Structure-sensitive resonance Raman bands of tetraphenyl and "picket fence" porphyrin-iron complexes, including an oxyhemoglobin analog

Burke, John M.; Kincaid, James R.; Peters, Sven; Gagné, Robert R.; Collman, James P.; Spiro, Thomas G.

doi:10.1021/ja00487a018

Cited by 164 publications

(178 citation statements)

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“…These vibrational data indicate the presence of a heme ferric peroxide species. The 4 band at 1,368 cm Ϫ1 and 2 band at 1,568 cm Ϫ1 are consistent with a low-spin 6-coordinate Fe III -heme (46). Thus, 1 of the 2 electrons needed to reduce O 2 to peroxide is derived from the heme, and hence, the other must be derived from Fe B .…”

Section: Resultssupporting

confidence: 60%

“…4A, blue line). This is indicative of oxidation of the Fe II heme to a Fe III in this intermediate (46,47). The data in the lower frequency region show 2 bands that are sensitive to isotopic substitution of O 2 .…”

Section: Resultsmentioning

confidence: 80%

“…Upon further warming, the reaction to 5°C the 4 band shifts to 1,371.6 cm Ϫ1 , the 2 shifts to 1,570 cm Ϫ1 (Scheme 1), and the isotope-sensitive ferryl bands lose all of their intensity. This indicates decay of both the ferryl species and formation of a low-spin Fe III heme species (46).…”

Section: Resultsmentioning

confidence: 96%

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O ₂ reduction by a functional heme/nonheme bis-iron NOR model complex

Collman

Dey

Yang

et al. 2009

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

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O2 reactivity of a functional NOR model is investigated by using electrochemistry and spectroscopy. The electrochemical measurements using interdigitated electrodes show very high selectivity for 4e O2 reduction with minimal production of partially reduced oxygen species (PROS) under both fast and slow electron flux. Intermediates trapped at cryogenic temperatures and characterized by using resonance Raman spectroscopy under single-turnover conditions indicate that an initial bridging peroxide intermediate undergoes homolytic OOO bond cleavage generating a trans heme/nonheme bis-ferryl intermediate. This bis ferryl species can oxygenate 2 equivalents of a reactive substrate.C ytochrome c oxidase (CcO) and nitric oxide reductase (NOR) belong to the heme copper oxidase superfamily of enzymes (1, 2). CcO is the terminal enzyme in the respiratory chain of higher organisms, located in their mitochondrial membrane, that reduces O 2 to H 2 O as source of energy. The O 2 reduction process in CcO generates a pH gradient across the bilayer membrane, which provides the driving force for ATP synthesis. The bimetallic active site of CcO has a heme ligated to the protein by a proximal histidine ligand and a distal Cu B site coordinated by 3 histidine ligands ( Fig. 1) (3). In addition to the bimetallic site, there is a conserved tyrosine ligand covalently attached to one of the histidines coordinated to Cu B (4, 5). The NORs are the older member of the family and are found in bacteria using NO 3 Ϫ as source of energy instead of O 2 (2, 6, 7). Although there are no high-resolution crystal structures of NOR, biochemical studies and computer modeling indicate that these enzymes have a histidine-ligated heme, quite like the CcOs, and a distal Fe B , unlike Cu B in CcO, coordinated by 3 histidines ( Fig. 1) (8-10). NORs do not have the conserved tyrosine residue of CcO but have a few conserved key glutamate residues (11,12). Although the NOR enzymes are proposed to have specific proton channels, they are probably not involved in generating proton gradients (13-16).These 2 enzymes exhibit complementary reactivity toward 2 very significant diatomic molecules in nature; O 2 and NO. In eukaryotes CcO (aa 3 type) reduces O 2 to H 2 O and is reversibly but strongly inhibited by [17][18][19][20]. Several other CcOs (ba 3 , caa 3 , cbb 3 ) are reported to exhibit limited (Ͻ1%) NOR activity, i.e., reduce NO to N 2 O (7, 21). On the other hand, NORs that reduce NO to N 2 O are reversibly but strongly inhibited by O 2 , and some of them show modest (Ϸ10%) O 2 reduction activity (12). The parallels in their reactivities toward O 2 and NO and similarities in their secondary structures have led to a hypotheses regarding NOR's and CcO's similar evolutionary origins (6,22).Electrochemistry is a very powerful technique that can provide fundamental insights into reaction mechanisms of redox catalysts (23-27). Conventionally, a catalyst is deposited on a conducting electrode material (e.g., graphite); however, this approach does not allow site isola...

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Section: Resultssupporting

confidence: 60%

Section: Resultsmentioning

confidence: 80%

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O ₂ reduction by a functional heme/nonheme bis-iron NOR model complex

Collman

Dey

Yang

et al. 2009

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

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“…Below 700 mV, the 820 * cm −1 mode is entirely supplanted by the 883 * cm −1 mode. In summary, as the membrane becomes hydrated, the dominant contributor to the 806 cm The peak at 564 cm −1 , attributed to Fe-O 2 stretching modes, [60][61][62][63] is present at all cell potentials under O 2 flow (left). It is non-discernable from the background under N 2 flow (right).…”

Section: Resultsmentioning

confidence: 99%

Operando Raman Micro-Spectroscopy of Polymer Electrolyte Fuel Cells

Kendrick

Fore

Doan

et al. 2016

J. Electrochem. Soc.

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Operando Raman micro-spectroscopy of the membrane electrode assembly (MEA) of a fully operating hydrogen/oxygen Nafion electrolyte fuel cell is described. Coarse depth profiling of the fuel cell system enabled appropriate positioning of the microspectroscopy laser focal point for MEA catalytic layer spectroscopy. An increase in the ionomer state-of-hydration, from oxygen reduction at the cathode, transitions ion exchange sites from the sulfonic acid to the dissociated sulfonate form. Visualization of density functional theory calculated normal mode eigenvector animations enabled assignments of Nafion side-chain vibrational bands in terms of the exchange site local symmetry: C 1 and C 3V modes correlate to the sulfonic acid and sulfonate forms respectively. The gradual transition of the MEA spectra from C 1 to C 3V modes, from the fuel cell open circuit voltage to the short circuit current respectively, demonstrate the utility of vibrational group mode assignments in terms of exchange site local symmetry.

