T. Salditt et al., SELF-ASSEMBLED DNA-CATIONIC-LIPID COMPLEXES - 2-DIMENSIONAL SMECTIC ORDERING, CORRELATIONS, AND INTERACTIONS, Physical review. E, Statistical physics, plasmas, fluids, and related interdisciplinary topics, 58(1), 1998, pp. 889-904
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.