Polynuclear water-soluble dinitrosyl iron complexes with cysteine or glutathione ligands: Electron paramagnetic resonance and optical studies

Mechanism and biological implications of the NO release of cis-[Ru(bpy)2L(NO)]n+ complexes: A key role of physiological thiols

“…This final species then releases slowly NO 0 (k= 6.4 × 10 − 4 s − 1 at 25°C), and also produces the same EPR spectrum profile observed for the compounds presented in this work [26]. In addition, the trans-K{[Fe II (cyclam)Cl(NO 0 )] [Fe II (cyclam)Cl(NO + )] 2 }(PF 6 ) 6 which has the {FeNO} 7 fragment presents the same EPR profile due to the presence of the NO group [27][28][29]. Therefore, accounting for the fact that [Ru(bpy) 2 LNO] n+ type complexes are EPR silent [30], we believe that we are observing the EPR spectrum for the coordinated NO 0 rather than that of a solvated NO 0 .…”

Redox conversions of dinitrosyl iron complexes with natural thiol-containing ligands

“…Our studies with 57 Fe-containing M-DNIC (the nuclear spin of 57 Fe is I = ½) established that the unpaired electron is predominantly localized on the iron atom in both original M-DNIC and M-DNIC undergoing two-electron reduction, as could be judged from the magnitude of the hyperfine splitting on the 57 Fe nucleus [3]. As far as the ability of M-DNIC to exist in the diamagnetic d 8 state is concerned, it was manifested after treatment of M-DNIC with a small dose of sodium dithionite, consisted in the disappearance of the EPR signal of the original M-DNIC (g \ = 2.04, g k = 2.014, g aver.…”

“…= 2.0 can be inferred from our current concepts on the original d 7 -d 7 electronic configuration of the iron atom in B-DNIC [3,4,8]. In the course of their single-electron reduction, B-DNIC pass into the paramagnetic state with the d 7 -d 8 ({Fe(NO) 2 } 7 -{Fe(NO) 2 } 8 ) electronic configuration of the iron atom, while their two-electron reduction yields a diamagnetic state with the electronic configuration d 8 -d 8 ({Fe(NO) 2 } 8 -{Fe(NO) 2 } 8 ) or d 7 -d 9 ({Fe(NO) 2 } 7 -{Fe(NO) 2 } 9 ).…”

“…= 2.03 (g \ = 2.04, g k = 2.014). The binuclear form (B-DNIC) is diamagnetic and represents a thiol ether of Roussin's red salt; its diamagnetic properties are provided by spin pairing (antiferromagnetic interaction) of two Fe(NO) 2 groups through sulfur bridges of B-DNIC [3,4]. Both forms of DNIC can exist in low-molecular and protein-bound states; in the latter case, thiol-containing ligands are represented by protein residues of cysteine [1].…”

“…Such a distribution of spin density was inferred from the analysis of the hyperfine structure (HFS) of the EPR signal of M-DNIC with thiol-containing ligands. In the framework of this hypothesis, the transition of reduced M-DNIC into the paramagnetic state is due to the capture of two electrons, as a result of which the electronic configuration of the iron atom changes to d 9 ({Fe(NO) 2 } 9 in the Feltham-Enemark presentation) [3]. After the capture of one electron, M-DNIC are converted into the intermediate (diamagnetic) form with the electronic configuration d 8 ({Fe(NO) 2 } 8 in the Feltham-Enemark presentation) [3,5].…”