Optimization of Liquid Crystalline Mixtures Enantioseparation on Polysaccharide-Based Chiral Stationary Phases by Reversed-Phase Chiral Liquid Chromatography

Enantioseparation of nineteen liquid crystalline racemic mixtures obtained based on (R,S)-2-octanol was studied in reversed-phase mode on an amylose tris(3-chloro-5-methylphenylcarbamate) (ReproSil Chiral-MIG) and a cellulose tris(3,5-dichlorophenylcarbamate) (ReproSil Chiral-MIC). These polysaccharide-based chiral stationary phase (CSP) columns for High-Performance Liquid Chromatography (HPLC) were highly effective in recognizing isomers of minor structural differences. The mobile phase (MP), which consists of acetonitrile (ACN)/water (H2O) at different volume ratios, was used. The mobile phases were pumped at a flow rate of 0.3, 0.5, or 1 mL·min-1 with a column temperature of 25 °C, using a UV detector at 254 nm. The order of the elution was also determined. The chromatographic parameters, such as resolution (Rs), selectivity (α), and the number of theoretical plates, i.e., column efficiency (N), were determined. The polysaccharide-based CSP columns have unique advantages in separation technology, and this study has shown the potential usefulness of the CSP columns in separating liquid crystalline racemic mixtures belonging to the same homologous series.

Homochiral π-Rich Covalent Organic Frameworks Enabled Chirality Imprinting in Conjugated Polymers: Confined Polymerization and Chiral Memory from Scratch

Optically active π-conjugated polymers (OACPs) have garnered increasing research interest for their resemblance to biological helices and intriguing chirality-related functions. Traditional methods for synthesizing involve decorating achiral conjugated polymer architectures with enantiopure side substituents through complex organic synthesis. Here, we report a new approach: the templated synthesis of unsubstituted OACPs via supramolecularly confined polymerizations of achiral monomers within nanopores of 2D or 3D chiral covalent organic frameworks (CCOFs). We show that the chiral π-rich nanospaces facilitate the in situ enantiospecific polymerization and self-propagation, akin to nonenzymatic polymerase chain reaction (PCR) system, resulting in chiral imprinting. The stacked polymer chains are kinetically inert enough to memorize the chiral information after liberating from CCOFs, and even after treatment at temperature up to 200 °C. The isolated OACPs demonstrate robust enantiodiscrimination, achieving up to 85 % ee in separating racemic amino acids. This underscores the potential of utilizing CCOFs as templates for supramolecularly imprinting optical activity into CPs, paving the way for synthetic evolution and advanced functional exploration of OACPs.

Chiral separation and molecular modeling study of decursinol and its derivatives using polysaccharide-based chiral stationary phases

Plant-based bioactive substances have long been used to treat inflammatory ailments, owing to their low toxicity and cost-effectiveness. To enhance plant treatment by eliminating undesirable isomers, optimizing the chiral separation techniques in pharmaceutical and clinical studies is important. This study reported a simple and effective method for chiral separation of decursinol and its derivatives, which are pyranocoumarin compounds with anti-cancer and anti-inflammatory properties. Baseline separation (Rs >1.5) was achieved using five different polysaccharide-based chiral stationary phases (CSPs) that differed in chiral origin, chiral selector chemistry, and preparation technique. To separate all six enantiomers simultaneously, n-hexane and three alcohol modifiers (ethanol, isopropanol, and n-butanol) were used as mobile phases in the normal-phase mode. The chiral separation ability of each column with various mobile phase compositions was compared and discussed. As a result, amylose-based CSPs with linear alcohol modifiers demonstrated superior resolution. Three cases of elution order reversal caused by modifications of CSPs and alcohol modifiers were observed and thoroughly analyzed. To elucidate the chiral recognition mechanism and enantiomeric elution order (EEO) reversal phenomenon, detailed molecular docking simulations were conducted. The R- and S-enantiomers of decursinol, epoxide, and CGK012 exhibited binding energies of -6.6, -6.3, -6.2, -6.3, -7.3, and -7.5 kcal/mol, respectively. The magnitude of the difference in binding energies was consistent with the elution order and enantioselectivity (α) of the analytes. The molecular simulation results demonstrated that hydrogen bonds, π-π interactions, and hydrophobic interactions have a significant impact on chiral recognition mechanisms. Overall, this study presented a novel and logical approach of optimizing chiral separation techniques in the pharmaceutical and clinical industries. Our findings could be further applied for screening and optimizing enantiomeric separation.

