8 research outputs found
Metalloporphyrins in coal. 4. TLC-NMR of iron porphyrins from coal: the direct characterization of coal hemes using paramagnetically shifted proton NMR spectroscopy
Studies of the reduction of the nickel(II) complex of 5,10,15,20-tetraphenyl-21-thiaporphyrin to form corresponding nickel(I) complexes
Reactions of the iron(III) tetraphenylporphyrin .pi. cation radical with triphenylphosphine and the nitrite anion. Formation of .beta.-substituted iron(III) porphyrins
Reactivity of Mono-Meso-Substituted Iron(II) Octaethylporphyrin Complexes with Hydrogen Peroxide in the Absence of Dioxygen. Evidence for Nucleophilic Attack on the Heme.
Treatment of the mono-meso-substituted iron(II) octaethylporphyrin complexes, (py)2FeII(meso-NO2-OEP), (py)2FeII(meso-CN-OEP), (py)2FeII(meso-HC(O)-OEP), (py)2FeII(meso-Cl-OEP), (py)2FeII(meso-OMe-OEP), (py)2FeII(meso-Ph-OEP), and (py)2FeII(meso-Bu-OEP), with hydrogen peroxide in pyridine-d5 at -30° in the strict absence of dioxygen was monitored by 1H NMR spectroscopy. The product oxophlorin complexes are stable as long as the samples are protected from exposure to dioxygen. Hydrogen peroxide reacts cleanly with mono-meso-substituted iron(II) porphyrins in pyridine soln. under an inert atm. to form mixts. of three possible oxygenation products, (py)2Fe(cis-meso-R-OEPO), (py)2Fe(trans-meso-R-OEPO), and (py)2Fe(OEPO). The yields of (py)2Fe(OEPO), which results from replacement of the unique meso substituent, as a function of the identity of the meso substituent decrease in the order NO2 > HC(O) � CN � Cl > OMe > Ph, Bu, which suggests that the species responsible for attack on the porphyrin periphery is nucleophilic in nature. A mechanism involving isoporphyrin formation through attack of hydroxide ion on a cationic iron porphyrin with an oxidized porphyrin ring is suggested. The identity of the unique meso functionality also affects the regiospecificity of substitution when the unique meso group is retained. Although random attack at the two different meso sites is expected to yield a cis/trans product ratio of 2, the obsd. ratios vary in the following order: cyano, 5.0; Bu, 4.9; chloro, 3.2; formyl, 2.6; methoxy, 1.9; Ph 1.4. [on SciFinder(R)
meso Substituent Effects on the Geometric and Electronic Structures of High-Spin and Low-Spin Iron(III) Complexes of Mono-meso-Substituted Octaethylporphyrins.
Introduction of a single meso substituent into ClFeIII(OEP) or K[(NC)2Fe(OEP)] results in significant changes in the geometric and/or spectroscopic properties of these complexes. The mono-meso-substituted iron(III) complexes ClFeIII(meso-Ph-OEP), ClFeIII(meso-Bu-OEP), ClFeIII(meso-MeO-OEP), ClFeIII(meso-Cl-OEP), ClFeIII(meso-NC-OEP), ClFeIII(meso-HC(O)-OEP), and ClFeIII(meso-O2N-OEP) were isolated and characterized by their UV/visible and paramagnetically shifted 1H NMR spectra. The structures of both ClFeIII(meso-Ph-OEP) and ClFeIII(meso-NC-OEP) were detd. by x-ray crystallog. Both mols. have five-coordinate structures typical for high-spin (S = 5/2) iron(III) complexes. However, the porphyrins themselves no longer have the domed shape seen in ClFeIII(OEP), and the N4 coordination environment possesses a slight rectangular distortion. These high-spin, mono-meso-substituted iron(III) complexes display 1H NMR spectra in chloroform-d soln. which indicate that the conformational changes seen in the solid-state structures are altered by normal mol. motion to produce spectra consistent with Cs mol. symmetry. In pyridine soln. the high-spin six-coordinate complexes {(py)ClFeIII(meso-R-OEP)} form. In methanol soln. in the presence of excess potassium cyanide, the low-spin six-coordinate complexes K[(NC)2FeIII(meso-R-OEP)] form. The 1H NMR spectra of these show that electron-donating substituents produce an upfield relocation of the meso-proton chem. shifts. This relocation is interpreted in terms of increased contribution from the less common (dxz,dyz)4(dxy)1 ground electronic state as the meso substituent becomes more electron donating. [on SciFinder(R)
ChemInform Abstract: PROTON NMR CHARACTERIZATION OF THE FERRYL GROUP IN MODEL HEME COMPLEXES AND HEMOPROTEINS: EVIDENCE FOR THE FEIVO GROUP IN FERRYL MYOGLOBIN AND COMPOUND II OF HORSERADISH PEROXIDASE
The proton NMR spectra of model porphyrin complexes possessing the ferryl, FeIV=O, group are reported and assigned. The only resonance shifted well outside the diamagnetic region is that of the meso protons. Moreover, these model compounds exhibit hyperfine shift patterns (particularly for the substituents found in natural porphyrins) that are different from those found for other characterized iron-porphyrin complexes. Deuterium labeling of the meso position of hemin reconstituted into sperm whale myoglobin and horseradish peroxidase reveals that both the hydrogen peroxide treated myoblobin (ferryl myoglobin) and horseradish peroxidase compound II exhibit only meso H resonances with significant hyperfine shift and that these shifts are essentially the same as those found in the low-spin FeIV=0 model complexes. Hence, the 1H NMR data can be taken as evidence for the presence of the ferryl group at the active site of both ferryl myoglobin and compound II of horseradish peroxidase. © 1983, American Chemical Society. All rights reserved
Proton NMR Characterization of the Ferryl Group in Model Heme Complexes and Hemoproteins: Evidence for the FeIV=O Group in Ferryl Myoglobin and Compound II of Horseradish Peroxidase
The proton NMR spectra of model porphyrin complexes possessing the ferryl, FeIV=O, group are reported and assigned. The only resonance shifted well outside the diamagnetic region is that of the meso protons. Moreover, these model compounds exhibit hyperfine shift patterns (particularly for the substituents found in natural porphyrins) that are different from those found for other characterized iron-porphyrin complexes. Deuterium labeling of the meso position of hemin reconstituted into sperm whale myoglobin and horseradish peroxidase reveals that both the hydrogen peroxide treated myoblobin (ferryl myoglobin) and horseradish peroxidase compound II exhibit only meso H resonances with significant hyperfine shift and that these shifts are essentially the same as those found in the low-spin FeIV=0 model complexes. Hence, the 1H NMR data can be taken as evidence for the presence of the ferryl group at the active site of both ferryl myoglobin and compound II of horseradish peroxidase. © 1983, American Chemical Society. All rights reserved