Solutions Of Deep Eutectic Solvents Research Articles

Pulse plating of Pd–Ag alloy films from deep eutectic solvents

ABSTRACTIn water based solutions, electrodeposition of Pd and Pd alloys is complicated due to hydrogen embrittlement. This can be avoided by using non-aqueous solutions like deep eutectic solvents (DES). In this study, the electrodeposition of Pd–Ag films were investigated on Cu from choline chloride/urea based deep eutectic solvents containing sulfosalicylic acid dihydrate (SSS) as an organic additive. The effects of pulse current, an organic additive and different Ag concentrations on the surface morphology and layer thickness were evaluated. Cyclic voltammetry experiments showed that the reduction of Pd(II) occurred prior to that of Ag(I). Scanning electron microscope (SEM) micrographs of the deposits revealed that the surface of the Pd–Ag films were typically granular to nodular and became more compact when the surface active compound was present in the DES solution. X-ray diffraction (XRD) experiments proved the existence of metallic Pd–Ag alloys.

Ultrasonication-assisted synthesis of alcohol-based deep eutectic solvents for extraction of active compounds from ginger.

An ultrasonication-assisted synthesis of alcohol-based deep eutectic solvents (DESs) is described. Several DESs were synthesized simultaneously under the same conditions. The prepared DESs were used for the extraction of gingerols from ginger powder via ultrasonication-assisted extraction. Notably, some of the prepared DESs exhibited superior extraction performance than those in traditional organic solvents. The viscosity of the DESs, which was suggested to be typically lower than 100mPa*s had a critical effect on extraction performance. However, the higher gingerol contents in the extracts did not translate to higher active antioxidant abilities. The extraction temperature was found to be a key determinant of the antioxidant capability of the extracted gingerols while the use of higher temperatures (>50°C) induced degradation and loss of phenolic compounds during extraction. Response surface methodology was applied for determining the optimal extraction conditions to achieve maximum antioxidant capacity with suitable gingerol content. All compounds used for the preparation of the DESs in this study have been widely employed in cosmetic and pharmaceutical fields. Therefore, the extracts in these DES solutions can be considered for direct application development without further product isolation.

Two-dimensional infrared spectroscopic study of cytochrome c peroxidase activity in deep eutectic solvent.

Deep eutectic solvents (DESs) prepared by mixing hydrogen-bond donor and acceptor molecules have been found to be of use in several applications. Recently, it was shown that DESs can enhance the peroxidation activity of cytochrome c. Here, to elucidate the effects of DESs on the peroxidase activity of cytochrome c, we carried out linear and nonlinear infrared spectroscopic studies of the CO stretch mode of carbon monoxide cytochrome c (COCytc) in ethylammonium chloride (EAC)/urea DES. The FTIR spectrum of COCytc shows a significant spectral shift upon addition of the DES. The broadening and red-shifting of the CO band are observed in both urea and DES solutions, which are induced by the change of the distal ligands around the heme. Although the FTIR study is sensitive to structural changes in the active site, it does not provide quantitative information about structural dynamics related to the catalytic activity itself. Thus, we carried out two-dimensional IR spectroscopy of the CO mode, which suggests that there is a different conformer that could be related to the enhanced catalytic activity in DES. In particular, the spectral diffusion dynamics of that conformer exhibits quite different behavior. The experimental results lead us to propose a hypothesis that the DES increases the population of the conformer with distal ligand lysines close to the reaction center through the combining effect of urea and EAC, which results in the enhancement of the peroxidase activity of cytochrome c. We anticipate that the present experimental work stimulates future investigations of the effects of DES on biocatalysis.

