Ionic condensation of sodium chondroitin sulfate in water-dioxane mixture

Abstract In a previous work, we have verified that sodium chondroitin sulfate in water at 25 °C, presents a correct Manning behavior ( α M  = 0.81). In contrast, we expect that the rate of condensation α is shifted from its Manning value ( α M  = 0.36) in water–dioxane (50% wt) mixture at 25 °C, ( α  ≅ 0.47). In order to verify this dioxane effect, we have compared experimental equivalent conductibility Λ exp of sodium chondroitin sulfate in water ( no shift ) and water–dioxane (50% wt) mixture ( positive shift ), to their theoretical values Λ M , Λ c th and Λ s th corresponding respectively to the Manning cylindrical and spherical models. Indeed, except some cases, α must obey to Ostwald's principle of dilution ( α  → 1 when C Na +  → 0), according to the following “rod-like model” approximation: ( 1 − α ) ≈ | Z i | ( π b S ) [ 4 ⁢ π Z i 2 L b ] [ − b S ″ α ] [ α C i R 2 ] [ 1 − b S ″ α ] ; with : b S ″ = α M − 1 However, only in pure water at 25 °C ( e  = 78.3), the exponent [1 −  b S ″ α ] of sodium chondroitin sulfate is zero and therefore: α  =  α M .