Enantioseparation performance of novel benzimido-β-cyclodextrins derivatized by ionic liquids as chiral stationary phases

Studies on the Removal of Malachite Green from Its Aqueous Solution Using Water-Insoluble β-Cyclodextrin Polymers

The rising global pollution of natural waters by dyes has brought to light the need for adaptable and efficient removal techniques. To create water-insoluble β-cyclodextrin (β-CD) polymers like CA/-CD, TA/-CD, and MA/-CD, several organic acids including citric acid (CA), tartaric acid (TA), and malic acid (MA) were cross-linked with β-cyclodextrin in this study. The obtained polymers were characterized by different advanced analytical techniques such as FTIR, SEM, and UV-vis spectrophotometry. Malachite green dye was removed from aqueous solutions using the synthesized polymers by adsorption. The adsorption investigation was conducted under several conditions, including pH, adsorbent mass, dye concentration, temperature, contact time, adsorption isotherm, and kinetics. The adsorbent CA/β-CD shows the highest adsorption of MG dye in all of the conditions because it contains a high number of carboxyl groups. The negatively charged carboxyl ions of CA/β-CD attract the positively charged MG dye electrostatically and remove MG from aqueous media with an efficiency of 91%. As a result, the findings indicated that water-insoluble polymers based on β-cyclodextrin are well-suited as inexpensive adsorbents to remove colors from aqueous media.

Recent advances in chiral liquid chromatography stationary phases for pharmaceutical analysis

Chirality is a common phenomenon in nature. Different enantiomers of chiral drug compounds have obvious differences in their effects on the human body. Therefore, the separation of chiral drugs plays an extremely important role in the safe utilization of drugs. High-performance liquid chromatography (HPLC) is an effective tool for the separation and analysis of compounds, in which the chromatographic packing plays a key role in the separation. Chiral pharmaceutical separation and analysis in HPLC rely on chiral stationary phases (CSPs). Thus, various CSPs are being developed to meet the needs of chiral drug separation and analysis. In this review, recent developments in CSPs, including saccharides (cyclodextrin, cellulose, amylose and chitosan), macrocycles (macrocyclic glycopeptides, pillar[n]arene and polyamide) and porous organic materials (metal-organic frameworks, covalent organic frameworks, and porous organic cages), for pharmaceutical analysis in HPLC were summarized, the advantages and disadvantages of various stationary phases were introduced, and their development prospects were discussed.

Recent development of chiral ionic liquids for enantioseparation in liquid chromatography and capillary electrophoresis: A review

Ionic liquids (ILs), which are salts in a molten state below 100 °C, have become a hot topic of research in various fields because of their negligible vapour pressure, high thermal stability, and tunable viscosity. Chiral ionic liquids (CILs) can be applied in chromatography and capillary electrophoresis fields to improve the performance of enantiomeric separation, such as chiral stationary phases (CSPs) and mobile phase additives in high-performance liquid chromatography (HPLC); CSPs in gas chromatography (GC); and background electrolyte additives (BGE), chiral ligands and chiral selectors (CSs) in capillary electrophoresis (CE). This review focuses on the applications of CILs in HPLC and CE for the separation of enantiomers in the past five years. The mechanism for separating enantiomers was explained, and the prospect of the application of CILs in chiral liquid chromatography (LC) and CE analysis was also discussed.

Degree and distribution of substitution of hydroxypropyl-β-cyclodextrin in enantioselective liquid-liquid extraction and countercurrent chromatographic enantioseparation

Nine types of hydroxypropyl-β-cyclodextrin (HP-β-CD) with different degrees and distributions of substitution were synthesised, and nine racemates were selected to investigate the effect of different degrees and distributions of substitution of HP-β-CD on the enantioseparation factor. ¹H NMR and GC/MS were used to characterise the synthesised HP-β-CD. The degree and distribution of substitution had a significant influence on enantioselective liquid-liquid extraction and enantioseparation by countercurrent chromatography. For most of the tested racemates, increasing both the degree of substitution and distribution of substitution at the C-2 position for HP-β-CD would lead to an increasing enantioseparation factor; the optimal enantioseparation factor of 2-phenylbutyric acid, tropic acid, 2,3-diphenylpropionic acid, 2-(4-hydroxylphenyl) propanoic acid, and naproxen was increased to 1.77, 1.53, 1.67, 1.61, and 1.75, respectively. The enantioseparation of racemic naproxen, 2-(4-hydroxylphenyl) propanoic acid, and 2,3-diphenylpropionic acid by countercurrent chromatography was optimised using HP-β-CD with a degree of substitution of 16.5, and peak resolution was significantly improved to 1.03, 1.35, and 1.01, respectively.

