Deep Eutectic Solvents Components Research Articles

Extraction of astaxanthin from Haematococcus pluvialis with hydrophobic deep eutectic solvents based on oleic acid

Three novel hydrophobic deep eutectic solvents (DESs) based on oleic acid and terpenes (thymol, dl-menthol, and geraniol) were prepared, characterized, and used to extract astaxanthin from the microalga Haematococcus pluvialis without any pre-treatment of the cells. The three DES were composed of Generally Recognized As Safe (GRAS) and edible ingredients. All the tested DESs gave astaxanthin recovery values of about 60 and 30% in 6 h if applied on freeze-dried biomass or directly on algae culture, respectively. The carotenoid profile was qualitatively identical to what was obtained by using traditional organic solvents, regardless of the DES used; the monoesters of astaxanthin with C18-fatty acids were the main compounds found in all the carotenoid extracts. The thymol:oleic acid DES (TAO) could preserve astaxanthin content after prolonged oxidative stress (40% of the astaxanthin initially extracted was still present after 13.5 h of light exposure), thanks to the superior antioxidant properties of thymol. The capacity of improving astaxanthin stability combined with the intrinsic safety and edibility of the DES components makes the formulation astaxanthin-TAO appealing for the food ingredients/additives industry.

Impact of deep eutectic solvents (DESs) and individual DES components on alcohol dehydrogenase catalysis: connecting experimental data and molecular dynamics simulations

The systematic study on the effects of DESs and their individual components with the joint forces of experiments and MD simulations for the design of enzyme-compatible green solvents.

Efficient Extraction of Fermentation Inhibitors by Means of Green Hydrophobic Deep Eutectic Solvents.

The methods for hydrogen yield efficiency improvements, the gaseous stream purification in gaseous biofuels generation, and the biomass pretreatment are considered as the main trends in research devoted to gaseous biofuel production. The environmental aspect related to the liquid stream purification arises. Moreover, the management of post-fermentation broth with the application of various biorefining techniques gains importance. Chemical compounds occurring in the exhausted liquid phase after biomass pretreatment and subsequent dark and photo fermentation processes are considered as value-added by products. The most valuable are furfural (FF), 5-hydroxymethylfurfural (HMF), and levulinic acid (LA). Enriching their solutions can be carried with the application of liquid–liquid extraction with the use of a suitable solvent. In these studies, hydrophobic deep eutectic solvents (DESs) were tested as extractants. The screening of 56 DESs was carried out using the Conductor-like Screening Model for Real Solvents (COSMO-RS). DESs which exposed the highest inhibitory effect on fermentation and negligible water solubility were prepared. The LA, FF, and HMF were analyzed using FT-IR and NMR spectroscopy. In addition, the basic physicochemical properties of DES were carefully studied. In the second part of the paper, deep eutectic solvents were used for the extraction of FF, LA, and HMF from post-fermentation broth (PFB). The main extraction parameters, i.e., temperature, pH, and DES: PFB volume ratio (VDES:VPFB), were optimized by means of a Box–Behnken design model. Two approaches have been proposed for extraction process. In the first approach, DES was used as a solvent. In the second, one of the DES components was added to the sample, and DES was generated in situ. To enhance the post-fermentation broth management, optimization of the parameters promoting HMF, FF, and LA extraction was carried under real conditions. Moreover, the antimicrobial effect of the extraction of FF, HMF, and LA was investigated to define the possibility of simultaneous separation of microbial parts and denatured peptides via precipitation.

Determination of Thiophanate-Methyl and Carbendazim from Environmental Water by Liquid-Liquid Microextraction (LLME) Using a Terpenoid-Based Hydrophobic Deep Eutectic Solvent and High-Performance Liquid Chromatography (HPLC)

A hydrophobic deep eutectic solvent (DES) based vortex-assisted liquid-liquid microextraction (LLME) procedure was developed for the effective and rapid determination of thiophanate-methyl (TM) and carbendazim (CA) in lake water and tap water samples, with an excellence extraction efficiency (recovery: 87.2% to 97.4%, enrichment factor: 87.2 to 97.4). Twelve hydrophobic DESs based on terpenoids and fatty acids/alcohols were prepared, and those with the highest recovery for TM and CA were selected. The main parameters, including assisting methods, molar ratio of DES components, volume of DES, and NaCl content that may affect vortex-assisted LLME, were optimized. The intra-day and inter-day relative standard deviation (RSD) of this method were from 1.7% to 3.8% and 1.8% to 4.1%, showing excellent precision. The proposed method exhibited suitable limits of detection (TM: 0.053 µg/mL; CA: 0.007 µg/mL) and limits of quantification (TM: 0.177 µg/mL; CA: 0.024 µg/mL).

