DNA-induced inter-particle cross-linking during expanded bed adsorption chromatography: Impact on future support design

We have investigated the effects of adsorbent size, ionic capacity and surface immobilised polymers on dynamic capacity and changes occurring to beds of anion-exchangers during the binding of DNA. During application of low concentrations of “3–20 kilobase” calf thymus DNA feeds to expanded beds of anion-exchangers, the bed heights dropped progressively as DNA molecules physically cross-linked neighbouring adsorbent particles together, to form severely aggregated fluidised beds. In plots of dynamic binding capacities and absolute changes in bed porosity at maximum contraction, against the inverse of the mean hydrated particle radii, the anion-exchangers were observed to split into three distinct, but different clusters in each case. The highest index of surface packing of DNA was observed for two prototype pellicular supports, one derivatised with highly charged high molecular mass polyethyleneimine (Mr∼50 000) and the other with long dextran (Mr∼500 000) chains weakly derivatised with DEAE. However, the ability of the surfaces of these two matrices to bring about bed contraction, was strikingly different. The highly charged surface afforded by coupling of polyethyleneimine exhibited a three-fold higher tendency to interact with neighbouring particles in the presence of DNA than that of the dextran DEAE support. The implications of these findings on the design of future expanded bed materials for separation of both proteins and nucleic acids are discussed.