Effects of alcohols and counterions on the phase behavior of 1-octyl-3-methylimidazolium chloride aqueous solution

Phase behavior of ternary systems involving 1-octyl-3-methylimidazolium chloride ([C8mim]Cl), water, and different alcohols (1-hexanol, 1-octanol, 1-decanol, and 1-dodecanol) is investigated at 25 degrees C. With the use of polarized optical microscopy and small-angle X-ray scattering techniques, lyotropic lamellar phases (Lalpha) are identified in all systems, the formation of which is considered as a synergetic result of the hydrophobic force and the hydrogen-bonded network comprising an imidazolium ring, Cl-, water, and alcohols. In these Lalpha phases, alcohol molecules play important roles not only because they could partly penetrate into the palisade layer with their hydroxyl groups extruded to form the network at the aggregate interface, but also because they could partly locate themselves in the interior of the hydrophobic bilayers to twist with the alkyl chains of [C8mim]Cl. Influencing factors such as the carbon chain length and content of different alcohols on these Lalpha phases are discussed. With comparison to analogous ternary systems of [C8mim]BF4 and [C8mim]PF6, it is found that the strong interaction between counterions and alcohols favors the appearance of ordered assemblies.     

Photoinduced electron-transfer reactions in two room-temperature ionic liquids: 1-butyl-3-methylimidazolium hexafluorophosphate and 1-octyl-3-methylimidazolium hexafluorophosphate

Photoinduced electron transfer in two room-temperature ionic liquids, 1-butyl-3-methylimidazolium hexafluorophosphate (BMIM-PF(6)) and 1-octyl-3-methylimidazolium hexafluorophosphate (OMIM-PF(6)), has been investigated using steady-state fluorescence quenching of 9,10-dicyanoanthracene with a series of single electron donors. From these fluorescence quenching rates, reorganization energy (lambda) values and k(diff) values can be derived from a Rehm-Weller analysis. In many cases, these fluorescence quenching reactions occur at rates larger than what would be expected based on the Smoluchowski equation. In addition, lambda values of 10.1 kcal/mol and 16.3 kcal/mol for BMIM-PF(6) and OMIM-PF(6), respectively, have been determined.     

The role of 1-octyl-3-methylimidazolium hexafluorophosphate in anticorrosion coating formula development

A hydrophobic ionic liquid (1-octyl-3-methylimidazolium hexafluorophosphate, C₈mimPF₆) with a function of inhibiting corrosion was encapsulated at different concentrations in the copolymer of poly (methyl methacrylate) and poly (butyl acrylate) through miniemulsion polymerization. These latexes were coated on steel samples whose corrosion properties were evaluated by electrochemical techniques. It was found that increasing the C₈mimPF₆ concentration from 0 wt% to 30 wt%, the corrosion inhibition efficiency was remarkably improved from 41% to 89% based on the charge transfer resistance and from 64% to 87% based on the corrosion current density, respectively. The ionic liquid did not attend the reaction during latex preparation but behaved as corrosion inhibitors on the steel surface. Such an anticorrosion effect could be ascribed to the physical adsorption of the C₈mim⁺ cation on the reaction sites and the hydrophobicity enhancement resulting from the hydrophobic PF₆^? anion.     

Effect of electrolytes on surface tension and surface adsorption of 1-hexyl-3-methylimidazolium chloride ionic liquid in aqueous solution

Surface and bulk properties of 1-hexyl-3-methylimidazolium chloride [C₆mim][Cl] as an ionic liquid (IL) have been investigated by surface tension and electrical conductivity techniques at various temperatures. Results reveal that the ionic liquid behaves as surfactant-like and aggregates in aqueous solution. Critical aggregation concentration (cac) values obtained by conductivity and surface tension measurements are in good agreement with values found in the literature. A series of important and useful adsorption parameters including cac, surface excess concentration (Γ), and minimum surface area per molecule (A_min) at the air + water interface were estimated from surface tension in the presence and absence of different electrolytes. Obtained data show that the surface tension as well as the cac of [C₆mim][Cl] is reduced by electrolytes. Also, values of surface excess concentration (Γ) show that the IL ions in the presence of electrolyte have much larger affinity to adsorption at the surface and this affinity increased in aqueous electrolyte solution in the order of I^? > Br^? > Cl^? for counter ion of salts that was explained in terms of a larger repulsion of chloride anions from interface to the bromide and iodide anion as well as difference in their excess polarizability.     

