Structural study of the DNA dipalmitoylphosphatidylcholine complex at the air-water interface.

We present here results that demonstrate the formation of a complex of DNA with zwitterionic dipalmitoylphosphatidylcholine (DPPC) monolayer at the air-water interface in the presence of Ca2+ ions; in particular, we show that the presence of Ca2+ cations is essential for the formation of the complex of DPPC with DNA. We characterize the resulting structure by X-ray reflectivity and by null-ellipsometry. We show that DNA maintains its native double helix form when attached to the zwitterionic lipid monolayer, at difference with the case of ammine containing monolayers. Our findings are discussed in view of other works that recently appeared on the interaction of DNA with zwitterionic phospholipids, emphasizing the role of DPPC as a potential vector for transfer of genetic material into mammalian cells by nonviral gene therapy and also suggesting Langmuir/Blodgett layers of zwitterionic phospoholipids as a method for nonconventional DNA immobilization.