Abstract:

Covalent organic frameworks (COFs) are an emerging class of porous crystalline materials composed of multidentate organic units connected by covalent bonds. COFs have been demonstrated to exhibit great potential and research value in many fields, including gas storage and separation, photoelectric devices, fluorescence sensors, catalysis, drug delivery, dye and pollutant adsorption, and electronic devices, and so on. The COFs obtained by post-synthesis modification tend to exhibit high crystallinities and porosities, thereby rendering them suitable materials for use in the fields of chiral resolution, asymmetric catalysis, and chromatography. In this work, TpPa-NO₂ was synthesized from 1,3,5-tricarbaldehyde phloroglucinol and 2-nitro-1,4-phenylenediamine, which was then reduced to TpPa-NH₂. Subsequently, this material was modified with D-glucose via a post-synthesis modification strategy to obtain the TpPa-NH₂-Glu. TpPa-NH₂-Glu were characterized by nuclear magnetic resonance (NMR) spectroscopy, Fourier transform-infrared (FT-IR) spectroscopy, X-ray powder diffraction (XRD) analysis, etc. In the XRD pattern, the peaks observed at 4.7°, 8.1°, 11.1°, and 27° were attributed to the TpPa-NH₂-Glu, and these peaks are consistent with previous reports, thereby confirming the successful synthesis of this derivative. In addition, circular dichroism experiments indicated that the TpPa-NH₂-Glu exhibited a Cotton effect, further confirming the chiral COF was prepared. Subsequently, this material was immobilized on the surface of spherical silica gel particles via the net-wrapping method to prepare a stationary phase for high performance liquid chromatographic column. Using n-hexane-isopropanol (9:1, v/v) or methanol-water (9:1, v/v) as mobile phases at a flow rate of 0.5 mL/min, 16 racemates and two benzene-based positional isomers (o,m,p-nitroaniline and o,m,p-Iodoaniline) were successfully resolved by this chiral column. In addition, under methanol-water (9:1, v/v) mobile phase conditions, five racemates were separated, among which propranolol hydrochloride, warfarin, and metoprolol reached baseline separation. Furthermore, under n-hexane-isopropanol (9:1, v/v) mobile phase conditions, 11 racemates were resolved, among which ethyl 2-bromopropionate and 3-butyn-2-ol reached baseline separation. Meanwhile, the effect of temperature on the TpPa-NH₂-Glu liquid chromatography column and the repeatability of the TpPa-NH₂-Glu liquid chromatography column were also explored. The HPLC column prepared by TpPa-NH₂-Glu had good repeatability, and its relative standard deviation (RSD) was 1.55% and 1.46%, respectively. It is demonstrated that the TpPa-NH₂-Glu material has good resolution ability for chiral compounds.

Key words: covalent organic framework materials (COFs), chiral stationary phase (CSP), chiral separation, high performance liquid chromatography (HPLC)