Chiral Covalent Organic Framework Core-shell Composites For Separation By High Performance Liquid Chromatography

Chiral covalent organic frameworks(CCOFs)have the advantages of large specific surface area,rich chiral recognition sites,good chemical stability in organic solvents,etc.,making them have a broad application prospect in enantiomer separation.However,due to the light weight,low density,irregular morphology,nonuniform particles and wide particle size distribution for conventional CCOFs used as chromatographic stationary phase,they will have some disadvantages such as difficult column preparation,low column efficiency,unsatisfactory chromatographic peak shape and high column back pressure.Therefore,the application of CCOFs in high performance liquid chromatography(HPLC)for enantiomeric separation is rarely reported.As HPLC stationary phase,the core-shell silica gel materials have the characteristics of high column efficiency,fast flow rate and low back pressure.In order to overcome the above-mentioned shortcomings of CCOFs in HPLC application,the CCOFs core-shell composites(CCOFs@SiO₂)were prepared by growing CCOFs on the surface of uniform SiO₂microspheres via an in-situ growth strategy.The as-prepared CCOFs@SiO₂were used as the stationary phases to explore their chiral recognition performance in HPLC.The specific research works are as follows:The first chapter is the introduction,which briefly introduces the significance of chirality and chiral resolution,HPLC and the classification of chiral stationary phases(CSPs),with emphasis on the application of COFs,CCOFs and CCOFs@SiO₂core-shell composites in the field of chromatographic separation.In the second chapter,three chiral COFs(CCOF-Tp Pa-1,CCOF-Tp BD,and CCOF-Tp Tab)with ketone configuration were successfully synthesized by adding(R)-1-phenylethylamine as chiral inducer in the condensation reaction of the C₃-symmetric 1,3,5-triformylphlor-oglucinol(Tp)with an achiral diamine or triamine.Three kinds of monodisperse chiral CCOFs@SiO₂(CCOF-Tp Pa-1@SiO₂,CCOF-Tp BD@SiO_2,and CCOF-Tp Tab@SiO₂)core-shell microspheres were prepared by an in-situ growth strategy using three kinds of CCOFs as shells and spherical aminated silica gel(SiO₂-NH₂)as cores,respectively.The as-prepared three core-shell composites CCOFs@SiO₂were used as the stationary phases for HPLC enantioseparation.The effects of the analyte mass and temperature on the separation performance and the reproducibility of the three CCOFs@SiO₂-packed column were investigated.The results showed that CCOF-Tp Pa-1@SiO₂,CCOF-Tp BD@SiO₂and CCOF-Tp Tab@SiO₂-packed columns showed high enantioselectivity and good chiral separation ability for 24,17 and 14 racemates,respectively.These chiral columns exibited good reproducibility and stability.In the third chapter,a novel chiral covalent triazine framework(CC-MP CCTF)core-shell composite CCTF@SiO₂(CC-MP CCTF@SiO₂)was prepared by an in-situ growth method using 3-aminopropyltriethoxyl-bonded silica gel as core and CCTF as shell.The core-shell composite CC-MP CCTF@SiO₂was applied for HPLC separation of enantiomers.The experimental results showed that the prepared CC-MP CCTF@SiO₂-packed column had good enantioseparation performance for 19 kinds of racemic compounds with good reproducibility.In the fourth chapter,the chiral core-shell composite MDI-?-CD-modified COF@SiO₂was prepared by an in-situ growth method using aminoated silica gel(SiO₂-NH₂)as the core and isocyanate-?-cyclodextrin-modified COF(MDI-?-CD-modified COF)as the shell,and used as stationary phase to prepare chiral columns for HPLC enantioseparation.Under certain chromatographic conditions,the chiral column offered good separation ability and good reproducibility for the separation of 11 chiral compounds and 5 positional isomers.