Amphiphilic calix[4]arenes as a highly selective gas chromatographic stationary phase for aromatic amine isomers

High-resolution performance of pillar[6]arene functionalized with imidazolium ionic liquids for gas chromatography

Pillar[n]arenes (P[n]A, n = 5-10) have attracted much attention because of their highly symmetric pillar-shaped architecture with π-electron rich cavity. Nevertheless, the use of ionic liquid functionalized P[n]A in chromatography has not been reported up to data. This work reports the investigation of the imidazolium ionic liquids functionalized pillar[6]arene (P6A-C10-IM-C8[NTf2]) as the stationary phase for gas chromatography (GC). The statically coated P6A-C10-IM-C8[NTf2] column (0.25 mm i.d.) showed moderate polarity and high column efficiency of 4733 plates/m determined by n-dodecane at 120 °C (k = 2.29). Owing to its unique amphiphilic conformation, the P6A-C10-IM-C8[NTf2] showed good column inertness and resolving capability for a wide range of analytes and isomers. Particularly, the P6A-C10-IM-C8[NTf2] column exhibited distinctly advantageous performance for the challenging isomers of halogenated benzenes, benzaldehydes, phenols and anilines over the common commercial columns, namely 5% phenyl methyl polysiloxane (HP-5) and 35% phenyl methyl polysiloxane (HP-35). In addition, it exhibited good column repeatability and reproducibility with RSD values on the retention times less than 0.05% for run-to-run, 0.38% for day-to-day and 2.94% for column-to-column, respectively. This work demonstrates the promising future of ionic liquid P[n]A stationary phases for chromatographic separations.

High Selectivity of A Novel Pillar[5]arene with Ester Units as a Gas Chromatographic Stationary Phase toward Aromatic Isomers

This work reports the first example of employing ester-functionalized pillar[5]arene (P5A-C10-OAc) stationary phase for gas chromatography (GC) separations. The as-fabricated P5A-C10-OAc column achieved improved column efficiency of 4270 plates/m and separation performance in contrast to the P5-C10-Br column. The P5A-C10-OAc column showed good separation performance for a wide range of analytes such as alkanes, bromoalkanes, ketones, fatty acid methyl esters, aldehydes, alcohols, halobenzenes, anilines, phenols, naphthalenes, and showed sharp and symmetrical peak shapes for analytes that are liable to peak-tailing in GC analysis. As testified by the challenging isomer mixtures (bromonitrobenzene, chloronitrobenzene, bromobenzaldehyde, chlorobenzaldehyde, nitrobenzaldehyde), the P5A-C10-OAc column exhibited comprehensively higher separation capability than the P5A-C10-Br, P5A-C10 and commercial HP-35 columns. This work demonstrates the great potential of pillararene-based stationary phases as a new type of stationary phases for GC separations.

Multipurpose new gas chromatography column based on pillararenes functionalized with imidazolium ionic liquids

BACKGROUND

Gas chromatography is worldwide recognized as one of the most important analytical techniques, due to its high versatility and reliability. The heart of a gas chromatograph is the column, that allows analyte peak separations and, consequently, accurate qualitative and qualitative analyses. New and more efficient columns are always requested to satisfy new and challenging analytical needs.

RESULTS

In this work, imidazolium ionic liquids functionalized pillar [5] arenes have been used for the first time as gas chromatographic stationary phases, considering their highly symmetric pillar-shaped architecture with cavities rich in π-electrons. Four imidazolium ionic liquids functionalized pillar [5] arenes have been tested as stationary phases with numerous analytes and isomers. In particular, one of these showed superior performances if compared to commercial columns, enabling challenging isomeric separations of halogenated benzenes, aromatic aldehydes, and aromatic anilines.

SIGNIFICANCE AND NOVELTY

To our knowledge, this is the first report on the use of the ionic liquid P[n]A as a stationary phase in chromatography, either in GC or liquid chromatography (LC) separations. This work demonstrates the promising potential of ionic liquid P[n]A stationary phases for chromatographic separations.

A new organic soluble cucurbit[7]uril-truxene derivative as stationary phase for gas chromatographic separation of some challenging isomers

The insolubility of parent cucurbit[n]uril or substituted-cucurbit[n]uril derivatives in organic solvents has always been a key factor restricting the column efficiency and selectivity of capillary gas chromatography column based on cucurbit[n]uril. In this work, a novel organic soluble cucurbit [7]uril-truxene derivative (Q [7]-Tr) was synthesized by Heck coupling reaction between the mono-iodinated hexahexyl-truxene and 4-vinylbenzyloxy-Q [7]. A capillary gas chromatographic column was prepared by static method with this derivative as stationary phase. The column exhibited moderate polarity and an efficiency of 5857 plates/m using n-dodecane as analyte at 120 °C, indicating the highest column efficiency of all the based-cucurbit[n]uril columns published. The Q [7]-Tr column showed high resolutions for a wide range of analytes with different polarities and better separated selectivity towards tough isomers such as aromatic amines isomers and xylene isomers compared to commercial HP-5, DB-35, Stabilwax and Q [7]-based columns. Moreover, the new column exhibited high thermal stability up to 320 °C and excellent repeatability, demonstrating a great potential as a new stationary phase in capillary gas chromatography.

