Rose Bengal, photosensitizer

A number of workers have looked at the effect of photooxidation and photodynamic sensitizers on DNA. Rose Bengal photosensitizes strand breaks in double-stranded, supercoiled, pBR322 DNA the effect follows first-order kinetics with respect to light fluence and dye concentration. The reaction is substantially more efficient in the absence of oxygen, but the quantum yield of strand breaks in air is only 10 8. The results are consistent with the initiation of chain scission by Rose Bengal triplet, with some additional mechanism coming into play in the presence of oxygen. 

Perhaps more important, Foote has shown that chemically generated singlet oxygen gives the same product distribution from (+)-limonene as obtained by the rose bengal-photosensitized oxidation.467 Moreover, the (—)-tra 5,-carveol formed in both types of oxidation has the same large optical activity. 

The mechanism of formation of (99) in Scheme 15 may also apply to the production of the aldehyde (101) on Rose Bengal-photosensitized oxidation of the dimethylamino-substituted benzenes (100) in methanol, during experiments... 

A polymer-bound rose-bengal photosensitizer is commercially available. The efficiency of SENSTTOX is about 65% of that of Rose-Bengal, but the high yields of the products and the ease of isolation more than compensate the slightly longer reaction periods (Scheme 17). 

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