Hydrodynamic behavior of quaternized chitosan at acidic and neutral pH

The study is devoted to estimation of the effect of quaternization on the molecular properties of polysaccharide chitosan. Solution properties of quaternized chitosan derivative, N-[(2-hydroxy-3-trimethylammonium)propyl]chitosan, have been studied in comparison with the initial chitosan in 0.33М СН₃СООН + 0.2М CH₃СООNa. The averaged quaternization degree of the modified samples was (90 ± 5) %. Hydrodynamics methods, translation isothermal diffusion and viscometry, and static/dynamic light scattering were applied for characterization of two homologues series of chitosans. The equilibrium chain rigidity value and Mark–Kuhn–Houwink relationships for intrinsic viscosity and diffusion coefficient have been received for the both polysaccharides at pH 3.54 and high ionic strength value. A change of thermodynamic conditions in the same solvent was detected for the modified chitosan in relation to initial analog. Even though the side substituents length is longer for the modified polysaccharide, the hydrodynamic dimension of its molecules could be smaller than initial polysaccharide of the same polymerization degree due to nonequivalent contributions of thermodynamic/electrostatic interactions to the total chain rigidity. The hydrodynamic behavior of quaternized chitosan in 0.33М СН₃СООН + 0.2М CH₃СООNa has been compared to its behavior in 0.2 M NaCl. The influence of the secondary amino group protonation on hydrodynamic properties of modified chitosan molecules was detected at neutral pH. Solution properties of quaternized chitosan in 0.2 M NaCl were identified as the concentration dependent.