The mechanistic aspects of the photochemistry of several iminosulfonate photoacid generators (PAGs) have been studied based on product analysis, nanosecond laser flash photolysis, and determination of acid generation efficiencies. Our findings support a competition between homolytic and heterolytic N-O dissociation mechanisms. By measuring the efficiencies of acid generation for each PAG in the presence and absence of an ion quencher, we were able to roughly quantify the degree of branching between heterolytic and homolytic photocleavage pathways for each PAG. The p-toluenesulfonyloxyl radical was detected upon laser flash photolysis of several PAGs and was found to have a lambda(max) at 540 nm. By quenching the 540 nm transient with a variety of reactive species, the rate constants for reaction of the p-toluenesulfonyloxyl radical with these substrates were determined. The p-toluenesulfonyloxyl radical is shown to be a highly reactive species, which undergoes rapid hydrogen transfer and is a powerful oxidizer.
In light of primary melanoma in sun-shielded regions such as the rectum, theories of causation other than sun exposure merit consideration. Factors such as genetics, immunosuppression, and virus infections, as well as ultraviolet radiation, may play a role in the etiology of melanoma.
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