Laurent Gaillon

Behaviour of a binary solvent mixture constituted by an amphiphilic ionic liquid, 1-decyl-3-methylimidazolium bromide and water: Potentiometric and conductimetric studies

We investigated the properties of 1-decyl-3-methylimidazolium bromide (DMImBr), a molten salt at room temperature, and its mixtures with water in the whole proportions. At low concentrations, this salt behaved like a classical cationic amphiphile. Its critical micellar concentration (cmc) was determined by conductimetry and by measuring electromotive forces (EMF) with bromide or cationic surfactant-selective electrodes. Moreover, the association rate of the counter ion to micelle has been determined on a wide range of concentrations, allowing characterising the micellisation equilibrium by a solubility product. The conductivity of this liquid electrolyte in mixtures with water was maximal at high concentrations. We modelled this behaviour, taking into account the molar volume fraction of both phases. Our results show that these solutions, which are composed of dispersed aggregates, behave like mixtures of two phases that interpenetrate themselves.

Electrochemistry of zeolite-encapsulated complexes: Part 3. Characterization of iron and manganese SALEN entrapped in Y faujasite type zeolite☆

Abstract [Mn III SALEN] + and [Fe III SALEN] + complexes have been entrapped in the supercages of zeolite Y. The redox properties of these zeolite-encapsulated complexes are investigated by cyclic voltammetry in acetonitrile and dimethyl sulphoxide solutions. The results show the existence of two kinds of entrapped [Fe III SALEN] + forms within the zeolite. Their existence is related to the mechanism of their preparation and depends on the electrolytic media. The electroactivity of encapsulated Mn-SALEN towards the biomimetic activation of molecular oxygen is discussed.

Electrochemical and Spectral Properties of Ferrocene (Fc) in Ionic Liquid: 1-Butyl-3-methylimidazolium Triflimide, [BMIM][NTf2]. Concentration Effects

Several earlier studies of the electrochemical oxidation of ferrocene (Fc) in room-temperature ionic liquids revealed an essentially nonlinear dependence of the oxidation current on the Fc concentration in its relatively dilute solutions, with its formally calculated diffusion coefficient strongly increasing with the concentration. Since no plausible mechanism leading to this very unusual finding had been proposed, our study of Fc solutions in 1-butyl-3-methylimidazolium triflimide, [BMIM][NTf(2)], was performed to verify whether the above observation originated from an incorrect determination of the dissolved Fc concentration. Our observations have demonstrated that reliable control of the Fc concentration in solution is complicated by factors such as the low amount of Fc used to prepare small-volume solutions or the great difficulty to dissolve completely a solid powder in a solvent with an extremely high viscosity. An unexpected additional complication is related to a sufficiently high volatility of Fc which manifests itself even at room temperature and especially at elevated temperatures or/and in the course of vacuum treatment of its solutions or its solid powder. Parallel measurements of electrochemical responses and UV-visible spectra for several series of Fc solutions of various concentrations (prepared with the use of different procedures) have shown a perfect parallelism between the peak current and the intensity of the absorption band in the range of 360-550 nm, leading us to the conclusion of a linear relationship between the oxidation current and the molecularly dissolved Fc concentration. The relations of these measured characteristics with the estimated Fc concentration in these solutions have demonstrated a much greater dispersion (attributed to the difficulty of a precise measurement of the latter) but without a significant deviation from the linearity in general. This finding has allowed us to estimate the diffusion coefficient of this species: D = (1.7 +/- 0.2) x 10(-7) cm(2)/s. The extinction coefficients for the maximum of the absorption band (at 440 nm) of Fc have been compared for a series of solvents: [BMIM][NTf(2)], acetonitrile, THF, heptane, CH(2)Cl(2), ethanol, and toluene. A simple method to estimate reliably the concentration of solute Fc in ionic liquids based on spectroscopic measurements has been proposed, owing to the proximity of Fc absorption properties for a great variety of solvents.

Electrochemical characterization of manganese porphyrins fixed onto silica and layered dihydroxide matrices

Immobilization of metalloporphyrin catalysts on polymer and inorganic supports has been researched intensively in recent years. Methods being actively pursued at present are the electrochemical polymerization of a suitably designed pyrrole-substituted porphyrin [l-7], the chemical polymerization of readily available halogenated metalloporphyrins [8,9], and the fixation of the complexes by adsorption on silica or alumina [lo-121 and by ion-exchange reaction on clay minerals (i.e. montmorillonite) [12-161, zeolites [171, layered dihydroxides [10,18,191 and ion-exchange resins [20-221. In the case of manganese porphyrins, these new supported catalysts have been used in oxidation catalysis and involved in efficient biomimetic systems. In fact, recent publications have shown that polypyrrole + manganese porphyrin films are good catalysts for electroassisted oxidation of hydrocarbons by molecular oxygen [23,241 and that multicharged porphyrins supported on silica and mineral clays are particularly efficient for alkene epoxidation and alkane hydroxydation by iodosylbenzene [lo-12,20-221 or molecular oxygen [El. A new easy access to polyhalogenated metalloporphyrins covalently bound to silica and polystyrene supports as efficient catalysts for hydrocarbon oxidation by iodosylbenzene has recently been reported by Battioni et al. [9].

