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Three hexacarbonyl diiron dithiolate complexes [Fe2(CO)6(μ-(SCH2)2X)] with different substituted bridgeheads (X=CH2, CEt2, CBn2 (Bn=CH2C6H5)), have been studied under the same experimental conditions by cyclic voltammetry in dichloromethane [NBu4][PF6] 0.2 M. DFT calculations were performed to rationalize the mechanism of reduction of these compounds. The three complexes undergo a two-electron transfer whose the mechanism depends on the bulkiness of the dithiolate bridge, which involves a different timing of the structural changes (Fe−S bond cleavage, inversion of conformation and CO bridging) vs redox steps. The introduction of a bulky group in the dithiolate linker has obviously an effect on normally ordered (as for propanedithiolate (pdt)) or inverted (pdtEt2, pdtBn2) reduction potentials. Et→Bn replacement is not theoretically predicted to alter the geometry and energy of the most stable mono-reduced and bi-reduced forms but such a replacement alters the kinetics of the electron transfer vs the structural changes.

International audience; A series of triiron clusters [Fe3(CO)5(2-dppe)(µ-pdtR2)(µ-pdt)] featuring different combination of dithiolate bridges have been prepared by using dinuclear and mononuclear precursors, [Fe2(CO)6(µ-xdt)] (xdt = pdt, pdtEt2, pdtBn2, adtBn) and [Fe(CO)2(2-dppe)(2-pdt)]. Novel triiron compounds, featuring sterically crowded dithiolate bridges (pdtEt2, pdtBn2), were spectroscopically and structurally characterized. Their protonation and redox behaviours are discussed. The effect of the dithiolate bridges on the electrochemical properties (oxidation and reduction) of the complexes [Fe3(CO)5(2-dppe)(µ-xdt)(µ-pdt)] has been examined by cyclic voltammetry and rationalized by DFT calculations. Studies of the protonation of these species and their proton reduction behaviour were considered.

The electrochemical reduction of complexes [Fe2 (CO)4 (κ2 -phen)(μ-xdt)] (phen=1,10-phenanthroline; xdt=pdt (1), adtiPr (2)) in MeCN-[Bu4 N][PF6 ] 0.2 m is described as a two-reduction process. DFT calculations show that 1 and its monoreduced form 1- display metal- and phenanthroline-centered frontier orbitals (LUMO and SOMO) indicating the non-innocence of the phenanthroline ligand. Two energetically close geometries were found for the doubly reduced species suggesting an intriguing influence of the phenanthroline ligand leading to the cleavage of a Fe-S bond as proposed generally for this type of complex or retaining the electron density and avoiding Fe-S cleavage. Extension of calculations to other complexes with edt, adtiPr bridge and even virtual species [Fe2 (CO)4 (κ2 -phen)(μ-adtR )] (R=CH(CF3 )2 , H) or [Fe2 (CO)4 (κ2 -phen)(μ-pdtR )] (R=CH(CF3 )2 , iPr) showed that the relative stability between both two-electron-reduced isomers depends on the nature of the bridge and the possibility to establish a remote anagostic interaction between the iron center {Fe(CO)3 } and the group carried by the bridged-head atom of the dithiolate group.

A series of dithiolate carbonyl diiron complexes with cyclic azadiphosphine, related to the active site of [FeFe]‐hydrogenases, has been prepared. Several combinations of diphosphines and dithiolate bridges have been examined in order to obtain information on the influence of electronic and steric effects of the group linked to the nitrogen atom of the phosphine (phenyl or benzyl) and the bridge‐head of the dithiolate (CH2, CEt2, CBn2). Products were spectroscopically and structurally characterized. Protonation experiments show that depending on the nature of the amine in the diphosphine, protonation processes are different. With NBn group, the process is arrested at N‐protonated species, while with NPh, the proton is transferred to the diiron site giving bridging‐hydride species. The effect of the bridge‐head group of the dithiolate is very slight on the electronic properties of compounds. Depending on the steric crowding of the bridge, different isomers related to the dibasal or basal‐apical position of the diphosphine, are observed in solution or in solid state. Electrochemical study was performed to examine the activity of these compounds in the presence of acid.

