Molecular Recognition Behavior For The ED-MIL-101@MIP Composites Toward Anti-hypertensive Compounds In Eucommia Ulmoides

In present work,several molecularly imprinted polymers composites（ED-MIL-101@MIP）based on metal-organic frameworks as the carrier were prepared by a surface imprint technique using such bioactive compounds as pinestinol diglucoside,aucubin,and so on as the templates.The fourier transforms infrared spectroscopy（FT-IR）,scanning electron microscopy（SEM）and X-ray diffraction（XRD）were used for the characterization of chemical groups,surface morphology and crystal structure of these imprint composites.Especially,the adsorption behavior,solid phase extraction application performance and chromatographic separation and analysis capacity for these molecularly imprinted polymers were studied in detail.（1）A pinestinol diglucoside imprinted composites was prepared by using an ethidene diamine-modified metal-organic frameworks（ED-MIL-101）as a carrier and characterized by using FT-IR,SEM and XRD technique,respectively.The adsorption behavior including adsorption dynamics,adsorption thermodynamics,and applicability in solid-phase extraction for this new material obtained were investigated.Adsorption kinetic tests indicated a more rapidly adsorption-desorption process,with an equilibrium time within 180min,and the second order kinetic model was shown more suitable for the description of this adsorption process.Under the same substrate concentration,the adsorption capacity for this imprint composites toward the template pinestinol diglucoside was much higher than that for the non-imprint composites.Freundlich model can best fit the isotherm data for this imprint polymer,indicating adsorption sites heterogeneity in this composite material matrix.A main chemical adsorption process might be deduced by a mean adsorption energy of 22.49 k J mol^-1obtained by Dubini–Radushkevich model fitting.In addition,this imprint composites material could selectively bind template and be utilized as the adsorbent in solid-phase extraction to capture target compound from crude extract of Eucommia ulmodies.This new material can also be reused many times with a slight decrease in adsorption capacity.（2）Chromatographic retention and separation and analysis efficiency for a novel stationary phase based on pinestinol diglucoside imprinted composites toward the template molecule and its structural analogues were studied.Chromatographic behavior for these imprint polymers obtained under different synthesis conditions was explored and the influence of chromatographic conditions on the retention capacity and separation efficiency of the molecularly imprinted polymer stationary phase evaluated.When the molar ratio of the template to functional monomer was 1:4 during preparation procedure,the obtained imprint polymer possessed higher permeability and a lower backpressure can be emerged using it as the stationary phase in liquid chromatography.In chromatographic analysis,a low retention value（such as retention time）can be obtained when using methanol as the mobile phase.However,with the increase of acetonitrile content in methanol mobile phase,retention time and capacity factor for this imprint stationary phase toward the template were enhanced,with a retention time of19.59 min and a capacity factor of 7.43 when using methanol-acetonitrile（1:1,v:v）as the mobile phase.Further increasing the acetonitrile percentage in methanol mobile phase phase leaded a flat chromatographic peak shape,unsuitable for following chromatographic analysis.When methanol solution containing 5%acetonitrile was used as the mobile phase,the moleuclarly imprinted stationary phase could produce a higher resolution（3.95）toward a binary make up of rutin-pinestinol diglucoside（3）A aucubin imprinted polymer was designed to be grafted on the surface of a metal organic frameworks（ED-MIL-101）to produce a aucubin-imprinted polymer composites and its chemical groups component and particle morphology structure were characterized by using FT-IR and SEM analysis.The adsorption kinetics,adsorption thermodynamics and adsorption selectivity for the imprinted polymer composites were investigated.This imprint composites has a more rapid adsorption dynamics toward aucubin,reaching adsorption equilibrium within 80 min,with an equilibrium adsorption capacity of 69.73 mg g^-1.The quasi-second-order model is more suitable to describe the adsorption dynamics of this molecularly imprinted polymer and a spontaneous and endothermic adsorption process can be revealed.Selectivity factor for this aucubin-imprinted composites toward the template relative was 1.979 and 2.634,relative to its structural analogs geniposide and rutin,respectively,showing a higher affinity.Additionally,this imprint composites displayed a higher applicability when it was used as the adsorbent in solid phase extraction to enrich aucubin from crude extract of Eucommia ulmoides.A novel aucubin-imprinted polymer composites based on the ED-MIL-101 as the matrix was prepared by using sol-gel method and used as the stationary phase in liquid chromatography in order to evaluate its retention behavior,capacity factor,selection and imprint efficiency when chromagographic test was performed under various column temperature using different mobile phase composition.Acetonitrile was used as the basic mobile phase since it leaded a lower column backpressure and more high permeability.Adding protonic solvent such as water into acetonitrile mobile phase could improve the elution efficiency to a certain extent and leaded to a decreased retention value of the analyte on this imprint composites stationary phase.At the same time,the selectivity coefficient for the novel stationary phase toward the template also decreased when acetonitrile containing water was used as the mobile phase.However,it was found that a slight decrease for the selectivity coefficient could be observed when the water content in acetonitrile mobile phase was higher than 5.0%.The imprint efficiency determined was the highest when acetonitrile was used as the mobile phase,with a value of 4.322.Column temperature can also affect the retention capacity of the molecularly imprinted polymer composites toward analytes and the capacity factor for this composites toward the template decreased from 10.68 to 6.623 when the column temperature was elevated from 298 K to 318 K.Furthermore,an elevated column temperature influence the selection factor slightly.In addition,a higher selective separation applicability for this imprint composites toward the target compound aucubin when it was used as the stationary phase in liquid chromatographic system,in comparison with C₁₈ stationary phase.