrin, its higher polarity weakened the inclusion effect compared to that for benzene rings, thus leading to poor chirality separation results. For chiral lactides, the intrinsic recognition ability of CD was good only for the separation of some samples. In the separation of chiral ketones, large steric hindrance effect inhibited the intrinsic recognition ability of CD, and the separation effect of such samples on CSP1 was not ideal. External functional groups were required in some cases to further regulate the chiral recognition performance. The molecular structure of dansyl amino acids played an important role in the separation effect, in addition to the intrinsic recognition ability of CD. The number of side chains in the substituent also affected the quality of separation. Lengthening the side chain or increasing the hydrophobicity could effectively improve the separation efficiency. The separation effect of flavanone samples on CSP1 was ordinary. The substituent positions also affected the separation effect. In order to further explore the intrinsic recognition ability of CD, the functional triazole-bridged CD-CSP (CSP2) and imidazole-bridged CD-CSP (CSP3) (the surface CD loadings of CSP2 and CSP3 were 0.51 μmol/m2 and 0.46 μmol/m2, respectively) prepared earlier were selected and compared under the same chromatographic conditions. The results showed that the separation of the sample was related not only to the structure of the chiral medium but also to the structure of the sample molecules. Functional modification of the bridge arm could improve the selectivity of some enantiomers, but would also cause partial loss of the intrinsic chiral recognition ability of CD. For samples with the intrinsic recognition ability of CD to facilitate separation, no functional group had to be added to the bridge arm when designing a chiral medium. This study provides a useful reference for the design of CD-based CSPs.

Preparation and performance of a poly(ethyleneimine) embedded N-acetyl-L-phenylalanine mixed-mode stationary phase for HPLC

Poly(ethyleneimine) and N-acetyl-L-phenylalanine were bonded on the surface of activated silica to prepare a new multifunctional polar embedded stationary phase material named Sil-PEI-APH. The material was characterized by Fourier transform infrared spectroscopy (FT-IR), elemental analysis (EA) and thermogravimetric analysis (TGA). Then the synthesized material was loaded into the empty column tube by high pressure driving homogenization method and used as mixed-mode chromatography involving mechanisms of reversed-phase (RPLC), hydrophilic (HILIC) and ion exchange interactions (IEC). Based on these interactions, successful separation could be achieved among several groups of aromatic compounds with different polarities. In detail, the separations of alkylbenzenes, polycyclic aromatic hydrocarbons (PAHs), biphenyl isomers and flavonoids were achieved in RPLC mode. Nucleotides/nucleosides were separated in HILIC mode. Additionally, phenols, benzoic acids were separated successfully in IEC mode. The separation of anilines depended on the various separation modes. Investigations about effects of mobile phase constitution and pH on retention further demonstrated the mixed-mode retention mechanisms of the column. Meanwhile, chiral resolution ability was proved by separation of warfarin as model analyte. In a word, the developed stationary phase exhibited multiple performances and the separations for types of analytes were thus achieved.

Chiral Metal-Organic Framework d-His-ZIF-8@SiO2 Core-Shell Microspheres Used for HPLC Enantioseparations.

Chiral metal-organic frameworks (MOFs) have aroused great attention in the chiral separation field based on their excellent characteristics, including abundant topological structures, large surface area, adjustable pore/channel sizes, multiple active sites, and good chemical stability. However, the irregular morphology and nonuniformity of the synthesized MOF particles cause low column efficiency and high column backpressure for MOF-packed columns, which significantly affects their separation performance. Herein, we prepared a homochiral d-his-ZIF-8@SiO2 composite by growing of d-his-ZIF-8 on the carboxylic-functionalized SiO2 microspheres via a simple one-pot synthesis approach. The d-his-ZIF-8@SiO2 core-shell microspheres with uniform particles and narrow size distribution were applied as the chiral stationary phase (CSP) for enantioseparations in HPLC. Various racemates were separated on the d-his-ZIF-8@SiO2-packed columns with n-hexane/isopropanol as the mobile phase. Eighteen racemates including alcohol, phenol, amine, ketone, and organic acid were well resolved on the homochiral d-his-ZIF-8@SiO2 CSP. The d-his-ZIF-8@SiO2 core-shell microspheres' CSP possesses an excellent chiral resolution ability toward various racemic compounds with good reproducibility and stability. Hence, the fabrication of chiral MOF@SiO2 core-shell microspheres is an effective strategy to improve the application of homochiral MOFs as CSPs in the field of chromatography.

Preparation and evaluation of biselector bonded-type multifunctional chiral stationary phase based on dialdehyde cellulose and 6-monodeoxy-6-monoamino-β-cyclodextrine derivatives.

