Structural characterization of the water-soluble porphyrin complexes [Fe(TPPS) (NO)] and [μ-O-([Fe(TPPS)])].

Iron water-soluble porphyrins have been long used as biomimetic compounds for modelling the active sites found in heme-enzymes. In this regard, the anionic porphyrin [Fe(TPPS)] and its coordination complexes have been repeatedly chosen as suitable water-soluble platforms for bioinorganic chemistry studies. In this work we report for the first time the crystal structure of the water-soluble nitrosyl complex [Fe(TPPS) (NO)] along with that of oxodimeric ferric species [μ-O-([Fe(TPPS)])].

HS/Thiols, NO, and NO/HNO: Interactions with Iron Porphyrins.

In the past decade, gasotransmitters NO and HS have been thoroughly studied in biological contexts, as their biosynthesis and physiological effects became known. Moreover, an additional intricate reaction scheme between these compounds and related species is thought to exist as part of the cascade signaling processes in physiological conditions. In this context, heme enzymes, as modeled by iron porphyrins, play a central role in catalyzing the key interconversions involved.

Azanone (HNO): generation, stabilization and detection.

HNO (nitroxyl, azanone), joined the 'biologically relevant reactive nitrogen species' family in the 2000s. Azanone is impossible to store due to its high reactivity and inherent low stability. Consequently, its chemistry and effects are studied using donor compounds, which release this molecule in solution and in the gas phase upon stimulation.

Synthesis, structure and reactivity of NO, NO˙ and NO pincer PCN-Rh complexes.

Synthesis of a pincer-type linear nitrosyl complex [Rh(PCN)(NO)] (3) is described. The product and all intermediates involved were fully characterized by FTIR, NMR, cyclic voltammetry and X-ray crystallography. Attempts at obtaining (3) from its chlorinated precursor Rh(PCN)(NO)Cl (2) revealed that a relative stabilization of this complex ion is introduced by the BArF counteranion, as other counteranions-PF, BF and triflate-proved to coordinate to the metal center.

Water-Soluble Nitroxyl Porphyrin Complexes FeTPPSHNO and FeTPPSNO Obtained from Isolated FeTPPSNO

The first biomimetic water-soluble Fe-porphyrin nitroxyl complexes were obtained and characterized by UV-vis in protonated and deprotonated forms by reduction of previously isolated and characterized FeTPPSNO. The p involved in the Fe-HNO ⇄ Fe-NO + H equilibrium was estimated to be around 9.7.

NO˙ disproportionation by a {RhNO} pincer-type complex.

The reactivity of the {RhNO} complex [Rh(PCPBu)(NO)]˙ (1˙) with NO˙ was studied. A disproportionation reaction takes place in which NO is released quantitatively, while the complex Rh(PCPBu)(NO)(NO) (2), with coordinated nitrite, is formed. The new complex 2 was fully characterized by multinuclear NMR techniques, IR and X-ray diffraction.

Reactions of HNO with metal porphyrins: underscoring the biological relevance of HNO.

Azanone ((1)HNO, nitroxyl) shows interesting yet poorly understood chemical and biological effects. HNO has some overlapping properties with nitric oxide (NO), sharing its biological reactivity toward heme proteins, thiols, and oxygen. Despite this similarity, HNO and NO show significantly different pharmacological effects.

Spectroelectrochemical evidence for the nitrosyl redox siblings NO+, NO*, and NO- coordinated to a strongly electron-accepting Fe(II) porphyrin: DFT calculations suggest the presence of high-spin states after reduction of the Fe(II)-NO- complex.

Experimental and computational results for the electron-deficient porphyrin complex [Fe(NO)(TFPPBr(8))] (1; TFPPBr(8)=2,3,7,8,12,13,17,18-octabromo-5,10,15,20-tetrakis(pentafluorophenyl)porphyrin) are reported with respect to its electron-transfer behavior. Complex 1 undergoes three one-electron processes: two reversible reductions and one irreversible oxidation. Spectroelectrochemical measurements (IR and UV/Vis/NIR spectroscopy) of (14)NO- and (15)NO-containing material indicate that the first reduction to 1(-) occurs largely on the NO ligand to produce nitroxyl anion (NO(-)) character, as evident from the considerable change in ν(NO) from 1715 to around 1550 cm(-1).

Successful stabilization of the elusive species {FeNO}8 in a heme model.

Nitroxyl (HNO/NO(-)) heme-adducts have been postulated as intermediates in a variety of catalytic processes carried out by different metalloenzymes. Hence, there is growing interest in obtaining and characterizing heme model nitroxyl complexes. The one-electron chemical reduction of the {FeNO}(7) nitrosyl derivative of Fe(III)(TFPPBr(8))Cl, Fe(II)(TFPPBr(8))NO (1) (TFPPBr(8) = 2,3,7,8,12,13,17,18-octabromo-5,10,15,20-[Tetrakis-(pentafluorophenyl)]porphyrin) with cobaltocene yields the significantly stable {FeNO}(8) complex, [Co(C(5)H(5))(2)](+)[Fe(TFPPBr(8))NO](-) (2).