title: Polyelectrolyte complexes from polysaccharides: formation and stoichiometry monitoring.
abstract: Colloids were obtained from non-stoichiometric polyelectrolyte complexes with two polysaccharides of opposite charge: chitosan and dextran sulfate (DS) as the polycation and polyanion, respectively. The complexes were elaborated by a one-shot addition of the polymer in default to the one in excess. The colloids were positively or negatively charged according to the nature of the polymer in excess. Dynamic light scattering (DLS) demonstrated that particles were formed at a very early stage in the complexation process. The consumption of the excess polyelectrolyte was monitored with a dye assay specific for dextran sulfate (toluidine blue) or chitosan (orange II). From these experiments, two different mechanisms of colloidal PEC formation were evidenced, according to the nature of the polymer in excess. On adding chitosan to DS in excess, regular consumption of the polyanion was observed at a constant stoichiometry, in the 1.5 to 1.85 range (sulfate residues for one glucosamine group), according to the molar mass of the polycation. When DS was added to chitosan in excess, the overall stoichiometry varied from ca. 6 (glucosamine residues for one sulfate group) down to 1 as the charge molar mixing ratio R=n+/n- decreased from 20 to 1. The existence of various mechanisms, according to the nature of the polymer in excess, could be attributed to the differences in chemical reactivity (strong vs low) of the ion in excess and the conformation and flexibility of the macromolecular chains related to their electrostatic potential.
authors: Unité mixte CNRS-BioMérieux, UMR 2714, ENS Lyon, 46, allée d'Italie, 69364 Lyon Cedex 07, France.
authors: Alexandre
authors: A
authors: Drogoz
authors: Laurent
authors: L
authors: David
authors: Cyrille
authors: C
authors: Rochas
authors: Alain
authors: A
authors: Domard
authors: Thierry
authors: T
authors: Delair
mesh_terms: D048271:Chitosan / Q000737:chemistry; D003102:Colloids; D016264:Dextran Sulfate / Q000737:chemistry; D004573:Electrolytes / Q000138:chemical synthesis* / Q000737:chemistry*; D008027:Light; D046911:Macromolecular Substances; D011134:Polysaccharides / Q000737:chemistry*; D012542:Scattering, Radiation; D013057:Spectrum Analysis; D014965:X-Rays
chemical_list: D003102:Colloids; D004573:Electrolytes; D046911:Macromolecular Substances; D011134:Polysaccharides; D048271:Chitosan; D016264:Dextran Sulfate