Thermodynamic Approach to Phase Coexistence in Ternary Phospholipid-Cholesterol Mixtures

We introduce a simple and predictive model for determining the phase stability of ternary phospholipid-cholesterol mixtures. Assuming that competition between the liquid and gel order of the phospholipids is the main driving force behind lipid segregation, we derive a Gibbs free energy of mixing, based on the thermodynamic properties of the lipids main transition. A numerical approach was devised that enables the fast and efficient determination of the ternary diagrams associated with our Gibbs free energy. The computed phase coexistence diagram of DOPC/DPPC/cholesterol reproduces well-known features for this system at $10°\mathrm{C}$, as well as its evolution with temperature.

Figure 1

(a) Discrete approximation to the ternary phase diagram obtained from the lower convex hull method explained in the text. (b) Final phase diagram determined from the analytical refinement of the discrete approximation.

Figure 2

Computed evolution of the DPPC/DOPC/Chol triangular diagram with temperature. The computed diagrams display the main expected features for this lipid mixture.