Fluid interfaces proteins

It would appear that, at fluid/fluid interfaces, proteins give adsorption isotherms for which interfacial pressure is a linear function of the logarithm of the bulk concentration over appreciable ranges as has been found for simpler compounds. What has not been satisfactorily explained is the reason for the very low values of A. Joos has inter-... 

Dickinson, E. (1999b). Adsorbed protein layers at fluid interfaces interactions, structure and surface rheology. Colloids and Surfaces B Biointerfaces, 15, 161-176. 

Globular proteins form close-packed monolayers at fluid interfaces. Hence a large contribution to the adsorbed layer viscoelasticity arises from short-range repulsive interactions between hard-sphere particles. In addition to, or instead of, this glass-like5 structure from hard spheres densely packed in two dimensions, many adsorbed proteins can exhibit attractive interactions leading to a more gel-like5 network structure. Hence the mechanical properties of an adsorbed layer depend on many... 

Atkinson, P.J., Dickinson, E., Horne, D.S., Leermakers, F.A.M., Richardson, R.M. (1996). Theoretical and experimental investigations of adsorbed protein structure at a fluid interface. Berichte der Bunsen-Gesellschaftfur Physikalische Chemie, 100, 994-998. 

Lucassen-Reynders, E.H., Benjamins, J. (1999). Dilational rheology of proteins adsorbed at fluid interfaces. In Dickinson, E., Rodriguez Patino, J.M. (Eds). Food Emulsions and Foams Interfaces, Interactions and Stability, Cambridge, UK Royal Society of Chemistry, pp. 195-206. 

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. 

Vol. 9 Hydrophile-Lipophile Balance of Surfactants and Solid Particles. Physicochemical Aspects and Applications. By P.M. Kruglyakov Vol. lO Particles at Fluid Interfaces and Membranes. Attachment of Colloid Particles and Proteins to Interfaces and Formation of Two-Dimensional Arrays. 

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). 

Similar questions apply concerning the interaction of proteins with fluid-fluid interfaces. Lipases, enzymes that degrade fats, act at aqueous-fat interfaces. The role of the interface in activating the enzyme and how more efficient enzyme-interfacial contact might be achieved (in a membrane, for example) are intriguing challenges in multiphase contacting, transport, and protein chemistry. 

The strongly amphipathic nature of proteins, resulting from their mixture of polar and nonpolar side chains, causes them to be concentrated at interfaces. As a result of their great stability in the adsorbed state, it is possible to study them at fluid interfaces by the classical techniques of insoluble monolayers. A review of early work along these lines in this series (Bull, 1947) serves as an excellent introduction to the subject. The effect of adsorption on the biological activity of proteins was treated by Rothen (1947) in the same volume. Further... 

At fluid/fluid interfaces, it is well established that proteins lose their tertiary structure. Measurements of II — A isotherms give areas that can be ascribed to unfolded polypeptide chains e.g., limiting... 

Distribution between trains and loops in molecules adsorbed at solid/Iiquid interfaces is also possible and has been shown to occur for flexible polymers. There are some indications that protein molecules at solid/liquid interfaces do not always undergo the drastic conformational changes that occur at fluid/fluid interfaces. At a solid/liquid interface, an adsorbing molecule cannot penetrate the solid phase. Furthermore, adsorption may be confined to sites and thus be localized. Using infrared difference spectroscopy, Morrissey and Stromberg (1974) found a bound fraction (number of carbonyl surface... 

Adsorption Data for Proteins at Fluid/Fluid Interfaces... 

Apart from those mentioned, other general features of protein adsorption at solid/liquid interfaces are as follows (1) Adsorption is sensitive to pH, as it is for fluid/fluid interfaces, a maximum usually being observed near the isoelectric point of the protein (Dillman and Miller, 1973 Norde, 1976). (2) Greater adsorption occurs at hydrophobic interfaces than at hydrophilic ones (MacRitchie, 1972 Brash and... 

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. 

Nino, Ma.R.R., Patino, J.M.R., Sanchez, C., Cejudo, M., and Navarro, J.M. Physicochemical characteristics of food lipids and proteins at fluid-fluid interfaces, Chem. Eng. Commun., 190,15, 2003. 

An increase in diffusion rates occurs as a consequence of increasing protein bulk concentration (Patino et al., 1999 Home and Patino, 2003 Baeza et al., 2004a). Excluded volume effects can have an effect similar to increasing protein concentration because of the increased thermod)mamic activity of the protein in the bulk solution — that would perform as a more concentrated one (Carp et al., 1999) — and can lead to an enhancement of protein adsorption at fluid interfaces (Tsapkina et al., 1992). 

FIGURE 12.12 Illustration of materials being adsorbed onto fluid interfaces (O-W or AW), thereby causing repulsion between two of such interfaces, (a) Anions, (b) soaps, (c) Tween-like surfactants, (d) neutral polymers, (e) proteins. Highly schematic the straight lines represent aliphatic chains. The repulsion is electrostatic (a and b), steric (c and d), or mixed (e). 

The adsorption of proteins at fluid interfaces is a key step in the stabilization of numerous food and non-food foams and emulsions.1 Our general goal is to relate the amino acid sequence of proteins to their surface properties, e. g. to the equation of state or other structural and thermodynamic properties. To improve this understanding, the effect of guanidine hydrochloride (Gu HC1) on /1-casein adsorption is evaluated in the framework of the block-copolymer model for the adsorption of this protein. At first the main features of the model are presented, and then the effect of Gu HC1 is interpreted using the previously introduced concepts. 

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