Homochiral Metallacycle Used as a Stationary Phase for Capillary Gas Chromatographic Separation of Chiral and Achiral Compounds.

Metallacycles are a novel class of supramolecular materials with circular structures, internal cavities, and abundant host-guest chemical properties that have exhibited good application prospects in many fields. However, to the best of our knowledge, no research on the use of metallacycles as stationary phases for gas chromatographic (GC) separations has been published yet. In this work, we report for the first time the use of a homochiral metallacycle, [ZnCl2L]2, as a stationary phase for GC separations. [ZnCl2L]2 was synthesized by reaction of (S)-(1-isonicotinoylpyrrolidin-2-yl)methyl-isonicotinate (L) with ZnCl2 via coordination-driven self-assembly. The [ZnCl2L]2-coated column displayed an excellent separation performance not only of organic isomers but also of racemic compounds. Sixteen racemates (including alcohols, esters, amino acid derivatives, ethers, organic acids, and epoxides) and 21 isomeric compounds (including positional, structural, and cis/trans-isomers) were well separated on the [ZnCl2L]2-coated column. Impressively, some racemates were resolved with high resolution values (Rs), including 1,2-butanediol diacetate (Rs = 25.86), ethyl 3-hydroxybutyrate (Rs = 20.97), 1,3-butanediol diacetate (Rs = 18.09), and threonine derivative (Rs = 18.61). Compared with the commercial ß-DEX 120 column for separation of the tested racemates, the [ZnCl2L]2-coated column exhibited good enantioseparation complementarity, enabling separation of some racemates that could not be separated, or were not well resolved, by the ß-DEX 120 column. In addition, many organic mixtures, such as n-alkanes, alkylbenzenes, n-alcohols, and a Grob test mixture, were also well separated on the [ZnCl2L]2-coated column. The column also has good reproducibility and thermal stability on separation. This work not only reveals the great potential of metallacycles for GC separations but also opens up a new application of metallacycles in separation science.

A chiral metal-organic cage [Fe4L6](ClO4)8 used for capillary gas chromatographic separations.

Metal-organic cages (MOCs), as a promising class of crystalline porous materials with well-defined cavities, have attracted wide attention due to their multifarious potential applications in gas storage, host-guest chemistry, molecular recognition, separation, catalysis, sensing, and drug delivery and so on. Herein, we report that a chiral MOC [Fe4L6](ClO4)8 coated capillary column was fabricated for high-resolution gas chromatographic separation of various analytes, including n-alkanes, n-alcohols, positional isomers, aromatic hydrocarbon mixture, especially for racemic compounds. A series of racemic compounds such as alcohols, epoxides, aldehydes, ketones, ethers, esters, alkenes, sulfoxides and amino acid derivatives could be well separated on the [Fe4L6](ClO4)8 coated capillary column with high enantioselectivity and good reproducibility. Comparing the chiral resolution ability of the MOC [Fe4L6](ClO4)8 coated column with the commercial ß-DEX 120 column and the porous organic cage (POC) CC10 coated column, the chiral MOC column can be complementary to the two different types of columns. The results show that the chiral MOC [Fe4L6](ClO4)8 exhibited excellent separation performance toward a wide range of organic compounds, which will be very attractive as a new chiral separation media and has potential application prospects in separation science.

A hydroxyl-functionalized homochiral porous organic cage for gas chromatographic separations.

