Protein adsorbed layer

Figure 4c shows one example of the time course of an SPR angle shift during exposure of a NH2-SAM to culture medium supplemented with 2% fetal bovine serum (FBS). It also includes the time course of the fraction of adherent cells on the same surface determined by TIRFM observation (Fig. 2). The SPR angle shift rapidly increased, and then leveled off within a few minutes. Cells adhered much more slowly than proteins. Those results indicated that serum proteins in a medium rapidly adsorbed to the surface then, cells interacted with the adsorbed protein layer, as shown schematically in Fig. 5.

When the surfaces of the protein molecules and the sorbent are predominantly polar, it is probable that some hydration water is retained between the adsorbed protein layer and the sorbent surface. Then, the contribution from changes in the state of hydration to the Gibbs energy of protein adsorption, AadsGhydr, will be minor. When the surfaces are... 

The 3D structure of a native protein (in aqueous solution) is only marginally thermodynamically stable and it is sensitive to changes in its environment. It is, therefore, not surprising that adsorption is often accompanied by rearrangements in the protein s 3D structure. It is commonly observed experimentally that the thickness of an adsorbed protein layer is comparable to the dimensions of the protein molecule in solution. It indicates that the adsorbed protein molecules remain compactly structured. 

Thickness of Adsorbed Protein Layers on Glass Adsorption of Proteins in Multilayers... 

V. Hlady, D. R. Reinecke, and J. D. Andrade, Fluorescence of adsorbed protein layers ... 

When the thickness of the draining film is less than twice the thickness of the adsorbed protein layer, (i.e. TLs), the approaching faces of the film experience a steric interaction because of the overlap of the adsorbed protein layers. 

From the above equation, the variation of equilibrium disjoining pressure and the radius of curvature of plateau border with position for a concentrated emulsion can be obtained. If the polarizabilities of the oil, water and the adsorbed protein layer (the effective Hamaker constants), the net charge of protein molecule, ionic strength, protein-solvent interaction and the thickness of the adsorbed protein layer are known, the disjoining pressure II(x/7) can be related to the film thickness using equations 9 -20. The variation of equilitnium film thickness with position in the emulsion can then be calculated. From the knowledge of r and Xp, the variation of cross sectional area of plateau border Qp and the continuous phase liquid holdup e with position can then be calculated using equations 7 and 21 respectively. The results of such calculations for different parameters are presented in the next session. 

FIGURE 2. Continuous phase liquid holdup profiles (CPLHP) for different centrifugal accelerations for droplet size R = 5jc10 /w, surface concentration r=5jcl0 il g//n, ionic strength m =0.1M,thickness of adsorbed protein layer L, = 12xl(T /n and zeta potential = 12mV. 

FIGURE 7. Continuous phase liquid holdup profiles (CPLHP) for different zeta potentials for droplet size / =50bcl0" /n, centrifugal acceleration Qc = 10 m lsec, ionic strength m=0.1Af, thickness of adsorbed protein layer Lg = 12xl(T m and surface concentration r = 5jc IQT kglnr. 

Another way to interpret the above observations would be in terms of the general principle that effective steric stabilization of polymer-coated droplets requires that the continuous phase be a good quality solvent for the polymeric stabilizer. Under poor quality solvent conditions (asi-casein at high ionic strength), the required entropic stabilizing repulsion of the adsorbed protein layer is converted into a destabilizing polymer-mediated attraction (Dickinson and Stainsby, 1982 Dickinson, 2006). 

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

Thermodynamically unfavourable interactions between two biopolymers may produce a significant increase in the surface shear viscosity (rf) of the adsorbed protein layer. This change in surface rheological behaviour is a consequence of the greater surface concentration of adsorbed protein. For instance, with p-casein + pectin at pH = 5.5 and ionic strength = 0.01 M (Ay = 2.6 x 10 m3 mol kg-2), the surface shear viscosity at the oil-water interface was found to increase by 20-30%, i.e., rp = 750 75 and 590 60 mN s m-1 in the presence and absence of polysaccharide. These values of rp refer to data taken some 24 hours following initial protein layer formation (Dickinson et al., 1998 Semenova et al., 1999a). 

Bos, M.A., van Vliet, T. (2001). Interfacial rheological properties of adsorbed protein layers and surfactants. Advances in Colloid and Interface Science, 91, 437-471. 

Benjamins, J., van Voorst Vader, F. (1992). The determination of the surface shear properties of adsorbed protein layers. Colloids and Surfaces, 65, 161-174. 

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