Phase Diagrams and Ordering in Charged Membranes: Binary Mixtures of Charged and Neutral Lipids

Abstract

We propose a model describing the phase behavior of two-component membranes consisting of binary mixtures of electrically charged and neutral lipids. We take into account the structural phase transition (main-transition) of the hydrocarbon chains, and investigate the interplay between this phase transition and the lateral phase separation. The presence of charged lipids significantly affects the phase behavior of the multicomponent membrane. Due to the conservation of lipid molecular volume, the main-transition temperature of charged lipids is lower than that of neutral ones. Furthermore, as compared with binary mixtures of neutral lipids, the membrane phase separation in binary mixtures of charged lipids is suppressed, in accord with recent experiments. We distinguish between two types of charged membranes: mixtures of charged saturated lipid/neutral unsaturated lipid and a second case of mixtures of neutral saturated lipid/charged unsaturated lipid. The corresponding phase behavior is calculated and shown to be very different. Finally, we discuss the effect of added salt on the phase separation and the temperature dependence of the lipid molecular area.

Long-lived ionic nano-domains can modulate the stiffness of soft interfaces

“…The existence of slowly evolving, correlated ionic networks is likely to have profound implications for processes occurring at the interface, including the physical properties of the bilayer itself. For example, it is well-known that ions modulate the phase behaviour, 37,46 cohesive strength 7 and bending moduli 27,47 of lipid membranes. These effects usually occur through liberation of bound water molecules and direct electrostatic screening that leads to a tighter lipid packing.…”

Coarse-grained molecular dynamics simulation of binary charged lipid membranes: Phase separation and morphological dynamics

“…In experiments with systems containing charged lipids, charged unsaturated lipids tend to suppress the phase separation compared with neutral lipid systems [14][15][16][17][18], whereas charged saturated lipids promote phase separation [18]. Several theoretical models [23][24][25][26] have also been proposed to explain the electrostatic effects on the lateral phase separation in charged lipid membranes.…”

Coarse-grained molecular dynamics simulation for uptake of nanoparticles into a charged lipid vesicle dominated by electrostatic interactions

“…For example, the suppression of the phase separation in unsaturated charged lipid-containing membranes was examined, and the addition of salt made the phase behavior similar to that of neutral membranes [9][10][11][12]. This behavior was explained by theoretical and numerical studies [13][14][15][16]. In addition, decreasing the temperature spontaneously changed the vesicle morphology from spherical to disk shape [17].…”