Enantioseparation of drugs by capillary electrochromatography using a stationary phase covalently modified with graphene oxide

In-silico mechanistic analysis of adsorption of Iodinated Contrast Media agents on graphene surface

The study aims at assessing the potential of graphene-based adsorbents to reduce environmental impacts of Iodinated Contrast Media Agents (ICMs). We analyze an extensive collection of ICMs. A modeling approach resting on molecular docking and Density Functional Theory simulations is employed to examine the adsorption process at the molecular level. The study also relies on a Quantitative Structure-Activity Relationship (QSAR) modeling framework to correlate molecular properties with the adsorption energy (Ead) of ICMs, thus enabling identification of the key mechanisms underpinning adsorption and of the key factors contributing to it. A collection of distinct QSAR-based models is developed upon relying on Multiple Linear Regression and a standard genetic algorithm method. Having at our disposal multiple models enables us to take into account the uncertainty associated with model formulation. Maximum Likelihood and formal model identification/discrimination criteria (such as Bayesian and/or information theoretic criteria) are then employed to complement the traditional QSAR modeling phase. This has the advantage of (a) providing a rigorous ranking of the alternative models included in the selected set and (b) quantifying the relative degree of likelihood of each of these models through a weight or posterior probability. The resulting workflow of analysis enables one to seamlessly embed DFT and QSAR studies within a theoretical framework of analysis that explicitly takes into account model and parameter uncertainty. Our results suggest that graphene-based surfaces constitute a promising adsorbent for ICMs removal, π-π stacking being the primary mechanism behind ICM adsorption. Furthermore, our findings offer valuable insights into the potential of graphene-based adsorbent materials for effectively removing ICMs from water systems. They contribute to ascertain the significance of various factors (such as, e.g., the distribution of atomic van der Waals volumes, overall molecular complexity, the presence and arrangement of Iodine atoms, and the presence of polar functional groups) on the adsorption process.

Implications of analytical nanoscience in pharmaceutical and biomedical fields: A critical view

This review summarizes recent progress performed in the design and application of analytical tools and methodologies using nanomaterials for pharmaceutical analysis, and specifically new nanomedicines at distinct phases of development and translation from preclinical to clinical stages. Over the last 10-15 years, a growing number of studies have utilized various nanomaterials, including carbon-based, metallic nanoparticles, polymeric nanomaterials, materials based on biological molecules, and composite nanomaterials as tools for improving the analysis of pharmaceutical products. New and more complex nanomaterials are currently being explored to influence different stages of the analytical process. These materials provide unique properties to support the extraction of analytes in complex samples, increase the selectivity and efficiency of chromatographic separations, and improve the analytical properties of many sensor applications. Indeed, nanomaterials, including electrochemical detection approaches and biosensing, are expanding at a remarkable rate. Furthermore, the analytical performance of numerous approaches to determine drugs in different matrices can be significantly improved in terms of precision, detection limits, selectivity, and time of analysis. However, the quality control and metrological characterization of the currently synthesized nanomaterials still depend on the development of new and improved analytical methodologies, and the application of specific and improved instrumentation. Therefore, there is still much to explore about the properties of nanomaterials which need to be determined even more precisely and accurately.

Preparation and evaluation of two chiral stationary phases based on imidazolyl-functionalized bromoethoxy pillar[5]arene-bonded silica

