Cation Alkyl Chain Research Articles

Theoretical studies on the noncovalent interaction of fructose and functionalized ionic liquids

As a new kind of solvent and catalyst, the functionalized ionic liquids (ILs) had been successfully used in the conversion of fructose to high value-added biofuels. In this work, a detailed density functional theory (DFT) calculation had been carried out to investigate the interactions of fructose-ILs system. To study the effect of different anions and cations on the interaction with fructose, 25 different kinds of functionalized imidazolium-based ILs were calculated by using M06-2X-D3/6-311 + G** level. It was found that the interaction energies of fructose-anions were higher than those of the fructose-cations. The interaction will become stronger for the fructose and ILs when the alkyl chain of imidazolium-based cations was replaced with a functional group (COOH, OH or HSO3). However, when the length of the alkyl chain increased, it will result in a decrease in interaction energy due to the steric effect. In the anions (Y–SO3), the greater electronegativity of SO3 will lead to strong interaction with fructose. Also, this work simulates the interaction of fructose and ion pairs, with the results showing that hydrogen bonds (H-bonds) and π-stacking play an important role in the system. The present study provided basic aids to understand the structures and noncovalent interaction of fructose and functionalized ILs as well as the microscopic mechanism of fructose dissolution in the ILs.

Separation of lithium, cobalt and nickel from spent lithium-ion batteries using TBP and imidazolium-based ionic liquids

Solvent extraction of lithium ions from sulfuric acid solutions was investigated using imidazolium-based ionic liquids as diluents and tri-n-butyl phosphate as specific ligand. Aqueous phases used were simulating leach liquors of spent lithium-ion batteries, with lithium, cobalt and nickel ions in acidic solutions. A low acidity and a large amount of extractant can ensure high extraction efficiency. But the better selectivity for the lithium ions over the transition metals is obtained using a low amount of extractant and a low pH (pH<3). The extraction of the lithium ions occurs by cation exchange with the ionic liquid cations. A sacrificial cation was introduced in the organic phase to prevent the losses, but the cation exchange is only reduced by 20%. The increase of the ionic liquid cation alkyl chain length can presumably suppress the cation exchange mechanism, reducing substantially the losses. But the addition of a lipophilic counter-anion in the organic phase is needed to ensure a mechanism of ion pairing with the lithium ion in the organic phase. Using the 1-decyl 3-methylimidazolium bis(trifluoromethylsulfonyl)imide ionic liquid associated to tri-butyl phosphate, a satisfying extraction efficiency is obtained for the lithium ion, together with a sufficient selectivity among the transition metal ions.

Ion-association vis á vis hydrophobic effect in novel ionic liquids-tetraalkylphosphonium/polyisobutylenesuccinimide-tethered tetraalkylammonium diarylphosphates/thiophosphates: Synthesis and application

A comprehensive study using conventional 1H, 31P NMR as well as advanced PFGSE-DOSY NMR on structurally unique ionic liquids (ILs) having, in one hand, both phosphorus based counter ions called tetraalkylphosphonium diarylphosphate (PP)/diarylthiophosphate (PTP), and on the other hand polyisobutylenesuccinimide-tethered tetraalkylammonium diarylphosphate (PIBSI-P)/diarylthiophosphate (PIBSI-TP) has been carried out in order to establish their structures and interactions between the counter ions in chloroform solution. It has been noticed that the ion association increases significantly by increasing the cationic alkyl chain length in PP and moderately in PTP owing to stronger hydrophobic interactions. However in polymeric ionic liquids (POILs), PIBSI-P and PIBSI-TP, it is the hydrophobic effect of the long chain PIB backbone which dominates the course, effect of cationic alkyl chain length was not much observed. The ILs were synthesized either from an anion exchange reaction between tetraalkylphosphonium bromides and diarylphosphate/thiophosphate (former) or from a reaction of same diarylphosphate/thiophosphate with tetraalkylammonium bromide derived from polyisobutylene succinic anhydride (PIBSA) (later). The synthetic procedure is very simple, efficient and high yielding. The developed ILs are found to be effective for application as lubricant additive.

Synthesis of Low-Viscosity Ionic Liquids for Application in Dye-Sensitized Solar Cells.

