Eosin, oxygen sensitizer

Competitive photooxygenation of the substrate pair 1-methyl-cyclopentene (AJ/l-methylcyclohexene (A2) was studied by Kopecky and Reich.123 Using rose bengal, erythrosin, and eosin, as well as methylene blue and hematoporphyrin as sensitizers, the ratio kg1/kg2 was found to be independent of the nature of the sensitizer used, in agreement with the assumption that singlet oxygen is the oxygenating intermediate. 

It has recently been shown by Spikes150 that uracil and a number of substituted uracils are subject to dye-sensitized photooxidation under certain conditions. Methylene blue and Eosin Y were active photosensitizers in the pH range 8-11.5, but were inactive below pH 8. FMN was very active over the pH range of 2.4-11.5. Photooxidation was measured with a rotating platinum oxygen electrode. 

There was a slight effect of the oxygen concentration ([02] = 10-3 to 10-2 mole/liter) on A02 when eosin and fluorescein were used as sensitizers. Assuming that this is due to the relatively long lifetimes of the corresponding excited singlet states which may allow these states to interact with oxygen, crude values of k6 were calculated (see Table II). 

Eosin generates singlet oxygen upon irradiation with visible light. Its ability to act as a photodynamic sensitizer has been known for many years [125], Irradiation of Eosin in the presence of oxygen is found to deactivate viruses [126] and yeasts [127] and to damage the photosystem II of leaf tissue [128,129], Eosin covalently immobilized in polystyrene beads has been used to remove E. coli from drinking water [130],... 

The localization of the sensitizer has a significant effect on the photodynamic activity. Eosin is scarcely taken up by cells, and Pooler and Girotti [131] report that Eosin isothiocyanate is 50-100 times more efficient for inducing photohemolysis of human erythrocytes. The spectral properties and quantum yields for singlet oxygen production are identical for both compounds. Therefore, they attribute the difference in photodynamic activity to the ability of the isothiocyanate derivative to bind covalently to band 3 protein. 

Pemberton and Johnson [175,176] have performed a thorough study of the photopolymerization of vinyl acetate in aqueous methanol sensitized by ethyl Eosin and ascorbic acid. In agreement with Oster s results, these authors find that polymer is not formed in the absence of oxygen. In addition, dye photobleaching without polymer formation is observed when water is excluded. 

The eosin-sensitized photo-oxygenation of 3jS-hydroxyandrosta-5,7-dien-17-one (181) provides a mixture of 5a,8-epidioxide (182a), 5,8-dien-7-one (182b), and both isomeric allylic alcohols (183a) and (183b). Palladium-catalysed treatment of (182a) gave the triol (184), which was then converted into the triene-dione (185) °. 

Triplet sensitization is the usual and most convenient means of generating singlet oxygen. Singlet oxygen is photogenerated from both ionized and unionized derivatives of triplet rose bengal and eosin Y in dilute solutions . The efficiency of... 

It has been found that certain dyes, such as methylene blue, eosin and Rose Bengal, sensitize the photo-oxidation of many organic compounds in solution [Refs. 242, 246-248, 328, 329, 371, 585, 639, 668]. More detailed investigations have shown that the photo-oxidation reaction takes place with the participation of singlet oxygen formed by the reaction between the dye excited to the triplet state and molecular oxygen. The energy of the triplet state dye molecules (Table 15) is sufficient to... 

Honma and Ban (307) have reported a second synthesis of deoxyaspidodispermine (158). Crucial in this scheme is the eosine-sensitized stereospecific addition of oxygen to the diene (716) in quantitative yield. Catalytic hydrogenation of 717 under pressure gave diol 718, from which water was eliminated, after basic hydrolysis of the urethane group, to give the indolenine 719. Lithium aluminum hydride reduction gave the indoline 720 which could be acetylated to deoxyaspidodispermine (158) under mild conditions (307) (Scheme 51). 

Photo-oxidation of thiouracil by singlet oxygen using eosin yellow, rose bengal and methylene blue as dye sensitizers affords two products, thiourea and acetylthiourea a mechanism has been proposed. ... 

The photochemical generation of singlet oxygen has suffered from the insolubility of those anionic dyes which are commonly used as sensitizers (see Fig. 11.1). It has recently been found that the photosensitizing dyes eosin and rose bengal can be solu-... 

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