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“…Certain "structure-sensitive" or "marker" bands of these naturally occurring porphyrin systems have been shown to shift frequency in a manner that reflects the coordination number and oxidation state of the metal center (5). For the more easily synthesized model oxygen carriers based on tetraphenylporphyrins, the resonance Raman spectra, and thus the structure-sensitive bands, differ from those of the naturally occurring materials (6,7). These marker bands have been investigated for only two series of tetraphenylporphyrin complexes.…”

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confidence: 99%

Structure-sensitive resonance Raman bands of capped tetraphenylporphyrinatoiron complexes

Linard¹,

Shriver²,

Basolo³

1980

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

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Resonance Raman spectra have been determined for the capped tetraphenylporphyrinatoiron complexes and their base adducts. The five-coordinate mono-base complexes of these porphyrin complexes dislay Raman spectra that are nearly identical to those previous y determined for fivecoordinate iron(II) tetraphenylporphyrin complexes in the marker regions around 1540, 1345, and 370 cm-1. A similar correspondence is found between Raman bands of iron(II) complexes of the capped complexes and those of tetraphenylporphyrin. By contrast, the unusual pseudo-six-coordinate iron(II) complexes more closely resemble high-spin five-coordinate systems in the 1540 and 1345 cm-regions, but in the 380 cm-1 region the resemblance is closer to the low-spin six-coordinate tetraphenylporphyrin complexes. These results provide spectroscopic confirmation for the unique nature of these nseudo-six-coordinate complexesThe capped tetraphenylporphyrins ( Fig. 1) provide an interesting testing ground for the molecular features that control reversible binding of dioxygen (1-4). Recently it was shown that the cap size has a profound influence on the binding of bases and dioxygen (3,4). When the cap is compact, x = 2 in Fig. 1, the iron(II) complex of the 5,10,15,20-[pyrromellitoyl(tetrakis-o-oxyethoxyphenyl)]porphyrinate ion is designated as Fe(Cap). A less sterically hindered iron(II) complex, 5,10,15, 20-[pyrromellitoyl(tetrakis - Fe(HmCap), is formed with the homologous cap porphyrin, for which x = 3 in Fig. 1. Detailed equilibrium measurements reveal that the more hindered Fe(Cap) adds only one ligand, such as 1-methylimidazole (1-MeIm) or pyridine (py), to form five-coordinate complexes. The less sterically hindered Fe(HmCap) is capable of forming pseudo-six-coordinate complexes with these same bases. These pseudo-six-coordinate complexes, such as Fe(HmCap)(1-MeIm)2, are of intermediate electronic spin (S = 1) and add oxygen without ligand displacement to give pseudo-sevencoordinate complexes-e.g., Fe(HmCap)(1-MeIm)2(02). Smaller bases, such as n-propylamine (n-PrNH2) and secbutylamine, add normally to Fe(HmCap) and give the expected diamagnetic bis-base complexes Fe(HmCap)(base)2. Bulky bases, such as t-butylamine and 1,2-dimethylimidazole, form only five-coordinate complexes with both iron(II) capped systems.In the present Raman spectroscopic investigations of these unusual systems our objectives were to extend the correlation of structure-sensitive bands to the capped tetraphenylporphinatoiron(II) complexes and then to investigate the behavior of the structure-sensitive vibrations for the unique complexes of Fe(HmCap) with hindered bases. In addition we were interested in the possibility of obtaining Raman spectroscopic evidence for porphyrin strain or other factors that might explainThe publication costs of this article were defrayed in part by page charge payment. This article must therefore be hereby marked "advertisenent" in accordance with 18 U. S. C. §1734 solely to indicate this fact. the difference in oxygen affinity of the...

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Structure-sensitive resonance Raman bands of tetraphenyl and "picket fence" porphyrin-iron complexes, including an oxyhemoglobin analog

Cited by 164 publications

References 8 publications

O ₂ reduction by a functional heme/nonheme bis-iron NOR model complex

O ₂ reduction by a functional heme/nonheme bis-iron NOR model complex

Operando Raman Micro-Spectroscopy of Polymer Electrolyte Fuel Cells

Structure-sensitive resonance Raman bands of capped tetraphenylporphyrinatoiron complexes

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Structure-sensitive resonance Raman bands of tetraphenyl and "picket fence" porphyrin-iron complexes, including an oxyhemoglobin analog

Cited by 164 publications

References 8 publications

O 2 reduction by a functional heme/nonheme bis-iron NOR model complex

O 2 reduction by a functional heme/nonheme bis-iron NOR model complex

Operando Raman Micro-Spectroscopy of Polymer Electrolyte Fuel Cells

Structure-sensitive resonance Raman bands of capped tetraphenylporphyrinatoiron complexes

Contact Info

Product

Resources

About

O ₂ reduction by a functional heme/nonheme bis-iron NOR model complex

O ₂ reduction by a functional heme/nonheme bis-iron NOR model complex