Peptide bond formation catalyzed by α-chymotrypsin in ionic liquids

α-Chymotrypsin catalyzed peptide bond formation was studied in ionic liquids using the synthesis of a protected fragment of Leu-enkephalin, ZTyrGlyGlyOEt, as model reaction. MOEMIM·PF₆ was found to be the most favorable solvent among the six different 1-alkyl-3-methylimidazolium hexafluorophosphates and tetrafluoroborates ionic liquids screened. With MOEMIM·PF₆ as reaction media, several di- or tripeptide derivatives were successfully prepared in 68-75% isolated yields.     

Sensitive determination of verticine and verticinone in Bulbus Fritillariae by ionic liquid assisted capillary electrophoresis-electrochemiluminescence system

CE/Ru(bpy)₃²⁺ electrochemiluminescence (ECL) system with the assistance of ionic liquids (ILs) was successfully established for sensitive determination of verticine and verticinone in Bulbus Fritillariae for the first time. Migration behavior of alkaloid largely relies on the hydrogen bonding interactions between alkyl imidazolium cations in ILs and the alkaloids. Running buffer containing 40 mmol/L 1-butyl-3-methylimidazolium tetrafluoroborate (BMImBF₄) IL-8 mmol/L phosphate resulted in significant changes in separation selectivity for alkaloids with similar structures. The highest sensitivity of the detection was obtained by maintaining the detection potential at 1.2 V. Under the optimized conditions, relative standard derivations of the ECL intensity and the migration time were 3.27 and 2.84% for verticine and 4.42 and 1.69% for verticinone, respectively. The standard curves were linear between 1 × 10⁻⁸ and 1 × 10⁻⁶ mol/L for verticine and between 5 × 10⁻⁸ and 1 × 10⁻⁶ mol/L for verticinone, respectively. Detection limits of 1.25 × 10⁻¹⁰ mol/L for verticine and 1 × 10⁻¹⁰ mol/L for verticinone were obtained (S/N = 3). Developed method was successfully applied to determine the amounts of alkaloids in Bulbus Fritillariae.     

Extension of the Ye and Shreeve group contribution method for density estimation of ionic liquids in a wide range of temperatures and pressures

An extension of the Ye and Shreeve group contribution method [C. Ye, J.M. Shreeve, J. Phys. Chem. A 111 (2007) 1456–1461] for the estimation of densities of ionic liquids (ILs) is here proposed. The new version here presented allows the estimation of densities of ionic liquids in wide ranges of temperature and pressure using the previously proposed parameter table. Coefficients of new density correlation proposed were estimated using experimental densities of nine imidazolium-based ionic liquids. The new density correlation was tested against experimental densities available in literature for ionic liquids based on imidazolium, pyridinium, pyrrolidinium and phosphonium cations. Predicted densities are in good agreement with experimental literature data in a wide range of temperatures (273.15–393.15 K) and pressures (0.10–100 MPa). For imidazolium-based ILs, the mean percent deviation (MPD) is 0.45% and 1.49% for phosphonium-based ILs. A low MPD ranging from 0.41% to 1.57% was also observed for pyridinium and pyrrolidinium-based ILs.     

Temperature dependence of viscosity and relation with the surface tension of ionic liquids

Viscosities of ionic liquids were correlated with two linear relations. The first one presents the temperature dependence of imidazolium-, pyridinium-, pyrrolidinium-, quaternary ammonium-, and nicotinium-based ionic liquids with high accuracy. The second one is a linear relation between logarithm of surface tension and fluidity involving the characteristic exponent ?, and fits the ionic liquids uniquely with ? = 0.30. Our previously measured surface tension data of ionic liquids and literature's were used in this study. The dependence of surface tension–fluidity relation of the imidazolium-based ionic liquids on the anion type is likely disappeared as alkyl chain length increases.     