International audience; The synthesis, characterization, and protonation of [Fe2(CO)6{(μ-SCH2)2(Et)P═O}] (1) using the moderately strong acid CF3CO2H (pKaMeCN = 12.7) are reported. Digital simulations of the cyclic voltammetry of 1 in the presence of CF3CO2H and DFT calculations have allowed us to obtain a detailed mechanistic picture of the processes underlying the catalytic hydrogen evolution reaction (HER) that 1 can mediate. Moreover, DFT has shed light on the role of the P═O functionality in the whole catalytic cycle of proton reduction. The reductive behavior of 1 features a double electron transfer with potential inversion, which is associated with deep structural rearrangement of the catalyst. The double reduction appears also functional to the intramolecular proton transfer from the P═O group to the diiron core, a crucial process for the H+/H– heterocoupling yielding H2. The key intermediate for the H2 formation and release is predicted to be a 3H+/3e– species, in which P═O is perfectly poised to shuttle protons from solution to the Fe–H–Fe moiety. Therefore, the R-P═O bridgehead installed in a dithiolato linker of a diiron core proves a valid and versatile alternative to the natural nitrogen-based Fe2 strap.

The electrochemical reduction of complexes [Fe

A novel complex featuring a mesoionic carbene [Fe2(CO)5(trz)(?-pdt)] (1) (trz = 1-phenyl-l,3-methyl,4-butyl-1,2,3-triazol-5-ylidene), was synthesized and spectroscopically and structurally characterized. The reductive behaviour of this compound in the presence and in the absence of acid (CH3CO2H) was examined by cyclic voltammetry (CV) that revealed the lack of efficient activity towards proton reduction.

International audience; Electrochemical oxidation of the complex [Fe2(CO)4(κ2‐dmpe)(µ‐adtBn)] (adtBn = (SCH2)2NCH2C6H5, dmpe = Me2PCH2CH2PMe2) (1) has been studied by cyclic voltammetry (CV) in acetonitrile and in dichloromethane in presence of various substrates L (L =MeCN, trimethylphosphite, isocyanide). The oxidized species, [1‐MeCN](PF6)2, [1‐(P(OMe)3)2](PF6)2 and [1‐(RNC)4](PF6)2 (R = tButyl, Xylyl), have been prepared and characterized by IR, NMR spectroscopies and, excepted [1‐MeCN](PF6)2, by X‐ray diffraction analysis. The crystallographic structures of the new FeIIFeII complexes reveal in any case that the association of one additional ligand (P(OMe)3 or RNC) occurs and, according to the nature of the substrates, further substitutions of one or three carbonyl groups, by P(OMe)3 or RNC, respectively, arise. Density functional theory (DFT) calculations have been performed for elucidating and discriminating, in each case, the mechanisms leading to the corresponding oxidized species. Moreover, the different degree of ligand substitution in the diiron core has been theoretically rationalized.

Electrochemical oxidation of the complex [Fe

International audience; Advances in Bioorganometallic Chemistry examines the synthesis, structure and reactivity of bioorganometallics, their pharmaceutical applications, hydrogenase, vitamin B12-like systems, and metalloproteins. It is written by the top researchers in the field and compiled by editors Toshikazu Hirao and Toshiyuki Moriuchi. Developments in this new field of bioorganometallic chemistry, a hybrid between biology and organometallic chemistry, happen very quickly and this comprehensive reference offers the latest research and findings in the field. The book features a discussion of the synthesis, structure, and reactivity of bioorganometallics, and an examination of hydrogenase-like systems, which were designed to demonstrate catalytic activities and functional properties. Advances in Bioorganometallic Chemistry also includes a discussion of bioorganometallics as they relate to medicinal chemistry, specifically applications of metalloproteins, metalloenzymes, and applications in bioimaging. The book concludes with coverage of vitamin B12-like systems, including the latest developments in derivatives designed to perform bio-inspired catalytic reactions.Table of Contents1. Synthesis, structure and reactivity2. Hydrogenase3. Medicinal Chemistry and Metallodrugs4. Metalloproteins and metalloenzymes5. Vitamin B12

