title: Formation of a highly oxidized iron biliverdin complex upon treatment of a five-coordinate verdoheme with dioxygen.
abstract: Treatment of a green solution of the five-coordinate octaethylverdoheme, XFeII(OEOP) 1 (X = Cl or Br), with dioxygen results in the formation of a new iron complex of octaethylbiliverdin, 2, within a matter of minutes. The reaction has been monitored by 1H NMR spectroscopy, and the product 2 (X = Cl) has been isolated and examined by X-ray crystallography. The structure of 2 (X = Cl) shows that the iron is five-coordinate with bonds to the four nitrogen atoms of the helical tetrapyrrole ligand and to an axial chloride. Treatment of 2 (X = Cl or Br) with zinc amalgam produces the known iron(III) complex of biliverdin, {FeIII(OEB)}2. The unusual pattern of resonances in the 1H NMR spectrum of 2 and its facile reduction to {FeIII(OEB)}2 indicate that 2 is an oxidized complex that can be formulated by resonance structures involving either an Fe(IV) ion bound to a bilindione trianion or an Fe(III) ion bound to an oxidized, dianionic, radical form of the ligand.
authors.affiliation: Department of Chemistry, University of California, Davis, One Shields Avenue, Davis, California 95616, USA.
authors.forename: Khoi T
authors.initials: KT
authors.lastname: Nguyen
authors.forename: Sankar Prasad
authors.initials: SP
authors.lastname: Rath
authors.forename: Lechosław
authors.initials: L
authors.lastname: Latos-Grazyński
authors.forename: Marilyn M
authors.initials: MM
authors.lastname: Olmstead
authors.forename: Alan L
authors.initials: AL
authors.lastname: Balch
mesh_terms: D001664:Biliverdine / Q000737:chemistry*; D006418:Heme / Q000031:analogs & derivatives* / Q000737:chemistry*; D007202:Indicators and Reagents; D007501:Iron / Q000737:chemistry*; D009682:Magnetic Resonance Spectroscopy; D008958:Models, Molecular; D008968:Molecular Conformation; D010084:Oxidation-Reduction; D010100:Oxygen / Q000737:chemistry*
chemical_list: D007202:Indicators and Reagents; C099547:verdoheme; D006418:Heme; D007501:Iron; D001664:Biliverdine; D010100:Oxygen