Laurent Le Pape

A Novel Dimanganese(II) Complex with Two Chloride Bridges − A Two-Electron Oxidation System

A new kind of binuclear μ-chloro complex of manganese with two bpea ligands [bpea = N,N-bis(2-pyridyl methyl) ethylamine] has been synthesized and structurally characterized. A thorough electrochemical study shows that this complex exhibits a two-electron reversible oxidation leading to the stable dimanganese(III) complex.

DHR51, the Drosophila melanogaster Homologue of the Human Photoreceptor Cell-Specific Nuclear Receptor, Is a Thiolate Heme-Binding Protein

Heme has been recently described as a regulating ligand for the activity of the human nuclear receptors (NR) REV-ERBalpha and REV-ERBbeta and their Drosophila homologue E75. Here, we report the cloning, expression in Escherichia coli, purification, and screening for the heme-binding ability of 11 NR ligand-binding domains of Drosophila melanogaster (DHR3, DHR4, DHR39, DHR51, DHR78, DHR83, HNF4, TLL, ERR, FTZ-F1, and E78), of unknown structure. One of these NRs, DHR51, homologous to the human photoreceptor cell-specific nuclear receptor (PNR), specifically binds heme and exhibits a UV-visible spectrum identical to that of heme-bound E75-LBD. EPR and UV-visible absorption spectroscopy indicates that, like in E75, the heme contains a hexa-coordinated low spin ferric iron. One of its axial ligands is a tightly bound cysteine, while the other one is a histidine. A dissociation constant of 0.5 microM for the heme was measured by isothermal titration calorimetry. We show that DHR51 binds NO and CO and discuss the possibility that DHR51 may be either a gas or a heme sensor.

N2O reduction at a dissymmetric {Cu2S}-containing mixed-valent center

Through our bio-inspired approach toward replicating nitrous oxide reductase (N2Or) activity, treatment of the LMe(MAM)S–S ligand with [Cu(CH3CN)4](OTf) (OTf = trifluoromethanesulfonate ion) leads to the isolation of a new dissymmetric mixed-valent (MV) dicopper(II,I) [2·(H2O)(OTf)]+ containing a {Cu2S} core with labile triflate and water molecules at the copper centers. Whilst [2·(H2O)(OTf)]+ is prone to ligand exchange under particular conditions, a raft of spectroscopic investigations, combined with theoretical calculations demonstrate that its structure is retained in acetone solution. Compared to our previously reported inactive parent complex [1] (Angew. Chem. Int. Ed., 2010, 49 (44), 8249–8252) featuring a symmetric and saturated coordination sphere (N and S atoms from the ligand), [2·(H2O)(OTf)]+ is reactive towards nitrous oxide in acetone. Spectroscopic and theoretical studies combined with kinetic measurements show that exchangeable positions are required for N2O interaction. The isolation of the final product and its characterization by X-ray crystallography as a doubly bridged (μ-thiophenolato)(μ-hydroxo) dicopper(II) species [3·(μ-OH)(OTf)2] help to support the proposed reaction pathway. Implications for N2Or mechanism are discussed.

Ribonucleotide reductase from the higher plant Arabidopsis thaliana : expression of the R2 component and characterization of its iron-radical center

Abstract Deoxyribonucleotides synthesis has not been biochemically characterized in higher plants. From a cDNA of the small component (protein R2) of ribonucleotide reductase from Arabidopsis thaliana, an inducible overexpression plasmid has been constructed. A recombinant 78-kDa homodimeric protein containing very little iron was purified to homogeneity. Addition of ferrous iron and oxygen resulted in a protein containing 1.2 tyrosyl radicals and 4 iron atoms per dimer. Light absorption and low-temperature EPR spectra indicated close similarity of the iron-radical centers in plant and mouse R2 proteins. It is then suggested that, as in all class I eukaryotic ribonucleotide reductase, the active site of R2 component contains a μ-oxo bridged di-iron center in strong interaction with a tyrosyl radical. The stability of the radical seems, however, to be larger in the plant R2 protein, as shown by its resistance to hydroxyurea.

Redox-Innocent Metal-Assisted Cleavage of S–S Bond in a Disulfide-Containing Ligand

Due to their redox capabilities, thiols have an important role in biological oxidative/reductive processes through the formation of disulfides or their oxidation to into sulfenic, sulfinic, or sulfonic derivatives being also relevant for specific enzyme activities. The mechanisms of these biological pathways often involve metal ion(s). In this case, deciphering metal-assisted transformation of the S-S bond is of primary interest. This report details the reactivity of the disulfide-containing 2,6-bis[(bis(pyridylmethyl)amino)methyl]-4-methylmercaptophenyldisulfide (L(Me(BPA)S-S)) ligand with Cu(II) using different experimental conditions (anaerobic, H2O-only, H2O/O2, or O2-only). Crystallographic snapshots show the formation of tetranuclear disulfide, dinuclear sulfinate, and sulfonate complexes. Mechanistic investigations using Zn(II) as control indicate a non-metal-redox-assisted process in all cases. When present, water acts as nucleophile and attacks at the S-S bond. Under anhydrous conditions, a different pathway involving a direct O2 attack at the disulfide is proposed.