Electronic Configuration of Five-Coordinate High-Spin Pyrazole-Ligated Iron(II) Porphyrinates

Hu, Chuanjiang; Noll, Bruce C.; Schulz, Charles E.; Scheidt, W. Robert

doi:10.1021/ic101469e

Cited by 12 publications

(9 citation statements)

References 43 publications

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“…20 The change in the axial nitrogen ligand does not lead to significant differences in either the molecular or electronic structure compared to the imidazole derivatives as shown by X-ray and Mössbauer studies.…”

Section: Imidazole Ligandsmentioning

confidence: 90%

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All high-spin (S = 2) iron(ii) hemes are NOT alike

Schulz

Scheidt

2015

Dalton Trans.

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A common structural motif in heme proteins is a five-coordinate species in which the iron is coordinated by a histidyl residue. The widely distributed heme proteins with this motif are essential for the well being of humans and other organisms. We detail the differences in molecular structures and physical properties of high-spin iron(II) porphyrin derivatives ligated by neutral imidazole, hydrogen bonded imidazole, and imidazolate or other anions. Two distinct (high spin) electronic states are observed that have differing d-orbital occupancies and discernibly different five-coordinate square-pyramidal coordination groups. The doubly occupied orbital in the imidazole species is a low symmetry orbital oblique to the heme plane whereas in the imidazolate species the doubly occupied orbital is a high symmetry orbital in the heme plane, i.e., the primary doubly-occupied d-orbital is different. Methods that can be used to classify a particular complex into one or the other state includes X-ray structure determinations, high-field Mössbauer spectroscopy, vibrational spectroscopy, magnetic circular dichroism, and even-spin EPR spectroscopy. The possible functional significance of the ground state differences has not been established for heme proteins, but is likely found in the pathways for oxygen transport vs. oxygen utilization.

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Section: Imidazole Ligandsmentioning

confidence: 90%

“…Two pyrazole-ligated iron(II) derivatives were also characterized, [Fe(TPP)(Hdmpz)] and [Fe(TpOCH 3 PP)(Hdmpz)]. 20 The change in the axial nitrogen ligand does not lead to significant differences in either the molecular or electronic structure compared to the imidazole derivatives as shown by X-ray and Mössbauer studies.…”

Section: Imidazole Ligandsmentioning

confidence: 99%

All high-spin (S = 2) iron(ii) hemes are NOT alike

Schulz

Scheidt

2015

Dalton Trans.

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“…Since this work, numerous 5C iron(II)-porphyrinate complexes have been generated and isolated following different methodologies, some of which have been characterized structurally. 56,72,79,412,417,418 Furthermore, despite being synthetically more demanding, several examples with porphyrinates with tethered axial bases have also been reported as an approach for generating stable 5C iron(II) complexes. 79,419–423 Due to the intramolecular iron-base coordination, these systems produce 5C Fe II complexes with greater yield and purity as compared to systems which require an exogenous base.…”

Section: Heme/dioxygen Interactions: From Biology To Model Systemsmentioning

confidence: 99%

Synthetic Fe/Cu Complexes: Toward Understanding Heme-Copper Oxidase Structure and Function

et al. 2018

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Heme-copper oxidases (HCOs) are terminal enzymes on the mitochondrial or bacterial respiratory electron transport chain, which utilize a unique heterobinuclear active site to catalyze the 4H+/4e− reduction of dioxygen to water. This process involves a proton-coupled electron transfer (PCET) from a tyrosine (phenolic) residue and additional redox events coupled to transmembrane proton pumping and ATP synthesis. Given that HCOs are large, complex, membrane-bound enzymes, bioinspired synthetic model chemistry is a promising approach to better understand heme-Cu-mediated dioxygen reduction, including the details of proton and electron movements. This review encompasses important aspects of heme-O2 and copper–O2 (bio)chemistries as they relate to the design and interpretation of small molecule model systems and provides perspectives from fundamental coordination chemistry, which can be applied to the understanding of HCO activity. We focus on recent advancements from studies of heme–Cu models, evaluating experimental and computational results, which highlight important fundamental structure–function relationships. Finally, we provide an outlook for future potential contributions from synthetic inorganic chemistry and discuss their implications with relevance to biological O2-reduction.

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“…8 One class is represented by those species with a neutral nitrogen donor, primarily imidazoles 30-35 but also including pyrazoles. 36 The other class is represented by anionic ligands, including imidazolate (deprotonated imidazole). 37 Differences between the two classes include structural, 37 Mössbauer, magnetic circular dichroism, and even-spin EPR properties.…”

Section: Introductionmentioning

confidence: 99%

Effects of Imidazole Deprotonation on Vibrational Spectra of High-Spin Iron(II) Porphyrinates

Peng

Silvernail

et al. 2013

Inorg. Chem.

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The effects of the deprotonation of coordinated imidazole on the dynamics of five-coordinate high-spin iron(II) porphyrinates have been investigated using nuclear resonance vibrational spectroscopy. Two complexes have been studied in detail with both powder and oriented single-crystal measurements. Changes in the vibrational spectra are clearly related to structural differences in the molecular structures that occur when imidazole is deprotonated. Most modes involving the simultaneous motion of iron and imidazolate are unresolved but the one mode that is resolved is found at higher frequency in the imidazolates. These out-of-plane results are in accord with earlier resonance Raman studies of heme proteins. We also show the imidazole vs. imidazolate differences in the in-plane vibrations that are not accessible to resonance Raman studies. The in-plane vibrations are at lower frequency in the imidazolate derivatives; the doming mode shifts are inconclusive. The stiffness, an experimentally determined force constant that averages the vibrational details to quantify the nearest-neighbor interactions, confirms that deprotonation inverts the relative strengths of axial and equatorial coordination.

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Electronic Configuration of Five-Coordinate High-Spin Pyrazole-Ligated Iron(II) Porphyrinates

Cited by 12 publications

References 43 publications

All high-spin (S = 2) iron(ii) hemes are NOT alike

All high-spin (S = 2) iron(ii) hemes are NOT alike

Synthetic Fe/Cu Complexes: Toward Understanding Heme-Copper Oxidase Structure and Function

Effects of Imidazole Deprotonation on Vibrational Spectra of High-Spin Iron(II) Porphyrinates

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