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ABSTRACT: The aggregation behavior of long-chain imidazolium ionic liquids, 1-alkyl-3-methyl-imidazolium bromide (CnmimBr, n = 12, 14, 16) was studied by surface tension measurements in a room temperature ionic liquid, ethylammonium nitrate (EAN),
at various temperatures. A series of parameters including critical micelle concentration (cmc), surface tension at the cmc
(γ
cmc), and the effectiveness of surface tension reduction (Πcmc) were obtained. In addition, from the cmc values and their temperature dependence, we estimated the thermodynamic parameters
of the micelle formation, DGm0 \Delta G_{\rm{m}}^0 , DHm0 \Delta H_{\rm{m}}^0 , and DSm0 \Delta S_{\rm{m}}^0 . The contribution of enthalpy term to the micelle formation is superior to that of entropy term. 1H NMR was performed to study the CnmimBr micelle formation mechanism in EAN.
KeywordsIonic liquid-CnmimBr-EAN-Micelle-Thermodynamic-
1H NMR
Colloid and Polymer Science 04/2012; 288(12):1225-1232. · 2.33 Impact Factor
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ABSTRACT: The phase behavior of a surfactant-like ionic liquid, N-hexadecyl-N-methylpyrrolidinium bromide (C(16)MPB), was studied in both water and a room temperature ionic liquid, ethylammonium nitrate (EAN). Polarized optical microscopy (POM) and small-angle X-ray scattering (SAXS) measurements were employed to investigate the phase behavior of the two systems and to determine which lyotropic liquid crystalline (LC) phases were formed. With increasing C(16)MPB concentration, an isotropic solution phase, a hexagonal (H(1)) phase, and a cubic phase (V(2)) are all present in either EAN or H(2)O. The structural parameters of the H(1) phase were calculated from SAXS patterns, which show the structural changes as a function of the amount of C(16)MPB. The rheological results reveal that the H(1) phase constructed by C(16)MPB in EAN displays a typical Maxwell behavior, whereas the H(1) phase formed by C(16)MPB in water shows a gel-like behavior, unlike traditional cationic surfactants. POM and differential scanning calorimetry (DSC) results demonstrate that the lyotropic LC phase in EAN has a higher thermal stability than that formed in H(2)O, which may be important to extend the applications of the LC phase.
The Journal of Physical Chemistry B 09/2010; 114(35):11382-9. · 3.70 Impact Factor
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ABSTRACT: To understand the composition and structure of microbial communities in acid (pH 3.0) mine drainage (AMD) associated with pyrite mine tailings in Anhui Province, China, molecular diversities of 16S rRNA and 18S rRNA genes were examined using a PCR-based cloning approach. Bacterial, archaeal and microeukaryotic clone libraries were constructed. In contrast to typical dominance of autotrophic acidophiles, genus Acidiphilium, which consists of mixotrophic acidophiles capable of chemoorganotrophic and photosynthetic metabolisms, was the largest group in the bacterial clone library. These mixotrophic organisms may be advantageous in the oligotrophic AMD environment of the study site (certain amounts of dissolved organic carbon and light) by switching between two modes of metabolisms. Unexpectedly, a large fraction of bacterial clones (12.7%) were related to the neutrophilic genus Legionella, which can cause Legionnaires' disease, a potentially lethal pneumonia. The eukaryotic 18S rRNA gene sequences were mostly related to Oxytricha, Nuclearia, and Penicillium. In the archaeal clone library, all the sequences were affiliated to the phylum Crenarchaeota, while the Euryarchaeota was not present.
Extremophiles 09/2010; 14(5):465-74. · 2.94 Impact Factor
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Berichte der deutschen chemischen Gesellschaft 01/2010; 2010(6):975 - 982. · 2.94 Impact Factor
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ABSTRACT: Uniform gold nanorods were prepared via a three-step seed-mediated growth method using a long-chain ionic liquid (IL), 1-dodecyl-3-methylimidazolium bromide (C12mimBr), as a capping agent. Both AgNO3 and HNO3 were used in the synthesis process. The aspect ratio, R, of the nanorods was increased when AgNO3 was replaced by HNO3. HRTEM revealed that these well-crystallized nanorods are all enclosed by five {100} facets and their cross section is pentagon. The interaction energies between the individual surfactants and different gold crystalline planes were calculated using a molecular dynamics simulation. The results showed that the interaction energies between the C12mimBr and different gold crystalline planes were smaller than those of CTAB based system. The catalytic experiments showed that the short gold nanorods had excellent catalytic efficiency for the reduction of nitro compounds.
