D-Camphoric Acid Modified Covalent Organic Frameworks For Enantioseparation Of Amino Acids

Amino acids are the basic building blocks of proteins,which have widely applications in foods,cosmetics,feed additives,agricultural fertilizers and pharmaceutical industries.Most amino acids have two enantiomers with different physiological activities,toxicology and pharmacological action,so it is of great significance to separate and purify the enantiomers of amino acids.Covalent-organic frameworks?COFs?are new crystalline organic porous materials formed by covalent bonding of small organic molecules,showing broad applications in diverse fields including chromatographic separation,heterogeneous catalysis,fluorescent sensing and opoelectronic materials due to the advantages of large specific surface area,good stability,low density,easy modification of skeleton,ordered structural units.However,the research of COFs in enantioseparation is still at the initial stage.In this thesis,D-camphoric acid functionalized COFs was designed and synthesized for the chiral separation of amino acids.The main results are as follows:A new chiral COF?CTzDa?was prepared by room temperature post-modification.The synthesis conditions of TzDa were optimized detaily,and TzDa with good stability,high crystallinity and a large number of active hydroxyl groups was synthesized at room temperature which the Brunauer–Emmett–Teller surface areas was calculated to be 1380 m²g^-1.The D-camphoric chloride was then reacted with the hydroxyl groups in TzDa to obtain CTzDa.The successful preparation of CTzDa was proved by Fourier transform infrared?FT-IR?,powder X-ray diffraction spectrometry?PXRD?,zeta potential and nitrogen adsorption experiment.The modification ratio of D-camphoric acid on TzDa was calculated to be 41.5%by toluidine blue O dye assay and the Brunauer–Emmett–Teller surface areas of the prepared CTzDa was calculated to be 403 m² g^-1.The synthesized chiral COF CTzDa has good thermal and chemical stability,and regular pore structure.This work provides a good foundation for application in chiral separation research.The application of CTzDa as sorbent was demonstrated for selective adsorption of amino acid enantiomers.The prepared CTzDa offered rapid adsorption kinetics,and exhibited higher adsorption capacity for the L-enantiomers of tryptophan,histidine,aspartic acid and serine than their D-enantiomers.For example,the adsorption capacity of CTzDa to L-tryptophan was 44.3 mg g^-1,and that to D-tryptophan was 29.1 mg g^-1.The adsorbed amino acids were well desorbed from CTzDa in 5 min.The CTzDa was stable after five cycles of adsorption and desorption.Auto Dock Vina?ADVina?based docking calculation showed that the binding energies for the adsorption of L-enantiomers were higher than those for D-enantiomers and the stereoscopic hydrogen was of great importance in adsorption process.This work provides a facile strategy for highly selective chiral adsorption of amino acids.CTzDa-MAA-co-EDMA monolithic column was prepared for chiral separation of amino acids by high performance liqud chromatography.A mixture containing 16 mg CTzDa,35?L functional monomer,400?L crosslinker,and 400 mg porogen were reacted at 70°C for 24 h to obtain a uniform morphology of CTzDa-MAA-co-EDMA monolithic column with good permeability and stability.Compared with the methacrylic monolithic column without CTzDa,the prepared CTzDa-MAA-co-EDMA monolithic column gave obviously better HPLC separation of four groups of probe analytes including non-polar to polar compounds,alkylbenzenes,polycyclic aromatic hydrocarbons and substituted aromatic hydrocarbons,and the resolition was improved by at least 2 times.Furthermore,the prepared monolithic column gave high resolution for HPLC separation of five enantiomers of cysteine,tryptophan,serine,aspartic acid and histidine?1.78,1.70,2.87,1.19 and 4.41,respectively?,showing the potential of CCOFs in HPLC separation of chiral compounds.