Hierarchical structure and dynamics of an ionic liquid 1-octyl-3-methylimidazolium chloride

We have performed the heat capacity, neutron diffraction, and neutron quasielastic scattering measurements of an ionic liquid 1-octyl-3-methylimidazolium chloride (C8mimCl). The heat capacity data revealed that C8mimCl exhibits a glass transition with a large heat capacity jump at T(g) = 214 K, which is lower than T(g) of C4mimCl with a shorter alkyl-chain. In the neutron diffraction measurement for a deuterated analogue, d-C8mimCl, the peaks associated with the inter-domain, inter-ionic, and inter-alkyl-chain correlations appeared at (3, 11, and 14) nm(-1), respectively. The temperature dependence of these peaks indicates that the packing of the alkyl-chains becomes more compact and the domains become more vivid and larger as decreasing temperature. The quasielastic neutron scattering measurements using neutron spin echo and time-of-flight type instruments demonstrated that C8mimCl has faster relaxations probably owing to the alkyl-group and a slower relaxation owing to the ions. The latter relaxation, which is related to the glass transition, is of non-exponential as in the α relaxation of glass-forming molecular liquids. The relaxation of domains could not be observed in the present experiment but should have relaxation times longer than 100 ns. This is the first report to clarify temperature dependence of the hierarchical structure and relaxations simultaneously for a typical ionic liquid.     

微波辅助溴化1-辛基-3-甲基咪唑盐提取黄芩苷机制初步探讨

在微波辅助法作用下,研究了[C8mim]Br水溶液作为提取溶剂从黄芩药材中提取黄芩苷的效果,并与药典提取方法进行了比较;进一步从溶解度、细胞破壁以及离子液体对植物酶活性抑制作用等方面,初步探讨了[C8mim]Br溶液提取黄芩苷的机制。研究结果表明:[C8mim]Br溶液作为提取溶剂可以有效提取黄芩药材中的黄芩苷,与药典提取方法比较提取时间由3 h缩短到5 min,提取率提高了0.79%;与70%乙醇和水相比,[C8mim]Br溶液对黄芩苷具有更好的溶解度;样品经不同溶剂提取后的扫描电镜图显示,[C8mim]Br溶液具有破碎细胞的作用;此外,[C8mim]Br溶液对黄芩药材中存在的黄芩苷水解酶的活性具有抑制作用。     

Structural studies of the phase, aggregation and surface behaviour of 1-alkyl-3-methylimidazolium halide + water mixtures

The surface, phase and aggregation behaviour of mixtures of 1-alkyl-3-methylimidazolium halide, [C(n)mim]X, where n is the alkyl chain length, with water has been explored using a variety of methods. Critical micelle concentrations (cmc) and micelle structures have been determined for aqueous [C(n)mim]Br solutions for n=2, 4, 6, 8, and 10. Small-angle neutron scattering (SANS) measurements reveal that for the n=8 and 10 systems, at concentrations just above the cmc, small near-spherical aggregates exist, which, after initial growth, possess core radii (aggregation numbers) at intermediate concentrations of 10.5+/-0.5 Angstrom (22+/-2) and 13.2+/-0.5 Angstrom (40+/-3), respectively, for n=8 and n=10. Towards higher concentrations, the aggregates appear to grow, with the aggregates in the [C(10)mim]Br system becoming increasingly elongated (prolate) with increasing concentration. No evident aggregates are formed in the systems with n=2 and 4. In the n=6 system, it appears that oblate aggregates with radius approximately 9 Angstrom form at the cmc and that the radius increases with increasing concentration. For longer alkyl chain lengths, at high concentrations lyotropic mesophases form in some systems. The mesophase region for the [C(8)mim]Cl system has been explored across the composition range using X-ray diffraction and (2)H NMR spectroscopy. Both techniques suggest that a major hexagonal phase with lattice parameter of 29.5+/-0.5 Angstrom coexists with a minor lamellar phase (23.5+/-0.3 Angstrom) or possibly a second hexagonal phase (27.1+/-0.4 Angstrom). The area per adsorbed molecule at the surface of [C(8)mim]Br solutions has been measured as a function of concentration using neutron reflectometry. A minimum in the area per molecule behaviour is coincident with a minimum identified in the surface tension isotherm occurring close to the cmc. The data suggest depletion of [C(8)mim]Br from the surface region occurs at concentrations immediately above the cmc.     