Partial molar volumes of selected gases in some ionic liquids

The partial molar volume of a gas that is dissolved at high dilution in a solvent is required to express the influence of pressure on Henry's constant as well as to describe the volume change (expansion) of the liquid caused by the dissolved gas. The correlations of recently published experimental results for the solubility of some selected gases (CO₂, Xe, CH₄, CF₄, H₂, CO, O₂) in three imidazolium-based ionic liquids (1-n-butyl-3-methylimidazolium hexafluorophosphate ([bmim][PF₆]), 1-n-butyl-3-methylimidazolium methyl sulfate ([bmim][CH₃SO₄]), and 1-n-hexyl-3-methylimidazolium bis(trifluoromethylsulfonyl)amide ([hmim][Tf₂N])) determined by the synthetic method were re-evaluated by also considering the experimentally determined volumetric properties. The new evaluation does not change the published results for Henry's constants, but additionally yields reliable information on the partial molar volume of those gases in the mentioned ionic liquids at temperatures from about 293 to 413 K.     

Extraction and mechanism investigation of trace roxithromycin in real water samples by use of ionic liquid-salt aqueous two-phase system

The ionic liquid, as a green solvent, has several advantages over the organic solvents in traditional liquid-liquid extraction. Aqueous two-phase system (ATPS) consisting of a hydrophilic ionic liquid (1-butyl-3-methylimidazolium tetrafluoraborate, [Bmim]BF₄) and Na₂CO₃, which is a novel, simple, non-toxic and effective sample pretreatment technique coupled with molecular fluorescence spectrophotometry, was developed for the simultaneous separation, enrichment and rapid analysis of roxithromycin. The extraction yield of roxithromycin in [Bmim]BF₄-Na₂CO₃ aqueous two-phase system is influenced by the types of salts, concentrations of Na₂CO₃ and [Bmim]BF₄, as well as the extracting temperature. Under the optimum conditions, the average extraction efficiency is up to 90.7%. The mechanism of ionic liquid-salt ATPS formation was discussed by hydration theory, and the extraction mechanism of the [Bmim]BF₄-salt ATPS was investigated by FT-IR spectroscopy and UV-vis spectroscopy. The results demonstrate that no chemical (bonding) interactions are observed between ionic liquid and roxithromycin, while the nature properties of the roxithromycin are not altered. This method was practical when applied to the analysis of roxithromycin in real water samples with the detection limit of 0.03 μg mL⁻¹, relative standard deviation (RSD) of 1.9% (n = 13), and linear ranges of 1.00-20.00 μg mL⁻¹. The proposed extraction technique will be promising in the separation of other small biomolecules.     

Epoxidation of chromones and flavonoids in ionic liquids

A convenient and efficient procedure for the epoxidation of chromone, isoflavone, and chalcone derivatives using 1-butyl-3-methyl imidazolium tetrafluoroborate [bmim]BF₄ as solvent and alkaline hydrogen peroxide as oxidant is described. All reactions proceed in good yields and faster than in conventional solvents. No evidence of formation of compounds derived from the opening of the epoxide ring was attained.     

A Convenient Synthesis of 2-Amino-1,3- selenazoles Using Ionic Liquid and Microwave Irradiation

Abstract

A simple and environmentally benign synthesis of 2-amino-1,3-selenazoles by microwave irradiation using 1-butyl-3-methylimidazolium tetrafluoroborate ([Bmim]BF₄) ionic liquid (IL) is described. Acyl halides, phenacyl halides, and α-bromo-β-keto esters easily undergo condensation with selenourea in ([Bmim]BF₄) by microwave irradiation to afford the desired products of good purity in excellent yields. The ionic liquid can be easily recovered and reused at least 10 times without losing its activity. The duration of the reaction ranges from 4–6 min.

Supplemental materials are available for this article. Go to the publisher's online edition of Phosphorus, Sulfur, and Silicon and the Related Elements to view the free supplemental file.

