MOLECULAR APPROACH TO PROTEIN POLYMER INTERACTIONS IN ION-EXCHANGE CHROMATOGRAPHY

A model was developed and implemented to aid in understanding and pred icting the retention behaviour of proteins in ion-exchange chromatogra phy. The model structures chosen were calcium-loaded and -depleted alp ha-lactalbumin (ALC) and hen egg white lysozyme (HEWL) and a compariso n was made with chromatographic measurements. A characteristic charge of -3.4 was found under the experimental conditions applied for both f orms of ALC, and HEWL was not retained. The model explicitly considers all of the atoms, each being assigned a set of force field parameters . Because of the computational time necessary to include them, water m olecules were not taken into account, but a sigmoidal function of the dielectric permittivity was introduced in the calculations. Interactio n potential energies from bulk down to the contact were evaluated for each protein. The results were in qualitative agreement with those of the chromatographic experiments. It was possible to reproduce the diff erence in retention between both forms of ALC and also the behaviour o f HEWL.