Decomposition of S‐Nitrosothiols Induced by UV and Sunlight

Abstract

Photochemical release of nitric oxide (NO) from the S‐nitroso derivatives of glutathione, L‐cysteine, N‐acetyl‐L‐cysteine, L‐cysteinemethylester, D,L‐penicillamine, N‐acetyl‐D,L‐penicillamine, and N‐acetylcysteamine has been investigated at neutral and acidic pH. The release of NO from RSNO is one of the key reactions that could be utilized in photodynamic therapy. The UV‐VIS and HPLC analyses have shown that under argon saturated conditions, disulfide (RSSR) is the major product of UV as well as sunlight induced decomposition. While in aerated conditions, nitirite—the end product of the oxidation of NO—was also observed along with disulfide. The formation of thiyl radical as the intermediate was reconfirmed by laser flash photolysis. The initial rate of formation of NO was on the order of 10−5 dm3 mol−1 s−1. The quantum yields of these reactions were in the range of 0.2–0.8. The high quantum yields observed in the photo induced release of NO from RSNO using both UV and sunlight demonstrate the potential application of these reactions in photodynamic therapy.