RESUMEN
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.
Asunto(s)
Quitina/análogos & derivados , Acetilación , Fenómenos Químicos , Química Física , Quitina/química , Quitosano , Peso Molecular , Concentración Osmolar , Solubilidad , ViscosidadRESUMEN
The use of the n.m.r. method in the investigation of chitosan carboxymethylation was evaluated. It seems to be the most effective technique to determine concurrently the degree and the position of substitution of the carboxymethylated chitosan derivatives. The 13C-n.m.r., by the DEPT method, 1H-1H and 1H-13C-n.m.r. correlations give much valuable information from the chemical shifts of the complex carboxymethylchitosan spectra. The relative reactivity of the functional groups of chitosan towards carboxymethylation was also determined assuming a higher reactivity of the C-6 position.