10/2009;
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ABSTRACT: In the present contribution, results concerning the effect of temperature on the nonionic surfactant Triton X-100 based 1-butyl-3-methylimidazolium tetrafluoroborate (bmimBF4)-in-cyclohexane and bmimBF4-in-toluene ionic liquid (IL) reverse microemulsions are reported. Dynamic light scattering (DLS) along with freeze-fracture transmission electron microscopy (FF-TEM) measurements revealed that the sizes of single microemulsion droplets increased with increasing temperature. However, a decreased temperature led to the appearance of droplet clusters, which have also been observed previously when the single microemulsion droplets were swollen by added bmimBF4 to a certain extent (Gao, Y. A.; Vogit, A.; Hilfert, L.; Sundmacher, K. ChemPhysChem, 2008, 9, 1603-1609). Compared to traditional aqueous microemulsions, IL microemulsions revealed relatively high temperature-independence. The droplet-shaped microstructure was always kept in a large range of temperature. The temperature-independence is ascribed to the temperature-insensitive electrostatic attraction between the solubilized bmimBF4 and Triton X-100, which was considered to be the driving force for solubilizing bmimBF4 into the cores of Triton X-100 aggregates. Two-dimensional rotating frame nuclear Overhauser effect (NOE) experiments (ROESY) further confirmed the microstructural change with temperature.
Langmuir 02/2009; 25(3):1360-5. · 4.19 Impact Factor
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ABSTRACT: The role of four organic solvents in the formation process of 1-butyl-3-methylimidazolium tetrafluoroborate (bmimBF4) based ionic liquid (IL) microemulsions is investigated. The results showed that the addition of Triton X-100 remarkably decreased the conductivity of bmimBF4. The added organic solvents provided a strong apolar environment for the hydrophobic tails of Triton X-100 and caused the surfactant molecules to aggregate into the interfacial film of oil-in-bmimBF4 (O/IL) microemulsions. As a result, the conductivities of the solutions were initially increased because the insulative Triton X-100 molecules were assembled, which corresponded to increasing the concentration of continuous bmimBF4 solutions. The hydrophobic interaction between the dispersed organic solvents and the hydrophobic tails of Triton X-100 may be the driving force for the formation of O/IL microemulsions. The droplets of O/IL microemulsions were successively swollen by organic solvents, and a bicontinuous IL-containing microemulsion was observed by freeze-fracture transmission electron microscopy for the first time. The current study can help in further understanding the ILs-containing microemulsions and thereby improve microemulsion theory.
The Journal of Physical Chemistry B 02/2009; 113(5):1389-95. · 3.70 Impact Factor
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ABSTRACT: Nonionic surfactant Triton X-100 was shown to aggregate and form micellar aggregation in ionic liquids (ILs), 1-butyl-3-methylimidazolium tetrafluoroborate (bmimBF(4)) and 1-butyl-3-methylimidazolium hexafluorophosphate (bmimPF(6)). The surface tension measurements revealed that the dissolution of Triton X-100 in ILs depressed the surface tension in a manner analogous to aqueous solutions, and a relatively higher critical micellar concentration (CMC) was obtained compared to that of water. Freeze-fracture transmission electron microscopy (FFTEM) shows that the micelles have an irregular droplet shape, which is larger than that formed in water. The micellar droplets preferred to assemble into larger clusters. (1)H NMR and two-dimensional rotating frame nuclear Overhauser effect (NOE) experiments (2D ROESY) show that the addition of Triton X-100 destroyed the ion pairs of pure ILs due to the electrostatic interaction between the positively charged imidazolium cation of ILs and the electronegative oxygen atoms of oxyethylene (OE) units of Triton X-100. The electrostatic interaction behaves similar to hydrogen bond that occurred between the OE units of nonionic surfactants and water molecules in aqueous micelles and cooperates with solvatophobicity, leading to the formation of IL micelles. The 2D ROESY analysis reveals that the microstructures of Triton X-100-based micelles in ILs are not regular spherical, which accords with the FFTEM image. Similar to the aqueous micellar systems, the hydrophobic interaction or solvatophobicity was found to drive the formation of micelles.
