On the complexation of Trolox with methyl-beta-cyclodextrin: characterization, molecolar modelling and photostabilizing properties

Exposure to UV radiations could reduce the efficiency of some antioxidants like Trolox (6-hydroxy-2,5,7,8-tetramethylchroman-2-carboxylic acid), a water-soluble vitamin E analogue largely employed in cosmetic products. Accordingly, in this paper we examined the possibility of increasing the stability of Trolox towards UVB irradiation by its complexation with methyl-β-cyclodextrin. Formation of the inclusion complex was confirmed by solubility diagrams, differential scanning calorimetry (DSC), and diffusion study through hydrophilic membrane. The stability constants and docking results suggested that the complexation phenomenon was related to the pH of the medium. The photodegradation studies were carried out in different topical formulations (gel, O/W emulsion, and W/O/W emulsion) containing Trolox free or complexed with methyl-β-cyclodextrin. Results showed that in all the cases Trolox degraded following pseudo-zero order kinetics. Moreover, the host molecule increased Trolox photostability also in the presence of TiO2, a physical sunscreen well-known as photocatalyzer.