55917-58-3Relevant academic research and scientific papers
ENDOR of NO-ligated cytochrome c′
Usov, Oleg M.,Choi, Peter S.-T.,Shapleigh, James P.,Scholes, Charles P.
, p. 5021 - 5032 (2006)
The five-coordinate NO-bound heme in cytochrome c′ from an overexpressing variant of denitrifying R. sphaeroides 2.4.3 was investigated by proton, nitrogen, and deuterium Q-band ENDOR (electron nuclear double resonance). ENDOR was a direct probe of the unpaired electron density on the nitrogen of NO and, as measured across the EPR line shape, showed a hyperfine coupling range from 36 to 44 MHz for 14NO and 51 to 63 MHz for 15NO. The smallest NO coupling occurred at an electronic g-tensor axis perpendicular to the FeNO plane, and the largest hyperfine coupling occurred in the FeNO plane where the highest nitrogen valence spin density is located. The isotropic component of the NO hyperfine coupling indicated that the electron spin on the NO is not simply in a π* orbital having only 2p character but is in an orbital having 2s and 2p character in a 1:2 ratio. ENDOR frequencies from heme meso-protons, assigned with reference to porphyrin models, were determined to result from an anisotropic hyperfine tensor. This tensor indicated the orientation of the heme with respect to the FeNO plane and showed that the FeNO plane bisects the heme N-Fe-N 90° angle. ENDOR provided additional structural information through dipolar couplings, as follows: (1) to the nearest proton of the Phe14 ring, ～3.1 A away from the heme iron, where Phe14 is positioned to occlude binding of NO as a 6th (distal) ligand; (2) to exchangeable deuterons assigned to Arg127 which may H-bond with the proximal NO ligand.
The first structurally characterized nitrosyl heme thiolate model complex
Xu, Nan,Powell, Douglas R.,Cheng, Lin,Richter-Addo, George B.
, p. 2030 - 2032 (2006)
The NO ligand in the formally {FeNO}6 compound [Fe(oep)(NO)(thiolate)] is bent, and does not impart a significant structural trans effect to the Fe-S bond. The Royal Society of Chemistry 2006.
Not Limited to Iron: A Cobalt Heme–NO Model Facilitates N–N Coupling with External NO in the Presence of a Lewis Acid to Generate N2O
Abucayon, Erwin G.,Khade, Rahul L.,Powell, Douglas R.,Zhang, Yong,Richter-Addo, George B.
supporting information, p. 18598 - 18603 (2019/11/14)
Some bacterial heme proteins catalyze the coupling of two NO molecules to generate N2O. We previously reported that a heme Fe–NO model engages in this N?N bond-forming reaction with NO. We now demonstrate that (OEP)CoII(NO) similarly reacts with 1 equiv of NO in the presence of the Lewis acids BX3 (X=F, C6F5) to generate N2O. DFT calculations support retention of the CoII oxidation state for the experimentally observed adduct (OEP)CoII(NO?BF3), the presumed hyponitrite intermediate (P.+)CoII(ONNO?BF3), and the porphyrin π-radical cation by-product of this reaction, and that the π-radical cation formation likely occurs at the hyponitrite stage. In contrast, the Fe analogue undergoes a ferrous-to-ferric oxidation state conversion during this reaction. Our work shows that cobalt hemes are chemically competent to engage in the NO-to-N2O conversion reaction.
Lewis Acid Activation of the Ferrous Heme-NO Fragment toward the N-N Coupling Reaction with NO to Generate N2O
Abucayon, Erwin G.,Khade, Rahul L.,Powell, Douglas R.,Zhang, Yong,Richter-Addo, George B.
supporting information, p. 4204 - 4207 (2018/04/05)
Bacterial NO reductase (bacNOR) enzymes utilize a heme/non-heme active site to couple two NO molecules to N2O. We show that BF3 coordination to the nitrosyl O-atom in (OEP)Fe(NO) activates it toward N-N bond formation with NO to generate N2O. 15N-isotopic labeling reveals a reversible nitrosyl exchange reaction and follow-up N-O bond cleavage in the N2O formation step. Other Lewis acids (B(C6F5)3 and K+) also promote the NO coupling reaction with (OEP)Fe(NO). These results, complemented by DFT calculations, provide experimental support for the cis:b3 pathway in bacNOR.
Over or under: hydride attack at the metal versus the coordinated nitrosyl ligand in ferric nitrosyl porphyrins
Abucayon,Khade,Powell,Shaw,Zhang,Richter-Addo
, p. 18259 - 18266 (2016/11/25)
Hydride attack at a ferric heme-NO to give an Fe-HNO intermediate is a key step in the global N-cycle. We demonstrate differential reactivity when six- and five-coordinate ferric heme-NO models react with hydride. Although Fe-HNO formation is thermodynamically favored from this reaction, Fe-H formation is kinetically favored for the 5C case.
Six-coordinate ferric porphyrins containing bidentate N-t-butyl-N-nitrosohydroxylaminato ligands: Structure, magnetism, IR spectroelectrochemisty, and reactivity
Xu, Nan,Christian, Jonathan H.,Dalal, Naresh S.,Abucayon, Erwin G.,Lingafelt, Colin,Powell, Douglas R.,Richter-Addo, George B.
