Loading-Controlled Stiffening in Nanoconfined Ionic Liquids

An important strategy for using ionic liquids is to immobilize them by impregnation of supports or incorporation into porous solids to obtain materials called “ionogels”. Of considerable importance for applications (electrolyte membranes, supported catalysts, etc.), such confinement results in dramatic changes in the physicochemical properties of the ionic liquid. Here, we report molecular simulations of a silica nanopore that is gradually filled with a typical imidazolium salt ionic liquid to obtain a realistic model of these ionogels. Despite the significant layering and stiffening of the ionic liquid in the vicinity of the silica surface, the pair correlation functions and magnitude of its dynamics clearly evidence liquid-like behavior. An increase in the self-diffusivity and ionic conductivity, associated with a decrease in the characteristic residence times of ions at the silica surface, is observed upon increasing the loading as the ionic liquid fills the nanopore center and tends to recover its bulk properties

Chiral Phosphine−Phosphonium Ylide Rhodium Complexes

The phosphonium methylide of (R)-BINAP acts as a novel chiral dissymmetric chelating ligand in the stable [Rh(cod)(BINAPCH2)]+ complex. A rationale for the conformation of the eight-membered metallacycle derived from chiral phosphine−phosphonium ylide ligands is proposed on the basis of DFT calculations on a model complex

Electropolymerization of Pyrrole-Tailed Imidazolium Ionic Liquid for the Elaboration of Antibacterial Surfaces

A strategy was developed to prepare antibacterial surfaces by electropolymerization of a pyrrole-functionalized imidazolium ionic liquid bearing an halometallate anion. The objective was to combine the antibacterial efficiency of polypyrrole (PPy) with those of the ionic liquid’s components (cation and anion). For this, N-(1-methyl-3-octylimidazolium)pyrrole bromide monomer [PyC8MIm]Br was synthesized and coordinated to ZnCl2 affording [PyC8MIm]Br-ZnCl2. The antibacterial properties of [PyC8MIm]Br-ZnCl2 monomer were evaluated against Escherichia coli and Staphylococcus aureus by measurement of the minimum inhibitory concentration (MIC) values. This monomer presents higher activity against S. aureus (MIC = 0.098 μmol·mL–1) than against E. coli (MIC = 2.10 μmol·mL–1). Mixtures of pyrrole and the pyrrole-functionalized ionic liquid [PyC8MIm]Br-ZnCl2 were then used for the electrodeposition of PPy films on Fluorine-doped tin oxide (FTO) substrates. The concentration of pyrrole was fixed to 50 mM, while the concentration of [PyC8MIm]Br-ZnCl2 was varied from 5 to 100 mM. The efficient incorporation of the imidazolium cation and zinc halometallate anion into the films was confirmed by X-ray photoelectron spectroscopy (XPS) measurements. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) measurements confirmed the homogeneity of the different films with structures that depend on the [PyC8MIm]Br-ZnCl2 concentration. The films’ thickness determined by profilometry varies only slightly with the [PyC8MIm]Br-ZnCl2 concentration from 7.4 μm at 5 mM to 8.9 μM at 100 mM. The films become more hydrophilic with an increase of [PyC8MIm]Br-ZnCl2 concentration with water contact angles varying from 47° at the lowest concentration to 32° at the highest concentration. The antibacterial activities of the different PPy films were determined both by the halo inhibition method and by the colony forming units (CFUs) counting method over time against Gram-positive S. aureus and Gram-negative E. coli bacteria. Films obtained by incorporation of [PyC8MIm]Br-ZnCl2 showed excellent antibacterial properties, at least two times higher than those of neat PPy, validating our strategy. Furthermore, a comparison of the antibacterial properties of the films obtained using the same [PyC8MIm]Br-ZnCl2 concentration (50 mM) evidenced much better activity against Gram-positive (no bacterial survival within 5 min) than against Gram-negative bacteria (no bacterial survival within 3 h). Finally, the antibacterial performances over time could be tuned by the concentration of the employed pyrrole-functionalized ionic liquid monomer. Against E. coli, using 100 mM of [PyC8MIm]Br-ZnCl2, the bacteria were totally killed within a few minutes, using 50 mM, they were killed after 2 h while using 10 mM, about 20% of bacteria survived even after 6 h

