Dynamics of DNA adsorption on and release from SDS-DDAB cat-anionic vesicles: a multitechnique study.

DNA adsorption and release from cat-anionic vesicles made of SDS-DDAB in non- stoichiometric amounts was investigated by different electrochemical, spectroscopic and bio-molecular strategies. The characterisation of the vesicular system was performed by dynamic light scattering, which allowed estimating both size and its distribution function(s). The interaction dynamics was followed by dielectric spectroscopy and ?-potential, as well as by agarose gel electrophoresis, AGE. Also, circular dichroism, CD, measurements were carried out, to ascertain possible structural rearrangements of DNA, consequent to the interactions with the cat-anionic vesicles. CD demonstrates that vesicle-bound DNA retains its native conformation. The results obtained by the aforementioned techniques are consistent and indicate that binding saturation is obtained at a [DNA/vesicles] charge ratio close to 0.8, considering only the excess surface charges on the vesicles. This result is apparently in contradiction with a purely electrostatic approach and is tentatively ascribed to the distance between charges on the biopolymer and the vesicle surface, respectively. A possible interpretation is discussed. The nucleic acid can be completely retrieved from the vesicles upon addition of adequate amounts of SDS, which is the minor surfactant in the vesicular system. Precipitation of the poorly soluble SD-DDA salt results in an almost complete release of DNA.