Moessbauer spectroscopic evidence for the electronic configuration of iron in horseradish peroxidase and its peroxide derivatives

Moss, Thomas H.; Ehrenberg, Anders; Bearden, Alan J.

doi:10.1021/bi00838a037

Cited by 173 publications

(82 citation statements)

References 21 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

“…The "picket fence" dioxygen complex (8) is a model for I. "Compounds II" in the peroxidase family (9) are heme analogues of the ferryl intermediate postulated, (II), in Fig. 2.…”

Section: (I Ii)mentioning

confidence: 99%

Synthesis and characterization of "face-to-face" porphyrins.

Collman¹,

Elliott²,

Halbert³

et al. 1977

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

136

View full text Add to dashboard Cite

The syntheses of four binary porphyrins, two of which are constrained to a "face-to-face" conformation, and their Co2+ and Cu2+ derivatives are described. Electron spin resonance indicates that the intermetallic separation in the binuclear "face-to-face" porphyrins is about 6.5-6.8 A. Electronic spectra and proton magnetic resonance spectra support the postulated "face-to-face" conformations. A hypothesis that related compounds may serve as multielectron redox catalysts for 02 and N2 is presented. The development of efficient catalysts for the reversible multielectron reduction of 02 and N2 would have great significance. Such catalysts are essential to the oxygen cathode of an air-powered fuel cell and to electrochemical nitrogen fixation.The major problem in catalyzing four-or six-electron reductions of 02 or N2 is that stepwise one-or two-electron paths must pass through relatively unstable intermediates (Fig. 1). The high energy content of these intermediates precludes rapid stepwise electron transfer operating near the reversible potential of the overall four-or six-electron reduction. The rapid reduction of oxygen, which has a triplet ground state, also requires a mechanism to overcome the conservation of spin and orbital angular momentum. The latter problem might be circumvented by using a metal catalyst that has low-lying paramagnetic states. These arguments have been developed by H. Taube (personal communication).Many monometallic macrocyclic complexes adsorbed on graphite have been examined as catalysts for oxygen reduction (3). The most effective macrocycles have four nitrogen donor atoms. In the phthalocyanine series, the order of reactivity is Fe > Co > Ni > Cu > Mn. However, such studies have failed to reveal any catalyst that is capable of reversible reduction of 02 to water, possibly because with a single metal center, initial 2e-reduction to H202 is always dominant.We have approached this problem by constructing a new class of so-called "face-to-face porphyrins" in which two porphyrin rings are held in parallel conformation. Thus, two metal atoms might act in concert to bind and reduce dioxygen (or dinitrogen) is carried out at 250, the measured rates are such that Greenwood and Gibson (4) conclude that any intermediates must have half-lives of less than 10 Msec. Several mono-and dioxygenases, which reduce oxygen with concomitant oxidation of organic substrates, also contain more than one functional metal ion.These include the monooxygenases laccase (mono-phenol monooxygenase, 4 Cu), and ascorbate oxidase (8 Cu) as well as the dioxygenase L-tryptophan oxygenase (2 hemes and 2 Cu).In contrast to the large number of biological systems that reduce 02, evolutionary processes appear to have developed only a single dinitrogen fixing system, nitrogenase (5). Although the molecular mechanism has not yet been elucidated, a binuclear metal site for dinitrogen reduction has been proposed.tAbiological support for the idea of binuclear 02 reduction by Fe2+ comesfrom Hammondand Wu'sstudy (7) ofthe ...

show abstract

“…On the basis of visible (6), Mossbauer (7), ESR (8), and electron nuclear double resonance (ENDOR) (9) spectral data, compound I has been assigned the structure of a low-spin oxo-ligated iron(IV) porphyrin ir-cation radical. This same entity is suggested to serve as the oxygen transfer agent formed at the active site of the cytochrome P-450 enzymes (10,11).…”

mentioning

confidence: 99%

Stabilization of higher-valent states of iron porphyrin by hydroxide and methoxide ligands: electrochemical generation of iron(IV)-oxo porphyrins.

Lee¹,

Calderwood²,

Bruice³

1985

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

View full text Add to dashboard Cite

An electrochemical study of hydroxide-and methoxide-ligated iron(II) tetraphenylporphyrins possessing ortho-phenyl substituents that block ,L-oxo dimer formation has been carried out. Ligation by these strongly basic oxyanions promotes the formation of iron(IV)-oxo porphyrins upon one-electron oxidation. Further one-electron oxidation of the latter provides the iron(IV)-oxo porphyrin ir-cation radical. (6), Mossbauer (7), ESR (8), and electron nuclear double resonance (ENDOR) (9) spectral data, compound I has been assigned the structure of a low-spin oxo-ligated iron(IV) porphyrin ir-cation radical. This same entity is suggested to serve as the oxygen transfer agent formed at the active site of the cytochrome P-450 enzymes (10, 11). One-electron reduction of the ir-cation radical of compound I results in the formation of an iron(IV)-oxo species termed compound 11 (12). Interestingly, compounds I and II of the peroxidases exhibit almost identical redox potentials (13).Only a few well-characterized model analogs of compounds I and II exist. These iron(IV) porphyrins have all been generated chemically at low temperatures. Until now, an iron(IV)-oxo porphyrin species has not been generated electrochemically. In the cyclic voltammogram of simple iron porphyrins, anodic sweeps beyond the iron(II)/iron(III) couple yield two reversible one-electron oxidation waves (32). Originally it was proposed that the first wave pertained to the iron(III)/iron(IV) couple and the second wave was due to porphyrin 1r-cation radical formation (14,15). This was shown to be incorrect in a report (16) which demonstrated that the redox potential of the first oxidation was independent of the many axial ligands employed (16) and that the physical properties of the oxidized species were consistent with an iron(III) porphyrin ir-cation radical structure (17). The second wave was attributed to an iron(III) porphyrin dication.In the literature, there is no mention of electrochemical investigations involving HO-, CH30-, etc. ligated iron porphyrins. This does not of course indicate an oversight (17) but simply reflects the instability, due to ,u-oxo dimer formation, of oxo-ligated iron(III) porphyrins. The inability to electrochemically generate a compound I or compound II analog could be due to the importance of oxo ligation to the stabilization of high-valent iron porphyrin species. It is well established that metals in their higher-valent oxidation states are generally stabilized by oxo ligation (18). Using sterically hindered porphyrins that are capable of hydroxide ligation, we have now been able to observe the electrochemical generation ofiron(IV)-oxo porphyrin species. In addition, the similarity of the iron(IV)-oxo and the porphyrin ir-cation redox potentials provides a rationale for the redox potentials of compounds I and II of the peroxidases. In the present study we describe the electrochemistry of porphyrins 1 to 5 when ligated to Cl-, HO-, and CH30 and discuss these results as they relate to studies involving the chemical ge...

show abstract

Moessbauer spectroscopic evidence for the electronic configuration of iron in horseradish peroxidase and its peroxide derivatives

Cited by 173 publications

References 21 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

Synthesis and characterization of "face-to-face" porphyrins.

Stabilization of higher-valent states of iron porphyrin by hydroxide and methoxide ligands: electrochemical generation of iron(IV)-oxo porphyrins.

Contact Info

Product

Resources

About