GRAPHICAL ABSTRACT      

Cyclic voltammetric study of the catalytic behavior of nickel(I) salen electrogenerated at a glassy carbon electrode in an ionic liquid (1-butyl-3-methylimidazolium tetrafluoroborate, BMIMBF4)

Cyclic voltammetry has been employed to examine the electrochemistry of nickel(II) salen at a glassy carbon electrode in an ionic liquid (1-butyl-3-methylimidazolium tetrafluoroborate, BMIM⁺BF₄⁻). Residual water in the ionic liquid can be eliminated by introduction of activated molecular sieves into the electrochemical cell. Nickel(II) salen exhibits a one-electron, quasi-reversible reduction to nickel(I) salen, and the latter species serves as a catalyst for the cleavage of carbon–halogen bonds in iodoethane and 1,1,2-trichlorotrifluoroethane (Freon^® 113). In BMIM⁺BF₄⁻ the diffusion coefficient for nickel(II) salen at room temperature has been determined to be 1.8×10⁻⁸ cm² s⁻¹, which is more than 500 times smaller than that (1.0×10⁻⁵ cm² s⁻¹) in a typical organic solvent–electrolyte system such as dimethylformamide (DMF) containing 0.10 M tetramethylammonium tetrafluoroborate.     

Convenient oxidation of alkylated phenols and methoxytoluenes to antifungal 1,4-benzoquinones with hydrogen peroxide (H2O2)/methyltrioxorhenium (CH3ReO3) catalytic system in neutral ionic liquid

Alkylated phenol and methoxytoluene derivatives were catalytically and selectively oxidized to the corresponding 1,4-benzoquinones in good conversions and yields. Reactions were performed with hydrogen peroxide (H₂O₂)/methyltrioxorhenium (CH₃ReO₃) in 1-butyl-3-methylimidazolium tetrafluoroborate [bmim]BF₄, a neutral ionic liquid. Compounds were tested in vitro for their antifungal activity against the growth of several widespread soil fungi. Some of them were proved to be potent inhibitors of Fusarium sp. than ketoconazole, a commercially available and expensive antifungal agent.     

Catalytic enantioselective allylation of aldehydes via a chiral indium(III) complex in ionic liquids

The ionic liquid [hmim][PF₆] has been demonstrated as an efficient and environmentally-friendly reaction medium for the enantioselective allylation of aldehydes via a chiral indium(III) complex. The allylation of a variety of aromatic, α,β-unsaturated and aliphatic aldehydes resulted in moderate to good yields and enantioselectivities (upto 92% ee).     

Synthesis and evaluation of multitopic bisbenzothiazolyl calix[4]arenes for ionic toxicants

Abstract

Two new benzothiazolyl calix[4]arene-based multitopic molecular receptors L-1 and L-2 have been synthesised and evaluated for recognition of ionic toxicants. The receptors selectively interact with copper, silver and fluoride ion toxicants as assessed through UV-visible, NMR and colorimetric techniques. The stability of L-1:Cu⁺² and L-2:Cu⁺² complexes was found to be higher than that of complexes formed with Ag⁺ and F^– complexes in the presence of trifluoroacetic acid. Superiority of L-1 over L-2 for analysis of identified toxicants has been determined by measurement of binding constants.     

On the use of ionic liquids as mobile phase additives in high-performance liquid chromatography. A review

The popularity of ionic liquids (ILs) has grown during the last decades in several analytical separation techniques. Consequently, the number of reports devoted to the applications of ILs is still increasing. This review is focused on the use of ILs (mainly imidazolium-based associated to chloride and tetrafluoroborate) as mobile phase additives in high-performance liquid chromatography (HPLC). In this approach, ILs just function as salts, but keep several kinds of intermolecular interactions, which are useful for chromatographic separations. Both cation and anion can be adsorbed on the stationary phase, creating a bilayer. This gives rise to hydrophobic, electrostatic and other specific interactions with the stationary phase and solutes, which modify the retention behaviour and peak shape. This review updates the advances in this field, with emphasis on topics not always deeply considered in the literature, such as the mechanisms of retention, the estimation of the suppressing potency of silanols, modelling and optimisation of the chromatographic performance, and the comparison with other additives traditionally used to avoid the silanol problem.     

