Dimerization and .pi.-bonding of a zinc porphyrin cation radical. Thermodynamics and fast reaction kinetics

Fuhrhop, J.‐H.; Wasser, P.; Riesner, Detlev; Mauzerall, D.

doi:10.1021/ja00778a011

Cited by 112 publications

(77 citation statements)

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“…Through one electron oxidation of zinc octaethylporphyrin, Fuhrhop et al generated cation porphyrin radical derivatives that self-assembled to produce dimeric complexes displaying a broad NIR absorption band centered around 950 nm (30). Similar phenomena were reported for the radical derivatives of some other metalloporphyrins (29,31).…”

Section: Resultsmentioning

confidence: 74%

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Tryptophan-mediated charge-resonance stabilization in the bis -Fe(IV) redox state of MauG

Geng

Dornevil

Davidson

et al. 2013

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

102

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The diheme enzyme MauG catalyzes posttranslational modifications of a methylamine dehydrogenase precursor protein to generate a tryptophan tryptophylquinone cofactor. The MauG-catalyzed reaction proceeds via a bis -Fe(IV) intermediate in which one heme is present as Fe(IV)=O and the other as Fe(IV) with axial histidine and tyrosine ligation. Herein, a unique near-infrared absorption feature exhibited specifically in bis -Fe(IV) MauG is described, and evidence is presented that it results from a charge-resonance-transition phenomenon. As the two hemes are physically separated by 14.5 Å, a hole-hopping mechanism is proposed in which a tryptophan residue located between the hemes is reversibly oxidized and reduced to increase the effective electronic coupling element and enhance the rate of reversible electron transfer between the hemes in bis -Fe(IV) MauG. Analysis of the MauG structure reveals that electron transfer via this mechanism is rapid enough to enable a charge-resonance stabilization of the bis -Fe(IV) state without direct contact between the hemes. The finding of the charge-resonance-transition phenomenon explains why the bis -Fe(IV) intermediate is stabilized in MauG and does not permanently oxidize its own aromatic residues.

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Section: Resultsmentioning

confidence: 74%

“…4B) (4,(28)(29)(30)(31)(32)(33). We term the former case with an odd number of spin/charge as type I CR and the latter case with an even number as type II CR.…”

Section: Resultsmentioning

confidence: 99%

Tryptophan-mediated charge-resonance stabilization in the bis -Fe(IV) redox state of MauG

Geng

Dornevil

Davidson

et al. 2013

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

102

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“…Since the use of free base porphyrins rules out the formation of a -oxo dimer, so frequent in the metalloporphyrin chemistry, peak 3 might be related to a dimer due the formation of a new -bond or of a new meso-carbon-carbon bond between the dication radical and the free base porphyrin present, as noted by Fuhrhop et al [27]. However, we cannot exclude the hypothesis of a quick degradation of the dication macrocyle to a reducible biliar pigment analog.…”

Section: The Oxidation Processesmentioning

confidence: 90%

Electrochemical and spectroelectrochemical characterization of meso-tetra-alkyl porphyrins

Paliteiro

Sobral

2005

Electrochimica Acta

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A series of three meso-tetra-alkyl porphyrins (H 2 TAPs) were synthesised and their electrochemical properties were studied in dichloromethane containing either tetra-butyl ammonium perclorate (TBAP) or tetra-butyl ammonium hexafluorophosphate TBA(PF 6 ) as supporting electrolyte (SE) by cyclic voltammetry and in situ UV/vis spectroelectrochemistry. Values of E 1/2 for the recorded four redox processes of these porphyrins and of the meso-tetra-phenyl porphyrin (H 2 TPP) on glassy carbon and platinum were measured and compared. The redox data collected on the first oxidation and the first reduction processes predict that the value of (LUMO − HOMO) for the H 2 TAPs is lower than for meso-tetra-phenyl porphyrin and, therefore, that the first Q band of the electronic spectra of the H 2 TAPs is red shifted relatively to the same band in the spectrum of H 2 TPP; this shift was indeed found. The second oxidation process of the H 2 TAPs is influenced by the supporting electrolyte used and the dication then formed is consumed by an irreversible chemical reaction. The species produced in this reaction is irreversibly reduced at a considerably lower potential. The electrochemical and spectroelectrochemical data collected are consistent with the occurrence of structural distortion in the macrocycle rings of the H 2 TAPs.

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“…The absorption band at l = 655 nm is typically assigned to the monomer porphyrin radical cation. [23] This outcome indicates that the initial three-electron oxidation of TPA-TPZn 3 forms TPATPZn 3 3 + , in which each porphyrin ring has undergone a one-electron oxidation.…”

Section: Resultsmentioning

confidence: 99%

Greatly Enhanced Intermolecular π‐Dimer Formation of a Porphyrin Trimer Radical Trications through Multiple π Bonds

Takai

Gros

Barbe

et al. 2011

Chemistry A European J

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A trefoil-like porphyrin trimer linked by triphenylamine (TPA-TPZn(3)) was synthesized. A three-electron oxidation of TPA-TPZn(3) forms a radical trication (TPA-TPZn(3)(3+)), in which each porphyrin ring undergoes a one-electron oxidation. The radical trication TPA-TPZn(3)(3+) spontaneously dimerizes to afford (TPA-TPZn(3))(2)(6+) in CH(2)Cl(2) . The characteristic charge-resonance band due to the charge delocalization over the π system of (TPA-TPZn(3))(2)(6+) was observed in the NIR region. The initial oxidation potential of TPA-TPZn(3) is negatively shifted relative to that of the corresponding monomer porphyrin, which results from the stabilization of the oxidized state of TPA-TPZn(3) associated with the dimerization. The thermodynamic parameters (i.e., ΔH, ΔS, and ΔG) for the formation of (TPA-TPZn(3))(2)(6+) were determined by measuring Vis/NIR spectra at various temperatures. The formation constant of (TPA-TPZn(3))(2)(6+) is significantly larger than that of the radical cation dimer of the corresponding monomer porphyrin (e.g., over 2000-fold at 233 K). The electronic states were investigated using EPR spectroscopic analysis. The greatly enhanced dimerization of TPA-TPZn(3)(3+) results from multiple π-bond formation between the porphyrin radical cations.

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Dimerization and .pi.-bonding of a zinc porphyrin cation radical. Thermodynamics and fast reaction kinetics

Cited by 112 publications

References 0 publications

Tryptophan-mediated charge-resonance stabilization in the bis -Fe(IV) redox state of MauG

Tryptophan-mediated charge-resonance stabilization in the bis -Fe(IV) redox state of MauG

Electrochemical and spectroelectrochemical characterization of meso-tetra-alkyl porphyrins

Greatly Enhanced Intermolecular π‐Dimer Formation of a Porphyrin Trimer Radical Trications through Multiple π Bonds

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