Small-angle X-ray scattering and ¹³C NMR investigation on the internal structure of "cubosomes"

A novel aqueous dispersion of particles with bicontinuous cubic phases in their interior (cubosomes) was prepared. A nonionic triblock copolymer, Pluronic F127, was used as an emulsifier of a liquid crystal phase of hydrated monoolein (MO). Dynamic light scattering showed that particles with an average diameter of 160-270 nm were formed by high-pressure emulsification. Particle size decreased as the weight ratio of F127 to MO increased up to 10%, whereas it was constant at higher than 10%. Small-angle X-ray scattering experiments confirmed the presence of two kinds of cubic structures (C_D and C_P). At 3% F127, the diffraction pattern corresponding to the C_D was dominant and the diffraction of the C_P was minimally detected, suggesting that the polymer preferably emerges to the surface of the particles and the interior has a CD structure consisting mostly of hydrated MO. The proportion of the C_P increased with F127 content, which suggests that preferentially concentrated F127 at the surface participates in the formation of the C_P phase. ¹³C NMR experiments with a paramagnetic shift reagent showed that the signal of the carbonyl carbon of oleic-1-¹³C acid mixed in the particles readily shifted to a lower magnetic field by addition of europium ion (Eu³⁺), indicating high accessibility of the ion into the water channel inside the particles.