Dipalmitoylphosphatidylcholine (DPPC) was hydrated in 0.2-60 mM solution of CaCl2 in heavy water and thoroughly homogenized by freezing-thawing process. Small-angle neutron scattering (SANS) shows formation of unilamellar vesicles in the range 1-60 mM of CaCl2. From the Kratky-Porod plot ln[I(Q)Q2] vs. Q2 of SANS intensity I(Q) in the range of scattering vectors Q corresponding to the interval 0.001 Å -2≤Q2≤0.006 Å-2, the vesicle bilayer radius of gyration Rg and the bilayer thickness parameter dg were obtained. The structure of the bilayer displays different behavior for the gel phase and the liquid-crystalline phase: In the gel phase (at 20°C), the values of dg indicate nonlinear changes in the lipid bilayer thickness, with a maximum at ∼5 mM CaCl2. In the liquid-crystalline phase (at 60°C), the parameter of the lipid bilayer thickness dg=43.2±0.3 Å is constant within the concentration range 1≤cCa≤40 mM. Vesicles prepared at 60 mM CaCl2 show within experimental error, the same values of d g as pure DPPC unilamellar vesicles prepared by extrusion using polycarbonate filter with pores of diameter 500 Å.
- Cationic vesicles
- Small-angle neutron scattering
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