Chiral pillar[5]arene-based mesoporous silica, an emerging class of chiral structure, possesses excellent characteristics such as abundant chiral active sites, encapsulated cavity and excellent chiral modification, which make them a promising candidate as new chiral stationary phases (CSPs) in enantioseparation. In this study, two imidazole-containing (S)-1-(4-phenyl-1H-imidazol-2-yl)ethanamine and (S)-Histidinol were respectively modified to bromoethoxy pillar[5]arene-bonded silica to construct new chiral stationary phases (sPIE-BP5-Sil and sHol-BP5-Sil) for the separation and analysis of enantiomers. The separation conditions such as mobile phase composition, flow rate and temperature were optimized. Under optimal conditions, both sPIE-BP5-Sil and sHol-BP5-Sil showed good separation performance for different types of enantiomers. Interestingly, sPIE-BP5-Sil and sHol-BP5-Sil showed better enantioselectivity for chiral aromatic compounds and chiral aliphatic compounds, respectively. This enantioseparation result was closely related to the presence of additional aromatic rings and abundant hydroxyl groups in the side chains of the two chiral groups. In addition, the enantioseparation process was further studied by molecular docking simulation. Therefore, this work provided a new strategy for the preparation and application of imidazolyl-derived pillar[5]arene-based chiral stationary phases, which can be efficiently used for screening and separating enantiomers.

Surface modified nanoparticles and their applications for enantioselective detection, analysis, and separation of various chiral compounds

The development of efficient enantioselective detection, analysis, and separation relies significantly on molecular interaction. In the scale of molecular interaction, nanomaterials have a significant influence on the performance of enantioselective recognitions. The use of nanomaterials for enantioselective recognition involved synthesizing new materials and immobilization techniques to produce various surface-modified nanoparticles that are either encapsulated or attached to surfaces, as well as layers and coatings. The combination of surface-modified nanomaterials and chiral selectors can improve enantioselective recognition. This review aims to offer engagement insights into the production and application of surface-modified nanomaterials to achieve sensitive and selective detection, better chiral analysis, and separation of numerous chiral compounds.

Enantioseparation/Recognition based on nano techniques/materials

Enantiomers show different behaviors in interaction with the chiral environment. Due to their identical chemical structure and their wide application in various industries, such as agriculture, medicine, pesticide, food, and so forth, their separation is of great importance. Today, the term "nano" is frequently encountered in all fields. Technology and measuring devices are moving towards miniaturization, and the usage of nanomaterials in all sectors is expanding substantially. Given that scientists have recently attempted to apply miniaturized techniques known as nano-liquid chromatography/capillary-liquid chromatography, which were originally accomplished in 1988, as well as the widespread usage of nanomaterials for chiral resolution (back in 1989), this comprehensive study was developed. Searching the terms "nano" and "enantiomer separation" on scientific websites such as Scopus, Google Scholar, and Web of Science yields articles that either use miniaturized instruments or apply nanomaterials as chiral selectors with a variety of chemical and electrochemical detection techniques, which are discussed in this article.

Carbon Nanodots from an In Silico Perspective

Carbon nanodots (CNDs) are the latest and most shining rising stars among photoluminescent (PL) nanomaterials. These carbon-based surface-passivated nanostructures compete with other related PL materials, including traditional semiconductor quantum dots and organic dyes, with a long list of benefits and emerging applications. Advantages of CNDs include tunable inherent optical properties and high photostability, rich possibilities for surface functionalization and doping, dispersibility, low toxicity, and viable synthesis (top-down and bottom-up) from organic materials. CNDs can be applied to biomedicine including imaging and sensing, drug-delivery, photodynamic therapy, photocatalysis but also to energy harvesting in solar cells and as LEDs. More applications are reported continuously, making this already a research field of its own. Understanding of the properties of CNDs requires one to go to the levels of electrons, atoms, molecules, and nanostructures at different scales using modern molecular modeling and to correlate it tightly with experiments. This review highlights different in silico techniques and studies, from quantum chemistry to the mesoscale, with particular reference to carbon nanodots, carbonaceous nanoparticles whose structural and photophysical properties are not fully elucidated. The role of experimental investigation is also presented. Hereby, we hope to encourage the reader to investigate CNDs and to apply virtual chemistry to obtain further insights needed to customize these amazing systems for novel prospective applications.

