SANS study of unilamellar DMPC vesicles: Fluctuation model of a lipid bilayer

Parameters of a polydisperse population of unilamellar DMPC vesicles are analyzed based on a model of separated form factors. The neutron-scattering length density across the membrane is described using a fluctuation model of a lipid bilayer. The distribution of water molecules in the bilayer is described by a sigmoid function. The results of fitting the experimental data obtained on a SANS-I PSI small-angle spectrometer (Switzerland) are as follows: the average vesicle radius is 272 +/- 0.4 Angstrom, the radius polydispersit is 27%, the membrane thickness is 50.6 +/- 0.8 Angstrom, the thickness of the hydrocarbon-tail region is 21.4 +/- 2.8 Angstrom, the number of water molecules per lipid molecule is 13 1, and the surface area of the DMPC molecule is 59 +/- 2Angstrom(2). The calculated function of water distribution across the membrane directly explains why water molecules easily penetrate the membrane. (C) 2004 MAIK "Nauka/Interperiodica".