Studies on metal-ligand binding

An exclusion chromatographic technique has been increasingly used for the studies on metal-ligand binding, which is known as the method of Hummel and Dreyer [ref. 127]. This method allows to determine the stability constants of metal complexes, as well as the metal-ligand binding ratio. The principle of the determination of the stability constants of metal complexes for a simplified model has been intelligibly described by Yoza [ref. 128]. 

The method developed by Hummel and Dreyer is a dynamic equilibration technique based on the fact that complexes, formed between metal ions and the ligand macromolecules, are excluded to a greater or lesser extent from the gel interior whereas the free metal ions completely permeate the gel, thus permitting a separation of the two species. 

The concentration stability constant, K, for the formation of a 1 1 metal complex, ML, is given by 

Because K can be usually regarded as constant independent of the concentrations of the metal ion and the ligand, the concentration ratio [ML]/[L] in the ligand-containing zone can be replaced by the corresponding amount ratio provided the concentration of free metal ion is constant. We may thus obtain the following expression 

16 enables us to determine the stability constant of a 1 1 metal complex by the exclusion chromatographic technique. 

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