The nanostructure of surfactant–DNA complexes with different arrangements

• The DNA orientation in the thin films is preferentially parallel to the film plane.
• The surfactant arrangement around DNA depends on the surfactant headgroup structure.
• ALA–DNA and LAM–DNA can accommodate 2:1 hexagonal packing arrangement that is more distorted than 3:1 obtained for CTAB and MTAB surfactants.

The nanostructure of DNA with different cationic surfactant has been studied in order to elucidate the detailed arrangement concerning the position of DNA and surfactant domains in the complexes. Also, the orientation of the DNA cylinders in the thin films of the complexes was investigated. Attention was directed on the preparation methods of the complexes and to how the different surfactant structure affects the compaction of the DNA. The cationic surfactant–DNA complexes were investigated by X-ray scattering, polarized light microscopy and elemental microanalysis. It was observed that the molecular organization of the complexes between DNA and cationic surfactant corresponds to a hexagonal structure with different packing arrangements. The nanostructure of the complexes depends on the hydrophobic/hydrophilic balance of the cationic surfactant. In particular the use of arginine derived surfactants, with a large polar head group able to interact not only by electrostatics but also by hydrogen bonding, allows for the formation of more compact structures. The results suggest that the smaller the lattice parameter the more compact and stable is the complex implying slower DNA release.

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