Novel imidazolium-embedded and imidazolium-spaced octadecyl stationary phases for reversed phase liquid chromatography

Adjustable chromatographic performance of silica-based mixed-mode stationary phase through the control of co-grafting amounts of imidazole and C18 chain

In this paper, three imidazole- and C18- bifunctional silica stationary phases (Sil-Im-C18) were prepared by adjusting introduction interval of octadecyltrichlorosilane (ODS) and 3-imidazol-1-ylpropyl(trimethoxy)silane (TMPImS), which can be used for reversed-phase liquid chromatography (RPLC) and ion exchange chromatography (IEC) with adjustable performance. The successful preparation of Sil-Im-C18 were confirmed by the characterizations of elemental analysis, infrared spectroscopy (FTIR) and contact angle (CA). Chromatographic performance of Sil-Im-C18 were evaluated by the separation of Tanaka test mixture, alkylbenzenes, linear PAHs and a set of analytes with different properties (uracil, phenol, 1,2-dinitrobenzene and naphthalene), and compared with commonly used C18 column. It was found that the chromatographic performance of Sil-Im-C18 changed significantly with the difference in bonding amount of imidazole and C18. Sil-Im-C18 demonstrated the excellent separation performance towards polycyclic aromatic hydrocarbons (PAHs), phenylesters, phenylamines, phenols and inorganic anions, and notably, nucleobases and nucleosides can be separated using pure water as mobile phases. The van Deemter plot showed that the column efficiency of Sil-Im-C18-3 was 64,933 plate·m-1 for naphthalene, indicated that Sil-Im-C18 was reasonably chromatographic columns. The RSD values of retention time were 0.22 %-0.61 % for 10 needles alkylbenzenes injected continuously at 50 °C to investigate thermal stability and repeatability, all the fluctuations of k of naphthalene were less than 2.3 % for Sil-Im-C18-1 during flushing 24 h with the mobile phase at different pH values (pH = 3 and 8), the retention time of alkylbenzenes were almost same for Sil-Im-C18-1 at different time, the RSD values of retention time of alkylbenzenes were 0.45 %-2.28 % for two batches Sil-Im-C18-1, revealing the excellent repeatability, thermal stability, durability and reproducibility of Sil-Im-C18, and implying a commercial prospect.

Grafting of Tetraphenylethylene on Silica Surface, Characterizations, and Their Chromatographic Performance as Reversed-Phase Stationary Phases

Surface modification is an effective way to functionalize the materials so as to get some special properties. Tetraphenylethylene (TPE) has been widely investigated as a well-known reagent which has the nature of aggregation-induced emission (AIE), but has never been reported in the liquid chromatography stationary phase. In this work, TPE-grafted silica (Sil-TPE) was obtained successfully using the derivative of 1-(4-hydroxyphenyl)-1,2,2-triphenylethylene as a ligand, and then characterized by elemental analysis, Fourier transform infrared spectra, thermogravimetric analysis, and so forth. Laser scanning confocal microscopy images reflected the AIE phenomenon of grafted TPE because the internal vibration and rotation of TPE molecules were restrained in the confined silica space. The contact angle test showed superhydrophobic properties of Sil-TPE. In order to understand thoroughly the mechanism of chromatographic performance and retention behavior for Sil-TPE, Tanaka test mixture, alkylbenzenes, polycyclic aromatic hydrocarbons (PAHs), and phenols were separated. This reveals that Sil-TPE has strong aromaticity and certain shape selectivity, especially, has excellent separation performance for PAHs and phenols. The thermodynamic properties and repeatability of Sil-TPE were further studied, which showed the stability of Sil-TPE. This work shows that TPE can be successfully grafted on silica surface and it has the potential to be a new kind of promising stationary phases in the future.

