Mixed Protein/Hexane Adsorption Layers Formed at the Surface of Protein Solution Drops Surrounded by Hexane Vapor

Abstract

The surface tension of aqueous solution drops of ß-casein, ß-lactoglobulin, and human serum albumin at the interface to air and hexane saturated air are measured by drop profile analysis tensiometry. The results indicate that the dynamic and equilibrium surface tension for a hexane vapor atmosphere are considerably lower as compared to the values at the interface with pure air. The experiments are performed with the initial adsorption of protein followed by hexane adsorption, and with subsequent removal of hexane from the measuring cell after equilibrium is attained. Two models are proposed, both of which assume the diffusion of protein in the solution and either diffusion-governed or barrier-governed hexane coadsorption. The new developed theoretical equilibrium model assumes a double layer adsorption in these systems, with the first layer composed of protein mixed with hexane and the second layer formed by hexane molecules only. The experimental and calculated equilibrium surface tension data are in a perfect agreement. Note the model parameters are exactly the same as those found for the individual compounds

Surface Tension and Adsorption Studies by Drop Profile Analysis Tensiometry

“…In particular, fluorocarbon gases in pulmonary disease therapies were studied. Experimental results and theoretical models for the concurrent adsorption of alkanes from the gas phase and surfactants (or proteins) from their solutions were presented in [49–52, 63, 101–108]. …”

“…We have further developed the model to describe mixed surface layers of a reorientable surfactant adsorbed from inside the drop, and a surfactant adsorbed from the ambient phase around the drop surface, in particular, for the adsorption of alkanes from the vapor phase surrounding the drop. For the case when the adsorption of a protein or long-chain surfactant from the solution drop occurs with the formation of the first adsorption layer, accompanied with the formation of an adjacent secondary layer formed exclusively by alkane molecules, a theoretical description was formulated [63–65]. Approximate expressions for polylayer adsorption of alkanes were proposed [53, 63, 65].…”

Multilayer Adsorption of Heptane Vapor at Water Drop Surfaces

“…It was shown [12] that the influence of hexane vapor on the surface tension of water depends also essentially on the air humidity. The dynamic surface tension dependencies for drops of aqueous C 14 EO 8 solutions at the interface to air saturated by pentane, hexane, heptane and toluene, respectively, and for drops of water at these interfaces were discussed [17]. The experimental results were well described by a model which implies a diffusion processes for the C 14 EO 8 molecules and the existence of a kinetic barrier for the alkane molecules.…”

“…Various experimental and theoretical studies of adsorption of alkanes from the gas phase on a water surface were previously reported [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17]. The thickness of such adsorbed alkane layers was determined with optical methods being maximum up to 4-5 nm [6].…”

“…During last years, a large pool of experimental data was collected, and theoretical models were developed for the adsorption of alkanes from the gas phase on the surface of a water drop [7][8][9][10][11][12][13][14][15][16][17]. It was shown, for instance, that the adsorption of alkanes from the gas phase results in a significant decrease of the surface tension of water or aqueous protein (surfactant) solutions.…”