Anelastic spectroscopy as a probe of dynamic properties in lipid membranes

We present the results of anelastic spectroscopy on the dynamic properties of lipid complexes widely used as DNA vectors in gene therapy. In particular we studied the cationic/neutral lipid mixtures DOTAP/DOPE, DOTAP/DMPC and the single lipids, DOTAP (di-oleoyl trimethylammonium propane), DOPE (di-oleoyl phosphatidylethanolamine), DMPC (dimyristoyl phosphatidylcholine) and DDAB (dimethyidioctadecylammonium), deposited on a solid silicon(1 0 0) substrate. Two relaxation processes have been observed at about 200 and 140 K in mixtures of cationic and neutral lipids, which are due to a dynamics in the membrane plane on time scales accessible to anelastie spectroscopy. The presence of the two processes appears to be a general phenomenon independent of the lipid type, and is connected to the motion of lipids and lipid domains in the membrane plane. (c) 2006 Elsevier B.V. All rights reserved.