EPR and Mössbauer Characteristics of Aqueous Solutions of 57Fe-Dinitrosyl Iron Complexes with Glutathione and Hydroxyl Ligands

Abstract

Our electron paramagnetic resonance (EPR) studies have demonstrated that at 293 K and 77 K, the spin–lattice relaxation time, T₁, of paramagnetic mononuclear dinitrosyl iron complexes (M-DNICs) with glutathione and hydroxyl ligands containing isotopes ⁵⁷Fe and ⁵⁶Fe notably exceeds the halflife of the Mössbauer transition, i.e., the lifetime of the ⁵⁷Fe nucleus in the first excited state (10⁻⁷ s). The Mössbauer spectra of M-DNIC with hydroxyl ligands, binuclear DNIC with glutathione (B-DNIC) and sodium dithionite-treated solution of B-DNIC with glutathione did not display the presence of the magnetic hyperfine structure (MHFS) characteristic of M-DNIC with glutathione. The Mössbauer spectra of all these DNICs were characterized by quadrupole splitting. The results of a comprehensive comparative analysis of MHFS of M-DNIC with glutathione and that in DMF reduced sodium nitroprusside suggest that M-DNIC with glutathione have a low-spin (S = ½) d⁷ electronic configuration with the predominant localization of the unpaired electron on the d_z² orbital of iron. This conclusion is fully consistent with the results of our previous studies of M-DNIC using the EPR method.