International audience; Electrochemical studies of [Fe2(CO)4(κ2-dmpe)(μ-dithiolate)] (dithiolate=adtBn, pdt) and density functional theory (DFT) calculations reveal the striking influence of an amine functionality in the dithiolate bridge on their oxidative properties. [Fe2(CO)4(κ2-dmpe)(μ-adtBn)] (1) undergoes two one-electron oxidation steps, with the first being partially reversible and the second irreversible. When the adtBn bridge is replaced with pdt, a shift of 60 mV towards more positive potentials is observed for the first oxidation whereas 290 mV separate the oxidation potentials of the two cations. Under CO, oxidation of azadithiolate compound 1 occurs according to an ECE process whereas an EC mechanism takes place for the propanedithiolate species 2. The dication species [1-CO]2+ resulting from the two-electron oxidation of 1 has been spectroscopically and structurally characterized. The molecular details underlying the reactivity of oxidized species have been explored by DFT calculations. The differences in the behaviors of 1 and 2 are mainly due to the presence, or not, of favored interactions between the dithiolate bridge and the diiron site depending on the redox states, FeIFeII or FeIIFeII, of the complexes.

The reduction of the compound [Fe2(CO)4(κ2-dmpe){μ-(SCH2)2NBn}] [dmpe = 1,2-bis(dimethylphosphino)ethane], which is considered as an FeI-FeI model of the [2Fe]H subsite of [Fe-Fe]H2ases with a rotated conformation in the solid state, was investigated by cyclic voltammetry. Under reductive conditions, [Fe2(CO)4(κ2-dmpe){μ-(SCH2)2NBn}] undergoes electron-transfer-catalyzed isomerization to afford an isomer featuring a bridging diphosphine [Fe2(CO)4(μ-dmpe){μ-(SCH2)2NBn}]. Comparison of the crystallographic structures of the two isomers affords unique and direct experimental evidence that dissymmetrical coordination of the chelate ligand is required to promote the rotated conformation at one iron atom in this compound. DFT calculations were performed to rationalize this isomerization process and the slightly distorted structure of [Fe2(CO)4(μ-dmpe){μ-(SCH2)2NBn}]. The symmetrization of the coordination sphere results in the disruption of the agostic interaction that stabilized the rotated isomer.

International audience; The electron transfer across the liquid|liquid interface between aqueous solutions (W) of FeIII/II compounds (hexacyanoferrates, chlorides) and a (t-butyl) substituted LuIIIbisphthalocyanine in dichlorohexane (DCH) or nitrobenzene (NB), has been studied by voltammetry at a microinterface and by spectrophotometry. The electron transfer wave has been observed only at the W|DCH. Coupling with an ion transfer facilitates this electron transfer: the LuIIIbisphthalocyanine has been oxidized or reduced across the W|NB interface, depending on the ion establishing the interfacial potential.

Proton transfer across the water│solvent (nitrobenzene, 1,6-dichlorohexane) interface is facilitated by the presence in the organic phase of a lutetium bisphthalocyanine. The driving force of the facilitatedfacilitated transfer of H+ is the redox disproportionation reaction of this compound (M0) occurring at the liquid│liquid interface: a reaction induced by the very high affinity of M-, the reduced bisphthalocyanine, for the proton (KA = 10-13.5 mol-1l). The lutetium bisphthalocyanine, which exits as the molecular form over ~0.4 V (Kd = 10-6.4) in the neutral solvent, disproportionates completely in acidic solutions (eg, in nitrobenzene: KdH = 107.1 mol-1l). At the water│nitrobenzene interface, this disproportionation reaction facilitates the proton transfer by almost 0.30 V. Voltammetry at a rotating disk electrode in nitrobenzene confirms the redox disproportionation reaction and the basicity of the reduced lutetium bisphthalocyanine.