Two types of ionic liquids (ILs), 1-(3-hexenyl)-3-methyl imidazolium iodide and 1-(3-butenyl)-3-methyl imidazolium iodide, are synthesized by introducing an unsaturated bond into the side alkyl chain of the imidazolium cation. These new ionic liquids exhibit high thermal stability and low viscosity (104 cP and 80 cP, respectively). The molecular dynamics simulation shows that the double bond introduced in the alkane chain greatly changes the molecular system space arrangement and diminishes the packing efficiency, leading to low viscosity. The low viscosity of the synthesized ionic liquids would enhance the diffusion of redox couples. This enhancement is detected by fabricating dye-sensitized solar cells (DSSCs) with electrolytes containing the two ILs and I2 . The highest efficiency of DSSCs is 6.85 % for 1-(3-hexenyl)-3-methyl imidazolium iodide and 5.93 % for 1-(3-butenyl)-3-methyl imidazolium iodide electrolyte, which is much higher than that of 5.17 % with the counterpart 1-hexyl-3-methyl imidazolium iodide electrolyte.

Effect of the chain lengthening on transport properties of imidazolium-based ionic liquids

The objective of this work is to study the effect of the lengthening of the linear alkyl chain of the imidazolium cation on some transport properties. We focused on hydrophobic ionic liquids based on bis(trifluoromethanesulfonyl)imide anion. Among the different properties, we measured at the viscosity and ionic conductivity of four different 1-alkyl-3-methylimidazolium ionic liquid in the temperature range between 293 and 333K. Thus, Electrochemical windows of these ionic liquids and the diffusion coefficient of ferrocenemethanol (FcMeOH) in the four ionic liquids were studied using cyclic voltammetry at 298K. The FcMeOH diffusion coefficient was found to be higher in shorter alkyl chain ionic liquids.

Side-chain effects on the capacitive behaviour of ionic liquids in microporous electrodes

Classical density functional theory (cDFT) is used to investigate electrosorption of ionic liquids in porous electrodes within the framework of a coarse-grained model. The purpose of this study is to clarify the influence of the side alkyl chains of imidazolium cations on the electric double layer (EDL) capacitance that was studied in a number of recent investigations but with contradictory trends. For an ionic liquid near a planar electrode, cDFT predicts that the capacitance falls by extending the alkyl chain length of cations because neutral segments reduce the packing density of counterions thus the charge density. The side-chain effect is more complicated for ionic liquids in micropores owing to space-charge competition. Adding neutral segments to imidazolium cations always reduces the capacitance in cases where the surface electrical potential of micropores is sufficiently large. However, the capacitance shows a nonmonotonic dependence on the alkyl chain length at intermediate surface potentials. Surprisingly, addition of neutral segments to the cations has the most pronounced effect on the EDL capacitance in cases when the surface potential is positively charged. These findings challenge the conventional assumption that the alkyl side chains of imidazolium ions only negatively impact ionic liquid performance in charge storage.

The structure-activity relationship of hydrophilic carbon dots regulated by the nature of precursor ionic liquids

The preparation of hydrophilic carbon dots (HCDs) with imidazolium dicyanamide ionic liquids (ILs) as precursor revealed a unique structure-activity relationship for the IL-HCDs. Their hydrophilicity, fluorescence nature and cytotoxicity are closely correlated to the alkyl side chain length of the imidazolium cationic moiety. (1) The hydrophilicity of the precursor ILs decreases with the alkyl chain length of their imidazolium cations (from ethyl, butyl, hexyl, octyl to decyl). On the contrary, that of the IL-HCDs increases with the alkyl chain length due to the emergence of COC, NH2 moiety. (2) The passivation effect of alkyl chain plays a dominative role in the enhancement of quantum yield (QY, from 4.6% to 48.0%) of IL-HCDs. The doping of nitrogen-containing moieties contributes marginally. (3) The increase of alkyl chain length leads to the weakening of IL-HCDs/bovine serum albumin (BSA) affinity with a decrease on the quenching constants from 12.59 × 104 to 1.779 × 104 L mol−1. (4) The cytotoxicity of IL-HCDs increases with the length of alkyl chain in the imidazolium cation, though the hydrophilicity of IL-HCDs is increased. In addition, the cytotoxicity of IL-HCDs/BSA is lower than that of IL-HCDs. The protective effect of BSA in the IL-HCDs/BSA ‘protein corona’ could be utilized to improve the biocompatibility of IL-HCDs.

