Facile preparation of water-soluble N-acetylated chitosan and molecular weight dependence of its water-solubility

A simple procedure to prepare water-soluble chitosan (partially N-acetylated chitosan) was developed, and the water-solubility of N-acetylated chitosan was investigated in detail, preparing a series of chitosan samples with various molecular weights. To reduce the molecular weight, chitosan was treated with NaBO3 under a homogeneous condition where chitosan was previously dissolved in an aqueous acetic acid. Weight-average molecular weights of chitosan samples obtained were determined by means of GPC equipped with a low angle laser light scattering photometer. Then each chitosan sample was N-acetylated with acetic anhydride under a homogeneous condition where chitosan was dissolved in a simple aqueous acetic acid. The degree of N-acetylation was estimated by H-1 NMR spectroscopy. As a result, the water-solubility of N-acetylated chitosan with about 50% substitution increased as the molecular weight decreased. The sequence of N-acetylglucosamine and glucosamine residues was also determined by H-1 NMR spectroscopy.