, p. 20121 - 20130 (2015/12/01)
NONOates (diazeniumdiolates) containing the [X{N2O2}]- functional group are frequently employed as nitric oxide (NO) donors in biology, and some NONOates have been shown to bind to metalloenzymes. We report the preparation, crystal structures, detailed magnetic behavior, redox properties, and reactivities of the first isolable alkyl C-NONOate complexes of heme models, namely (OEP)Fe(η2-ON(t-Bu)NO) (1) and (TPP)Fe(η2-ON(t-Bu)NO) (2) (OEP = octaethylporphyrinato dianion, TPP = tetraphenylporphyrinato dianion). The compounds display the unusual NONOate O,O-bidentate binding mode for porphyrins, resulting in significant apical Fe displacements (+0.60 ? for 1, and +0.69 ? for 2) towards the axial ligands. Magnetic susceptibility and magnetization measurements made from 1.8-300 K at magnetic fields from 0.02 to 5 T, yielded magnetic moments of 5.976 and 5.974 Bohr magnetons for 1 and 2, respectively, clearly identifying them as high-spin (S = 5/2) ferric compounds. Variable-frequency (9.4 GHz and 34.5 GHz) EPR measurements, coupled with computer simulations, confirmed the magnetization results and yielded more precise values for the spin Hamiltonian parameters: gavg = 2.00 ± 0.03, D = 3.89 ± 0.09 cm-1, and E/D = 0.07 ± 0.01 for both compounds, where D and E are the axial and rhombic zero-field splittings. IR spectroelectrochemistry studies reveal that the first oxidations of these compounds occur at the porphyrin macrocycles and not at the Fe-NONOate moieties. Reactions of 1 and 2 with a histidine mimic (1-methylimidazole) generate RNO and NO, both of which may bind to the metal center if sterics allow, as shown by a comparative study with the Cupferron complex (T(p-OMe)PP)Fe(η2-ON(Ph)NO). Protonation of 1 and 2 yields N2O as a gaseous product, presumably from the initial generation of HNO that dimerizes to the observed N2O product.
Electrochemistry and spectroelectrochemistry of iron porphyrins in the presence of nitrite
Wei, Zhongcheng,Ryan, Michael D.
, p. 49 - 57 (2008/10/08)
The reaction of nitrite with ferric and ferrous porphyrins was examined using visible, infrared and NMR spectroscopy. Solutions of either ferric or ferrous porphyrin were stable in the presence of nitrite, with only complexation reactions being observed. Under voltammetric conditions, though, a rapid reaction between nitrite and iron porphyrins was observed to form the nitrosyl complex, Fe(P)(NO), where P=porphyrin. The products of the reduction of ferric porphyrins in the presence of nitrite were confirmed by visible spectroelectrochemistry to be Fe(P)(NO) and [Fe(P)]2O. Visible, NMR and infrared spectroscopy were used to rule out the formation of Fe(P)(NO) by the iron-catalyzed disproportionation of nitrite. A reaction between iron porphyrins and nitrite only occurred by the presence of both oxidation states (ferric/ferrous). The kinetics of the reaction were monitored by visible spectroscopy, and the reaction was found to be first-order with respect to Fe(OEP)(Cl) and Fe(OEP). The products were the same as those observed in the spectroelectrochemical experiment. The rate was not strongly dependent upon the concentration of nitrite, indicating that the coordinated, not the free nitrite, was the reaction species. The kinetics observed were consistent with a mixed oxidation state nitrite-bridged intermediate, which carried out the oxygen transfer reaction from nitrite to the iron porphyrin. The effect of nitrite coordination on the reaction rate was examined.
Electronic origin of variable denitrosylation kinetics from isostructural {FeNO}7 complexes: X-ray crystal structure of [Fe(oetap)(NO)]
Bohle, D. Scott,Debrunner, Peter,Fitzgerald, Jeffrey P.,Hansert, Bernhard,Hung, Chen-Hsiung,Thomson, Andrew J.
, p. 91 - 92 (2007/10/03)
In contrast to the nitrosyl derivative of iron(II) octaethylporphyrin [Fe(oep)(NO)], the isostructural octaethyltetraazaporphyrin complex [Fe(oetap)(NO)] exhibits fast ligand-promoted nitric oxide dissociation in the presence of pyridine and N-methylimidazole.
Reactions of σ-bonded alkyl- and aryliron porphyrins with nitric oxide. Synthesis and electrochemical characterization of six-coordinate nitrosyl σ-Bonded Alkyl- and aryliron porphyrins
Guilard,Lagrange,Tabard,Lan?on,Kadish
, p. 3649 - 3656 (2008/10/08)
The synthesis and physical characterization of 12 six-coordinate nitrosyl σ-bonded alkyl- and aryliron porphyrins were investigated in nonaqueous media. The ligands σ bonded to the nitrosyliron octaethylporphyrin or tetraphenylporphyrin complexes were CH3, n-C4H9, C6H5, C6H4Me-p, C6H4OMe-p, and C6F4H. Each neutral complex was characterized by 1H NMR, IR, and UV-visible spectroscopy, and on the basis of these data, the central metal was assigned as being in the Fe(II) oxidation state. The electrochemistry of two complexes, (OEP)Fe(C6H5)(NO) and (TPP)Fe(C6H5)(NO), was carried out, and results of this study were evaluated with respect to the spectroscopic characterization of the complexes. Finally, comparisons were made between the reactivities and physicochemical properties of the investigated six-coordinate complexes and other related iron σ-bonded alkyl and iron nitrosyl complexes in the literature.
