Determination of the Mark-Houwink equation for chitosans with different degrees of deacetylation

Effect of temperature on the intrinsic viscosity and conformation of chitosans in dilute HCl solution

The effects of temperature on the intrinsic viscosity and on the conformation of chitosans in dilute HCI solution were studied. Ten chitosans with the same degree of deacetylation but different molecular weights were produced by alkali deacetylation of chitin which was prepared from red shrimp wastes. The degree of deacetylation at 83% and weight average molecular weight of the chitosans ranging 78-914 kDa were determined by infrared spectroscopy and static light scattering, respectively. The intrinsic viscosities ([eta]) of these 10 chitosans in 0.01 M hydrochloric acid were measured at 10, 20, 30, 40, and 50 degrees C. Then, d ln [eta]/d(l/T) and the Mark-Houwink exponents were calculated as the indices for chain flexibility and molecule conformation, respectively. These results showed: the intrinsic viscosities decreased linearly with increasing temperature, therefore, a temperature-induced conformational transition did not occur for all 10 different molecular weight chitosans in the temperature range studied. Values of d In [eta]/d(l/T) were between 633 and 1334 and increased with decreasing molecular weight, indicating that higher molecular weight chitosans are more flexible. Between 10 degrees and 50 degrees C, the Mark-Houwink exponents ranged 0.64-0.76 and increased with increasing temperature, indicating that the conformation of these chitosans were all in random coil, and a temperature-induced conformational transition did not occur. The a* and a** Mark-Houwink exponents represent those chitosans whose molecular weights are larger and smaller than 223 kDa, respectively, and were obtained by using 223 kDa as the break point in the double logarithmic plots of the intrinsic viscosities and weight average molecular weight. Values of a** were between 0.41 and 0.54, while the a* values were from 0.96 to 1.07. These values for a** and a* indicate that larger and smaller molecular weight chitosans were in random coil and rod shape, respectively.

Effect of molecular weight and urea on the conformation of chitosan molecules in dilute solutions

The effects of molecular weight and urea on the magnitude of the Mark-Houwink exponent a and the relative stiffness parameter B of chitosan molecules in dilute solutions were analyzed. The results show that in solutions with ionic strengths between 0.01 and 0.3 M, the relative chain stiffness parameter B and the Mark-Houwink exponent a of chitosans whose molecular weights were between 22.3 x 10(4) and 91.4 x 10(4) fell between 0.143 and 0.152 and from 0.404 to 0.497, respectively; whereas for chitosans whose molecular weights were between 7.8 x 10(4) and 14.8 x 10(4) these values fell between 0.110 and 0.138 and from 0.653 to 1.009, respectively. Both results indicate that the stiffness and conformations of small molecular weight chitosans were more stiff and extended, respectively, than higher molecular weight ones, and that molecular weight-induced conformational transition occurred. Chitosans in solutions containing 4 M urea possessed a rod-shaped conformation in both molecular weight domains, and no molecular weight-induced conformational transitions occurred.

Viscosity and flow properties of concentrated solutions of chitosan with different degrees of deacetylation

The effects of the degree of deacetylation (DD) on the viscosity and flow behaviour of concentrated solutions of chitosan were investigated using 0.2 M CH3COOH and 0.2 M CH3COOH/0.1 M CH3COONa aqueous solutions as solvents. The results indicated that the viscosity and flow properties of the solutions differed with the DD of chitosan. The solution viscosities and the non-Newtonian flow properties as well as the flow activation energies E gamma increased with the increasing DD of chitosan. However, the additional salt decreased the viscosities and the non-Newtonian flow properties of the solutions of chitosan, but did not change the flow activation energies E gamma of the solutions.

Characterization of chitosan. Influence of ionic strength and degree of acetylation on chain expansion

This paper concerns a new method of characterizing chitosans with different degrees of acetylation (DA = 2, 11.5 and 21%); it consists of steric exclusion chromatography using a multidetection instrument allowing determination of M, [eta] and RG for each point of the chromatograms. From these data, the Mark-Houwink parameters for intrinsic viscosity and the exponent relating RG and M are determined. In the same way, the role of the solvent is discussed and the solvent AcOH 0.3 M/AcONa 0.2 M is proposed to reduce the presence of aggregates which perturbs static molecular weight determination by light scattering. The role of the ionic concentration and of the degree of acetylation on the stiffness of chitosan is then discussed and a theoretical treatment is proposed allowing the determination of the intrinsic persistence length (Lp = 50 A) and the prediction of the dimensions in solution (RG and [eta]). Lp is found to be independent of DA in the range tested.

Hydrodynamic characterization of chitosans varying in degree of acetylation

The molecular weights and gross aqueous solution conformation of two chitosans of different degrees of acetylation, 'Sea Cure +210' (11% acetylated) and KN50 (58% acetylated) were characterized by viscometry, analytical ultracentrifugation and dynamic light scattering. The hydrodynamic parameters obtained were used to determine both the molecular weights and the gross solution conformation of the two chitosans. Using the Wales-Van Holde ratio of sedimentation coefficient concentration regression coefficient (ks) to intrinsic viscosity [eta], the Sea Cure +210 chitosan, which is much less acetylated than the KN50, is highly asymmetric in conformation. This, in conjunction with the charge on the molecule, would suggest a rod-like conformation in solution. The two largest KN50 chitosans have widely differing values for the Wales-Van Holde ratio, suggesting different solution conformation. However, when the series is examined as a whole using the Mark-Houwink-Kuhn-Sakurada relationships relating molecular weight to both intrinsic viscosity and translational diffusion coefficient, then a more spheroidal structure, approximating to a random coil, is predicted.