DNA – DOPC – gemini surfactants complexes: effect of ionic strength

The effect of ionic strength on DNA condensation by cationic liposomes prepared as a mixture of ethane-1,2-diylbis(dodecyl-dimethylammonium bromide) (C2GS12) and dioleoylphosphatidylcholine (DOPC) was studied using fluorescence spectroscopy. The DNA condensation followed by changes in emission intensity of ethidium bromide shows a strong dependence on the ionic strength of the solution. At physiologically relevant ionic strength (0.15 mol/l NaCl), the amount of DNA condensed between lipid bilayers is approximately 40% lower compared to 0.005 mol/l NaCl. The structure of formed complexes was studied using small angle X-ray diffraction (SAXD). DNA–C2GS12–DOPC complexes form a condensed lamellar phase organisation, which is partially disrupted by the increase of ionic strength. Both the lamellar repeat distance and DNA–DNA distance show dependence on C2GS12/DOPC molar ratio, temperature and also on ionic strength. We found that the method of preparation significantly affects both the quality of organisation and the structural parameters of complexes as discussed in the paper.