Growth of two-layer copolymer as the stationary phase with very high separation efficiency for separating peptides in capillary electrochromatography

Open tubular CEC (OT-CEC) column with a very high separation efficiency was prepared for peptides separation. A pretreated silica-fused capillary was reacted with 3-(methacryloxy) propyltrimethoxysilane followed by vinylbenzyl chloride and divinylbenzene to produce first thin monolithic monolayer. The second copolymer layer was formed on thin monolithic monolayer of the capillary by reversible addition-fragmentation transfer polymerization of N-phenylacrylamide and styrene. The key parameters including buffer pH value and organic modifier were systematically evaluated to provide the optimal chromatographic condition. The resultant OT-CEC columns were validated by separating a synthetic mixture of peptides and cytochrome C tryptic digest in capillary electrochromatography. The number of theoretical plates as high as 2.4 million per column was achieved for synthetic mixture peptides. In addition, the fabricated OT-CEC column also resolved more than 18 high-efficiency digestion peptides from a mixture containing tryptic digest of cytochrome C. The column to column and inter- to intraday repeatabilities of OT-CEC column through RSD% were found better than 3.0%, exhibiting satisfactory stability and repeatability of the two-layer deposited OT-CEC column. The results reveal that the open tubular capillary column modified with two-layer copolymer shows the great prospect for the separation of proteins in capillary electrochromatography.

Immobilization of cellulase on monolith supported with Zr(IV)-based metal-organic framework as chiral stationary phase for enantioseparation of five basic drugs in capillary electrochromatography

Metal-organic framework (UiO-66-NH₂)-incorporated organic polymer monolith was prepared by thermal polymerization. By virtue of the superior physical and chemical properties, the UiO-66-NH₂-modified organic monolith was then functionalized by chiral selector cellulase via the condensation reaction between the primary amino groups and aldehyde groups. The synthesized materials were characterized by Fourier transform infrared spectroscopy, high-resolution transmission electron microscopy, scanning electron microscopy, X-ray photoelectron spectrometry, thermogravimetric analysis, and nitrogen sorption isotherm. The cellulase@poly(glycidyl methacrylate-UiO-66-NH₂-ethylene glycol dimethacrylate) (cellulase@poly(GMA-UiO-66-NH₂-EDMA)) monolith was applied to enantiomerically separate the basic racemic forms of metoprolol, atenolol, esmolol, bisoprolol, and propranolol. In contrast to the cellulase@poly(GMA-co-EDMA) monolith without UiO-66-NH₂, the cellulase@poly(GMA-UiO-66-NH₂-EDMA) monolith reveals significantly improved enantiodiscrimination performance for metoprolol (Rs: 0 → 1.67), atenolol (Rs: 0 → 1.50), esmolol (Rs: 0 → 1.52), bisoprolol (Rs: 0 → 0.36), and propranolol (Rs: 0 → 0.44). The immobilization pH of cellulase, buffer pH, UiO-66-NH₂ concentration, and the proportion of organic modifier were evaluated in detail with enantiomerically separating chiral molecules. The intra-day, inter-day, column-to-column, and inter-batch precision have been discussed, the result was preferable, and the relative standard deviation (RSD) of separation parameters was <4.3%. Schematic representation of the preparation of a UiO-66-NH₂-modified organic polymer monolith for enantioseparating five racemic β-blockers. UiO-66-NH₂ was synthesized and converted into a monolith as the stationary phase. Then, the modified monolith containing cellulase as the chiral selector was applied in a capillary electrochromatography system for enantioseparating chiral drugs.

Chiral Graphene Hybrid Materials: Structures, Properties, and Chiral Applications

Chirality has become an important research subject. The research areas associated with chirality are under substantial development. Meanwhile, graphene is a rapidly growing star material and has hard-wired into diverse disciplines. Rational combination of graphene and chirality undoubtedly creates unprecedented functional materials and may also lead to great findings. This hypothesis has been clearly justified by the sizable number of studies. Unfortunately, there has not been any previous review paper summarizing the scattered studies and advancements on this topic so far. This overview paper attempts to review the progress made in chiral materials developed from graphene and their derivatives, with the hope of providing a systemic knowledge about the construction of chiral graphenes and chiral applications thereof. Recently emerging directions, existing challenges, and future perspectives are also presented. It is hoped this paper will arouse more interest and promote further faster progress in these significant research areas.

