Adsorption behavior of DNA on phosphatidylcholine at the air-water interface

In this paper, the adsorption behavior of DNA on 1,2-dipalmitoyl-sn-glycero-3- phosphocholine (DPPC) and 1-palmitoy1-2-oleoyl-sn-glycero-3-phosphocholine (POPC) mixed lipid monolayers had been studied at the air water interface through the surface pressure-area curves (pi-A), adsorption curves (pi/pi(0)-t), excess mean area (Delta A(exc)), excess Gibbs free energy (Delta G(ex)) and the atomic force microscopy (AFM). pi-A isotherms showed that the curves moved to larger mean molecular area after DNA added into subphase, however, the curves shifted to smaller mean molecular area when the concentration of DNA was higher than 1.2 mu g/mL. The result of adsorption curves indicated that DNA molecules were spread by combining with polar head groups of lipids except the concentration of DNA was 0.4 mu g/mL. Delta A(exc) and Delta G(ex) demonstrated that DNA enlarged the interval between DPPC and POPC, and the strongest position happened at the concentration of DNA was 1.2 mu g/mL. These phenomena might be the steric hindrance between DNA molecules. Morphology of surface observed by AFM was agreement with the results above, which verified our conclusion from a more intuitive aspect. This work provides useful theoretical basis for the development of novel DNA delivery materials.