The non-electrostatic effects associated with protein adsorption on an anion-exchange adsorbent

Ion-exchange chromatography is a very popular and useful purification technique that is widely used in the pharmaceutical industry. With the very recent expansion of the biopharmaceutical sector, the role of IEC as a purification technique is more critical than ever. Despite the popularity of this technique, much is still unknown about the underlying mechanism of protein adsorption onto ion-exchange adsorbents.; In this study, flow microcalorimetry was extensively used to examine the adsorptive behavior of proteins. Calorimetric results have shown the protein adsorption onto an anion-exchange adsorbent was endothermic in all cases even when the protein surface and the ion-exchanger surface possessed charges of opposite polarity. This clearly demonstrated that the entropic component of the Gibbs Free Energy is the driving force for adsorption. Moreover it was shown that the heat-of-adsorption is highly dependent on surface coverage and temperature.; Preferential interaction analysis revealed that water-release associated with the adsorption of proteins onto an ion-exchange surface is not necessarily negligible. In fact can on the same order of magnitude as for hydrophobic interaction chromatography (HIC). These data support the calorimetric data in that the adsorptive driving force consists of more than just simple electrostatics.; The colloidal ion-exchange model was used to simulate protein isotherms in presence of 3 different salts at two different temperatures. This approach was chosen because the model framework allowed for the incorporation of repulsive and entropic effects. Simulation results clearly demonstrated that the entropic contribution arising from water-release is a major component of the adsorptive driving force underlying protein adsorption onto an anion-exchange adsorbent. Moreover it was also shown that repulsive interactions between adsorbed molecules are also a vital component of any isotherm model.