Polymorphic Modifications of Chitosan

This work describes the analysis of the crystal structures of chitosan, its main polymorphic modifications, and its characteristic mutual chain packing and hydrogen bond systems in the crystalline regions of conformers. The analysis takes into consideration the crystal structures of chitosan complexes (salts) with organic and inorganic acids and their structural transformations. Notably, the transformation of the hydrated form of chitosan into anhydrous is found to be irreversible and occurs either at high temperatures or through a less stable form of hydrated salts. The interaction with polyanions during the formation of multilayer films can be considered as a way to form the anhydrous crystalline form of chitosan.