Mössbauer spectra of unstable iron porphyrins Models for compound II of peroxidase

Simonneaux, Gérard; Scholz, William F.; Reed, Christopher A.; Lang, Georgina

doi:10.1016/0304-4165(82)90195-7

Cited by 30 publications

(22 citation statements)

References 13 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Table 1 summarizes the values in the literature and our results on a series of spectra from various complexes with different porphyrins, counter ions and solvents. The ferryl oxidation state of iron in these complexes is suggested from the isomer shifts which are consistent with published data on other complexes containing the [Fe0I3+ unit [l8, 27,32,[34][35][36][37][38][39].…”

Section: Mosshauer and Epr Spectroscopysupporting

confidence: 89%

Evidence for variable metal‐radical spin coupling in oxoferrylporphyrin cation radical complexes

Bill

Ding

Bominaar

et al. 1990

European Journal of Biochemistry

View full text Add to dashboard Cite

Oxoferrylporphyrin cation radical complexes were generated by m-chloroperoxybenzoic acid oxidation of the chloro and trifluoromethanesulfonato complexes of tetramesitylporphyrinatoiron(II1) [(TMP)Fe] and the trifluoromethanesulfonato complex of tetra(2,6-dichlorophenyl)porphyrinatoiron(IlI) [TPP(2,. Coupling between ferry1 iron (S = 1) and porphyrin radical (S' = 1/2) spin systems was investigated by Mossbauer and EPR spectroscopy. The oxoferrylporphyrin cation radical systems generated from the TMP complexes show strong ferromagnetic coupling. Analysis of the magnetic Mossbauer spectra, using a spin Hamiltonian explicitly including a coupling tensor J , suggests an exchange-coupling constant J > 80 cm-'. The EPR spectra show non-zero rhombicity, the origin of which is discussed in terms of contributions from the usual zero-field effects of iron and from iron-radical spin-dipolar interaction. A consistent estimate of zero-field splitting parameter D = + 6 cm-' was obtained by EPR and Mossbauer measurements. EPR and Mossbauer parameters are shown to be slightly dependent on solvent, but not on the axial ligand in the starting (TMP)Fe complex. In contrast to the TMP complex, the oxoferrylporphyrin cation radical system generated from [TPP(2,6-C1)FeOS02CF3] exhibits Mossbauer and EPR spectra consistent with weak iron-porphyrin radical coupling of IJI = 1 cm-'.High-valency oxoheme complexes, formally two-electron oxidized above the ferric state, have been of considerable interest because of their importance in the chemistry of catalase and peroxidase enzymes [l, 21 and because they play a putative role in monooxygen transfer to organic substrates by cytochrome P450 [3, 41. Efforts to model biochemical function and to characterize better the electronic structure of these intermediates have resulted in the synthesis of oxoheme complexes in the same oxidation state as the enzymatic transients [5, 61 and in mimicking some of the biochemical functions of cytochrome P450 [5 -151. The sum of the physicochemical evidence marshalled to date best describes the complexes as oxoferrylporphyrin cation radical complexes [5, 16 -291. Despite the potential importance of the synthetic complexes for the elucidation of the electronic structures of the biological transients, only the oxoferrylporphyrin cation radical system [(TMP)Fe = 0 1 +Cl-, derived from tetramesitylporphyrinatoiron(II1) chloride [(TMP)FeCl], has been the object of serious efforts at characterization (complexes like [(TMP)Fe = O](Cl-), the counter ions are written in parentheses to indicate uncertainty as to the exact nature of their association with the iron(1V) center}. A large variety of spectroscopic techniques has been used for investigation of this species [6,16,18, 231. Strong ferromagnetic coupling between the electron spins of iron and the tetramesitylporphyrin radical has been demonCorrespondenre to A.

show abstract

Section: Mosshauer and Epr Spectroscopysupporting

confidence: 89%

Evidence for variable metal‐radical spin coupling in oxoferrylporphyrin cation radical complexes

Bill

Ding

Bominaar

et al. 1990

European Journal of Biochemistry

View full text Add to dashboard Cite

show abstract

“…[7,25] Mössbauer studies have shown a positive, large zero-field splitting (D % 30 cm À1 ) for both heme and nonheme Fe IV = O complexes. [14,26,27] Importantly, the calculated geometric and electronic-structure descriptions for the heme and non-heme Fe IV = O species correlate well with experimental data (Table 2). …”

supporting

confidence: 75%

Comparison of Fe^IVO Heme and Non‐heme Species: Electronic Structures, Bonding, and Reactivities

