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 $B\left(d\right)$ as a function of the interhelical spacing $d$ of the 2D smectic, with $25<d<\mathrm{}60\mathrm{}Å$, is not described by hard core repulsions but, rather, is dominated at larger spacings $d>\mathrm{}35\mathrm{}Å$ by long-range electrostatic repulsions.