The Study On The Preparation Of Amphiphilic Chitosan Derivatives And Their Self-assembled Nano-micelle Application

In this thesis, we studied amphiphilic chitosan derivatives which possess hydrophilic groups(carboxymethyl) and hydrophobic groups (long chain alkyl, long chain acyl and polylacticacid). Taking advantage of the new solvent system of ionic liquid, the hydrophobicmodification of chitosan could be carried out in homogeneous media and the challenge ofpreparing amphiphilic chitosan derivatives with both high surfactant activity and high Mwwas successfully addressed. After modification, the amphiphilic chitosan derivatives canself-assemble into nano-sized micelles with core-shell structure driven by the hydrophobicinteractions. The self-assembly behavior of amphiphilic chitosan in aqueous solution wasaffected by the molecular structure of chitosan derivatives, including the kind of hydrophobicand hydrophilic groups, the degree of substitution of hydrophobic groups, molecular weightand the property of solution (such as ionic strength, pH value and etc.).We have systematically studied the self-assembly behavior in aqueous solution and theeffect factors of micelle structure from amphiphilic chitosan through fluorescencespectrometry, UV absorption spectrometry,1H NMR, DLS, AFM and TEM. In further, thechitosan-based nanomicelles were used to solubilize hydrophobic fluorescent CdSe/ZnS QDsdirectly in water. After encapsulation, the hydrophobic QDs could be stably dispersed in waterand still keeping high fluorescent quantum yields. Using yeast cell (Saccharomyces cerevisiae)as model cell, the potential application of chitosan-based nanomicelles encapsulating QDs asfluorescent bioprobe was investigated. It was found that the fluorescent chitosan-basedmicelles could internalize and image live cells. This method provides a promisingnano-carrier for hydrophobic QDs, through which the complex surface ligands exchangingprocedures necessary for the application of QDs in bioimaging and diagnosis are greatlysimplified. In addition, the potential application of chitosan-based nanomicelles as additivesof cosmetics formulation was evaluated. It was found that chitosan-based nanomicelles couldefficiently encapsulate hydrophobic anti-oxidant active components and make them slowlyreleased in aqueous media. The study in this thesis provides fundamental reference for the preparation of amphiphilic chitosan derivatives and their self-assembled nanomicelles, andtheir applications in bioimaging and cosmetics additives.