Ecotoxicity evaluation towards Vibrio fischeri of imidazolium- and pyridinium-based ionic liquids for their use in separation processes

The non-volatility character of the ionic liquids makes them environmentally attractive to new separation processes development, but their water solubility emphasizes the importance of the study of their impact on the aquatic environment. The present work reports the toxicity of 24 imidazolium- and pyridinium-based ionic liquids through Vibrio fischeri inhibition basic test. The toxicity-structure relationship of the ionic liquids has been studied through the anion and cation core, the cation alkyl chain length, and the presence of functional groups on the cation alkyl chain. Ionic liquids whose chemical structure includes pyridinium cations, long cation alkyl chains, and bis(trifluoromethylsulfonyl) imide ([Tf2N]) anions present the highest toxicity. Finally, considering ionic liquids as potential solvents for the aromatic/aliphatic separation process, their toxicity has been compared to that of sulfolane, which is the current organic solvent used in this kind of process. Most of the studied ionic liquids can be classified as harmless or practically harmless; meanwhile, only four of them present a slightly or moderately toxicity, the same than that of sulfolane. The present study suggests that not only the atmospheric pollution would be decreased, but the aquatic impact as well by using ionic liquids as alternative solvents. Ionic liquids (ILs) stand as more environmentally friendly solvents in the petrochemical industry. Their toxicity towards Vibrio fischeri bacteria is lower than most of the “green” alternative deep eutectic solvents (DESs) and much lower than the current solvent, sulfolane.

Molecular-Level Understanding of Structures and Dynamics of Imidazolium-Based Ionic Liquids around Single-Walled Carbon Nanotubes: Different Effects between Alkyl Chains of Cations and Nanotube Diameters

Here, we have performed a series of molecular dynamics simulations to investigate the solvation structures and dynamics of imidazolium-based ionic liquids (i.e., [Emim][BF4] and [Bmim][BF4]) around single-walled carbon nanotubes (CNTs) with two different diameters. We make an effort to address the effects of both the alkyl chains of cations and the CNT diameters on the interfacial properties as well as the reasons behind these effects. Our simulation results demonstrate that increasing the CNT diameter can lead to a larger interaction between the ions and the CNTs so that more cations and anions tend to aggregate around the larger CNT, while the alkyl chain is found to have a negligible effect on the relevant structures in the first solvation shell. Meanwhile, the imidazolium rings of cations prefer to be almost parallel to the CNT surface and the preference can be further enhanced by the larger CNT diameter and the longer alkyl chain. On the other hand, either increasing the CNT diameter or the alkyl chain length can result in slower rotational motions of cations around the CNT, but the latter has a more considerable effect, which is significantly different from their effects on the solvation structures. In addition, the anions have the same dependence of their rotational motions around the CNTs on the alkyl chain length as the cations. Our simulation analysis further reveals that the same dependence results from that the alkyl chains of cations can affect the hydrogen bonds between cations and anions so that they have an indirect and considerable influence on the rotational motions of anions.

Systematic estimation and interpretation of fractional free volume in 1-alkyl-3-methylimidazolium-based ionic liquids

With the aim of providing a plausible explanation for fractional free volume (FFV) behavior in ionic liquids (ILs) such as 1-alkyl-3-methylimidazolium-based cations paired with common anions like [BF4]−, [PF6]−, and bis(trifluoromethane)sulfonamide ([NTf2]−), we comprehensively estimated the van der Waals volume of the ions and subsequently determined the FFV behavior present within these liquids with the aid of quantum chemical calculations. Unlike the values seen in previous studies, our results showed an increase in the FFV character of the IL under investigation when either the cation's alkyl chain was lengthened and/or the size of the anion was expanded. The sizes of cations and anions present in the IL were shown to affect the FFV values in different ways: whereas the effect of the anion's size could be accounted for by looking at changes in the Coulomb interaction between cations and anions in the polar (charge localized) domains, the effect exerted by the alkyl chain was found to be related to the alkyl chain's dependence on the FFV obtained for alkanes due to the introduction of non-polar (alkyl group aggregated) domains to ILs with increasing alkyl chain lengths. An empirical equation was proposed in order to calculate FFV values for alkyl-imidazolium-based ILs.

