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

Abstract

Dipalmitoylphosphatidylcholine (DPPC) was hydrated in 0.2–60 mM solution of CaCl2in 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.Q2of SANS intensityI(Q)in the range of scattering vectorsQcorresponding to the interval 0.001 Å−2≤Q2≤0.006 Å−2, the vesicle bilayer radius of gyrationRgand the bilayer thickness parameterdgwere 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 ofdgindicate 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 thicknessdg=43.2±0.3 Å is constant within the concentration range 1≤cCa≤40 mM. Vesicles prepared at 60 mM CaCl2show within experimental error, the same values ofdgas pure DPPC unilamellar vesicles prepared by extrusion using polycarbonate filter with pores of diameter 500 Å.

Interaction of short-fragmented DNA with dipalmitoylphosphatidylcholine bilayers in presence of zinc

“…Zwiterionic phospholipids in a solution of divalent metal cations spontaneously form vesicles with a positive surface charge. For example, 1 mmol/l solution of CaCl 2 promotes the formation of DPPC unilamellar vesicles (Inoko et al 1975;Akashi et al 1998;Uhríková et al 2007b). Cationic vesicles interact electrostatically with DNA polyanion, forming aggregates.…”

“…In presence of 20 mmol/l ZnCl 2 , we observe a small increase in the lipid bilayer thickness. Due to binding to the zwitterionic phospholipid bilayer, calcium induces structural changes, affecting thickness, area per lipid molecule as well as hydration (Uhríková et al 2007b(Uhríková et al , 2008. Zinc affects the DPPC lipid bilayer thickness in a similar way, as indicates the d g of DPPC in 20 mmol/l ZnCl 2 .…”

Swelling of phospholipid membranes by divalent metal ions depends on the location of the ions in the bilayers

“…While Mg 2+ and Fe 2+ caused monotonic increases in d z , a plateau in d z was observed for Ca 2+ and Zn 2+ , as reported previously for Ca 2+ . 11,32 Salts have been shown previously to increase the lamellar spacing of multi-lamellar membrane samples. [11][12][13] The number of water molecules per lipid, n W , was determined using eqn (4), and the results are shown in Fig.…”

Lipid bilayer – DNA interaction mediated by divalent metal cations: SANS and SAXD study

“…Unilamellar vesicles are also formed spontaneously when the surface charge density is higher than 1-2 µC/cm 2 [33], e.g. multilamellar DPPC dispersion in 1 mM CaCl 2 completely converts into unilamellar vesicles [25,34]. Figure 2b-e shows SANS curves of unilamellar DPPC vesicles formed spontaneously in solutions of studied ions.…”