Modulations in Self-Organization Properties of Surfactant in Aqueous Ionic Liquid Media

Ionic liquids (ILs) give a wide scope of favorable applications due to their much-upgraded properties. The strong electrostatic interactions between the cationic moiety of IL and the anionic surfactant play a very important role in the assembly of the large aggregates. We have investigated the aggregation behavior of anionic surfactants and IL in aqueous solution. Different temperatures and concentrations of IL have been taken to study the effect on critical micelles concentrations of surfactant. The critical micelle concentration values obtained by conductivity measurements are further confirmed by the fluorescence studies. The method is based on the fit of the experimental obtained raw data of fluorescence spectroscopy to a simple nonlinear category of a Boltzmann type sigmoidal function. Thermodynamical parameters of micellization Δ H m 0 $\Delta H_{m}^{0}$ , Δ G m 0 $\Delta G_{m}^{0}$ and Δ S m 0 $\Delta S_{m}^{0}$ have been considered to study the effect of aqueous IL 1-butyl-3-methylimidazolium bromide concentration and temperature on aggregation behavior of surfactant sodium dodecyl sulfate. FT-IR spectra have been studies to verify the structural changes arise in the aqueous IL and surfactant system.

Possible sensor applications of selected DNA-surfactant complexes

Although much research has been performed on DNA complexes carrying long alkyl chains (C10, C16, and C18), there is no information about physicochemical characterization of synthesized composites with allyl imidazole-based ionic liquids and quaternary ammonium salts with n-butyl chains. Here, complexes were synthesized by ion-exchange reactions between sonicated DNA and three ionic liquids (ILs) formed from two imidazole-based compounds, 1-allyl-3-methylimidazolium bromide (Amim) or 1-butyl-3-methylimidazolium bromide (Bmim), and from the quaternary ammonium salt tetra-n-butylammonium bromide (TBAB). Signals in UV-Vis, IR, and CD spectra indicating inclusion of small molecules into the DNA structure confirmed the formation of DNA complexes. Both IR and CD spectra indicated that the B-form conformation of the DNA did not change after the formation of the complexes. Similarly, X-ray diffraction patterns revealed that the formation of IL-DNA complexes did not change the structure of native B-form DNA. Molecular weight (M_w) and radii of gyration (R_g) values of IL-DNA complex chains, established by high-performance size exclusion chromatography coupled with multiangle-laser light-scattering with a differential refractive index detector, were significantly lower than those values found for native DNA molecules due to DNA fragmentation by sonication during complex formation and the direct effects of the IL on the DNA. Scanning electron microscopy images indicate the formation of nanofibres in DNA-Amim and DNA-Bmim complexes, whereas the formation of nanowires was found in samples of DNA-TBAB complexes. Changes in optical properties confirmed by UV and photoluminescence make DNA-IL complexes potential candidates for biosensor application.

Extraction and recovery processes for cynaropicrin from Cynara cardunculus L. using aqueous solutions of surface-active ionic liquids

Due to the wide range of relevant biological activities and high commercial value of cynaropicrin, and aiming at developing cost-effective processes, aqueous solutions of ionic liquids (ILs) were investigated for the extraction and recovery of cynaropicrin from the leaves of Cynara cardunculus L. Both cationic (1-alkyl-3-methylimidazolium chloride) and anionic (cholinium carboxylate) surface-active ILs were investigated, as well as a wide range of conventional surfactants and molecular organic solvents, allowing us to conclude that aqueous solutions of cationic surface-active ILs display a better performance for the extraction of cynaropicrin. Operational conditions were optimized, leading to a cynaropicrin extraction yield of 3.73 wt%. The recycling of both the biomass and the solvent were further investigated to appraise the extraction media saturation and to achieve a higher cynaropicrin extraction yield (6.47 wt%). Finally, it was demonstrated that 65 wt% of the extracted cynaropicrin can be efficiently recovered by precipitation from the IL aqueous extract through the addition of water as anti-solvent, allowing us to put forward both the extraction and recovery processes of the target value-added compound from biomass followed by solvent recycling. This approach opens the door to the development of more sustainable processes using aqueous solutions of ILs instead of the volatile organic solvents commonly used in biomass processing.