Alkyl Methyl Imidazolium-Based Ionic Liquids at the Au(111) Surface: Anions and Alkyl Chain Cations Induced Interfacial Effects

The structure, stability, and adsorption mechanism on the Au(111) surface of hydrophilic/hydrophobic ionic liquids (ILs) with various lengths of the alkyl chain group in the cation were investigate...

Synthesis and characterization of analogues of glycine-betaine ionic liquids and their use in the formation of aqueous biphasic systems

A series of novel analogues of glycine-betaine ionic liquids (AGB-ILs), viz. 1-(4-ethoxy-4-oxobutyl)-1-methylpyrrolidin-1-ium, N,N,N-tri(n-butyl)(4-ethoxy-4-oxobutyl)-1-phosphonium and N,N,N-trialkyl(4-ethoxy-4-oxobutyl)-1-aminium cations with ethyl, n-propyl and n-butyl alkyl chains, combined with the bromide anion, have been synthesized and characterized. Their synthesis and characterization by spectroscopic methods and elemental analysis is here reported. These ILs were further characterized in what concerns their thermal properties and ecotoxicity against Allvibrio fischeri, and compared with the commercial tetra(n-butyl)ammonium and tetra(n-butyl)phosphonium bromide. The novel AGB-ILs described in this work have low melting points, below 100 °C, display high degradation temperatures (180–310 °C), and low toxicity as shown by being harmless or practically harmless towards the marine bacteria Allvibrio fischeri. Finally, the ability of the synthesized AGB-ILs to form aqueous biphasic systems with potassium citrate/citric acid (at pH 7) was evaluated, and the respective ternary phase diagrams were determined. It is shown that the increase of the cation alkyl chain length facilitates the creation of ABS, and that phosphonium-based ILs present a slightly better separation performance in presence of aqueous solutions of the citrate-based salt.

Stability of Titania Nanomaterials Dispersed in Aqueous Solutions of Ionic Liquids of Different Alkyl Chain Lengths

Charging and aggregation of titania nanosheets (TNS) and spherical titania nanoparticles (TNP) were studied in aqueous solutions of ionic liquids. The pH and the length of the alkyl chain of the IL cations [1-methylimidazolium (MIM+), 1-ethyl-3-methylimidazolium (EMIM+), and 1-butyl-3-methylimidazolium (BMIM+)] were systematically varied in the experiments. No detectable interaction was observed between the IL cations and the positively charged TNS or TNP surfaces at low pH, where the imidazolium derivatives are the co-ions. For the negatively charged titania nano-objects, significant adsorption of MIM+ and EMIM+ took place, leading to charge neutralization and overcharging at appropriate concentrations. The BMIM+ behaved like a simple salt constituent causing charge screening. For both TNS and TNP, the MIM+ < EMIM+ < BMIM+ counterion order was obtained in the critical coagulation concentrations, indicating that MIM+ was the most effective in destabilization of the dispersions. The major interparticle for...

Effects of phosphonium-based ionic liquids on the lipase activity evaluated by experimental results and molecular docking.

In this work, the effect of several phosphonium-based ionic liquids (ILs) on the activity of lipase from Burkholderia cepacia (BCL) was evaluated by experimental assays and molecular docking. ILs comprising different cations ([P4444 ]+ , [P444(14) ]+ , [P666(14) ]+ ) and anions (Cl- , Br- , [Deca]- , [Phosp]- , [NTf2 ]- ) were investigated to appraise the individual roles of IL ions on the BCL activity. From the activity assays, it was found that an increase in the cation alkyl chain length leads to a decrease on the BCL enzymatic activity. ILs with the anions [Phosp]- and [NTf2 ]- increase the BCL activity, while the remaining [P666(14) ]-based ILs with the Cl- , Br- , and [Deca]- anions display a negative effect on the BCL activity. The highest activity of BCL was identified with the IL [P666(14) ][NTf2 ] (increase in the enzymatic activity of BCL by 61% at 0.055 mol·L-1 ). According to the interactions determined by molecular docking, IL cations preferentially interact with the Leu17 residue (amino acid present in the BCL oxyanion hole). The anion [Deca]- has a higher binding affinity compared to Cl- and Br- , and mainly interacts by hydrogen-bonding with Ser87, an amino acid residue which constitutes the catalytic triad of BCL. The anions [Phosp]- and [NTf2 ]- have high binding energies (-6.2 and -5.6 kcal·mol-1 , respectively) with BCL, and preferentially interact with the side chain amino acids of the enzyme and not with residues of the active site. Furthermore, FTIR analysis of the protein secondary structure show that ILs that lead to a decrease on the α-helix content result in a higher BCL activity, which may be derived from an easier access of the substrate to the BCL active site.

