Preparation of a homochiral metal-organic cage and its bonded silicas for efficient enantioseparation in high-performance liquid chromatography and gas chromatography

Abstract

Developing a chiral material as versatile and universal chiral stationary phase (CSP) for chiral separation in diverse chromatographic techniques simultaneously is of great significance. In this study, we demonstrated for the first time that a chiral metal-organic cage (MOC), [Zn 6 M 4 ], as a universal chiral recognition material for both multi-mode high-performance liquid chromatography (HPLC) and capillary gas chromatography (GC) enantioseparation. Two novel HPLC CSPs with different bonding arms (CSP-A with a cationic imidazolium bonding arm and CSP-B with an alkyl chain bonding arm) were prepared by clicking of functionalized chiral MOC [Zn 6 M 4 ] onto thiolated silica via thiol-ene click chemistry. Meanwhile, a capillary GC column statically coated with the chiral MOC [Zn 6 M 4 ] was also fabricated. The results showed that the chiral MOC exhibits excellent enantioselectivity not only in normal phase HPLC (NP-HPLC) and reversed phase (RP-HPLC) but also in GC, and various racemates were well separated, including alcohols, diols, esters, ketones, ethers, amines, and epoxides. Importantly, CSP-A and CSP-B are complementary to commercially available Chiralcel OD-H and Chiralpak AD-H columns in enantioseparation, which can separate some racemates that could not be or could not well be separated by the two widely used commercial columns, suggesting the great potential of the two prepared CSPs in enantioseparation. This work reveals that the chiral MOC is potential versatile chiral recognition materials for both HPLC and GC, and also paves the way to expand the potential applications of MOCs. A homochiral metal-organic cage and its clicked silicas were prepared and used as chiral stationary phases for both multi-mode HPLC (NP-HPLC and RP-HPLC) and GC enantioseparation with excellent enantioselectivity.

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