Supported Ionic Liquids Used as Chromatographic Matrices in Bioseparation-An Overview

Liquid chromatography plays a central role in biomanufacturing, and, apart from its use as a preparative purification strategy, either in biopharmaceuticals or in fine chemicals industries, it is also very useful as an analytical tool for monitoring, assessing, and characterizing diverse samples. The present review gives an overview of the progress of the chromatographic supports that have been used in the purification of high-value products (e.g., small molecules, organic compounds, proteins, and nucleic acids). Despite the diversity of currently available chromatographic matrices, the interest in innovative biomolecules emphasizes the need for novel, robust, and more efficient supports and ligands with improved selectivity. Accordingly, ionic liquids (ILs) have been investigated as novel ligands in chromatographic matrices. Given herein is an extensive review regarding the different immobilization strategies of ILs in several types of supports, namely in silica, Sepharose, and polymers. In addition to depicting their synthesis, the main application examples of these supports are also presented. The multiple interactions promoted by ILs are critically discussed concerning the improved selectivity towards target molecules. Overall, the versatility of supported ILs is here considered a critical point to their exploitation as alternatives to the more conventional liquid chromatographic matrices used in bioseparation processes.

Synthesis of octadecylamine-derived carbon dots and application in reversed phase/hydrophilic interaction liquid chromatography

In order to make up for the deficiencies of traditional C18 column for separating strong polar compounds, combined with the good hydrophilicity of carbon dots (CDs), novel octadecylamine-derived CDs denoted as C18-CDs are designed, synthesized and applied in RPLC/HILIC mixed-mode chromatography with good separation performance towards both hydrophobic and hydrophilic compounds. C18-CDs are synthesized by simple one-step solvothermal method using octadecylamine and citric acid as carbon sources, and C18-CDs with proper polarity are collected through column chromatography purification. This C18-CDs decorated silica column showed good separation performance for polycyclic aromatic hydrocarbons and alkylbenzenes under RPLC mode. Hydrophilic compounds including sulfonamides, nucleosides and nucleobases also achieved good resolution in HILIC mode. Hydrophobic and π-π stacking interactions play major retaining roles in RPLC, whereas hydrophilic partitioning and hydrogen bond interactions turn to the main retention interactions under HILIC mode. This C18-CDs/SiO₂ column was applied for the fast detection of chloramphenicol in milk without complex sample pretreatment process. Quantitative relationship between the peak area and the concentration of chloramphenicol was established with linear equation of A = 1677c + 173. Satisfactory spiked recoveries in the range of 94.1-109.0% were obtained. This work not only proposes a simple method for improving the polarity of C18 column through forming octadecane into CDs, but also provides novel CDs with certain hydrophobicity/hydrophily suitable for mixed-mode chromatography.

Amphipathic carbon quantum dots-functionalized silica stationary phase for reversed phase/hydrophilic interaction chromatography

Carbon quantum dots (CQDs) are considered as good chromatographic separation materials. However, due to the hydrophily of the synthesized CQDs, their applications in HPLC are limited to HILIC for separating strong polar compounds only. In this work, a novel amphipathic CQDs with both hydrophobicity and hydrophily is developed as mixed-mode stationary phase for RPLC/HILIC. To give CQDs certain hydrophobicity, 1,8-diaminooctane is chosen as one of the carbon sources for introducing alkyl chain into CQDs. The amphipathic CQDs modified silica (CQDs/SiO₂) stationary phase has typical characteristic of RPLC/HILIC. Both hydrophobic and hydrophilic compounds including alkylbenzenes, polycyclic aromatic hydrocarbons, nucleosides and bases, amino acids, β-adrenoceptor blockers and agonists, sulfonamides, antibiotics and alkaloids obtain satisfactory separation on this CQDs/SiO₂ column. 14 nucleosides and bases commonly existing in living organisms achieve good separation on this amphipathic CQDs/SiO₂ column within 25 min and the resolutions reach 1.33-13.83 with an average column efficiency of 18,800. The retention mechanism of this novel CQDs/SiO₂ column is investigated by linear solvation energy relationship model. It is found that hydrophobic interaction, π-π stacking, hydrogen-bonding and electrostatic interactions are main retention interactions under RPLC mode. This work provides a new approach for synthesis of amphipathic CQDs. Also, it indicates that amphipathic CQDs with versatile functional properties have great prospect in separation science.

