Geneviève Blondin

Atomic Energy and Alternative Energies Commission, Fontenay, Île-de-France, France

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Publications (72)384.36 Total impact

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    ABSTRACT: A series of new phenoxido-bridged mixed-valent FeIIFeIII complexes is characterized. In acetonitrile, the aniline or the 1H-benzimidazole ligand can be deprotonated upon the addition of NEt3, the resulting anilide or benzimidazolide being coordinated to the high-spin ferric ion. Before and after the action of NEt3, 1H NMR studies evidence mixtures of the cis- and trans-isomers. Titration monitored by NMR and/or optical spectroscopies allows the determination of the acid strength of the two isomers.
    Inorganic Chemistry 06/2015; DOI:10.1021/acs.inorgchem.5b00449 · 4.79 Impact Factor
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    ABSTRACT: Identifying the active nucleophile in hydrolysis reactions catalyzed by binuclear hydrolases is a recurrent problem and a matter of intense debate. We report on the phosphate ester hydrolysis by a Fe(III) Fe(II) complex of a binucleating ligand. This complex presents activities in the range of those observed for similar biomimetic compounds in the literature. The specific electronic properties of the Fe(III) Fe(II) complex allowed us to use (1) H NMR and Mössbauer spectroscopies to investigate the nature of the various species present in the solution in the pH range of 5-10. Both techniques showed that the hydrolysis activity is associated to a μ-hydroxido Fe(III) Fe(II) species. Further (1) H NMR experiments show that binding of anions or the substrate changes this bonding mode suggesting that a terminal hydroxide is the likely nucleophile in these hydrolysis reactions. This view is further supported by the structure determination of the hydrolysis product. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    Chemistry - A European Journal 04/2015; 21(22). DOI:10.1002/chem.201500977 · 5.70 Impact Factor
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    ABSTRACT: Reaction of a trinuclear iron(II) complex, Fe3Br3L (1), with KC8 under N2 leads to dinitrogen activation products (2) from which Fe3(NH)3L (2-1; L is a cyclophane bridged by three β-diketiminate arms) was characterized by X-ray crystallography. 1H NMR spectra of the protonolysis product of 2 synthesized under 14N2 and 15N2 confirm atmospheric N2 reduction, and ammonia is detected by the indophenol assay (yield ∼30 %). IR and Mössbauer spectroscopy, and elemental analysis on 2 and 2-1 as well as the tri(amido)triiron(II) 3 and tri(methoxo)triiron 4 congeners support our assignment of the reduction product as containing protonated N-atom bridges.
    Angewandte Chemie International Edition 12/2014; 127(5). DOI:10.1002/anie.201409676 · 11.34 Impact Factor
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    ABSTRACT: Fur family proteins, ubiquitous in prokaryotes, play a pivotal role in microbial survival and virulence in most pathogens. Metalloregulators, such as Fur and PerR, regulate the transcription of genes connected to iron homeostasis and response to oxidative stress, respectively. In Bacillus subtilis Fur and PerR bind with high affinity to DNA sequences differing at only 2 nucleotides. In addition to these differences in the PerR and Fur boxes, we identify in this study a residue located on the DNA binding motif of the Fur protein that is critical to discriminate the two close DNA sequences. Interestingly, when this residue is introduced into PerR, it lowers the affinity of PerR for its own DNA target but confers to the protein the ability to interact strongly with the Fur DNA binding sequence. The present data shows how two closely related proteins have distinct biological properties just by changing a single residue.
    ACS Chemical Biology 12/2014; 10(3). DOI:10.1021/cb500783g · 5.36 Impact Factor
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    ABSTRACT: The design of the new FeMo heterobimetallic species [FeMo(CO)5(κ(2)-dppe)(μ-pdt)] is reported. Mössbauer spectroscopy and density functional theory calculations give deep insight into the electronic and structural properties of this compound.
    Inorganic Chemistry 10/2014; 53(21). DOI:10.1021/ic501875q · 4.79 Impact Factor
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    ABSTRACT: We have recently reported a deprotonation-induced valence inversion within a phenoxido-bridged mixed-valent diiron(II,III) complex. The initial aniline coordinated to the FeII site reacts with triethylamine, and the resulting complex contains an anilide ligand coordinated to the FeIII ion. The behavior of these complexes in acetonitrile is indeed more intricate. Owing to the very distinctive spectroscopic signatures of the complexes, the conjunction of NMR, Mössbauer, and UV–visible absorption spectroscopies allows one to evidence two isomerization reactions, one involving the aniline linked to FeII and the other the anilide on FeIII. Theoretical calculations sustain this conclusion. Aniline in the cis position versus the bridging phenoxide is shown to be the most stable isomer while the anilide trans to the phenoxido bridge is favored. The trans isomer of the aniline complex is more acidic than the cis one by 1 pKa unit. Isomerization of the anilide complex is 10 times faster than the analogous isomerization of the aniline complex. Both reactions are proposed to proceed through a unique mechanism. This is the first time that such isomerization reactions are evidenced in dinuclear complexes.