Application of nanoparticles in chiral analysis and chiral separation

Chiral molecules in relation to particular biological roles are stereoselective. Enantiomers differ significantly in their biochemical responses in biological environment. Despite the current advancement in drug discovery and pharmaceutical biotechnology, the chiral separation of some racemic mixtures continues to be one of the greatest challenges, because the available techniques are too costly and time consuming for the assessment of therapeutic drugs in the early stages of development worldwide. Various nanoparticles became one of the most investigated and explored nanotechnology-derived nanostructures especially in chirality where several studies are reported to improve enantiomeric separation of different racemic mixtures. The production of surface-modified nanoparticles has contributed to these limitations in terms of sensitivity, accuracy, and enantioselectivity that can be optimized and therefore makes these surface-modified nanoparticles convenient for enantiomeric identification and separation.

A porous layer open-tubular capillary column supported with pepsin and zeolitic imidazolate framework for enantioseparation of four basic drugs in capillary electrochromatography

New material zeolitic imidazolate framework-4, 5-imidazoledicarboxylic acid (ZIF-IMD) located on the pore surface of porous layer open-tubular (PLOT) column previously functionalized with N-(3-aminopropyl)-imidazole have been prepared via a layer-by-layer self-assembly strategy. This new ZIF-IMD coating hybrids are used as solid-phase carriers for chiral selector pepsin immobilization. The ZIF-IMD material was characterized by scanning electron microscopy, energy-dispersive spectroscopy, transmission electron microscope and X-ray diffraction. The synthesized pepsin@ZIF-IMD@POLT column achieved the baseline separation of hydroxychloroquine (HCQ), chloroquine (CHQ) and hydroxyzine (HXY) (the resolution of HCQ: 2.19; CHQ: 1.84; HXY: 1.53). Compared with the pepsin@PLOT column (without ZIF-IMD material), the chiral separation capability of the pepsin@ZIF-IMD@POLT column can be remarkably improved. Several key parameters including concentration of chiral selector, buffer pH, applied voltage and buffer concentration were systematically evaluated to provide the optimal enantioseparation condition. The relative standard deviations (RSDs) of intra-day, inter-day, column-to-column and inter-batch of migration time and Rs of the HCQ were evaluated in detail, respectively (RSD < 7.21%). Additionally, the potential mechanism of increased resolution was discussed in the article.

β-Cyclodextrin covalent organic framework-modified organic polymer monolith as a stationary phase for combined hydrophilic and hydrophobic aqueous capillary electrochromatographic separation of small molecules

A β-Cyclodextrin covalent organic framework (β-CD COF) was successfully prepared under ambient temperature with a mild chemistry strategy from heptakis(6-amino-6-deoxy)-β-cyclodextrin and terephthalaldehyde. It was embedded into the poly[(glycidyl methacrylate)-co-(ethylene dimethacrylate)] [poly(GMA-co-EDMA)] monolith and served as the β-CD COF material-incorporated monolith. The synthetic materials were characterized by field emission scanning electron microscopy, energy-dispersive X-ray mapping analysis, transmission electron microscopy, thermogravimetric analysis, Fourier transform infrared spectroscopy, and N₂ adsorption-desorption isotherm. The β-CD COF material-incorporated monolith achieved baseline separation in capillary electrochromatographic separation of three amides, three amino acids, three nucleosides, four aromatic acids, and three positional isomers (with resolution values of three amides, 1.75 and 1.54; three amino acids, 5.24 and 1.75; three nucleosides, 2.56 and 1.77; four aromatic acids, 6.96, 2.74, and 1.64; three positional isomers, 1.61 and 1.50). In comparison with the original monolith, the β-CD COF material-incorporated monolith shows significantly enhanced resolution for mixed molecules. The effect of pH and concentration of buffer and applied voltage were discussed in detail. The fabricated monolith showed good stability and reproducibility (relative standard deviation (RSD) < 6.9%). Molecular modeling illuminated the interactions between the small molecules and stationary phase, and provided a sufficient theoretical basis for experimental data. Graphical abstract Schematic presentation of the preparation of β-cyclodextrin covalent organic framework (β-CD COF) material-incorporated organic polymer monolith for separating the amides, amino acids, nucleosides, aromatic acids, and positional isomers. β-CD COF materials were synthesized and incorporated into the monolith as the stationary phase. Then, the incorporated monolith was applied in the capillary electrochromatography system for separating small molecules.

