Cloverleaf Monolayer Domains

Two-component monolayers of dipalmitoylphosphatidylcholine (DPPC) (or dimyristoylphosphatidylcholine (DMPC)) and dihydrocholesterol (DChol) form cloverleaf domains at a surface pressure just above 0 mN/m and for monolayer concentrations of less than 30% mol DChol. A cloverleaf domain consists of DChol-rich lobes attached to a small gas cavity. Upon further expansion of the monolayer, at constant surface pressure, the gas cavity in the center of the cloverleaf domain expands. The stability of a cloverleaf domain is studied using a line tension−dipole repulsions model. In this model, the equilibrium shape of a constant-area monolayer domain arises from a competition between the line tension of the domain boundary and the dipole−dipole repulsions between the molecular dipoles in the monolayer. The energies of the three-leaf, four-leaf, and five-leaf clover domains are compared with the energies of three, four, and five circular domains, respectively. The results show that a cloverleaf domain is stabilized by the small gas cavity to which the DChol-rich lobes are attached.