Binding of cadmium cations to pectin

Abstract

Using two experimental techniques (dialysis and polarography) the binding of cadmium ions to the pectin carboxylic groups was studied as a function of their degree of esterification E in the range of E 0 to 84.2%. Stability constants for the binding of cadmium ions to magnesium pectinates (ionic strength I = 0.30 mol l-1) were determined by the dialysis technique, the constants for the binding of cadmium to potassium pectinates by the polarographic technique. In both cases stoichiometric binding of cadmium ions was demonstrated using the theory of multiple equilibria. The stability constants K of cadmium pectinates depend considerably on E. With the decrease of the degree of esterification the value of K increases similarly as in the case of the binding of Ca2+ and Sr2+ ions to pectin.