Solid-state NMR for the study of membrane systems: The use of anisotropic interactions

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Ionic association and interactions in aqueous methylsulfate alkyl-imidazolium-based ionic liquids

International audienceSeveral experimental techniques were used to study ionic association and interactions in aqueous [C1C2Im][MeSO4], 1-ethyl-3-methylimidazolium methylsulfate, and [C1C4Im][MeSO4], 1-butyl-3-methylimidazolium methylsulfate. Two transport properties, viscosity and electrical conductivity, were determined for these two binary mixtures. For a better assessment of the ionic association and the perturbation of water into the molecular structure of the ionic liquid, diffusion coefficients of ions and water molecules were obtained by NMR spectroscopy while molecular interactions were probed by IR spectroscopy.The comparison of the two ionic liquids shows that for the shorter alkyl chain the viscosity was lower and the electrical conductivity was higher. While the viscosity of the mixture drops already with small additions of water, the electrical conductivity of the solution is only significantly increased for high water concentrations. A maximum is observed for compositions around xwater = (0.90 to 0.95). The SO3 asymmetric stretching band of the IR spectrum can be used as a probe to observe the evolution of the structure around the anion which was mainly occurring for high concentrations of water. Several experimental techniques show than the main change in the ionic association was only observed for high water contents (water mole fraction > 0.8)

Quantification of the impact of water as an impurity on standard physico-chemical properties of ionic liquids

International audienceThe objective of this work was to quantify the effect of the presence of water as impurity in ionic liquids. First, density and viscosity of five ionic liquids as well as their aqueous solutions were measured. For hydrophobic dried ionic liquids, traces of water (50 ppm) have measurable impact neither on the density nor on the viscosity values. In the concentration range studied (up to 5000 ppm), a linear evolution of the molar volume of the mixture with the mole fraction composition is observed. Practically, this allows to estimate the density of an neat ionic liquid provided (i) the water quantity and (ii) the density of the undried sample are known. This is particularly useful for hydrophilic ionic liquids that are difficult to dry. In the studied concentration range, a linear evolution of the relative viscosity was also depicted as a function of the mass fraction composition. It is thus possible to evaluate the viscosity of the pure ionic liquid knowing the water quantity and the viscosity of the undried sample. The comparison of the results obtained using two viscosimeters confirms that a Stabinger viscosimeter is appropriate to precisely measure ionic liquids viscosities. Second, NMR and IR spectroscopies were used to characterize the pure ionic liquids and their solutions with water. The sensitivity of IR spectroscopy does allow neither the quantification nor the detection of water below 1 mol%. With NMR spectroscopy, water can be quantified using either the intensity or the chemical shift of the water proton peak for mole fractions as low as 200 ppm. It is even possible to detect water in the dried hydrophobic ionic liquids, few ppm of water, as long as the water peak does not overlap the ionic liquid signal

An Entry to 1,7-Dioxaspiro[5.6]dodecanes and 1,6-Dioxaspiro[4.6]undecanes

International audienceKetones 11a–c obtained by iterative alkylation of acetone N,N-dimethylhydrazone with iodides 6 and 8a,b or epoxide 9 followed by SiO2/H2O-induced cleavage of the hydrazone were quantitatively transformed into 1,6-dioxaspiro[4.6]undecanes 12a,c and 1,7-dioxaspiro[5.6]dodecanes 12b using Yb(OTf)3 in CH3CN

The role of association of ions in ionic liquid/molecular solvent mixtures on metal extraction

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Branched and cyclic alkyl groups in imidazolium-based ionic liquids: Molecular organization and physico-chemical properties.

International audienceIn the present work, three imidazolium bis{(trifluoromethyl)sulfonyl}imide ionic liquids with a linear alkyl chain (1-pentyl-3-butylimidazolium bis{(trifluoromethyl)sulfonyl}imide, [C4C5Im][Tf2N]), with branching (1-isopentyl-3-butylimidazolium bis{(trifluoromethyl)sulfonyl}imide [C4iC5Im][Tf2N]), or with a cyclic group (1-cyclopentyl-3-butylimidazolium bis{(trifluoromethyl)sulfonyl}imide, [C4cC5Im][Tf2N]) were synthesized for the first time. Such variation in structure could be of interest to possible applications of the present ionic liquids as task-specific ionic liquids. To understand the influence of the structure on their macroscopic properties, their density and two transport properties (viscosity and electrical conductivity), were measured as function of temperature. The introduction of branching has no effect on the density values whereas these show an increase when a cycle is substituted to the cation. Both branching of the alkyl chain and the presence of the cyclic group increase the viscosity. Surprisingly, the electrical conductivity of [C4cC5Im][Tf2N] is the highest despite its high viscosity. From the measurement of ion diffusion coefficients by Nuclear Magnetic Resonance (NMR) spectroscopy, the ionicity could be evaluated. The cycloalkane-substituted [C4cC5Im][Tf2N] was found to be more dissociated compared to the other two ionic liquids which explains the behaviour observed for the conductivity. This could mean that the cycloalkane-substituted ionic liquid might find its use in electrochemistry. The experimental viscosity, conductivity, and diffusion coefficient data were described by equations of the Vogel-Tamman-Fulcher type using a regression along a gnostic influence function. In this way, a robust global optimization algorithm could be used to obtain reliable model parameters, but also to critically evaluate the experimental data

Can the tricyanomethanide anion improve CO2 absorption by acetate-based ionic liquids?

