Department of Chemical Engineering, University of Virginia, Charlottesville, VA 22901, USA.
J Chromatogr A. 2012 Aug 31;1253:83-93. doi: 10.1016/j.chroma.2012.06.100. Epub 2012 Jul 11.
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, tetra-n-butylammonium (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.
研究了含带电聚合物接枝的阳离子交换剂以及大孔基质在 pH 5 醋酸盐缓冲液中的蛋白质结合平衡和传质动力学，以钠离子、四丁基氢氧化铵（TBAH）、精氨酸和钙离子作为反离子，以单克隆抗体（mAb）作为模型蛋白。动态光散射表明，反离子类型对 mAb 水相扩散系数没有显著影响。反离子类型也不会对聚合物接枝的结构产生实质性影响，也不会影响蛋白质离子交换过程的化学计量。对于大孔基质，蛋白质传质动力学也没有观察到反离子效应，而对于聚合物接枝基质，则观察到非常大的效应，蛋白质吸附速率按 Ca⁺⁺>Arg⁺>Na⁺>TBAH⁺的顺序急剧增加。这个顺序与相对蛋白质结合强度降低的顺序相同。因此，导致蛋白质结合较弱的反离子也会导致蛋白质扩散更快。尽管定量方面有所不同，但不同蛋白质（溶菌酶和乳铁蛋白）和也含有接枝聚合物的琼脂糖基质（Capto™ S）的相同趋势仍然存在。潜在的机制与蛋白质通过吸附在接枝聚合物形成的明显灵活网络结构内的蛋白质浓度驱动的跳跃过程进行传输在定性上是一致的。从实际的角度来看，结果表明通过选择特定的反离子，可以在聚合物接枝阳离子交换剂中获得改善的蛋白质吸附动力学，从而提高性能。