Ferrocene derivatives with planar chirality and their enantioseparation by liquid-phase techniques

In the last decade, planar chiral ferrocenes have attracted a growing interest in several fields, particularly in asymmetric catalysis, medicinal chemistry, chiroptical spectroscopy and electrochemistry. In this frame, the access to pure or enriched enantiomers of planar chiral ferrocenes has become essential, relying on the availability of efficient asymmetric synthesis procedures and enantioseparation methods. Despite this, in enantioseparation science, these metallocenes were not comprehensively explored, and very few systematic analytical studies were reported in this field so far. On the other hand, enantioselective high-performance liquid chromatography has been frequently used by organic and organometallic chemists in order to measure the enantiomeric purity of planar chiral ferrocenes prepared by asymmetric synthesis. On these bases, this review aims to provide the reader with a comprehensive overview on the enantioseparation of planar chiral ferrocenes by discussing liquid-phase enantioseparation methods developed over time, integrating this main topic with the most relevant aspects of ferrocene chemistry. Thus, the main structural features of ferrocenes and the methods to model this class of metallocenes will be briefly summarized. In addition, planar chiral ferrocenes of applicative interest as well as the limits of asymmetric synthesis for the preparation of some classes of planar chiral ferrocenes will also be discussed with the aim to orient analytical scientists towards 'hot topics' and issues which are still open for accessing enantiomers of ferrocenes featured by planar chirality.

Quaternized chitin used as chiral stationary phase for HPLC and the high enantioseparation of 1,2,3,4-tetrahydro-1-naphthalenamine racemates

Quaternized chitin (QC) with different degrees of substitution (DSs) and molecular weight (M_w) were homogeneously synthesized. Eight novel chiral stationary phases (CSPs) for HPLC were prepared by coating the QC on 3-aminopropyl silica gel, which were firstly used to separate 1,2,3,4-tetrahydro-1-naphthalenamine (THNA) racemates. Enantioseparation capability of the CSPs was evaluated and the influence factors including DS and M_w of QCs were explored respectively. The results demonstrated that the successful separation of THNA enantiomers was obtained by all the new CSPs of the chitin derivatives. Resolution (R_s) increased from 1.12 to 1.58 with the increase of DS of QC from 0.40 to 0.62, while the R_s decreased with the reduction of M_w of the products from 2.8 × 10⁵ to 9.7 × 10⁴. The maximum R_s is 2.29. A simple pathway for the fabrication of novel CSPs of cationic chitin derivatives is developed, which has potential application for the separation of THAN racemates.

Recent advances of the ionic chiral selectors for chiral resolution by chromatography, spectroscopy and electrochemistry

Ionic chiral selectors have been received much attention in the field of asymmetric catalysis, chiral recognition, and preparative separation. It has been shown that the addition of ionic chiral selectors can enhance the recognition efficiency dramatically due to the presence of multiple intermolecular interactions, including hydrogen bond, π-π interaction, van der Waals force, electrostatic ion-pairing interaction, and ionic-hydrogen bond. In the initial research stage of the ionic chiral selectors, most of work center on the application in chromatographic separation (capillary electrophoresis, high-performance liquid chromatography, and gas chromatography). Differently, more and more attention has been paid on the spectroscopy (nuclear magnetic resonance, fluorescence, ultraviolet and visible absorption spectrum, and circular dichroism spectrum) and electrochemistry in recent years. In this tutorial review as regards the ionic chiral selectors, we discuss in detail the structural features, properties, and their application in chromatography, spectroscopy, and electrochemistry.

L-Histidinium Chiral Ionic Liquid Functionalized β-Cyclodextrin as Chiral Selector in Capillary Electrophoresis

Nowadays, ionic liquids (ILs) functionalized cyclodextrins (CDs) have drawn increasing attention in chiral separation. Herein, a novel β-CD derivative functionalized by L-histidinium IL, mono-6-deoxy-6-L-histidinium-β-cyclodextrin chloride (L-HMCDCl), was synthesized for the first time and utilized for enantioseparation of nefopam and chlorphenamine in capillary electrophoresis. The L-HMCDCl exhibited superior enantioselectivity compared with native β-CD. The effect of some key parameters such as chiral selector concentration, buffer pH and applied voltage on the enantioseparation was investigated in detail. In the interest of the chiral discrimination mechanism and the enhanced enantioselectivity of L-HMCDCl, molecular modeling with AutoDock was employed to study the interaction, which was in good agreement with experimental results.