Insights into the effect of imidazolium-based ionic liquids on chemical structure and hydrolytic activity of microbial lipase.

This work studied the effect of the cation alkyl chain length of 1-alkyl-n-methylimidazolium chloride ([Cnmim]Cl)-based ILs on the activity of Aspergillus niger lipase. First, the lipase activity in the presence of different ILs concentration over time was determined. ILs with shorter cation alkyl side chain length, namely [C4mim]Cl and [C6mim]Cl, promoted an increase of lipase activity; while, [C8mim]Cl, depending on its concentration, maintained or decreased the enzyme activity. In the presence of ILs with longer cation alkyl chain length, i.e., [C10mim]Cl and [C12mim]Cl, the lipase relative activity was reduced with 0.1 (%v/v) and until suppressed ([C12mim]Cl at 0.3 (%v/v)) as a result of irreversible changes in its secondary structure. Fluorescence and circular dichroism spectroscopy analysis confirmed the results achieved. These findings show that [Cnmim]Cl-based ILs can exert different behavior on the lipase' activity (enhance, maintain or even inhibit) and structural conformation, depending on the cation alkyl chain length and their relative concentration.

Density, sound velocity, viscosity, and refractive index of new morpholinium ionic liquids with amino acid-based anions: Effect of temperature, alkyl chain length, and anion

In this work, room temperature synthesis of twenty new ionic liquids (ILs) based on the N-alkyl-N-methylmorpholinium ([Mor1,R], R = 2, 3, 4, 6, 8) cation and N-acetyl-L-amino acid anions (L-alaninate, L-valinate, L-leucinate, L-isoleucinate) was described. The synthesized ILs were characterized by various spectroscopic techniques and high-resolution mass spectrometry. Furthermore, density (ρ), sound velocity (v), viscosity (η) and refractive index (nD) have been measured within the temperature range of T = (298.15 to 318.15) K and at 0.1 MPa pressure. The density, sound velocity and viscosity values were fitted to linear and Vogel–Tammann–Fulcher (VTF) equation. Moreover, on the basis of the refractive index values, molar refraction (Rm) and free volume (Vf) were calculated using the Lorentz–Lorenz equation. The thermodynamic properties such as thermal expansion coefficient (α) and isentropic compressibility (κS) were calculated using the experimental values of density and sound velocity. Finally, the obtained data were evaluated in order to determine the effect of such parameters as temperature, the nature of the anion and the length of the cation alkyl chain.

Density functional theory study of the stability of the tetrabutylphosphonium and tetrabutylammonium montmorillonites

AbstractThe stability of organoclays prepared from smectites and organic cations depends on the type of used cation, among other factors. This study provides a prediction of the structure, stability and dynamic properties of organoclays based on montmorillonite (Mt) intercalated with two types of organic cations – tetrabutylammonium (TBA) and tetrabutylphosphonium (TBP) – using first-principle density functional theory. The results obtained from simulations were also used in the interpretation of the experimental infrared spectrum of the TBP-Mt organoclay. Analysis of interatomic distances showed that weak C–O···H hydrogen bonds were important in the stabilization of both TBA- and TBP-Mt models, with slightly stronger hydrogen bonds for the TBP cation. Calculated intercalation and adsorption reaction energies (ΔEint//ΔEads*/ΔEads**) confirmed that TBP-Mt structures (–72.4//–32.8/–53.8 kJ/mol) were considerably more stable than TBA-Mt structures (–56.7//–22.6/–37.4 kJ/mol). The stronger interactions of the alkyl chains of the TBP cation with Mt basal surfaces in comparison to those of the TBA cation were also correlated with the positions of the calculated bands of the C–H stretching vibrations.