Effect of a copolymer poly(4-styrenesufonic acid-co-maleic acid) sodium salt on aggregation behavior of surface active ionic liquid 1-tetradecyl-3-methylimidazolium bromide and structurally similar conventional surfactant tetradecyltrimethylammonium bromide in aqueous media

The complex formation of anionic copolymer poly(4-styrenesufonic acid-co-maleic acid) sodium salt (PSSA-co-MA) with surfactant tetradecyltrimethylammonium bromide (TTAB) and surface active ionic liquid (SAIL) 1-tetradecyl-3-methylimidazolium bromide ([C₁₄mim][Br]) has been studied in aqueous media by utilizing various techniques such as tensiometry, conductometry and fluorimetry. Conductometric and tensiometric curve of all the investigated systems demonstrate four break points corresponding to four transition states. All the thermodynamic and surface properties of surfactant-polyelectrolyte systems have been determined by conductance and surface tension measurements respectively. The value of cmc decreases with increasing the concentration of polyelectrolyte for studied systems. But it has been observed that, the lowering in cmc values is more in [C₁₄mim][Br]-PSSA-co-MA system than TTAB-PSSA-co-MA system, although the differences in cmc are not much significant. The lowering in cmc of [C₁₄mim][Br]-PSSA-co-MA system shows that ionic attractions between cationic head group [C₁₄mim]⁺ and anionic parts (SO₃^? and COOH), are stronger than those in TTA⁺ and anionic parts (SO₃^? and COOH). The results indicated that the [C₁₄mim][Br]-PSSA-co-MA complexes are comparatively more surface active than TTAB-PSSA-co-MA complexes. The fluorescence probe behaviour also confirms cmc value and provides aggregation number (N_agg). Finally all the findings of [C₁₄mim][Br] and TTAB have been compared.     

Temperature dependence of the microstructure of 1-butyl-3-methylimidazolium tetrafluoroborate in aqueous solution

Many applications of ionic liquids (ILs) are closely related with their microstructure in mixtures. For example, morphology and pore size of the MCM-41 prepared in aqueous ILs are greatly dependent on the aggregation behavior of the ILs in water. Therefore, the study on the microstructure of ILs in aqueous solutions is of great importance. In this work, ¹H NMR, dynamic light scattering and attenuated total reflection infrared spectroscopy have been used to investigate the temperature effect on the structures of aqueous 1-butyl-3-methylimidazolium tetrafluoroborate ([C₄mim][BF₄]) solutions. It was shown that the size of the IL aggregates becomes larger with decreasing temperature. When the system temperature is below the upper critical solution temperature (UCST) of the binary mixture at about 4 °C, the aggregate size of the IL is larger than 1000 nm. Additionally, the two-dimensional IR results reveal that at low IL concentrations, H₂O can interact with [BF₄]⁻ prior to the CH groups of the imidazolium ring, whereas cation and anion of the IL tend to form aggregate at high IL concentrations. With the decrease of temperature, the interactions between cation and anion of the IL become stronger, but those between the IL and water become weaker, thereby resulting in the growth of the aggregate of cation with anion of the IL. This result may give a reasonable explanation for the origin of the UCST behavior of aqueous [C₄mim][BF₄] solution.     

Influence of the Hofmeister anions on self-organization of 1-decyl-3-methylimidazolium chloride in aqueous solutions

Inorganic salts usually influence water structure affecting the hydration of the molecules which lead to a salting-in or a salting-out effect of hydrophobic compounds. Specific conductivity and isothermal titration calorimetry have been used to study the effect of inorganic salts on aggregation of the cationic surfactant 1-decyl-3-methylimidazolium chloride in aqueous solutions. The effect of the concentration, the nature of the anion and temperature on micelle formation were studied. A decreasing critical micelle concentration (CMC) due to the weakening electrostatic repulsion between the headgroups was observed. The salts used in this investigation decreased the CMC and degree of micelle ionization in the order of Cl(-)相似文献   

Molecular recognition with micellar and micelle-like aggregates in aqueous media

In this article, attention is directed to molecular recognition by micellar aggregates made with ionic surfactants involving directed interactions of substrates. Particular emphasis is placed on chiral recognition of enantiomers by hydrogen bonding functionalities incorporated in hydrophobic micellar interior. Hydrophobic properties within micelles, the ordering of their polar headgroups containing chiral functionalities essential for the recognition and the cessation of micellar kinetic association-dissociation with polymerization and immobilization of the surfactants on the support are discussed.     

