Nitrosonium Cation Release from Dinitrosyl Iron Complexes in the Decomposition Induced by Superoxide Anions or Ethylenediaminetetraacetate

Abstract

Spectral methods have been applied to demonstrate the complete decomposition of the binuclear dinitrosyl iron complex with glutathione after the addition of a 100-fold excess of potassium superoxide (KO₂) or EDTA. According to the resonance structure [(RS^–)₂${\text{Fe}}_{2}^{{2 + }}$(NO⁺)₂(NO)₂] of the complex, its decomposition, induced by the interaction of thiol and NO components of the complex with superoxide ions O$_{2}^{ - }$, leads to nitrosonium (NO⁺) cation release into the solution. The nitrosonium cations are then hydrolyzed to nitrite anions in the amount equaling half of the nitrosyl ligands present in the original complex. When the complex is decomposed by EDTA as an iron chelator, the released NO⁺ cations are not hydrolyzed but are bound to tertiary amino groups in EDTA. It has been shown by EPR that the dinitrosyl iron complex with glutathione is transformed in this process to a high-spin (S = 3/2) EPR-active mononitrosyl iron complex. These findings support the concept that dinitrosyl iron complexes with thiol-containing ligands can serve as donors of both neutral NO molecules and nitrosonium cations in living organisms.