pH-dependent stability of scleroglucan borate gels

Scleroglucan, a neutral exopolysaccharide, forms strong physical gels by crosslinking with borate anions, and undergoes a conformational transition at pH > 13 (triple-helix to coil). A study of stability of scleroglucan/borate gels has been carried out over a wide range of pH and we have clearly observed a pH-dependence on the structure of these systems. The gel is dissolved in very alkaline media due to the conformational transition of scleroglucan and in acidic media, in agreement with thermodynamical competition between dissociation constant of boric acid and complexation constant of scleroglucan/borate system. Influence of polymer and borax concentrations have been also studied and it appeared that erosion of these matrices could be easily controlled as a function of the density of the network and pH. The pH-dependence of scleroglucan/borate gels could be used for controlling the release of macromolecular active substances.