Preparation And Chiral Resolution Performance Of ?-CD-modified Thermosensitive Magnetic Carbon Nanomaterials

Chirality is a common phenomenon in nature.Amino acids?AAs?,as one important part of life organisms,are also chiral and usually have two stereoisomers?D-form and L-form?that exhibit significantly disparate biologic or physiological activities.Therefore,it is highly desired to carry out effective chiral resolution of AAs enantiomers.Traditional separation methods of AAs enantiomers,such as chromatography,membrane separation and capillary electrophoresis,are restricted due to their shortcomings including complicated operation,high cost and low efficiency.As a result,it is extremely desirable to develop a simple,low cost and highly efficient method for chiral separations of AAs enantiomers.Carbon nanotubes?CNTs?and graphene oxide?GO?are the most widely investigated carbon nanomaterials currently.Their unique physicochemical characteristics enable them to own great application potentials in the fields of mass separations,biomedicines,catalysts,etc.The composite nanomaterials composed of Fe₃O₄ nanoparticles and carbon nanomaterials have convenient magnetic separability,which provides the possibility for its recycling.Poly?N-isopropylacrylamide??PNIPAM?is an excellent thermosensitive polymer,and?-cyclodextrin??-CD?molecules with unique cavity structures show high chiral recognition and enantiomeric selectivity for numerous chiral molecules via forming host-guest inclusion complexes.Therefore,two kinds of novel functional magnetic canbon nanomaterials are expected to achieve through surface modifcation of MGO and MCNTs using PNIPAM and?-CD,and used for direct enantioseparations of AAs enantiomers,which could solve those problems of traditional discrimination methods of AAs enantiomers.Based on which,two novel kinds of magnetic canbon nanomaterials have been designed and developed for direct chiral resolution of AAs enantiomers in this thesis.The main study contents were as follows:?1?Magnetic graphene oxide nanosheets?MGO?were first synthesized by a simple one-step solvothermal method to endow them with convenient magnetic separability.Then thermo-responsive?-CD-polymer-brushes modified MGO?MGO@PNG-CD?was prepared by combining PDA chemistry,surface-initiated atom transfer radical polymerization?SI-ATRP?and ring-opening reaction of epoxy groups by grafting PNG-CD functional polymer chains on the surface of MGO.And the direct resolution of DL-Trp by MGO@PNG-CD and the recyclabilityof the MGO@PNG-CD were also investigated systematically.?2?Based on the work mentioned above,another novel kind of thermosensitive magnetic carbon nanotubes?MCNTs-PNG-CD?with better separation performance towards DL-Trp was also synthesized by grafting PNG-CD functional polymer brushes on the surface of magnetic carbon nanotubes?MCNTs?.The direct enantioseparation of DL-Trp by MCNTs-PNG-CD and the recyclability of MCNTs-PNG-CD were also investigated systematically.The obtained results indicate that both two functional magnetic carbon nanomaterials exhibit excellent thermosensitive chiral recognition and enantioselectivity toward DL-Trp.The enantiomeric excess?e.e.?values of the direct enantiomeric separation of DL-Trp can reach up to100%at low operating temperature,and the lower the initial concentration of the enantiomeric solution,the higher the separation efficiency.Compared with the MGO@PNG-CD,MCNTs-PNG-CD demonstrated effective separation efficiency toward DL-Trp with higher concentrations.In addition,both two novel functional magnetic carbon nanoselectors developed in this study can be easily recovered and reused under an external magnetic field,which is more economical and environmentally friendly compared with those traditional chiral selectors.