Octyl p-methoxycinnamate loaded microemulsion based on Ocimum basilicum essential oil. Characterization and analytical studies for potential cosmetic applications

A O/W microemulsion based on biocompatible materials was designed for a potential topical use as UVB filter, antiinflamatory and mosquito repellent. Octyl-p-methoxy cinnamate (OMC) is one of the most widely used sunscreen compounds. Nevertheless, their efficiency as UV filter is affected by irradiation because a photolysis process occurs. Ocimum basilicum essential oil is utilized in traditional medicine and as repellent of insects, among others. Hence, the proposed O/W microemulsion consisted of 6.0% of Ocimum basilicum essential oil (oil phase), 23% of a 2:1 mixture of decaethylene glycol mono-dodecyl ether (surfactant) and ethanol (co-surfactant), and 71% of water. OMC was successfully loaded in the O/W microemulsion (1.5%). The loaded system presented a particle size of (12.60 +/- 0.10) nm and a polydispersity index of 0.389 +/- 0.042. A spherical morphology and droplet sizes in nanometric range were corroborated by transmission electronic microscopy. The higher photostability of OMC in the O/W microemulsion with respect to the free-OMC was demonstrated by calculating the photolysis kinetic constants (0.00186 s(-1) and 0.00457 s(-1), respectively) which were obtained through a photolysis study assisted by multivariate curve resolution-alternating least squares algorithm. Moreover, the stability of the system over time and under different conditions was demonstrated. On the other hand, a chromatographic analysis of the essential oil corroborated the presence of estragole (93.2%) which presents a documented antiinflammatory activity, and seven compounds with a well reported mosquito repellent activity, such as linalool (2.81%), cineole (0.57%), among others. On this form, the proposed O/W microemulsion presents optimal chemical and physicochemical characteristics for a potential application in cosmetic products.