Tryptophan Chiral Separation Of Imprinting

Chiral resolution is the bottleneck of separation science. Molecular imprinted polymer/membrane (MIP/MIM) is promising molecular recognition materials with high selectivity to targeted molecule. There are much imprinting cavaties which are exactly matched with the target molecule in the arrangement of functional groups and dimension. The "tailored" recognition sites allowed a high enantiomeric recognition to chiral compounds. However, the deficiency of functional monomers in imprinting technology restrained the practicality of MIP/MIM. It is of great significance to design a novel functional monomer to a specific molecule for the developing an imprinting material. After reviewing the relevant literatures, three kinds of novel and chiral functional monomers (lactam, ester, and β-keto ester) were designed and synthesized aimed to L-tryptophan. A series of L-tryptophan imprinted polymers and membranes were prepared with various imprinting parameters to achieve a satisfied chiral separation. The major work included:1. Three of novel functional monomers with chirality, including (L)-N-propylpyrrolidine-2-boxamide-methane (L-PPC),(L)-allylpyrrolidine-2-car-boxylate (L-APLC),(L)-5-isopropyl-2-methylcyclohex-2-en-1-yl-3-oxobutanoate (L-IMCO), were designed aimed to the target molecule L-tytrophenand. Their structures and properties were characterized by infrared spectrum, nuclear magenetic resonance (NMR) and ultraviolet spectrum. The results revealed that L-IMCO could tautomerize between keto form and enol form with the change of pH value. L-IMCO could bind L-Trp via multiple hydrogen bonding at the molar ratio of2:1with a high stability constant as7.21×105L2/mol2, which is more stably than other two of monomers. It was expected that a "smart" pH-stimulative L-Trp imprinted polymer with high chiral recognition would be prepared with L-IMCO as the functional monomer.2. A imprinting polymer model with chiral recognition to L-Trp was established successfully with β-diketo ester functional monomer L-IMCO. The imprinted system was optimized comprehensively concerning preparation method and the major compositions involving the type and usage of functional monomer, the usage of crosslinker and porogenic agent. The optimized polymer was characterized on the structure, recognition performance and applicability in solid phase extraction (SPE). The results showed that the optimum imprinted polymer MIP14, which was prepared by sacrified silica gel method with L-IMCO as functional monomer under molar ratio of L-Trp,(L)-IMCO and cross linker as1:6:20in methanol/water (1:1, v/v), has a larger adsorption capacity (105.3mg/g) and a higher imprinting factor (2.27) to L-Trp. MIP14have high chiral resolution ability in ethanol/water (4:1, v/v) at pH=8to DL-Trp with a satisfied chiral selective factor. Under the optimized conditions, the molecularly imprinted solid phase extraction column (MIP14-SPE) could separate racemic tryptophan with higher recovery to L-Trp (76.5%) than D-Trp (56.0%)。3. A series of L-tryptophan imprinted composite membranes were synthesized with various kinds of functional monomer, porogen solvent and supporting membrane, the dosage of functional monomer and cross linker as well as the extension of soaking-time. Their recognition abilities to L-Trp were estimated by the equilibrium adsorption experiment method. The optimum membrane was characterized on structure, binding property and transmission ability to DL-Trp. The results showed the membrane MICM13, which was prepared with (L)-APLC as functional monomer at a fixed molar ratio of L-Trp,(L)-APLC and cross linker as1:4:40in methanol/water (1:1, v/v) with PVDF membrane as supporting membrane, gave high affinity and recognition selectivity to L-Trp. Due to the difference in the surface morphology and polar structures between MICM13and NICM13, MICM13can transfer L-Trp preferentially to D-Trp with chiral selective factor as1.37. The results implied an application potential of MICM13in the separation of racemic tryptophan.