Proteins water-fluid interfaces

Miller, R., Fainerman, V.B., Makievski, A.V., Kragel, J., Grigoriev, D.O., Kazakov, V.N., Sinyachenko, O.V. (2000a). Dynamics of protein and mixed protein + surfactant adsorption layers at the water-fluid interface. Advances in Colloid and Interface Science, 86, 39-82. 

V. B. Fainerman, E. H. Lucassen-Reynders and R. Miller, Description of the adsorption behaviour of proteins at water/fluid interfaces in the framework of a two-dimensional solution model, Adv. Colloid Interface Sci. 106, 237-259 (2003). 

Proteins and Lipids Can Alter the Thermodynamic and Dynamic Characteristics of Water at Fluid Interfaces... 

Solutes are one of the major components of foods, and they have significant effects on their adsorption at fluid interfaces. In addition, the study of the effects of ethanol and/or sucrose on protein adsorption at fluid interfaces is of practical importance in the manufacture of food dispersions. The presence of ethanol in the bulk phase apparently introduces an energy barrier for the protein diffusion towards the interface. This could be attributable to competition with previously adsorbed ethanol molecules for the penetration of the protein into the interface. However, if ethanol causes denaturation and/or aggregation of the protein in the bulk phase, the diffusion of the protein towards the interface could be diminished. The causes of the higher rate of protein diffusion from aqueous solutions of sucrose, in comparison with that observed for water, must be different in aqueous ethanol solutions. Since protein molecules are preferentially hydrated in the presence of sucrose, it is possible that sucrose limits protein unfolding in the bulk phase and reduces protein-protein interactions in the bulk phase and at the interface. Both of these phenomena may increase the rate of protein diffusion towards the interface. Clearly, the kinetics of adsorption of proteins at interfaces are highly complex, especially in the presence of typical food solutes such as ethanol and sucrose in the aqueous phase. 

When a soluble LMWE (like Tween 20) as well as a protein is present in water both components will form adsorbed films at the air-water interface. At low LMWE concentrations, protein reduces the surface tension to a greater extent than protein-LMWE mixed systems. However, the opposite was observed at high LMWE concentrations, above the critical micelle concentration (CMC), because the protein molecules are displaced from the interface by the LMWE. Over the intermediate region, close to the CMC, both protein and LMWE coexist at interface. However, tensiometric studies indicate that the compatibility of proteins and nonionic emulsifier at fluid interfaces is very poor, in contrast to mixtures of ionic-surface-active homologues. 

The structure of biological and model membranes is frequently viewed in the context of the fluid mosaic model [4], Since biological membranes are composed of a mixture of various lipids, proteins, and carbohydrates the supra-structure or lateral organization of the components is not necessarily random. In order to model biological membranes, lipid assemblies of increasing complexity were studied. Extensive investigation of multicomponent monolayers (at the air-water interface) as well as bilayers have been reported. 

---