Study On The Amphipathicity And Functionality Of Cholesteryl Chitosan Carbonate

In this thesis,the amphiphilic chitosan derivatives were obtained by hydrophobic modification with cholesterol chloroformate.Amphiphilic polymers can form monomolecular films at the air/water interface.The monomolecular film can be transferred to the substrate surface by the Langmuir-Blodgett(LB)technique to form a multilayer film called LB membrane.Since LB film has the advantages of thin film,controllable film thickness,uniformity and denseness,the molecular imprinting technique possesses characteristics of preordainment,identificability and practicality,and the electrochemical detection shows rapid and convenient.Combined with these three methods,molecularly histamine-imprinted LB film was fabricated on the surface of glass electrode.In addition,amphiphilic nonhomogeneous surface(chemical and morphological)has good anti-protein adsorption property.Nonspecific adsorption of protein is a widespread phenomenon,this phenomenon causes blood coagulation on the blood contact surface for certain materials,and bacteria adsorption and biological fouling at the solidjliquid interface.The specific and non-specific adsorptions of the above-mentioned chitosan derivatives were researched in the following four aspects.1.Cholesteryl chitosan carbonate was synthesized by an amino protection method.Usingmethanesulfonic acid as solvent and protective agent of amino groups on chitosan chain,a series of amphiphilic chitosan derivatives with different degree of substitution were prepared from chitosan and cholesteryl chloroformate at different raw ratio.The chemical structure of the resulting cholesteryl chitosan carbonate(CHCS)was characterized by FT-IR,13C-NMR and GPC,indicating that cholesteryl chloroformate was bonded to chitosan by carbonate group.The contact angle test results show that the static contact angle of CHCS to water increased with the decrease of the molar ratio of chitosan to cholesteryl chloroformate.On the other hand,the wettability of these amphiphilic chitosan derivatives were improved.(2)In order to explore the amphiphilic properties of cholesteryl chitosan,Langmuir technique was applied to investigate the monolyer behavior of cholesteryl chitosan carbonate.The isothermal curves of the surface pressure(π)and the average molecular area(A)of the monolayers were recorded during the formation of the monolayer,which indicating that cholesteryl chitosan carbonate with certain degree of substitution could form a stable monolayer at the air-water interface.The average limit area and collapse pressure of the monolayer membrane was 310.30 cm2 and 47.25 mN/m,respectively.Theπ-A isotherm curves of the monolayer of CHCS with different concentrations were recorded,and it was showed that the π-A isotherm shifted to the big area as the CHCS loading was increased.In addition,the pH value of the subphase directly affected the properties of the monomolecular film,and it was showed that the monolayer of cholesteryl chitosan carbonate could be stably present in acidic and weakly alkaline environments.The Langmuir film on the water was transferred onto a silicon wafer,and then the LB film were obtained by LB technique.(3)The two-component monolayer of CHCS and histamine was formed by reconstitution through the interaction between CHCS Langmuir membrane and histaminein subphase.The resulting two-component monolayer was transferred to the ITO electrode by LB technique.Subsequently,the electrode-modified(His-CHCS@ITO)molecularly imprinted LB membrane was obtained by removal of histamine molecules from two-component LB film.Combination with electrochemical and molecular imprinting methods,the electrochemical responses and recognition performances of the modified electrode for histamine were researched.The adsorption performances of His-CSCH@ITO to histamine were investigated by cyclic voltammetry.The results showed that the His-CSCH@ITO could recognize histamine molecules under the optimal.adsorption conditions(the adsorption time of template at 8 min and test solution pH at 7.0).The adsorption performances of His-CSCH@ITO to histamine with different concentrations were inspected by differential pulse voltammograms.The linear range of the detection histamine was 0.01-1.5 M and detection limit was 0.09 μM.The selectivity,repeatability and stability of His-CSCH@ITO to recognizing histamine were also observed.In addition,the spiked beer and wine were tested using added aconitine recovery,showing that the average recoveries was 98.3 to 105.9%and 99.8 to 105.2%,respectively,and the standard deviations was 2.7 to 3.5%and 1.9 to 4.3%,respectively.It was concluded that His-CHCS@ITO sensor displayed sensitive electrochemical response to histamine and could be utilized to detect trace amounts of histamine in beer and wine rapidly and sensitively.(4)The amphiphilic cholesterol chitosan carbonate and CS membrances were fabricated by spin coating method.Bovine serum albumin(BSA)was selected as non-specific adsorption protein.The anti-protein adsorption performance of CHCS and CS against BSA was evaluated by BCA protein quantitative method.The anti-protein adsorption rates of CHCS and CS membrances in 0.5 and 1.0 mg/mL BSA solution exhibited the trend as follows:CHCS 1:3>CHCS 1:2>CHCS 1:1>CHCS 1:0.5>CS>CHCS 1:4>CHCS 1:5(the raw ratio of chitosan to cholesteryl chloroformate),and among these CHCS derivatives,the CHCS 1:3 showed the best protein resistance.XPS,AFM and SEM measurements were used to characterize the amphiphilic cholesterol chitosan carbonate and CS membrances before and after adsorption of BSA.Amphiphilic heterogeneities on surfaces meight weaken and obstruct the protein adsorption processes.The results showed that amphiphilic polymers could effectively resist the adsorption of proteins due to their microphase-separated amphiphilic special structures.