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Visible‐light Photochemistry and Phototoxicity of Thiarubrines
Author(s) -
Page Jonathan E.,
Block Eric,
Towers G. H. Neil
Publication year - 1999
Publication title -
photochemistry and photobiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.818
H-Index - 131
eISSN - 1751-1097
pISSN - 0031-8655
DOI - 10.1111/j.1751-1097.1999.tb07984.x
Subject(s) - phototoxicity , photochemistry , chemistry , visible spectrum , photodissociation , sulfur , irradiation , thiophene , pigment , yield (engineering) , mass spectrometry , nuclear chemistry , chromatography , organic chemistry , materials science , biochemistry , in vitro , optoelectronics , physics , nuclear physics , metallurgy
. Thiarubrines, a group of intensely red, sulfur‐containing pigments produced by asteraceous plants, are photola‐bile, yielding thiophenes and elemental sulfur upon exposure to UV or visible light. The mechanism of this light‐induced conversion for thiarubrines A (la), B (lb) and D (lc), isolated from the roots of Ambrosia chamis‐sonis (Asteraceae), was investigated. Visible‐light irradiation of thiarubrines resulted in the formation of novel 2,6‐dithiabicyclo[3.1.0]hex‐3‐ene polyyne photointerme‐diates (photosulfides) that rapidly undergo desulfuriza‐tion to yield thiophenes. Six photosulfides, photosulfides 3a and 3a' from thiarubrine A (la), photosulfides 3b and 3b' from thiarubrine B (lb) and photosulfides 3c and 3c' from thiarubrine D (lc) were characterized. Thiarubrine photointermediates are short‐lived and unstable, with the photosulfides formed from thiarubrine A having a half‐life of 12.3 min at room temperature. While the immediate fate of the extruded sulfur is unknown, we identified cyclooctasulfur (S 8 ) in photolysis solutions of thiarubrine A using electron impact mass spectrometry. Visible‐light irradiation of Candida albicans cell suspensions treated with thiarubrine A led to a 99% decrease in cell viability, suggesting that the photosulfides, or other molecules generated by the exposure of thiarubrines to light, have significant toxicity.