Separation of plasmid DNA from protein and bacterial lipopolysaccharides using displacement chromatography

Cooperative multimodal retention of IgG, fragments, and aggregates on hydroxyapatite

Retention mapping of chimeric monoclonal IgG(1), Fc, Fab, F(ab')(2), and aggregated antibody was conducted on hydroxyapatite (HA) by systematically varying phosphate and chloride concentrations during gradient elution in order to characterize the interactions of each solute with calcium and phosphate residues on the solid phase. Lysozyme was used as a control to model cation exchange-dominant interactions. Bovine serum albumin was used as a control for calcium affinity-dominant interactions. Calcium affinity and phosphoryl cation exchange were positively cooperative for IgG-related species. Fc retention was dominated by calcium affinity, while retention of Fab was dominated by cation exchange. F(ab')(2) exhibited a curve shape similar to Fab, but stronger retention. The retention curve for intact IgG incorporated the distinctive elements of its fragments but stronger retention than that predicted by their addition to one another. Aggregate retention paralleled the curve for non-aggregated antibody, with stronger retention by both binding mechanisms. Experimental data revealed evidence of charge repulsion between IgG carboxyls and HA phosphate at low conductivity values. Electrostatic repulsion of amino residues and attraction of carboxyls by HA calcium appeared to be blocked by strong complexation of calcium with mobile phase phosphate.

DNA purification by triple-helix affinity precipitation

Recent advances in DNA-based medicine (gene therapy, genetic vaccination) have intensified the necessity for pharmaceutical-grade plasmid DNA purification at comparatively large scales. In this contribution triple-helix affinity precipitation is introduced for this purpose. A short, single-stranded oligonucleotide sequence (namely (CTT)(7)), which is capable of recognizing a complementary sequence in the double-stranded target (plasmid) DNA, is linked to a thermoresponsive N-isopropylacrylamide oligomer to form a so-called affinity macroligand (AML). At 4 degrees C, i.e., below its critical solution temperature, the AML binds specifically to the target molecule in solution; by raising the temperature to 40 degrees C, i.e., beyond the critical solution temperature of the AML, the complex can be precipitated quantitatively. After redissolution of the complex at lower temperature, the target DNA can be released by a pH shift to slightly alkaline conditions (pH 9.0). Yields of highly pure (plasmid) DNA were routinely between 70% and 90%. Non-specific co- precipitation of either the target molecule by the non-activated AML precursor or of contaminants by the AML were below 7% and presumably due to physical entrapment of these molecules in the wet precipitate. Ligand efficiencies were at least 1 order of magnitude higher than in triple-helix affinity chromatography.

Characterization and modeling of monolithic stationary phases: application to preparative chromatography

A methodology for characterizing and modeling preparative separations on monolithic ion-exchange stationary phases is presented. A dimensionless group analysis was carried out to determine the relative importance of mass transfer and kinetic resistances on this stationary phase. In contrast to conventional beaded morphologies, the continuous bed stationary phase was found to possess enhanced mass transport properties resulting in kinetic resistance as the dominant non-ideality. Accordingly, a reaction-dispersive steric-mass action formalism was successfully utilized for simulating preparative displacement chromatography on this resin. Since kinetics were found to be important on this column morphology, mobile phase salt concentration was found to be an important variable during displacement chromatography on this stationary phase. An increase in the mobile phase salt concentration was found to significantly improve the displacement separation of a model protein mixture. The formalism presented in this paper provides a better understanding of preparative chromatography in monolithic resin systems and a means of simulating separations on this class of chromatographic stationary phases.

Comparison of particulate and continuous-bed columns for protein displacement chromatography

A conventional anion exchange column packed with porous particles (BioScale Q2), and a novel continuous-bed column (UNO Q1) were compared for displacement separation of dairy whey proteins with polyacrylic acid as displacer. The steric mass action model was investigated as a means to aid and accelerate this development. Characteristic charges and steric factors were measured for the proteins and the displacer according to the model, and used together with the affinity constant derived from the adsorption isotherms for simulations, as well as for the construction of the affinity and operating regime plots. If possible, the latter two were used to select conditions for the actual experiments. In the case of the particle-based column, experimental results and simulations did not agree. In addition, the operating regime plot could not be constructed. The affinity plot did predict the order in the displacement train correctly, but gave misleading information concerning the possible effect of a change in displacer concentration. This is taken to be a result of the porous nature of the particles, which handicaps, to some extent, the interaction of the proteins and the displacer molecules with the adsorptive surface. Results were considerably better in case of the continuous-bed column, where there is no intraparticulate surface.

Polycations as displacer in high-performance bioseparation

Displacement chromatography is an interesting but up to now rarely used type of preparative biochromatography. The lack of well-engineered and accessible displacer contributes to this phenomenon. In this paper a novel type of displacer is introduced for cation-exchange displacement chromatography, which will soon become commercially available. The molecule is a well-defined PolyDADMAC [poly(diallyldimethylammonium chloride)] with a molar mass of less than 35000 g/mol, an exclusively linear structure and a molar mass polydispersity of less than 1.5. A method for synthesizing such a polymer at high yields is described. The PolyDADMAC is shown to be an efficient displacer of basic proteins from strong cation-exchange columns.