Figure 8.

(A) Synchrotron SAXS profiles of CL-sDNA complexes containing 11 bp DNA with 2-T non-sticky overhangs (11bp DNA-2T) as a function of neutral lipid mole fraction (Φ_NL). The (00L) diffraction peaks result from the multilamellar structure of the complexes. Lines point to relatively sharp sDNA–sDNA correlation peaks indicative of the new type of columnar nematic phase (Fig. 1C) as described in the text. Arrows point to broad sDNA peaks characteristic of the isotropic phase. (B–E) Plots of the interlayer spacing d (B), the average spacing between sDNA molecules d_DNA (C), the correlation length L_C (D), and L_C in units of d_DNA (E) as a function of Φ_NL for CL–sDNA complexes containing 11bp DNA-2T (open circles) and for comparison 11bp DNA-5T (open squares) and 11bp DNA-10T (open triangles). The parameters result from line shape fits of the q₀₀₂ and q_sDNA peaks in the SAXS profiles of the corresponding complexes with a double Lorentzian. The observed values of L_C (D) and L_C/d_DNA (E) for 11bp DNA-2T show a highly correlated nematic phase with L_C/d_DNA ranging between six and ten, in contrast to the isotropic phase with L_C/d_DNA < 1 observed for 11bp DNA-10T and 11bp DNA-5T. This new phase undergoes a transition to the isotropic phase for Φ_NL > 0.5 (where L_C/d_DNA decreases to ≈1). The building blocks of this highly correlated nematic phase (labeled columnar nematic, N_C) are 1D stacks of 11bp DNA-2T rods that result from the onset of strong sDNA end-to-end interactions. Applying Onsager's criterion to this phase gives an estimate of the stack length as on average 4 rods, as shown in Fig. 1C.