Formation of unilamellar dipalmitoylphosphatidylcholine vesicles promoted by Ca2+ ions: A small-angle neutron scattering study

Uhríková, Daniela and Teixeira, José and Lengyel, Adrián and Almásy, László (2007) Formation of unilamellar dipalmitoylphosphatidylcholine vesicles promoted by Ca2+ ions: A small-angle neutron scattering study. SPECTROSCOPY-AN INTERNATIONAL JOURNAL, 21. pp. 43-52. ISSN 0712-4813

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Abstract

Dipalmitoylphosphatidylcholine (DPPC) was hydrated in 0.2-60 mM solution of CaCl 2 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 CaCl 2. From the Kratky-Porod plot ln[I(Q)Q 2] vs. Q 2 of SANS intensity I(Q) in the range of scattering vectors Q corresponding to the interval 0.001 Å -2≤Q 2≤0.006 Å -2, the vesicle bilayer radius of gyration R g and the bilayer thickness parameter d g 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 d g indicate nonlinear changes in the lipid bilayer thickness, with a maximum at ∼5 mM CaCl 2. In the liquid-crystalline phase (at 60°C), the parameter of the lipid bilayer thickness d g=43.2±0.3 Å is constant within the concentration range 1≤c Ca≤40 mM. Vesicles prepared at 60 mM CaCl 2 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.

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