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 (F-A=0.05-0.65) and different molecular weights (M-W = 36.000-460.000) were studied by size-exclusion chromatography combined with multi-angle laser light scattering (MALS) and viscosity detectors to provide R-G-M and [eta]-M data as basis for further analysis using the wormlike chain model. In both cases intrinsic persistence lengths (q(0)) in the range 5.1-7.6 nm were obtained, with little or no detectable dependence on F-A. 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 Smidsrod 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. (C) 2008 Elsevier Ltd. All rights reserved.