    Inorganic Chemistry 09/2014; 53(19). DOI:10.1021/ic501793v · 4.79 Impact Factor
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    ABSTRACT: The preparation of [FeIV(O)(MePy2tacn)]2+ (2, MePy2tacn = N-methyl-N,N-bis(2-picolyl)-1,4,7-triazacyclononane) by reaction of [FeII(MePy2tacn)(solvent)]2+ (1) and PhIO in CH3CN and its full characterization are described. This compound can also be prepared photochemically from its iron(II) precursor by irradiation at 447 nm in the presence of catalytic amounts of [RuII(bpy)3]2+ as photosensitizer and a sacrificial electron acceptor (Na2S2O8). Remarkably, the rate of the reaction of the photochemically prepared compound 2 towards sulfides increases 150-fold under irradiation and 2 is partially regenerated after the sulfide has been consumed; hence the process can be repeated several times. The origin of this rate enhancement has been established by studying the reaction of chemically generated compound 2 with sulfides under different conditions, which demonstrated that both light and [RuII(bpy)3]2+ are necessary for the observed increase in the reaction rate. A combination of nanosecond time-resolved absorption spectroscopy with laser pulse excitation and other mechanistic studies has led to the conclusion that an electron transfer mechanism is the most plausible to explain the observed rate enhancement. According to this mechanism, the in situ generated [RuIII(bpy)3]3+ oxidizes the sulfide to form the corresponding radical cation, which is eventually oxidized by 2 to the corresponding sulfoxide.
    Journal of the American Chemical Society 02/2014; 136(12). DOI:10.1021/ja412059c · 11.44 Impact Factor
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    ABSTRACT: Given its ability to detect all iron centers, to identify their electronic structures, and to quantify the ratios of the different iron forms present in a sample, many researchers turn to Mössbauer spectroscopy when wanting to address structural and mechanistic questions involving iron proteins. Yet, this technique applied to biochemistry is provided by only a few dedicated teams in the world. Technical difficulties ranging from sample preparation to data analysis and interpretation make necessary the collaboration between biochemists and Mössbauer spectroscopists. This chapter will be confined to iron Mössbauer. It will focus on giving biologists and biochemists the keys to understand what essential information Mössbauer spectroscopy can yield, and how to engage in successful collaborations with spectroscopists. After introducing the basic principles of a Mössbauer experiment, we will describe first how to prepare a suitable Mössbauer sample, then how this technique is applied to the identification of different iron species inside proteins.
    Methods in molecular biology (Clifton, N.J.) 01/2014; 1122:153-70. DOI:10.1007/978-1-62703-794-5_11 · 1.29 Impact Factor
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    ABSTRACT: Let the Fur fly: Mutation of a single glutamate into an aspartate was shown to make the Fe sensor Fur as reactive to H2 O2 as the peroxide sensor PerR. In vivo and in vitro peroxide sensitivities of a series of PerR and Fur Asp/Glu mutants were studied by mass spectrometry. A combination of Mössbauer spectroscopy analyses and DFT calculations gave a structural rationale for this behavior.
    Angewandte Chemie International Edition 09/2013; 52(39). DOI:10.1002/anie.201304021 · 11.34 Impact Factor
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    ABSTRACT: Superoxide reductase (SOR) is a non-heme iron metalloenzyme that detoxifies superoxide radical in microorganisms. Its active site consists of an unusual non-heme Fe(2+) center in a [His4Cys1] square pyramidal pentacoordination, with the axial cysteine ligand proposed to be an essential feature in catalysis. Two NH peptide groups from isoleucine 118 and histidine 119 establish hydrogen bonds involving the sulfur ligand (Desulfoarculus baarsii SOR numbering). To investigate the catalytic role of these hydrogen bonds, the isoleucine 118 residue of the SOR from Desulfoarculus baarsii was mutated into alanine, aspartate, or serine residues. Resonance Raman spectroscopy showed that the mutations specifically induced an increase of the strength of the Fe(3+)-S(Cys) and S-Cβ(Cys) bonds as well as a change in conformation of the cysteinyl side chain, which was associated with the alteration of the NH hydrogen bonding involving the sulfur ligand. The effects of the isoleucine mutations on the reactivity of SOR with O2 (•-) were investigated by pulse radiolysis. These studies showed that the mutations induced a specific increase of the pK a of the first reaction intermediate, recently proposed to be an Fe(2+)-O2 (•-) species. These data were supported by density functional theory calculations conducted on three models of the Fe(2+)-O2 (•-) intermediate, with one, two, or no hydrogen bonds involving the sulfur ligand. Our results demonstrated that the hydrogen bonds between the NH (peptide) and the cysteine ligand tightly control the rate of protonation of the Fe(2+)-O2 (•-) reaction intermediate to form an Fe(3+)-OOH species.
