Design And Synthesis Of Hydrophilic Macrolide Antibiotics Molecularly Imprinted Polymers Assisted With Molecular Simulation

Macrolide antibiotic(MA)occupies a large proportion of all antibiotic production and usage in China.In order to overcome the drawbacks in traditional separation technique,including low selectivity and being unfriendly to environment,to improve the separation and purification efficiency of antibiotics and to reduce antibiotic residue in industrial waste,it is necessary to design and prepare an efficient separation medium for the extraction and enrichment of these MA antibiotics.Using target molecule as "template",polymer prepared by molecular imprinting technology is identified as molecularly imprinted polymer(MIP).It can specifically recognize template with high efficiency,which has been widely utilized in the research area of separationa and purification.The properties of template molecules,solvents,functional monomers,crosslinking agents,and formula ratio are important parameters.Traditional optimization methods rely on experience and trial-and-error method,which often consumes a lot of resources.With the development of computer technology,the quantum chemical calculation is gradually adopted by scientists to analyze the properties of composites,for example,calculating the binding energy between template and monomers.Molecular dynamics software,such as Materials Studio,has been widely used in material design and material performance evaluation.In current stage,molecular simulation on molecular imprinting has just reached to the preassemblysystem,which exits a larger space to be further exploited.In this thesis,a complete set of molecular simulation methods are constructed to assist the design of MIP,including the selection of preparation parameters,the optimization of self-assembly system,the construction of imprinting sites,the construction of a MIP model,and the adsorption simulation.The study by molecular simulation made we have new understanding for the mechanism of molecular imprinting that the pre-assembly system is dynamic and has the characteristics of probability distribution in terms of statistics.Based on the design assited with molecular simulation,rational parameters were selected,and two different types of macrolide antibiotic molecularly imprinted polymer(MA-MIP)were prepared and used in selectively separating MA from real samples.The surface morphology,particle size,functional groups,specific surface area,and pore size of these MIPs were characterized by means of transmission electron microscopy,dynamic light scattering,fourier transform infrared spectroscopy,BET specific surface area and porosity analysis,respectively.Also,the effects of these parameters were analyzed,and the static and dynamic adsorption behaviors were studied and compared with non-imprinted polymers.The first type of MA-MIP is based on the non-covalent bond method.For typical MA,using methacrylic acid as the functional monomer and EGDMA as the crosslinker,a core-shell polymer was designed and synthesized by RAFT and seeded precipitation polymerization.The MA-MIP has high adsorption capacity,fast mass transfer rate,and good reuse ability.It was found that,when the maximum imprinting factor(IF)value was 3.6,the adsorption capacity was 106.5 mg/g,and the selection coefficient(α)value was 3.3.The adsorption type of MAMIP was divided into low-affinity sites and high-affinity binding sites,and the maximum adsorption capacity was 326.0 mg/g for low-affinity and 86.0 mg/g for high-affinity.Using molecularly imprinted solid phase extraction chromatography combined with gradient elution in methanol,the maximum efficiency for purifying antibiotics from diluted tylosin fermentation broth can be achieved,and the crystallization in methanol solution can be obtained.The second type is boronate affinity MA-MIP for MA containing diol.Firstly,based on density functional theory,study found that VPBA and the glycosyl containing dihydroxyl group(diol)could form complex system in aqueous environment.Using VPBA and DMAEMA as the pH-responding functional monomers,and two crosslinking agents,EGDMA and MBAA,mixed to balance hydrophilicity,boronate affinity MA-MIP was designed and synthesized.The MA-MIP has the advantages of fast pH response,large adsorption capacity,and high selectivity in the water environment.Scatchard analysis showed that the high-affinity adsorption capacity of MIPs was 74.3 mg/g,42.8 mg/g higher than NIP.The selection coefficient to template is 7.3.The one-step experiment of molecularly imprinted solid phase extraction showed that MA-MIP could effectively extract MA from fermentation broth with a recovery of 75.6±5.6%and 80.5%purity by HPLC.Moreover,the binding behavior of the imprinted cavity to the target molecule is simulated by molecular dynamics.It is speculated that the combination of VPBA and DMAEMA can endow the imprinted cavity with pH-responsiveness,which greatly improved the selectivity towards template.Different polymerization methods result in polymers with various physical morphology that has an impact on the adsorbent properties.Apart from the precipitation polymerization added with active seeds,based on ATRP technique,this thesis also proposed a novel method to prepare multi-functional Core@Brush microspheres.The material with this unique structure has a large number of accessible adsorption sites,more suitable for adsorbing biomacromolecules.It can selectively capure β-casein via the synergistic function of stable iron chelation and reversible Schiff base bio-conjugation,with an excellent capture capacity of over 2.0 g/g.This preparation method is expected to be utilized in the preparation of various MIPs with novel structure and to improve the performace.Overall,molecular simulation technology is used in this thesis to present molecular binding force in the form of readable data,and dynamically visualize the behavior of molecules that are difficult to observe,which effectively assists the rational design of MIP.Based on the new understanding of molecular imprinting technology,the above two efficient types of MA-MIPs and a new type of multifunctional Core@Brush microspheres were prepared,and their adsorption mechanisms were studied in depth to achieve effective extraction and enrichment of the target molecules.These researches have certain scientific value in terms of the theoretical study of molecular imprinting technology,and meanwhile,it has potential application value for the preparation of bio-separation medium.