Vapor pressures and vapor phase compositions of choline chloride urea and choline chloride ethylene glycol deep eutectic solvents from molecular simulation.

Despite the widespread acknowledgment that deep eutectic solvents (DESs) have negligible vapor pressures, very few studies in which the vapor pressures of these solvents are measured or computed are available. Similarly, the vapor phase composition is known for only a few DESs. In this study, for the first time, the vapor pressures and vapor phase compositions of choline chloride urea (ChClU) and choline chloride ethylene glycol (ChClEg) DESs are computed using Monte Carlo simulations. The partial pressures of the DES components were obtained from liquid and vapor phase excess Gibbs energies, computed using thermodynamic integration. The enthalpies of vaporization were computed from the obtained vapor pressures, and the results were in reasonable agreement with the few available experimental data in the literature. It was found that the vapor phases of both DESs were dominated by the most volatile component (hydrogen bond donor, HBD, i.e., urea or ethylene glycol), i.e., 100% HBD in ChClEg and 88%-93% HBD in ChClU. Higher vapor pressures were observed for ChClEg compared to ChClU due to the higher volatility of ethylene glycol compared to urea. The influence of the liquid composition of the DESs on the computed properties was studied by considering different mole fractions (i.e., 0.6, 0.67, and 0.75) of the HBD. Except for the partial pressure of ethylene glycol in ChClEg, all the computed partial pressures and enthalpies of vaporization showed insensitivity toward the liquid composition. The activity coefficient of ethylene glycol in ChClEg was computed at different liquid phase mole fractions, showing negative deviations from Raoult's law.

Structure and hydrogen bonds of hydrophobic deep eutectic solvent‐aqueous liquid–liquid interfaces

AbstractHydrophobic deep eutectic solvents (DESs) emerge as candidates to extract organic substrates from aqueous solutions. The DES‐aqueous liquid–liquid interface plays a vital role in the extraction ability of DESs because the nonbulk structure of interfacial molecules could cause thermodynamic and kinetic barriers. One question is how the DES compositions affect the structural features of the interface. We investigate the density profile, dipole moment, and hydrogen bonds of eight hydrophobic DES‐aqueous interfaces using molecular dynamics simulations. The eight DESs are composed of four organic compounds: decanoic acid, menthol, thymol, and lidocaine. The results show the variations of dipole moment and hydrogen bond structure and dynamics at the interfaces. These variations could influence the extraction ability of DES through adjusting the partition and kinetics of organic substrates in the DES‐aqueous biphasic systems. We also analyze the relationship between the variation of these interfacial features and the size and hydrophobicity of DES components.

Deep Eutectic Solvents and Pharmaceuticals

Deep eutectic solvents (DES) are eutectic mixtures that present a deviation from the ideal thermodynamic solid–liquid phase behavior, where a significant depression in the melting temperature occurs. If properly designed and chosen, DES may be liquid at room and the human body’s temperatures and display a biocompatible character, thus representing relevant options in the pharmaceutical field. Accordingly, DES have been studied as alternative solvents or in formulations of pharmaceuticals to improve their solubility and stability. Depending on the DES components, these mixtures might exhibit interesting biological activities compatible with several applications. The use of DES as functional agents or as novel liquid forms of active pharmaceutical ingredients (API-DES) with the goal of improving bioavailability, permeability and therapeutic efficacy of a given API stands as alternative strategies in the pharmaceutical field for drug delivery purposes.

Application of curcumin as a green and new sorbent in deep eutectic solvent-based dispersive micro-solid phase extraction of several polycyclic aromatic hydrocarbons from honey samples prior to gas chromatography-mass spectrometry determination.