Recent advances in the enantioseparation promoted by ionic liquids and their resolution mechanisms

More and more various chemical media are being applied in enantioseparation; among them, ionic liquids (ILs) have attracted the long-term attention in this decade as green designable solvents. This paper provides comprehensive overview for the applications of ILs in chiral extraction, gas chromatography, liquid chromatography, capillary electrophoresis and other techniques for enantioseparation. Additionally, the important resolution mechanisms based on ILs have also been summarized and discussed. This review focuses on the latest development of enantioseparation methods by using ILs in various modes, leading to meaningful and valuable information to related fields and thus promotes further research and application of reported methods.

Chiral Ionic Liquids: Structural Diversity, Properties and Applications in Selected Separation Techniques

Ionic liquids (ILs) are chemical compounds composed of ions with melting points below 100 °C exhibiting a design feature. ILs are commonly used as the so-called green solvents, reagents or highly efficient catalysts in varied chemical processes. The huge application potential of ionic liquids (IL) justifies the growing interest in these compounds. In the last decade, increasing attention has been devoted to the development of new methods in the synthesis of stable chiral ionic liquids (CILs) and their application in various separation techniques. The beginnings of the successful use of CILs to separate enantiomers date back to the 1990 s. Most chiral ILs are based on chiral cations or chiral anions. There is also a limited number of CILs possessing both a chiral cation and a chiral anion. Due to the high molecular diversity of both ions, of which at least one has a chiral center, we have the possibility to design a large variety of optically active structures, thus expanding the range of CIL applications. Research utilizing chiral ionic liquids only recently has become more popular. However, it is the area that still has great potential for future development. This review aimed to describe the diversity of structures, properties and examples of applications of chiral ionic liquids as new chiral solid materials and chiral components of the anisotropic environment, providing chiral recognition of enantiomeric analytes, which is useful in liquid chromatography, countercurrent chromatography and other various CIL-based extraction techniques including aqueous biphasic (ABS) extraction systems, solid-liquid two-phase systems, liquid-liquid extraction systems with hydrophilic CILs, liquid-liquid extraction systems with hydrophobic CILs, solid-phase extraction and induced-precipitation techniques developed in the recent years. The growing demand for pure enantiomers in the pharmaceutical and food industries sparks further development in the field of extraction and separation systems modified with CILs highlighting them as affordable and environmentally friendly both chiral selectors and solvents.

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.

A fully derivatized 4-chlorophenylcarbamate-β-cyclodextrin bonded chiral stationary phase for enhanced enantioseparation in HPLC

This paper reports an effective approach for the fabrication of a per-4-chlorophenylcarbamate-β-cyclodextrin (β-CD) bonded chiral stationary phase (CPCDP) in high-performance liquid chromatography. The morphology and structure of the ligand and the chiral stationary phase (CSP) were characterized by scanning electron microscopy, transmission electron microscopy, solid state ¹³C nuclear magnetic resonance spectra, fourier transform infrared spectra, elemental analysis and thermogravimetric analysis. Because CPCDP was a kind of multimode enantioseparation materials, the enantioseparation of chiral compounds including twelve azole antifungal agents, five proton pump inhibitors and five dihydropyridine calcium antagonists were studied in both reversed-phase and normal-phase chromatography. All analytes were obtained enantiomeric separation. Especially, the resolution of azoles was excellent. The selectivity and resolution of voriconazole reached 15.41 and 16.80, which was an exciting achievement for the enantioseparations by β-CD based chiral stationary phases. Compared with the commercial 3,5-dimethylphenyl carbamate-β-CD based chiral stationary phase (DMP), enhanced enantioselectivities for all the above compounds (except ilaprazole) were obtained on CPCDP column, which indicated that the 4-chlorophenylcarbamate group was conducive to the chiral recognition. Chromatographic studies elucidated that enhancement of analyte-chiral substrate interactions were attributed to the inclusion complexation, π-π stacking interaction, hydrogen-bonding, dipole-dipole interaction and steric hindrance. For further study, we also prepared semi-preparative chromatographic columns to obtain a single enantiomer. In addition to excellent chromatographic performance, the prepared CD-based column is stable and much cheaper than commercial columns, which can reduce the cost of test and has a good application prospect in chiral drug analysis.

HPLC Enantioseparation on Cyclodextrin-Based Chiral Stationary Phases

As one of the commonly used chiral separation materials, cyclodextrin-based chiral stationary phases (CD-CSP) have been developed rapidly in the past 30 years. A large number of CD-CSPs have been designed and applied for enantioseparation in high-performance liquid chromatography (HPLC). The development of novel CD-CSPs focuses on two aspects: the immobilization chemistry and the functionalization of the CD skeleton. Although such studies are not regarded as the prime research topic in analytical chemistry, there are still many recent works pushing this research forward tardily. In this chapter, the fabrication procedure of a triazole-bridged duplex CD-CSP and its application to HPLC enantioseparations is described.