Unique Combination of Mechanical Strength, Thermal Stability, and High Ion Conduction in PMMA−Silica Nanocomposites Containing High Loadings of Ionic Liquid

Unique Combination of Mechanical Strength, Thermal Stability, and High Ion Conduction in PMMA−Silica Nanocomposites Containing High Loadings of Ionic Liqui

Surfactant Behavior of Ionic Liquids Involving a Drug: From Molecular Interactions to Self-Assembly

Aggregates formed in an aqueous medium by three ionic liquids C_<i>n</i>MImIbu made up of 1-alkyl-3-methyl-imidazolium cation (<i>n</i> = 4, 6, 8) and ibuprofenate anion are investigated. Dynamic light scattering (DLS), cryogenic transmission electron microscopy (cryo-TEM), ¹H nuclear magnetic resonance measurements, and atom-scale molecular dynamics simulations are used to shed light on the main interactions governing the formation of the aggregates and their composition. At high concentration, mixed micelles are formed with a composition that depends on the imidazolium alkyl chain length. For the shortest alkyl chain, micelles are mainly composed of ibuprofenate anions with some imidazolium cations intercalated between the anions. Upon increasing the alkyl chain length, the composition of the aggregates gets enriched in imidazolium cations and aggregates of stoichiometric composition are obtained. Attractive interactions between these aggregates led to the formation of larger aggregates. As suggested by molecular simulations, these larger aggregates might constitute the early stage of phase separation. Transitions from micelles to vesicles or ribbons are observed due to dilution effects and changes in the chemical composition of the aggregates. We also show that aggregation can be probed using simple microscopic quantities such as radial distribution functions and average solvation numbers

Conductometric Sensor Based on Electropolymerized Pyrrole-Tailed Ionic Liquids for Acetone Detection

In the chemical industry and research institutes, acetone serves routinely as a solvent, a reactant, and an extractant. However, due to its high volatility and toxicity, monitoring its vapor concentration is of great necessity for health and industrial safety. Besides this, simple and easy-to-use portable sensors are still lacking. In this work, a conductometric transducer was developed for the detection of acetone vapor. For this, interdigitated electrodes were functionalized by electropolymerization of a series of N-(1-methyl-3-octylimidazolium)­pyrrole [PyC8MIm]­X monomers that contain different counteranions X–, namely, hexafluorophosphate (PF6–), tetrafluoroborate (BF4–), and bis­(trifluoromethylsulfonyl)­imide (TFSI–). The functionalized interdigitated electrodes were widely characterized. The analytical performances of the microsensors were determined in the presence of gaseous acetone, chloroform, ethanol, methanol, and toluene, collected from the headspace of the above aqueous solutions of known concentrations. The gas-sensing responses of the films were measured at room temperature through differential conductometric measurements conducted at 10 kHz. Among the different sensors, the one bearing BF4– anions presented the best analytical performances and was able to selectively detect acetone vapors. The sensor’s response time (tres) varied from 6 to 13 s from lower to higher concentrations. The detection limit was 0.76 v/v % (7600 ppm) in the gas phase. The relative standard deviation was 6% for lower concentrations and 2% for higher concentrations. The acetone sensor presented 2 times lower sensitivity for ethanol and 4 times lower sensitivity for methanol. Detection of acetone in the headspace of a nail varnish remover sample led to an acetone content that was in compliance with the value given by the producer

Symmetrical Diacetylenes Outfitted with Ionic Liquid-like Groups: Structural, Polymerization, and Carbonization Studies