Photoluminescent ellipsometric circular dichroism

A novel spectroscopic technique, photoluminescent ellipsometric circular dichroism (PECD), which distinguishes all radiative electronic transitions related to molecular chiral centers. Additionally, it is proposed as complementary to the ellipsometric Raman spectroscopy (ERS) technique, thus establishing a relationship between vibrational modes and electronic transitions, associated with molecular chiral centers. In this way, PECD turns into a powerful technique for chiral material characterization. The PECD technique was performed on a chiral oligomer (1R,2R)-diiminocyclohexane, and its derivative polymer. A complete photophysical characterization in solution was performed to corroborate the new PECD technique.

Enantioseparation, quantification, molecular docking and molecular dynamics study of five β-adrenergic blockers on Lux-Cellulose-2 column

Enantioseparation of five β-adrenergic blockers was studied using two mobile phases on a cellulose tris(3-chloro-4-methylphenylcarbamate) (Lux-Cellulose-2) chiral column in normal phase mode. The first mobile phase composed of n-hexane: ethanol: diethylamine 60: 40: 0.1 by volume has successfully resolved the chromatographic peaks of three pairs of β-adrenergic blockers namely, bisoprolol, carvedilol and atenolol. A mixture of n-hexane: ethanol: diethyl amine 75: 25: 0.1 by volume was used as the second mobile phase to separate the four pairs of enantiomers, metoprolol, carvedilol, nebivolol and atenolol with high resolution values. The mobile phases were pumped at a flow rate 1 mL/min with column temperature 25 °C using a UV detector at 230 nm. Molecular docking simulations of the five pairs of enantiomers was carried out in the cavities of the chiral stationary phase to gain a better understanding of the interaction between analyte enantiomers and chiral stationary phase and to better understand the mechanism of chiral recognition. According to the results, hydrogen bond interactions and π-π- interactions were the main types of interaction involved in the chiral recognition. Molecular dynamics simulation was performed to investigate the solvent effect on the interaction of the five pair of enantiomers in the chiral stationary phase cavity under dynamic conditions.

Conglomerate, Racemate, and Achiral Crystals of Polymetallic Europium(III) Compounds of Bis- or Tris-β-diketonate Ligands and Circularly Polarized Luminescence Study

This work reports (a) conglomerate and racemic crystal structures of [(Δ,Δ,Δ,Δ,Δ,Δ)- or/and (Λ,Λ,Λ,Λ,Λ,Λ)-Eu^III ₆(TTP)₈(OH₂)₆Na₄] _n coordination polymers, (b) racemic crystal structures of (Δ,Δ,Δ,Δ)-/(Λ,Λ,Λ,Λ)-Eu^III ₄(TTP)₄(bipy)₄(MEK)₂(OH₂)₂ tetrahedral clusters, and (c) the achiral crystal structure of the [Eu^III ₂(BTP)₄(OH₂)₂Na₂] _n coordination polymer (where BTP = dianionic bis-β-diketonate, TTP = trianionic tris-β-diketonate, and bipy = 2,2'-bipyridine). The screw coordination arrangement of the TTP ligand has led to the formation of homoconfigurational racemic Eu^III products. The conglomerate crystallization of [Eu^III ₆(TTP)₈(OH₂)₆Na₄] _n appears to be caused by the presence of the sodium, Na⁺ counterions, and interactions between oxygen atoms and the trifluoromethyl unit of the TTP ligand and Na⁺ ions. All the Eu^III compounds exhibit characteristic red luminescence (⁵D₀ → ⁷F_J, J = 0-4) in solution or in the solid crystalline state. Circularly polarized luminescence (CPL) was observed in the chiral Eu^III ₆(TTP)₈(OH₂)₆Na₄] _n species, displaying a |g _lum| value in the range of 0.15 to 0.68 at the ⁵D₀ → ⁷F₁ emission band. Subtle changes of the [Eu^III ₆(TTP)₈(OH₂)₆Na₄] _n structure which may be due to selection of twinned crystals or crystals that do not correspond to a perfect spontaneous resolution, are considered to be responsible for the variation in the observed CPL values.

