title: Synthesis of Co(II)-NO(-) Complexes and Their Reactivity as a Source of Nitroxyl.
abstract: Metal-nitroxyl (M-HNO/M-NO(-)) coordination units are found in denitrification enzymes of the global nitrogen cycle, and free HNO exhibits pharmacological properties related to cardiovascular physiology that are distinct from nitric oxide (NO). To elucidate the properties that control the binding and release of coordinated nitroxyl or its anion at these biological metal sites, we synthesized {CoNO}(8) (1, 2) and {CoNO}(9) (3, 4) complexes that contain diimine-dipyrrolide supporting ligands. Experimental (NMR, IR, MS, EPR, XAS, XRD) and computational data (DFT) support an oxidation state assignment for 3 and 4 of high spin Co(II) (SCo = 3/2) coordinated to (3)NO(-) (SNO = 1) for Stot = 1/2. As suggested by DFT, upon protonation, a spin transition occurs to generate a putative low spin Co(II)-(1)HNO (SCo = Stot = 1/2); the Co-NO bond is ∼0.2 Å longer, more labile, and facilitates the release of HNO. This property was confirmed experimentally through the detection and quantification of N2O (∼70% yield), a byproduct of the established HNO self-reaction (2HNO → N2O + H2O). Additionally, 3 and 4 function as HNO donors in aqueous media at pH 7.4 and react with known HNO targets, such as a water-soluble Mn(III)-porphyrin ([Mn(III)(TPPS)](3-); TPPS = meso-tetrakis(4-sulfonatophenyl)porphyrinate) and ferric myoglobin (metMb) to quantitatively yield [Mn(TPPS)(NO)](4-) and MbNO, respectively.
authors: Department of Chemistry and Center for Metalloenzyme Studies, The University of Georgia , 140 Cedar Street, Athens, Georgia 30602, United States.
authors: Melody R
authors: MR
authors: Walter
authors: Departments of Pharmaceutical Sciences, Biochemistry, and Molecular Biology, Wayne State University , Detroit, Michigan 48201, United States.
authors: Stephen P
authors: SP
authors: Dzul
authors: Departments of Pharmaceutical Sciences, Biochemistry, and Molecular Biology, Wayne State University , Detroit, Michigan 48201, United States.
authors: Andria V
authors: AV
authors: Rodrigues
authors: Departments of Pharmaceutical Sciences, Biochemistry, and Molecular Biology, Wayne State University , Detroit, Michigan 48201, United States.
authors: Timothy L
authors: TL
authors: Stemmler
authors: Department of Biological, Chemical, and Physical Sciences, Roosevelt University , 430 South Michigan Avenue, Chicago, Illinois 60605, United States.
authors: Joshua
authors: J
authors: Telser
authors: Department of Chemistry, University of the Free State , 9300 Bloemfontein, Republic of South Africa.
authors: Jeanet
authors: J
authors: Conradie
authors: Department of Chemistry and Center for Theoretical and Computational Chemistry, University of Tromsø , N-9037 Tromsø, Norway.
authors: Abhik
authors: A
authors: Ghosh
authors: Department of Chemistry and Center for Metalloenzyme Studies, The University of Georgia , 140 Cedar Street, Athens, Georgia 30602, United States.
authors: Todd C
authors: TC
authors: Harrop
mesh_terms: D004563:Electrochemistry; D008667:Metalloproteins / Q000737:chemistry* / Q000378:metabolism*; D008958:Models, Molecular; D015394:Molecular Structure; D058458:Nitrogen Cycle; D009589:Nitrogen Oxides / Q000737:chemistry*
chemical_list: D008667:Metalloproteins; D009589:Nitrogen Oxides; C039900:nitroxyl