The structure - Activity correlation in the family of dicationic imidazolium surfactants: Antimicrobial properties and cytotoxic effect

BACKGROUND

The development of new effective microbicide surfactants and the search for the structure-biological activity relationship is an important and promising problem. Surfactants containing imidazolium fragment attract attention of researchers in the field of chemotherapy, because these compounds often exhibit high antimicrobial activity. The aim of this work is to identify the newly synthesized surfactants from the viewpoint of their potential usefulness in pharmacology and medicine. For this purpose, a detailed study of antimicrobial, hemolytic and cytotoxic activity of dicationic alkylimidazolium surfactants of the m-s-m (Im) series with a variable length of a hydrocarbon tail (m = 10, 12) and a spacer fragment (s = 2, 3, 4) was carried out.

METHODS

Aggregation of surfactants in solutions was estimated by tensiometry and conductivity. Antimicrobial activity was determined by the serial dilution technique. Cytotoxic effects of the test compounds on human cancer and normal cells were estimated by means of the multifunctional Cytell Cell Imaging system. Cell Apoptosis Analysis was made by flow cytometry.

RESULTS

The test compounds show high antimicrobial activity against a wide range of test microorganisms and do not possess high hemolytic activity. Importantly, some of them display a bactericidal activity comparable to ciprofloxacin fluoroquinolone antibiotic against Gram-positive bacteria, including methicillin-resistant strains of S. aureus (MRSA). The cytotoxicity of the compounds against normal and tumor human cell lines has been tested as well, with cytotoxic effect and selectivity strongly controlled by structural factor and kind of cell line. Superior results were revealed for compound 10-4-10 (Im) in the case of HuTu 80 cell line (duodenal adenocarcinoma), for which IC₅₀ value at the level of doxorubicin and a markedly higher selectivity index (SI 7.5) were demonstrated. Flow cytometry assay shows apoptosis-inducing effect of this compound on HuTu 80 cells, through significant changes in the potential of mitochondrial membrane.

MAJOR CONCLUSIONS

Antibacterial properties are shown to be controlled by alkyl chain length, with the highest activity demonstrated by surfactants with decyl tail, with the length of the spacer fragment showing practically no effect. The results indicate that the mechanism of cytotoxic effect of the compounds can be associated with the induction of apoptosis via the mitochondrial pathway.

GENERAL SIGNIFICANCE

Selectivity against pathogenic microorganisms and low toxicity against eukaryotic cells allow considering dicationic imidazolium surfactants as new effective antimicrobial agents. At the same time, high selectivity against some cancer cell lines indicates the prospect of their using as components of new anticancer drugs.

Improved ionic-liquid-functionalized macroporous supports able to purify nucleic acids in one step

Nucleic acids are relevant biopolymers in therapy and diagnosis, for which their purity and biological activity are of crucial relevance. However, these features are difficult to achieve by cost-effective methods. Herein, we report the functionalization of a macroporous chromatographic support functionalized with an ionic liquid (IL) with remarkable performance to purify nucleic acids. An initial screening with distinct IL chemical structures supported in silica was carried out, allowing to identify the IL 1-methyl-3-propylimidazolium chloride as the most promising ligand. A chromatographic macroporous matrix able to be used in preparative liquid chromatography was then functionalized and binding/elution studies were performed. The IL 1-methyl-3-propylimidazolium chloride acts as a multimodal ligand with a remarkable dynamic binding capacity. This macroporous support allows the (one-step) purification of nucleic acids, namely small RNAs, ribosomal RNA, and genomic DNA, from a bacterial lysate, and can be regenerated and reused without compromising its separation performance.

