Macromolecular conformation of chitosan in dilute solution: A new global hydrodynamic approach

Abstract

Chitosans of different molar masses were prepared by storing freshly prepared samples for up to 6 months at either 4, 25 or 40 °C. The weight-average molar masses, M w and intrinsic viscosities, [ η] were then measured using size exclusion chromatography coupled to multi-angle laser light scattering (SEC-MALLS) and a “rolling ball” viscometer, respectively. The solution conformation of chitosan was then estimated from: (a) the Mark–Houwink–Kuhn–Sakurada (MHKS) power law relationship [ η] = kM w a and (b) the persistence length, L p calculated from a new approach based on equivalent radii [Ortega, A., & Garcia de la Torre, J. (2007). Equivalent radii and ratios of radii from solution properties as indicators of macromolecular conformation, shape, and flexibility. Biomacromolecules, 8, 2464–2475]. Both the MHKS power law exponent ( a = 0.95 ± 0.01) and the persistence length ( L p = 16 ± 2 nm) are consistent with a semi-flexible rod type (or stiff coil) conformation for all 33 chitosans studied. A semi-flexible rod conformation was further supported by the Wales–van Holde ratio, the translational frictional ratio and sedimentation conformation zoning.