Methodology to determine the NMR chemical shifts of carbon atoms with radical character: A case of low-spin bis(tert-butylisocyanide) complex of (meso-tetrapropylporphyrinato)iron(III)

Niibori, Yuka; Ikezaki, Akira; Nakamura, Mikio

doi:10.1016/j.inoche.2011.05.049

Cited by 3 publications

(1 citation statement)

References 25 publications

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“…The values for the proportionality constants used can be found in Table S3. If multiple Fermi contact shifts of the heme nuclei are known, the above eqs – can be combined with eq and simultaneously solved to estimate the spin density distribution on the core heme nuclei, as has been performed before for other iron porphyrins. ,, It is important to note that eqs – are derived from simple models, assuming no deviations from the Curie law and only π-delocalization of the unpaired electron onto the porphyrin ligand. Therefore, the results should be considered to be qualitative in nature.…”

Section: Results and Analysismentioning

confidence: 99%

The Influence of Heme Ruffling on Spin Densities in Ferricytochromes c Probed by Heme Core ¹³C NMR

2013

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The heme in cytochromes c undergoes a conserved out-of-plane distortion known as ruffling. For cytochromes c from the bacteria Hydrogenobacter thermophilus and Pseudomonas aeruginosa, NMR and EPR spectra have been shown to be sensitive to the extent of heme ruffling and to provide insights into the effect of ruffling on electronic structure. Using mutants of each of these cytochromes that differ in the amount of heme ruffling, NMR characterization of the low-spin (S=1/2) ferric proteins has confirmed and refined the developing understanding of how ruffling influences spin distribution on heme. The chemical shifts of the core heme carbons were obtained through site-specific labeling of the heme via biosynthetic incorporation of 13C-labeled 5-aminolevulinic acid derivatives. Analysis of the contact shifts of these core heme carbons allowed Fermi contact spin densities to be estimated, and changes upon ruffling to be evaluated. The results allow a deconvolution of contributions to heme hyperfine shifts and a test of the influence of heme ruffling on electronic structure and hyperfine shifts. The data indicate that as heme ruffling increases, the spin densities on the β-pyrrole carbons decrease, while the spin densities on the α-pyrrole carbons and meso carbons increase. Furthermore, increased ruffling is associated with stronger bonding to the heme axial His ligand.

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Section: Results and Analysismentioning

confidence: 99%

The Influence of Heme Ruffling on Spin Densities in Ferricytochromes c Probed by Heme Core ¹³C NMR

2013

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Metal‐Porphyrin Orbital Interactions in Paramagnetic Iron Complexes Having Planar and Deformed Porphyrin Ring

Nakamura

Ikezaki

Takahashi

2012

J Chinese Chemical Soc

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1H and 13C NMR chemical shifts of iron porphyrin complexes are determined mainly by the spin densities at the peripheral carbon and nitrogen atoms caused by the interaction between paramagnetic iron 3d and porphyrin molecular orbitals. This review describes how the half‐occupied iron 3d orbitals such as dπ(dxz, dyz), dxy, d z 2, and d x 2‐ y 2 interact with a specific porphyrin molecular orbital and affect the 1H and 13C NMR chemical shifts in planar, ruffled, saddled, and domed complexes. Revealing the relationship between the orbital interactions and NMR chemical shifts is quite important to determine the fine electronic structures of synthetic iron porphyrin complexes as well as naturally occurring heme proteins.

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Electronic structure of low-spin six-coordinate iron(III)meso-tetrapropylchlorin complexes

Ikezaki

Ono

Ohgo

et al. 2014

J. Porphyrins Phthalocyanines

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Low-spin iron(III) tetrapropylchlorins [ Fe ( T n PrC ) L 2]± (L = HIm, 1-MeIm, DMAP, CN-, 4-CNPy, tBuNC) adopt the dxy-type ground state regardless of the nature of axial ligands. Among the complexes examined, [ Fe ( T n PrC )( t BuNC )2]+ has shown quite unique spectroscopic properties as described below. (1) 1 H NMR signals were extremely broad as compared with those of other complexes. In particular, 5,20- CH 2(α) signal was too broad to detect. (2) No signals except C γ were observed in 13 C NMR spectra. (3) Tetragonal splitting parameter (|Δ|) estimated by the EPR g values at 4.2 K reached as much as 12.4 λ, which is the largest |Δ| value among all the low-spin iron(III) porphyrins and porphyrinoids reported previously. On the basis of these results, we have concluded that [ Fe ( T n PrC )( t BuNC )2]+ adopts the low-spin iron(III) with (dxz, dyz)4(dxy)1 electronic ground state at 4.2–30 K where the EPR spectra are taken, while it should be expressed as the low-spin Fe ( II ) chlorin π-radical cation [ Fe II ( T n PrC .)( t BuNC )2]+ at ambient temperature where the NMR spectra are taken.

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Methodology to determine the NMR chemical shifts of carbon atoms with radical character: A case of low-spin bis(tert-butylisocyanide) complex of (meso-tetrapropylporphyrinato)iron(III)

Cited by 3 publications

References 25 publications

The Influence of Heme Ruffling on Spin Densities in Ferricytochromes c Probed by Heme Core ¹³C NMR

The Influence of Heme Ruffling on Spin Densities in Ferricytochromes c Probed by Heme Core ¹³C NMR

Metal‐Porphyrin Orbital Interactions in Paramagnetic Iron Complexes Having Planar and Deformed Porphyrin Ring

Electronic structure of low-spin six-coordinate iron(III)meso-tetrapropylchlorin complexes

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Methodology to determine the NMR chemical shifts of carbon atoms with radical character: A case of low-spin bis(tert-butylisocyanide) complex of (meso-tetrapropylporphyrinato)iron(III)

Cited by 3 publications

References 25 publications

The Influence of Heme Ruffling on Spin Densities in Ferricytochromes c Probed by Heme Core 13C NMR

The Influence of Heme Ruffling on Spin Densities in Ferricytochromes c Probed by Heme Core 13C NMR

Metal‐Porphyrin Orbital Interactions in Paramagnetic Iron Complexes Having Planar and Deformed Porphyrin Ring

Electronic structure of low-spin six-coordinate iron(III)meso-tetrapropylchlorin complexes

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The Influence of Heme Ruffling on Spin Densities in Ferricytochromes c Probed by Heme Core ¹³C NMR

The Influence of Heme Ruffling on Spin Densities in Ferricytochromes c Probed by Heme Core ¹³C NMR