Sketch of experimental phase diagram for DPPC/cholesterol system (Ref. 53) (reproduced from Ref. 39). At high temperatures and low cholesterol concentrations, there is a liquid-disordered (ld) phase, which is a fluid phase characterized by lipid acyl chains with a low degree of conformational order. When the temperature is lowered, the system goes through the main phase transition at to a solid-ordered (so) phase. The so phase is a solidlike phase in which the acyl chains are conformationally ordered and there is translational order in the plane of the bilayer. Finally, at high cholesterol concentrations, there is a liquid-ordered (lo) phase, characterized both by a high degree of acyl chain ordering and the lack of translational order. At intermediate cholesterol concentrations there are wide ld-lo and so-lo coexistence regions. The dots represent the concentrations at which the atomic-scale molecular dynamics simulations have been performed.
Radial distribution functions calculated from MD simulations for different pairs of CG structural units. Pairs that have virtually identical RDFs have been merged and only the average RDF is shown. The RDFs have been calculated from the CM positions of the structural units, projected to the plane of the bilayer.
Average area per molecule as a function of cholesterol concentration, calculated from MD simulations (Ref. 14).
Effective interaction potentials for different pairs of coarse-grained particles and different cholesterol concentrations. The bottom row shows data for intramolecular interactions through corresponding effective interactions.
Comparison between RDFs from CG model (gray lines) and atomistic MD simulations (black lines) for a pure DPPC system. The solid lines are for small systems ( per monolayer) and the dashed lines for larger systems ( for MD, for CG). Only the tail-tail RDF is shown, but the results are similar for the other cases. The inset shows a zoomed view of the first peaks.
Static structure factors for pure DPPC system. The solid black line shows the total structure factor, and the other lines show the head-head (solid gray line), tail-tail (dashed line), and head-tail (dotted line) structure factors. The inset shows a snapshot of the system. In the snapshot, only the tail particles are shown. The CG simulations were run with , i.e., with 16 times the linear size of the original 128 lipid system.
Static structure factors for different cholesterol concentrations: (a) 5%, (b) 13%, (c) 20%, and (d) 30%. The solid black line shows the total structure factor, and the other lines show the head-head (solid gray line), tail-tail (dashed black line), and cholesterol-cholesterol (dashed gray line) structure factors. The other pairs are not shown for clarity. The insets show snapshots of the systems. In the snapshot, only the cholesterol particles are shown. For the 30% concentration, the peak at the smallest values is probably due to very slow equilibration of the system.
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