Abstract: Cholic acid (CA) possesses special facial amphiphilic structure with unusual distribution of hydrophobic and hydrophilic regions. Accordingly, this biological molecule can self-assemble to form micelles or superstructures in vivo and in vitro, which incorporate liposoluble and water soluble substances separately. The polymers containing cholic acid reserved these properties. Inspired by the facial amphiphilicity and self-assembly properties of cholic acid, amphiphilic cholic acidmodified chitosan was synthesized in this work. First, water-soluble hydroxyethyl chitosan was synthesized by reacting alkalified chitosan with 2-chloroethanol. Then, cholic acid was chemically bonded to hydroxyethyl chitosan using 1-ethyl- 3-(3-dimethylaminopropyl)-carbodiimide hydrochloride (EDC) as the catalyst to obtain amphiphilic chitosan. The chemical structure of CA-modified chitosan was characterized by 1H nuclear magnetic resonance (1H NMR) and Fourier transform infrared (FT-IR) spectroscopy. The self-assembly behavior of amphiphilic chitosan in aqueous solution was investigated by pyrene fluorescence probe method. The size of chitosan microcapsules loading vitamin A was investigated by dynamic light scattering. The results showed that amphiphilic chitosan could effectively encapsulate vitamin A in aqueous solution. Vitamin A in the microcapsules was mainly released in simulated intestinal fluid, while it executed controlled release in phosphate buffered saline (PBS) (pH 7.4). These results demonstrated that this kind of microcapsules is useful in the fields of food and medicine.

Key words: amphiphilicity, cholic acid, chitosan, vitamin A, microcapsule, self-assembly