Functionalized Calixarenes as Promising Antibacterial Drugs to Face Antimicrobial Resistance

Since the discovery of polyphenolic resins 150 years ago, the study of polymeric compounds named calix[n]arene has continued to progress, and those skilled in the art perfectly know now how to modulate this phenolic ring. Consequently, calix[n]arenes are now used in a large range of applications and notably in therapeutic fields. In particular, the calix[4]arene exhibits multiple possibilities for regioselective polyfunctionalization on both of its rims and offers researchers the possibility of precisely tuning the geometry of their structures. Thus, in the crucial research of new antibacterial active ingredients, the design of calixarenes finds its place perfectly. This review provides an overview of the work carried out in this aim towards the development of intrinsically active prodrogues or metallic calixarene complexes. Out of all the work of the community, there are some excellent activities emerging that could potentially place these original structures in a very good position for the development of new active ingredients.

Efficient gas chromatographic separation of xylene and other aromatic isomers by using pillar[6]arene-based stationary phase

The separation of aromatic isomers, in particular xylene isomers, represents a big issue in chemical and petroleum industries, owing to their similar molecular sizes and boiling points. In this work, the investigation ofpillar[6]arene derivative modified by long alkyl chains (P6A-C10) as a stationary phase for high-resolution gas chromatographic (GC) separations of xylene isomers is presented. Pillar[n]arenes are a new class of macrocyclic hosts that can accommodate specific guests due to their highly symmetrical and rigid pillar architectures with π-electron rich cavities. The P6A-C10 column showed high-resolution performance towards xylene isomers, with peculiar advantages if compared with the commercial HP-5, HP-35, DB-17, and PEG-20Mcolumns.A quantum chemistry calculation has been performed, showing a difference in non-covalent interactions with the P6A-C10 pillar framework, which leads to specific selectivity for xylene isomers.Furthermore, the P6A-C10 column exhibited good repeatability.

Separation performance of the calix[8]arene functionalized with polyethylene glycol units for capillary gas chromatography

In this paper, an amphiphilic calix[8]arene with polyethylene glycol unit branches (C8A-PEG) was synthesized and applied for capillary gas chromatography (GC). The C8A-PEG was coated on the inner wall of a capillary column by a static method with the column efficiency of 3165 plates/m and polar nature. As demonstrated, the C8A-PEG column has excellent physicochemical properties and separation performance since it has π-electron-rich 3D cavity which combines with polar PEG units. Compared with two columns corresponding to the construction units C8A and PEG, the C8A-PEG column shows distinctly advantageous performance for the mixture of 22 components with diverse types. Impressively, it shows satisfactory resolution for positional isomers and cis-/trans- isomers, especially the challenging isomers of toluidine and dimethylaniline. The outstanding distinguishing capability of the C8A-PEG stationary phase is mainly attributed to the abundant molecular recognition interactions, including van der Waals, dipole-dipole, H-bonding and π-π stacking interactions. This work has proved that the new GC stationary phases constructed by different units can complement each other's advantages, improve their physicochemical properties and separation performance, and have broad application prospects in chromatographic analysis.

Chromatographic Separation of Aromatic Amine Isomers: A Solved Issue by a New Amphiphilic Pillar[6]arene Stationary Phase

In this work, the fabrication, synthesis, and characterization of a new stationary phase based on an amphiphilic pillar[6]arene (P6A-C10-2NH₂) for gas chromatographic analyses are reported. The gas chromatography (GC) column prepared with P6A-C10-2NH₂ stationary phase exhibited a medium polarity, an efficiency of 3219 plates/m, and unmatched resolving capabilities toward chloroaniline, bromoaniline, iodoaniline, and toluidine isomers. Furthermore, the P6A-C10-2NH₂ column showed excellent repeatability with maximum relative standard deviations equal to 0.02, 0.07, and 2.56% for run-to-run, day-to-day, and column-to-column, respectively, demonstrating a great potential as a new stationary phase in separation science.

A New Capillary Gas Chromatography Column Based on Poly(ethylene glycol) Methyl Ether-Functionalized Calix[4]arene

In this work, a novel capillary column (C4A-mPEG) with a calixarene-based polymer stationary phase (poly(ethylene glycol) methyl ether-functionalized 4-tert-butylcalix[4]arene) was designed and used for gas chromatographic (GC) separations. The C4A-mPEG capillary column, prepared by the static coating method, showed moderate polarity and a column efficiency of 2332 plates/m, determined by 1-octanol at 120 °C. The separation features of C4A-mPEG stationary phase, resulting from its unique structure and multiple molecular recognition processes with analytes, including π-π, H-bonding, dipole-dipole, and van der Waals interactions, allowed to obtain high-resolution performances for a wide range of compounds and their isomers, especially benzaldehydes, phenols, and anilines. Moreover, compared with 4-tertbutyl calix[4]arene (C4A) and polyethylene glycol (PEG) stationary phases, a higher resolving capability was also observed for the separation of toluidine and xylidine isomers.