Galvanic deposition of Ni on Al alloy from a choline chloride based ionic liquid for electroless Ni–P pretreatment

A Ni layer on Al alloy was deposited by galvanic replacement reaction in an environmental friendly deep eutectic solvent (DES) comprising choline chloride (ChCl) and ethylene glycol (EG). Thermodynamic feasibility and kinetics of galvanic replacement reaction of Ni on Al alloy were studied by cyclic voltammetry, open circuit potential (OCP) and electrochemical noise (ECN) analysis. The characterization of Ni layer was investigated using scanning electron microscopy (SEM) and x-ray diffraction (XRD) analysis. Results showed that the Ni galvanic replacement on Al alloy was thermodynamically feasible and sustained in the ChCl-EG DES solution. The presence of the galvanic replacement Ni layer can serve as pretreatment layer for electroless Ni–P on Al alloy, resulting in obtaining a continuous and uniform Ni–P coating. The Ni–P coatings possessed typical spherical nodules structure and showed well corrosion resistance, which was similar to the result of Ni–P coatings on Al alloy with other pretreatments. The galvanic replacement Ni layer obtained from the deep eutectic solvent provided an alternative pretreatment method for electroless Ni–P coatings on Al alloy.

Performance of Local Composition Models to Correlate the Aqueous Solubility of Naproxen in Some Choline Based Deep Eutectic Solvents at T = (298.15-313.15) K

Background: To overcome low solubility of naproxen (NAP), deep eutectic solvents (DESs) based on choline chloride (ChCl) with glycerol (G) and oxalic acid (OA) as green solvents have been used up to 0.9 mole fraction of DES at T = (298.15 to 313.15) K. Methods: DESs were prepared by combination of the two components with the molar ratios: ChCl/glycerol (1:2) and ChCl/oxalic acid (1:1). The solubility of NAP in the aqueous DESs solutions was measured at different temperatures with shake flask method. Results: The solubility in these solvents increased with increasing the weight fraction of DESs, especially in ChCl/OA. The solubility data were correlated by e-NRTL, Wilson and UNIQUAC models. Also, the thermodynamic functions, Gibbs energy, enthalpy, and entropy of dissolution were obtained. Conclusion: Oxalic acid based DES exhibits higher solubility than glycerol based DES. The thermodynamic models were successfully used to correlate solubility data. In addition, the results show that, the main contribution for NAP solubility in the aqueous DES solutions is the enthalpy.

Crude oil-bubble attachment in aqueous solutions of Deep Eutectic Solvents (DESs)

Flotation technology can be employed as a soil remediation technique in the removal of oil from contaminated soil. Studies have demonstrated that the efficiency of flotation technology can be significantly improved by using surfactants. Today, Deep Eutectic Solvents (DESs) which are referred to as “green” solvents are increasingly used as a replacement to traditional surfactants. In this study, the attachment of bubbles to crude oil was investigated in various molar ratios (1:2, 1:3 and 1:4) and concentrations (1000, 8000, 15,000, 18,500 and 22,000ppm) of DES. Characteristics of DESs including surface tension, interfacial tension and pH were initially measured. The attachment between bubble and crude oil was then investigated by measuring the contact angle and zeta potential in DES. These experimental results were then verified using the Derjaguin-Landau, Verwey-Overbeek (DLVO) theory. Results showed that DES is able to reduce the IFT of the crude oil-water system. DES 1:2 demonstrated the highest reduction in IFT at a concentration of 22,000ppm (32.4 mN/m) compared to DES 1:3 (35.3 mN/m) and DES 1:4 (35.8 mN/m) at the same concentration. This is hypothesized to be due to the decreasing proportion of cations (choline) to hydrogen bonds. Although the contact angle showed a decreasing trend with increase in DES concentration, the contact angle displayed good attachment (more than 90°) at all concentrations. Based on zeta potential measurements, the optimum attachment is suggested to occur at concentrations between 18,500 and 22,000ppm for all molar ratios of DESs. The DLVO theory further demonstrated that DES 1:2 exhibited the lowest energy barrier for all concentrations in comparison to DES 1:3 and DES 1:4. This theory also verified that DES concentrations above 18,500ppm are preeminent for optimum attachment between crude oil and bubble.

Hydrotropy and Cosolvency in Lignin Solubilization with Deep Eutectic Solvents

The mechanisms responsible for the good solubility of lignin in aqueous solutions of deep eutectic solvents are here investigated using both monomer model compounds and technical lignins (kraft and...

