Uracil Imprinted Recognition And Mechanism Of Action Of The Modified Membrane

Molecular imprinting technique is an effective method to encode information such as molecular shapes and molecular functions in the polymer materials. The cooperation of molecular imprinting technique and membrane separation procedure can improve the separation performance of the synthesized membrane, and is still a new territory.In most of the researches, molecular imprinting was mainly achieved via the formation of hydrogen-bonding site between the template and the polymer material, but the hydrogen-bonding could be broken by the presenting of polar solvent. Contrastly, electrostatic interaction used for imprinting will keep stable in polar-solvent (such as alcohol and water). To investigate the mechanism of the electrostatic interaction in the imprinting membrane, in this study, uracil (URA) was used as template molecule, PAN and P(AN-co-VSMA) which was synthesized by radical polymerization of AN and amphiphilic monomer stearyldimethylamine vinyl styrene chloride (VSMA) were used as membrane materials. Hybrid membranes with variable ratios of PAN and P(AN-co-VSMA) were prepared by phase inversion imprinting method. We monitored the imprinting efficiency of the uracil imprinted membrane so as to discuss the function and recognizing mechanism of the hybrid imprinted membranes.It was found that the cross-section and the surface structure of the hybrid membrane were strongly affected by the content of the P(AN-co-VSMA). SEM and AFM photographs had showed that, the resultant membranes had an typically asymmetric porous structure with the decrease content of the P(AN-co-VSMA) in the membrane. However, the dense outer surface of the membrane became thicker and the finger holes of the membrane became smaller and finally disappeared with the increase of the content of P(AN-co-VSMA). When the content of P(AN-co-VSMA) rose from 10wt% up to 54wt%, the surface roughness of the membrane decreased from 5.428nm to 1.784nm. This suggested that the structure of the hybrid membrane become denser and smoother followed by the arising content of P(AN-co-VSMA), and these results were in good agreement with the results of permeability measurement.We further observed the absorption performance of the hybrid membranes by oscillation experiment and substrate permeation experiment. In the oscillation experiment, the reinforcement of electrostatic interaction induced by the increasing of P(AN-co-VSMA) proportion resulted in the increasing absorption of URA. However, the absorption amount of URA on the imprinted membrane was lower than that of the non-imprinting membrane. It was because that the formation speed of the imprinted membrane was faster and led to lower distributing density of N~+ radicals on the surface of the imprinted membrane than on the non-imprinting membrane. In contrast, the absorbability of the imprinted membrane was stronger than that of the non-imprinted membrane during the substrate permeation experiment. In addition, the recognition of the membrane was dependent on the composition of the membrane. This revealed that the recognition ability of imprinted membrane based on electrostatic interaction was not only related with the charge distribution, but also depended on the structure and morphology of the resultant membrane.In our previous study, we found that the P(AN-co-MAA) imprinting membrane obtained by phase inversion imprinting method had effective absorbability for URA. Herein, we adopted the rheologic method to investigate the rheological behavior of the casting membrane solutions of P(AN-co-MAA) and PAN so as to study the interaction between membrane material and template molecule. In the static rheological experiment, it was observed that the viscosity of the casting solution increased with the increase of URA content and decreased with the increase of temperature. For the copolymer system, the viscosity of the casting solution was strongly influenced by the hydrogen bonding interaction. Higher the content of URA was, more sensitive to the temperature the viscosity became. In the dynamic rheological experiment, the composite viscosity almost remained stable when the oscillation frequency was lower than 1.26Hz, but it decreased remarkablely with the increase of oscillation frequency when it was higher than 3.47Hz. As for the copolymer system, the composite viscosity achieved at peak when the content of URA was 1wt%. The results confirmed the formation of hydrogen-bonding between the URA and the carboxyl groups of the membrane material.