Protein hydration layer molecular structure

Figure 46. A unified molecular mechanism of protein hydration dynamics and coupled water-protein fluctuations. The initial ultrafast dynamics in a few picoseconds (ii) represents local collective orientation or small translation motions, which mainly depend on local electrostatic interactions. On the longer time (12), the water networks undergo structural rearrangements in the layer, which are strongly coupled with both protein fluctuations and bulk-water dynamic exchange.

Proteins adsorbed at an oil-water interface may stabilize the oil droplets by the Derjaguin, Landau, Verwey, and Overbeek (DLVO) interactions and/or the steric stabilization mechanism. The proteins may possess or be capable of adopting extended structures, which protrude into a solution for a considerable distance from the interface. This extended hydrated layer may form the basis for steric stabilization of the emulsion. Interactions between the adsorbed protein layers can involve a reduction in conhgurational entropy as molecular chains overlap (Darling and Birkett, 1987). In addition, hydration of adsorbed hydrophilic components can lead to an enthalpic repulsion when two particles are in close proximity. This tends to force the oil droplets apart (Darling and Birkett, 1987). 

Thus we regard the hydrated protein double-layer as a two-dimensional gel-phase, with molecular linkages formed by hydrophobic interaction and/or ionic bonds. The rinsing experiments show that the upper protein layer is loosely attached, which indicates that this outer layer has a structure closer to the native state. The reduction in adsorbed amount and the electrical changes upon rinsing are in good agreement with such a structure. 

Protein function at solid-liquid interfaces holds a structural and a dynamic perspective [31]. The structural perspective addresses macroscopic adsorption, molecular interactions between the protein and the surface, collective interactions between the individual adsorbed protein molecules, and changes in the conformational and hydration states of the protein molecules induced by these physical interactions. Interactions caused by protein adsorption are mostly non-covalent but strong enough to cause drastic functional transformations. All these features are, moreover, affected by the double layer and the electrode potential at electrochemical interfaces. Factors that determine protein adsorption patterns have been discussed in detail recently, both in the broad context of solute proteins at solid surfaces [31], and in specific contexts of interfacial metalloprotein electrochemistry [34]. Some important elements that can also be modelled in suitable detail would be ... 

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