Genes controlling carotenoid synthesis were cloned from Erwinia herbicola and expressed in an Escherichia coli strain. Carotenoids protect against high fluences of near-UV (NUV; 320 to 400 nm) but not against far-UV (200-300 nm). Protection of E. coli cells was not observed following treatment with either psoralen or 8-methoxypsoralen plus NUV. However, significant protection of cells producing carotenoids was observed with three photosensitizing molecules activated by NUV (alpha-terthienyl, harmine, and phenylheptatriyne) which are thought to have the membrane as an important lethal target. Protection of carotenoid-producing cells against inactivation was not observed with acridine orange plus visible light but was seen with toluidine blue O plus visible light.

Abstract— The photophysical and photochemical properties of thiophene derivatives have been studied by fluorescence and by 353 nm laser flash spectroscopy. α‐Terthienyl and its derivatives show a moderate fluorescence quantum yield (less than 0.1) in cyclohexane, ethanol, or TritonX–100 micelles. An additional thiophene ring increases this value to 0.2 in ethanol or micelles. The transient triplet state of the six thiophenes is characterized by strong absorptions (ε⋍ 50000 M‐1 cm‐1) in the visible region. These triplet states are very long lived. They react with oxygen, producing singlet oxygen very efficiently because of their high quantum yield of triplet formation (0.1 to 0.3). They do not react with excellent hydrogen or electron donors such as indole, N‐acetyl tryptophanamide or cysteine. The hydrophobic thiophenes investigated are, therefore, Type II photodynamic agents almost exclusively.

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caled for C11H1203S2 m/e 256.0229, obsd m/e 256.0255. 25. The metalation of 21b (100 mg, 0.39 mmol) was conducted in THF (4 mL) at -70 °C, using n-BuLi (0.39 mmol) over 10 min. Dimethyl disulfide (0.04 mL, 0.44 mmol) was added, the solution was stirred for 15 min at-70 °C, and the reaction was quenched with aqueous Na2C03. Workup followed by filtration of the crude product through neutral alumina (activity III, 1.5 X 6 cm column, 10% Et^O/PE as eluant) gave 92 mg of 25 as a pale yellow oil:

Alpha-terthienyl is toxic to late embryonic stages ofRana pipiens in the presence of sunlight. Neither α-terthienyl alone in the dark nor a previously photolyzed solution of α-terthienyl has comparable activity. The LC50 was 0.11 ppm with 30 min of exposure and 0.018 ppm with 2 hr of exposure to sunlight. Anthracene, a representative example of polycyclic aromatic hydrocarbons widely distributed in the environment, also showed similar phototoxicity, with an LC50 of 0.065 ppm after 30 min of exposure and 0.025 ppm after 5 hr.