Dinitrosyl Iron Complexes with Thiol-Containing Ligands as Sources of Universal Cytotoxins, Nitrosonium Cations

It has been shown that the release of half of nitrosyl ligands from iron-dinitrosyl fragments in binuclear dinitrosyl iron complexes with thiol-containing ligands in the form of nitrosonium (NO⁺) cations during the decay of these complexes in acidic solutions increased with a decrease in the stability of these complexes and completely stopped with an increase in the concentration of free thiols (not included in binuclear dinitrosyl iron complexes) to the level exceeding the concentration of iron-dinitrosyl fragments by two or more times. The first factor manifested itself in the fact that less stable complexes with mercaptosuccinate decomposed in an acidic medium at room temperature, whereas the decay of more stable complexes with glutathione occurred only when their solutions were heated at 80°C. The cessation of the release of NO⁺ cations from complexes with an increase in the level of free thiols in solution was determined by the ability of the latter to initiate the reduction of NO⁺ cations to NO.