Implications from the grafting density and ionic capacity effects on protein adsorption to poly (N,N-dimethylaminopropyl acrylamide)-grafted sepharose FF

Our previous study reported a novel protein ion-exchanger, N,N-dimethylaminopropyl acrylamide (DMAPAA)-grafted Sepharose FF, of very high protein adsorption capacity and uptake rate. To gain new insight into the polymer grafting effects on protein adsorption and chromatography, 18 DMAPAA-grafted anion exchangers of four grafting densities and various chain lengths (i.e., ionic capacities, ICs) were prepared and named as FF-Brx-pDMAPAAn (x represents grafting density and n stands for IC in mmol/L). It was found that an optimal IC existed at each grafting density to present a maximal capacity. Of the four optimal-IC resins, FF-Br3-pDMAPAA587 showed the highest capacity (377 mg/mL), but the protein uptake rate, defined as the ratio of effective pore diffusivity to free diffusivity (D-e/D-0), was smaller than the resin of a similar ionic capacity but lower grafting density (FF-Br2-pDMAPAA592). Consequently, the dynamic binding capacity (DBC) of FF-Br2-pDMAPAA592 was higher than that of FF-Br3-pDMAPAA587 at flow velocities higher than 450 cm/h. Moreover, FF-Br3-pDMAPAA587 showed higher adsorption capacity than FF-Br2-pDMAPAA592 at 0-150 mmol/L NaCl, leading to its higher DBC values as compared to FF-Br2-pDMAPAA592 in the same salt concentration range. Taken together, DMAPAA-grafted resins of different grafting densities would be useful for purifying feedstocks of different ionic strengths.