Analysis of hen egg white lysozyme adsorption on Si(Ti)O2 | aqueous solution interfaces at low ionic strength:: a biphasic reaction related to solution self-association

Adsorption kinetics of hen-egg white lysozyme at concentrations of 10(-7), 10(-6), 10(-4) M and at pH 8.0 have been measured on Si0.8Ti0.2O2 surfaces by means of optical waveguide lightmode spectroscopy and were found to proceed in two distinct kinetic regimes: a fast and quasi linear increase of the surface concentration followed by slower kinetics that could be described qualitatively by the theory of random sequential adsorption. The transition between these two kinetic regimes was correlated with abrupt changes in the values of the mean refractive index and of the thickness of the adsorbed layer as well as in the desorption kinetics performed either before or after the transition from the first regime to the second. Experiments carried out at the same ionic strength but at different pH values showed that the adsorption behaviour of lysozyme is related to its self-association properties in highly concentrated solutions. (C) 2000 Elsevier Science B.V. All rights reserved.