Abstract
The effect of adding divalent ions on the deoxyribonucleic acid (DNA) adsorption by a cationic lipid monolayer at the air-water interface was investigated by X-ray reflectivity on Langmuir-Blodgett films supported on silicon wafers. The films were prepared from a DC-Chol {3-β-[N-(N′, N′-dimethylaminoethane)carbamoyl]cholesterol} monolayer with 1 μM DNA in the subphase with different amounts of calcium ions added. It is found in this study that adding divalent ions, such as calcium ions, can enhance the DNA adsorption to interfaces. The adsorbed DNA layer thickness as determined by X-ray reflectivity is found to vary linearly with the square root of the ion concentration. This indicates that charge-screening effects and ion-mediated condensation play an important role in the DNA-cationic lipid monolayer interaction. © International Union of Crystallography 2007.