On conformational analysis of chitosan

Chitosan, a natural polyelectrolyte with manyfold applications, is often described as a semi-flexible copolymer with linear chain behavior. Knowledge of the conformation of this polymer is relevant for viscosity-based molecular weight measurements as well as for gelation studies and use as thickener. However, conformational studies reveal a higher variety from compact to relatively stiff chain behavior than expected from the given structure. In this study, we found on the one hand semi-flexible chain behavior and on the other hand dextran-like compact behavior using a size-exclusion chromatography (SEC) system with online triple detection array (refractive index (RI), right and low angle light scattering (RALS, LALS) and viscometry detection). Using different theoretical models different Kuhn segment lengths lK were found for the “semi-flexible” sample: 24 nm using the Benoit-Doty model and Rg-M data, 19 nm using the Odijk-Houwart model and Rg-M data as well as 17.5 nm using the Bohdanecký model and [η]-M data. Our results are in accordance with the expected behavior of semi-flexible linear chains from literature. However, the “compact” sample showed values of 9.8 nm in the high molecular weight part with similarity to reports on dextran.