Ultracold neutron scattering study of local lipid mobility in bilayer membranes

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Abstract
The dynamics of lipid bilayers is studied for the first time by quasielastic scattering of ultracold neutrons (UCN). Measurements of the energy transfer from lipids to the scattered UCN as a function of temperature and - in combination with spin echo experiments - of the wave vector lead to the conclusion that it is determined, on the microsecond time scale investigated, by lateral diffusion of lipid molecules. For dipalmitoyl-phosphatidyl-choline bilayers at 45 °C a diffusion coefficient of D = 2.6 × 10-7 cm2/s is obtained which is slightly larger than the value obtained by the conventional photobleaching technique. The present UCN-scattering method is complementary to the photobleaching technique since it measures the local lipid diffusion over short distances of some 20 Å whereas the latter monitors the lateral motion over some 10 μm