    European Journal of Biochemistry 08/2013; 18(7). DOI:10.1007/s00775-013-1025-1 · 3.16 Impact Factor
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    ABSTRACT: A model of rubredoxin based on a cyclic peptide with a linear tail is presented. This model reproduces almost perfectly the fold, the spectroscopic characterizations and the redox activity of rubredoxins.
    Chemical Communications 03/2013; 49(28). DOI:10.1039/c3cc40517f · 6.72 Impact Factor
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    ABSTRACT: High-valent oxo-metal complexes are involved in key biochemical processes of selective oxidation and removal of xenobiotics. The catalytic properties of cytochrome P-450 and soluble methane monooxygenase enzymes are associated with oxo species on mononuclear iron haem and diiron non-haem platforms, respectively. Bio-inspired chemical systems that can reproduce the fascinating ability of these enzymes to oxidize the strongest C-H bonds are the focus of intense scrutiny. In this context, the development of highly oxidizing diiron macrocyclic catalysts requires a structural determination of the elusive active species and elucidation of the reaction mechanism. Here we report the preparation of an Fe(IV)(µ-nitrido)Fe(IV) = O tetraphenylporphyrin cation radical species at -90 °C, characterized by ultraviolet-visible, electron paramagnetic resonance and Mössbauer spectroscopies and by electrospray ionization mass spectrometry. This species exhibits a very high activity for oxygen-atom transfer towards alkanes, including methane. These findings provide a foundation on which to develop efficient and clean oxidation processes, in particular transformations of the strongest C-H bonds.
    Nature Chemistry 10/2012; 4(12):1024-9. DOI:10.1038/nchem.1471 · 23.30 Impact Factor
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    ABSTRACT: The heterodinuclear complexes [Fe(III)Mn(II)(L-Bn)(μ-OAc)(2)](ClO(4))(2) (1) and [Fe(II)Mn(II)(L-Bn)(μ-OAc)(2)](ClO(4)) (2) with the unsymmetrical dinucleating ligand HL-Bn {[2-bis[(2-pyridylmethyl)aminomethyl]]-6-[benzyl-2-(pyridylmethyl)aminomethyl]-4-methylphenol} were synthesized and characterized as biologically relevant models of the new Fe/Mn class of nonheme enzymes. Crystallographic studies have been completed on compound 1 and reveal an Fe(III)Mn(II)μ-phenoxobis(μ-carboxylato) core. A single location of the Fe(III) ion in 1 and of the Fe(II) ion in 2 was demonstrated by Mössbauer and (1)H NMR spectroscopies, respectively. An investigation of the temperature dependence of the magnetic susceptibility of 1 revealed a moderate antiferromagnetic interaction (J = 20 cm(-1)) between the high-spin Fe(III) and Mn(II) ions in 1, which was confirmed by Mössbauer and electron paramagnetic resonance (EPR) studies. The electrochemical properties of complex 1 are described. A quasireversible electron transfer at -40 mV versus Ag/AgCl corresponding to the Fe(III)Mn(II)/Fe(II)Mn(II) couple appears in the cyclic voltammogram. Thorough investigations of the Mössbauer and EPR signatures of complex 2 were performed. The analysis allowed evidencing of a weak antiferromagnetic interaction (J = 5.72 cm(-1)) within the Fe(II)Mn(II) pair consistent with that deduced from magnetic susceptibility measurements (J = 6.8 cm(-1)). Owing to the similar value of the Fe(II) zero-field splitting (D(Fe) = 3.55 cm(-1)), the usual treatment within the strong exchange limit was precluded and a full analysis of the electronic structure of the ground state of complex 2 was developed. This situation is reminiscent of that found in many diiron and iron-manganese enzyme active sites.