International audience; The study by voltammetry of hydrophilic ion transfers across the interface between an aqueous solution and an immiscible organic solvent is limited by the presence of supporting electrolytes in both phases. Such a study is impossible for ions having for water a higher affinity than ions of the electrolytes. Indirectly, methods based on modified solid electrodes can be used ; these are obtained by the deposition of an organic phase containing a molecule having redox properties, the modified electrode being in contact with an aqueous solution of the appropriate electrolyte. The three-phase electrode is very convenient for that purpose. However, this experimental tool also has its own limitation, due mainly to the redox species produced in the organic phase. The oxidized, or reduced, form of the redox molecule must have a very low affinity for water, as otherwise its transfer masks that of the ion under study. Ferrocene is almost useless because of the affinity of the ferrocenium cation for water, decamethylferrocene being a better choice. The present work illustrates how the use of lutetium bisphthalocyanines expands widely the possibilities, as these molecular sandwich complexes can be reduced as well as oxidized, the products of the reactions having a very low affinity for water. This made possible the determination of the Gibbs energy for the transfers of highly hydrophilic ions from water to nitrobenzene: Cl- (40 kJ mol-1), F- (57 kJ mol-1), H2PO4- (64 kJ mol-1). Nothing being really known about the transfer of F- or H2PO4- from water to organic solvents, these are the first values ever published. H+, OH- and HSO4- have also been studied, showing that these species, which have a poor affinity for nitrobenzene, are prone to association reactions with the reduced or oxidized forms of the lutetium bisphthalocyanine.

International audience; Hydrocarbons in solutions have been the subject of very few investigations despite their relevance, in particular, in situations where environmental mechanisms are involved. We present, here, a synthesis of several studies conducted within our laboratory about the adsorption, at the water surface, of benzene and cyclohexane from under-saturated solutions. The coadsorption of lead nitrate is also evidenced, though it does not adsorb in absence of organic molecules in the surface. Most of the data reported here were collected from series of measurements made with a very uncommon method: the bubble column; this technique, though being very time-demanding and lacking of userfriendliness, proved its usefulness and relevance in the study of such weakly adsorbable, surface-tension inactive compounds. The study of mixtures is simple and requires no model, which is precious in environmental research. The gathered data demonstrate that, through mechanical mechanisms such as bubbling, coadsorption can lead to the passing from water to the atmosphere of harmful non-soluble, poorly surface-active, components.

cited By 27; International audience; A comparative study of the behavior of different sorts of three-phase electrodes applied for assessing the thermodynamics and kinetics of the ion transfer across the liquid |liquid (L|L) interface is presented. Two types of three-phase electrodes are compared, that is, a paraffin-impregnated graphite electrode at the surface of which a macroscopic droplet of an organic solvent is attached and an edge pyrolytic graphite electrode partly covered with a very thin film of the organic solvent. The organic solvent contains either decamethylferrocene or lutetium bis(tetra-tert-butylphthalocyaninato) as a redox probe. The role of the redox probe, the type of the electrode material, the mass transfer regime, and the effect of the uncompensated resistance are discussed. The overall electrochemical process at both three-phase electrodes proceeds as a coupled electron-ion transfer reaction. The ion transfer across the L|L interface, driven by the electrode reaction of the redox compound at the electrode|organic solvent interface, is independent of the type of redox probe. The ion transfer proceeds without involving any chemical coupling between the transferring ion and the redox probe. Both types of three-phase electrodes provide consistent results when applied for measuring the energy of the ion transfer. Under conditions of square-wave voltammetry, the coupled electron-ion transfer at the three-phase electrode is a quasireversible process, exhibiting the property known as "quasireversible maximum". The overall electron-ion transfer process at the three-phase electrode is controlled by the rate of the ion transfer. It is demonstrated for the first time that the three-phase electrode in combination with the quasireversible maximum is a new tool for assessing the kinetics of the ion transfer across the L|L interface. © 2005 American Chemical Society.

