55917-58-3Relevant articles and documents
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.
Fujita, Etsuko,Fajer, Jack
, p. 6743 - 6745 (1983)
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.
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.