    Inorganic Chemistry 09/2012; 51(19):10447-60. DOI:10.1021/ic301725z · 4.79 Impact Factor
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    ABSTRACT: The kinetics of proton-induced intervalence charge transfer (IVCT) may be measured electrochemically by generating one of the members of the IVCT couple in situ and following its conversion by means of the electrochemical signature of the other member of the couple. In the case of the diiron complex taken as an example, the reaction kinetics analysis, including the H/D isotope effect, clearly points to the prevalence of the concerted proton-intervalence charge transfer pathway over the stepwise pathways. A route is thus open toward systematic kinetic studies of proton-induced IVCT aiming at uncovering the main reactivity parameters and the factors that control the occurrence of concerted versus stepwise pathways.
    Journal of the American Chemical Society 02/2012; 134(4):1906-9. DOI:10.1021/ja2075482 · 11.44 Impact Factor
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    ABSTRACT: The coupling of electron and proton transfers is currently under intense scrutiny. This Communication reports a new kind of proton-coupled electron transfer within a homodinuclear first-row transition-metal complex. The triply-bridged complex [Fe(III)(μ-OPh)(μ(2)-mpdp)Fe(II)(NH(2)Bn)] (1; mpdp(2-) = m-phenylenedipropionate) bearing a terminal aminobenzyl ligand can be reversibly deprotonated to the anilinate complex 2 whose core [Fe(II)(μ-OPh)(μ(2)-mpdp)Fe(III)(NHBn)] features an inversion of the iron valences. This observation is supported by a combination of UV-visible, (1)H NMR, and Mössbauer spectroscopic studies.
    Inorganic Chemistry 06/2011; 50(14):6408-10. DOI:10.1021/ic2007414 · 4.79 Impact Factor
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    ABSTRACT: The aerobic reaction of the Schiff-base ligand N-(benzimidazol-2-yl)salicylaldimine (Hbisi) with iron(II) perchlorate in methanol leads to the formation of the remarkable coordination compound [Fe(4)(mu(4)-O)(mu-MeO)(4)(bisi)(4)](ClO(4))(2) x 4 MeOH (1), whose single-crystal X-ray structure reveals the presence of a discrete Fe(III)(4)(mu(4)-O) core. Magnetic and Mossbauer studies both show that the exchange interaction within the square tetranuclear iron(III) unit is dominated by the central bridging mu(4)-oxido ligand, the involvement of the mu-methoxido bridges being negligible.
    Inorganic Chemistry 03/2010; 49(5):2427-34. DOI:10.1021/ic902360x · 4.79 Impact Factor
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    ABSTRACT: Post-translational modifications of ribosomal proteins are important for the accuracy of the decoding machinery. A recent in vivo study has shown that the rimO gene is involved in generation of the 3-methylthio derivative of residue Asp-89 in ribosomal protein S12 (Anton, B. P., Saleh, L., Benner, J. S., Raleigh, E. A., Kasif, S., and Roberts, R. J. (2008) Proc. Natl. Acad. Sci. U. S. A. 105, 1826–1831). This reaction is formally identical to that catalyzed by MiaB on the C2 of adenosine 37 near the anticodon of several tRNAs. We present spectroscopic evidence that Thermotoga maritima RimO, like MiaB, contains two [4Fe-4S] centers, one presumably bound to three invariant cysteines in the central radical S-adenosylmethionine (AdoMet) domain and the other to three invariant cysteines in the N-terminal UPF0004 domain. We demonstrate that holo-RimO can specifically methylthiolate the aspartate residue of a 20-mer peptide derived from S12, yielding a mixture of mono- and bismethylthio derivatives. Finally, we present the 2.0 Å crystal structure of the central radical AdoMet and the C-terminal TRAM (tRNA methyltransferase 2 and MiaB) domains in apo-RimO. Although the core of the open triose-phosphate isomerase (TIM) barrel of the radical AdoMet domain was conserved, RimO showed differences in domain organization compared with other radical AdoMet enzymes. The unusually acidic TRAM domain, likely to bind the basic S12 protein, is located at the distal edge of the radical AdoMet domain. The basic S12 protein substrate is likely to bind RimO through interactions with both the TRAM domain and the concave surface of the incomplete TIM barrel. These biophysical results provide a foundation for understanding the mechanism of methylthioation by radical AdoMet enzymes in the MiaB/RimO family.
