DNA Phase Behavior in the Presence of Oppositely Charged Surfactants

The interaction between DNA and alkyltrimethylammonium bromides of various chain lengths has been investigated. It is known that these systems phase separate with the formation of a precipitate; this important feature allows, for example, purification of nucleic acids. Phase maps were drawn for the aqueous systems illustrating the associative phase separation. The boundary of the two-phase region for the dilute part of the phase diagram was evaluated by turbidimetry, in both the absence and presence of salt. The extension of the precipitate region increases strongly with the surfactant alkyl chain length, and we observed no redissolution with an excess of surfactant. The addition of NaBr led to novel interesting findings. The phase diagram studies were correlated with the single molecule conformational behavior of the same systems as studied for very diluted solutions by fluorescence microscopy. DNA exhibits a discrete phase transition in the presence of cationic surfactants from coils to globules. Result...