An Evaluation of Immobilized Poly-(S)-N-(1-phenylethyl)acrylamide Chiral Stationary Phases

In this study, brush type and polymer type stationary phases were prepared based on (S)-N-(1-phenylethyl) acrylamide, and the polymeric stationary phase demonstrated superior chiral recognition ability. The two polymeric stationary phases were synthesized by two strategies, one was the “grafting from” method, which obtained polymer CSP by initiating monomer polymerization on the surface of 3-methacrylatepropyl silica gel, and the other was “grafting to”, which fixed the copolymer of (S)-N-(1-phenylethyl) acrylamide and trimethoxysilylpropyl methacrylate on silica gel. A comparison of these two bonding modes revealed that the stationary phase produced by “grafting to” had higher chiral recognition ability. Further improvement can be achieved by the end-capping of silanol groups with trimethylchlorosilane to reduce non-enantioselective retention caused by residual silanol groups and improve the peak shape of enantiomers. Chiral separation in subcritical fluid chromatography was also studied. Similar enantioselectivity results with higher resolution were observed due to the improvement of peak shape.

Recognition in the Domain of Molecular Chirality: From Noncovalent Interactions to Separation of Enantiomers

It is not a coincidence that both chirality and noncovalent interactions are ubiquitous in nature and synthetic molecular systems. Noncovalent interactivity between chiral molecules underlies enantioselective recognition as a fundamental phenomenon regulating life and human activities. Thus, noncovalent interactions represent the narrative thread of a fascinating story which goes across several disciplines of medical, chemical, physical, biological, and other natural sciences. This review has been conceived with the awareness that a modern attitude toward molecular chirality and its consequences needs to be founded on multidisciplinary approaches to disclose the molecular basis of essential enantioselective phenomena in the domain of chemical, physical, and life sciences. With the primary aim of discussing this topic in an integrated way, a comprehensive pool of rational and systematic multidisciplinary information is provided, which concerns the fundamentals of chirality, a description of noncovalent interactions, and their implications in enantioselective processes occurring in different contexts. A specific focus is devoted to enantioselection in chromatography and electromigration techniques because of their unique feature as "multistep" processes. A second motivation for writing this review is to make a clear statement about the state of the art, the tools we have at our disposal, and what is still missing to fully understand the mechanisms underlying enantioselective recognition.

Enantioseparation of syn- and anti-3,5-Disubstituted Hydantoins by HPLC and SFC on Immobilized Polysaccharides-Based Chiral Stationary Phases

The enantioseparation of syn- and anti-3,5-disubstituted hydantoins 5a–i was investigated on three immobilized polysaccharide-based columns (CHIRAL ART Amylose-SA, CHIRAL ART Cellulose-SB, CHIRAL ART Cellulose-SC) by high performance liquid chromatography (HPLC) using n-hexane/2-PrOH (90/10, v/v) or 100% dimethyl carbonate (DMC) as mobile phases, respectively, and by supercritical fluid chromatography (SFC) using CO2/alcohol (MeOH, EtOH, 2-PrOH; 80/20, v/v) as a mobile phase. The chromatographic parameters, such as separation and resolution factors, have indicated that Amylose-SA is more suitable for enantioseparation of the most analyzed syn- and anti-3,5-disubstituted hydantoins than Celullose-SB and Cellulose-SC in both HPLC and SFC modalities. All three tested columns showed better enantiorecognition ability toward anti-hydantoins compared to syn-hydantoins, both in HPLC and SFC modes. We have demonstrated that environmentally friendly solvent DMC can be efficiently used as the mobile phase in HPLC mode for enantioseparation of hydantoins on the immobilized polysaccharide-based chiral stationary phases.

