Figure 1.
Comparison of the present and original SDP-models [3] for DPPC at 50 °C. The two models mainly show differences in the low-q region of SAXS (a), whereas they overlap in the case of SANS in 100% D2O (b). The vertical black line in (a) marks the lower limit of the accessible range in the original study. (c) shows volume probability distributions p(z) of the lipid moieties through the bilayer profile. The resulting neutron SLD (black) and electron density profiles (cyan) are drawn in (d). Dashed lines correspond to the original, solid lines to the new model. MD-simulations confirm the presence of higher-density water around the headgroup region, where the volume-per-water molecule is decreased by up to 10% (e). This effect is schematically illustrated in a simulation snapshot of a DPPC bilayer (f) where bulk water is shown in blue (with z > 25 Å) and hydration water in yellow (with z < 25 Å). Lipids are drawn in a licorice representation with carbons in cyan, nitrogen in blue, phosphate in tan and oxygen in red.