934736-92-2

Upstream product

• 616-47-7 1-methyl-1H-imidazole 
• 16591-56-3 5,10,15,20-tetraphenyl porphyrin iron 
• 1641-69-6 [13C]Carbon monoxide 
• 74902-03-7 [Fe(meso-tetraphenylporphyrin)(CO)(1-methylimidazole)] 
• 16456-81-8 meso-tetraphenylporphyrin iron(III) chloride 

Relevant academic research and scientific papers

An experimental and quantum chemical investigation of CO binding to heme proteins and model systems: A unified model based on 13C, 17O, and 57Fe nuclear magnetic resonance and57Fe mossbauer and infrared spectroscopies

We have investigated the question of how CO ligands bind to iron in metalloporphyrins and metalloproteins by using a combination of nuclear magnetic resonance (NMR), 57Fe Mossbauer, and infrared spectroscopic techniques, combined with density functional theoretical calculations to analyze the spectroscopic results. The results of 13C NMR isotropic chemical shift, 13C NMR chemical shift anisotropy, 17O NMR isotropic chemical shift, 17O nuclear quadrupole coupling constant, 57Fe NMR isotropic chemical shift, 57Fe Mossbauer quadrupolar splitting, and infrared measurements indicate that CO binds to Fe in a close to linear fashion in all conformational substates. The 13C-isotropic shift and shift anisotropy for an A(o) substate model compound: Fe(5,10,15,20-tetraphenylporphyrin)(CO)(N-methylimidazole), as well as the 17O chemical shift, and the 17O nuclear quadrupole coupling constant (NQCC) are virtually the same as those found in the A(o) substate of Physeter catodon CO myoglobin and lead to most probable ligand tilt (τ) and bend (β) angles of 0°and 1°when using a Bayesian probability or Z surface method for structure determination. The infrared V(co) for the model compound of 1969 cm-1 is also that found for A(o) proteins. Results for the A1 substate (including the 57Fe NMR chemical shift and Mossbauer quadrupole splitting) are also consistent with close to linear and untilted Fe-C-O geometries (τ = 4°, β = 7°), with the small changes in ligand spectroscopic parameters being attributed to electrostatic field effects. When taken together, the 13C shift, 13C shift anisotropy, 17O shift, 17O NQCC, 57Fe shift, 57Fe Mossbauer quadrupole splitting, and v(co) all strongly indicate very close to linear and untilted Fe-C-O geometries for all carbonmonoxyheme proteins. These results represent the first detailed quantum chemical analysis of metal-ligand geometries in metalloproteins using up to seven different spectroscopic observables from three types of spectroscopy and suggest a generalized approach to structure determination.

Differential sensing of protein influences by NO and CO vibrations in heme adducts

Heme proteins bind the gaseous ligands XO (X = C, N, O) via backbonding from Fe dπ electrons. Backbonding is modulated by distal interactions of the bound ligand with the surrounding protein and by variations in the strength of the trans proximal ligand. Vibrational modes associated with FeX and XO bond stretching coordinates report on these interactions, but the interpretive framework developed for CO adducts, involving anticorrelations of νFeC and νCO, has seemed not to apply to NO adducts. We have now obtained an excellent anticorrelation of νFeN and νNO, via resonance Raman spectroscopy on (N-methylimidazole)Fe(II)TPP-Y(NO), where TPP-Y is tetraphenylporphine with electron-donating or -withdrawing substituents, Y, that modulate the backbonding; the problem of laser-induced dissociation of the axial base was circumvented by using frozen solutions. New data are also reported for CO adducts. The anticorrelations are supported by DFT calculations of structures and spectra. When protein data are examined, the NO adducts show large deviations from the modeled anticorrelation when there are distal H-bonds or positive charges. These deviations are proposed to result from closing of the FeNO angle due to a shift in the valence isomer equilibrium toward the Fe(III)(NO-) form, an effect that is absent in CO adducts. The differing vibrational patterns of CO and NO adducts provide complementary information with respect to protein interactions, which may help to elucidate the mechanisms of ligand discrimination and signaling in heme sensor proteins.

Carbonyl complexes of iron(II), ruthenium(II), and osmium(II) 5,10,15,20-tetraphenylporphyrinates: A comparative investigation by x-ray crystallography, solid-state NMR spectroscopy, and density functional theory

We have synthesized and characterized via single-crystal X-ray diffraction methods iron(II), ruthenium(II), and osmium(II) carbonyl derivatives of (1-methylimidazole)(5,10,15,20- tetraphenylporphyrinate)[(5,10,15,20-tetraphenylporphyrinate = TPP)], Fe(TPP)(CO)(1-MeIm)·toluene, Ru(TPP)(CO)(1-MeIm)·chloroform, and Os(TPP)(CO)(1-MeIm)·chloroform, together with the osmium(II) pyridine adduct Os(TPP)-(CO)(py)·2benzene. The crystallographic results permit a detailed structural comparison between all of the six carbonyl metalloporphyrins which can be prepared from TPP, Fe, Ru, Os, and the two axial bases 1- methylimidazole and pyridine. The structures of all three (Fe, Ru, Os) 1- methylimidazole complexes display major saddle distortions, with the extent of the distortions being Fe > Ru ~ Os. For the pyridine complexes, deviations from planarity of the porphyrin ring are about an order of magnitude smaller than those for the 1-methylimidazole species. The M-C-O bond angles in all complexes are in the range 176.8-179.3°. We also determined the 13C and 17O NMR isotropic chemical shifts, the 13C NMR chemical shift tensor elements, and, for the three 1-MeIm adducts, the 17O nuclear quadruple coupling constants. We then used density functional theory (DFT) to relate the experimental spectroscopic results to the experimental structures. For the 13C and 17O isotropic shifts, there are excellent correlations between theory and experiment (13C, R2 value = ~0.99; 17O, R2 value = ~.99), although the slopes (13C, ~-0.97; 17O, ~-1.27) deviate somewhat from the ideal values. For the 17O nuclear quadruple coupling constant, our results indicate an rms error between theory and experiment of 0.20 MHz, for experimental values ranging from (+)1.0 to (- )0.40 MHz, where the signs are deduced from the calculations. The ability to predict spectroscopic observables in metalloporphyrin systems having relatively well characterized structures by using density functional theory provides additional confidence in the application of these theoretical methods to systems where structures are much less certain, such as heme proteins.