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

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 Mossbauer transition, i.e., the lifetime of the 57Fe nucleus in the first excited state (10−7 s). The Mossbauer 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 Mossbauer 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 z 2 orbital of iron. This conclusion is fully consistent with the results of our previous studies of M-DNIC using the EPR method.