Ambient temperature fabrication of a covalent organic framework from 1,3,5-triformylphloroglucinol and 1,4-phenylenediamine as a coating for use in open-tubular capillary electrochromatography of drugs and amino acids

A covalent organic framework (COF) named TpPa-1 was designed and synthesized at ambient temperature by an ultrasound-assisted method from 1,3,5-triformylphloroglucinol (Tp) and 1,4-phenylenediamine (Pa-1). It was utilized as a stationary phase in open-tubular capillary electrochromatography (OT-CEC). The column was coated with TpPa-1 using a covalent bonding strategy. The coated capillary was characterized by morphology, crystallography, and mesoporous analysis to confirm the successful fabrication. The OT-CEC method was utilized for the analysis of tetracyclines, sulfonamides, cephalosporins and amino acids with high-resolution (Rs > 1.81) and good precision (RSD < 4.9%). It takes about 12 h from COF preparation to OT-CEC separation. Graphical abstract A covalent organic framework (COF) named TpPa-1 was synthesized at ambient temperature by an ultrasound-assisted method from 1,3,5-triformylphloroglucinol (Tp) and 1,4-phenylenediamine (Pa-1). COF-TpPa-1 modified capillary column was utilized for the analysis of tetracyclines, sulfonamides, cephalosporins and amino acids with high-resolution and good precision.

An organic polymer monolith modified with an amino acid ionic liquid and graphene oxide for use in capillary electrochromatography: application to the separation of amino acids, β-blockers, and nucleotides

The preparation of an organic polymer monolithic column modified with an amino acid ionic liquid and graphene oxide (AAIL-GO) and its application to capillary electrochromatography (CEC) was described. The AAIL tetramethylammonium-L-arginine was bonded to a monolithic column that was previously modified with graphene oxide by using an hydrochloride/N-hydroxysuccinimide coupling reaction. The morphology of a poly(glycidyl methacrylate-co-ethylene dimethacrylate) monolith was examined by scanning electron microscopy. The incorporation of AAIL and graphene oxide was detected by infrared spectroscopy and elemental analysis. The resulting monolithic column produced a strong and stable electroosmotic flow from the anode to the cathode in the pH range from 3 to 9. Compared with a column modified with AAIL or graphene oxide only, the AAIL-GO-modified column has a better separation ability for amino acids, β-blockers, and nucleotides (the resolution of three amino acids: 2.231 and 2.036, β-blockers: 2.779 and 2.470 and nucleotides: 8.345 and 3.321). Molecular modeling was applied to demonstrate the separation mechanism of small molecules which showed a good support for experimental results. Graphical abstract Schematic representation of capillary electrochromatography (CEC) systems with an amino acid ionic liquid-graphene oxide modified organic polymer monolithic column as stationary phases for separation of amino acids, β-blockers, and nucleotides.

Metal organic framework HKUST-1 modified with carboxymethyl-β-cyclodextrin for use in improved open tubular capillary electrochromatographic enantioseparation of five basic drugs

