title: Photochemistry and phototoxicity of aloe emodin.
abstract: Photochemical pathways leading to the phototoxicity of the aloe vera constituent aloe emodin were studied. The results indicate a photochemical mechanism involving singlet oxygen to be the most likely pathway responsible for the observed phototoxicity. Aloe emodin was found to efficiently generate singlet oxygen when irradiated with UV light (phidelta = 0.56 in acetonitrile). The survival of human skin fibroblast cells in the presence of aloe emodin was found to decrease upon irradiation with UV light. A further decrease in cell survival was observed in D2O compared with H2O, suggesting the involvement of singlet oxygen as the primary pathway. Laser flash photolysis experiments were also carried out on aloe emodin alone and in the presence of various biological substrates. Aloe emodin proved to be relatively photostable (phi = 1 x 10(-4)) and a poor photo-oxidant (E*red = +1.02 V). Only absorption bands caused by the triplet state of aloe emodin (lambdamax = 480 nm) and the aloe emodin conjugate base (lambdamax = 520 nm) were observed in the transient spectra.
authors: Department of Chemistry and Biochemistry, University of Maryland, College Park 20742, USA.
authors: Peter
authors: P
authors: Vath
authors: Wayne G
authors: WG
authors: Wamer
authors: Daniel E
authors: DE
authors: Falvey
mesh_terms: D000880:Anthraquinones; D002470:Cell Survival; D004247:DNA / Q000378:metabolism; D004642:Emodin / Q000009:adverse effects* / Q000737:chemistry* / Q000378:metabolism; D010777:Photochemistry; D026082:Singlet Oxygen; D014466:Ultraviolet Rays
chemical_list: D000880:Anthraquinones; D026082:Singlet Oxygen; D004247:DNA; C518327:aloe emodin; D004642:Emodin