Photolysis study of octyl p-methoxycinnamate loaded microemulsion by molecular fluorescence and chemometric approach

• Published in: Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy Molecular and biomolecular spectroscopy, 2018-02, Vol.191, p.277-282
• Main Authors: Nascimento, Danielle Silva, Insausti, Matías, Band, Beatriz Susana Fernández, Grünhut, Marcos
• Format: Article
• Language: English
• Subjects: Molecular fluorescence; Multivariate curve resolution-alternating least squares; O/W microemulsion; Octyl p-methoxycinnamate; Photolysis
• ISSN: 1386-1425
• DOI: 10.1016/j.saa.2017.10.025

Octyl p-methoxycinnamate (OMC) is one of the most widely used sunscreen agents. However, the efficiency of OMC as UV filter over time is affected due to the formation of the cis-isomer which presents a markedly lower extinction coefficient (εcis=12,600L mol−1cm−1 at 291nm) than the original trans-isomer (εtrans=24,000L mol−1cm−1 at 310nm). In this work, a novel carrier for OMC based on an oil-in-water microemulsion is proposed in order to improve the photostability of this sunscreen. The formulation was composed of 29.2% (w/w) of a 3:1 mixture of ethanol (co-surfactant) and decaethylene glycol mono-dodecyl ether (surfactant), 1.5% (w/w) of oleic acid (oil phase) and 69.2% (w/w) of water. This microemulsion was prepared in a simple way, under moderate stirring at 25°C and using acceptable, biocompatible and accessible materials for topical use. OMC was incorporated in the vehicle at a final concentration of 5.0% (w/w), taking into account the maximum permitted levels established by international norms. Then, a photolysis study of the loaded formulation was performed using a continuous flow system. The direct photolysis was monitored over time by molecular fluorescence. The recorded spectra data between 370 y 490nm were analyzed by multivariate curve resolution-alternating least squares algorithm. The kinetic rate constants corresponding to the photolysis of the trans-OMC were calculated from the concentration profiles, resulting in 0.0049s−1 for the trans-OMC loaded microemulsion and 0.0131s−1 for the trans-OMC in aqueous media. These results demonstrate a higher photostability of the trans-OMC when loaded in the proposed vehicle with respect to the free trans-OMC in aqueous media. [Display omitted] •A new carrier for octyl p-methoxycinnamate based on a O/W microemulsion is proposed•A photolysis study of octyl p-methoxycinnamate was performed using a flow system•The photolysis of the UV filter was monitored on-line by molecular fluorescence•Kinetic rate constants were obtained by means of hybrid soft and hard-modelling•The O/W microemulsion improved the photostability of the octyl p-methoxycinnamate