The Journal of Physical Chemistry B 01/2009; 113(1):123-30. · 3.70 Impact Factor
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ABSTRACT: Three amphiphilic poly(oxyethylene)-poly(oxypropylene)-poly(oxyethylene) ethers triblock copolymers, denoted Pluronic L61 (PEO3PPO30PEO3), Pluronic L64 (PEO13PPO30PEO13), and Pluronic F68 (PEO79PPO30PEO79) were shown to aggregate and form micelles in ionic liquids (ILs) 1-butyl-3-methylimidazolium tetrafluoroborate (bmimBF4) and 1-butyl-3-methylimidazolium hexafluorophosphate (bmimPF6). The surface tension measurements revealed that the dissolution of the copolymers in ILs depressed the surface tension in a manner analogous to aqueous solutions. The cmcs of three triblock copolymers increase following the order of L61, L64, F68, suggesting that micellar formation was driven by solvatophobic effect. cmc and gamma cmc decrease with increasing temperature because hydrogen bonds between ILs and hydrophilic group of copolymers decrease and accordingly enhance the solvatophobic interaction. Micellar droplets of irregular shape with average size of 50 nm were observed. The thermodynamic parameters DeltaGm0, DeltaHm0, DeltaSm0 of the micellization of block copolymers in bmimBF4 and bmimPF6 were also calculated. It was revealed that the micellization is a process of entropy driving, which was further confirmed by isothermal titration calorimetry (ITC) measurements.
The Journal of Physical Chemistry B 08/2008; 112(33):10228-33. · 3.70 Impact Factor
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Berichte der deutschen chemischen Gesellschaft 07/2008; 2008(24):3769 - 3775. · 2.94 Impact Factor
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ABSTRACT: A common ionic liquid (IL), 1-butyl-3-methylimidazolium tetrafluoroborate (bmimBF(4)), is used as polar solvent to induce the formation of a reverse bmimBF(4)-in-toluene IL microemulsion with the aid of the nonionic surfactant Triton X-100. The swelling process of the microemulsion droplets by increasing bmimBF(4) content is detected by dynamic light scattering (DLS), conductivity, UV/Vis spectroscopy, and freeze-fracture transmission electron microscopy (FF-TEM). The results show that the microemulsion droplets initially formed are enlarged by the addition of bmimBF(4). However, successive addition of bmimBF(4) lead to the appearance of large-sized microemulsion droplet clusters (200-400 nm). NMR spectroscopic analysis reveal that the special structures and properties of bmimBF(4) and Triton X-100 together with the polar nature of toluene contribute to the formation of such self-assemblies. These unique self-assembled structures of IL-based microemulsion droplet clusters may have some unusual and unique properties with a number of interesting possibilities for potential applications.
ChemPhysChem 07/2008; 9(11):1603-9. · 3.41 Impact Factor
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ABSTRACT: In the present contribution, results concerning the role of small amounts of water in the 1-butyl-3-methylimidazolium tetrafluoroborate (bmimBF4)-in-cyclohexane ionic liquid (IL) reverse microemulsions are reported. Dynamic light scattering (DLS) revealed that the size of microemulsion droplets decreased remarkably with increasing water content although water is often used as a polar component to swell reverse microemulsions. It was thus deduced that the number of microemulsion droplets was increased which was confirmed by conductivity measurements. The states of dissolved water were investigated by Fourier transform IR (FTIR) spectroscopic analysis showing that water molecules mainly act as bound water. 1H NMR along with two-dimensional rotating frame nuclear Overhauser effect (NOE) experiments (ROESY) further revealed that water molecules were mainly located in the periphery of the polar core of the microemulsion droplets and behave like a chock being inserted in the palisade layer of the droplet. This increased the curvature of the surfactant film at the IL/cyclohexane interface and thus led to the decrease of the microemulsion droplet size. The order of surfactant molecules arranged in the interface film was increased and thus induced a loss of entropy. Isothermal titration calorimetry (ITC) indicated that an enthalpy increase compensates for the loss of entropy during the process of microstructural transition.
