Effect of dextran layer on protein uptake to dextran-grafted adsorbents for ion-exchange and mixed-mode chromatography

In the current research, a series of dextran-grafted adsorbents were prepared using sulfopropyl and 4-(1H-imidazol-1-yl) aniline as chromatographic ligands for ion-exchange (IEC) and mixed-mode chromatography (MMC) to respectively investigate the influence of dextran layer on adsorption of γ-globulin. Experimental evidences of static adsorption on dextran-grafted IEC adsorbents showed that adsorption capacity of γ-globulin increased with dextran content. It could be attributed to the multilayer adsorption of charged protein in dextran layer and thus further induced a significant electrical potential gradient at the boundary of adsorbed area and its proximity, improving mass transfer in combination with concentration gradient. In contrast to IEC adsorbents, adsorption capacity and effective diffusivity of dextran-grafted MMC adsorbents did not change obviously with dextran grafting. It was considered that hydrophobic ligands immobilized onto dextran-grafted MMC adsorbents were stuck together at pH 8.0, resulting in the collapse of dextran layer. In concert with measured effective porosity for γ-globulin at pH 4.0, it was confirmed that dextran layer in MMC adsorbent was more complicated and influenced significantly by buffer pH. It was also manifested by protein adsorption at different pHs. Thus, it revealed the complexity in intraparticle mass transfer of the protein in dextran-grafted MMC adsorbent.