A green, simple, and efficient dispersive micro-solid phase extraction method was developed for the extraction of polycyclic aromatic hydrocarbons from honey samples. In this method, for the first time, curcumin was used as an efficient and green sorbent to extract the analytes from the sample. After that the adsorbed analytes were eluted using a deep eutectic solvent prepared by mixing tetrabutylammonium chloride: ethylene glycol and analyzed by gas chromatography-mass spectrometry. Important experimental factors affecting adsorption and desorption steps of the method were optimized and under optimal experimental conditions, low limits of detection (0.14-0.37ng/g) and quantification (0.49-1.3ng/g), wide linear range (1.3-500ng/g) with a coefficient of determination ≥0.994 were obtained. Relative standard deviation values for intra- and interday precisions were ≤7.5% for all of the analytes at a concentration of 2ng/g for each analyte (n=6). Extraction recovery of the method was in the range of 72-81%. Finally, 20 honey samples were analyzed and the analytes were successfully detected. The method is environment friendly because of the use of curcumin as a sorbent. Also, biodegradability of the used deep eutectic solvent components is another advantage of the method.

Fate of a Deep Eutectic Solvent upon Cosolvent Addition: Choline Chloride-Sesamol 1:3 Mixtures with Methanol.

The changes upon methanol (MeOH) addition in the structural arrangement of the highly eco-friendly deep eutectic solvent (DES) formed by choline chloride (ChCl) and sesamol in 1:3 molar ratio have been studied by means of attenuated total reflection Fourier transform infrared spectroscopy, small- and wide-angle X-ray scattering (SWAXS), and molecular dynamics simulations. The introduction of MeOH into the DES promotes the increase of the number of Cl–MeOH hydrogen bonds (HBs) through the replacement of sesamol and choline molecules from the chloride anion coordination sphere. This effect does not promote the sesamol–sesamol, choline–choline, and sesamol–choline interactions, which remain as negligible as in the pure DES. Differently, the displaced sesamol and choline molecules are solvated by MeOH, which also forms HBs with other MeOH molecules, so that the system arranges itself to keep the overall amount of HBs maximized. SWAXS measurements show that this mechanism is predominant up to MeOH/DES molar ratios of 20–24, while after this ratio value, the scattering profile is progressively diluted in the cosolvent background and decreases toward the signal of pure MeOH. The ability of MeOH to interplay with all of the DES components produces mixtures with neither segregation of the components at nanoscale lengths nor macroscopic phase separation even for high MeOH contents. These findings have important implications for application purposes since the understanding of the pseudophase aggregates formed by a DES with a dispersing cosolvent can help in addressing an efficient extraction procedure.

Volumetric and compressibility studies on aqueous mixtures of deep eutectic solvents based on choline chloride and carboxylic acids at different temperatures: Experimental, theoretical and computational approach

Deep eutectic solvents (DESs) constitute a new class of green solvents, the studies on which are going at a fast pace. The binary mixtures of DESs with water are attracting a great deal of interest for various industrial applications owing to their unique properties not exhibited by the neat components. Therefore, thermodynamic properties of DESs-water mixtures should be explored to better understand the prevailing intermolecular interactions for enhancing the application arena of such binary mixtures. Herein, the density (ρ) and speed of sound (u) of binary mixtures of DESs (choline chloride: acetic acid; 1: 2; and choline chloride: L-(+)-lactic acid; 1: 2) with water has been measured over whole composition range at different temperatures (T = 298.15 to 313.15 K) and atmospheric pressure. The values of various thermodynamic parameters have been derived and discussed in terms of the varying extent of intermolecular interactions governed by the components of DESs. The negative values of excess molar volumes (VmE) are ascribed to the stronger hydrogen bond interactions and efficient molecular packing in the binary mixtures over repulsive interactions. The VmE values have been analyzed using Prigogine-Flory-Patterson (PFP) theory, which satisfactorily explained the volumetric behaviour of the binary mixtures. Density functional theory (DFT) calculations have been made to support the variation in VmE and the underlying interactions prevailing between the components. Further, isentropic compressibility (ks) and excess isentropic compressibility (ksE) have been evaluated from the speed of sound data. It is expected that such studies will be beneficial from the academic as well as industrial point of view considering the increasing utilization of DESs for various applications.

Evaluation of canonical choline chloride based deep eutectic solvents as dye-sensitized solar cell electrolytes.