Solubility modelling and thermodynamic properties of allopurinol in aqueous solutions of four deep eutectic solvents

The aqueous solubilities of allopurinol in some choline chloride (ChCl) based deep eutectic solvents (DESs) with urea, glycerol, citric acid and glycol as neoteric green solvents were measured by the shake-flask method at T = (293.15–333.15) K under atmospheric pressure p = 101.1 kPa. The solubility in these solvents increased more than approximately 27.8-fold for ChCl/urea system, 45.6-fold for ChCl/glycerol system, 31-fold for ChCl/glycol system and 56-fold for ChCl/citric acid system with increasing the weight fraction of DESs. The solubility data was accurately correlated by the λh equation and modified Apelblat equation. The largest percentage of relative average deviation was 1.49 × 10−2, and the maximum value of root-mean-square deviation was 2.43 × 10−5. Also, in order to describe the thermodynamic behaviour of allopurinol in the aqueous DESs solutions, the transfer properties were derived. The negative Gibbs free energy (ΔtrGo) and enthalpy (ΔtrHo) values indicated that the transfer of allopurinol from neat water to aqueous DESs solutions was spontaneous and energetically favourable. Additionally, the ΔtrGo and ΔtrHo values decreased with the increase in the DESs concentrations, indicating that solubilization was more favourable with the increase in the DESs concentrations. In particular, the ΔtrGo values considerably decreased for ChCl/citric acid compared to ChCl/urea, ChCl/glycerol and ChCl/glycol mixtures. ChCl/citric acid is an effective additive for improving the solubility of allopurinol. Furthermore, the excess enthalpy of solution was obtained according to the λh equation.

Understanding the peculiar effect of water on the physicochemical properties of choline chloride based deep eutectic solvents theoretically and experimentally

Deep Eutectic Solvents (DES), the novel eco-friendly solvents and are analogous to ionic liquids (IL) are also termed as the new age alternatives to the volatile organic solvents owing to their unique physicochemical properties similar to ILs. Water, either present as an unavoidable impurity or added purposefully to lower the cost and viscosities of DES/ILs have peculiar effect on their physicochemical properties. It is imperative to study the effect of water on these eco-friendly solvents. Herein, we report the experimentally determined densities (ρ) and speeds of sound (u) for aqueous DES solution over the entire range of composition and temperature ranges from 293.15 K to 323.15 K at atmospheric pressure. The equimolar ratio of choline chloride as the hydrogen bond acceptor (HBA) with malonic acid and glutaric acid as the hydrogen bond donors (HBD) was used to prepare the DESs. The dependence of DES and H2O composition, role of HBD and temperature is discussed on the excess molar volumes VmE and excess molar isentropic compressibilities Ks, mE. The negative VmE and Ks, mE indicate the dominance of intermolecular interactions over the intra-molecular interactions. The formation of H-bond between ion-water and HBD-water interactions is also discussed in terms of DES composition and temperature. We have used the Prigogine−Flory−Patterson (PFP) theory and for the first time extended real association model (ERAS) to evaluate the non-ideal behaviour of the studied systems. Results of highly unpredictable, distinct contours excess properties over the entire range of composition of DES could be helpful in designing various industrial processes and for the thermodynamic modeling of DES.

Surface Sensitive Nickel Electrodeposition in Deep Eutectic Solvent

The first steps of nickel electrodeposition in a deep eutectic solvent (DES) are analyzed in detail. Several substrates from glassy carbon to Pt(111) were investigated pointing out the surface sensitivity of the nucleation and growth mechanism. For that, cyclic voltammetry and chronoamperometry, in combination with scanning electron microscopy (SEM), were employed. X-ray diffraction (XRD) and atomic force microscopy (AFM) were used to more deeply analyze the Ni deposition on Pt substrates. In a 0.1 M NiCl2 + DES solution (at 70 °C), the nickel deposition on glassy carbon takes place within the potential limits of the electrode in the blank solution. Although, the electrochemical window of Pt|DES is considerably shorter than on glassy carbon|DES, it was still sufficient for the nickel deposition. On the Pt electrode, the negative potential limit was enlarged while the nickel deposit grew, likely because of the lower catalytic activity of the nickel toward the reduction of the DES. At lower overpotentials, ...