A hydroxyl-functionalized homochiral porous organic cage (POC) was synthesized and characterized by FTIR, NMR, thermogravimetric analysis (TGA), MALDI-TOF-MS, and elemental analysis. The synthesized homochiral POC was used as stationary phase to prepare a capillary gas chromatography (GC) column by a static coating method. The fabricated column shows excellent selectivity not only for the separation of positional isomers but also for the resolution of various racemates. Thirty-nine racemates have been resolved on the column, including alcohols, diols, halohydrocarbons, epoxides, esters, lactones, ketones, ethers, and organic acids. Compared to the commercial ß-DEX 120 column and previously reported chiral POCs (CC3-R, CC9, and CC10)-coated columns, there are 11, 10, 24, and 15 tested racemates that cannot be resolved on ß-DEX 120 column, CC3-R column, CC9 column, and CC10 column, respectively. This reveals that the fabricated column has prominent complementarity or superior separation performance to these columns in enantioseparation. Besides, the fabricated column can achieve some enantioseparations which are not possible using all previously reported chiral POC-based columns. Some positional isomers (xylenes, dichlorobenzenes, dibromobenzenes, nitrochlorobenzenes, and nitrobromobenzenes) were also separated with high-resolution values. The column exhibits good repeatability, reproducibility, and stability. The relative standard deviation (RSD) values of retention times were 0.03-0.18%, 0.11-0.92%, and 2.1-6.6% for run-to-run (n = 5), day-to-day (n = 5), and column-to-column (n = 3), respectively. The experimental results demonstrate the great potential of POCs for practical application in GC. Graphical Abstract A hydroxyl-functionalized homochiral porous organic cage was used as stationary phase for gas chromatography separation of racemates and positional isomers. The resolution of racemates mainly depended on hydrogen bonding, π-interaction, host-guest inclusion, steric fit, etc., while separation of positional isomers by shape-selective guest binding.

A homochiral porous organic cage with large cavity and pore windows for the efficient gas chromatography separation of enantiomers and positional isomers.

Porous organic cages composed of discrete cage molecules have attracted considerable recent attention as gas adsorption materials and separation media. In this study, we report a homochiral porous organic cage CC5 with a large cavity and pore windows as a novel stationary phase for high-resolution gas chromatographic separations. The capillary column was prepared by a static coating method. A large number of racemic compounds have been resolved on the coated capillary column, including derivatized amino acids, alcohols, alcohol amines, esters, ethers, ketones, and epoxides. It is interesting that the CC5-coated capillary column exhibits significant chiral recognition complementarity to a commercial ß-DEX 120 column and a previously reported homochiral porous organic cage CC3-R-coated column, which could expand the range of the analytes amenable to separation on porous organic cage-based capillary columns. Moreover, the fabricated column also shows excellent selectivity for the separation of positional isomers, including the challenging ethylbenzene and xylene isomers. Experimental results demonstrate an excellent separation performance and stability of the CC5-coated column, making it promising for gas chromatography applications.

A chiral porous organic cage for molecular recognition using gas chromatography.

Molecular organic cages as shape-persistent organic molecules with permanent and accessible cavities have attracted a lot of interest because of their importance as host-guest systems. Herein, we report a chiral porous organic cage (POC) CC9 diluted with a polysiloxane OV-1701 to fabricate a CC9-coated capillary column, which was used for the high-resolution gas chromatographic separation of organic compounds, including positional isomers and racemates. On the CC9-coated capillary column, a large number of racemic compounds such as chiral alcohols, esters, ethers and epoxides can be resolved without derivatization. By comparing the chiral recognition ability of the CC9-coated column with the commercially available ß-DEX 120 column and the POC CC3-R coated column recently reported by our group, the CC9-coated column offered good resolution during the separation of some racemates, that were not separated using the ß-DEX 120 column or POC CC3-R coated column. Therefore, the CC9-coated column can be complementary to the ß-DEX 120 column and CC3-R coated column. The results indicated that the CC9-coated column exhibited great potential for application in the separation of positional isomers and enantiomers with great selectivity, high resolution and good reproducibility.

Homochiral Porous Organic Cage with High Selectivity for the Separation of Racemates in Gas Chromatography.

Porous organic molecular cages as a new type of porous materials have attracted a tremendous attention for their potential applications in recent years. Here we report the use of a homochiral porous organic cage (POC) (CC3-R) diluted with a polysiloxane (OV-1701) as a stationary phase for high-resolution gas chromatography (GC) with excellent enantioselectivity. A large number of optical isomers have been resolved without derivatization, including chiral alcohols, diols, amines, alcohol amines, esters, ketones, ethers, halohydrocarbons, organic acids, amino acid methyl esters, and sulfoxides. Compared with commercial ß-DEX 120 and Chirasil-L-Val columns, the CC3-R coated capillary column offered more preeminent enantioselectivity. In addition, CC3-R also exhibits good selectivity for the separation of isomers, linear alkanes, alcohols, and aromatic hydrocarbons. The excellent resolution ability, repeatability, and thermal stability make CC3-R a promising candidate as a novel stationary phase for GC. The study described herein first proves useful commercially. This work also indicates that porous organic molecular materials will become more attractive in separation science.