A simple preparation of half N-acetylated chitosan highly soluble in waterand aqueous organic solvents

A simple and improved method of preparing highly soluble chitosan (half N-a cetylated chitosan) was developed using a series of chitosan samples of low molecular weights, and the solubility of the half N-acetylated chitosan in water and organic solvents was investigated in detail. To reduce the molec ular weight, chitosan was treated with NaBO3 under the condition that chito san was homogeneously dissolved in aqueous acetic acid. Weight-average mole cular weights of the obtained chitosan samples were determined using a size -exclusion chromatography system equipped with a low-angle laser light-scat tering photometer. Each chitosan sample was then N-acetylated with acetic a nhydride under the condition that chitosan was homogeneously dissolved in a queous acetic acid again. The water solubility of the half N-acetylated chi tosan thus prepared increased with decreasing molecular weight. From H-1 NM R spectroscopy, it was suggested that the sequence of N-acetylglucosamine a nd glucosamine residues was random. The solubility of the half N-acetylated chitosan of low molecular weight was rather high even in aqueous dimethyla cetamide and dimethylsulfoxide. (C) 2000 Elsevier Science Ltd. All rights r eserved.