Abstract
The interaction between the UV filter, 2-ethylhexyl-p-dimethylaminobenzoate, and unmodified and modified alpha-, beta- or gamma-cyclodextrins was studied in water by phase-solubility analysis. Of the cyclodextrins available, only hydroxypropyl-beta-cyclodextrin caused a marked increase in the aqueous solubility of 2-ethylhexyl-p-dimethylaminobenzoate. The data from the solubility study indicated the formation of a 1:1 (sunscreen-cyclodextrin) complex. The inclusion of the sunscreen agent into the hydroxypropyl-beta-cyclodextrin cavity was confirmed by thermal analysis and by nuclear magnetic resonance spectroscopy. Irradiation-induced degradation of 2-ethylhexyl-p-dimethylaminobenzoate was reduced by complexation with hydroxypropyl-beta-cyclodextrin, this effect being more pronounced in solution (the extent of degradation was 25.5% for the complex compared with 54.6% for free 2-ethylhexyl-p-dimethylaminobenzoate) than in the emulsion vehicle (the extent of degradation was 25.1% for the complex compared with 33.4% for free 2-ethylhexyl-p-dimethylaminobenzoate). Although photodegradation of the sunscreen agent is significantly reduced by formation of the inclusion complex it is important to design a suitable vehicle. Inclusion of 2-ethylhexyl-p-dimethylaminobenzoate-DMAB into the hydroxypropyl-beta-cyclodextrin cavity limits interaction of the UV filter with the skin reducing the side-effects of the formulation.
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