S‐Nitrosothiol and Disulfide Formation through Peroxynitrite‐Promoted Oxidation of Thiols

Peroxynitrite reacts with thiols 1 at acidic pH to give the corresponding S-nitrosothiols 2 and disulfides 3. The formation of nitrosothiols 2, the yield of which is strongly pH-dependent, can be rationalized in terms of acid-catalyzed decomposition of the undissociated HPN, probably through the intermediacy of the protonated form H2PN+, leading to a species, X−NO, capable of nitrosating the thiol function. In contrast, the formation of disulfides 3 occurs in a manner independent of the pH, without the intermediacy of sulfanyl radicals. Under basic conditions, the peroxynitrite anion (PN) oxidizes the thiolate ion to sulfanyl radicals, eventually leading to disulfide 3, or undergoes a thiol-catalyzed decomposition. The former is the exclusive reaction exhibited by peroxynitrite at pH > 13.