Deep eutectic solvents (DESs) are beginning to attract interest as electrolyte alternatives to conventional organic solvents and ionic liquids within dye-sensitized solar cells (DSSCs). The precise roles played by DES components and whether they simply represent a benign medium for mobilizing charge carriers or present beneficial functionality that impacts device performance remain unclear. To begin to address this deficiency in understanding, we performed a comprehensive characterization of the three "canonical" choline chloride-based DESs (i.e., reline, ethaline, and glyceline) as DSSC electrolytes hosting the iodide-triiodide (I-/I3 -) redox couple. The measurement of electrolyte viscosities, determination of triiodide diffusion coefficients, and photovoltaic performances assessed for water contents up to 40 wt. % allow the emergence of several important insights. A comparison to the observed photovoltaic performance arising from the individual components aids in further clarifying the impact of DES chemistry and solution viscosity on photovoltaic and charge carrier diffusion characteristics. Finally, we introduce the DES guaniline-consisting of a 1:1 molar ratio mixture of choline chloride with guanidinium thiocyanate-demonstrating it to be a superior DSSC electrolyte over those formulated from the three most widely studied canonical DESs at all water contents investigated.

Beneficial and detrimental effects of choline chloride-oxalic acid deep eutectic solvent on biogas production.

Deep eutectic solvents (DES), a new class of alternative solvents, have recently been used in the pre-treatment of lignocellulosic biomass. Due to the ability to dissolve phenolic compounds, they have been efficiently applied as delignification agents. However, to extend DES application to bioprocesses, such as Anaerobic Digestion (AD), their toxicity to microbial consortia must be evaluated. In this work, an effective delignifying DES, composed of choline chloride (ChCl) and oxalic acid (OA) (1:1) was prepared and its effect evaluated, for the first time, in biogas production. Results show that the presence of DES had both beneficial and detrimental effects on the anaerobic consortium, depending on its concentration. In the concentration range of 0.3-12.5g/L, the presence of DES led to a lag-phase of 1 to 8 d as the DES concentration increased. However, after the lag-phase has been surpassed, DES up to a concentration of 12.5g/L improved the biogas production, reaching an accumulated biogas volume three times higher than the control assay for the concentration of 12.5g/L. For the highest DES concentrations (19.8-78.1g/L), the biogas production was inhibited. The assays performed with DES components alone have indicated that OA at 3.2g/L was the main responsible for the inhibition of biogas production (50% less biogas produced than the control). ChCl at 4.9g/L has not presented a lag-phase and produced an accumulated biogas volume like the control assay (1200mL for 30 d incubation). This work points out that ChCl:OA DES may be used in the delignification of biomass further submitted to AD, provided the inhibitory concentrations of OA are not achieved.

Phase separation property of a hydrophobic deep eutectic solvent-water binary mixture: A molecular dynamics simulation study.

Over the past decade, deep eutectic solvents (DESs) have earned applicability in numerous fields as non-flammable, non-volatile, and greener alternatives to conventional organic solvents. In a first of its kind, a hydrophobic DES composed of a 1:1 mixture of oleic acid and lidocaine was recently reported, possessing a lower critical solution temperature in water. The thermoreversible phase property of this DES-water system was utilized to sequester out dye molecules from their aqueous solutions. In this article, we explore the phase separation phenomena for this particular DES in its aqueous solution using an all-atom molecular dynamics simulation. A 50 wt.% solution of the DES in water was studied at three different temperatures (253, 293, and 313K) to understand the various molecular interactions that dictate the phase segregation property of these systems. In this work, we have elaborated on the importance of hydrogen bonding interactions and the non-bonding interactions between the components and the competition between the two that leads to phase separation. Overall, we observe that the increase in unfavorable interaction between the DES components and water with increasing temperature determines the phase separation behavior. We have also studied the modification in the dynamical properties of water molecules close to the phase boundary. Such molecular insights would be beneficial for designing novel solvent systems that can be used as extraction-based media in industries.