How ionic species structure influences phase structure and transitions from protic ionic liquids to liquid crystals to crystals

Phase behaviour of n-alkylammonium (C6 to C16) nitrates and formates was characterised using synchrotron small angle and wide angle X-ray scattering, differential scanning calorimetry, cross polarised optical microscopy and FTIR.

Aqueous ionic liquids and their effects on protein structures: an overview on recent theoretical and experimental results

Ionic liquids (ILs) are used in a variety of technological and biological applications. Recent experimental and simulation results reveal the influence of aqueous ionic liquids on the stability of protein and enzyme structures. Depending on different parameters like the concentration and the ion composition, one can observe distinct stabilization or denaturation mechanisms for various ILs. In this review, we summarize the main findings and discuss the implications with regard to molecular theories of solutions and specific ion effects. A preferential binding model is introduced in order to discuss protein-IL effects from a statistical mechanics perspective. The value of the preferential binding coefficient determines the strength of the ion influence and indicates a shift of the chemical equilibrium either to the native or the denatured state of the protein. We highlight the role of water in order to explain the self-association behavior of the IL species and discuss recent experimental and simulation results in the light of the observed binding effects.

Synthesis and characterization of 2′,3′-epoxy propyl-N-methyl-2-oxopyrrolidinium salicylate ionic liquid and study of its interaction with water or methanol

Important physico-chemical properties of ionic liquids (ILs) can be manipulated by adjusting the nature of the cation or anion.

Protein Stabilization and Enzyme Activation in Ionic Liquids: Specific Ion Effects

There are still debates on whether the hydration of ions perturbs the water structure, and what is the degree of such disturbance; therefore, the origin of Hofmeister effect on protein stabilization continues being questioned. For this reason, it is suggested to use the 'specific ion effect' instead of other misleading terms such as Hofmeister effect, Hofmeister series, lyotropic effect, and lyotropic series. In this review, we firstly discuss the controversial aspect of inorganic ion effects on water structures, and several possible contributors to the specific ion effect of protein stability. Due to recent overwhelming attraction of ionic liquids (ILs) as benign solvents in many enzymatic reactions, we further evaluate the structural properties and molecular-level interactions in neat ILs and their aqueous solutions. Next, we systematically compare the specific ion effects of ILs on enzyme stability and activity, and conclude that (a) the specificity of many enzymatic systems in diluted aqueous IL solutions is roughly in line with the traditional Hofmeister series albeit some exceptions; (b) however, the specificity follows a different track in concentrated or neat ILs because other factors (such as hydrogen-bond basicity, nucelophilicity, and hydrophobicity, etc) are playing leading roles. In addition, we demonstrate some examples of biocatalytic reactions in IL systems that are guided by the empirical specificity rule.

One-pot synthesis and loading of mesoporous SiO2 nanocontainers using micellar drugs as a template

A new approach is proposed for creating of pH-sensitive mesoporous silica nanocontainers with ultrahigh capacity for amphiphilic functional compounds.

Water-in-ionic liquid microemulsion formation in solvent mixture of aprotic and protic imidazolium-based ionic liquids

We report that water-in-ionic liquid microemulsions (MEs) are stably formed in an organic solvent-free system, i.e., a mixture of aprotic (aIL) and protic (pIL) imidazolium-based ionic liquids (ILs) containing the anionic surfactant dioctyl sulfosuccinate sodium salt (AOT). Structural investigations using dynamic light, small-angle X-ray, and small-angle neutron scatterings were performed for MEs formed in mixtures of aprotic 1-octyl-3-methylimidazolium ([C8mIm(+)]) and protic 1-alkylimidazolium ([CnImH(+)], n = 4 or 8) IL with a common anion, bis(trifluoromethanesulfonyl)amide ([TFSA(-)]). It was found that the ME structure strongly depends on the mixing composition of the aIL/pIL in the medium. The ME size appreciably increases with increasing pIL content in both [C8mIm(+)][TFSA(-)]/[C8ImH(+)][TFSA(-)] and [C8mIm(+)][TFSA(-)]/[C4ImH(+)][TFSA(-)] mixtures. The size is larger for the n = 8 system than that for the n = 4 system. These results indicate that the shell part of MEs is composed of both AOT and pIL cation, and the ME size can be tuned by pIL content in the aIL/pIL mixtures.

