Self-Assembly Of Biocompatible Cholic Acid With Mixed Catanionic Surfactants

Supramolecular aggregates of vesicles are a class of adjustable soft nanoparticles,which provides a model system for the study of bionics due to their having structures of bilayer membrane similar to biological cells.Vesicles of small molecular surfactants can be taken as a kind of system in bionic research and practical application,such as the drug carrier for sustained and targeted release.Thus improving the stability of bilayer is one of the key topics while maintaining the premise of soft material properties.The purpose of this work is the use of dextrans modified with the pendant groups-sodium cholate(NaCA)to decorate the mixed surfactant vesicles so that the stability of the vesicles can be enhancedIn this work,sodium cholate(NaCA)and the polymers modified with cholic acid were used to construct their mixed systems with anionic surfactant,cationic surfactant and vesicles including both anionic/cationic surfactants,respectively,thus the thermodynamics of molecular self-assembling and phase behaviors between these species were investigated by isothermal titration calorimetry(ITC)acted as the main method,combined with Cryo-Transmission electron microscopy(Cryo-TEM),turbidity,conductivity and dynamic light scattering(DLS).The effects of hydrophobic side chain,charge,composition of solution and surfactant concentration were carefully analyzed on the molecular self-assembling process in these complex fluids,and the synergy between amphiphilic molecules was also discussed in detail.Finally the regulation of the component NaCA on the aggregation transition of mixed vesicles and the thermodynamic behavior of intermolecular interactions in these complex fluids were carefully explained in terms of macroscopic thermodynamic properties and molecular structure.The research content and results are summarized as follows:1.Thermodynamics of NaCA micellization in aqueous solution.The effect of NaCA concentrationon on micellization process was investigated by ITC and conductivity measurements.The two critical concentrations(critical pre-micelle concentration and the critical micelle concentration)of NaCA and the enthalpy changes corresponding to the two transition processes were obtained by ITC.It was found that the biosurfactant(NaCA)presents a pre-micellization process at very low concentration of NaCA.Further the enthalpy change of premicelle formation of NaCA in aqueous solution was clearly specified for the first time.2.The mixed surfactant system of the same charges — NaCA/sodium dodecyl sulfate(SDS)The interaction enthalpy changes between NaCA and similarly charged SDS with the different initial concentration of SDS were obtained by ITC.These results show that the ITC is the most accurate and direct method to study the weak synergistic effect and hydrophobic interactions between surfactant molecules of the same charges.3.The mixed surfactant system of opposite charges — NaCA/gemini surfactant(12-10-12Br2).The thermodynamics and phase behavor of transition processes were investigated from micelle to liquid crystalline and again to mixed micelle,and thus the phase boundaries were obtained.The effect of gemini surfactant concentration on the aggregation behavior of the mixed system was discussed in detail.4.Regulation of NaCA for aggregation behavior of mixed surfactant vesicles(SDS/12-10-12Br2).The complex systems with three surfactants(NaCA,SDS and 12-10-12Br2)were constructed in aqueous solution,and the morphological changes of aggregates and the thermodynamic behavior for swelling and rupture processes of mixed vesicles induced by NaCA were studied by ITC,Cryo-TEM,turbidity and DLS.The important thermodynamic parameters,the critical concentration and the enthalpy change for the rupture process of mixed vesicle were obtained.5.Interaction between the polymers modified with NaCA(Dex-xCACOONa and Dex-4CA)and mixed surfactant vesicles.Based on these works as mentioned above,this research was extended to a more complex system that included the amphiphilic polymer modified with the pendant group NaCA and the mixed surfactant vesicle.This was aimed at controlling the stability of the mixed surfactant vesicle and its aggregation behavior.The thermodynamic properties and self-assembling behavior of these studied polymers are first characterized by ITC in aqueous solution.Further the mixed systems,Dex-xCACOONa or Dex-4CA /vesicles(SDS and 12-10-12Br2)were also constructed in aqueous solution,and the effects of polymer pendant group NaCA and its degree of substitution on molecular self-assembling behavior in the mixed systems including the vesicles were discussed in detail.All the results will provide a good insight into further developing research and application of these complex systems.This work is supported by the National Natural Science Foundation of China(Project Nos.21273061 and 21327003).During the period of graduate study,one research work has been published on The Journal of Chemical Thermodynamics(100(2016)131-139)and three papers from national and international conferences have been published.Two drafts are being prepared.One topic is about the interaction of NaCA with mixed vesicles,and another is about the regulation and thermodynamics of hydrophobically modified polymer on the the aggregation behavior of mixed vesicles.