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1.
ChemSusChem ; 13(9): 2419-2427, 2020 May 08.
Article in English | MEDLINE | ID: mdl-32315495

ABSTRACT

To reduce the amount of conducting additives generally required for polynitroxide-based electrodes, a stable radical (TEMPO) is combined with a conductive copolymer backbone consisting of 2,7-bisthiophene carbazole (2,7-BTC), which is characterized by a high intrinsic electronic conductivity. This work deals with the synthesis of this new polymer functionalized by a redox nitroxide. Fine structural characterization using electron paramagnetic resonance (EPR) techniques established that: 1) the nitroxide radicals are properly attached to the radical chain (continuous wave EPR) and 2) the polymer chain has very rigid conformations leading to a set of well-defined distances between first neighboring pairs of nitroxides (pulsed EPR). The redox group combined with the electroactive polymer showed not only a very high electrochemical reversibility but also a perfect match of redox potentials between the de-/doping reaction of the bisthiophene carbazole backbone and the redox activity of the nitroxide radical. This new organic electrode shows a stable capacity (about 60 mAh g-1 ) and enables a strong reduction in the amount of carbon additive due to the conducting-polymer skeleton.

2.
Chem Commun (Camb) ; 54(52): 7175-7178, 2018 Jun 26.
Article in English | MEDLINE | ID: mdl-29888350

ABSTRACT

The crystal structure of the Escherichia coli O2-sensitive C19G [NiFe]-hydrogenase-1 variant shows that the mutation results in a novel FeS cluster, proximal to the Ni-Fe active site. While the proximal cluster of the native O2-tolerant enzyme can transfer two electrons to that site, EPR spectroscopy shows that the modified cluster can transfer only one electron, this shortfall coinciding with O2 sensitivity. Computational studies on electron transfer help to explain how the structural and redox properties of the novel FeS cluster modulate the observed phenotype.


Subject(s)
Escherichia coli Proteins/metabolism , Escherichia coli/enzymology , Hydrogenase/metabolism , Iron-Sulfur Proteins/metabolism , Oxygen/metabolism , Crystallography, X-Ray , Escherichia coli Proteins/chemistry , Hydrogenase/chemistry , Iron-Sulfur Proteins/chemistry , Models, Molecular , Oxygen/chemistry
3.
Chem Sci ; 7(2): 945-950, 2016 Feb 01.
Article in English | MEDLINE | ID: mdl-29896365

ABSTRACT

Graphitic carbon nitride (g-CN) has interesting catalytic properties but is difficult to study due to its structure and how it is produced. In this study, linear s-heptazine oligomers were synthesized to serve as well-defined molecular models for g-CN. Cyclic voltammetry, absorption and emission spectroscopies showed a clear shift of properties towards those of g-CN as the number of heptazine units increased. DFT calculations supported the characterizations, and helped refine the properties observed.

4.
Nature ; 499(7456): 66-69, 2013 Jul 04.
Article in English | MEDLINE | ID: mdl-23803769

ABSTRACT

Hydrogenases are the most active molecular catalysts for hydrogen production and uptake, and could therefore facilitate the development of new types of fuel cell. In [FeFe]-hydrogenases, catalysis takes place at a unique di-iron centre (the [2Fe] subsite), which contains a bridging dithiolate ligand, three CO ligands and two CN(-) ligands. Through a complex multienzymatic biosynthetic process, this [2Fe] subsite is first assembled on a maturation enzyme, HydF, and then delivered to the apo-hydrogenase for activation. Synthetic chemistry has been used to prepare remarkably similar mimics of that subsite, but it has failed to reproduce the natural enzymatic activities thus far. Here we show that three synthetic mimics (containing different bridging dithiolate ligands) can be loaded onto bacterial Thermotoga maritima HydF and then transferred to apo-HydA1, one of the hydrogenases of Chlamydomonas reinhardtii algae. Full activation of HydA1 was achieved only when using the HydF hybrid protein containing the mimic with an azadithiolate bridge, confirming the presence of this ligand in the active site of native [FeFe]-hydrogenases. This is an example of controlled metalloenzyme activation using the combination of a specific protein scaffold and active-site synthetic analogues. This simple methodology provides both new mechanistic and structural insight into hydrogenase maturation and a unique tool for producing recombinant wild-type and variant [FeFe]-hydrogenases, with no requirement for the complete maturation machinery.