Experimental determination and correlation of acetaminophen solubility in aqueous solutions of choline chloride based deep eutectic solvents at various temperatures

The aqueous solubility of acetaminophen (ACP) in some choline chloride (ChCl) based deep eutectic solvents (DESs) with urea, oxalic acid and malonic acid as neoteric green solvents were measured up to 0.90 wt fraction of DESs at T = (293.15–318.15) K and at atmospheric pressure. The solubility in these solvents increased more than forty–fold with increasing the weight fraction of DESs, especially in DES containing malonic acid. The solubility data were accurately correlated by the NRTL, Wilson and UNIQUAC activity coefficient models. Also, to describe the thermodynamic behavior of ACP in the aqueous DES solutions, the thermodynamic functions, Gibbs energy, enthalpy, and entropy of dissolution and mixing were obtained by using the van't Hoff and Gibbs equations. The results indicate that the main contribution to the solubility of ACP in the aqueous DES solutions is enthalpic.

Deep Eutectic Solvent Aqueous Solutions as Efficient Media for the Solubilization of Hardwood Xylans.

This work contributes to the development of integrated lignocellulosic-based biorefineries by the pioneering exploitation of hardwood xylans by solubilization and extraction in deep eutectic solvents (DES). DES formed by choline chloride and urea or acetic acid were initially evaluated as solvents for commercial xylan as a model compound. The effects of temperature, molar ratio, and concentration of the DES aqueous solutions were evaluated and optimized by using a response surface methodology. The results obtained demonstrated the potential of these solvents, with 328.23 g L-1 of xylan solubilization using 66.7 wt % DES in water at 80 °C. Furthermore, xylans could be recovered by precipitation from the DES aqueous media in yields above 90 %. The detailed characterization of the xylans recovered after solubilization in aqueous DES demonstrated that 4-O-methyl groups were eliminated from the 4-O-methylglucuronic acids moieties and uronic acids (15 %) were cleaved from the xylan backbone during this process. The similar Mw values of both pristine and recovered xylans confirmed the success of the reported procedure. DES recovery in four additional extraction cycles was also demonstrated. Finally, the successful extraction of xylans from Eucalyptus globulus wood by using aqueous solutions of DES was demonstrated.

Self-assembly of a short-chain ionic liquid within deep eutectic solvents.

Ionic liquids (ILs) and deep eutectic solvents (DESs) are receiving increased attention from both academic and industrial research due to their immense application potential. These designer solvents are environmentally friendly in nature with tunable physicochemical properties. In the present investigation, we have studied the aggregation behavior of a short-chain IL 1-butyl-3-methylimidazolium octylsulphate [Bmim][OS] within aqueous DESs using fluorescence, UV-vis, dynamic light scattering (DLS) and FT-IR spectroscopic techniques. We have prepared two DESs, ChCl–urea and ChCl–Gly, which are obtained by heating a mixture of an ammonium salt choline chloride with hydrogen bond donor urea or glycerol, respectively, in 1 : 2 molar ratios. The local microenvironment and size of the aggregates are obtained from steady state fluorescence (using pyrene and pyrene-1-carboxaldehyde as polarity probes) and DLS measurements, respectively. DLS results shows that IL [Bmim][OS] forms relatively larger micelles within the aqueous solution of DES ChCl–urea (avg. hydrodynamic radii = 209 nm) than compared to ChCl–Gly (avg. hydrodynamic radii = 135 nm). A significant decrease in the critical micelle concentration and increase in the aggregation number (Nagg) are observed within DES solutions as compared to that in water, thus indicating that the micellization process of the IL [Bmim][OS] is much favored in the DES solutions. Molecular interactions of [Bmim][OS] in DESs are revealed from FT-IR spectroscopic investigation. Furthermore, these systems were applied to study the IL-drug binding of the antidepressant drug promazine hydrochloride (PH).