Adjusting the chromatographic properties of poly(ionic liquid)-modified stationary phases by substitution on the imidazolium cation

Poly(ionic liquid)-modified stationary phases can have multiple interactions with solutes. However, in most stationary phases, separation selectivity is adjusted by changing the poly(ionic liquid) anions. In this work, two poly(ionic liquid)-modified silica stationary phases were prepared by introducing the cyano or tetrazolyl group on the pendant imidazolium cation on the polymer chains. Various analytes were selected to investigate their mechanism of retention in the stationary phases using different mobile phases. Two poly(ionic liquid)-modified stationary phases can provide various interactions toward solutes. Compared to the cyano-functionalized poly(ionic liquid) stationary phase, the tetrazolyl-functionalized poly(ionic liquid) stationary phase provides additional cation-exchange and π-π interactions, resulting in different separation selectivity toward analytes. Finally, applicability of the developed stationary phases was demonstrated by the efficient separation of nonsteroidal anti-inflammatory drugs.

The Influence of Ionic Liquids on the Effectiveness of Analytical Methods Used in the Monitoring of Human and Veterinary Pharmaceuticals in Biological and Environmental Samples-Trends and Perspectives

Recent years have seen the increased utilization of ionic liquids (ILs) in the development and optimization of analytical methods. Their unique and eco-friendly properties and the ability to modify their structure allows them to be useful both at the sample preparation stage and at the separation stage of the analytes. The use of ILs for the analysis of pharmaceuticals seems particularly interesting because of their systematic delivery to the environment. Nowadays, they are commonly detected in many countries at very low concentration levels. However, due to their specific physiological activity, pharmaceuticals are responsible for bioaccumulation and toxic effects in aquatic and terrestrial ecosystems as well as possibly upsetting the body's equilibrium, leading to the dangerous phenomenon of drug resistance. This review will provide a comprehensive summary of the use of ILs in various sample preparation procedures and separation methods for the determination of pharmaceuticals in environmental and biological matrices based on liquid-based chromatography (LC, SFC, TLC), gas chromatography (GC) and electromigration techniques (e.g., capillary electrophoresis (CE)). Moreover, the advantages and disadvantages of ILs, which can appear during extraction and separation, will be presented and attention will be given to the criteria to be followed during the selection of ILs for specific applications.

Column Characterization and Selection Systems in Reversed-Phase High-Performance Liquid Chromatography

Reversed-phase high-performance liquid chromatography (RP-HPLC) is the most popular chromatographic mode, accounting for more than 90% of all separations. HPLC itself owes its immense popularity to it being relatively simple and inexpensive, with the equipment being reliable and easy to operate. Due to extensive automation, it can be run virtually unattended with multiple samples at various separation conditions, even by relatively low-skilled personnel. Currently, there are >600 RP-HPLC columns available to end users for purchase, some of which exhibit very large differences in selectivity and production quality. Often, two similar RP-HPLC columns are not equally suitable for the requisite separation, and to date, there is no universal RP-HPLC column covering a variety of analytes. This forces analytical laboratories to keep a multitude of diverse columns. Therefore, column selection is a crucial segment of RP-HPLC method development, especially since sample complexity is constantly increasing. Rationally choosing an appropriate column is complicated. In addition to the differences in the primary intermolecular interactions with analytes of the dispersive (London) type, individual columns can also exhibit a unique character owing to specific polar, hydrogen bond, and electron pair donor-acceptor interactions. They can also vary depending on the type of packing, amount and type of residual silanols, "end-capping", bonding density of ligands, and pore size, among others. Consequently, the chromatographic performance of RP-HPLC systems is often considerably altered depending on the selected column. Although a wide spectrum of knowledge is available on this important subject, there is still a lack of a comprehensive review for an objective comparison and/or selection of chromatographic columns. We aim for this review to be a comprehensive, authoritative, critical, and easily readable monograph of the most relevant publications regarding column selection and characterization in RP-HPLC covering the past four decades. Future perspectives, which involve the integration of state-of-the-art molecular simulations (molecular dynamics or Monte Carlo) with minimal experiments, aimed at nearly "experiment-free" column selection methodology, are proposed.

