Two-dimensional chiral metal-organic framework nanosheets L-hyp-Ni/Fe@SiO2 composite for HPLC separation.

In this study, we have synthesised a chiral l-hyp-Ni/Fe@SiO2 composite as a chiral stationary phase (CSP) for high-performance liquid chromatography (HPLC) for the first time. This was achieved by coating two-dimensional (2D) chiral metal-organic framework nanosheets (MONs) l-hyp-Ni/Fe onto the surface of activated SiO2 microspheres using the "wrapped in net" method. The separation efficiency of the l-hyp-Ni/Fe chromatographic column was systematically evaluated in normal-phase HPLC (NP-HPLC) and reversed-phase HPLC (RP-HPLC) configurations, employing various racemates as analytes. The findings revealed that 16 chiral compounds were separated using NP-HPLC, and five were separated using RP-HPLC, encompassing alcohols, amines, ketones, esters, alkanes, ethers, amino acids and sulfoxides. Notably, the resolution (Rs) of nine chiral compounds exceeded 1.5, indicating baseline separation. Furthermore, the resolution performance of the l-hyp-Ni/Fe@SiO2-packed column was compared with that of Chiralpak AD-H. It was observed that certain enantiomers, which either could not be resolved or were inadequately separated on the Chiralpak AD-H column, attained separation on the 2D chiral MONs column. These findings suggest a complementary relationship between the two columns in racemate separation, with their combined application facilitating the resolution of a broader spectrum of chiral compounds. In addition, baseline separation was achieved for five positional isomers on the l-hyp-Ni/Fe@SiO2-packed column. The effects of the analyte mass and column temperature on the resolution were also examined. Moreover, during HPLC analysis, the l-hyp-Ni/Fe columns demonstrated commendable repeatability, stability and reproducibility in enantiomer separation. This research not only advances the utilisation of 2D chiral MONs as CSPs but also expands their applications in the separation sciences.

Cyclodextrin Incorporation into Covalent Organic Frameworks Enables Extensive Liquid and Gas Chromatographic Enantioseparations.

The separation of enantiomers using high-performance chromatography technologies represents great importance and interest. In this aspect, ß-cyclodextrin (ß-CD) and its derivatives have been extensively studied as chiral stationary phases (CSPs). Nevertheless, ß-CD that was immobilized on a traditional matrix often exhibited low stabilities and limited operating ranges. Recently, covalent organic frameworks (COFs) with highly ordered nanopores are emerging as promising CSPs for enantioseparations, but their practical applications are still hampered by the difficulty of monomer and COF synthesis. Herein, two ß-CD-driven COFs are synthesized via a fast and facile plasma-induced polymerization combined postsynthesis modification strategy. The precisely defined COF channels enhanced the accessibility of the accommodated ß-CD to the analytes and acted as robust protective barriers to safeguard the ß-CD from harsh environments. Therefore, the ß-CD-modified COFs can be potentially general CSPs for extensive enantioseparation in both gas chromatography and high-performance liquid chromatography, and a wide range of racemates were separated. Compared to the commonly employed commercial chiral columns, these COF-based columns exhibited comparable resolution capability and superior application versatility. This work integrates the advantages and overcomes the defects of COFs and ß-CD, thus advancing COFs as platforms for chiral selector modification and giving great promise for practical chromatographic enantioseparation.