Betaproteobacteria dominance and diversity shifts in the bacterial community of a PAH-contaminated soil exposed to phenanthrene.

International audienceIn this study, the PAH-degrading bacteria of a constructed wetland collecting road runoff has been studied through DNA stable isotope probing. Microcosms were spiked with (13)C-phenanthrene at 34 or 337 ppm, and bacterial diversity was monitored over a 14-day period. At 337 ppm, PAH degraders became dominated after 5 days by Betaproteobacteria, including novel Acidovorax, Rhodoferax and Hydrogenophaga members, and unknown bacteria related to Rhodocyclaceae. The prevalence of Betaproteobacteria was further demonstrated by phylum-specific quantitative PCR, and was correlated with a burst of phenanthrene mineralization. Striking shifts in the population of degraders were observed after most of the phenanthrene had been removed. Soil exposed to 34 ppm phenanthrene showed a similar population of degraders, albeit only after 14 days. Results demonstrate that specific Betaproteobacteria are involved in the main response to soil PAH contamination, and illustrate the potential of SIP approaches to investigate PAH biodegradation in soil

Influence of the copper coordination spheres on the N2Or activity of a mixed-valent copper complex containing a {Cu2S} core

International audienceA new mixed-valent dicopper complex [5] was generated from ligand exchange by dissolving a bis(CH3CN) precursor [3] in acetone. Introduction of a water molecule in place of an acetonitrile ligand was evidenced by base titration and the presence of a remaining coordinated CH3CN by IR, 19F NMR, and theoretical methods. The proposed structure (CH3CN–Cu–(SR)–Cu–OH2) was successfully DFT-optimized and the calculated parameters are in agreement with the experimental data. [5] has a unique temperature-dependence EPR behavior, with a localized valence from 10 to 120 K that undergoes delocalized at room temperature. The electrochemical signatures are in the line of the other aquo parent [2] and sensibly different from the rest of the series. Similar to the case of [2], [5] was finally capable of single turnover N2O reduction at room temperature. N2 was detected by GC-MS, and the redox character was confirmed by EPR and ESI-MS. Kinetic data indicate a reaction rate order close to 1 and a rate 10 times faster compared to [2]. [5] is thus the second example of that kind and highlights not only the main role of the Cu–OH2 motif, but also that the adjacent Cu-X partner (X = OTf– in [2] and CH3CN in [5]) is a new actor in the casting to establish structure/activity correlations

Unexpected Migration and O to S Benzylic Shift of Thiocarbamate-containing Salicylaldehyde Derivatives

International audienceAn unexpected reactivity of the O-dimethylthiocarba-mate function has been evidenced concomitantly with the reduction of an aldehyde function presents at its ortho (o-) position. A systematic study using various substrates showed the exclusive formation of the rearranged compounds after 24 h and confirmed that the only-reduced compounds are reaction intermediates. However, electronic/steric contributions of the aromatic ring substituents on the composition of the reaction mixture (reduction of the aldehyde vs. migration) were observed at the early stage of the reaction (2 h). These new benzyl S-thiocarbamates compounds could be of particular interest as precursors for not trivial and functionalized free methylthiobenzyl alcohols

Water-assisted photocatalytic sulfide and alcohol oxidation by a Ru-Ru dyad

International audienceMoving toward eco-friendly and ecoenvironmentally processes to perform specific organic transformations is more than ever at stake. Inspired by Nature that uses light as inducer with PSII, a new Rubased dyad combining a photosensitizer with a catalytic partner was developed. Upon irradiation with low power consumption blue LEDs, this system has proven its effectiveness during the catalytic oxidation of various sulfides and alcohols with water as unique oxygen atom source

Water-assisted photocatalytic sulfide and alcohol oxidation by a Ru-Ru dyad

International audienceMoving toward eco-friendly and ecoenvironmentally processes to perform specific organic transformations is more than ever at stake. Inspired by Nature that uses light as inducer with PSII, a new Rubased dyad combining a photosensitizer with a catalytic partner was developed. Upon irradiation with low power consumption blue LEDs, this system has proven its effectiveness during the catalytic oxidation of various sulfides and alcohols with water as unique oxygen atom source

Controlled O 2 reduction at a mixed-valent (II,I) Cu 2 S core

International audienceInspection of Oxygen Reduction Reactions (ORRs) using a mixedvalent Cu2S complex as a pre-catalyst revealed a tuneable H2O2 vs.H2O production under mild conditions by controlling the amountof sacrificial reducer. The fully reduced bisCuI state is the mainactive species in solution, with fast kinetics. This new catalyticsystem is robust for H2O2 production with several cycles achievedand opens up perspectives for integration into device

Conformational H-bonding Modulations of the Iron Active SiteCysteine Ligand of Superoxide Reductase: Absorption andResonance Raman Studies

International audienceSuperoxide reductases (SORs) are mononuclear nonheme iron enzymes involved in superoxide radical detoxification in somemicroorganisms. Their atypical active site is made of an iron atom pentacoordinated by four equatorial nitrogen atoms fromhistidine residues and one axial sulfur atom from a cysteinate residue, which plays a central role in catalysis. In most SORs,the residue immediately following the cysteinate ligand is an asparagine, which belongs to the second coordination sphereand is expected to have a critical influence on the properties of the active site. In this work, in order to investigate the roleof this asparagine residue in the Desulfoarculus baarsii enzyme (Asn117), we carried out, in comparison with the wild-typeenzyme, absorption and resonance Raman (RR) studies on a SOR mutant in which Asn117 was changed into an alanine. ARR analysis was developed in order to assign the different bands using an excitation in the (Cys116)-S- Fe3+ charge transferband. By investigating the correlation between the (Cys116)-S- Fe3+ charge transfer band maximum with the frequency ofeach RR band in different SOR forms, we assessed the contribution of the ν(Fe-S) vibration among the different RR bands.The data showed that Asn117, by making hydrogen bond interactions with Lys74 and Tyr76, allows a rigidification of thebackbone of the Cys116 ligand, as well as that of the neighboring residues Ile118 and His119. Such a structural role of Asn117has a deep impact on the S-Fe bond. It results in a tight control of the H-bond distance between the Ile118 and His119 NHpeptidic moiety with the cysteine sulfur ligand, which in turn enables a fine tuning of the S-Fe bond strength, an essentielproperty for the SOR active site. This study illustrates the intricate roles of second coordination sphere residues to adjustthe ligand to metal bond properties in the active site of metalloenzymes

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

International audienceThrough our bio-inspired approach toward replicating nitrous oxide reductase (N(2)Or) 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 center dot(H2O)(OTf)](+) containing a {Cu2S} core with labile triflate and water molecules at the copper centers. Whilst [2 center dot(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 center dot(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 (mu-thiophenolato)(mu-hydroxo) dicopper(II) species [3 center dot(mu-OH)(OTf)(2)] help to support the proposed reaction pathway. Implications for N(2)Or mechanism are discussed

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

International audienceDue 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 (LMe(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