Nanogold hybrid silica gel and its 1-octadecanethiol self-assembled modified composite as a stationary phase for liquid chromatography

Au nanoparticle-hybridized silica (Au@sil) spheres were synthesized in one step as a liquid chromatographic stationary phase for the first time.

Preparation and evaluation of maltose modified polymer-silica composite based on cross-linked poly glycidyl methacrylate as high performance liquid chromatography stationary phase

A new maltose modified polymer-silica composite was fabricated and applied as high performance liquid chromatography (HPLC) stationary phase. The cross-linked poly glycidyl methacrylate (pGMA) layer was chemically bonded to the outer surface as well as pore inner surface of silica beads via in-situ polymerization, and then maltose was modified onto the polymer layer via a [3 + 2] "click" reaction. The porous spherical silica (4 μm diameter) with 300 Å pore size was selected as the matrix so that the 3.25 nm-thick polymer layer fabricated on the pore inner surface would not affect its permeability. The typical 'U-shape' retention curves indicated a mixed-mode retention mechanism of the as-synthesized stationary phase. Both polar and non-polar analytes could be well separated on the stationary phase with column efficiency reaching 123809 plates/m for guanosine in hydrophilic interaction liquid chromatography (HILIC) mode and 46808 plates/m for fluorene in reversed-phase liquid chromatography (RPLC) mode, respectively. Nucleotides and their bases were baseline separated with good peak shape without any buffer salt in mobile phase, suggesting the effective shielding of the silanol groups. The packing material also showed excellent chromatographic repeatability with intraday RSDs of the retention time of five nucleosides less than 0.048% (n = 3) and interday RSDs less than 0.33% (n = 7) and great pH stability (from 1.5 to 10.2). Finally, the stationary phase was applied to the separation of ginseng extract.

Investigation of the retention characteristics of a 26-membered aromatic-aliphatic azamacrocycle bonded silica gel stationary phase for high performance liquid chromatography

A 26-membered aromatic-aliphatic azamacrocycle bonded silica gel stationary phase for high performance liquid chromatography was prepared and characterized.

Recent development in liquid chromatography stationary phases for separation of Traditional Chinese Medicine components

Traditional Chinese Medicine (TCM) is an ancient medical practice which has been used to prevent and cure diseases for thousands of years. TCMs are frequently multi-component systems with mainly unidentified constituents. The study of the chemical compositions of TCMs remains a hotspot of research. Different strategies have been developed to manage the significant complexity of TCMs, in an attempt to determine their constituents. Reversed-phase liquid chromatography (RPLC) is still the method of choice for the separation of TCMs, but has many problems related to limited selectivity. Recently, enormous efforts have been concentrated on the development of efficient liquid chromatography (LC) methods for TCMs, based on selective stationary phases. This can improve the resolution and peak capacity considerably. In addition, high-efficiency stationary phases have been applied in the analysis of TCMs since the invention of ultra high-performance liquid chromatography (UHPLC). This review describes the advances in LC methods in TCM research from 2010 to date, and focuses on novel stationary phases. Their potential in the separation of TCMs using relevant applications is also demonstrated.

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.

Glucaminium ionic liquid-functionalized stationary phase for the separation of nucleosides in hydrophilic interaction chromatography

A glucaminium-based ionic liquid stationary phase was prepared via facile epoxy-amine reaction and subsequent quaternization. Successful immobilization of glucaminium-based ionic liquid onto silica surface was validated by elemental analysis and infrared spectroscopy. The new stationary phase was evaluated for the separation of nucleosides in hydrophilic interaction liquid chromatography (HILIC). Effects of various factors, such as acetonitrile concentration, salt concentration, pH value, as well as column temperature, on the chromatographic behavior toward nucleosides were studied in detail. The results indicated that this new stationary phase can be used for separation of water-soluble polar substances in HILIC mode. The retention of solutes on the stationary phase was influenced by a mixed-mode retention mechanism with a combination of adsorptive and partitioning interactions.