The Journal of Physical Chemistry B 04/2008; 112(12):3711-9. · 3.70 Impact Factor
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ABSTRACT: We demonstrate a novel ionic liquid (IL) microemulsion, consisting of 1-butyl-3-methylimidazolium tetrafluoroborate (bmimBF4) and nonionic surfactant Triton X-100 prepared in triethylamine which is used either as an organic solvent or a Lewis base. The effects of small amounts of added water on the microstructure of the IL microemulsion are investigated by various techniques. UV/Vis spectroscopic analysis and FTIR spectra indicate that these water molecules are not solubilized into the IL pools of the microemulsions. 1H NMR spectra further show that the added water binds with triethylamine to form a surrounding OH- base environment. Some of OH- ions enter the palisade layers of the IL microemulsions and a continuous base interface is created. The unique solubilization behavior of water reveals that it is possible to use the triethylamine microemulsions as a template to prepare metal hydroxides as well as metal oxides in the microemulsions, which is not possible when using traditional microemulsions.
ChemPhysChem 11/2007; 8(15):2211-7. · 3.41 Impact Factor
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ABSTRACT: Nonaqueous ionic liquid (IL) microemulsion consisting of IL, 1-butyl-3-methylimidazolium tetrafluoroborate (bmimBF(4)), surfactant TX-100, and toluene was prepared and the phase behavior of the ternary system was investigated. Electrical conductivity measurement was used for investigating the microregions of the nonaqueous IL microemulsions. On the basis of the percolation theory, the bmimBF(4)-in-toluene (IL/O), bicontinuous, and toluene-in-bmimBF(4) (O/IL) microregions of the microemulsions were successfully identified using insulative toluene as the titration phase. However, this method was invalid when conductive bmimBF(4) acted as the titration phase. The microregions obtained by conductivity measurements were further proved by electrochemical cyclic voltammetry experiments. The results indicated that the conductivity method was feasible for identifying microstructures of the nonaqueous IL microemulsions.
Journal of Colloid and Interface Science 10/2006; 301(2):612-6. · 3.07 Impact Factor
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ABSTRACT: Accumulated reports have suggested that activation of protein kinase C (PKC) isoforms may involve the activation of extracellular signal-regulated kinases 1/2 (ERK1/2) in the neuronal response to hypoxic stimuli. We have previously demonstrated that the membrane translocation or activation of conventional PKC (cPKC) betaII, gamma and novel PKC (nPKC) epsilon are increased in the early phase of cerebral hypoxic preconditioning in mice. However, the role of ERK1/2 in the development of cerebral hypoxic preconditioning is unclear. In the current study, we used Western blot analysis to investigate the effects of repetitive hypoxic exposure (H0-H6, n=6 for each group) on the levels of phosphorylation and protein expression of ERK1/2 in the frontal cortex and the whole hippocampus of mice. We found that the levels of phosphorylated ERK1/2, not protein expression of ERK1/2, decreased significantly in both cortex and hippocampus of the early hypoxic preconditioned mice (H1-H4), when compared to that of the normoxic group (p<0.05). In addition, a significant decrease (p<0.05) in the ERK1/2 protein expression, not the phosphorylated form of ERK1/2, was found both in the frontal cortex and hippocampus of mice followed hypoxia with previous hypoxia (H5 and H6). These results suggest that the decreased phosphorylation and downregulation of protein expression of ERK1/2 might be involved in the development of hypoxic preconditioning.
Neuroscience Letters 04/2006; 397(3):307-12. · 2.11 Impact Factor
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ABSTRACT: Cerebral ischemic/hypoxic preconditioning (I/HPC) is a phenomenon of endogenous protection that renders the brain tolerant to sustained ischemia/hypoxia. This profound protection induced by I/HPC makes it an attractive target for developing potential clinical therapeutic approaches. However, the molecular mechanism of I/HPC is unclear. Cyclic AMP (cAMP) response element binding protein (CREB), a selective nuclear transcriptional factor, plays a key role in the neuronal functions. Phosphorylation of CREB on Ser-133 may facilitate its transcriptional activity in response to various stresses. In the current study, we observed the changes in CREB phosphorylation (Ser-133) and protein expression in the brain of auto-hypoxia-induced HPC mice by using Western blot analysis. We found that the levels of phosphorylated CREB (Ser-133), but not protein expression of CREB, increased significantly (p<0.05) in the hippocampus and the frontal cortex of mice after repetitive hypoxic exposure (H2-H4, n=6 for each group), when compared to that of the normoxic (H0, n=6) or hypoxic exposure once group (H1, n=6). In addition, a significant enhancement (p<0.05) of CREB phosphorylation (Ser-133) could also be found in the nuclear extracts from the whole hippocampus of hypoxic preconditioned mice (H2-H4, n=6 for each group). These results suggest that the phosphorylation of CREB might be involved in the development of cerebral hypoxic preconditioning.
