Structural thermodynamics of lamellar cationic lipid-DNA complex: DNA compressibility modulus.
We have studied theoretically the compressibility modulus B of DNA and complexation adsorption isotherms of DNA and lipids, as a function of DNA spacing d(DNA) and NaCl electrolyte concentration, respectively, in isoelectric states of lamellar DNA/cationic lipid (CL) self-assemblies. The electrostatic free energy derived from the Poisson-Boltzmann theory predicts partial agreement with measured B values for interhelical separations d(DNA)>33 A when use is made of a fit of hydration repulsion from bulk DNA hexagonal phases in solution. For lower interchain separations the prediction worsens due to the hydration interaction that overcomes the electrostatic contribution. An exact match of the system's counterion electrochemical potentials and the coions of salt in aqueous phase leads to the electrostatic part of the free energy that renders isotherms of d(DNA) versus ionic strength in qualitative consistency with general trends of available experimental data of CL-DNA complexes.
González-Amezcua
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Departamento de Física, Centro de Investigación y Estudios Avanzados del Instituto Politécnico Nacional, A.P. 14-740, México Distrito Federal, Zacatenco CP 07360, Mexico.
Hernández-Contreras
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D000327:Adsorption; D001703:Biophysics / Q000379:methods*; D004247:DNA / Q000737:chemistry*; D004563:Electrochemistry / Q000379:methods*; D019277:Entropy; D007477:Ions; D007525:Isoelectric Focusing; D008055:Lipids / Q000737:chemistry*; D046911:Macromolecular Substances; D015233:Models, Statistical; D008968:Molecular Conformation; D009690:Nucleic Acid Conformation; D055672:Static Electricity; D013816:Thermodynamics; D014867:Water / Q000737:chemistry
D007477:Ions; D008055:Lipids; D046911:Macromolecular Substances; D014867:Water; D004247:DNA