Shin-Ichiro Nishimura

Solubilization of a rigid polysaccharide: Controlled partial N-Acetylation of chitosan to develop solubility

Abstract The solubility-structure relationship was studied in the acetylation of chitosan to elucidate key factors for solubilization of rigid polysaccharides. N -Acetylation of chitosan proceeded smoothly and reproducibly in a highly swollen state, and the degree of substitution was easily controlled. Evaluation of the properties of the resulting acetylated chitosans indicated the importance of the distribution mode of acetyl groups as well as the extent of substitution for solubilization. The chitosan derivatives with about 50% substitution prepared under appropriate conditions exhibited high solubility in water, and the presence of half a molar amount of randomly distributed substituents on the amino groups was confirmed to be an essential requirement in developing solubility. The present procedure is much simpler to prepare the water-soluble chitin than the conventional method involving partial deacetylation of chitin.

Preparation and biodegradability of chitin derivatives having mercapto groups

Abstract Two kinds of chitin derivatives having mercapto groups have been prepared, and the properties, including solubility and susceptibility to lysozyme, are discussed. Chitosan was first modified by N -acylation with S -protected mercaptoacetic acid, followed by selective acetylation of the remaining amino groups and deprotection to give derivatives having mercaptoacetyl groups at the C-2 amino groups. In an alternative preparation of mercapto-chitins, tosylchitin was treated with potassium thioacetate and then with alkali to afford derivatives having mercapto groups at the C-6 positions. The derivatives showed much enhanced swelling and solubility in organic solvents. Biodegradability of the mercapto derivatives was evaluated with lysozyme, and they turned out to be more susceptible to enzyme hydrolysis than the original chitin.

Reactivity characteristics of a new form of chitosan

SummaryA new form of chitosan prepared by deacetylating squid β-chitin was subjected to N-phthaloylation to evaluate the reactivity as compared with that of the conventional chitosan prepared from shrimp α-chitin. The reaction proceeded much more efficiently with squid chitosan than shrimp chitosan to give N-phthaloylchitosan, indicating considerable differences in higher-order structures between the two kinds of chitosans. Squid chitosan thus proved to show enhanced reactivity and be superior to shrimp chitosan as a starting material for controlled regioselective chemical modifications of chitin.