Effect of alkali halide salt additives on the structure of poly(vinyl alcohol) films cast from aqueous solutions

The molecular structures of poly(vinyl alcohol) films cast from polymer aqueous solutions (1 mol/L) containing 0.1 mol/L of LiCl, NaF, NaCl, KCl, CsCl, KBr, and KI salts are studied via FTIR spectroscopy. The addition of any of these salts except LiCl leads to an increase in the degree of crystallinity of poly(vinyl alcohol) in a film by a factor of 1.3–1.6. In contrast, LiCl significantly decreases the crystallinity of the polymer. It is found that, in the IR spectra of the films containing salt additives, the position of the maximum in the band of the stretching vibrations of OH groups of the polymer is shifted relative to its position in the IR spectra of the films free of salt additives. The magnitude and direction of this band shift depend on the types (anion or cation) and radii of ions comprising salts. The observed effects are interpreted in terms of existing ideas on the interactions of salt ions with the OH groups of water and other hydroxyl-containing molecules.     

Structure and conformation properties of 1-alkyl-3-methylimidazolium halide ionic liquids: a density-functional theory study

The structures and conformational properties of 1-alkyl-3-methylimidazolium halide ionic liquids have been studied with a Becke's 3 Parameter functional method. The interaction mechanisms between the cation and the anion in 1-ethyl-3-methylimidazolium (Emim+) halide and 1-butyl-3-methylimidazolium (Bmim+) halide ionic liquids were investigated using 6-31G*, 6-31++G**, and 6-311++G** basis sets. Forty structures of different ion pairs were optimized and geometrical parameters of them have been discussed in details. Halide ions (Cl- or Br-) have been gradually placed in different regions around imidazolium cation and the interaction energies between the anion and the cation have been calculated. Theoretical results indicate that there are four activity regions in the vicinity of the imidazolium cations, in these regions the imidazolium cations and the halide anions formed stable ion pairs. Imidazolium cations can form hydrogen bond interactions with one, two or three but no more than three nearest halide anions. The halide ions are situated in hydrogen bond positions rather than at random.     

Enzymatic saccharification of cellulose in aqueous-ionic liquid 1-ethyl-3-methylimidazolium dimethylphosphate-DMSO media

Ionic liquid (IL) 1-ethyl-3-methylimidazolium dimethylphosphate ([Emim]DMP) was chosen as an environment-friendly solvent to enzymatically hydrolyze cellulose in situ. Under optimal reaction condition, 80.2 % of cellulose (10 mg mL⁻¹) were converted to glucose in aqueous-IL-DMSO (φ _r = 74: 25: 1) media at 55°C in 18 h. Finally, fermentability of the recovered hydrolyzates was evaluated using Saccharomyces cerevisiae which is able to ferment hydrolyzates efficiently, the ethanol production was 0.44 g g⁻¹ of glucose within 24 h of the process. Such information is vital for the saccharification of more complex cellulose materials and for the fermentation of hydrolyzates into biofuel.     

Effects of l-arginine on aggregates of fatty-acid/potassium soap in the aqueous media

In the present study, we investigated the effects of l-arginine on aggregates of fatty acid/fatty soap in the aqueous media as a function of pH, by means of hydrogen ion titration, viscoelastic measurement, cryo-transmission electron microscopy and phase contrast microscopy. We found out that l-arginine effectively inhibits the oil droplet growth of oleic acid or octanoic acid. The effect is explained in terms of the adsorption of arginine at the microscopic drop surface, or at the oil/water microinterface through the hydrophobic effect assisted by the hydrogen bonds between carboxyl group of fatty acid and carboxylate of arginine. As to the crystallization of lauric acid at temperatures below the melting point of the hydrocarbon chain, arginine is not effective. In addition, we also found out that the strong binding of arginine cation to anionic oleate micells induces the dominant micellar growth. l-arginine has been used in many refolding systems to suppress protein aggregation. These effects of l-arginine on the aggregates of fatty acid/fatty soap in the aqueous media observed in the present study is expected to form a basis to the specific function displayed in the protein refolding.     

