High‐Field EPR Study of Frozen Aqueous Solutions of Iron(<scp>III</scp>) Citrate Complexes

Biaso, Frédéric; Duboc, Carole; Barbara, B.; Serratrice, Guy; Thomas, Fabrice; Charapoff, Denis; Béguin, Claude

doi:10.1002/ejic.200400414

Cited by 12 publications

(10 citation statements)

References 62 publications

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“…Finally, these fine structure parameters are typical of mononuclear, high-spin iron(III) sites. Such species have been extensively characterized by EPR, most often at X-band (∼9 GHz), but also at higher frequencies . To facilitate the comparison of these results with our study we have recorded, for a neat powder sample of 1 , several low-temperature X-band EPR spectra; see Figure S4.…”

Section: Resultsmentioning

confidence: 99%

“…Such species have been extensively characterized by EPR, most often at X-band (∼9 GHz), but also at higher frequencies. 32 To facilitate the comparison of these results with our study we have recorded, for a neat powder sample of 1, several low-temperature X-band EPR spectra; see Figure S4. Moreover, we also present some representative theoretical spectra predicted for 1, see Figure S5, and their rationalization, see Figures S6 and S7.…”

Section: Development Of the Mpmae-h Ligand And Thementioning

confidence: 87%

See 1 more Smart Citation

Structural, Spectroscopic, and Theoretical Investigation of a T-Shaped [Fe₃(μ₃-O)] Cluster

Stoian¹,

Peng

Beedle³

et al. 2017

Inorg. Chem.

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The synthesis, X-ray crystal and electronic structures of [Fe(μ-O)(mpmae)(OAc) Cl], 1, where mpmae-H = 2-(N-methyl-N-((pyridine-2-yl)methyl)amino)ethanol, are described. This cluster comprises three high-spin ferric ions and exhibits a T-shaped site topology. Variable-frequency electron paramagnetic resonance measurements performed on single crystals of 1 demonstrate a total spin S = 5/2 ground state, characterized by a small, negative, and nearly axial zero-field splitting tensor D = -0.49 cm, E/D ≈ 0.055. Analysis of magnetic susceptibility, magnetization, and magneto-structural correlations further corroborate the presence of a sextet ground-spin state. The observed ground state originates from the strong anti-ferromagnetic interaction of two iron(III) spins, with J = 115(5) cm, that, in turn, are only weakly coupled to the spin of the third site, with j = 7(1) cm. These exchange interactions lead to a ground state with magnetic properties that are essentially entirely determined by the weakly coupled site. The contributions of the individual spins to the total ground state of the cluster were monitored using variable-field Fe Mössbauer spectroscopy. Field-dependent spectra reveal that, while one of the iron sites exhibits a large negative internal field, typical of ferric ions, the other two sites exhibit small, but not null, negative and positive internal fields. A theoretical analysis reveals that these small internal fields originate from the mixing of the lowest S = 5/2 excited state into the ground state which, in turn, is induced by a minute structural distortion.

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Section: Resultsmentioning

confidence: 99%

Section: Development Of the Mpmae-h Ligand And Thementioning

confidence: 87%

Structural, Spectroscopic, and Theoretical Investigation of a T-Shaped [Fe₃(μ₃-O)] Cluster

Stoian¹,

Peng

Beedle³

et al. 2017

Inorg. Chem.

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“…The values of D 0 ) 0.32 cm -1 and λ ) 0.31 are fairly typical for tris chelation to oxygen or nitrogen bidentate ligands to iron. 56,57 Reviewing the simulation parameters in Table 1, the most visible trend is that of the increase in the median value of λ as the number of coordinated catecholates increases. The [Fe(cat) 3 ] 3complex is expected to have a trigonally distorted octahedral geometry for which the median value of λ ) 0.31 is quite reasonable.…”

Section: Resultsmentioning

confidence: 99%

EPR Investigation and Spectral Simulations of Iron−Catecholate Complexes and Iron−Peptide Models of Marine Adhesive Cross-Links

Weisser¹,

Nilges²,

Sever³

et al. 2006

Inorg. Chem.

