Thermodynamics of protein adsorption

Norde W and Lykiema J 1979 Thermodynamics of protein adsorption J. Colloid Interface Sci. 71 350-66... 

It has been known that adsorption kinetics and/or thermodynamics of proteins depend on the electric or electrochemical properties of solid supports on which the proteins are adsorbed. This has led us to elucidate the effects of electrode potential on the adsorption behavior of avidin on the electrode surface. For this purpose, the electrode potential of a Pt electrode was varied systematically in the range of -0.5-+2.0 V in an avidin solution (pH 7.4). Although the data was somewhat scattered, a general trend was observed that the adsorption of avidin is suppressed by the application of a positive potential (+1.0-+2.0 V). This may be originating from the fact that avidin is a basic protein and has net positive charges in the solution of neutral pH. In the potential range tested, no significant acceleration in the adsorption was induced. 

In line with the Gibbs adsorption equation (equation 3.33 in chapter 3), the presence of thermodynamically unfavourable interactions causes an increase in protein surface activity at the planar oil-water interface (or air-water interface). As illustrated in Figure 7.5 for the case of legumin adsorption at the n-decane-water interface (Antipova et al., 1997), there is observed to be an increase in the rate of protein adsorption, and also in the value of the steady-state interfacial pressure n. (For the definition of this latter quantity, the reader is referred to the footnote on p. 96.)... 

Table 7.1 shows that rather similar results were also found by Makri et al. (2005) for samples of coarse emulsions containing thermodynamically incompatible mixtures of legume seed protein + xanthan gum. The protein surface load was found to be enhanced in the presence of xanthan gum, especially at elevated ionic strengths. That is, there was observed to be an increase in the adsorption of legume seed proteins at the surface of the emulsion droplets which could be attributed to an increase in the thermodynamic activity of the proteins in the system in the presence of the incompatible polysaccharide (see Table 7.1). Associated with the greater extent of protein adsorption, the authors reported an enhancement in the emulsion stability.

We will briefly outline the principle thermodynamic considerations that comprise the underlying key issues of protein adsorption on surfaces. Subsequently, we will describe strategies that have been followed for the design of protein-repellent surface coatings. For details on protein adsorption, as well as further discussion on this particular topic, the reader is referred to more comprehensive reviews [31, 32],... 

Miller R, Fainerman VB, Aksenenko EV, Makievski AV, Kraegel J, Liggieri L, Ravera F, Wuestneck R, and Loglio G (2000) "Surfactant Adsorption Kinetics and Exchange of Matter for Surfactant Molecules with Changing Orientation within the Adsorption Layer" in Emulsion, Foams, and Thin Films, Mittal and Kumar Editors, Ch. 18, Marcel Dekker, pp. 313-327 Miller R, Fainerman VB, Makievski AV, Leser M, Michel M and Aksenenko EV (2004) Determination of Protein Adsorption by Comparative Drop and Bubble Profile Analysis Tensiometry. Colloids Surfaces B 36 123-126 Neumann AW and Spelt JK Eds., Applied Surface Thermodynamics, Surfactant Science Series, Vol. 63, Marcel Dekker Inc., New York, 1996 Noskov B and Logho G (1998) Dynamic surface elasticity of surfactant solutions. Colloids Surfaces A 143 167-183... 

The state of the art of the thermodynamic description of protein adsorption layers was recently described in detail elsewhere.1 On its basis also the kinetics of adsorption can be explained much better, i.e. taking into account the peculiarities of proteins arriving at the interface.2 On the other hand, rheological studies are still on a more descriptive level and quantitative models do not exist yet to explain the relaxation processes going on in adsorption layers during perturbations. 

Adsorption kinetics, mainly studied by dynamic surface tension measurements, shows many features very much different from that of typical surfactants (Miller et al. 2000). The interfacial tension isotherms for standard proteins such as BSA, HSA, (3-casein and (3-lactoglobulin were measured at the solution/air interface by many authors using various techniques. The state of the art of the thermodynamics of adsorption was discussed in Chapter 2 while isotherm data for selected proteins were given in the preceding Chapter 3. Here we want to give few examples of the dynamic surface pressure characteristics of protein adsorption layers. 

The model, in terms of protein adsorption, is based on surface thermodynamic considerations Consider a protein molecule (P) initially suspended in a buffer solution (L) adsorbing to a solid surface (S) which is also immersed in the same buffer as illustrated schematically in Figure 4. In the absence of specific interactions of the receptor-ligand type, the change in the Helmhotz free energy due to the process of adsorption is ... 

When a medical device is in contact with body fluid such as blood, the first thing that occurs on the surface is protein adsorption [96-98]. Proteins in solution trying to minimize the total surface energy is the thermodynamic driving force of protein adsorption on solid surfaces. In blood contact protein adsorption is believed to be the initial event in thrombus formation [99-101], calcification [102-104], and biofilm attachment [105-107], which leads to the failure of implanted devices. Therefore, protein-reducing surface modifications of polyurethane biomaterials have been applied to improve the service life of implants. Previous studies of protein adsorption have focused on adsorption of albumin, IgG, and Fg, which are the predominant three proteins in blood plasma. Surface protein adsorption can be quantitated by several methods such as quartz crystal microbalance (QCM) [108-112], surface plasmon resonance (SPR) [113-118], and iodonization radiolabeling [78,119-125]. 

The thermodynamics of snrface adsorption has been extensively described by Gibbs adsorption theory (Chattoraj and Birdi, 1984 Spaull, 2004 Zhou, 1989). Further, Gibbs adsorption theory has also been applied in the analyses of diverse phenomena (snch as solid-liqnid or Uqnidj-liqnidj, adsorption of solute on polymers, etc.). In fact, in any systan where adsorption takes place at an interface the Gibbs theory will be applicable (such as solid-liquid protein molecnle-solntion with solutes that may adsorb). 

In summary, then, the following general statements can be made regarding protein adsorption. The surface activity of a protein is a cumulative property influenced by many factors, including size, shape, charge, surface hydrophobicity, and thermodynamic stability. Protein adsorption exhibits diversity in behavior from one surface to another and from one protein to another. This diversity results from the complexity of the protein structure itself and from the many variables on which protein adsorption depends. 

Mitropoulos, V., Miitze, A., Fischer, P. (2014). Mechanical properties of protein adsorption layers at the arr/water and oil/water interface A comparison in light of the thermodynamical stability of proteins. Advance in Colloid and Interface Science, 206, 195-206. 

J, G. E. M. Fraaije, W. Norde, J. Lyklema, Interfacial thermodynamics of protein adsorbtion and ion co-adsorption. 111. Electrochemistry of bovine serum albumin adsorption on silver iodide, Biophys. Chem., 1991,41, pp. 263-276. 

Upon surface-thermodynamic analysis of protein adsorption onto hydrophilic surfaces such as silica or glass, based on the known surface properties of the hydrophilic protein as well as of the hydrophihc mineral substratum, one would arrive at the conclusion that the macroscopic-scale interactions in a neutral aqueous medium are so strongly repulsive that adsorption should not occur, cf. van Oss et al. (1995a). In spite of this prediction, protein adsorption onto hydrophilic glass, silica, etc. does take place, at neutral pH (MacRitchie, 1972 van Oss et al., 1995b). The mechanism of protein adsorption onto hydrophilic surfaces is quite different from that operative with... 

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