Figure 1.

Schematic drawings of the distinct packing phases of sDNA rods (all of which contain non-sticky overhangs) in cationic liposome–short DNA (CL–sDNA) complexes. The complexes are multilamellar assemblies of alternating cationic lipid bilayers of thickness d_M and water layers of thickness d_W. The water layer contains a monolayer of sDNA molecules. The multilamellar unit cell dimension is d = d_W + d_M. (A) The isotropic phase with short-range positional and orientational order, as observed for 11bp DNA-10T (11 bp DNA core with a 10-T non-sticky overhang at each end), with small shape anisotropy (length/width = L/D ≈ 1.9). (B) The nematic liquid crystal phase, as observed for 48 bp DNA rods with non-sticky ends (L/D ≈ 8.16). Formation of this phase by sDNA rods with sufficiently anisotropic shape is consistent with Onsager's model of LC ordering of anisotropic rods. For 5-T and 2-T non-sticky ends, some transient dimers may form, indicating the onset of sDNA end-to-end interactions. All rods are the same length (apparently shorter rods are shown cut off at the edges). (C) A new type of 2D columnar nematic phase, as observed for 11bp DNA-2T rods. The onset of strong DNA end-to-end interactions for 11 bp DNA with very short (2 T) non-sticky overhangs leads to the formation of a distribution of 1D stacks of sDNA rods, which become the building blocks of the nematic phase. The 1D stacks have an average size of ≈4 rods, corresponding to an effective length to width ratio L/D ≈ 7.3). In parts B and C, d_DNA corresponds to the average interhelical spacing. The “Onsager nematic” (N) (part B) and columnar nematic (N_C) (part C) phases exhibit long-range orientation and short-range position order. The drawings are not meant to imply that the orientation of sDNA rods is correlated between layers.