Electrochemical Decomposition of Ethylene Glycol-Choline Chloride Deep Eutectic Solvent

Deep eutectic solvents (DES) are a form of ionic liquid that can offer a larger electrochemical window than water while remaining relatively conductive as compared to other non-aqueous options. DES are made from the eutectic combination of a variety of hydrogen bond donors and acceptors. At a molar ratio of donor and acceptor specific to each DES, the melting point of the mixture is significantly depressed resulting in a room temperature liquid with a high boiling point. As a result, they are considerably less volatile and therefore a safer alternative to traditional organic solvents such as acetonitrile. The low vapor pressure associated with a deep eutectic composition allows for operation at elevated temperatures for faster kinetics, increased conductivity and lower viscosity. DES can also contain a greater concentration of supporting charge carries than many organic solvents (up to 8 M) and many redox active organic compounds are also highly soluble in DES. These factors make DES a promising electrolyte for redox flow batteries, with the potential for higher energy densities than can be achieved in aqueous electrolytes.One of the most commonly studied DES is a 1:2 molar ratio mixture of choline chloride and ethylene glycol respectively. This mixture, commonly called ‘ethaline’ is one of the most conductive, lowest viscosity DES. While these are desirable characteristics, the stable electrochemical window is only ≈2 V which is only somewhat larger than the usable window of an alkaline aqueous electrolyte. The objective of this effort is to investigate the electrochemical decomposition of ethaline at the anodic and cathodic limits.Relatively little literature exists on the decomposition of ethaline. It has been claimed that at the anode, several different chlorinated organics are created by various mechanisms and that hydrogen is evolved at the cathode from water contained in the electrolyte.1 While the oxidation of ethylene glycol (EG) is well studied2 , 3, the oxidation of ethaline and the reduction of EG and ethaline both are somewhat unknown. A series of electrolysis experiments using a divided cell were carried out using dry ethaline prepared in a glove box with a water vapor content below 5 ppm. The water content in the electrolyte was determined by Karl Fischer titration to be less than 300 ppm. The products of these experiments were analyzed using mass spectroscopy (of both the anodic and cathodic electrolytes and of the headspace above each) and FTIR. These results show that the positive decomposition involves the oxidation of ethylene glycol to glycolaldehyde, and subsequent formation of the glycolaldehyde dimer in solution. At the negative limit, hydrogen is evolved in direct proportion to the current passed. However, it can be conclusively shown that the reduction current can exceed the maximum possible current due to the reduction of water, implying that the reduction of the DES components is necessary. GC-MS analysis of the negative electrolyte showed the presence of higher molecular weight fragments consistent with the reaction scheme shown in Fig 1 below. In this scheme, the reduction of ethylene glycol results in the generation of H2 gas as observed, and the formation of ethylene oxide. The ethylene oxide produced then can react chemically with ethylene glycol to yield dimers and trimers of polyethylene glycol whose molecular masses are consistent with the peaks observed in the GC-MS analysis.The identification of these breakdown pathways will provide insight into safety concerns related to overcharge of ethaline electrolytes and will allow for the development of alternative formulations that can extend the potential limits to allow for the incorporation of higher voltage redox couples in redox flow batteries based on DES electrolytes.

Betaine and l-carnitine ester bromides: Synthesis and comparative study of their thermal behaviour and surface activity

Six esters of both betaine and l-carnitine bromides, featuring alkyl groups ranging from C8 to C18 in length, have been synthesized. The thermal behaviour of these twelve bio-based salts has been analyzed and compared by thermal gravimetric analysis and differential scanning calorimetry. The l-carnitine alkyl ester bromides melted below 100 °C and can hence be considered ionic liquids (ILs) with full rights. Conversely, the betaine alkyl ester bromides, with the exception of the shortest member of the series, melted slightly above this upper limit. Also, they resulted less thermally stable when compared to their l-carnitine analogues. Moreover, the self-aggregation behavior of these structurally related betaine and l-carnitine alkyl ester bromides, inspected through surface tension, conductivity measurements and isothermal titration calorimetry, varied significantly. The critical micelle concentration (CMC) values for the l-carnitine series were lower than those of the betaine series, and the former ILs were also capable of adsorbing more efficiently at the air/water interface as well as of reducing surface tension. A potential use of these organic salts as components of deep eutectic solvents is envisaged, thus showcasing the applicability of this natural trimethylammonium cation.

