Ethanol-induced compaction of DNA: a viscosimetry and dynamic light scattering study

The condensation effect of ethanol on the DNA conformation in ethanol-water mixtures has been investigated by means of viscosimetry and dynamic light scattering measurements. A conformational transition was observed at a volume fraction close to 40%, where a sort of structural transition occurs from normal B-DNA to a more compact form. This behaviour differs from that experienced by the same system when the condensation effects are induced by charged surfactants. In this latter case, the analysis of the scattered light autocorrelation functions indicate the presence of a bimodal chain size distribution, characterized by two different average values and indicating the simultaneous presence of a coil and compact globule state. In the present case, a monomodal distribution is found and the mechanisms of DNA compaction are preferably governed by solvent interactions both of electrostatic nature, through changes in the solvent permittivity, as well as interactions associated with some kind of "hydrophobic clustering" of alcohol molecules, above a threshold concentration