Structure of natural polyelectrolyte solutions: role of the hydrophilic/hydrophobic interaction balance

A method allowing the evaluation of the solvophilic/solvophobic character of polyelectrolytes from their conformation in solution is discussed. Analyzed systems are salt-free aqueous solutions of natural copolysaccharides with controlled chemical structures. Small-angle X-ray scattering diagrams revealed their conformation by the "polyelectrolyte peak". The study of this peak allowed the determination of cb, the crossover concentration associated with the transition between the two structural organization regimes predicted by the scaling model of hydrophobic polyelectrolytes developed by Dobrynin and Rubinstein. A structural law of behavior as a function of the chain primary structure is built for chitosan, showing an increasing hydrophobic character when the fraction of N-acetyl-D-glucosamine residues (DA) increases. The results concerning this random copolymer are compared with those obtained for hyaluronan. Consistently, in the case of alginates, the relative content of the constitutive units is shown not to influence the polymer hydrophobicity.