Cooperative dynamics and speciation in deep eutectic solvent + DMSO mixtures

Dielectric relaxation (DR) spectra within the frequency range of 0.05 ≤ ν/GHz ≤ 89 were measured at T = 308.15 K to reveal structure and dynamics of mixtures of deep eutectic solvents (DESs) with dimethylsulfoxide (DMSO). Studied DESs were reline, glyceline and ethaline, ie. 1:2 molar ratio mixtures of choline chloride (ChCl) and the hydrogen bond donors (HBDs) urea, glycerol and ethylene glycol. The obtained DR spectra were best fit by a superposition of relaxations associated with the reorientation of dipolar DES components and individual DMSO molecules. In contrast to previously studied mixtures of glyceline and reline with water, the analysis of the obtained relaxation amplitudes revealed that the present DES/DMSO systems cannot be simply regarded as mixtures of individual Ch+, Cl−, HBD and DMSO units over the entire mixture range. Instead, a significant amount of ChCl contact ion pairs (CIPs) is formed at moderate DES concentrations. Due to their high dipole moment these CIPs cause pronounced maxima at ChCl:HBD:DMSO ratios of ~1 : 2 : 9 in the static permittivity of the mixtures. Pronounced solute-solvent interactions slow down the rotational motion of solvating DMSO molecules. At infinite dilution the derived total effective solvation numbers, Zt, extrapolate to ~8 − 9 DMSO per ethaline, ~16 per glyceline and ~7 − 8 per reline unit but numbers decrease rapidly with rising DES mole fraction. For the latter two DESs Zt could be split into ChCl and HBD contributions. Finally, careful analysis of the relaxation times provided evidence for pronounced micro-heterogeneity of the studied mixtures.

Tools for extending the dilution range of the “solvent-in-DES” regime

Deep eutectic solvents (DESs) and dilutions thereof are currently gaining increased interest in sustainable processes. DES dilutions are particularly interesting in the so-called “solvent-in-DES” regime where the intriguing features of DESs remain (coming from hydrogen bonding among the components) and some typical drawbacks (e.g., high viscosity, low electrical conductivity, etc.) are mitigated. Actually, DES dilutions may exhibit excellent performances (more so than the original neat DESs) in certain applications. Knowing about the tools that allow predicting (and eventually extending) the dilution range of the “solvent-in-DES” regime is obviously of interest. With this aim, we herein studied two sets of DES dilutions. In the first set, we used the DES composed of choline chloride (ChCl) and urea (U) and its dilutions in H2O, methanol (MeOH) and ethanol (EtOH). In the second set, we studied two DESs composed of ethylene glycol (EG) and either tetraethylammonium bromide (TEABr) or tetrabutylammonium bromide (TBABr), and their dilutions in H2O. Data coming from DSC, 1H NMR spectroscopy, and Brillouin spectroscopy revealed how the dilution range of the “solvent-in-DES” regime in ChClU dilutions in H2O, MeOH and EtOH increased in the order H2O < MeOH < EtOH while in aqueous dilutions of TEABrEG and TBABrEG increased in the order TEABrEG < TBABrEG. Our results suggest that the extension of the dilution range of the “water-in-DES” regime could be tuned by both the DES components solubility in the different solvents, and the strength and/or number of the hydrogen bonds established between DES components and solvent molecules.

β-glucosidase from Streptomyces griseus: Ester hydrolysis and alkyl glucoside synthesis in the presence of Deep Eutectic Solvents

Deep Eutectic Solvents (DES) are ionic liquid analogs that have attracted considerable attention as green solvents for biocatalytic transformations. The use of DES as part of a ‘solvent engineering’ approach to enhance enzyme stability holds great promise since they are biodegradable, relatively inexpensive and environmentally safe media for enzyme reactions. However, the behaviour of specific enzymes in such solvents is complex; some enzymes are inhibited in DES, while others appear to be activated.Glucosidases are among the most widely used enzymes for commercial chemoenzymatic synthesis. In particular, their application in the synthesis of biodegradable alkyl glucosides by reverse hydrolysis is of great interest. Previous work in this laboratory identified Streptomyces griseus glucosidase (Sgβgl) as an interesting enzyme for biotechnological applications. In this study, we examined its behaviour in the presence of DES as a co-solvent using choline chloride as hydrogen bond donor and using glycerol, glucose and urea as hydrogen bond acceptors. We show that Sgβgl activity depends on both the nature of DES components, and their ratio in the eutectic mixture, as well as the water content of the reaction medium. A choline chloride/glycerol DES mixture at a level of 40% (v/v) caused activation of Sgβgl and increased its optimum temperature from 70 to 80 ​°C: it also led to a striking increase in its thermostability, doubling its half-life at 60 ​°C and almost tripling its half-life at 80 ​°C.The synthesis of alkyl glucosides was explored using DES as a co-solvent. In the presence of DES, Sgβgl catalysed the formation of a range of alkyl glucosides. The presence of DES resulted in enhanced product yield, which was observed to increase with increasing temperature, up to 60 ​°C.These studies show that the application of DES at relatively low % (v/v) levels can dramatically effect enzyme activity and stability. Specifically, enhanced thermostability can significantly increase the operating range for glucosidases for biocatalytic applications. Solvent engineering offers a simple and effective way to enhance glucosidase stability and will be useful as an alternative and/or adjunct to more complex methods such as immobilisation or protein engineering.

