Adsorption of Proteins at the Liquid/Air Interface

Abstract

Thermodynamic equations for describing protein adsorption layers at liquid/fluid interfaces are derived as a generalization of a theory published recently [J. Colloid Interface Sci. 1996, 183, 26]. In this new theory the nonideality of enthalpy (Flory−Huggins' parameter) and entropy of mixing are taken into account, and also the effect of the electric charge of the protein molecules on surface pressure is considered. The model is verified by experimental dynamic and equilibrium surface tension data for HSA solutions obtained from pendent drop experiments (ADSA). The derived isotherm is in good agreement with the experimental data. The values of the isotherm parameters surface area per molecule, electric charge of the HSA molecule, and the adsorption layer thickness are close to values obtained by other methods in literature. It follows that HSA molecules undergo almost no denaturation at the solution/air interface and occupy a surface area of about 50 nm2, independent of the packing in the adsorption layer, which is in agreement with the concept of a triple-domain structure.

β-Casein Bilayer Adsorption at the Solution/Air Interface: Experimental Evidences and Theoretical Description

“…In one model a decrease of the constant a el was allowed with a proceeding saturation of the adsorption layer (11,12), in the other case a 2D aggregation of the protein in the surface layer was considered (19). The first model predicts that the surface pressure becomes independent of the concentration or adsorption above a critical value c , while the second model leads to a rather weak dependence on the adsorption for > c .…”

“…In (4) a 3-dimensional scaling model of the surface layer was used to describe the adsorption of β-casein within the range of 3 to 6 mg/m 2 . The second aim of the present investigations is therefore to apply a recently developed theory (10)(11)(12) to evaluate the probable formation of a second adsorption layer qualitatively suggested by Graham and Phillips. 257 0021-9797/02 $35.00…”

The Elasticity of Adsorption Layers of Reorientable Surfactants

“…For high surface pressures (and, therefore, high surfactant bulk concentrations) the diffusion relaxation frequency 0 increases, which, according to Eq. [9], results in a decrease of the viscoelasticity caused by the surfactant exchange between the surface layer and the solution bulk.…”

“…(2). For example, the asymmetry of a surfactant molecule can be the reason that it changes its orientation and hence may occupy different areas in the adsorption layers at liquid-gas or liquid-liquid interfaces (2)(3)(4)(5)(6)(7)(8)(9). It was shown that the adsorbed molecules characterized by a certain partial molar area depend on the surface pressure (3).…”

Heterogeneity of Protein Environments in Frozen Solutions and in the Dried State

“…Protein sorption on solution/air interface is well-documented, e.g., [41], and will not be discussed here. Therefore, protein sorption on the air bubbles created as a result of freezing can be expected, with a corresponding increase in the surface concentration of protein in dried material and protein destabilization.…”