A novel biselector bonded-type multifunctional chiral stationary phase (MCSP) was prepared by covalently crosslinking dialdehyde cellulose (DAC) with 6-monodeoxy-6-monoamino-β-cyclodextrine (CD) via Schiff base reaction. The biselector bonded-type MCSP had good chiral and achiral chromatographic performance in normal phase (NP) and reversed phase (RP) modes. Seven and eight enantiomers were successfully separated on the prepared biselector bonded-type MCSP in NP and RP modes, respectively. The biselector bonded-type MCSP showed enhanced chiral resolution ability compared with single selector chiral stationary phases due to the simultaneous introduction of DAC and 6-monodeoxy-6-monoamino-β-CD on the surface of silica gel. Aromatic compounds including polycyclic aromatic hydrocarbons, anilines, phenols, phenylates, and aromatic acids were choosed as analytes to investigate the achiral chromatographic performance of the biselector bonded-type MCSP in NP and RP modes. Chromatographic evaluation results showed that the above aromatic compounds were essentially capable of achieving baseline separation by hydrophobic interaction, π-π interaction, and π-π electron-donor-acceptor interaction. Moreover, the host-guest inclusion effect of 6-monodeoxy-6-monoamino-β-CD and the multiple interactions made the biselector bonded-type MCSP have good steric selectivity. The preparation method of the biselector bonded-type MCSP was simple and provided a new idea and strategy for the preparation of the subsequent novel biselector MCSP.

De novo synthesis of microspheical cellulose 3,5-dichlorophenylcarbamates: An organic-inorganic hybrid chiral stationary phase for enantiospearation

High-performance liquid chromatography (HPLC) is one of the most powerful methods to obtain optically pure enantiomers, and chiral stationary phase (CSP) with high mechanical strength and excellent chiral recognition performance is a key for the development of preparative chiral chromatography. Compared to traditional CSPs prepared by coating or immobilizing onto macro-porous silica gel with disadvantages of a limited specific surface area and narrow range of eluents, organic-inorganic hybrids materials on basis of sol-gel chemistry may feature a high density of chiral selectors and excellent mechanical strength. Herein, we reported a de novo synthesis strategy for preparing organic-inorganic hybrid CSPs with good chiral resolution ability and high mechanical strength by sol-gel reactions followed by an end-capping process to eliminate the residual silica hydroxyl groups using cellulose 3,5-dichlorophenylcarbamates and tetraethyl orthosilicate (TEOS) as precursors. The synthesized cellulose-derived CSP was comprehensively characterized by 29Si CP/MAS NMR, FT-IR, TGA, SEM, EDX and BET surface area analysis. Furthermore, seven typical enantiomers were used to evaluate the enantioseparation ability of hybrid CSPs by HPLC, which demonstrated that the hybrid CSPs exhibited similar and even higher chiral recognition abilities to immobilized-type CSP and commercially available Chiralpak IC, such as trans-2,3-diphenyloxirane, 2-phenylcyclohexanone, and benzoin with separation factor (α) of 1.65, 1.44 and 1.10. A series of characterization and results indicated that the organosilica hybrid CSPs prepared in this work have adequate chiral recognition ability for enantioseparation.

Chiral PLLA particles with tunable morphology and lamellar structure for enantioselective crystallization

Poly(L-lactide) (PLLA) porous materials have become increasingly important for practical applications. However, the methods for preparing PLLA-based porous particles are quite limited. The chirality of PLLA materials remains scarcely explored even though PLLA is a well-known chiral polymer. In this paper, we establish an unprecedented, facile approach for preparing PLLA particles with lamellar structures by precipitation polymerization. By adjusting polymerization conditions (solvent and temperature), a series of PLLA particles with tunable morphology was fabricated. The resulting particles were characterized by SEM, CD, XRD, DSC, and GPC measurements. We further explored chiral resolution ability of the PLLA particles used as chiral additive to induce enantioselective crystallization. According to SEM, CD, and XRD characterizations, PLLA particles show considerable enantioselectivity and preferentially induce l-threonine to crystallize from the racemic solution. Besides, enhancing the crystallinity of PLLA particles is beneficial for improving the particles’ enantiodifferentiating ability. The present study provides a versatile platform for developing novel PLLA materials, which deserve more attention as chiral biomaterials.

Facile Synthesis of Optically Active and Thermoresponsive Star Block Copolymers Carrying Helical Polyisocyanide Arms and Their Thermo-Triggered Chiral Resolution Ability.

A left-handed helical poly(phenyl isocyanide) bearing a norbornene unit and a Pd(II) complex on each terminus was prepared. The norbornene terminus was core cross-linked with a bisnorbornene linker via ring-opening metathesis polymerization (ROMP), yielding a star polymer carrying left-handed helical arms decorated with Pd(II) units at the exterior. The optical activities of the helical arms were maintained after the cross-linking reaction. The Pd(II) units on the surface of the star polymer were chain extended with a new phenyl isocyanide bearing three hydrophilic triethylene glycol monomethyl chains, which afforded an amphiphilic star block copolymer carrying helical arms. Such a star block copolymer showed excellent thermoresponsiveness with the lower critical solution temperature (LCST) around 55 °C. This optically active and thermoresponsive star polymer can enantioselectively capture the S-enantiomer of racemic methyl benzyl alcohol solution at a temperature lower than the LCST and precipitated when the temperature was higher than the LCST, leaving the R-enantiomer in the solution. The enantiomeric excess (ee) of the isolated enantiomer is up to 75%.

