Solvent- and Wavelength-Dependent Photochemistry of 1,3-Dihydroxyacetone Studied by TREPR: Implications for Commercial Sunless Tanning Lotions

Abstract

1,3-Dihydroxyacetone (DHA) is the active ingredient in commercial personal care products for the production of a “sunless” tan on human skin. The DHA molecule is the simplest ketose sugar, and it reacts with amino acids on the surface of the skin in a biochemical pathway known as the Maillard reaction. However, DHA is known to be photochemically active and will produce free radicals with high quantum yield under ultraviolet (UV) excitation. We report here a detailed study of the free radicals produced by DHA photolysis as a function of wavelength and solvent. In contrary to the previous optical and steady-state electron paramagnetic resonance (EPR) studies, X-band time-resolved (TR)-EPR spectra reveal a complex reactivity pattern: Norrish I α-cleavage is observed in almost all cases, but when good H-atom donors are present, H-atom abstraction by the solvent is observed. Changing the wavelength of excitation from 308 to 248 nm can reverse this observation. Comparison of TREPR spectra obtained from commercially available sunless tanning lotions shows that many free radicals, including those from DHA, can be detected using direct detection TREPR upon photolysis of the lotions themselves. The results suggest that caution should be observed in the use of these products in conjunction with UV exposure.