Three symmetrical diacetylenes (DAs) bearing tetraalkylammonium substituents have been prepared, namely, 1,6-bis(triethylammonium)hexa-2,4-diyne diiodide (2), dinitrate (3), and bis[bis(trifluoromethylsulfonyl)imide] (4). For these three salts, the duality between polymerization and carbonization has been investigated, and the results have been rationalized in terms of solid-state organization and molecular structure. These DAs have been irradiated at 254 nm with concomitant annealing at 80 °C (4) or 110 °C (2 and 3), and the lack of polydiacetylene (PDA) formation is in agreement with the fact that the CC–CC rods do not have a suitable orientation for 1,4-addition. Compound 4 is an ionic liquid. This DA starts melting at 88 °C with a maximum peak value of 104 °C, as ascertained by differential scanning calorimetry and thermogravimetric analyses. It is stable in the liquid state at 120 °C for several hours and remains unchanged at 170 °C for a few minutes without any sign of PDA formation, which means that if some kind of organization exists in the liquid phase, it is not helpful for 1,4-polymerization. Thermolyses of 2–4 have been conducted under a nitrogen flow up to 220 °C (3) and 1200 °C (2 and 4). In all three cases, graphite-like carbon materials were obtained. The graphite-like structures start to form around 200 °C, which is the temperature at which cycloaromatization of the triple bonds takes place. The residues from the pyrolyses of 2 and 4 exhibit nitrogen contents of 1.75 and 1.40 wt %, respectively, and powder X-ray diffraction and Raman analyses indicate that these materials have coherently scattering domain sizes in the range of 1–3 nm depending on the crystallographic direction. The Brunauer, Emmett, and Teller specific surface area of 2@1200 derived from dinitrogen sorption experiments is 88 m2 g–1 and that of 4@1200 is 33 m2 g–1. These values are much higher than those measured in previous works for carbon residues prepared at 1100 °C from imidazolium- and benzimidazolium-appended diacetylenes, thereby highlighting the pivotal influence of the size of the cation on the microstructure of the resulting carbon material. In addition, 2@1200 appears to be mostly microporous and 4@1200 mesoporous, which suggests that the anion also plays a central part in the structuring of the final solid. Last, X-ray photoelectron spectroscopy analysis of 4@1200 indicates that, besides nitrogen, this residue also contains small amounts of fluorine and sulfur, thus making carbonization of ionic diacetylenes an alternative method to introduce doping elements in a graphite structure

Ionic Liquid Mediated Sol-Gel Synthesis in the Presence of Water or Formic Acid: Which Synthesis for Which Material?

Sol-gel syntheses involving either neutral water or formic acid as a reactant have been investigated (1) to determine the best conditions to confine a maximum of ionic liquid (IL) inside silica-based matrixes and (2) to reach the highest porosity after removing the IL from the ion gels (washed gels). Several sets of ionogels were prepared from various 1-butyl-3-methylimidazolium ILs and various silica or organosilica sources. The study evidenced a critical effect of the anion on the morphology (monolith, powder) and texture of the resulting washed gels. Particularly, tetrafluoroborate anion led to monolith ionogels by a simple hydrolytic method, affording highly condensed mesoporous silicas with some fluorinated surface sites. Such sites have never been reported before and were evidenced by ¹⁹F NMR. On the other hand, formic acid solvolysis turned out to be the only method to get non-exuding, crack-free, and transparent monoliths from ILs containing bis­(trifluoromethylsulfonyl)­imide [NTf₂] anion, with promising applications in photochemistry or photosensing. With bulky imidazolium and pyridinium cations, removal of the IL led to highly porous silicas with pore diameters and pore volumes as high as 10–15 nm and 3 cm³ g^–1, respectively. These silicas could find applications as supports for immobilizing bulky molecules

All-Optical Orientation of Photoisomerizable Octupolar Zinc(II) Complexes in Polymer Films

A new type of 4,4‘-bis(styryl)-2,2‘-bipyridine functionalized by a dialkylamino-azobenzene group has been prepared. This ligand has allowed the preparation of photoisomerizable octupolar tris(bipyridyl)zinc(II) complexes and the corresponding star-shaped polymer by atom transfer radical polymerization (ATRP) of methyl methacrylate (MMA). The photoisomerization properties of such new metallo-chromophores have been studied. The macroscopic molecular orientation of the corresponding doped and grafted NLO-polymer films is reported for the first time