Analytical Sciences

Changes in Interfacial Tension of a Lipid Membrane Formed at the Water/Chloroform Interface upon DNA Complex Formation

Masashi OHNO,* Taro TOYOTA,**,*** Tomonori NOMOTO,* and Masanori FUJINAMI*

*Department of Applied Chemistry and Biotechnology, Chiba University, 1-33 Yayoi, Inage, Chiba 263-8522, Japan
**Department of Basic Science, The University of Tokyo, 3-8-1 Komaba, Meguro, Tokyo 153-8902, Japan
***Precursory Research for Embryonic Science and Technology (PRESTO), Japan Science and Technology Agency (JST), 4-1-8 Honcho, Kawaguchi, Saitama 332-0012, Japan

Changes in the interfacial tension of a lipid monolayer membrane formed at the water/chloroform interface upon DNA addition were measured using the quasi-elastic laser scattering (QELS) method. A cationic lipid, N-[1-(2,3-dioleoyloxy)propyl]-N,N,N-trimethylammonium chloride (DOTAP), as well as zwitterionic lipids, 1,2-dioleoyl-sn-glycero-3-phosphoethanolamine (DOPE) and 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC), were used to form lipid monolayer membranes at different calcium ion concentrations. A rapid decrease of the interfacial tension resulting from electrostatic interactions between DOTAP and DNA was observed within 10 s. However, such rapid decreases were not observed for DOPE or DOPC. A decrease in the interfacial tension was exhibited by DOPE after 1000 s from the addition of DNA, which may be due to an overall structural change in the DOPE membrane. A DOTAP/DOPE complex system showed behaviors attributable to both DOTAP and DOPE, whereas the behavior of the DOTAP/DOPC system resembled that of DOPC alone. The current results provide a model for the so-called lipoplex carriers used in gene therapy.

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