This work shows that the metal organic framework (MOF) HKUST-1 of type Cu₃(BTC)₂ (also referred to as MOF-199; a face-centered-cubic MOF containing nanochannels) is a most viable coating for use in enantioseparation in capillary electrochromatography (CEC). A HKUST-1 modified capillary was prepared and characterized by scanning electron microscopy, transmission electron microscopy, Fourier transform infrared spectra, elemental analysis and thermogravimetric analysis. CEC-based enantioseparation of the basic drugs propranolol (PRO), esmolol (ESM), metoprolol (MET), amlodipine (AML) and sotalol (SOT) was performed by using carboxymethyl-β-cyclodextrin as the chiral selector. Compared with a fused-silica capillary, the resolutions are improved (ESM: 1.79; MET: 1.80; PRO: 4.35; SOT: 1.91; AML: 2.65). The concentration of chiral selector, buffer pH value, applied voltage and buffer concentration were optimized, and the reproducibilities of the migration times and R_s values were evaluated. Graphical abstract Schematic presentation of the preparation of a HKUST-1@capillary for enantioseparation of racemic drugs. Cu(NO₃)₂ and 1,3,5-benzenetricarboxylic acid (BTC) were utilized to prepare the HKUST-1@capillary. Then the capillary was applied to construct capillary electrochromatography system with carboxymethyl-β-cyclodextrin (CM-β-CD) for separation of basic racemic drugs.

Advances in capillary electro-chromatography

Capillary electrochromatography (CEC) is a micro-scale separation technique which is a hybrid between capillary electrophoresis (CE) and liquid chromatography (LC). CEC can be performed in packed, monolithic and open-tubular columns. In recent three years (from 2016 to 2018), enormous attention for CEC has been the development of novel stationary phases. This review mainly covers the development of novel stationary phases for open-tubular and monolithic columns. In particular, some biomaterials attracted increasing interest. There are no significant breakthroughs in technology and principles in CEC. The typical CEC applications, especially chiral separations are described.

Graphene quantum dots functionalized β-cyclodextrin and cellulose chiral stationary phases with enhanced enantioseparation performance

Graphene quantum dots (GQD) functionalized β-cyclodextrin (β-CD) and cellulose silica composites were first prepared and applied in HPLC as chiral stationary phases (CSP) to investigate the effect of GQDs on chiral separation. Through comparing the enantioseparation performance of GQDs functionalized β-CD or cellulose CSPs and unmodified β-CD or cellulose CSPs, we found GQDs enhanced the enantioseparation performance of nature β-CD, β-CD-3,5-dimethylphenylcarbamate derivative and cellulose-3,5-dimethylphenylcarbamate derivative. Molecular modeling was applied to understand and theoretically study the enhancement mechanism of GQDs for enantioseparation. According to molecular simulation results, GQDs provide extra interactions such as hydrophobic, hydrogen bond and π-π interaction when chiral selector interacts with enantiomers, which enhances the chiral recognition ability indirectly. The molecular simulation results showed a good agreement with the experimental results. Our work reveals the enhancement performance of GQDs for chiral separation, it can be expected that GQDs-based chiral composites and chiral GQDs have great prospect in chiral separation and other research fields such as asymmetric synthesis, chiral catalysis, chiral recognition and drug delivery.

Open-tubular capillary electrochromatography with β-cyclodextrin-functionalized magnetic nanoparticles as stationary phase for enantioseparation of dansylated amino acids

Magnetic nanoparticles (MNPs) modified with β-cyclodextrin and mono-6-deoxy-6-(1-methylimidazolium)-β-cyclodextrin tosylate (an ionic liquid), which called MNP-β-CD and MNP-β-CD-IL, were coated into the capillary inner wall. Compared to an uncoated capillary, the new systems show good reproducibility and durability. The systems based on the use of MNP-β-CD or MNP-β-CD-IL as stationary phases were established for enantioseparation of Dns-modified amino acids. Improved resolutions were obtained for both CEC systems. Primary parameters such as running buffer pH value and applied voltage were systematically optimized in order to obtain optimal enantioseparations. Under the optimized conditions, the capillaries exhibited excellent chiral recognition ability for six Dns-amino acids (the DL-forms of alanine, leucine, lsoleucine, valine, methionine, glutamic acid) and provided a promising way for the preparation of chiral column. Graphical Abstract Schematic presentation of the open-tubular capillary electrochromatography systems with MNP-β-CD and MNP-β-CD-IL as stationary phases for enantioseparation of dansylated amino acids.

