关键词: 气相色谱, 手性分离, 手性固定相, 多孔有机分子笼

Abstract: Porous organic molecular cages (POCs) are novel porous materials assembled from three-dimensional cage-like molecules with stable internal cavities via weak intermolecular interactions. They exhibit good solubility and solution processability, and show promising applications in gas adsorption, catalysis, sensing, separation, bioimaging and other fields. In this work, a chiral porous aromatic molecular cage, PAC 1-S, was synthesized via Schiff-base condensation of S-(‒)1,1'-bi-2-naphthylamine and 2,4,6-triformylphloroglucinol. The synthesized PAC 1-S was characterized by powder X-ray diffraction (PXRD), nuclear magnetic resonance (NMR), and matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF MS). Thermogravimetric analysis (TGA) indicates that PAC 1-S exhibits excellent thermal stability and can remain stable without decomposition below 405 ℃, making it suitable as a stationary phase for gas chromatography (GC). It was used as a stationary phase to fabricate a GC capillary column by the static coating method. The number of theoretical plates was determined to be 3 240 plates/m using n-dodecane as test compound. The average McReynolds constant was calculated to be 231 with five selected probes (benzene, 1-butanol, 2-pentanone, 1-nitropropane, and pyridine), indicating that the stationary phase is of medium polarity. The chromatographic separation performance of the fabricated PAC 1-S capillary column was systematically investigated. The results demonstrate that the PAC 1-S column exhibits good separation capability not only for diverse organic mixtures and organic isomers but also for various racemates. Four organic mixtures including n-alkanes, n-alcohols, alkylbenzenes, and Grob reagent were well separated on the PAC 1-S column. Meanwhile, nineteen organic isomers were effectively separated, including disubstituted benzene positional isomers, structural isomers, and cis-/trans-isomers. More importantly, twelve racemates were successfully resolved, including esters, alcohols, epoxides, and amino acid derivatives. Among them, eight racemates achieved baseline separated, and some racemates were separated with high resolution values (R_s), such as 1,2-butanediol diacetate (R_s=12.48), proline derivative (R_s=15.74), and mandelic acid derivative (R_s=8.50). Compared with the widely used commercial β-DEX 120 GC chiral column, the PAC 1-S capillary column showed favorable complementarity in chiral separation. It successfully separated many racemates that were unresolved or poorly resolved on the β-DEX 120 column. For example, ethyl 3-hydroxybutyrate, threonine derivative, and proline derivative could not be resolved on the β-DEX 120 column, but were well resolved on the PAC 1-S column. The values of separation factor (α) and R_s for the resolution of β-butyrolactone, 1,2-butanediol diacetate, 1,2-propanediol diacetate, and mandelic acid derivative on the PAC 1-S column were all higher than those on the β-DEX 120 column. Furthermore, the PAC 1-S column exhibited good reproducibility and stability in separation. The separation performance remained almost unchanged after 300 consecutive injections, thermal treatment at 250 ℃, and storage for one month. This study confirms that the chiral porous aromatic molecular cage PAC 1-S is a good GC stationary phase and possesses considerable application value. Moreover, this research also holds significant importance for the development of novel GC stationary phases based on POCs.

Key words: gas chromatography （GC）, chiral separation, chiral stationary phase, porous organic molecular cage