Layered structures of hydrophobically modified chitosan derivatives

Two series of chitosan derivatives, N-aliphatic acyl chitosans (Cn-CS) and N-aliphatic-O-dicinnamoyl-chitosans (Cn-CinCS) with n=2, 4, 8, 12 and 18, were prepared through regioselective reactions. The solid state structures were studied by FTIR and X-ray diffraction techniques. Two different types of layered structures were found to exist in the powder samples of Cn-CS and Cn-CinCS. The Cn-CS series crystallized into a sheet-type structure, in which all the flexible side chains lied down in the sheet in a direction normal to the backbones and partially interdigitated with each other. For the Cn-CinCS series, the polar backbones were stacked into sheets, and the flexible side chains occupied the space between sheets in a direction inclined to the backbones. The relationship between the structures and the solubilities are discussed.