l-Cysteine modified metal-organic framework as a chiral stationary phase for enantioseparation by capillary electrochromatography.

A new kind of chiral zirconium based metal-organic framework, l-Cys-PCN-222, was synthesized using l-cysteine (l-Cys) as a chiral modifier by a solvent-assisted ligand incorporation approach and utilized as the chiral stationary phase in the capillary electrochromatography system. l-Cys-PCN-222 was characterized by X-ray diffraction, thermogravimetric analysis, X-ray photoelectron spectroscopy, Fourier-transform infrared spectra, nitrogen adsorption/desorption, circular dichroism spectrum, zeta-potential and so on. The results revealed that l-Cys-PCN-222 had the advantages of good crystallinity, high specific surface area (1818 m2 g-1), thermal stability and chiral recognition performance. Meanwhile, the l-Cys-PCN-222-bonded open-tubular column was prepared using l-Cys-PCN-222 particles as the solid phase by 'thiol-ene' click chemistry reaction and characterized by scanning electron microscopy, which proved the successful bonding of l-Cys-PCN-222 to the column inner wall. Finally, the stability, reproducibility and chiral separation performance of the l-Cys-PCN-222-bonded OT column were measured. Relative standard deviations (RSD) of the column efficiencies for run-to-run, day-to-day, column-to-column and runs were 1.39-6.62%, and did not obviously change after 200 runs. The enantiomeric separation of 17 kinds of chiral compounds including acidic, neutral and basic amino acids, imidazolinone and aryloxyphenoxypropionic pesticides, and fluoroquinolones were achieved in the l-Cys-PCN-222-bonded OT column. These results demonstrated that the chiral separation system of the chiral metal-organic frameworks (CMOFs) coupled with capillary electrochromatography has good application prospects.

Chiral fluorescence recognition of glutamine enantiomers by a modified Zr-based MOF based on solvent-assisted ligand incorporation.

In this study, three types of chiral fluorescent zirconium-based metal-organic framework materials were synthesized using l-dibenzoyl tartaric acid as the chiral modifier by the solvent-assisted ligand incorporation method, which was the porous coordination network yellow material, denoted as PCN-128Y. PCN-128Y-1 and PCN-128Y-2 featured unique chiral selectivity for the Gln enantiomers amongst seven acids and the highly stable luminescence property, which were caused by the heterochiral interaction and aggregation-induced emission. Furthermore, a rapid fluorescence method for the chiral detection of glutamine (Gln) enantiomers was developed. The homochiral crystals of PCN-128Y-1 displayed enantiodiscrimination in the quenching by d-Gln such that the ratio of enantioselectivity was 2.0 in 30 seconds at pH 7.0, according to the Stern-Volmer quenching plots. The detection limits of d- and l-Gln were 6.6 × 10-4 mol L-1 and 3.3 × 10-4 mol L-1, respectively. Finally, both the maximum adsorption capacities of PCN-128Y-1 for the Gln enantiomers (Q e(l-Gln) = 967 mg g-1; Q e(d-Gln) = 1607 mg g-1) and the enantiomeric excess value (6.2%) manifested that PCN-128Y-1 had strong adsorption capacity for the Gln enantiomers and higher affinity for d-Gln.