Characteristic and complementary chiral recognition ability of four recently developed immobilized chiral stationary phases based on amylose and cellulose phenyl carbamates and benzoates

To date, various immobilized chiral stationary phases (CSPs) have been developed. The immobilized CSPs have opened up possibilities not only maintaining the high chiral recognition abilities as well as corresponding coated ones but also affording high durability to various mobile phase. This report directed to investigate enantioseparation of recently launched four immobilized CSPs with cellulose and amylose backbones under normal phase liquid chromatography conditions. Their chiral recognition abilities were compared with previously developed six immobilized CSPs. Particularly, we focused on the complementarity for chiral recognitions. Among them, amylose tris(3‐chloro‐5‐methylphenylcarbamate) CSP, namely, CHIRALPAK IG, showed notable chiral recognition abilities to various racemates. As expected, the investigated immobilized CSPs represented remarkable durability to wide range of mobile phases, whereas the corresponding coated CSPs could not be run due to the irreversible degradation. Taking advantage of unrestricted solvent compatibility, chiral separation selectivities were improved for some racemates.

Application of Polysaccharide-Based Chiral High-Performance Liquid Chromatography Columns for the Separation of Regio-, E/Z-, and Enantio-Isomeric Mixtures of Allylic Compounds

Daicel Chiralpak IA, IB, and IC, which are the polysaccharide-based chiral stationary phase (CSP) columns for high-performance liquid chromatography (HPLC), were applied in the separation of the non-enantiomeric isomeric mixtures obtained by the various allylation reactions and were highly effective in separating the regio- and (E)/(Z)-isomers in the allylation products. Due to the close structural similarity of the isomeric allylic compounds in the reaction mixtures, separations of the isomers are laborious and could not be accomplished by the conventional methods such as silica gel column chromatography, silica gel HPLC, preparative GPC, distillation, and so forth. This study has shown potential advantages of using the polysaccharide-based CSP columns in the separation of not only enantiomeric but also non-enantiomeric isomeric mixtures.

Our research cooperation with Professor Yoshio Okamoto

This article summarizes our cooperation with the research group of Prof. Yoshio Okamoto at Nagoya University during the period of time between 1992 and 2005. Although the text deals entirely with enantioseparations in high-performance liquid chromatography, capillary electrophoresis, and capillary electrochromatography, this is not a detailed review in any of these areas. The text highlights selected aspects of these techniques, which have been the subject of our joint research and in part their reflection in follow-up research by our and other research groups. Together with more systematically studied topics, aspects such as ultrafast separation of enantiomers, uncommonly high separation factor of enantiomers and other related issues are also addressed.

Solvent-dependent helix inversion in optically active poly(diphenylacetylene)s and their chiral recognition abilities as chiral stationary phases for high-performance liquid chromatography

We report the first example of solvent-dependent helix inversion in poly(diphenylacetylene) (PDPA) derivatives. Asymmetrically substituted PDPAs bearing optically active substituents linked through amide bonds formed preferred-handed helical conformations because of the optically active substituents in the pendants, whose helix-senses were inverted upon thermal annealing in polar solvents such as N,N-dimethylformamide and dimethylsulfoxide and in nonpolar solvents such as tetrachloroethane. Unlike the solvent-dependent helix inversion reported for other dynamic helical polymers, the macromolecular helicity induced in the polymer backbone of these PDPAs upon thermal annealing was stably maintained at room temperature, independent of the solvent polarity. These diastereomeric PDPAs with opposite helix-senses generated almost mirror-imaged left- and right-handed circularly polarized light in the same solvent at room temperature. Taking advantage of this unique solvent-dependent helix inversion property, the diastereomeric PDPAs with opposite helix-senses were coated on macroporous silica gel and applied to chiral stationary phases for high-performance liquid chromatography. Despite having the same optically active substituents on the pendant phenyl rings, they showed completely different chiral recognition abilities toward many racemates depending on the helix-sense of the polymer backbone, and the elution order of the enantiomers was reversed for some racemates. The combination of the helix-sense of the polymer backbone and the chirality of the pendants, which afforded a higher chiral recognition ability, differed depending on the racemates.

