title: Polynuclear water-soluble dinitrosyl iron complexes with cysteine or glutathione ligands: electron paramagnetic resonance and optical studies.
abstract: Electron paramagnetic resonance and optical spectrophotometric studies have demonstrated that low-molecular dinitrosyl iron complexes (DNICs) with cysteine or glutathione exist in aqueous solutions in the form of paramagnetic mononuclear (capital EM, Cyrillic-DNICs) and diamagnetic binuclear complexes (B-DNICs). The latter represent Roussin's red salt esters and can be prepared by treatment of aqueous solutions of Fe(2+) and thiols (small er, Cyrilliccapital EN, Cyrillic 7.4) with gaseous nitric oxide (NO) at the thiol:Fe(2+) ratio 1:1. capital EM, Cyrillic-DNICs are synthesized under identical conditions at the thiol:Fe(2+) ratios above 20 and produce an EPR signal with an electronic configuration {Fe(NO)(2)}(7) at g(aver.)=2.03. At neutral pH, aqueous solutions contain both M-DNICs and B-DNICs (the content of the latter makes up to 50% of the total DNIC pool). The concentration of B-DNICs decreases with a rise in pH; at small er, Cyrilliccapital EN, Cyrillic 9-10, the solutions contain predominantly M-DNICs. The addition of thiol excess to aqueous solutions of B-DNICs synthesized at the thiol:Fe(2+) ratio 1:2 results in their conversion into capital EM, Cyrillic-DNICs, the total amount of iron incorporated into M-DNICs not exceeding 50% of the total iron pool in B-DNICs. Air bubbling of cys-capital EM, Cyrillic-DNIC solutions results in cysteine oxidation-controlled conversion of capital EM, Cyrillic-DNICs first into cys-B-DNICs and then into the EPR-silent compound capital HA, Cyrillic able to generate a strong absorption band at 278 nm. In the presence of glutathione or cysteine excess, compound capital HA, Cyrillic is converted into B-DNIC/M-DNIC and is completely decomposed under effect of the Fe(2+) chelator small o, Cyrillic-phenanthroline or N-methyl-d-glucamine dithiocarbamate (MGD). Moreover, MGD initiates the synthesis of paramagnetic mononitrosyl iron complexes with MGD. It is hypothesized that compound capital HA, Cyrillic represents a polynuclear DNIC with cysteine, most probably, an appropriate Roussin's black salt thioesters and cannot be prepared by simple substitution of capital EM, Cyrillic-DNIC cysteine for glutathione. Treatment of capital EM, Cyrillic-DNIC with sodium dithionite attenuates the EPR signal at g(aver.)=2.03 and stimulates the appearance of an EPR signal at g(aver.)=2.0 with a hypothetical electronic configuration {Fe(NO)(2)}(9). These changes can be reversed by storage of DNIC solutions in atmospheric air. The EPR signal at g(aver.)=2.0 generated upon treatment of B-DNICs with dithionite also disappears after incubation of B-DNIC solutions in air. In all probability, the center responsible for this EPR signal represents capital EM, Cyrillic-DNIC formed in a small amount during dithionite-induced decomposition of B-DNIC.
authors.affiliation: N.N. Semyonov Institute of Chemical Physics, Russian Academy of Sciences, Moscow, Russia. vanin@polymer.chph.ras.ru
authors.forename: Anatoly F
authors.initials: AF
authors.lastname: Vanin
authors.forename: Alexander P
authors.initials: AP
authors.lastname: Poltorakov
authors.forename: Vasak D
authors.initials: VD
authors.lastname: Mikoyan
authors.forename: Lyudmila N
authors.initials: LN
authors.lastname: Kubrina
authors.forename: Dosymzhan S
authors.initials: DS
authors.lastname: Burbaev
mesh_terms: D003545:Cysteine / Q000737:chemistry*; D004578:Electron Spin Resonance Spectroscopy; D005978:Glutathione / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D007501:Iron / Q000737:chemistry*; D058085:Iron Compounds; D008024:Ligands; D009569:Nitric Oxide; D009589:Nitrogen Oxides / Q000737:chemistry*; D055095:Optics and Photonics; D012995:Solubility; D012996:Solutions / Q000737:chemistry; D014867:Water / Q000737:chemistry*
chemical_list: D058085:Iron Compounds; D008024:Ligands; D009589:Nitrogen Oxides; D012996:Solutions; D014867:Water; D009569:Nitric Oxide; C106536:Roussin's red salt; C073661:dinitrosyl iron complex; D007501:Iron; D005978:Glutathione; D003545:Cysteine