Structure of Mixed Multilayers of Palmitoyloleoylphosphatidylcholine and Oligo(oxyethylene glycol) Monododecyl Ether Determined by X-ray and Neutron Diffraction

Abstract

The structure of oriented multilayers of the zwitterionic phospholipid palmitoyloleoylphosphatidylcholine containing nonionic surfactants (oligo(oxyethylene glycol) monododecyl ethers, C12En with n ) 2, 4, and 6) was studied by X-ray and neutron diffraction. Investigations were done at T ) 20 °C in the lamellar liquid-crystalline phase with surfactant/lipid molar ratios RA/L ) 0.5 and 1 and hydration levels corresponding to 85 and 97% relative humidity. The transbilayer distribution of the surfactant was determined by neutron diffraction using selectively deuterated C12En. The incorporation of surfactant causes a decrease of the repeat distance and of the thickness of the hydrocarbon core of the membrane. The effect increases with the number of oxyethylene units and with the concentration of the surfactant as well as with the relative humidity. The R-methylene group of the surfactants is anchored near the boundary of the hydrophobic core. The oxyethylene moieties are mainly located in the polar membrane/water interface region. The impact of molecular disorder on the diffraction data is discussed.

X-Ray Diffraction Study of the Lamellar–Hexagonal Phase Transition in Phospholipid/Surfactant Mixtures

“…Addition nm as calculated by molecular modeling (28). This is about of oligo(ethylene oxide)alkyl ethers leads to dehydration of 0.4 nm longer than obtained from X-ray diffraction data of the phospholipid (5,7,20). Thus, it is expected that POPC POPC in the gel phase (26), indicating a tilted orientation in mixtures with C 12 E 2 will remain in the lamellar gel phase.…”

“…On dehydration a slightly inverted conical molecular shape is adopted, but undulations occur within the lameller stacks and lamellae start to fuse locally. By this process adjacent layers transform POPC still adopts lamellar gel or liquid crystalline phases (5,8). On addition of C 12 E 2 the geometric requirements into series of rods and successively the whole stack of bilayers becomes a stack of closely packed rods.…”

“…The main reaing of both phospholipid and surfactant, the longer alkyl son for this interest is the possible role of nonlamellar phases chains of the phospholipid can now fill the void in the interin membrane processes such as membrane fusion or adhestices of the hexagonal packing stabilizing the H II phase sion. Thus, the lyotropic phase behavior of a large variety (5,6). of isolated membrane lipids as well as of lipid mixtures Compared to the fast and reversible two-state process inhas been investigated.…”

“…The thickness of the hydrophobic core of the composite particle bilayer d hc can be obtained by d hc Å 2V hc /S, [5] where V hc Å V hc(L) / R S/L V hc(S) [6] is the molecular volume of the hydrophobic part of the composite particle, hence V hc(L) Å 0.744 nm 3 and V hc(S) Å 0.280 nm 3 .…”

Thermodynamic and structural behaviour of equimolar POPC/CnE4 (n=8, 12, 16) mixtures by sorption gravimetry, 2H NMR spectroscopy and X-ray diffraction

“…they enable a relatively large population of gauche conformers and free volume. The increasing number of gauche conformers leads to a decrease of the effective length of the hydrocarbon chain with respect to the membrane normal and likewise to a reduction of the repeat distances (Klose et al, 1996). To show the reduced hydrocarbon chain length, the Luzzatti model (Luzzati and Chapman, 1968) can be used such as shown in Fig.…”