BILAYER THICKNESS IN UNILAMELLAR EXTRUDED EGG-YOLK PHOSPHATIDYLCHOLINE LIPOSOMES - A SMALL-ANGLE NEUTRON-SCATTERING STUDY

Using the small-angle neutron scattering and the Kratky-Porod plot, th e bilayer thickness d(L) = 41.7 +/- 0.3 Angstrom has been determined i n unilamellar egg yolk phosphatidylcholine liposomes dispersed in heav y water and prepared by extrusion through 500 Angstrom pores in polyca rbonate filters. The peak-peak distance across the bilayer obtained fr om the data of small-angle X-ray scattering on the liquid-crystalline L-alpha phase of fully hydrated egg yolk phosphatidylcholine is 37.4 A ngstrom less than or equal to d(PP) less than or equal to 38.1 Angstro m. Using this value and the bilayer hydrocarbon region thickness of d( HC) = 28.4 +/- 0.6 Angstrom, the bilayer thickness 47.4 Angstrom less than or equal to d(L) I 48.1 Angstrom, the phospholipid molecule surfa ce area 64.0 Angstrom(2) less than or equal to A(L) less than or equal to 64.6 Angstrom(2) at the bilayer/water interface, the number of wat er molecules 9.17 less than or equal to n(h) less than or equal to 9.5 7 penetrated into the polar region of the bilayer per one phospholipid and the mean molecular volume 28 Angstrom(3) less than or equal to V- w' less than or equal to 30 Angstrom(3) of penetrated water have been obtained from the small-angle X-ray scattering repeat distance of the liquid-crystalline L-alpha phase of egg yolk phosphatidylcholine hydra ted by 13 < n < 20 water molecules per one lipid.