International audienceCarbon dioxide absorption by mixtures of two ionic liquids with a common cation—1-butyl-3-methylimidazolium acetate, [C4C1Im][OAc], and 1-butyl-3-methylimidazolium tricyanomethanide, [C4C1Im][C(CN)3]—was determined experimentally at pressures below atmospheric pressure as a function of temperature between 303 K and 343 K, and at 303 K as a function of pressure up to 10 bar. It is observed that the absorption of carbon dioxide decreases with increasing tricyanomethanide anion concentration and with increasing temperature, showing a maximum of 0.4 mole fraction of carbon dioxide in pure [C4C1Im][OAc] at 303 K. At this temperature, the CO2 absorption in the mixtures [C4C1Im][OAc](1−x)[C(CN)3]x is approximately the mole-fraction average of that in the pure ionic liquids. By applying an appropriate thermodynamic treatment, after identification of the species in solution, it was possible to calculate both the equilibrium constant, Keq, and Henry's law constant, KH, in the different mixtures studied thus obtaining an insight into the relative contribution of chemical and physical absorption of the gas. It is shown that chemical sorption proceeds through a 1 : 2 stoichiometry between CO2 and acetate-based ionic liquid. The presence of the C(CN)3− anion does not significantly affect the chemical reaction of the gas with the solvent (Keq = 75 ± 2 at 303 K) but leads to lower Henry's law constants (from KH = 77.8 ± 0.6 bar to KH = 49.5 ± 0.5 bar at 303 K), thus pointing towards larger physical absorption of the gas. The tricyanomethanide anion considerably improves the mass transfer by increasing the fluidity of the absorbent as proven by the larger diffusivities of all the ions when the concentration of the C(CN)3− anion increases in the mixtures

Environmental scenarii for the degradation of oxo-polymers

International audienceThe fate of oxo-polymers in nature is strongly dependent on environmental conditions, mainly on the intensity and duration of sunshine, which vary with the season and the climate. In this work, we report the effect of different scenarii on the production and the molecular composition of oligomers released from oxo-biodegradable HDPE films. Under our experimental conditions, the duration of accelerated weathering corresponded to a period of 3 months to 3 years of exposure to outside conditions under temperate climate. In addition, the oligomers were extracted in three different solvents: i) water to mimics the natural environment; ii) acetone and chloroform to identify oligomers trapped in the polymer matrix. The combination of high-resolution mass spectrometry and 1H NMR spectroscopy gives an extensive picture of the relative concentrations and the structural compositions of the extracted oligomers in the different tested conditions. In particular, the masses, the number of oxygen and carbon atoms could be determined for up to 2283 molecules. Globally the concentration and the size of oligomers increased with the duration of extraction, the level of aging of the polymer and the use of non-polar solvents. Surprisingly, the presence of highly oxidized molecules in acetone and chloroform extract, suggested an important swelling of HPDE films in these solvents and a better diffusion of these oligomers in the matrix. In nature, the biodegradability of oligomers could result from processes occurring both at the molecular (oxidation) and the macromolecular (diffusion and release) levels

Tailoring the properties of acetate-based ionic liquids using the tricyanomethanide anion.

International audienceThe equilibrium and transport properties of mixtures of two ionic liquids – [C4C1Im][OAc] and [C4C1Im][C(CN)3] – were determined and interpreted at the molecular level using vibration spectroscopy, NMR and molecular dynamics simulation. The non-ideality of the mixtures [C4C1Im][OAc](1−x)[C(CN)3]x was characterized by VE = +0.28 cm3 mol−1 (293 K, x = 0.65) and HE = −2.2 kJ mol−1 for x = 0.5. These values could be explained by a rearrangement of the hydrogen-bond network of the mixture that favours the interaction of the acetate anion with the imidazolium cation at position C2. The dynamic properties of the mixture are also dramatically influenced by the composition with a decrease of the viscosity and an increase of self-diffusion coefficients of the ions when the amount of tricyanomethanide anion increases in the mixture

Characterization of oxidized oligomers from polyethylene films by mass spectrometry and NMR spectroscopy before and after biodegradation by a Rhodococcus rhodochrous strain

International audienceThe objective of this work was to develop a new approach to assess the specificity and the efficiency of biodegradation of oxidized oligomers extracted from aged HDPE polyethylene films and to bring insight on the mechanisms occurring during biodegradation. 1H NMR spectroscopy and LC Orbitrap™ mass spectrometry were combined together with data processing using Kendrick mass defect calculation and Van Krevelen Diagram.We showed that the molecular weight of extracted oligomers was lower than 850 Da with maximum chain length of 55 carbon atoms. The oligomers were divided into 11 classes of molecules with different oxidation state ranging from 0 to 10. All classes included series of chemically related compounds including up to 19 molecules.95% of the soluble oligomers were assimilated by a strain of Rhodococcus rhodocchrous after 240 days of incubation. Large highly oxidized molecules completely disappeared while the other classes of molecules were still represented. Molecules containing 0–1 oxygen atom were less degraded. A strong shift to smaller molecules (<450 Da, 25 carbon atoms) was observed suggesting that longer molecules disappeared more rapidly than the smaller ones. It opens new perspectives on biodegradation processes as not only intracellular β-oxidation must be considered but also extracellular mechanisms leading to chain cleavages