Crystal and molecular structure of bis(imidazole)(meso-tetraphenylporphinato)iron(III) chloride. A classic molecule revisited

Scheidt, W. Robert; Osvath, Sarah R.; Lee, Young Ja

doi:10.1021/ja00241a010

Cited by 68 publications

(94 citation statements)

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“…Porphyrin compounds (Fe(TPP)(Py) 2 , LS Fe(II), 1; Fe(TPP)(THF) 2 , HS Fe(II), 2; and Fe(TPP)Cl, HS Fe(III), 3; TPP, tetraphenylporphyrin; Py, pyridine; THF, tetrahydrofurane) were synthesized as described (40,61) and grinded with solid BN (wt/wt 1:10). Bovine HB and equine-heart MB (met) were purchased from Sigma-Aldrich, at 12 mM heme dissolved in buffer A (100 mM Tris·HCl, 150 mM NaCl, 2.5 mM EDTA, pH 8), and reduced with sodiumdithionite (50 mM) to yield deoxy.…”

Section: Methodsmentioning

confidence: 99%

Effective intermediate-spin iron in O ₂ -transporting heme proteins

Schuth

Mebs

Huwald

et al. 2017

Proc. Natl. Acad. Sci. U.S.A.

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Proteins carrying an iron-porphyrin (heme) cofactor are essential for biological O2 management. The nature of Fe-O2 bonding in hemoproteins is debated for decades. We used energy-sampling and rapid-scan X-ray Kβ emission and K-edge absorption spectroscopy as well as quantum chemistry to determine molecular and electronic structures of unligated (deoxy), CO-inhibited (carboxy), and O2-bound (oxy) hemes in myoglobin (MB) and hemoglobin (HB) solutions and in porphyrin compounds at 20–260 K. Similar metrical and spectral features revealed analogous heme sites in MB and HB and the absence of low-spin (LS) to high-spin (HS) conversion. Amplitudes of Kβ main-line emission spectra were directly related to the formal unpaired Fe(d) spin count, indicating HS Fe(II) in deoxy and LS Fe(II) in carboxy. For oxy, two unpaired Fe(d) spins and, thus by definition, an intermediate-spin iron center, were revealed by our static and kinetic X-ray data, as supported by (time-dependent) density functional theory and complete-active-space self-consistent-field calculations. The emerging Fe-O2 bonding situation includes in essence a ferrous iron center, minor superoxide character of the noninnocent ligand, significant double-bond properties of the interaction, and three-center electron delocalization as in ozone. It resolves the apparently contradictory classical models of Pauling, Weiss, and McClure/Goddard into a unifying view of O2 bonding, tuned toward reversible oxygen transport.

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Section: Methodsmentioning

confidence: 99%

Effective intermediate-spin iron in O ₂ -transporting heme proteins

Schuth

Mebs

Huwald

et al. 2017

Proc. Natl. Acad. Sci. U.S.A.

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“…Considering a Fe-N(ImH) bond length of 1.96-1.99A for Fe(III)PP(ImH)2 (Collins et al 1972;Scheidt et al 1987) and using Badger's rule (Herschbach and Laurie 1961), the present Raman data indicate that the axial bond lengths are shortened by 0.08/~ when the imidazoles are deprotonated. Up to now, a single crystal structure of a CTABr solutions; the final hydroxide concentrations were adjusted at 0.12 M using NaOH (or NaOD) in H20 (or D20); C effects of ligand perdeuterations on the 150-250 cm-1 regions of RR spectra of Fe(II)PP(Im )z with Fe(II)PP(ImH)(Im-) in 2% aqueous CTABr solutions; the final hydroxide concentrations were adjusted at 2.3 M using NaOH (or NaOD) in H20 (or D20 ).…”

Section: Stretching Modes Of Axial Bondsmentioning

confidence: 69%

Redox control of proton transfers in membrane b-type cytochromes: an absorption and resonance Raman study on bis(imidazole) and bis(imidazolate) model complexes of iron-protoporphyrin

