Chain stiffness and extension of chitosans and periodate oxidised chitosans studied by size-exclusion chromatography combined with light scattering and viscosity detectors

Chitosans with different chemical compositions (FA = 0.05–0.65) and different molecular weights (Mw = 36.000–460.000) were studied by size-exclusion chromatography combined with multi-angle laser light scattering (MALS) and viscosity detectors to provide RG–M and [η]–M data as basis for further analysis using the wormlike chain model. In both cases intrinsic persistence lengths (q0) in the range 5.1–7.6 nm were obtained, with little or no detectable dependence on FA. These values are significantly lower than values obtained for alginates (12 nm), including homopolymeric mannuronan, using the same approach. This finding is also corroborated by differences in the Smidsrød B-parameter, confirming that chitosans are less extended than alginates, despite the similarity in basic chain geometry (cellulose type) and linear charge density. Partial periodate oxidation of chitosans led to a pronounced increase in the chain flexibility as shown by a gradual decrease in persistence length, approaching 2 nm for the most oxidised samples.