Optical activity anisotropy of chitosan-based films

The optical activity [α] of films of chitosan and chitosan acetate was studied. [α] depended on the orientation angle θ of the film sample around the light beam. The angular dependences [α] = f(θ) (indicatrices) were processed to extract the constant term [α]₀and four harmonics ([α]_i, Fourier's series) determined by structure elements with the corresponding symmetry: the amorphous (isotropic) phase of chitosan ([α]₀), irregular-shaped structures ([α]₁), rod-shaped ones in the film plane ([α]₂), helical ones located perpendicular to the film surface ([α]₃), and crystalline structures ([α]₄). The contribution of individual supramolecular structures to the overall optical activity of chitosan was estimated: [α]₂ and [α]₄ predominated for the fresh chitosan acetate films, while [α]₄ did for the chitosan ones. The results of the numerical decomposition of indicatrices are in satisfactory agreement with X-ray diffractometry data. The observed regularities predetermine prospects for obtaining stereoselective chiro-optic chitosan-based materials with novel functional properties.