A 13C NMR Study of Aqueous Dispersions of Reversed Lipid Phases

Monoolein (GMO) forms a bicontinuous cubic phase that can coexist in equilibrium with a water phase, and this phase can be dispersed into colloidal particles. Poloxamer is an efficient stabilizer for dispersions of this phase. By adding a small amount of triolein to GMO, a reversed hexagonal phase is formed at room temperature. This phase can be dispersed into submicron particles in water in the same way. The inner molecular arrangement of these dispersions was investigated by 13 C NMR relaxation. The 13 C NMR relaxation rates of the various GMO carbon atoms obtained from the dispersed particles compared to those obtained from the nondispersed phases indicate that the lipid organization and dynamic properties of the original nondispersed phases are retained. It is also demonstrated that the cubic phase is transformed into the reversed hexagonal phase, within six months, due to hydrolysis of GMO. A remarkable observation is that no significant hydrolysis occurs during this time in the corresponding dispersed samples. This indicates that solubilization of a few wt % of Poloxamer into the GMO bilayer provides protection against degradation.