Protein adsorption at the oil/water interface: characterization of adsorption kinetics by dynamic interfacial tension measurements

The dynamics of protein adsorption at an oil/water interface are examined o ver time scales ranging from seconds to several hours. The pendant drop tec hnique is used to determine the dynamic interfacial tension of several prot eins at the heptane/aqueous buffer interface. The kinetics of adsorption of these proteins are interpreted from tension/log time plots, which often di splay three distinct regimes. (I) Diffusion and protein interfacial affinit y determine the duration of an initial induction period of minimal tension reduction. A comparison of surface pressure profiles at the oil/water and a ir/water interface reveals the role of interfacial conformational changes i n the early stages of adsorption. (II) Continued rearrangement defines the second regime, where the resulting number of interfacial contacts per prote in molecule causes a steep tension decline. (III) The final regime occurs u pon monolayer coverage, and is attributed to continued relaxation of the ad sorbed layer and possible build-up of multilayers. Denaturation of proteins by urea in the bulk phase is shown to affect early regimes. (C) 1999 Elsev ier Science B.V. All rights reserved.