Structural effect of imidazolium-type ionic liquid adsorption to montmorillonite

The adsorption of 1-alkyl-3-methylimidazolium-type ionic liquids (ITILs) coupled with different counteranions (Tf2N−, PF6−, BF4−, and Cl−) with variational cation alkyl chain lengths (n = 2, 4, 6, and 8) to montmorillonite was investigated to explore the structural effect of ITILs on their adsorption. A series of montmorillonite with different cation exchange capacities (CECs) and possessing a set of homoionic K- and Cs-exchanged interlayer cations were also examined to assess the influence of montmorillonite structure and characteristics. The adsorption of ITILs to Na-saturated montmorillonite (Na-MAz) was counteranion-independent but increased with the increase in the alkyl chain length of the imidazolium cation. X-ray diffraction results indicated that ITIL cations with different alkyl chains lay flat between the montmorillonite interlayers with different contact angles. The uptake of ITILs by Na-MAz increased with the increase in the solution pH and decrease in ionic strength. Na-MAz exhibited greater adsorption than K- and Cs-saturated MAz due to the larger hydrated radii of Na+ than those of K+ and Cs+. The uptake of ITILs to Na-MZj (CEC = 64 mmol/100 g) was almost half compared with that of Na-MAz (CEC = 117 mmol/100 g). Consequently, this work demonstrated that the ITIL adsorption to montmorillonite was dependent on the structures of both adsorbate and adsorbent.

Influence of temperature and alkyl chain length on physicochemical properties of trihexyl- and trioctylammonium based protic ionic liquids

A series of trialkylammonium cation and carboxylate anion based room temperature protic ionic liquids (PILs) were synthesized by varying cation alkyl chain length to hexyl, octyl and anion chain length to butanoate, hexanoate, and octanoate. The corresponding ILs are named as trihexylammonium butanoate ([THA][But]), trihexylammonium hexanoate ([THA][Hex]), trihexylammonium octonoate ([THA][Oct]), trioctylammonium butanoate ([TOA][But]), trioctylammonium hexanoate ([TOA][Hex]), and trioctylammonium octonoate ([TOA][Oct]). The thermophysical properties such as density (ρ), speed of sound (u), viscosity (η) and refractive index (nD) were measured over a wide temperature range. The calculated parameters from experimental data such as thermal expansion coefficient, isentropic compressibility decreased linearly with the number of carbon atoms in cation or anion, whereas they increased with the temperature. Thermogravimetric analysis revealed an increase in the thermal stability of the ILs with the increase in total chain length. The shear-dependent viscosity measurements suggest that all the studied PILs showed fluid nature and Newtonian behavior at 298.15 K. The effect of alkyl chain length of cation or anion and temperature on the physicochemical properties were discussed with respect to the structure of ILs and in correlation with the reported structurally similar ILs.

Small‐Sized CuS Nanoparticles/N, S Co‐Doped rGO Composites as the Anode Materials for High‐Performance Lithium‐Ion Batteries

AbstractIn this work, small‐sized CuS nanoparticles/N, S co‐doped rGO composites (CuS@N/S‐G‐Cn) are synthesized by a facile route with the metal‐containing ionic liquids (MILs) [CnMMim]2[CuCl4] (n is 6, 8, 10 representing the number of C atoms in the alkyl chain of imidazolium cation) as the precursors. In the composites, the CuS nanoparticles with small size of sub‐20 nm are homogeneously dispersed in nitrogen and sulfur co‐doped reduced graphene oxide (rGO). The highly dispersed nanosized CuS are embedded on excellent conductive doped rGO substrates to supply not only large quantity of accessible active sites for lithium‐ion insertion but also short diffusion length for lithium ions, while the N and S co‐doping in rGO can efficiently restrain the polysulfides dissolution and circumvent the volume expansion/contraction associated with lithium insertion/extraction during charge–discharge processes. Bestowed by these advantages, the CuS@N/S‐G‐Cn composites exhibit enhanced electrochemical performance for lithium storage. Especially, when [C6MMim]2[CuCl4] is chosen as the precursor, the obtained electrode material CuS@N/S‐G‐C6 delivers a reversible capacity as high as 603.5 mAh g−1 at 200 mA g−1 after 300 cycles and 530 mAh g−1 at 2 A g−1 after 1000 cycles.