Decker

Solomon

2005

Angew Chem Int Ed

View full text Add to dashboard Cite

Extremely similar electronic structures and FeO bonding characterize FeIVO S=1 heme and non‐heme species as a result of a decoupling of the oxoiron unit from the porphyrin (Por) π system in the heme complex (see scheme). However, along the reaction coordinate towards an FeIIIOH product, the Por π system interacts with the iron d orbitals, thus resulting in different reactivities for heme and non‐heme complexes.

show abstract

“…Above pH 11, the hydroxide species begins to convert to a new species with Mössbauer parameters ( σ = 0.08 mm/s, Δ E Q = 1.51 mm/s) that are consistent with the formation of an Fe IV = O intermediate, Figure 9. 23,28,34 A plot of the relative concentration of these species as a function of pH results in a titration curve with p K a = 13.1, Figure 10. The p K a of this transition appears to be independent of the ferric conformation (green or brown) used to prepare HPC-II at low pH (see Supporting Information).…”

Section: Resultsmentioning

confidence: 99%

“…18–20 The interplay between these two lines of investigations led to considerable insight into the structure (both electronic and geometric) as well as the function of these high-valent systems. 13–17,20–23 As a result of these efforts, it is now well understood that in heme proteins the ferryl moiety lies at the center of two reactive intermediates called compound I and compound II. 2 Prototypical compound I species are best described as ferryl porphyrin radicals, 24–27 while prototypical compound II species are the iron(IV)-oxo porphyrins obtained by the one electron reduction of compound I.…”

Section: Introductionmentioning

confidence: 99%

Spectroscopic Investigations of Catalase Compound II: Characterization of an Iron(IV) Hydroxide Intermediate in a Non-thiolate-Ligated Heme Enzyme

et al. 2016

View full text Add to dashboard Cite

We report on the protonation state of Helicobacter pylori catalase compound II. UV/visible, Mössbauer, and X-ray absorption spectroscopies have been used to examine the intermediate from pH 5 to 14. We have determined that HPC-II exists in an iron(IV) hydroxide state up to pH 11. Above this pH, the iron(IV) hydroxide complex transitions to a new species (pKa = 13.1) with Mössbauer parameters that are indicative of an iron(IV)-oxo intermediate. Recently, we discussed a role for an elevated compound II pKa in diminishing the compound I reduction potential. This has the effect of shifting the thermodynamic landscape toward the two-electron chemistry that is critical for catalase function. In catalase, a diminished potential would increase the selectivity for peroxide disproportionation over off-pathway one-electron chemistry, reducing the buildup of the inactive compound II state and reducing the need for energetically expensive electron donor molecules.

show abstract

Mössbauer spectra of unstable iron porphyrins Models for compound II of peroxidase

Cited by 30 publications

References 13 publications

Evidence for variable metal‐radical spin coupling in oxoferrylporphyrin cation radical complexes

Evidence for variable metal‐radical spin coupling in oxoferrylporphyrin cation radical complexes

Comparison of Fe^IVO Heme and Non‐heme Species: Electronic Structures, Bonding, and Reactivities

Spectroscopic Investigations of Catalase Compound II: Characterization of an Iron(IV) Hydroxide Intermediate in a Non-thiolate-Ligated Heme Enzyme

Contact Info

Product

Resources

About

Mössbauer spectra of unstable iron porphyrins Models for compound II of peroxidase

Cited by 30 publications

References 13 publications

Evidence for variable metal‐radical spin coupling in oxoferrylporphyrin cation radical complexes

Evidence for variable metal‐radical spin coupling in oxoferrylporphyrin cation radical complexes

Comparison of FeIVO Heme and Non‐heme Species: Electronic Structures, Bonding, and Reactivities

Spectroscopic Investigations of Catalase Compound II: Characterization of an Iron(IV) Hydroxide Intermediate in a Non-thiolate-Ligated Heme Enzyme

Contact Info

Product

Resources

About

Comparison of Fe^IVO Heme and Non‐heme Species: Electronic Structures, Bonding, and Reactivities