A chiral metal-organic cage Al-CMOC for high-resolution gas chromatographic separation

Chiral metal-organic cages (CMOCs) represent a novel class of porous materials featuring tunable chiral cavities and distinctive chiral microenvironments, endowing them with remarkable advantages in enantiomeric separation. However, the reported CMOCs are mostly constructed with noble or transition metal ions, limiting their prospects in energy sustainability and green development. Furthermore, although existing CMOCs exhibit outstanding separation performance, their enantioseparation ability and application scope are still restricted. Therefore, developing novel CMOC materials that combine low cost and outstanding chiral recognition performance for chromatographic applications is of great significance.

Herein, a chiral Al-based CMOC (Al-CMOC) was fabricated and utilized as a novel stationary phase for high-resolution gas chromatographic separation of diverse organic compounds, including n-alkanes, alkylbenzenes, n-alcohols, isomers, as well as chiral analytes involving alcohols, esters, ethers, and arenes. The Al-CMOC column exhibits high column efficiency (3100 plates·m^-1 for n-dodecane) and achieves a maximum resolution of 9.71 for ethyl 3-hydroxybutyrate. The enantioseparation performance of the Al-CMOC column was compared with that of commercially available β-DEX 120 column and the previously reported Fe₄^IIL₄ column, and the results demonstrated that the three columns exhibit favorable complementarity. In addition, the reproducibility studies revealed that the relative standard deviations (RSDs) of peak area and retention time were below 1.0% for ethyl 3-hydroxybutyrate and nitrotoluene, demonstrating the exceptional stability of the Al-CMOC column.

Al-based CMOCs constructed from aluminum featuring high crustal abundance, low biotoxicity, and low cost, overcome the limitations of conventional CMOC materials, which largely rely on precious and transition metal centers. Moreover, the as-prepared Al-CMOC serves as a promising chiral separation medium, which not only broadens the application scope of CMOCs in chromatographic analysis, but also provides a feasible strategy for developing advanced gas chromatographic chiral stationary phases.