Preparation Of Tea Saponins Imprinted Polymers And Its Application On Separation And Purification Of Crude Extracts

Tea saponin is a class of pentacyclic triterpenoid substances, containinghydrophilic glycoside and hydrophobic ligand group. As a natural surfactant, teasaponin has the performances of emulsifying, dispersion and wetting, and has manybioactivities such as antimicrobial, anti-inflammatory, antioxidant, antiallergic, etc.How to get high purity of tea saponin is primary important in its industrial applicationarea. Molecular imprinted polymers (MIPs), which are man-made polymers with apredetermined selectivity and affinity towards a given target or a group of structuralsimilar species related to the templates imprinted, have been widely adopted in theenrichment and preparation of natural products from herb extracts or other complicatedmatrices. In this study, three molecular imprinting polymers were prepared andsuccessfully applied in the purification of the tea saponin crude extract, whichindicated great potential in the industrial application. The main research contents are asfollows.(1) Tea saponin standard was prepared and evaluated. The crude tea saponinfrom cake of camellia oleifera seeds was got by ultrasonic assisted extraction, and thenthe AB-8macroporous resin column was employed for separation and high purity oftea saponin was obtained. The purity of the product was evaluated by measuring themelting point, UV-visible spectrum and high performance liquid chromatography withelectrospray ionization mass spectrometry (HPLC-ESI-MS) analysis. Experimentalresults showed that the melting point of the products was222-224℃, UV absorptionspectrum had a strong absorption peak at203nm, and the molecular weight of all thesaponins were around1200. The purified tea saponin can be used as the template toprepare tea saponin molecularly imprinted polymers.(2) Tea saponin molecularly imprinted polymer was prepared using acrylamide asfunctional monomer. The Fourier Transform Infrared Reflectance spectroscopy (FTIR),Scanning electron microscope (SEM) and thermal gravimetric analysis (TGA) wereused to characterize the polymer structures. The properties involving adsorptionisotherm, adsorption kinetics and selective recognition capacity were evaluated. Itshowed that the micro meter level of particles was got through this method. Isothermaladsorption experiments results fitted the Langmuir adsorption model well (R2=0.9898)and has a maximum adsorption capacity of10.02mg/g, which is much higher than thatof non-imprinted polymer and imprinted polymer (2.77mg/g). Adsorption kineticsexperiment results fitted the pseudo-second adsorption model (R2=0.9990), the adsorption equilibrium could be arrived in180min. The relative selectivity factorbetween tea saponin with glycyrrhizic acid, and glycyrrhetinic acid were0.94and12.08, respectively.(3) In order to improve the adsorption capacity and selectivity of the MIP,-cyclodextrin, which has strong hydrophilic property and envelope effect wasintroduced into the polymer. MIP with acrylamide--cyclodextrin and acrylamide asbifunctional monomers was synthesized and the adsorption properties wereinvestigated. The isothermal adsorption results fitted the Langmuir adsorption modelvery well (R2=0.9870), and the maximum adsorption capacity of the imprintedpolymer and non-imprinted polymer were13.12mg/g and4.92mg/g, respectively.Adsorption kinetics data fitted the pseudo-second adsorption model well (R2=0.9956)and it can get the equilibrium within180min. The relative selectivity factor betweentea saponin with glycyrrhizic acid, and glycyrrhetinic acid were1.16and17.18,respectively. All the results showed that the introduction of-cyclodextrin can increasethe adsorption capacity and selectivity of molecularly imprinted polymer to teasaponin.(4) In order to further improve the rigidity and thermal stability of tea saponinimprinted polymers, polyhedral oligomeric silsesquioxane methacryl substituted(POSS-MA) reagent was introduced as cross-linker to create high mechanical andthermal stability poly spheres for the regarding purpose, and the reversibleaddition-fragmentation chain transfer (RAFT) radical polymerization was employed toprepare the tea saponin molecularly imprinted polymers. It showed that the resultedpolymer has uniform morphology in SEM analysis and the TAG results found that thethermal stability of the polymer was increased obviously and also indicated theexistence of POSS in the polymer. Adsorption kinetics experimental data fitted thepseudo-second adsorption model well (R2=0.9980) and which has an equilibrium timeof120min. Isothermal adsorption experiments fitted the Langmuir adsorption model(R2=0.9940), and the maximum adsorption capacity of imprinted polymer andnon-imprinted polymer were14.24mg/g and3.18mg/g, respectively. The relativeselectivity factor between tea saponin with glycyrrhizic acid, and glycyrrhetinic acidwere1.59and11.59, respectively.(5) The performance of the MIPs as solid phase extraction materials wasinvestigated. The sample loading, eluting conditions, the adsorption capacity of thethree polymers in the MIP condition, the reuse time of the column and purificationeffect to the crude tea saponin were investigated systemically. The results showed that the optimum loading and eluting condition were10%methanol solution and90%methanol containing10%acetic acid, respectively. For36mL of200mg/L of teasaponin solution, the recovery rate was between85.1%-102.7%. Tea saponinmolecularly imprinted polymer which prepared by the POSS-based hybrid reversibleaddition-fragmentation chain transfer radical polymerization has the best adsorptionproperty, and a high purify product which containing of72.5%of tea saponin wasobtained, and recovery rate was93.2%after passing through the solid extractioncolumn. The recovery rate for the tea saponin can also get to94.5%after the columnwas used for5times, indicating that the polymer containing POSS has highmechanical property.