Urea-induced conformational changes of chitosan molecules and the shift of break point of Mark-Houwink equation by increasing urea concentration

Abstract

Chitosan solutions of the same 83% degree of deacetylation (DD) but different weight average molecular weights (M w s) (78 -914 kDa) in 0.01M HCl containing different concentrations of urea (0 -6M) were prepared. Intrinsic viscosity ([]) and weight average molecular weight (M w ) of chitosan were measured with a capillary viscometer and light scattering, respectively. Mark-Houwink exponent a was used as the parameter of conformational index. The Mark-Houwink exponent a increased with increasing concentrations of urea. When solutions contained 0, 2, 3, 4, and 6M urea, the value of a increased from 0.715 to 0.839, 0.894, 1.000, and 1.060, respectively. This indicates the occurrence of urea-induced conformational transitions of chitosans. The break point shifted from 223 kDa in solutions containing no urea to 280 kDa in 2M urea solutions, to 362 kDa in 4M urea solutions and further to 481 kDa in 6M urea solutions.

Exploring the Factors Affecting the Solubility of Chitosan in Water

“…[35,36] Few studies report the effects of urea on the hydrodynamic behavior of chitosan in solutions; Gamzazade et al [37] and Sklyar et al [38] showed that the intrinsic viscosity of chitosan solutions increased in the presence of 8 mol Á L À1 urea. Similarly, Chen and Tsaih [39,40] demonstrated increased intrinsic viscosity of chitosan in solutions containing urea compared to chitosan solutions without urea. The authors hypothesized that an extended conformation of the chitosan chains results from disruption of intra-and intermolecular hydrogen bonds in the polymer caused by urea.…”

“…The viscosity of chitosan in solutions containing 8 mol Á L À1 urea is higher than in urea-free aqueous solutions for the same pH, in good agreement with previous viscometric studies. [37][38][39][40] This effect is probably due to the specific association between macromolecules of chitosan and urea, presumably, via hydrogen bonding. In fact, urea acts as a co-solvent and provides additional solvation to the macromolecules of chitosan, in agreement with the IR results discussed above.…”

Self-healing inside a scratch of oxetane-substituted chitosan-polyurethane (OXE-CHI-PUR) networks

“…4) -C-O-C-of the OXE ring, which undergo bond cleavages when the OXE-CHI-PUR network is mechanically damaged and exposed to UV radiation. These processes generate reactive free radicals (b1, b2, and b3) and a carbocation (b4) during the self-repairing process, where the OXE ring opening reaction (b4) propagates cationically, [3][4][5]18,19 but -NHCONH-(PUA) and -C-O-C-bond cleavage generate free radicals (b2). 1,11,12 On the other hand, close packing and/or network shrinkage upon UV exposure due to chair-to-boat conformational changes (Fig.…”

Viscoelastic properties of chitosan solutions: Effect of concentration and ionic strength

“…Several have been focusing on the investigation of the physical properties of dilute solutions (Anthonsen, Vårum, & Smidstrød, 1993;Chen & Tsaih, 2000;Tsaih & Chen, 1997;Wetton, Marsh, & Ven-de-Velde, 1991) looking at the effect of pH, ionic strength, DDA and molecular weight on the conformation of the chitosan molecule. Other studies have dealt with the rheological properties of concentrated chitosan solutions (Desbrières, 2002;Mucha, 1997;Nystrom, Kjøniksen, & Iversen, 1999;Wang & Xu, 1994).…”