EXCESS ADSORPTION OF LYSOZYME AND WATER AT SOLID-LIQUID INTERFACES

Adsorption isotherms of lysozyme at solid-water interfaces have been studied as a function of protein concentration, ionic strength of the medium, pH and temperature using silica, alumina, carbon, chromium and Sephadex as solid surfaces. Adsorption of lysozyme is affected strongly by change of pH, temperature and ionic strength. In most cases adsorption isotherms attained a state of adsorption saturation. On chromium, lysozyme is either expanded laterally or negatively adsorbed. In some cases, adsorption isotherms were S shaped, showing the existence of some kind of interactions within the adsorbed protein layer. Adsorption of lysozyme on Sephadex at pH 5.0 and 7.5 is negative due to the excess adsorption of water by this material. The standard free energies (DELTAG-degrees) of positive and negative adsorption of lysozyme per square meter, signifying the relative affinity of adsorption in the state of monolayer saturation, have been calculated. The magnitude of the standard free energy of transfer (DELTAG(B)-degrees) of one mole of protein from solution to the surface is observed to be 40.3 kJ mol-1 and the value is independent of pH, ionic strength, nature of the surface and temperature.