Solubilization of DNA−Cationic Lipid Complexes in Hydrophobic Solvents. A Single-Molecule Visualization by Fluorescence Microscopy

The solubilization of DNA−lipid complexes in low-polar organic solvents was studied with the use of the fluorescence microscopy technique. It was demonstrated that the transfer of large T4 DNA complexed with cetyltrimethylammonium bromide (CTAB) and didodecyldimethylammonium bromide (DDAB) is not possible from the aqueous DNA−CTAB and DNA−DDAB solutions. On the other hand, dry DNA−CTAB and DNA−DDAB complexes were successfully dissolved and visualized in some of the studied organic solvents. DNA−DDAB complexes were found to be better soluble, compared to the DNA−CTAB complexes, due to the higher hydrophobicity of DDAB. The ability of the organic solvents to solubilize DNA−lipid complexes was also found to be different, as follows: chlorobenzene > toluene > chloroform, cyclohexane. It was shown that an increase of temperature enhances the solubilization of DNA−lipid complexes. The hydrodynamic radii of T4 DNA−lipid complexes in organic solvents were calculated from the corresponding translational diffusion constants. The obtained data implied that T4 DNA−lipid complexes in hydrophobic liquids have a highly compacted globular conformation and consist of a single T4 DNA macromolecule.