Micellization of sodium laurylethoxysulfate (SLES) and short chain imidazolium ionic liquids in aqueous solution

In the present study the interactions between an anionic surfactant sodium laurylethoxysulfate (SLES) and three short chain imidazolium (1-butyl-3-methylimidazolium) based ionic liquids (bmim-octyl SO4, bmim-methyl SO4 and bmim-BF4) in aqueous solution have been investigated. Generally when a surfactant is dissolved in a hydrophilic ionic liquid aqueous solution the critical micelle concentration (cmc) obtained is attributed to the surfactant because the ionic liquid (IL) is considered to be only a cosolvent. However, some short hydrophilic ionic liquids posses surface activity in aqueous solution and behave like a surfactant. In that case mixed aggregates between surfactant and ionic liquid can be formed. The three SLES/IL systems here studied have been treated as typical binary surfactant mixtures in aqueous solution. Surface tension measurements have revealed that mixed aggregates and monolayers of surfactant and ionic liquid instead of single surfactant are responsible for the surface active properties of these aqueous solutions. From the Regular Solution Theory, negative interaction parameters (β) for mixed aggregates and monolayers have been found for all SLES/IL mole ratios indicating synergism between the anionic surfactant and the ionic liquids.

Solvent nanostructure, the solvophobic effect and amphiphile self-assembly in ionic liquids

The ability of ionic liquids (ILs) to support amphiphile self-assembly into a range of mesophase structures has been established as a widespread phenomenon. From the ILs evaluated as self-assembly media, the vast majority have supported some lyotropic liquid crystal phase formation. Many neat ionic liquids have been shown to segregate into polar and non-polar domains to form a nanostructured liquid. A very strong correlation between the nanostructure of the ionic liquid and its characteristics as an amphiphile self-assembly solvent has been found. In this review we discuss ionic liquids as amphiphile self-assembly media, and identify trends that can be used to distinguish which ionic liquids are likely to have good promotion properties as self-assembly media. In particular these trends focus on the nanostructure of neat ionic liquids, their solvent cohesive energy density, and the related solvophobic effect. We forecast that many more ILs will be identified as amphiphile self-assembly solvents in the future.

Ionic and Molecular Liquids: Working Together for Robust Engineering

Because of their outstanding versatility, room-temperature ionic liquids (RTILs) are utilized in an ever increasing number of novel and fascinating applications, making them the Holy Grail of modern materials science. In this Perspective, we address the fundamental research and prospective applications of RTILs in combination with molecular liquids, concentrating on three significant areas: (1) the use of molecular liquids to decrease the viscosity of RTILs; (2) the role of RTIL micelle formation in water and organic solvents; and (3) the ability of RTILs to adsorb pollutant gases. Current achievements are examined, and future directions for the potential uses of RTILs are outlined.

Interaction of nonionic surfactants and hydrophilic ionic liquids in aqueous solutions: can short ionic liquids be more than a solvent?

The interaction between an ethoxylated nonionic surfactant (C(12-14)EO(8)) and three conventional hydrophilic imidazolium-based ionic liquids (bmim-octyl SO(4), bmim-methyl SO(4), and bmim-BF(4)) in aqueous solution has been investigated. In most of the reported studies where a surfactant is dissolved in an ionic liquid aqueous solution, conventional ionic liquids are merely considered to be solvents. Consequently, the resulting critical micelle concentration (cmc) is considered to be that of the surfactant. However, given that the three ionic liquids selected showed the typical shape of a surface-active compound when the surface tension was plotted against concentration, the role of these compounds as secondary surfactants and consequently the possibility of mixed-micelle formation have been investigated. Different series of experiments where a surfactant and an ionic liquid were combined in a wide range of mole ratios have been performed and treated as typical binary surfactant systems in aqueous solution. It has been found for the three surfactant/ionic liquid systems that depending on the surfactant mole fraction, α(1), attractive or repulsive interactions in mixed-micelle formation are produced. Therefore, when we select the appropriate α(1) these systems can be adjusted to a given application, depending on whether monomers or micelles are mainly required.