Performance and selectivity of amphiphilic pillar[5]arene as stationary phase for capillary gas chromatography

Pillar[n]arenes possess highly symmetrical and rigid pillar-shaped architecture with π-electron rich cavity that afford their reliable host-guest recognition interactions towards matched guests. In this work, a novel amphiphilic pillar[5]arene (P5A-C10-2NH₂) was designed, synthesized and employed as the stationary phase for capillary gas chromatography. To date, they have not been reported in the field of chromatography. The P5A-C10-2NH₂ capillary column (10 m × 0.25 mm i.d.) was prepared by static coating method. Its capillary column exhibited moderate polarity and column efficiency of 2265 plates/m determined by naphthalene at 120 °C. As evidenced, the P5A-C10-2NH₂ column achieved advantageous separation performance for a mixture of 24 analytes of diverse types and exhibited different chromatographic selectivity from two pillar[5]arene derivatives columns and commercial HP-35 column with 35%-phenyl-methylpolysiloxane. Moreover, the P5A-C10-2NH₂ column baseline resolved more than a dozen positional and cis-trans isomers. Furthermore, the separation mechanism of P5A-C10-2NH₂ column was discussed by quantum chemical calculations. In addition, the P5A-C10-2NH₂ column had high thermal stability and excellent separation repeatability 0.01-0.04% for run-to-run, 0.03-0.17% for day-to-day and 3.2-3.9% for column-to-column. The special amphiphilic structure and high resolution for various analytes reveal the good potential of pillararenes as a new class of stationary phases for chromatographic analyses. Moreover, the TPG column achieved improved thermal stability over the GIL column and excellent repeatability.

The selectivity of a polydimethylsiloxane-based triblock copolymer as the stationary phase for capillary gas chromatography

A triblock copolymer (PCL-PDMS-PCL) constructed from polydimethylsiloxane (PDMS) and poly(ε-caprolactone) (PCL) chains was synthesized and used as the stationary phase for capillary gas chromatography (GC).

Adenine-functionalized polypropylene glycol: A novel stationary phase for gas chromatography offering good inertness for acids and bases combined with a unique selectivity

This work presents the investigation of utilizing adenine-functionalized polypropylene glycol (APPG) for capillary gas chromatographic separations. The statically coated APPG column (0.25 mm i.d.) showed moderate polarity and high column efficiencies of 4660 plates/m and 4376 plates/m determined by n-octanol and naphthalene, respectively. Remarkably, the APPG column baseline resolved all the components of the Grob test mixture and displayed good peak shapes for some stringent analytes that are prone to peak tailing or severe adsorption. Also, it achieved complete separation of dimethylaniline isomers, which are difficult to be resolved due to their high resemblance in structures and properties. The above results demonstrate the high selectivity and inertness of the APPG column and its distinct advantages over the polypropylene glycol (PPG) column and commercial polyethylene glycol (PEG) column. In addition, its separation performance has good repeatability with the RSD values on retention times below 0.05% for run-to-run, 0.11-0.12% for day-to-day and 1.7-1.9% for column-to-column, respectively. Further, the APPG column was applied to determination of isomer impurities in commercial dimethylaniline products and to determination of the additives of anilines and phenols in a hair-dye product, proving its great potential for practical GC analysis.

Amphiphilic Block Copolymer PCL-PEG-PCL as Stationary Phase for Capillary Gas Chromatographic Separations

This work presents the first example of utilization of amphiphilic block copolymer PCL-PEG-PCL as a stationary phase for capillary gas chromatographic (GC) separations. The PCL-PEG-PCL capillary column fabricated by static coating provides a high column efficiency of 3951 plates/m for n-dodecane at 120 °C. McReynolds constants and Abraham system constants were also determined in order to evaluate the polarity and possible molecular interactions of the PCL-PEG-PCL stationary phase. Its selectivity and resolving capability were investigated by using a complex mixture covering analytes of diverse types and positional, structural, and cis-/trans-isomers. Impressively, it exhibits high resolution performance for aliphatic and aromatic isomers with diverse polarity, including those critical isomers such as butanol, dichlorobenzene, dimethylnaphthalene, xylenol, dichlorobenzaldehyde, and toluidine. Moreover, it was applied for the determination of isomer impurities in real samples, suggesting its potential for practical use. The superior separation performance demonstrates the potential of PCL-PEG-PCL and related block copolymers as stationary phases in GC and other separation technologies.