Analysis of carbohydrates and glycoconjugates by matrix-assisted laser desorption/ionization mass spectrometry: An update for 2013-2014

This review is the eighth update of the original article published in 1999 on the application of Matrix-assisted laser desorption/ionization mass spectrometry (MALDI) mass spectrometry to the analysis of carbohydrates and glycoconjugates and brings coverage of the literature to the end of 2014. Topics covered in the first part of the review include general aspects such as theory of the MALDI process, matrices, derivatization, MALDI imaging, fragmentation, and arrays. The second part of the review is devoted to applications to various structural types such as oligo- and poly- saccharides, glycoproteins, glycolipids, glycosides, and biopharmaceuticals. Much of this material is presented in tabular form. The third part of the review covers medical and industrial applications of the technique, studies of enzyme reactions, and applications to chemical synthesis. © 2018 Wiley Periodicals, Inc. Mass Spec Rev 37:353-491, 2018.

Adsorption behavior and mechanism of β-cyclodextrin–styrene-based polymer for cationic dyes

These figures show that the cyclodextrin polymer was synthesized successfully and possessed good thermal stability.

Chromatographic and spectroscopic studies on β-cyclodextrin functionalized ionic liquid as chiral stationary phase: Enantioseparation of NSAIDs

Recently, we reported a new chiral stationary phase prepared using β-cyclodextrin functionalized with aromatic ionic liquid which is aimed to enhance the performance of enantioseparation of flavonoids and β-blockers. In this paper, the characteristics and performance of previously prepared chiral stationary phase denoted as β-CD-BIMOTs were compared with the newly synthesized chiral stationary phase denoted as β-CD-DIMOTs. β-CD-DIMOTs were prepared by functionalization of β-cyclodextrin with aliphatic ionic liquid. The obtained β-CD-BIMOTs and β-CD-DIMOTs stationary phases were compared with native β-CD stationary phase for the enantioseparation of non-steroidal anti-inflammatory drugs (NSAIDs) (ibuprofen, indoprofen, ketoprofen and fenoprofen). The β-CD-BIMOTs stationary phase showed greater chiral resolution capabilities rather than β-CD-DIMOTs and native β-CD stationary phases. Further, in order to understand the interaction of enantioseparation, the inclusion complex formation between NSAIDs and β-CD-BIMOTs was studied using 1H NMR, NOESY and UV/Vis. The enantioseparated NSAIDs were found to form multiple interactions with β-CD-BIMOTs-CSP.

Synthesis of novel chiral imidazolium stationary phases and their enantioseparation evaluation by high-performance liquid chromatography

Two novel chiral stationary phases (CSPs) were prepared by bonding chiral imidazoliums on the surface of silica gel. The chiral imidazoles were derivatized from chiral amines, 1-phenylethylamine and 1-(1-naphthyl)ethylamine. The obtained CSPs were characterized by Fourier Transform Infrared (FT-IR) spectroscopy and elemental analysis (EA), demonstrating the bonding densities of CSP 1 and CSP 2 were 0.43 mmol g^-1 and 0.40 mmol g^-1, respectively. These two CSPs could be used to availably separate 8 pharmaceuticals, 7 mandelic acid/its derivatives, 2 1-phenylethylamine derivatives, 1 1,1'-bi-2-naphthol, and 1 camphorsulfonic acid in high-performance liquid chromatography (HPLC). It is found that CSP 1 could effectively enantioseparate most chiral analytes, especially the acidic components, while CSP 2 could enantiorecognize all chiral analytes, although a number of components did not achieve baseline separation. Additionally, the effects of mobile phase composition, mobile phase pH and salt content, chiral selector structures, and analyte structures on the enantiorecognitions of the two CSPs were investigated. It is found that high acetonitrile content in mobile phases was conducive to enantiorecognition. Mobile phase pH and salt content could alter the retention behaviors of different enantiomers of the same chiral compound, resulting in better enantioresolution. Moreover, both chiral selector structures and substituted groups of analytes played a significant role in the separation of chiral solutes.

Recent development of ionic liquid stationary phases for liquid chromatography

Based on their particular physicochemical characteristics, ionic liquids have been widely applied in many fields of analytical chemistry. Many types of ionic liquids were immobilized on a support like silica or monolith as stationary phases for liquid chromatography. Moreover, different approaches were developed to bond covalently ionic liquids onto the supporting materials. The obtained ionic liquid stationary phases show multi-mode mechanism including hydrophobic, hydrophilic, hydrogen bond, anion exchange, π-π, and dipole-dipole interactions. Therefore, they could be used in different chromatographic modes including ion-exchange, RPLC, NPLC and HILIC to separate various classes of compounds. This review mainly summarizes the immobilized patterns and types of ionic liquid stationary phases, their retention mechanisms and applications in the recent five years.