Exploitation of the Coil−Globule Plasmid DNA Transition Induced by Small Changes in Temperature, pH Salt, and Poly(ethylene glycol) Compositions for Directed Partitioning in Aqueous Two-Phase Systems

In this study, the interplay of two linked equilibria is examined, one concerning an aqueous two-phase system (ATPS) composed of poly(ethylene glycol) (PEG) and salt employed to partition plasmid DNA (pDNA), and the other a potential structural transition of pDNA depending on PEG and salt concentration and other system parameters. The boundary conditions for pDNA partitioning are set by PEG and salt concentrations, PEG molecular weight, pH, and temperature. While investigating these parameters, it was found that a small increase/decrease of the respective values led to a drastic and significant change in pDNA behavior. This behavior could be attributed to a coil−globule transition of the pDNA triggered by the respective phase conditions. The combination of this structural change, aggregation effects linked to the transition process, and the electrostatic potential difference found in PEG−salt systems thus offers a sensitive way to separate nucleic acid forms on the basis of their unique property to undergo coil−globule transitions under distinct system properties.