Structural diversity of chitosan and its complexes

The lattice parameters for a number of chitosan specimens were classified into two, hydrated and anhydrous, groups. Polymers in them have the same extended two-fold helical structure, while the packing arrangements and water contents are quite different. Chitosan complexes with acid or metal salts can be classified into two types. Type I has a 10.3 ? axial repeat similar to hydrated and anhydrous chitosan, while Type II has a 40 ? axial repeat; by using X-ray data from highly oriented specimens, plausible crystal structures have been obtained in each case. The Type II conformation corresponds to a less-extended two-fold helical model with a tetrasaccharide repeat in a helical asymmetric unit.