title: Modeling the influence of adsorbed DNA on the lateral pressure and tilt transition of a zwitterionic lipid monolayer.
abstract: Certain lipid monolayers at the air-water interface undergo a second-order transition from a tilted to an untilted liquid-crystalline state of their lipid hydrocarbon chains at sufficiently large lateral pressure. Recent experimental observations demonstrate that in the presence of divalent cations DNA adsorbs onto a zwitterionic lipid monolayer and decreases the tilt transition pressure. Lowering of the tilt transition pressure indicates that the DNA condenses the lipid monolayer laterally. To rationalize this finding we analyze a theoretical model that combines a phenomenological Landau approach with an extension of the Poisson-Boltzmann model to zwitterionic lipids. Based on numerical calculations of the mean-field electrostatic free energy of a zwitterionic lipid monolayer-DNA complex in the presence of divalent cations, we analyze the thermodynamic equilibrium of DNA adsorption. We find that adsorbed DNA induces a 10% reduction of the electrostatic contribution to the lateral pressure exerted by the monolayer. This result implies a small but notable decrease in the tilt transition pressure. Additional mechanisms due to ion-ion correlations and headgroup reorientations are likely to further enhance this decrease.
authors: Faculty of Health Sciences, University of Ljubljana, SI-1000 Ljubljana, Slovenia. klemen.bohinc@fe.uni-lj.si
authors: Klemen
authors: K
authors: Bohinc
authors: Gerald
authors: G
authors: Brezesinski
authors: Sylvio
authors: S
authors: May
mesh_terms: D000327:Adsorption; D000388:Air; D004247:DNA / Q000737:chemistry* / Q000378:metabolism; D008055:Lipids / Q000737:chemistry*; D008962:Models, Theoretical; D055672:Static Electricity; D013816:Thermodynamics; D014867:Water / Q000737:chemistry
chemical_list: D008055:Lipids; D014867:Water; D004247:DNA