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Electron paramagnetic resonance (EPR) spectra are presented for iron complexes of catecholate, tironate, and a 3,4-dihydroxyphenylalanine (DOPA)-containing peptide of sequence Ac-Ala-DOPA-Thr-Pro-CONH2 ("AdopaTP"). This peptide was prepared to model potential metal-protein cross-links in the adhesive used by marine mussels, Mytilus edulis, for affixing themselves to surfaces. Spectra are shown for iron bound to each ligand in mono, bis, and tris coordination environments. For example, the catecholate complexes {Fe(cat)}, {Fe(cat)2}, and [Fe(cat)3]3- are provided. Detailed simulations are presented to describe the origin of spectra for the iron-catecholate and iron-peptide species, which show that the spectral features can be accounted for only with the inclusion of D- and E-strain. The spectroscopy of each compound is shown under both anaerobic and aerobic conditions. When exposed to air, the high-spin Fe3+ signal of [Fe(AdopaTP)3]3- decreases and an organic radical is formed. No other sample exhibited an appreciable radical signal. These data are discussed in light of the biomaterial synthesis carried out by marine mussels.

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“…The available crystal structures for ferric citrate complexes indicate that the hydroxyl proton is lost when citrate coordinates iron(III) 20, 22 and definitive evidence that this group exists in the alkoxide form in aqueous ferric citrate complexes was obtained utilizing high-field EPR spectroscopy. 33 It is important to note that the high-field EPR study was carried out at iron : citrate molar ratios of 1 : 20 and under these conditions it was unequivocally demonstrated that the species present in solution is the mononuclear dicitrate complex.…”

Section: Discussionmentioning

confidence: 99%

Iron(iii) citrate speciation in aqueous solution

et al. 2009

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Citrate is an iron chelator and it has been shown to be the major iron ligand in the xylem sap of plants. Furthermore, citrate has been demonstrated to be an important ligand for the non-transferrin bound iron (NTBI) pool occurring in the plasma of individuals suffering from iron-overload. However, ferric citrate chemistry is complicated and a definitive description of its aqueous speciation at neutral pH remains elusive. X-Ray crystallography data indicates that the alcohol function of citrate (Cit4-) is involved in Fe(III) coordination and that deprotonation of this functional group occurs upon complex formation. The inability to include this deprotonation in the affinity constant calculations has been a major source of divergence between various reports of iron(III)-citrate affinity constants. However the recent determination of the alcoholic pKa of citric acid (H4Cit) renders the reassessment of the ferric citrate system possible. The aqueous speciation of ferric citrate has been investigated by mass spectrometry and EPR spectroscopy. It was observed that the most relevant species are a monoiron dicitrate species and dinuclear and trinuclear oligomeric complexes, the relative concentration of which depends on the solution pH value and the iron : citric acid molar ratio. Spectrophotometric titration was utilized for affinity constant determination and the formation constant for the biologically relevant [Fe(Cit)2]5- is reported for the first time.

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High‐Field EPR Study of Frozen Aqueous Solutions of Iron(III) Citrate Complexes

Cited by 12 publications

References 62 publications

Structural, Spectroscopic, and Theoretical Investigation of a T-Shaped [Fe₃(μ₃-O)] Cluster

Structural, Spectroscopic, and Theoretical Investigation of a T-Shaped [Fe₃(μ₃-O)] Cluster

EPR Investigation and Spectral Simulations of Iron−Catecholate Complexes and Iron−Peptide Models of Marine Adhesive Cross-Links

Iron(iii) citrate speciation in aqueous solution

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High‐Field EPR Study of Frozen Aqueous Solutions of Iron(III) Citrate Complexes

Cited by 12 publications

References 62 publications

Structural, Spectroscopic, and Theoretical Investigation of a T-Shaped [Fe3(μ3-O)] Cluster

Structural, Spectroscopic, and Theoretical Investigation of a T-Shaped [Fe3(μ3-O)] Cluster

EPR Investigation and Spectral Simulations of Iron−Catecholate Complexes and Iron−Peptide Models of Marine Adhesive Cross-Links

Iron(iii) citrate speciation in aqueous solution

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Structural, Spectroscopic, and Theoretical Investigation of a T-Shaped [Fe₃(μ₃-O)] Cluster

Structural, Spectroscopic, and Theoretical Investigation of a T-Shaped [Fe₃(μ₃-O)] Cluster