223522-39-2

Upstream product

• 616-47-7 1-methyl-1H-imidazole 
• 28755-93-3 chloro(2,3,7,8,12,13,17,18-octaethylporphyrinato-N,N',N'',N''')iron(III) complex 
• 586-96-9 Nitrosobenzene 

Relevant academic research and scientific papers

Six-coordinate ferric porphyrins containing bidentate N-t-butyl-N-nitrosohydroxylaminato ligands: Structure, magnetism, IR spectroelectrochemisty, and reactivity

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.

Solid-state NMR, Moessbauer, crystallographic, and density functional theory investigation of Fe-O2 and Fe-O2 analogue metalloporphyrins and metalloproteins

We have synthesized and studied via solid-state NMR, Moessbauer spectroscopy, single-crystal X-ray diffraction, and density functional theory the following Fe-O2 analogue metalloporphyrins: Fe(5,10,15,20-tetraphenylporphyrinate) (nitrosobenzene)(1-methylimidazole); Fe(5,10,15,20-tetraphenylporphyrinate) (nitrosobenzene)(pyridine); Fe(5,10,15,20-tetraphenylporphyrinate)(4-nitroso-N,N-dimethylaniline)(pyridine); Fe-(2,3,7,8,12,13,17,18-octaethylporphyrinate) (nitrosobenzene)(1-methylimidazole) and Co(2,3,7,8,12,13,17,18-octaethylporphyrinate)(NO). Our results show that the porphyrin rings of the two tetraphenylporphyrins containing pyridine are ruffled while the other three compounds are planar: reasons for this are discussed. The solid-state NMR and Moessbauer spectroscopic results are well reproduced by the DFT calculations, which then enable the testing of various models of Fe-O2 bonding in metalloporphyrins and metalloproteins. We find no evidence for two binding sites in oxypicket fence porphyrin, characterized by very different electric field gradients. However, the experimental Moessbauer quadrupole splittings can be readily accounted for by fast axial rotation of the Fe-O2 unit. Unlike oxymyoglobin, the Moessbauer quadrupole splitting in PhNO·myoglobin does not change with temperature, due to the static nature of the Fe·PhNO subunit, as verified by 2H NMR of Mb·[2H5]PhNO. Rotation of O2 to a second (minority) site in oxymyoglobin can reduce the experimental quadrupole splittings, either by simple exchange averaging, or by an electronic mechanism, without significant changes in the Fe-O-O bond geometry, or a change in sign of the quadrupole splitting. DFT calculations of the molecular electrostatic potentials in CO, PhNO, and O2-metalloporphyrin complexes show that the oxygen sites in the PhNO and O2 complexes are more electronegative than that in the CO system, which strongly supports the idea that hydrogen bonding to O2 will be a major contributor to O2/CO discrimination in heme proteins.