Eur. Phys. J. B 4, 75-88 (1998)
https://doi.org/10.1007/s100510050353

Electrostatics of DNA-cationic lipid complexes: isoelectric instability

Physics Department, University of California, Los Angeles, CA, 90024, USA

Corresponding author: ^a bruinsma@physics.ucla.edu

Received: 21 July 1997
Revised: 19 January 1998
Accepted: 5 March 1998
Published online: 15 July 1998

Abstract

We propose a Poisson-Boltzmann electrostatic theory for DNA/cationic lipid complexes modeled as a stack of aligned DNA chains intercalated with lipid bilayers, a structure suggested by the recent X-ray synchrotron studies of Radler et al. Poisson-Boltzmann theory is shown to predict that the isoelectric point -where the DNA and cationic lipid charges are in balance -is unstable against absorption of extra DNA or lipid material. The instability is caused by the entropy gain obtained following the release of small ions inside the complex and is manifested by singular behavior of the rod-rod spacing near the isoelectric point. We apply the theory to a discussion of the results of Radler et al.