Subject(s)
Biomimetic Materials/chemical synthesis , Biomimetic Materials/metabolism , Chlamydomonas reinhardtii/enzymology , Hydrogenase/metabolism , Thermotoga maritima/enzymology , Apoproteins/chemistry , Apoproteins/metabolism , Biocatalysis , Biomimetics , Catalytic Domain , Clostridium acetobutylicum/genetics , Clostridium acetobutylicum/metabolism , Electron Spin Resonance Spectroscopy , Enzyme Activation , Ligands , Spectroscopy, Fourier Transform Infrared
5.
J Biol Inorg Chem ; 12(4): 509-25, 2007 May.
Article in English | MEDLINE | ID: mdl-17237942

ABSTRACT

The catalase from Proteus mirabilis peroxide-resistant bacteria is one of the most efficient heme-containing catalases. It forms a relatively stable compound II. We were able to prepare samples of compound II from P. mirabilis catalase enriched in (57)Fe and to study them by spectroscopic methods. Two different forms of compound II, namely, low-pH compound II (LpH II) and high-pH compound II (HpH II), have been characterized by Mössbauer, extended X-ray absorption fine structure (EXAFS) and UV-vis absorption spectroscopies. The proportions of the two forms are pH-dependent and the pH conversion between HpH II and LpH II is irreversible. Considering (1) the Mössbauer parameters evaluated for four related models by density functional theory methods, (2) the existence of two different Fe-O(ferryl) bond lengths (1.80 and 1.66 A) compatible with our EXAFS data and (3) the pH dependence of the alpha band to beta band intensity ratio in the absorption spectra, we attribute the LpH II compound to a protonated ferryl Fe(IV)-OH complex (Fe-O approximately 1.80 A), whereas the HpH II compound corresponds to the classic ferryl Fe(IV)=O complex (Fe=O approximately 1.66 A). The large quadrupole splitting value of LpH II (measured 2.29 mm s(-1) vs. computed 2.15 mm s(-1)) compared with that of HpH II (measured 1.47 mm s(-1) vs. computed 1.46 mm s(-1)) reflects the protonation of the ferryl group. The relevancy and involvement of such (Fe(IV)=O/Fe(IV)-OH) species in the reactivity of catalase, peroxidase and chloroperoxidase are discussed.


Subject(s)
Catalase/chemistry , Chloride Peroxidase/chemistry , Iron/chemistry , Models, Biological , Peroxidases/chemistry , Proteus mirabilis/enzymology , Protons , Binding Sites , Catalase/metabolism , Chloride Peroxidase/metabolism , Hydrogen-Ion Concentration , Hydroxylation , Iron/metabolism , Isomerism , Molecular Structure , Peroxidases/metabolism , Spectrum Analysis
6.
J Inorg Biochem ; 100(4): 477-9, 2006 Apr.
Article in English | MEDLINE | ID: mdl-16442627

ABSTRACT

The Proteus mirabilis catalase is one of the most efficient heme-containing catalase and forms a relatively stable compound II. Samples of compound II were prepared from PMC enriched in (57)Fe. For the first time, two different forms of compound II, namely low pH compound II (LpH II) (43%) and high pH compound II (HpH II) (25%), have been characterized by Mössbauer spectroscopy at pH 8.3. The ratio LpH II/HpH II increases irreversibly with decreasing pH. The large quadrupole splitting value of LpH II (DeltaE(Q)=2.29 (2) mm/s, with delta(/Fe)=0.03 (2) mm/s), compared to that of HpH II (DeltaE(Q)=1.47 (2) mm/s, with delta(/Fe)=0.07 (2) mm/s), reflects the protonation of the ferryl group. Quadrupole splitting values of 1.46 and 2.15mm/s have been computed by DFT for optimized models of the ferryl compound II (model 1) and the protonated ferryl compound II (model 2), respectively, starting from the Fe(IV)O model initially published by Rovira and Fita [C. Rovira, I. Fita, J. Phys. Chem. B 107 (2003) 5300-5305]. Therefore, we attribute the LpH II compound to a protonated ferryl Fe(IV)-OH complex, whereas the HpH II compound corresponds to the classical ferryl Fe(IV)O complex.


Subject(s)
Catalase/chemistry , Iron/chemistry , Proteus mirabilis/enzymology , Catalase/metabolism , Computer Simulation , Hydrogen-Ion Concentration , Iron/metabolism , Models, Chemical , Proteus mirabilis/chemistry , Spectroscopy, Mossbauer
7.
J Magn Reson ; 153(2): 238-45, 2001 Dec.
Article in English | MEDLINE | ID: mdl-11740900

ABSTRACT

(57)Fe Q-band ENDOR has been used to study the [4Fe-4S](1+) state created by gamma irradiation of single crystals of the synthetic model compound [N(C(2)H(5))(4)](2)[Fe(4)S(4)(SCH(2)C(6)H(5))(4)] enriched in (57)Fe. This compound is an excellent biomimetic model of the active sites of many 4 iron-4 sulfur proteins, enabling detailed and systematic studies of its oxidized [4Fe-4S](3+) and reduced [4Fe-4S](1+) paramagnetic states. Taking advantage of the fact that Q-band ENDOR, in contrast with X-Band ENDOR, allows for a very good separation of the (57)Fe transitions from those of the protons, the complete hyperfine tensors of the four iron atoms for the [4Fe-4S](1+) species has been measured with precision. For each iron atom, the electron orbital and electron spin isotropic contributions have been determined separately. Moreover, it is remarkable that two (57)Fe hyperfine tensors attributed to the ferrous pair of iron atoms are very different. In effect, one tensor presents a much larger anisotropic part and a much smaller isotropic part than those of the other. This difference has been interpreted in terms of a differential electron orbital hyperfine interaction among the two ferrous ions.

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