Proteins adsorption hysteresis

Measurements with oxygen-plasma-treated probes were performed in air, deionized water, and the same PBS buffer as used in the protein-adsorption experiments. Force-versus-distance curves in air with an oxygen-plasma-treated probe (k = 0.03 N/m) revealed no significant differences between the EG3-OMe SAMs on gold and silver. A large adhesion hysteresis primarily due to capillary forces was found for both surfaces. Pull-off... 

Lin et al. [24] studied adsorption-desorption isotherm hysteresis exhibited by /-lactoglo-bufin A on a weakly hydrophobic surface. They found that the desorption isotherm at pH 6.0 overlapped with the adsorption isotherm and that the adsorption-desorption process of /-lactoglobulin A under this condition could be characterized by a fully reversible Langmuir model. The desorption isotherm at pH 4.5, however, did not coincide with the adsorption isotherm, giving rise to hysteresis. This would suggest that protein adsorption experiments carried out under mild conditions of pH at relatively hydrophilic siufaces might be treated with the assumption that reversible equihbrium exists between the bulk and interface. 

The adsorption of macromolecules is rarely an equilibrium process. Just as the properties of synthetic polymers are often dependent on non-equilibrium processes and relaxation phenomena30), so do the properties of adsorbed proteins depend on time, metastable states, and hysteresis processes. 

Clearly, proteins with a high concentration of binding sites on their surfaces may adsorb in the proper orientation, resulting in a multipoint attachment and high adsorption-free energy, even without any conformational adjustment. Thus, hysteresis can be present in some systems even at very short contact times. Proteins with very stable tertiary or quaternary structures may not show significant time-dependence due to the low probability for conformational change. 

Adsorption of polymers, including proteins, polysaccharides, and so on, is usually irreversible with respect to changes in the concentrations of these components in solution. It implies that, within the time of the experiment, the ascending branch of the adsorption isotherm F/c ) does not coincide with the descending branch, or, in other words, that the adsorption isotherm contains a hysteresis loop. This situation is schematically depicted later in Figure 15.13. 

The complexity of the phenomena undergone by a protein after adsorption of polar molecules explains why this matter is so difficult to model. The first attempts to account for them were tried by one of the present authors, who formulated a model to account for heterogeneity, allostericity and hysteresis m water adsorption on proteins [60, 61], and have been recently reconsidered using a modification of a model proposed by Landsberg [62] to account of the Elovich equation in chemisorption phenomena. 

Fabric woven T. reesei TC, CBH-rich, EG-rich Effects of agitation on the adsorption-desorption behaviour Weight loss, strength loss, softness, shear and bending hysteresis, bound protein, reducing sugars... 

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