Interactions between protein layers

The interest in vesicles as models for cell biomembranes has led to much work on the interactions within and between lipid layers. The primary contributions to vesicle stability and curvature include those familiar to us already, the electrostatic interactions between charged head groups (Chapter V) and the van der Waals interaction between layers (Chapter VI). An additional force due to thermal fluctuations in membranes produces a steric repulsion between membranes known as the Helfrich or undulation interaction. This force has been quantified by Sackmann and co-workers using reflection interference contrast microscopy to monitor vesicles weakly adhering to a solid substrate [78]. Membrane fluctuation forces may influence the interactions between proteins embedded in them [79]. Finally, in balance with these forces, bending elasticity helps determine shape transitions [80], interactions between inclusions [81], aggregation of membrane junctions [82], and unbinding of pinched membranes [83]. Specific interactions between membrane embedded receptors add an additional complication to biomembrane behavior. These have been stud-... 

Interactions between proteins and polysaccharides give rise to various textures in food. Protein-stabilized emulsions can be made more stable by the addition of a polysaccharide. A complex of whey protein isolate and carboxymethylcellulose was found to possess superior emulsifying properties compared to those of the protein alone (Girard et al., 2002). The structure of emulsion interfaces formed by complexes of proteins and carbohydrates can be manipulated by the conditions of the preparation. The sequence of the addition of the biopolymers can alter the interfacial composition of emulsions. The ability to alter interfacial structure of emulsions is a lever which can be used to tailor the delivery of food components and nutrients (Dickinson, 2008). Polysaccharides can be used to control protein adsorption at an air-water interface (Ganzevles et al., 2006). The interface of simultaneously adsorbed films (from mixtures of proteins and polysaccharides) and sequentially adsorbed films (where the protein layer is adsorbed prior to addition of the polysaccharide) are different. The presence of the polysaccharide at the start of the adsorption process hinders the formation of a dense primary interfacial layer (Ganzelves et al., 2008). These observations demonstrate how the order of addition of components can influence interfacial structure. This has implications for foaming and emulsifying applications. 

Thus, if the pH is less than the isoelectric point (p/ 4.7), a protein is positively charged, while the inner layer of polyelectrolyte microcapsules is presented as a polycation, the protein molecules are distributed throughout its volume. Protein molecules lose their chaige values near the isoelectric point and are concentrated in the wall space of the capsule due to hydrophobic interactions with a polyelectrolyte shell. If the polyanion PSS was nsed as the first layer in the formation of a shell, the protein at all pH valnes in the range stndied was located in the wall space (Figure 3). We attribute this to the electrostatic interaction between protein molecules and the polyelectrolyte at low pH and hydrophobic interactions in the region of the isoelectric point. 

The formation of a two-dimensional viscous layer along the surface. Repulsive interactions between adsorbed layers Adsorbed surface-active components, e.g. proteins, peptides and lipids. Absences of defoaming components such as free oil... 

Figure 5. Three physical pictures representing the possible nature of the interactions between proteins and low molecular weight polymers (a) Picture 1, physical exclusion only (b) Picture 2, a weak attraction exists between the polymer and the protein in addition to physical exclusion and (c) Picture 3, a stronger attraction between the polymer coils and the protein causes the formation of an adsorbed polymer layer about the protein.

Exploratory in vivo experiments show the influence of coating on the adsorbed protein layer in the prosthesis and the deposit of microthrombi. From this the basic significance of interaction between proteins and the biomaterial, as well as the significance of coatings as surface modifications were stressed. 

The interactions between proteins and low-molecular-weight surfactants at interfaces have crucial effects on physical states of interfaces, such as interfacial energy, interfacial rheological properties, C potential, and thickness of adsorbed layer. The competitive displacement of globular proteins by surfactants at liquid interfaces (normally, oil-water interfaces) has been extensively... 

PLA outer layers and observed that the mechanical properties of the SPI film were improved by lamination with PLA layers, which were comparable to those of low- and high-density polyethylene (LDPE and HOPE, respectively). More recently, Ghanbarzadeh and Oromiehi (2009) prepared bilayer films based on plasticized whey protein films. They also prepared olive oil-plasticized zein films by casting and subsequently laminated them by compression-moulding and discovered that there was an improvement in tensile properties due to favourable interactions between the layers. 

Ions can significantly influence the structure of water at interfaces. Hydration can be caused by the overlap of layers of hydrated ions adsorbed on the surfaces. On mica, for example, the dehydration of adsorbed cations is most likely the main cause for the short-range repulsion between two approaching surfaces [451]. Computer simulations between smooth hydrophilic surfaces confirm a layered structure of the water molecules and as a result a periodic force [1159,1160]. Paunov et al. [1171] used this hypothesis to explain the interaction between proteins in suspensions. 

Protein adsorption has been studied with a variety of techniques such as ellipsome-try [107,108], ESCA [109], surface forces measurements [102], total internal reflection fluorescence (TIRE) [103,110], electron microscopy [111], and electrokinetic measurement of latex particles [112,113] and capillaries [114], The TIRE technique has recently been adapted to observe surface diffusion [106] and orientation [IIS] in adsorbed layers. These experiments point toward the significant influence of the protein-surface interaction on the adsorption characteristics [105,108,110]. A very important interaction is due to the hydrophobic interaction between parts of the protein and polymeric surfaces [18], although often electrostatic interactions are also influential [ 116]. Protein desorption can be affected by altering the pH [117] or by the introduction of a complexing agent [118]. 

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