Protic ionic liquids: solvents with tunable phase behavior and physicochemical properties

Methylammonium formate as a mobile phase modifier for totally aqueous reversed-phase liquid chromatography

Although alkylammonium ionic liquids (ILs) such as ethylammonium nitrate and ethylammonium formate have been used as mobile phase "solvents" for liquid chromatography (LC), we have shown that the IL methylammonium formate (MAF), in part because of its lower viscosity as compared to other ILs, can be an effective replacement for methanol (MeOH) in reversed-phase LC. Plots of log retention factor versus the fraction of MeOH and MAF in the mobile phase indicate quite comparable solvent strength slope values of 2.50 and 2.05, respectively. Using a polar endcapped C18 column, furazolidone and nitrofurantoin using 20% MAF-80% water could be separated in 22 min but no baseline separation is possible using MeOH as the modifier, even down to 10%. Suppression of silanol peak broadening effects by MAF is important, permitting a baseline separation of pyridoxine, thiamine, and nicotinamide using 5% MAF-95% water at 0.7 mL/min. Using 5% MeOH-95% water, severe peak broadening for thiamine is evident. The compatibility of MAF as a mobile phase modifer at the 5% level for LC with mass spectrometry detection of water-soluble vitamins is also shown.

Synthesis and characterization of new pyrrolidinium based protic ionic liquids. Good and superionic liquids

New pyrrolidinium-cation-based protic acid ionic liquids (PILs) were prepared through a simple and atom-economic neutralization reactions between pyrrolidine and Brønsted acids, HX, where X is NO 3 (-), HSO 4 (-), HCOO (-), CH 3COO (-) or CF 3COO (-) and CH 3(CH 2) 6COO (-). The thermal properties, densities, electrochemical windows, temperature dependency of dynamic viscosity and ionic conductivity were measured for these PILs. All protonated pyrrolidinium salts studied here were liquid at room temperature and possess a high ionic conductivity (up to 56 mS cm (-1)) at room temperature. Pyrrolidinium based PILs have a relatively low cost, a low toxicity and exhibit a large electrochemical window as compared to other protic ionic liquids (up 3 V). Obtained results allow us to classify them according to a classical Walden diagram and to determinate their "Fragility". Pyrrolidinium based PILs are good or superionic liquids and shows extremely fragility. They have wide applicable perspectives for fuel cell devices, thermal transfer fluids, and acid-catalyzed reaction media as replacements of conventional inorganic acids.

Diversifying the Solid State and Lyotropic Phase Behavior of Nonionic Urea-Based Surfactants

The solid state and lyotropic phase behavior of 10 new nonionic urea-based surfactants has been characterized. The strong homo-urea interaction, which can prevent urea surfactants from forming lyotropic liquid crystalline phases, has been ameliorated through the use of isoprenoid hydrocarbon tails such as phytanyl (3,7,11,15-tetramethyl-hexadecyl) and hexahydrofarnesyl (3,7,11-trimethyl-dodecyl) or the oleyl chain (cis-octadec-9-enyl). Additionally, the urea head group was modified by attaching either a hydroxy alkyl (short chain alcohol) moiety to one of the nitrogens of the urea or by effectively "doubling" the urea head group by replacing it with a biuret head group. The solid state phase behavior, including the liquid crystal-isotropic liquid, polymorphic, and glass transitions, is interpreted in terms of molecular geometries and probable hydrogen-bonding interactions. Four of the modified urea surfactants displayed ordered lyotropic liquid crystalline phases that were stable in excess water at both room and physiological temperatures, namely, 1-(2-hydroxyethyl)-1-oleyl urea (oleyl 1,1-HEU) with a 1D lamellar phase (Lalpha), 1-(2-hydroxyethyl)-3-phytanyl urea (Phyt 1,3-HEU) with a 2D inverse hexagonal phase (HII), and 1-(2-hydroxyethyl)-1-phytanyl urea (Phyt 1,1-HEU) and 1-(2-hydroxyethyl)-3-hexahydrofarnesyl urea (Hfarn 1,3-HEU) with a 3D bicontinuous cubic phase (QII). Phyt 1,1-HEU exhibited rich mesomorphism (QII1, QII2, Lalpha, LU, and HII), as did one other surfactant, oleyl 1,3-HEU (QII1, QII2, Lalpha, LU, and HII), in the study group. LU is an unusual phase which is mobile and isotropic but possesses shear birefringence, and has been very tentatively assigned as an inverse sponge phase. Three other surfactants exhibited a single lyotropic liquid crystalline phase, either Lalpha or HII, at temperatures >50 degrees C. The 10 new surfactants are compared with other recently reported nonionic urea surfactants. Structure-property correlations are examined for this novel group of self-assembling amphiphiles.

Formation of amphiphile self-assembly phases in protic ionic liquids

A range of protic ionic liquids (PILs) have been identified as being capable of supporting the self-assembly of the nonionic surfactants myverol 18-99 K (predominantly monoolein) and phytantriol. PIL-surfactant penetration scans have provided a high throughput technique to determine which lyotropic liquid crystalline phases were formed in the 40 PIL-surfactant systems investigated. Lamellar, inverse hexagonal, and bicontinuous cubic phases that are stable in excess PIL have been observed in surfactant-PIL systems. The studied PILs possess a wide range of solvent properties, including surface tension and viscosity. The nature of the formed amphiphile self-assembly phases is discussed in terms of the PIL structure and solvent properties.

Interface between Ionic and Nonionic Liquids: Theoretical Study

We use a Flory-Huggins type approach to calculate the structure and the surface tension coefficient of the boundary between ionic and nonionic liquids. The mixture of ionic and nonionic liquids is treated as a "three-component" system including anions, cations, and neutral molecules. We show that if the affinities of the cations and the anions to the neutral molecules are different, the interface comprises an electric double layer. The presence of this layer (uncompensated electric field) stabilizes the interface: the field inhibits the ions segregation at the interface and increases the surface tension. On the other hand, the short-range volume interactions promote the segregation and decrease the surface tension. Furthermore, the surface tension coefficient can be negative, if the difference of the affinities is high enough. It implies a possibility of microphase separation of the system.

Many protic ionic liquids mediate hydrocarbon-solvent interactions and promote amphiphile self-assembly

A large number of protic ionic liquids (PILs) have been found to mediate solvent-hydrocarbon interactions and promote amphiphile self-assembly. Hexagonal, cubic, and lamellar lyotropic liquid crystalline phases were observed in PIL-hexadecyltrimethylammonium bromide systems. The driving force for the formation of the self-assembled aggregate structures has been attributed to an entropic contribution to the free energy of association, analogous to the hydrophobic effect in water. The specific aggregate structures formed depend upon the cationic and anionic components of the PIL and their interactions with the amphiphiles.

Protic Ionic Liquids and Ionicity

Protic ionic liquids (PILs) are a subset of ionic liquids formed by the equimolar mixing of a Brønsted acid and a Brønsted base. PILs have been categorized as poor ionic liquids. However, the issue of assessing the ionicity of PILs is still a matter of debate. In this work we studied some physicochemical properties of three chosen PILs, namely, ethanolammonium acetate (EOAA), 2-methylbutylammonium formate (2MBAF), and pentylammonium formate (PeAF), at the initial equimolar (stoichiometric) acid/base ratio and in the presence of excess acid and base. DSC phase-transition studies along with NMR, IR, and Raman spectroscopy were performed on the chosen PILs. The results are discussed in terms of the degree of ionization (extent of proton transfer from the Brønsted acid to Brønsted base), and the possibility of the formation of polar 1:1 complexes and larger aggregates in the neat stoichiometric PILs.