Enantiomeric Recognition and Separation by Chiral Nanoparticles

Chiral molecules are stereoselective with regard to specific biological functions. Enantiomers differ considerably in their physiological reactions with the human body. Safeguarding the quality and safety of drugs requires an efficient analytical platform by which to selectively probe chiral compounds to ensure the extraction of single enantiomers. Asymmetric synthesis is a mature approach to the production of single enantiomers; however, it is poorly suited to mass production and allows for only specific enantioselective reactions. Furthermore, it is too expensive and time-consuming for the evaluation of therapeutic drugs in the early stages of development. These limitations have prompted the development of surface-modified nanoparticles using amino acids, chiral organic ligands, or functional groups as chiral selectors applicable to a racemic mixture of chiral molecules. The fact that these combinations can be optimized in terms of sensitivity, specificity, and enantioselectivity makes them ideal for enantiomeric recognition and separation. In chiral resolution, molecules bond selectively to particle surfaces according to homochiral interactions, whereupon an enantiopure compound is extracted from the solution through a simple filtration process. In this review article, we discuss the fabrication of chiral nanoparticles and look at the ways their distinctive surface properties have been adopted in enantiomeric recognition and separation.

Polyethylene Glycols for the Dispersion Development of Graphene in an Aqueous Surfactant Solution Studied by Affinity Capillary Electrophoresis

Water-soluble nonionic polymers of polyethylene glycol (PEG), poly(vinyl alcohol) (PVA), and polyvinylpyrrolidone (PVP) were examined to develop the dispersion of graphene in an aqueous surfactant solution. Sodium dodecylbenzenesulfonate was used as an anionic surfactant to disperse graphene in an aqueous solution and to give negative charge on it. The dispersion of graphene was monitored through the electropherograms in affinity capillary electrophoresis; a broad peak for the dispersed graphene and shot signals for the aggregated one. When PEG was added in the separation buffer as an affinity reagent, the number of the shot signals in the electropherogram was reduced; PEG can develop the dispersion of graphene in an aqueous surfactant solution. The dispersion was also developed with PVP or PVA. The effective electrophoretic mobility of the dispersed graphene was reduced by using the polymer as an affinity reagent. The result suggested that the anionic surfactant on the graphene surface was competitively substituted with the nonionic polymer. The degree of the decrease in the effective electrophoretic mobility was larger with PEG with a high-molecular mass. The broad peak of the dispersed graphene got narrower by the addition of PEG, and the number of theoretical plates was improved.

Enantioseparation of propranolol, amlodipine and metoprolol by electrochromatography using an open tubular capillary modified with β-cyclodextrin and poly(glycidyl methacrylate) nanoparticles

The inner wall of a capillary was coated with glycidyl methacrylate (GMA) to form tentacle-type coating, and poly(glycidyl methacrylate) nanoparticles (PGMA NPs) were then immobilized on the film. Ethanediamine-β-cyclodextrin as chiral selector was covalently bonded into the PGMA NPs through the ring-open reaction. The materials were characterized by SEM, TEM and FT-IR. The modified column was applied to the enantioseparation of the racemates of propranolol, amlodipine and metoprolol. Compared to a capillary with a single layer of CD-PGMA (without GMA coating) and to a CD-GMA system (without PGMA nanoparticles), the performance of the capillary is strongly improved. The effects of buffer pH value and applied voltage were optimized. Best resolutions (propranolol: 1.27, metoprolol: 1.01 and amlodipine: 2.93) were obtained when using the PGMA-coated capillary system. The run-to-run, day-to-day and column-to-column reproducibility were tested and found to be highly attractive. The new stationary phase is likely to have a large potential and scope in that it may also be applied to chiral separations of other enantiomers, such as amino acids and biogenic amines. Graphical abstract Schematic presentation of the preparation of a capillary column with glycidyl methacrylate (GMA) coating which was then immobilized with poly(glycidyl methacrylate) nanoparticles and ethanediamine-β-cyclodextrin. This novel open tubular column was applied to construct capillary electrochromatography system for separation of basic racemic drugs.

