DNA Displacers:-

Nucleic acids such as DNA and RNA constitute a second important group of biological macromolecules besides proteins. While proteins have for some time now been isolated  preparatively in fairly large scales, DNA purification has only recently entered that realm.

Compared to proteins, which are constructed from more than 20 amino acids of varied hydrophobicity and which in addition can contain complex sugars, lipids, or even metal ion, the structure of the DNA molecule is much simpler. From a chromatographic point of view, DNA can be considered as a very large linear polyanion with a very homogeneous charge distribution. Both anion exchange and hydroxyapatite chromatography can be used for its purification.

Nevertheless, DNA also presents some specific challenges to large-scale preparation. Concentrated DNA solutions are very viscous. Especially in elution chromatography, this causes problems since the peak maximum should stay below the viscosity/concentration limit. As a result only low concentration preparations can be obtained. In this context, displacement chromatography has the theoretical advantage of allowing to keep the concentration in the entire zone just below the viscosity/concentration limit. The overall concentration of the “product fraction” will be higher in this case.

According to a recent publication, the separation of protein and plasmid DNA as well as  that of DNA and  lipopolysaccharides is possible by displacement chromatography. Linear  polyacrylic acid was successfully used as displacer. A particularity was the fact that conventional stationary phase materials based on porous anion exchanger or hydroxyapatite beads could not be used for the separation of the plasmid DNA from a standard protein . The use of a monolithic column, on the other hand, yielded promising results. In this case protein and DNA capacities were comparable. Further research is obviously necessary. However, the investigation of DNA displacement also offers some principal opportunities, for example, to elucidate the effect of size and rigidity, or charge density and chemistry for the competitive adsorption of linear polyelectrolytes.