Desbois

Lutz

1992

Eur Biophys J

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Abstract. Optical absorption spectra and resonance Raman (RR) spectra, obtained with Soret excitation, are reported for bis(imidazole) and bis(imidazolate) complexes of iron(II)-and iron(III)-protoporphyriri IX, prepared in aqueous conditions. Perdeuteration experiments on the axial ligands permitted the assignment of the symmetric Fe-(ligand)2 stretching mode of Fe[x]PP(L)2 to RR bands at 203 (x=II; L=ImH), 212 (x=II; L=Im-), 201 (x=III; L=ImH) and 226 cm -1 (x = III; L = Im-). These frequency differences indicate a strengthening of the axial bonds when the imidazole deprotonations occur. The larger difference observed for the ferric derivatives reflects the stronger a-donor capability of the Ira-anion for iron(III) over iron(II). For the ferrous derivatives, the frequencies of several skeletal porphyrin modes (v4, Vlo, vll and V3s ) are downshifted by 2-10 cm-J upon deprotonation of the ligands. This effect corresponds to an increased back-bonding from the metal atom to the porphyrin ring when the axial ligand decreases its n-acid strength. Bringing further support to this interpretation, an inverse linear relationship is established between the frequencies of v (Fe(II)-L2) and v~t. This correlation is expected to monitor the overall Hbonding state of histidine ligands of reduced cytochromes b. On the other hand, absorption measurements have characterized large pK~ differences for the sequential imidazole ionizations of Fe Abbreviations: RR, resonance Raman; EPR, electron paramagnetic resonance; PP, protoporphyrin IX; ImH, imidazole; Ira-, imidazolate; Im*, imidazole or imidazolate; 1Melm, t-methylimidazole; HisH, histidine; His-, histidinate; CTABr, cetyltrimethylammonium bromide; NaDS, sodium dodecylsulphate; VLP, very low potential; LP, low potential; HP, high potential good proton-acceptor and proton-donor, respectively, and suggest a model by which heme, located in a favorable environment inside a cytochrome, could couple a cycle of electron transfer with a proton transfer. Based on sequence data and structural models, it is further proposed that, in several membrane cytochromes b (b, b6, b559) , a positively charged amino acid residue and an imidazolate ligand of the ferriheme could form an ion pair involved in a redox control of proton transfer.

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“…[Fe(TpivPP)(1-VinylIm) 2 ] ·2C 7 H 8 A translucent red plate crystal with the dimensions of 0.28×0.16×0.12 mm 3 was used for the structure determination. The asymmetric unit contains one bis-ligated "picket fence" porphyrin complex and two toluene solvent molecules.…”

Section: X-ray Structure Determinationsmentioning

confidence: 99%

Relative Axial Ligand Orientation in Bis(imidazole)iron(II) Porphyrinates: Are “Picket Fence” Derivatives Different?

Nair

Noll

et al. 2008

Inorg. Chem.

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The synthesis of three new bis(imidazole)-ligated iron(II) picket fence porphyrin derivatives, [Fe (TpivPP)(1-RIm) 2 ] 1-RIm = 1-methyl-, 1-ethyl-, or 1-vinylimidazole) are reported. X-ray structure determinations reveal that the steric requirements of the four α,α,α,α-o-pivalamidophenyl groups lead to very restricted rotation of the imidazole ligand on the picket side of the porphyrin plane; the crowding leads to an imidazole plane orientation eclipsing an iron-porphyrin nitrogen bond. An unusual feature for these diamagnetic iron(II) species is that all three derivatives have the two axial ligands with a relative perpendicular orientation; the dihedral angles between the two imidazole planes are 77.2°, 62.4°, and 78.5°. All three derivatives have nearly planar porphyrin cores. Mössbauer spectroscopic characterization shows that all three derivatives have quadrupole splitting constants around 1.00 mm/s at 100K.

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Crystal and molecular structure of bis(imidazole)(meso-tetraphenylporphinato)iron(III) chloride. A classic molecule revisited

Cited by 68 publications

References 3 publications

Effective intermediate-spin iron in O ₂ -transporting heme proteins

Effective intermediate-spin iron in O ₂ -transporting heme proteins

Redox control of proton transfers in membrane b-type cytochromes: an absorption and resonance Raman study on bis(imidazole) and bis(imidazolate) model complexes of iron-protoporphyrin

Relative Axial Ligand Orientation in Bis(imidazole)iron(II) Porphyrinates: Are “Picket Fence” Derivatives Different?

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Crystal and molecular structure of bis(imidazole)(meso-tetraphenylporphinato)iron(III) chloride. A classic molecule revisited

Cited by 68 publications

References 3 publications

Effective intermediate-spin iron in O 2 -transporting heme proteins

Effective intermediate-spin iron in O 2 -transporting heme proteins

Redox control of proton transfers in membrane b-type cytochromes: an absorption and resonance Raman study on bis(imidazole) and bis(imidazolate) model complexes of iron-protoporphyrin

Relative Axial Ligand Orientation in Bis(imidazole)iron(II) Porphyrinates: Are “Picket Fence” Derivatives Different?

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Effective intermediate-spin iron in O ₂ -transporting heme proteins

Effective intermediate-spin iron in O ₂ -transporting heme proteins