COMPARISON OF SEMIANALYTICAL METHODS TO ANALYZE COMPLEXATION WITH HETEROGENEOUS LIGANDS

The binding of ions to natural ligands is influenced by the chemical heterogeneity of these ligands. Two approaches to calculate the affinity distribution are compared in terms of theory and practicality. The local isotherm approximation (LIA) methods use an approximation of the local binding function in order to solve the integral adsorption equation for the distribution function. The differential equilibrium function (DEF) method is based on the law of mass action, but it is shown that the method can also be interpreted within the LIA concept. The results obtained with the LOGA method, on the basis of accurate synthetic data on binding, are fairly good, but in general the distribution is somewhat flattened. The DEF distributions are asymmetrically distorted, but the position of a small peak at the high-affinity end of a distribution is clearly discernable.