Redox-switched amphiphilic ionic liquid behavior in aqueous solution.

A new redox amphiphilic ionic liquid (AIL) containing ferrocene as a redox-active group was synthesized, 1-(11-ferrocenylundecyl)-3-methylimidazolium bromide (Fc11MIm+). Adsorption and aggregation of both reduced and oxidized forms of this ferrocenated AIL in aqueous solution were studied by surface tension measurements. The micellization was favored for the reduced ferrocenated AIL (Fc11MIm+) as compared with the oxidized ferrocenated AIL (Fc+11MIm+). Minimum areas at the air/aqueous solution interface were identical whereas limiting surface tensions were slightly different. This corroborated the formation of an expanded monolayer of redox active AIL at the interface. The electrochemical behavior of redox active AIL was investigated. The electrochemical responses of Fc11MIm+ aqueous solution interestingly differed, depending on its concentration. Below the cmc, the electrochemical reaction was dominated by ferrocenated AIL adsorbed onto the electrode surface; then above the cmc, it was controlled by the Fc11MIm+ diffusing to the electrode. For the latter, the electrochemical mechanism was suggested to couple with the disruption reaction of the reduced form micelles.

ELECTROCHEMISTRY OF MANGANESE PORPHYRIN INTERCALATED INTO MONTMORILLONITE

Here we describe the electrochemical investigation of the tetracationic chloro(meso-tetra(4-N-methylpyridinio)-porphyrinato)manganese(III) tetrachloride, Mn(TMPyP)Cl, supported on montmorillonite, so as to assess the possibility of using this supported catalyst in electroassisted catalytic oxidation of hydrocarbons by molecular oxygen, where the complete catalytic process involves the Mn III /Mn II redox system and several electrochemical reduction steps

Insights into the polymerization kinetics of some α-silylated thiophene oligomers

Abstract Oxidation of several silylthiophene oligomers has been studied in dichloromethane and acetonitrile by cyclic voltammetry. Detailed mechanistic studies show that the oxidative coupling of silyloligothiophenes involves the carbon-carbon bond formation between two cation-radicals, as previously observed for other non-silylated oligothiophenes. The lifetimes of the cation-radicals are found to be dependent on the solvent, indicating a nucleophilic assistance to the CSi cleavage. This behavior is in agreement with a reversible coupling step leading to the formation of a dimeric cation followed by the irreversible cleavage of the CSi bond. Evidence for the existence of an equilibrium between the monomeric cation-radical and an associated form (π-dimerization) has been obtained from the variation of the redox potential with the temperature and concentration for the most stable cation-radical.

Electroassisted Oxidation of Cis-Cyclooctene and Adamantane by Molecular Oxygen Catalyzed by Polypyrrole Manganese Porphyrin Films

Abstract The electrochemical polymerisation of pyrrole-substituted manganese porphyrin complex on carbon and graphite electrodes has been performed in acetonitrile solution. The redox and catalytic properties of the polymer films have been examined by cyclic voltammetry. Electroassisted oxidation reactions of cis-cyclooctene and adamantane with molecular oxygen, under atmospheric pressure, in acetonitrile and dichloromethane solutions are described using the manganese porphyrin-coated electrodes as catalysts. One remarkable aspect of the results is the large activity of the porphyrin catalyst when it is attached on the electrode.

Cyclic voltammetry of zeolite-supported manganese porphyrins

The electrochemical behaviour of adsorbed 5,10,15,20-tetra(4-N-methylpyridinium)porphyrinatomanganese(III) complex on ZSM-5 and EMC-2 zeolites and VPI-5 molecular sieve has been investigated by cyclic voltammetry. The results show that the redox potential of the MnIII/MnII process of the fixed porphyrins can be measured by this technique by using a pressed powder composite electrode. These potentials are positively shifted, by 50 to 380 mV according to the zeolite matrices, relative to the unlinked complex.

Sequence and analysis of a 26·9 kb fragment from chromosome XV of the yeast Saccharomyces cerevisiae

We have determined the nucleotide sequence of a fragment of chromosome XV of Saccharomyces cerevisiae cloned into cosmid pEOA048. The analysis of the 26 857 bp sequence reveals the presence of 19 open reading frames (ORFs), and of one RNA‐coding gene (SNR17A). Six ORFs correspond to previously known genes (MKK1/SSP32, YGE1/GRPE/MGE1, KIN4/KIN31/KIN3, RPL37B, DFR1 and HES1, respectively), all others were discovered in this work.