Thermophysical properties of aqueous solutions of the 1-ethyl-3-methylimidazolium tricyanomethanide ionic liquid

Thermophysical behavior of the binary system [water + 1-ethyl-3-methylimidazolium tricyanomethanide ionic liquid (IL)] was thoroughly characterized through systematic measurements of (vapor + liquid) equilibria (water activity a_w), mixing enthalpy, density, viscosity, and refractive index. The measurements were performed in the entire composition range and/or specifically in the highly dilute IL region, at T = 298.15 K or as a function of temperature in the range from (288.15 to 318.15) K. Effective experimental methods minimizing IL sample consumption, using flow arrangements, instrument couplings and high degree of automation were preferably employed. In particular, the a_w determination based on the chilled-mirror dew point technique and implemented by an AquaLab 4TE instrument was identified as a generally superior approach to study VLE of (water + IL) systems. Excess thermodynamic properties (Gibbs free energy, enthalpy, heat capacity, and volume) and property deviations from the linear mixing rule (viscosity, refractive index) were evaluated, Padé approximants being used to correlate adequately their complex composition dependences. The extensive a_w data were processed by a two-step procedure fitting first the temperature dependence at each isopleth and subsequently the composition dependence at each isotherm. Good estimates could be thus obtained for derivative thermal properties (enthalpy, heat capacity). Alternatively, the water activity and excess enthalpy data were correlated simultaneously by a NRTL-type model, providing their compact, thermodynamically consistent and adequate representation. Despite small absolute values of excess Gibbs free energy (G^E), the system is revealed to be highly nonideal, the small G^E resulting from close compensation of its large enthalpy and entropy contributions. Large endothermic effects and an enhanced increase of entropy upon mixing found for this system indicate relative weakness of interactions between unlike molecules and a massive structure breakage in the solution. Positive values of excess volume and negative values of viscosity and refractive index deviations found in the major part of the composition range corroborate this general energetic and structural pattern, although the situation appears to be more complicated in the highly dilute IL region, where these properties congruently exhibit a sign inversion.     

Thermophysical properties of 1-methyl-3-methylimidazolium dimethylphosphate and 1-ethyl-3-methylimidazolium diethylphosphate

The density and surface tension of 1-methyl-3-methylimidazolium dimethylphosphate, [C₁mim](CH₃O)₂PO₂ and 1-ethyl-3-methylimidazolium diethylphosphate, [C₂mim](CH₃CH₂O)₂PO₂ ionic liquids have been measured over the temperature range from (283.15 to 338.15) K. The coefficients of thermal expansion were calculated from the experimental density results using an empirical correlation for T = (283.15 to 338.15) K. Molecular volume and standard entropies of these ILs were calculated from the experimental density values. The surface properties of ILs were investigated. The critical temperature and enthalpy of vapourization were also discussed.     

Nucleophilicity in ionic liquids. 3. Anion effects on halide nucleophilicity in a series of 1-butyl-3-methylimidazolium ionic liquids

We have continued the study of halide nucleophilicity in ionic liquids, concentrating on the effect of changing the anion ([BF(4)](-), [PF(6)](-), [SbF(6)](-), [OTf](-), and [N(Tf)(2)](-)) when the cation is [bmim](+) (where bmim = 1-butyl-3-methylimidazolium). It was found that the nucleophilicities of all the halides were lower in all of the ionic liquids than in dichloromethane. Changing the anion affected the order of halide nucleophilicity, e.g., in [bmim][BF(4)] the order of nucleophilicity was Cl(-)>Br(-)>I(-) while in [bmim][N(Tf)(2)] the order was Cl(-)相似文献   

Intermolecular energy transfer from Tb3+ to Eu3+ in aqueous aggregates and on the surface of human cells

Efficient intermolecular energy transfer from carbostyril 124-sensitized Tb(3+) to Eu(3+) in aqueous aggregates is reported. This energy transfer was also recapitulated on the cell surface of a human kidney cell line (HEK-293T) and imaged by fluorescence microscopy as an example for the applicability of this energy transfer probe for imaging in biological systems.