Characterization of polyelectrolyte features in polysaccharide systems and mucin

This review elucidates several aspects on the behavior of charged polysaccharides and mucin. Viscosification of dilute aqueous solutions of hyaluronan (HA) occurs in the course of time at lowshear flow,whereas shear thinning as time evolves is found atmoderate shear rates. Hydrogen bonds and electrostatic interaction play an important role for the emergence of these features. No time effect of the viscosity is observed for semidilute HA solutions. A degradation of HA is observed at low and high pH and this effect continues over long times, and it is only in the approximate interval 5<pH<10 that HA is stable. Small angle neutron scattering (SANS) measurements on semidilute aqueous solutions of mucin at pH=7 reveal a fractal dimension of 1.4, and the effect of temperature is insignificant on the fractal structure. This suggests that themucin chains on a semi-local dimensional scale are rodlike. Fromvarious experimentalmethods on solutions ofmucinitwas found that at pHvalues around2 (uncharged polymer), the intensive hydrophobic interactions lead to large association complexes, whereas at pH2 the negative charges suppress the tendency of forming associations. At pH<2, themucin chains are compressed and they are decorated by some positive charges. In the semidilute regime, a fragmented network is developed. The intense association in semidilute solutions ofmucin at pH=2 is further supported by the results from rheo-small angle light scattering measurements. Effects of ionic strength on the radius of gyration (Rg) for dilute solutions of HA (pH=7) and positively charged hydroxyethylcellulose (HEC(+)) are studied with the aid of Monte Carlo simulations, and essential features of the polyelectrolyte effect on Rg are captured in the computer simulation. Strong interactions are observed in aqueous mixtures of an anionic polysaccharide (HEC(-)) and an oppositely charged surfactant (cetyltrimethylammonium bromide; CTAB); this gives rise to extensive associations and macroscopic phase separation is approached. The massive association complexes are disclosed in the SANS experiments by a pronounced upturn in the scattered intensity at low values of the wave vector. © 2010 Elsevier B.V. All rights reserved.