Macromolecular helicity induction and static helicity memory of poly(biphenylylacetylene)s bearing aromatic pendant groups and their use as chiral stationary phases for high-performance liquid chromatography

Two novel poly(biphenylylacetylene)s (PBPAs) bearing achiral alkylphenyl groups at the 4'-position of the biphenyl pendant through ester linkers with different sequences were synthesized by the rhodium-catalyzed polymerization of the corresponding monomers. The influence of the alkylphenyl pendants and the ester sequences on the macromolecular helicity induction and subsequent static helicity memory was investigated. In addition, the chiral recognition ability as chiral stationary phases for high-performance liquid chromatography of the helicity-memorized PBPAs was also examined. Both polymers formed almost perfect right- and left-handed helical conformations through noncovalent chiral interactions with enantiomeric alcohols, and their induced macromolecular helicities were completely retained ("memorized") after removal of the helix inducer. A PBPA bearing a 4-n-butylphenoxycarbonyl pendant group with a static helicity memory showed a remarkably high chiral recognition ability toward a wide variety of chiral aromatics, including simple point chiral compounds, axially chiral biaryls, a chiral spiro compound, helicenes, and planar chiral cyclophanes, particularly under the reversed-phase conditions.

Polysaccharides as separation media for the separation of proteins, peptides and stereoisomers of amino acids

Reliable separation of peptides, amino acids and proteins as accurate as possible with the maximum conformation and biological activity is crucial and essential for drug discovery. Polysaccharide, as one of the most abundant natural biopolymers with optical activity on earth, is easy to be functionalized due to lots of hydroxyl groups on glucose units. Over the last few decades, polysaccharide derivatives are gradually employed as effective separation media. The highly-ordered helical structure contributes to complex, diverse molecular recognition ability, allowing polysaccharide derivatives to selectively interact with different analytes. This article reviews the development, application and prospects of polysaccharides as separation media in the separation of proteins, peptides and amino acids in recent years. The chiral molecules mechanism, advantages, limitations, development status and challenges faced by polysaccharides as separation media in molecular recognition are summarized. Meanwhile, the direction of its continued development and future prospects are also discussed.

Helical supramolecular polymers with rationally designed binding sites for chiral guest recognition

Since various helical supramolecular polymers became available, their application to molecular chirality recognition have been anticipated but not extensively studied. So far, only a few examples of chiral reactions have been reported, but none for chiral separation. Here, we report the application of a helical supramolecular polymer to the enantio-separation of chiral guest molecules. The monomer of this supramolecular polymer is the salt-pair of a dendritic carboxylic acid with an enantiopure amino alcohol. In an apolar solvent, this salt-pair stacks via hydrogen bonds to form a helical polymer. In conjunction with this carboxylic acid, various amino alcohols afford supramolecular polymers, whose helical handedness is determined by the stereochemistry of the amino alcohols. When two salts with the same chirality are mixed, they undergo copolymerization, while those with opposite chirality do not. Owing to this stereoselective copolymerizability, the helical supramolecular polymer could bias the enantiomeric composition of chiral amino alcohols.

Since various helical supramolecular polymers became available, their application in molecular chirality recognition have been anticipated but not extensively studied. Here, the authors report the application of a helical supramolecular polymer for the enantio separation of chiral guest molecules.

Chiral covalent organic frameworks: design, synthesis and property

Owing to the unique structural features and facile tunability of the subcomponents and channels, chiral COFs show great potential in heterogeneous catalysis, enantioselective separation, and recognition.