    Journal of Biological Chemistry 02/2010; 285(8):5792-5801. · 4.60 Impact Factor
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    ABSTRACT: Post-translational modifications of ribosomal proteins are important for the accuracy of the decoding machinery. A recent in vivo study has shown that the rimO gene is involved in generation of the 3-methylthio derivative of residue Asp-89 in ribosomal protein S12 (Anton, B. P., Saleh, L., Benner, J. S., Raleigh, E. A., Kasif, S., and Roberts, R. J. (2008) Proc. Natl. Acad. Sci. U. S. A. 105, 1826–1831). This reaction is formally identical to that catalyzed by MiaB on the C2 of adenosine 37 near the anticodon of several tRNAs. We present spectroscopic evidence that Thermotoga maritima RimO, like MiaB, contains two [4Fe-4S] centers, one presumably bound to three invariant cysteines in the central radical S-adenosylmethionine (AdoMet) domain and the other to three invariant cysteines in the N-terminal UPF0004 domain. We demonstrate that holo-RimO can specifically methylthiolate the aspartate residue of a 20-mer peptide derived from S12, yielding a mixture of mono- and bismethylthio derivatives. Finally, we present the 2.0 Å crystal structure of the central radical AdoMet and the C-terminal TRAM (tRNA methyltransferase 2 and MiaB) domains in apo-RimO. Although the core of the open triose-phosphate isomerase (TIM) barrel of the radical AdoMet domain was conserved, RimO showed differences in domain organization compared with other radical AdoMet enzymes. The unusually acidic TRAM domain, likely to bind the basic S12 protein, is located at the distal edge of the radical AdoMet domain. The basic S12 protein substrate is likely to bind RimO through interactions with both the TRAM domain and the concave surface of the incomplete TIM barrel. These biophysical results provide a foundation for understanding the mechanism of methylthioation by radical AdoMet enzymes in the MiaB/RimO family.
    Journal of Biological Chemistry 12/2009; DOI:10.1074/jbc.M109.065516 · 4.60 Impact Factor
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    ABSTRACT: The trinuclear oxo bridged manganese cluster, [Mn(IV)(3)O(4)(terpy)(terpyO(2))(2)(H(2)O)](S(2)O(8))(2) (5) (terpy = 2,2':2'',6'-terpyridine and terpyO(2) = 2,2':2'',6'-terpyridine 1,1''-dioxide), was isolated in an acidic aqueous medium from the reaction of MnSO(4), terpy, and oxone as chemical oxidant. The terpyO(2) ligands were generated in situ during the synthesis by partial oxidation of terpy. The complex crystallizes in the monoclinic space group P21/n with a = 14.251(5) A, b = 15.245(5) A, c = 24.672(5) A, alpha = 90.000(5) degrees, beta = 92.045(5) degrees, gamma = 90.000(5) degrees, and Z = 4. The triangular {Mn(IV)(3)O(4)}(4+) core observed in this complex is built up of a basal Mn(mu-O)(2)Mn unit where each Mn ion is linked to an apical Mn ion via mono(mu-O) bridges. The facial coordination of the two tridentate terpyO(2) ligands to the Mn(mu-O)(2)Mn unit allows the formation of the triangular core. 5 is also the first structurally characterized Mn complex with polypyridinyl N-oxide ligands. The variable-temperature magnetic susceptibility data for this complex, in the range of 10-300 K, are consistent with an S = 1/2 ground state and were fit using the spin Hamiltonian H(eff) with S(1) = S(2) = S(3) = 3/2, J(a) = -37 (+/-0.5) and J(b) = -53 (+/-1) cm(-1), where J(a) and J(b) are exchange constants through the mono-mu-oxo and the di-mu-oxo bridges, respectively. The doublet ground spin state of 5 is confirmed by EPR spectroscopic measurements. Density functional theory (DFT) calculations based on the broken symmetry approach reproduce the magnetic properties of 5 very well (calculated values: J(a) = -39.4 and J(b) = -55.9 cm(-1)), thus confirming the capability of this quantum chemical method for predicting the magnetic behavior of clusters involving more than two metal ions. The nature of the ground spin state of the magnetic {Mn(IV)(3)O(4)}(4+) core and the role of ancillary ligands on the magnitude of J are also discussed.
    Inorganic Chemistry 10/2009; 48(21):10281-8. DOI:10.1021/ic901409y · 4.79 Impact Factor

Publication Stats

1k Citations
384.36 Total Impact Points

Institutions

  • 2014
    • Atomic Energy and Alternative Energies Commission
      Fontenay, Île-de-France, France
  • 2013–2014
    • Cea Leti
      Grenoble, Rhône-Alpes, France
  • 2005–2014
    • University of Grenoble
      Grenoble, Rhône-Alpes, France
    • University of Barcelona
      Barcino, Catalonia, Spain
  • 2012–2013
    • University Joseph Fourier - Grenoble 1
      • Laboratoire de Chimie et Biologie des Métaux
      Grenoble, Rhône-Alpes, France
  • 1990–2008
    • Université Paris-Sud 11
      • Institut de Chimie Moléculaire et des Matériaux d'Orsay (ICMMO)
      Orsay, Île-de-France, France