Facile synthesis of optically active helical poly(phenyl isocyanide) brushes on a silicon surface and their chiral resolution ability

Optically active helical poly(phenyl isocyanide) brushes grafted on a silicon surface were prepared and their chiral resolution ability was investigated.

Sequence requirements of oligonucleotide chiral selectors for the capillary electrophoresis resolution of low-affinity DNA binders.

We recently reported that a great variety of DNA oligonucleotides (ONs) used as chiral selectors in partial-filling capillary electrophoresis (CE) exhibited interesting enantioresolution properties toward low-affinity DNA binders. Herein, the sequence prerequisites of ONs for the CE enantioseparation process were studied. First, the chiral resolution properties of a series of homopolymeric sequences (Poly-dT) of different lengths (from 5 to 60-mer) were investigated. It was shown that the size increase-dependent random coil-like conformation of Poly-dT favorably acted on the apparent selectivity and resolution. The base-unpairing state constituted also an important factor in the chiral resolution ability of ONs as the switch from the single-stranded to double-stranded structure was responsible for a significant decrease in the analyte selectivity range. Finally, the chemical diversity enhanced the enantioresolution ability of single-stranded ONs. The present work could lay the foundation for the design of performant ON chiral selectors for the CE separation of weak DNA binder enantiomers.

Synthesis of l -phenylalanine imprinted hydrogels with anti-biofouling capability by using a novel zwitterionic functional monomer

Abstract A novel zwitterion was synthesized and used as a functional monomer in the synthesis of l -phenylalanine ( l -phe) imprinted hydrogel (MIH). Molecular simulation demonstrated that the binding energy of the zwitterion with l -phe was −23.50 kcal mol−1 in the aqueous phase, which was higher than the binding energies of l -phe with other traditional functional monomers. Binding experiments also showed that MIH made using the zwitterion had a higher adsorption capacity and imprinting factor (IF) compared to MIHs made using either acrylic acid or 4-vinylpyridine. Optimization studies showed that the best recognition ability of MIH was obtained when the molar ratio of zwitterion to l -phe was 2:1 in the synthesis of MIH. Adsorption kinetics experiments showed that MIH could equilibrate within 120 min, and adsorption isotherms obtained experimentally demonstrated that MIH had a good adsorption capacity of 9.8 mg g−1 with a high imprinting factor of 2.0 in 0.3 mg mL−1 concentrated l -phe solution. Circular dichroism spectroscopy confirmed the excellent chiral resolution ability of MIH for racemic phenylalanine. Furthermore, MIH prepared using the zwitterion exhibited strong anti-fouling capability and could be utilized to extract l -phe from the protein solution.

A gas chromatographic stationary of homochiral metal-peptide framework material and its applications

Homochiral metal-organic frameworks(HMOFs) have special properties, such as high surface area, fasci-nating structures and excellent chemical and thermal stability and they have broad application prospects. In this work, we reported the use of HMOF Co-L-GG(L-GG, dipeptide H-Gly-L-Glu) as the stationary phase for separating race-mates in gas chromatography. Co-L-GG coated fused silica capillary column(10 m×250 μm i.d.) was prepared via a dynamic coating method. Thirty racemates belonging to different classes of organic compounds were resolved in-cluding halohydrocarbons, ketones, esters, ethers, organic acids, epoxyalkanes, alcohols and sulfoxides. When com-pared with the previously reported chiral MOFs-coated capillary columns, the Co-L-GG coated column exhibited broader chiral resolution ability towards chiral compounds.

Preparation and chiral recognition of heterosubstituted amylose derivatives-based chiral stationary phases

Two novel amylose derivatives, namely amylose 2-benzoate-3-(4-methylphenylcarbamate)-6-(3,5-dichlorophenylcarbamate) and amylose 2-benzoate-3-(3,5-dichlorophenylcarbamate)-6-(4-methylphenylcarbamate), were prepared utilizing a serial regioselective process. After coated onto aminopropyl silica gel, they were utilized as chiral stationary phases (CSPs) for high performance liquid chromatography. Investigations indicated that the CSPs exhibited characteristic chiral recognition and their chiral recognition abilities were much higher than those of amylose tris(3,5-dichlorophenylcarbamate) (ADCPC), a homosubstituted derivative. The nature and position of the substituents at 3-, and 6-positions of a glucose unit had great influence on the chiral resolution abilities of the amylose derivatives. Some chiral compounds which were not effectively resolved on the commercial column Chiralpak AD were effectively separated on the new CSPs. Moreover, with all the eight tested racemates resolved, amylose 2-benzoate-3-(4-methylphenylcarbamate)-6-(3,5-dichlorophenylcarbamate) exhibited relatively high chiral recognition and might be a potential useful CSP.