Antimony is a naturally occurring element. It belongs to group 15 of the periodic table of the elements. Antimony can exist in a variety of oxidation states (–III, 0, III, V) but it is mainly found in two oxidation states (III and V) in environmental, biological, and geochemical samples. Although antimony was already known to the ancients, it is still often overlooked, both as an element of environmental concern and as a subject for study, probably because of its lower abundance and the relative insolubility of most of its compounds. This is reflected in the poor standard of existing data on the behavior of antimony in natural waters. However, interest in the study of this element seems to be growing and an increasing number of papers on the subject are being published. A useful series of comprehensive reviews on antimony in the environment has recently been published (1, 2).

cited By 3; International audience; Cathodic adsorptive stripping voltammetry is one of the most sensitive analytical methods for ultratrace analysis. The detection limit is usually lower than 10-9 mol/L. Most adsorptive stripping procedures have been focused on the one ligand/one analyte approach. In order to reduce analysis time and sample volume, the possibility of simultaneously determining several metals by cathodic stripping voltammetry using a mixture of ligands was explored, e.g., by Colombo and van den Berg (1997). Here, we describe a new procedure for quantifying chromium and copper using 2,2′-bipyridine and 8-hydroxyquinoline (oxine). The effect of various operational parameters such as buffer type, ligand concentration, potential and time collection were assessed and optimized. Possible interferences by trace metals and organic matter were also investigated. Applicability for fresh water is illustrated. © Springer-Verlag 2003.

The [FeFe] hydrogenase is a highly sophisticated enzyme for the synthesis of hydrogen via a biological route. The rotated state of the H-cluster in the [FeIFeI] form was found to be an indispensable criteria for an effective catalysis. Mimicking the specific rotated geometry of the [FeFe] hydrogenase active site is highly challenging as no protein stabilization is present in model compounds. In order to simulate the sterically demanding environment of the nature's active site, the sterically crowded meso-bis(benzylthio)diphenylsilane (2) was utilized as dithiolate linker in an [2Fe2S] model complex. The reaction of the obtained hexacarbonyl complex 3 with 1,2-bis(dimethylphosphino)ethane (dmpe) results three different products depending on the amount of dmpe used in this reaction: [{Fe2(CO)5{μ-(SCHPh)2SiPh2}}2(μ-dmpe)] (4), [Fe2(CO)5(κ2-dmpe){μ-(SCHPh)2SiPh2}] (5) and [Fe2(CO)5(μ-dmpe){μ-(SCHPh)2SiPh2}] (6). Interestingly, the molecular structure of compound 5 shows a [FeFe] subsite comprising a semi-rotated conformation, which was fully characterized as well as the other isomers 4 and 6 by elemental analysis, IR and NMR spectroscopy, X-ray diffraction analysis (XRD) and DFT calculations. The herein reported model complex is the first example so far reported for [FeIFeI] hydrogenase model complex showing a semi-rotated geometry without the need of stabilization via agostic interactions (Fe⋯H-C). This journal is

The utilization of light and inexpensive catalysts to afford hydrogen represents a huge challenge. Following our interest in silicon-containing [FeFe]-hydrogenase ([FeFe]-H2ase) mimics, we report a new model approach for a photocatalytic [FeFe]-H2ase mimic 1, which contains a 1-silafluorene unit as a photosensitizer. Thereby, the photoactive ligand is linked to the [2Fe2S] cluster through S–CH2–Si bridges. Photochemical H2 evolution experiments were performed and revealed a turnover number (TON) of 29. This is the highest reported photocatalytic efficiency for an [FeFe]-H2ase model complex in which the photosensitizer is covalently linked to the catalytic center.

The determination of the total concentration of a trace element gives only few informations about its toxicity and its bioavailability which depend mainly on the different chemical forms under which it is present. The studies of the chemical speciation is thus particularly important. We propose, in this paper, a selenium speciation model for the studies of natural waters based on Se(IV) voltammetric determination. The separation of the organic and inorganic forms was realized by a rapid ion exchange method and total selenium was determined after a u.v. irradiation.