Determination of common ginsenosides in Kang'ai injection by aqueous two-phase extraction with deep eutectic solvents and HPLC-UV/DAD

In this work, four kinds of deep eutectic solvents (DESs), composed of choline chloride (ChCl) and several alcohols, were synthesized and characterized by 1H NMR and FT-IR spectra. Based on DES (ChCl and 1,4-butanediol) and inorganic salt solution (dipotassium phosphate, K2HPO4), aqueous two-phase system (ATPS) coupled with high-performance liquid chromatography has been developed and applied. This method was used for the efficient extraction and determination of eight common ginsenosides (including ginsenoside Rg1, Re, Rf, Rg2, Rb1, Rc, Rb2 and Rd) in the traditional Chinese medicine injection named Kang'ai injection. To achieve optimum extraction performance, the experimental conditions were optimized, including type and amount of DES and salt, ultrasound time, temperature and pH value. In the dynamic linearity range, experimental results showed satisfactory recoveries of analytes ranging from 92.7–110.8% with the relative standard deviations (RSDs) ranging from 1.2–3.9%. It has been proved that DES-ATPS has great potential for determination of active ingredients in traditional Chinese medicine injection as well as samples in other analytical science field.

Effect of choline chloride/ethylene glycol or glycerol as deep eutectic solvents on the solubility and thermodynamic properties of acetaminophen

To overcome low solubility of acetaminophen (ACP), deep eutectic solvents (DESs) based on choline chloride (ChCl) with glycerol (G) and ethylene glycol (EG) as green solvents have been used up to 0.8mol fraction of DES at T=(298.15 to 313.15)K. Deep eutectic solvents were prepared by combination of the two components with the molar ratios: ChCl/G (1:2) and ChCl/EG (1:2). The solubility of ACP was measured in the aqueous DESs solutions at different temperatures. The solubility in these solvents was increased with increasing the weight fraction of DESs especially in ChCl/EG. The solubility data were correlated by modified Apelblat, λh (Buchowski), Yalkowsky, NRTL, Wilson and UNIQUAC models. In addition, to study the interactions between the components, the thermodynamic properties including volumetric and compressibility have been investigated using density and speed of sound measurements. Also the thermodynamic functions, Gibbs energy, enthalpy, and entropy of dissolution and mixing were obtained. The solubility data of ChCl/EG is more effective on the ACP solubility rather than the DES containg glycerol. The calculated thermodynamic funtions also confirm the presence of strong solute–solvent interactions between ACP–DESs. The results also show that the main contribution for ACP solubility in the aqueous DES solutions is the enthalpy.

Deep Eutectic Solvents as Efficient Media for the Extraction and Recovery of Cynaropicrin from Cynara cardunculus L. Leaves.

In recent years a high demand for natural ingredients with nutraceutical properties has been witnessed, for which the development of more environmentally-friendly and cost-efficient extraction solvents and methods play a primary role. In this perspective, in this work, the application of deep eutectic solvents (DES), composed of quaternary ammonium salts and organic acids, as alternative solvents for the extraction of cynaropicrin from Cynara cardunculus L. leaves was studied. After selecting the most promising DES, their aqueous solutions were investigated, allowing to obtain a maximum cynaropicrin extraction yield of 6.20 wt %, using 70 wt % of water. The sustainability of the extraction process was further optimized by carrying out several extraction cycles, reusing either the biomass or the aqueous solutions of DES. A maximum cynaropicrin extraction yield of 7.76 wt % by reusing the solvent, and of 8.96 wt % by reusing the biomass, have been obtained. Taking advantage of the cynaropicrin solubility limit in aqueous solutions, water was added as an anti-solvent, allowing to recover 73.6 wt % of the extracted cynaropicrin. This work demonstrates the potential of aqueous solutions of DES for the extraction of value-added compounds from biomass and the possible recovery of both the target compounds and solvents.

