277724 Counterion Effects On Protein Adsorption Equilibrium and Kinetics in Polymer-Grafted Cation Exchangers

Tuesday, October 30, 2012: 12:30 PM
404 (Convention Center )
Ernie Perez Almodovar, Chemical Engineering, University of Virginia, Charlottesville, VA and Giorgio Carta, Department Chemical Engineering, University of Virginia, Charlottesville, VA

Protein binding equilibrium and mass transfer kinetics are studied for cation exchangers containing charged polymer grafts as well as for a macroporous matrix in pH 5 acetate buffers using sodium, tetrabutyl ammonium (TBAH), arginine, and calcium as counterions and a monoclonal antibody (mAb) as a model protein. Dynamic light scattering shows that there is no significant effect of the counterion type on the mAb aqueous diffusivity. The counterion type also does not affect substantially the structure of the polymer grafts, nor does it affect the stoichiometry of the protein ion exchange process. While no counterion effects are also observed on the protein mass transfer kinetics for the macroporous matrix, very large effects are seen for the polymer grafted matrices with protein adsorption rates increasing dramatically in the order Ca++ > Arg+ > Na+ > TBAH+. This order is the same order in which the relative protein binding strength decreases. Accordingly, the counterions leading to weaker protein binding also lead to faster protein diffusion. Although the quantitative aspects are different, the same trends hold for different proteins (lysozyme, and lactoferrin) and for an agarose-based matrix also containing grafted polymers (Capto  S) . The underlying mechanism is qualitatively consistent with protein transport occurring through a hopping process driven by the adsorbed protein concentration within the apparently flexible network structure formed by the grafted polymers. From a practical viewpoint, the results show that improved protein adsorption kinetics in polymer-grafted cation exchanger and, hence, improved performance, can be obtained by selecting particular counterions.

Extended Abstract: File Not Uploaded
See more of this Session: Advances In Bioseparations
See more of this Group/Topical: Separations Division