Electrochemical Determination and Antioxidant Capacity Modulation of Polyphenols in Deep Eutectic Solvents

Deep eutectic solvents (DES) are currently developed as ecofriendly and efficient solvents for polyphenol extraction. However, a challenge remains in these processes concerning polyphenol determination that is routinely performed through colorimetric Folin–Ciocalteu assays. Besides the fact that these assays use toxic reagents, they may have serious limitations in some DES media due to possible side reactions or interferences with the DES components as found herein with ethaline (choline chloride/ethylene glycol (1:2)) or betaine/citric acid (2:3). An alternative method based on simple electrochemical analyses directly performed in DES-based media is proposed. Since the direct electrochemistry of polyphenols in DES has been hardly explored, nine polyphenolic standards including seven flavonoids are examined and their electrochemical behaviors are found closely related to those classically obtained in traditional solvents, notably in aqueous solutions. A linear relationship is obtained between concentration and peak current intensity for quercetin in the range 10–⁵–10–⁴ mol·L–¹, demonstrating the potential of the method for polyphenol content quantitation. More importantly, their antioxidant capacity is evaluated by differential pulse voltammetry through the measurements of the redox potentials. An interesting variation is observed according to the nature of the DES components, suggesting that the antioxidant activity of polyphenols can be modulated through the choice of the DES. Moreover, a good stability of the polyphenol samples in the DES–water mixture under study is obtained after storage for 10 months at 30 ° C. These results open appealing perspectives in polyphenol extraction processes using eutectic solvents as extracting media that can be part of formulation for cosmetic or pharmaceutical applications, resulting in high-added-value extracts.

Selective extraction of quinolizidine alkaloids from Sophora flavescens Aiton root using tailor-made deep eutectic solvents and magnetic molecularly imprinted polymers

In this study, an eco-friendly extraction method that used tailor-made deep eutectic solvents (DESs) for the extraction of oxymatrine and matrine from Sophora flavescens Aiton root was implemented for the first time. The extraction parameters, including the DES type, DES water content, solid-to-liquid ratio, extraction time, and extraction temperature, which affected the extraction efficiencies of oxymatrine and matrine were optimised. High-performance liquid chromatography with a diode-array detector and quantitative analysis of the DES components was conducted. The highest oxymatrine and matrine extraction yields (21.04 and 1.53 mg·g−1, respectively) were obtained using DES-2 (comprising choline chloride and malonic acid; molar ratio of 1:2) with 50% water and DES-8 (comprising choline chloride and ethylene glycol; molar ratio of 1:2) with 30% water as the extraction solvents, respectively. Furthermore, magnetic molecularly imprinted polymers (MMIPs) were successfully synthesised using oxymatrine, acrylic acid, ethylene glycol dimethylacrylate, azobisisobutyronitrile, and acetonitrile–methylbenzene (3:1, v/v) as the template, functional monomer, cross-linker, initiator, and porogen, respectively. The MMIPs were characterised using transmission electron microscopy, Fourier-transform infrared spectroscopy, and X-ray diffraction analyses, and the results demonstrated the successful preparation of MMIPs. The adsorption properties of MMIPs were further analysed using static and dynamic adsorption experiments, and the results indicated that MMIPs presented good adsorption capacities for oxymatrine and matrine (110.8 and 63.4 mg·g−1, respectively). Lastly, MMIPs were used as sorbents for the extraction and enrichment of oxymatrine and matrine from DES extracts of S. flavescens roots. The extraction efficiencies of oxymatrine and matrine (80.21–89.15% and 85.33–95.28%, respectively) were satisfactory. The proposed DES-based extraction followed by MMIPs secondary enrichment appeared to be an effective method for the selective extraction of specific components from complex samples.