Density, excess and limiting properties of (water and deep eutectic solvent) systems at temperatures from 293.15 K to 343.15 K

Deep eutectic solvents (DESs) are derived from two or more salts as the hydrogen bond acceptors (HBAs) and hydrogen bond donors (HBDs). In this work, DES namely allyltriphenyl phosphonium bromide-diethylene glycol (ATPPB-DEG) was prepared by using three molar ratios of 1:4, 1:10 and 1:16 salt to HBD. The volumetric properties of aqueous DESs, such as density, molar volume, isobaric thermal expansion, apparent molar volume and apparent molar expansibility were reported at several temperatures from 293.15 to 343.15K. A mathematical equation, so-called Jouyban–Acree model (JAM), was used to correlate the experimental density and molar volume data of aqueous solution of DESs with respect to the concentration and temperature. The results disclosed that this model is an accurate and reliable model for the prediction of aqueous DES properties. The excess properties, such as excess molar volume and excess isobaric thermal expansion were reported and fitted to two different equations. In order to calculate the limiting apparent molar volume values, the apparent molar volume values were fitted into a Redlich–Mayer equation. By applying the Hepler equation, it was found that DESs with molar ratios of 1:4 and 1:10 are as structure-maker solutes, while the DES 1:16 is a structure-breaking solute in aqueous solutions at different temperatures.

Ultrasonic study of binary aqueous mixtures of three common eutectic solvents

ABSTRACTUltrasonic velocities have been measured for different binary mixtures of common choline chloride-based deep eutectic solvents (DESs), namely, reline, glyceline and ethaline with water, in the range of temperature: 303.15–353.15 K. The experimental data measurements with different mole fractions of DES–water solutions were utilised in fitting four different models for speed of sound. These models correlate the speed of sound with some physical properties such as molar volumes, molar components sound velocity, densities, molecular weights, collision factors etc. A close match was obtained with these models with an average relative error of less than 4% for all data points used. It was observed that the ultrasonic velocity increases with the concentration of DES solvent and decreases with temperature. Moreover, this study roughly indicated that the intermolecular interactions in reline and ethaline aqueous mixtures exist in the form of disruption of dipole–dipole interactions (that varies considerably as a function of DES mixture composition and solution temperature). On the other hand, the interactions on the molecular level in glyceline aqueous solution are mainly due to dipole–dipole intermolecular forces.

Viscosity of aqueous ionic liquids analogues as a function of water content and temperature

Ionic liquids analogues known as Deep Eutectic Solvents (DESs) are gaining a surge of interest by the scientific community, and many applications involving DESs have been realized. Moisture content is one of the important factors that affects the physical and chemical characteristics of these fluids. In this work, the effect of mixing water with three common type III DESs on their viscosity was investigated within the water mol fraction range of (0–1) and at the temperature range (298.15–353.15 K). Similar trends of viscosity variation with respect to molar composition and temperature were observed for the three studied systems. Due to the asymmetric geometry of the constituting molecules in these fluids, their viscosity could not be modeled effectively by the conventional Grunberg and Nissan model, and the Fang–He model was used to address this issue with excellent performance. All studied aqueous DES mixtures showed negative deviation in viscosity as compared to ideal mixtures. The degree of intermolecular interactions with water reaches a maximum at a composition of 30% aqueous DES solution. Reline, the most studied DES in the literature, showed the highest deviation. The information presented in this work on the viscosity of aqueous DES solutions may serve in tuning this important property for diverse industrial applications involving these novel fluids in fluid flow, chemical reactions, liquid–liquid separation and many more.

On the behaviour of aqueous solutions of deep eutectic solvents at lipid biomembranes

The cytotoxicity of deep eutectic solvents is studied at molecular level using molecular dynamics simulations with a 1-palmitoyl-2-oleoylphosphatidylcholine lipid bilayer as a model of cell membranes and its interaction with eleven choline chloride – based deep eutectic solvents considering different hydrogen bond donors that allows to cover a wide spectrum of molecular variations. The possible insertion of molecules forming the deep eutectic solvent in the lipid bilayer and the changes in bilayer properties upon interaction with DESs are analysed as a function of the molecular structure of the considered hydrogen bond donors. The results confirm the pivotal role of the used hydrogen bond donor for deep eutectic solvents development on the interaction and insertion in the lipid bilayer, and thus on the deep eutectic solvent cytotoxicity. Likewise, molecular dynamics studies on deep eutectic solvents – lipid bilayers are a suitable tool for in silico screening and design of deep eutectic solvents with suitable environmental and toxicity profiles.