A two-phase model for determining the stability constants for interactions between copper and alginic acid

Abstract

The two-phase model used previously to calculate the polymer-subphase volume of alginic acid was applied to interpret the dependence of apparent metal binding equilibrium on environmental conditions. In this model, the polymer subphase, a small aqueous region surrounding the polymer chain, was considered as a separate phase in the aqueous solution and as a protonation-deprotonation and metal binding reaction zone. Three factors were taken into account when treating experimental data: (1) the electric field due to the charged ligands on the polymer molecule, (2) the effective concentration of ligands based on polymer-subphase volume, and (3) the competition from hydrogen ions for the metal binding sites. The data of base titration of alginic acid in the presence of trace amounts of copper at different alginic acid concentrations and ionic strengths yielded unique intrinsic stability constants for complexes formed between a cupric ion and one or two binding ligands.