The stability of the binuclear form of dinitrosyl iron complexes with various thiol-containing ligands, such as glutathione, L-cysteine, N-acetyl-L-cysteine, mercaptoethanol, and mercaptosuccinate, has been compared based on the results of exposure of these complexes in an aqueous medium at pH 1.0–2.0, leading to their decomposition as a result of protonation of the thiol group of thiol-containing ligands with the release of nitric oxide from the complexes (NO) and nitrosonium (NO+) cations. Complexes with L-cysteine and mercaptosuccinate turned out to be the least stable: they decomposed in acidic solutions at room temperature, whereas the more stable complexes with N-acetyl-L-cysteine, mercaptoethanol, or glutathione decomposed when their solutions were heated at 70–80°C. The decomposition of all these complexes under these conditions occurred within a few minutes with a concentration ratio of “free” (not included in the complexes) thiols and the complexes themselves not exceeding 1 : 2. With an increase in this ratio, the decay time of the complexes increased symbatically with the level of free thiols. The mononuclear form of the thiosulfate complexes decomposed at a thiosulfate-to-complex concentration ratio of 2 for several minutes in an aqueous solution at neutral pH values.
Vanin Af (Wed,) studied this question.