Singlet oxidation, inhibition

Thiols can also be converted to disulfides, as in the CdS-photocatalyzed conversion of cysteine to cystine In the latter reaction, the uptake of oxygen was pH dependent. Since the reaction rate was not increased in deuterium oxide and was not decreased by added azide, the authors conclude that singlet oxygen is not involved. Since superoxide dismutase inhibited the conversion, a photoinduced electron transfer is probably responsible for the observed transformations. Such organosulfide oxidations may be environmentally important since naturally occurring hematite suffers a photoassisted dissolution in the presence of thiols... 

Ascorbic acid inhibits light-induced yellowing for a finite time, 1 to 2 hours when irradiated with near-uv light with an intensity of 9.2 mW/cm2 (6). This limitation has been attributed in part to photooxidation of ascorbic acid. In addition to air oxidation, ascorbic acid is oxidized by photochemically produced peroxyl radicals, superoxide radical anion and singlet oxygen (27,28). If ascorbic acid is to be an effective inhibitor of light-induced yellowing it s oxidation must be slowed. 

Sortino et al. reported the use of light irradiation on SAMs supporting the anticancer drug flutamide to study its photoreactivity and product release of nitric oxide. The authors were able to conduct studies in the absence of noxious side effects such as singlet-oxygen photosensitization and observed that nitric oxide production halted when the light was turned off [103], Another photoactive molecule, azobenzene, has recently been exploited in the SAM community to aid in studies on cell adhesion and enzyme inhibition [104], Pearson and coworkers described the use of photoisomerizable SAMs of azobenzene to conduct a series of serine and cysteine protease inhibition experiments. When light of 340-380 nm is used, the... 

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