Small angle scattering of neutrons and x-rays from aqueous dispersions of dipalmitoyl phosphatidylcholine

SANS and SAXS from aqueous dispersions of DPPC and Egg-PC were measured at temperatures in the range from 20 to 50 deg C. The SANS patterns in the Egg-PC-D2O system changed little with the temperature T. On the other hand, the SANS patterns in the DPPC-D2O system changed drastically at the main transition temperature Tm2; the diffraction peak which corresponds to the repeat distance of the lipid bilayers was observed above Tm2, but below Tm2 it disappeared and a large diffuse scattering appeared. On the contrary, such a drastic change at Tm2 was not observed in SAXS measurements on the DPPC-D2O system and the DPPC-H2O system; distinct diffraction peaks were observed, but such a large diffuse scattering as was found for SANS was not observed, even below Tm2. The origin of the difference between the results of SANS and those of SAXS is interpreted in terms of the difference of the form factor of both scatterings. (author)