Biochemical and Biophysical Research Communications 02/2006; 340(2):661-7. · 2.48 Impact Factor
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ABSTRACT: Large-size single-crystal gold nanosheets have been successfully prepared by microwave heating of HAuCl(4) in ionic liquid, 1-butyl-3-methylimidazolium tetrafluoroborate, without any additional template agent. Transmission electron microscopy (TEM), electron diffraction (ED), scanning electron microscopy (SEM), and X-ray powder diffraction (XRD) were used to characterize the resultant gold nanosheets. It was demonstrated that the ionic liquid could act as template agent for the formation of gold nanosheets. The present synthesis route is very simple and fast. It can be expected that the method can be extended to the fabrication of other metal nanosheets in ionic liquids.
The Journal of Physical Chemistry B 09/2005; 109(30):14445-8. · 3.70 Impact Factor
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ABSTRACT: Both ionic liquids and water are typical green solvents. In this work, the phase behavior of the ternary system consisting of ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate (bmimPF6), TX-100, and water was determined at 25.0 degrees C. The water-in-bmimPF6, bicontinuous, and bmimPF6-in-water microregions of the microemulsions were identified by cyclic voltammetry method using potassium ferrocyanide K4Fe(CN)6 as the electroactive probe. Dynamic light scattering (DLS) and the UV-vis method were used to characterize the microemulsions. It was demonstrated that the hydrodynamic diameter (Dh) of the bmimPF6-in-water microemulsions is nearly independent of the water content but increases with increasing bmimPF6 content due to the swelling of the micelles by the ionic liquid. The UV-vis further confirmed the existence of water domains in the water-in-bmimPF6 microemulsions, and the salt potassium ferricyanide K3Fe(CN)6 could be dissolved in the water domains.
Langmuir 07/2005; 21(13):5681-4. · 4.19 Impact Factor
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ABSTRACT: Phase diagrams of two ionic liquids: hydrophobic 1-butyl-3-methylimidazolium hexafluorophosphate (bmim-PF(6)) and relatively hydrophilic 1-butyl-3-methylimidazolium tetrafluoroborate (bmim-BF(4)) in aqueous solutions of Brij 97 were determined at 25 degrees C. Two hexagonal liquid crystalline phases formed in bmim-PF(6)- and bmim-BF(4)-containing ternary systems were investigated by means of small-angle X-ray scattering (SAXS) and rheological techniques, with comparison of composition and temperature effects. From analysis of the SAXS data, bmim-PF(6) is dominantly penetrated between the oxyethylene chains of surfactant molecules, whereas bmim-BF(4) is mainly located in the water layer of hexagonal phases. The strength of the network of hexagonal phase formed in the Brij 97/water/bmim-BF(4) system is appreciably stronger than that of the Brij 97/water/bmim-PF(6) system, indicated by the smaller area of the surfactant molecule at the interface and the higher moduli (G', G' '). Temperature has a converse effect on the lattice parameters of the two hexagonal phases.
Langmuir 06/2005; 21(11):4931-7. · 4.19 Impact Factor
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ABSTRACT: Dodecyl polyoxyethylene(4) polyoxypropylene(5) ether (LS45) is an outstanding microemulsifier in supercritical CO2. The dynamic surface tension (DST) of this nonionic surfactant was investigated by using the maximum bubble pressure instrument. The effects of concentration and temperature on DST parameters (n, ti, t*, tm, and R1/2) and its adsorption mechanism were discussed by Rosen's empirical equation and the asymptotic Ward and Tordai equation for the LS45 solution system. Finally, the parameters at 1 s related to Draves's wetting performance, pC20(1s), C1s (i)*, and C1s*, analyzed. The results showed that were with increase of bulk concentration and temperature, dynamic surface activity increased. Parameters at 1 s indicated that LS45 is of high surface activity and a very good wetting agent. One‐second related parameters, C1s (i)* and C1s*, are valuable in the treatment of practical applications of surfactants. Optimum wetting can be expected at the concentration of 4.8×10−4 mol/dm3 for LS45 solution.
Journal of Dispersion Science and Technology 01/2005; 26(6):745-751. · 0.56 Impact Factor
