Two-dimensional smectic ordering of linear DNA chains in self-assembled DNA-cationic liposome mixtures

We report a synchrotron x-ray scattering study of linear DNA chains and cationic liposome mixtures which spontaneously self-assemble into a coupled two-dimensional (2D) smectic phase of DNA chains imbedded between lipid bilayers of a 3D smectic phase. The DNA peak is quantitatively described by anisotropic exponentially decaying chain-chain correlations. The measured interchain compressibility modulus B(d) as a function of the interhelical spacing d of the 2D smectic, with 25 < d < 60 Angstrom, is not described by hard core repulsions but, rather, is dominated at larger spacings d > 35 Angstrom by long-range electrostatic repulsions.