NOTE
Electrostatic Contribution to the Energy and Entropy of Protein Adsorption and proton dissociation. In addition, van der Waals (primarily dispersion) interactions may play a role (4).
Protein adsorption is complicated by the many contributions to
We focus here on electrostatics, which are dominant in such important the overall thermodynamics, and as a result there is a need for applications as ion-exchange chromatography. In the model of Norde and mechanistic models in interpreting experimental data. We focus on Lyklema (3, 5), the electrostatic contribution is found by treating the adthe electrostatic contribution to the adsorption thermodynamics and, sorbed protein as a flat sheet comprising multiple planar layers, differing specifically, on calculating the relative contributions of enthalpic and in dielectric constant and charge distribution, adjacent to the adsorbent entropic driving forces to the electrostatic component of the free surface. The electrical potential is thus a function only of distance from the energy of adsorption. The model used is a colloidal one in which adsorbent surface, and protein-protein interactions within the adsorbate the protein, modeled as a sphere carrying a point charge at its center, layer are not included. The enthalpy and entropy of adsorption are found interacts with a planar adsorbent surface of opposite charge as well by differentiation of the expression for the free energy of adsorption, but as with neighboring adsorbent molecules. It is found that the entropic since the temperature dependence of the Debye parameter k is neglected, the entropic part that is found arises solely from the temperature dependence contribution dominates the protein-surface interaction, which is of the dielectric constants of the layers. The purpose of the present contribugenerally but not uniformly attractive; this contribution reflects the tion is to present a new analysis of the electrostatic contribution to the liberation of counterions from the double layers adjacent to the enthalpy and entropy of adsorption that accounts more realistically for the protein and adsorbent surfaces. Protein-protein interactions are molecular structure of the adsorbate layer.
found to be generally repulsive but weak, with energetic and entropic contributions similar in magnitude. The dominance of entropic ef-THEORY AND METHODS fects is consistent with several reported calorimetric measurements, but additional effects, such as the release of water molecules from Although protein electrostatics calculations that account for both intrathe interacting surfaces, confound attempts to compare theory and and extramolecular charges can be undertaken in different ways, continuum experiment directly.