Study of the self-diffusion coefficients of cations in the presence of an acidic polysaccharide.

Abstract

AbstractSelf‐diffusion coefficient measurements have been applied to the study of Na+, Ca++, and Sr++ in the presence of a linear acidic polysaccharide extracted from cartilage, i.e., chondroitin sulfate. A series of experimental determinations was made with and without supporting electrolytes, and an analysis of experiments involving the separation of the electrostatic interaction terms by an extension of Manning's theory produced results showing the preponderant nature of these electrostatic terms. The specificity of each type of ion or the influence of the pH can be considered merely as higher order corrections with respect to the preceding interactions. Counterion concentration ranges and pH ranges were determined, where either the alkaline‐earth counterions become free and hence move with their normal diffusion rate, or these cations are associated with the polyelectrolyte molecule, thus giving a diffusion coefficient similar to that of the macromolecule, or the apparent diffusion coefficients vary between these two extreme diffusion rates as a function of the association equilibria. This variation can be expressed as a function of the linear charge density parameter ξ related to the structure of the polyelectrolyte, the value of which was determined and found in good agreement with published values.