Structural diversity of chitosan and its complexes

The lattice parameters for a number of chitosan specimens were classified i nto two, hydrated and anhydrous, groups. Polymers in them have the same ext ended two-fold helical structure, while the packing arrangements and water contents are quite different. Chitosan complexes with acid or metal salts c an be classified into two types. Type I has a 10.3 Angstrom axial repeat si milar to hydrated and anhydrous chitosan, while Type II has a 40 Angstrom a xial repeat; by using X-ray data from highly oriented specimens, plausible crystal structures have been obtained in each case. The Type II conformatio n corresponds to a less-extended two-fold helical model with a tetrasacchar ide repeat in a helical asymmetric unit. (C) 2000 Elsevier Science Ltd. All rights reserved.