Rotated geometry: The first example of a dinuclear iron(I)-iron(I) complex featuring a fully rotated geometry related to the active site of [Fe-Fe] hydrogenase is reported (see figure). Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

The reaction between 1,2-dihydroxyanthraquinone-3-sulphonic acid and chlorine dioxide, in phosphate buffer medium, was studied spectrophotometrically and electrochemically. An electroanalytical method is proposed for the determination of traces of ClO2 with a detection limit of 2 μg l−1. The stoichiometry of the reaction, the effects of various operational parameters and the influence of foreign ions are reported.

A method is described for the determination of copper in seawater by adsorptive stripping voltammetry after accumulation of a 1,2-dihydroxyanthraquinone-3-sulfonic acid (DASA) complex. The effects of various operational parameters (pH, ligand concentration, potential, and accumulation time) on the reduction current of the adsorbed chelate are discussed. A linear current concentration relationship was observed up to 5 × 10−8 M. The detection limit is 0.3 nM.

International audience; The silver-based MOF material Ag3(3-phosphonobenzoate) was evaluated as a bactericidal material. A sustainable release of Ag+, which was quantified by cathodic stripping voltammetry, was responsible for bactericidal activity against the 6 bacterial strains tested.

1,6-dichlorohexane (DCH) is a solvent with a low permittivity ( ɛ = 8.8) in which ion-pairing affects electrolytic solutions. This can be noticed from voltammetric experiments at a microinterface between water (W) and DCH. Because most ion-association constants are unknown, the experimental measurements cannot be adequately corrected to calculate standard values for partition parameters, so that only conditional partition potentials can be measured. A formal ion partition potential scale is presented (electrolytes: 10 −2 M Li 2 SO 4 in W; 10 −2 M THATPBCl in DCH) for a few tetraalkylammonium cations and some anions (hexafluorophosphate, perchlorate, picrate).

In acidic chloride media (pH 2), a chelate of Mo(VI) with 1, 10-phenanthroline is adsorbed on a hanging mercury drop electrode and reduced at −0.575 V. In presence of fulvic acids, the signal is strongly enhanced owing to the formation of a mixed complex which is more readily adsorbed. The effect of various operational parameters (pH, ligand, and molybdenum concentrations, potential and time collection) on the response is discussed, and a sensitive adsorptive voltammetric procedure is developed.

A sensitive procedure for the determination of chromium(VI) is described. A chelate of chromium with an organic ligand is adsorbed on a hanging mercury drop electrode and the reduction current of the accumulated chelate is measured by differential-pulse voltammetry. The effects of various parameters (pH, ligand concentration, potential and collection time) on the response are discussed. Possible interferences by trace metals and organic matter are considered.

International audience; The transfers of the ions of tetraalkylammonium picrates (-methyl, -ethyl, -propyl, -butyl), from water (W) to nitrobenzene (NB), 1,2-dichloroethane (DCE) or 1,6-dichlorohexane (DCH), have been studied by voltammetry at liquid/liquid microinterfaces. Electrochemistry is possible in the absence of supporting electrolytes in both phases, even in the less dissociating solvents, DCE and DCH, when the concentration of the picrate is lower than 103 M, the main difficulty however being the lack of reference electrodes. Without an electrolyte in the organic phase, the limiting current for an ionic transfer from the solvent to water is two times the diffusion current, due to the migration. This is not the case when the transferring ions are in water where an adventitious electrolyte is always present. Comparing voltammetry of the ion transfers with and without electrolytes has shown that ion-pairing in DCE and DCH influences the partition of the salts, which has been confirmed by some spectrophotometrical measurements. As a consequence, the partition potential scales derived from experiments performed in DCE and DCH in the presence of electrolytes are conditional.

