Evaluation of small-angle neutron scattering curves of unilamellar phosphatidylcholine liposomes using a multi shell model of bilayer neutron scattering length density

Computer simulated small-angle neutron scattering curves of spherical poly disperse extruded unilamellar liposomes from saturated 1,2-diacylphosphatidylcholines in the aqueous phase are evaluated by using a multi shell model, which divides the lipid bilayer of liposomes into the polar head group region, and the nonpolar hydrocarbon region consisting of the chains of methylene groups and of the region of methyl groups. In the each of these regions, the coherent neutron scattering length density is supposed to by homogeneous. The evaluation is based on obtaining of radius of gyration from Kratky-Porod plot of small-angle neutron scattering data in the Guinier region of small scattering vector values. From radii of gyration obtained at several different molar fractions ND2O/(ND-2O + NH2O) in the aqueous phase (contrasts) and independent volumetric data, the lipid surface area AL (or the bilayer thickness dL) and the number of water molecules NL penetrated into the bilayer polar region can be evaluated. (authors)