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Structural thermodynamics of lamellar cationic lipid-DNA complex: DNA compressibility modulus
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Image of FIG. 1.
FIG. 1.

Unit cell of DNA and lipid self-assembly. Two parallel slabs of cationic lipid bilayers enclosing two halves of DNA molecules and NaCl electrolyte.

Image of FIG. 2.
FIG. 2.

Comparison of experimental data on DNA’s compressibility modulus with theory results, as a function of interhelical spacing (a). All components of are given in (b) at salt concentration for the eight isoelectric complexes considered in (a). The solid lines are guides to the eye.

Image of FIG. 3.
FIG. 3.

Complexation isotherms of DNA and lipids, given as curves of vs concentration of salt NaCl for molar fractions of charged lipids on membrane (a), 0.7 (b), and 0.6 (c), respectively. In all plots, theory predictions are depicted with exact match of ion’s chemical potentials (, with ◻ symbols) and under the approximation (, with ▵ symbols). The solid lines are guides to the eye.

Image of FIG. 4.
FIG. 4.

Nondimensionalized density profile of positive lipids vs DNA spacing . The case of fixed cationic lipid molar fraction on the bilayer and two salt concentrations (a) and (b). Theory calculations with as a condition for ion’s chemical equilibrium (, dash line) and (continuous line). In (a) and (b) are shown the large segregation of lipids produced by inhomogeneous screening of ions on the DNA’s and bilayer’s electric fields due to the high salt concentration. Positive ions form a void in the spatial region around the DNA molecule, while negative ions deplete from this region accumulating more in the middle of the cell (see also Fig. 6). The inset in (a) at shows that lipid segregation on the bilayer is almost negligible when the salt content in the solution is very small.

Image of FIG. 5.
FIG. 5.

Density functions of positive (a) and negative (b) ions around the DNA molecule, and their contour plots (c) and (d), respectively. The molar fraction of charged lipids on the membrane is with aqueous NaCl concentration . Note in (c) the compact double layer formed by positive ions around the DNA.

Image of FIG. 6.
FIG. 6.

Same as Fig. 5 for ion’s distribution functions and with and . Inside (c) there is a region of vacuum, , formed by positive ions on the surface of the DNA, while they are concentrated more in the space between DNA strands. (d) depicts the large accumulation of negative ions onto the lipid bilayer. They form a narrow cloud that shows the depletion of ions close to the DNA surface.


Generic image for table
Table I.

Experimental values of isoelectric CL-DNA system cell size at of NaCl.


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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Structural thermodynamics of lamellar cationic lipid-DNA complex: DNA compressibility modulus