A study of the interaction of copper(II). zinc(II), and cadmium(II) with transfusion gelatin

Abstract

The binding of copper, zinc, and cadmium with transfusion gelatin has been measured indirectly by observing the displacement of hydrogen ions from the acidic groups of transfusion gelatin. It is seen that the binding data obtained from pH measurements agree well with those obtained from equilibrium dialysis. Copper, zinc, and cadmium show the characteristic binding with the carboxyl groups in the pH range 3-5.5 for which the log K values are found to be 2.18, 1.87, and 1.96 respectively. Potentiometric titration data also indicate that the interaction is a competitive one, i.e. the metal ions compete with the hydrogen ions for common sites. The extent of copper and zinc binding increases with increase in pH, whereas cadmium binding remains unaffected. It is, therefore, concluded that copper and zinc combine with the imidazole groups also (log K values are 3.40 and 2.91 respectively), but cadmium fails to react with the imidazole groups.