Enantioseparation of N-acetyl-dl-cysteine as o-phtaldialdehyde derivatives obtained with various primary aliphatic amine additives on polysaccharide-based chiral stationary phases

A sensitive and rapid high-performance liquid chromatography (HPLC) method was developed to enantioseparation of N-acetyl-dl-cysteine after precolumn derivatization using o-phthaldialdehyde and primary aliphatic amines. Seven polysaccharide-based chiral columns were tested in a reversed phase mode. Under the optimal chromatographic conditions, N-acetyl-dl-cysteine derivatives were completely enantioseparated on Chiralcel OZ-3R column with the resolution more than 2.5. The impact of various primary aliphatic amine additives as co-reagents (ethyl-, 1-propyl-, 1-butyl-, 1-pentylamine, (R)-sec-butylamine, tert-butylamine, isobutylamine, cyclopropyl-, cyclobutyl-, cyclopentyl and cyclohexylamine) used in precolumn derivatization step on the retention behavior (retention factor, selectivity and column efficiency) of N-acetyl-dl-cysteine derivatives was investigated. The effect of chromatographic conditions including acetonitrile content in the mobile phase, mobile phase pH, salt concentration in the mobile phase and column temperature on the retention and selectivity was investigated. The developed method was properly validated in terms of linearity, sensitivity (limit of detection and limit of quantification), accuracy, precision, intermediate precision and selectivity according to International Council for Harmonisation (ICH) of Technical Requirements for Pharmaceuticals for Human Use guidelines using internal normalization procedure. Proposed HPLC method was successfully applied to the determination of optical purity in commercially available N-acetyl-L-cysteine samples.

Helicity induction and memory effect in poly(biphenylylacetylene)s bearing various functional groups and their use as switchable chiral stationary phases for HPLC

Poly(biphenylylacetylene)s bearing various functional groups were demonstrated to be used as elution order switchable chiral stationary phases for HPLC.

Polysaccharide-Based Chiral Stationary Phases for Enantioseparations by High-Performance Liquid Chromatography: An Overview

This chapter summarizes the application of polysaccharide-based chiral stationary phases (CSPs) for separation of enantiomers in high-performance liquid chromatography (HPLC). Since this book contains dedicated chapters on enantioseparations using supercritical fluid chromatography (SFC), or capillary electrochromatography (CEC), the application of polysaccharide-based materials in these modes of liquid-phase separation techniques is touched just superficially. Special emphasis is directed toward a discussion of the optimization of polysaccharide-based chiral selectors, their attachment onto the carrier, and the optimization of the support. The optimization of the separation of enantiomers based on various parameters such as mobile phase composition and temperature is discussed.

Optical Activity of Homochiral Polyamides in Solution and Solid State: Structural Function for Chiral Induction

In this work, we have explored a simple and facile approach to prepare optically active helical polyamides. The hydroxyl groups of l-TA and d-TA were protected by O-alkoyl ester, and the resulting enantiomers, l-2,3-di-O-acetyl-tartaric acid (l-ATA) and d-2,3-di-O-acetyl-tartaric acid (d-ATA) crystals, were obtained. A pair of aliphatic homochiral polyamides of PA-l and PA-d are prepared using l-ATA, d-ATA, and achiral 1,11-undecanediamine as building blocks via interfacial polycondensation. PA-l and PA-d display negative and positive mirror circular dichroism (CD) spectra images in both solution and solid state. Moreover, the polyamides in solid state display different CD signals and stronger optical activity compared to those in ethanol and even the related chiral monomers in solid state, which was due to the helical conformation of the polyamides in solid state. Scanning electron microscopy results indicated that the aggregations of PA-l express left-handed helical sense, whereas those of PA-d express right-handed helix. In addition, the induced CD signals from the chiral conformation of the backbone become weaker when increasing the temperature from 0 to 60 °C in dilute solution. Either of the polyamides displays relatively stable CD images in solid state when elevating the temperature from 0 to 90 °C.

Optically active distorted cyclic triptycenes: chiral stationary phases for HPLC

A pair of optically active triptycene derivatives ((R,R)- and (S,S)-8) with a distorted cyclic structure were synthesized via an intramolecular etherification and evaluated as a novel chiral selector for high-performance liquid chromatography. The (R,R)- and (S,S)-8-based chiral stationary phases (CSPs) were found to be particularly effective in the resolution of axially chiral biaryl compounds. The importance of the distorted cyclic structure present in 8 for chiral recognition was demonstrated by comparisons with the corresponding non-cyclic model compound ((R,R)-9), which did not display enantioselectivity in the separation of the test racemates.

We have succeeded in developing triptycene-based chiral stationary phases with a distorted cyclic structure, which can resolve a series of axially chiral compounds.