Synthesis of substituted imidazolines via [3+2]-cycloaddition of aziridines with nitriles

An efficient synthesis of 2,4-disubstituted 1H-imidazolines from aziridines and nitriles in the presence of BF₃-Et₂O or triethyloxonium tetrafluoroborate has been described. The reaction proceeds via a [3+2]-cycloaddition reaction. Most of the nitriles successfully underwent cycloaddition reactions with aziridines even at room temperature in a very short time.     

Thiophene separation from aliphatic hydrocarbons using the 1-ethyl-3-methylimidazolium ethylsulfate ionic liquid

The ionic liquid 1-ethyl-3-methylimidazolium ethylsulfate has been tested as solvent for the separation of thiophene from aliphatic hydrocarbons. Liquid–liquid equilibrium data have been determined for ternary systems containing the ionic liquid, thiophene and C₆, C₇, C₁₂ or C₁₆ alkanes at T = 298.15 K. The performance of the ionic liquid as solvent in such systems has been evaluated. The experimental data were correlated using the NRTL and UNIQUAC equations, and the binary interaction parameters have been reported. The phase diagrams for the ternary mixtures including both the experimental and calculated tie-lines have been presented.     

Deep extractive desulfurization of diesel fuels by FeCl3/ionic liquids

The extractive desulfurization of dibenzothiophene（DBT）,benzothiophene（BT）,and 4,6-dimethyldi-benzothiophene （4,6-DMDBT） in model oil was carried out using anhydrous FeCl₃ and 1-methyl-3-octylimidazolium chloride system（[Omim|Cl·2FeCl₃）.This new system exhibited high extractive efficiency and the sulfur removal of DBT in model oil(V_IL/V_oil=1/20) could reach 99.4%at room temperature for 30 min,which was obviously superior to single[Omim]Cl as extractant（22.9%）.When the[Omim|CI·2FeCl₃ was used,the S-removal of 4,6-DMDBT and BT could also be up to 99.3%and 96.2%, respectively.Moreover,the ionic liquid could be recycled five times without a significant decrease in extractive ability.     

CH3ReO3/H2O2 in room temperature ionic liquids: an homogeneous recyclable catalytic system for the Baeyer-Villiger reaction

The Baeyer-Villiger oxidation of cyclic ketones can be effected by methyltrioxorhenium/hydrogen peroxide in the ionic liquid [bmim]BF₄. After simple extraction of the lactone with diethyl ether, the catalyst can be repeatedly recycled and efficiently reused for the lactonisation process in the same reaction medium.     

Electrocatalytic activity of hemoglobin in sodium alginate/SiO<Subscript>2</Subscript> nanoparticle/ionic liquid BMIMPF<Subscript>6</Subscript> composite film

A novel biocompatible composite film containing sodium alginate (SA), room temperature ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate (BMIMPF₆), SiO₂ nanoparticle, and hemoglobin (Hb) was fabricated and covered on the surface of a traditional carbon paste elecrode (CPE). The immobilized Hb on the electrode surface showed good direct electrochemical behaviors, and a pair of quasi-reversible redox peaks of Hb was obtained, which indicated that the direct electron transfer of Hb with the electrode surface had been achieved. The SA/nano-SiO₂/BMIMPF₆/Hb/CPE showed dramatically electrocatalytic activity to the reduction of trichloroacetic acid, hydrogen peroxide (H₂O₂), and oxygen (O₂). The kinetic parameters for the electrocatalytic reactions were evaluated. The composite film showed the potential to the biosensor and biocatalysis.