Study On Fabrication And Recognition Performances Of Molecularly Imprinted Polymers Based On Chitin And Its Derivatives Via "Sacrifice Spacer" Strategy

Cholesterol is an intermediate in the biogenesis of biologically important steroids,such as bile acids,adrenal cortical hormones and sex hormones.Additionally,cholesterol possesses rigid fused ring structures which enable the construction of a rigid cavity fitting to template molecule.On the basis of these,cholesterol has been choosed as the target molecule in this thesis.In order to employ the "sacrifice spacer" molecular imprinting technology,novel functional macromonomers based on chitin and its derivatives(chitosan)were designed,which incorporated the carbonate as a spacer.Subsequently,two kinds of molecularly imprinted polymers(MIPs)were prepared to create specific recognition sites for cholesterol.The recognition properties and selectivity for these molecularly imprinted polymers were investigated.The main work involved in this thesis was as follows.Firstly,the cholesterol-chitin complexation,a carbonate,was synthetized in the presence of N,N'-carbonyldiimidazole containing two acylimidazole leaving groups,introducing a carbonyl acted as "sacrifice spacer".The molecularly cholesterol-imprinted polymer(Chol-MIP-CHT)was formed after cross-linking with a diisocyanate and subsequent removing template molecule after hydrolysis.Second,the reaction occurred between cholesterol chloroformate and the amine-protected chitosan,producing cholesteryl chitin carbonate,where the carbonyl brigdes fulfilled the role of "sacrifice spacer".The resulting cholesteryl chitin carbonate was cross-linked with glutaraldehyde to generate the pre-cross-linked polymer.In order to avoid the embedding of the template molecule in the MIP and quick rebinding of the template molecule,the cholesterol-imprinted polymer(Chol-MIP-CS)nanoparticles and nanofibers were obtained by coagulating and electrospinning,respectively,after hydrolytic cleavage of the template.Thirdly,the chemical structure of molecularly imprinted polymers and their precursors were identified by FT-IR and NMR.The FE-SEM observations showed that the surface on Chol-MIP-CS nanoparticles had rough morphology and their average particle size was about 150 nm,and Chol-MIP-CS nanofibers possessed the porous and rough surface and the diameter for the fibers was from 400 to 600nm.The isothermal adsorption,adsorption kinetics,competitive adsorption and repeat utilization tests were carried out and the recognition performances for three MIPs were investigated.The experimental results indicated that Chol-MIP-CHT powders and Chol-MIP-CS nanofibers had equilibrium adsorption capacities at 13.60 and 21.59 mg/g,and they had strong recognition ability with an imprinting factor of 2.86 and 4.12 compared with NIPs,respectively.The adsorption processes of both MIPs could be preferably described by Freundlich adsorption isotherm model.The adsorption kinetics features of two MIPs were in accord with pseudo-second order kinetic model.The MIPs had better selectivity to cholesterol than estradiol and stigmasterol as template analogues.Both of two MIPs had very good stability,high reusability and constant adsorption capacities of 98.4 and 98.7%,respectively,after the adsorption-desorption cycle was repeated five times using the same adsorbent.Fourthly,the molecularly imprinted polymers were used to determinate the cholesterol in milk and yolk,and the absorption rates of two MIPs were 93.7 and 95.1%for milk,95.7 and 96.8%for yolk,respectively.Finally,to attempt to explore the more sensitive recognition effect for cholesterol,the molecularly imprinted hybrids with nano-silver particles were also synthetized by reducting modified chitosan-silver coordination polymer in view of the characteristics for surface enhanced Raman technology.