Preparation And Characterization Of Tryptophan Molecularly Imprinted Polymers With β - Cyclodextrin Derivatives As Functional Monomers

Molecular imprinting technology (MIT) is an important method for the chiral separation of active compounds. It is of practical meaning for developing highly selective chiral separation material by design and synthesis of chiral functional monomer. L-tryptophan, an essential amino acid, is widely used in medicine, food, and feed. Hence, it is important to chiral resolution of tryptophan by MIT method.The present study reviewed the theory of MIT, chemical modification and application of cyclodextrin in MIT, the surface imprinting technique, and chiral chromatography method of amino acids. On basis of these theory and technology, four kinds of chiral functional monomer were designed and synthesized. The imprinting components and polymerization methods were optimized by orthogonal experiments and single-factor optimization, and the optimal polymers achieved chiral separation of tryptophan were obtained. The detailed researches were listed as follows:1. A imprinting model (MIP13) was screened and synthesized with L-tryptophan as a template, β-cyclodextrin (β-CD), methylated-β-cyclodextrin (β-CD-RM), and maleic anhydride monoester-β-cyclodextrin (MAH-β-CD) as chiral functional monomers, which was prepared by surface imprinting method with Nano-SiO2as supported material,β-CD-RM as chiral functional monomer, and the amount of crosslinking agent(EGDMA) as15mmol, under the mole ratio of β-CD-RM and L-Trp as1:1in N, N-dimethylformamide/water (1:1, v/v). The adsorption characteristics, structural feature, and chiral separation potency of MIP13were characterized. The results showed that MIP13has a higher imprinting factor (1.684) and adsorption capacity (86.50mg/g). The data obtained revealed a porous material with many uniform ducts. There are two classes of binding sites predominating in the polymer. MIP13can adsorb L-Trp obviously superior to D-Trp in the DL-Trp solution with a chiral resolution factor of2.784. Even in the complex system composed by racemic tryptophan, tyrosine and phenylalanine, MIP13shows good chiral resolution ability to tryptophan with a resolution factor of1.830, indicating MIP13can be used as a high-selective separation enrichment material, which is potential in the field of separation science.2.β-cyclodextrin (β-CD) and its derivatives maleic anhydride monoester-β--cyclodextrin (MAH-β-CD), randomly methylated-β-cyclodextrin (β-CD-RM) were used as the functional monomers to build the chiral environment for racemic tryptophan imprinting system. Using DL-Trp as the template, a imprinting model (MIP14) which was prepared by surface imprinting method with Nano-SiO2as supported material, with MAH-β-CD as chiral functional monomer, and the amount of crosslinking agent (EGDMA) as15mmol, under the mole ratio of MAH-β-CD and DL-Trp as1:1in methanol/water (1:1, v/v), was established after the systmetic optimization of imprinting components. The adsorption characteristics, structural feature, and chiral separation potency of MIP14were characterized. The results showed that MIP14has a large imprinting factor (1.470) and adsorption capacity (80.07mg/g). The obtained data reveal a porous material with many uniform ducts. There are two classes of binding sites predominating in the polymer. MIP14can adsorb L-Trp superior to D-Trp in the DL-Trp solution with a chiral resolution factor of1.480. Even in the complex system composed by racemic tryptophan, tyrosine and phenylalanine, MIP14shows good chiral resolution ability to tryptophan with a resolution factor of1.477. The results demonstrated the feasibility to prepare chiral molecularly imprinted materials with racemic molecules.3. The monodisperse hybrid silica microspheres (SiO2-MH) with alkenyl propionyloxy groups was synthesized in ammonium hydroxide media using the precursors of tetraethylorthosilicate (TEOS) and3-methylacryloxypropyl trimethoxysilane (MATES), which solved the difficult problem of SiO2surface modification. A L-tryptophan-imprinting model MIP14which was prepared by surface imprinting method with0.2g SiO2-MH as supported material and phenoxy-2-hydroxypropyl-β-cyclodextrin (PO-2-HP-β-CD) as chiral functional monomer, and the amount of crosslinking agent (EGDMA) as5mmol, under the mole ratio of PO-2-HP-P-CD and L-Trp as4:1in N,N-dimethylformamide/water(1:1, v/v), was established. MIP14was characterized in structure and recognition properties. The results showed that MIP14has a higher imprinting factor (1.614) and adsorption capacity (84.04mg/g). The obtained data reveal MIP14as porous particles with uniform size. The polymer processes two classes of binding sites. It has superior chiral recognition abiltity with a resolution factor of3.030for DL-Trp mixture. Even in the complex system composed by racemic tryptophan, tyrosine and phenylalanine, MIP14showed good chiral resolution ability to tryptophan with a resolution factor of3.016, demonstrating MIP14has the potential application.