Figure 2.

Phase diagram (charge versus PIP₂-fraction) and snapshots from simulation of charged-neutral mixed lipid monolayers exposed to divalent salt. (a) Phase diagram obtained using a divalent ion radius R_CI = 2 Å. (Solid disks in the shaded coexistence region) Where clustering was observed. (Open circles) Mixed samples. (Gray disks are too close to the boundary to determine their behavior with certainty.) (b) Larger divalent ions require a higher lipid charge to induce clustering (shown for ϕ_PIP = 0.05). (c) The simulation (PIP₂ charge q_PIP = −4, PIP₂ fraction ϕ_PIP = 0.25, and divalent ion radius R_CI = 2 Å) after 3.5 ns of coarsening. Charged and neutral lipids are dark green and light gray discs, respectively, and divalent ions that are close to the lipid monolayer are indicated with smaller dark red dots. (d) Strength (shaded contours) and direction (streamlines) of the electric field around a stringlike domain taken from the simulation, illustrating that further growth of the domain is likely to occur at the end.