The picosecond dynamics of the phospholipid dimyristoylphosphatidylcholine in mono- and bilayers

The dynamics of the fully hydrated phospholipid dimyristoylphosphatidylcholine (DMPC) were studied on a time scale of about 60 picoseconds with quasielastic neutron scattering. Three types of samples were employed: multibilayers without solid support, single bilayers in vesicles, and monolayers in emulsions of perdeuterated hexadecane. The vesicles and emulsion droplets had diameters of about 130 nanometres; some of the emulsions also contained sodium glycocholate to enhance the stability. It could be shown that the mobility of the phospholipid molecules in the observed time regime increases from multibilayers over single bilayers to monolayers. Additionally, the high quality of the data of the multibilayer samples allows an evaluation of the molecular mechanism of the motions: while the interpretation in the frame of flow-like motions fits well at temperatures shortly above the main phase transition, the model of diffusive motions fits better at high temperatures of up to 80 degrees C.