International audience; Transfer reactions across water-2-nitrophenyloctyl ether (W|NPOE) interface for a series of monovalent inorganic ions and tetraalkylammonium cations are studied by means of square-wave (SWV) and cyclic voltammetry at thin organic-film-modified (TFE) and three-phase electrodes (TPE). Both electrode configurations are assembled using lutetium bis(tetra-tert-butylphthalocyaninato) as a redox probe, whose redox properties enable assessment of both anion and cation transfer reactions in a single voltammetric experiment. It is demonstrated that TFE can be effectively applied to measure the Gibbs energy of ion transfer reactions when the transferring ion is a common ion for both liquid phases, controlling the Galvani potential difference at the W|NPOE interface. A comparative study of the thermodynamics of ion transfer reactions performed with TFE and TPE reveals that both electrode configurations provide a consistent set of data. Kinetic measurements referring to the transfers of ClO4-, and a series of tetraalkylammonium cations have been conducted by combining TFE and SWV according to the method known as “quasireversible maximum” in thin-film voltammetry (Mirčeski, V. J. Phys. Chem. B 2004, 108, 13719).

Ion transfer reactions across a liquid interface between an aqueous electrolyte and 1-hexyl-3- methylimidazolium tris(pentafluoroethyl)trifluorophosphate ([hmim] [fap]) room temperature ionic liquid (RTIL) were studied with the help of three-phase electrodes. The electrode assembly comprised edge plane pyrolytic graphite modified with a thin layer of [hmim][fap] containing lutetium bis(tetra-tert- butylphthalocyaninato) (Lu[tBu4Pc]2) as a redox probe. Lu[tBu4Pc]2 can be oxidized and reduced to a stable hydrophobic monovalen cation and anion, respectively, hence allowing interrogation of the transfer of cations and anions in one and the same voltammetric experiments. In spite of the strong hydrophobicity of the salt [hmim][fap], the electrode reactions of the redox probe studied in contact with various inorganic aqueous electrolytes, were frequently accompanied by expulsion of ions constituting the RTIL into the aqueous phase. Using ionic chromatography it was found that the distribution of ions in the aqueous electrolyte/RTIL biphasic system is strongly determined by ion exchange reactions. The affinity of the ions of the RTIL for the aqueous phase was assessed with respect to the water/nitrobenzene (w/nb) system, and the following Gibbs energies of the transfer were found: = -16.6  0.9 kJ mol-1 and = -22.4  0.3 kJ mol-1.

International audience; Catalytic mechanism at thin film-modified electrodes is studied both theoretically and experimentally under conditions of square-wave voltammetry (SWV). The electrode system considered consists of a solid electrode covered with an electrochemically inactive thin film (e.g. a layer of a water-immiscible organic solvent) containing a neutral redox probe (R1). The modified electrode is immersed into an electrolyte solution (typically aqueous electrolyte solution) that contains a second redox probe (R2), present in a large excess compared to R1. The product of the assumed one-electron electrode reaction O1+, confined within the film, is transformed back to the initial reactant R1 by means of a catalytic redox reaction with the R2. If the permeation of the R2 in the thin film is significant, the catalytic reaction undergoes as a homogeneous process confined within the boundaries of the thin film. Otherwise, the catalytic reaction undergoes as a heterogeneous process involving electron transfer across the interface between the thin film and the electrolyte solution.

International audience; The weak solubility of carbofuran allows adsorption at the air/water interface. Carbofuran-rich layers can then induce the coadsorption of metallic salts such as lead nitrate; on the other hand, when carbofuran is missing, no adsorption of this salt takes place. This phenomenon was quantitatively studied through surface tension measurements under concentration conditions close to the environmental ones. Heavy metal salt adsorbed about ten times more than carbofuran. Evidence was then provided that the simultaneous presence of both pollutants in water favours their adsorption and passing from water to the atmosphere through mechanisms such as bubbling.