Chromatographic enantioseparation by poly(biphenylylacetylene) derivatives with memory of both axial chirality and macromolecular helicity

Novel poly(biphenylylacetylene) derivatives bearing two acetyloxy groups at the 2- and 2'-positions and an alkoxycarbonyl group at the 4'-position of the biphenyl pendants (poly-Ac's) were synthesized by the polymerization of the corresponding biphenylylacetylenes using a rhodium catalyst. The obtained stereoregular (cis-transoidal) poly-Ac's folded into a predominantly one-handed helical conformation accompanied by a preferred-handed axially twisted conformation of the biphenyl pendants through noncovalent interactions with a chiral alcohol and both the induced main-chain helicity and the pendant axial chirality were maintained, that is, memorized, after complete removal of the chiral alcohol. The stability of the helicity memory of the poly-Ac's in a solution was lower than that of the analogous poly(biphenylylacetylene)s bearing two methoxymethoxy groups at the 2- and 2'-positions of the biphenyl pendants (poly-MOM's). In the solid state, however, the helicity memory of the poly-Ac's was much more stable and showed a better chiral recognition ability toward several racemates than that of the previously reported poly-MOM when used as a chiral stationary phase for high-performance liquid chromatography. In particular, the poly-Ac-based CSP with a helicity memory efficiently separated racemic benzoin derivatives into enantiomers.

Chiral stationary phases consisting of π-conjugated polymers bearing glucose-linked biphenyl units: reversible switching of resolution abilities based on a coil-to-helix transition

We have succeeded in developing a novel chiral stationary phase that can reversibly switch resolution abilities based on a coil-to-helix transition in a column.

Synthesis of Optically Active Poly(diphenylacetylene)s Using Polymer Reactions and an Evaluation of Their Chiral Recognition Abilities as Chiral Stationary Phases for HPLC

A series of optically active poly(diphenylacetylene) derivatives bearing a chiral substituent (poly-2S) or chiral and achiral substituents (poly-(2Sx-co-31-x)) on all of their pendant phenyl rings were synthesized by the reaction of poly(bis(4-carboxyphenyl)acetylene) with (S)-1-phenylethylamine ((S)-2) or benzylamine (3) in the presence of a condensing reagent. Their chiroptical properties and chiral recognition abilities as chiral stationary phases (CSPs) for high-performance liquid chromatography (HPLC) were investigated. Poly-2S and poly-(2Sx-co-31-x) (0.06 < x < 0.71) formed a preferred-handed helical conformation with opposite helical senses after thermal annealing despite possessing the same chiral pendant (h-poly-2S and h-poly-(2Sx-co-31-x)). Furthermore, h-poly-2S and h-poly-(2S0.36-co-30.64) emitted circularly polarized luminescence with opposite signs. h-Poly-2S showed higher chiral recognition abilities toward a larger number of racemates than poly-2S without a preferred-handed helicity and the previously reported preferred-handed poly(diphenylacetylene) derivative bearing the same chiral substituent on half of its pendant phenyl rings. h-Poly-(2S0.36-co-30.64) also exhibited good chiral recognition abilities toward several racemates, though the elution order of some enantiomers was reversed compared with h-poly-2S.

Preparation and evaluation of immobilized 4-methylbenzoylcellulose stationary phases for enantioselective separations

A photochemical method for immobilizing polysaccharide derivatives on silica gel has been developed and applied to 4-methylbenzoyl cellulose (PMBC). The photochemically immobilized materials have been used as chiral stationary phases (CSPs) for the chromatographic separation of the stereoisomers of chiral molecules. Through to the immobilization which makes the chromatographic material insoluble in almost all organic solvents, there no restriction regarding the kind of solvent used in the mobile phase. This feature permits to considerably extend the possibilities to improve the selectivity of the separations and or the solubility of the solute in the mobile phase. The influence of various parameters such as immobilization process, cross-linker type and amount on the chromatographic properties and chiral recognition ability of the resulting CSPs has been investigated using a set of chiral molecules. The impact of the amount of coated polysaccharide material on chiral recognition ability was also examined.