SELF-ASSEMBLED DNA-CATIONIC-LIPID COMPLEXES - 2-DIMENSIONAL SMECTIC ORDERING, CORRELATIONS, AND INTERACTIONS

We report a synchrotron small-angle x-ray scattering (SAXS) study of t he mutilayered, self-assembled structure (complex) that is formed by m ixing DNA with cationic liposomes, In these complexes the DNA is confi ned between charged lipid bilayers and orders asa two-dimensional (2D) smectic liquid crystal. The power-law bilayer-bilayer correlations of the 3D multilayer smectic liquid crystal, which are coupled to the 2D lattice of DNA chains, are found to deviate significantly from those described by the standard Caille model of smectic-A phases. To model t he DNA ordering, the 2D smectic correlation function and the correspon ding structure factor are derived from the smectic Hamiltonian in harm onic approximation. The resulting line shape is then fitted to the DNA correlation peak. It is found that for samples of higher d. short-ran ge correlations between the DNA in adjacent sheets have to be assumed to explain the data. From the least-square fitting, the 2D DNA interch ain compressibility modulus B is extracted as a function of d and disc ussed in view of different possible microscopic interactions responsib le for the ordering.