International audience; Knowledge of antimony redox kinetics is crucial in understanding the impact and fate of antimony in the environment. The oxidation of Sb(III) with iodate was measured in 0.5 mol L1 NaCl solutions as a function of pH at environmentally significant concentrations of antimony and iodate. The oxidation of Sb(III) with iodate is pH dependent: no measurable oxidation is observed below pH 9. The undissociated Sb(OH)3 does not react with iodate and the formation of significant amounts of Sb(OH)4 is needed for the reaction to take place. It is thus unlikely that iodate oxidizes Sb(III) in seawater. Our results support that the observed presence of the thermodynamically unstable Sb(III) in oxic waters can be due to the kinetic stabilization of the trivalent state vis-a`-vis some common abiotic oxidants at natural pH values. However, caution must be exercised because the presence of iodate in seawater favours fast oxidation of Sb(III) if water samples are acidified, as is the case in many analytical procedures.

cited By 5; International audience; Despite its importance for understanding the behaviour of antimony in the environment, the oxidation kinetics of Sb(III) with natural oxidants is still not well understood. We have studied the oxidation of Sb(III) by hydrogen peroxide on a time scale of hours in the presence of some trace metals, Cu(II), Mn(II), Zn(II) and Pb(II), under pH and concentration conditions close to natural ones. The effects that these trace metals have on Sb(III) oxidation by hydrogen peroxide vary. Zn(II) had no catalytic effect at all, but Cu(II), Mn(II) and Pb(II) did, though their effects were not uniform. Cu(II) significantly accelerated the reaction, which remained first-order with respect to Sb(III) at any Cu(II) concentration tested. Pb(II) and Mn(II) also enhanced the reaction rates, but the apparent order of the reaction with respect to Sb(III) changed to two. The trace metal effect observed was concentration dependent for Pb(II). The addition of the hydroxyl radical scavenger 2-propanol suggests that the trace metal catalytic effect observed involves the action of hydroxyl radicals, but that they are not responsible for the oxidation of Sb(III) by H2O2 in the absence of trace metals. The fact that Sb(III) can be oxidized by hydroxyl radicals present in water, even if it is not capable of producing them, has important environmental implications because hydroxyl radicals are known to be abundant in many natural waters such as seawater, humic-rich surface waters or rainwater. © The Royal Society of Chemistry 2005.

cited By 9; International audience; The possible occurrence of polluted aerosols formed by a bubbling mechanism from hydrocarbon-rich aqueous surface layers was investigated in laboratory through the determination of hydrocarbon adsorption from diluted solutions. Benzene and cyclohexane both exhibited positive adsorption. Further to our previous demonstration of lead nitrate coadsorption with benzene near the solubility limit (Sadiki et al., 2003. Atmospheric Environment 37, 3551-3559) the present study revealed a positive coadsorption of lead nitrate with both hydrocarbons, even in diluted solutions. The use of the bubble-column (Wan, Tokunaga, 1998. Environment Science and Technology 32, 3293-3298) as an experimental tool is discussed as well as the physico-chemical mechanisms involved in adsorption and coadsorption processes with their impact on the environment. © 2005 Elsevier Ltd. All rights reserved.

cited By 39; International audience; Knowledge of antimony redox kinetics is crucial in understanding the impact and fate of Sb in the environment and optimizing Sb removal from drinking water. The rate of oxidation of Sb(III) with H2O 2 was measured in 0.5 mol L-1 NaCl solutions as a function of [Sb(III)], [H2O2], pH, temperature, and ionic strength. The rate of oxidation of Sb(III) with H2O2 can be described by the general expression: -d[Sb(III)]/dt = k[Sb(III)][H 2O2][H+]-1 with log k= -6.88 (±0.17) [k: min-1]. The undissociated Sb(OH)3 does not react with H2O2: the formation of Sb(OH) 4 - is needed for the reaction to take place. In a mildly acidic hydrochloric acid medium, the rate of oxidation of Sb(III) is zeroth order with respect to Sb(III) and can be described by the expression -d[Sb(III)]/dt = k[H2O2][H+][Cl-] with log k = 4.44 (±0.05) [k: L2 mol-2 min -1]. The application of the calculated rate laws to environmental conditions suggests that Sb(III) oxidation by H2O2 may be relevant either in surface waters with elevated H2O2 concentrations and alkaline pH values or in treatment systems for contaminated solutions with millimolar H2O2 concentrations.