Evaluation of the enantioselectivity of capillary electrokinetic chromatography using ethanediamine-bonded poly (glycidyl methacrylate) microspheres as the pseudostationary phases

In this work, a new capillary electrokinetic chromatography (EKC) approach using ethanediamine-bonded poly (glycidyl methacrylate) (Ami-PGMA) microspheres as pseudostationary phases (PSPs) for enantioseparation with a polysaccharide, chondroitin sulfate E (CSE), as the chiral selector. The CSE@Ami-PGMA EKC system was applied to enantioseparate basic drugs, and distinct improved separations of tested enantiomers were obtained while comparing with the single CSE system (the resolution increased from 0.41 to 1.26 for nefopam, from 1.24 to 2.15 for laudanosine, and from 0.92 to 2.36 for amlodipine). The Ami-PGMA microspheres were fully characterized by scanning electron microscopy (SEM) and Fourier Transform Infrared (FT-IR) spectroscopy, and the results showed Ami-PGMA microspheres were uniform and spherical in size (1 μm). Several principal parameters were systematically investigated, and the optimal chiral separations were obtained with Tris/H₃ PO₄ (20 mM, pH 2.4, and 3.4 for NEF) containing 2.5% (w/v) CSE and 20-μg Ami-PGMA microspheres in 20°C. Subsequently, the concentrations of Ami-PGMA microspheres and CSE were proved to be the dominant factors for the separation in the CSE@Ami-PGMA EKC system by Statistical Product and Service Solutions (SPSS).

Surface-modified three-dimensional graphene nanosheets as a stationary phase for chromatographic separation of chiral drugs

Carbon-based stationary phases for chromatographic separation have been commercially available since the 1980s. Porous graphitic carbon liquid chromatography columns are known to be highly resistant to aggressive mobile phases and extreme pH values of solvents and eluents, an important advantage compared to conventional silica-based alternatives. In our work, we demonstrate a new variant of carbon-based stationary phases for liquid chromatography, specifically developed for chiral separation. Mesoporous three-dimensional graphene nanosheets (3D GNS), functionalized with tetracyanoethylene oxide (TCNEO) and (S)-(+)-2-pyrrolidinemethanol, demonstrate pharmaceutical-grade chiral separation of model ibuprofen and thalidomide racemic mixtures when used as Chiral Stationary Phases (CSPs), with performance parameters comparable to currently commercially available CSPs. Simple covalent attachment of functionalization groups to the surface of mesoporous three-dimensional graphene nanosheets makes these carbon-based CSPs chemically stable and up to an order of magnitude less expensive than standard silica-based analogues.

Enantiomeric separation of adrenaline, noradrenaline, and isoprenaline by capillary electrophoresis using streptomycin-modified gold nanoparticles

Enantiomeric separations of the adrenergic compounds adrenaline, noradrenaline, and isoprenaline were studied. Electromigrative separations were performed in uncoated fused silica capillaries using streptomycin-modified gold nanoparticles (ST-AuNPs) as an additive to the background electrolyte. The ST-AuNPs are shown to serve as an effective chiral selector. The modified AuNPs were characterized in terms of size and zeta potential, and by IR and UV-vis spectra. The effects of ST-AuNP concentration, pH value, temperature, and separation voltage on the separations were systematically studied. Under optimized experimental conditions, racemic mixtures of the respective adrenergic drugs were baseline-separated within 7 min with a resolution of up to 7.5. The relative standard deviations of the resolution in inter-day and intra-day studies (n = 5) were generally <5%. Graphical abstract Schematic of the method for enantiomeric separations. (A): At low concentrations of streptavidinylated gold nanoparticles (ST-AuNPs), the better matching enantiomer is preferably "transported" by the ST-AuNPs; (B) ST-AuNP concentration increased to an optimal value; (C): The ST-AuNP concentration is too high; even poorly matching enantiomers will be transported simultaneously.