Deep Eutectic Systems Research Articles

Effect of water on the structure and dynamics of choline chloride/glycerol eutectic systems

Deep Eutectic Systems (DESs) are an emerging class of green solvents with a myriad of applications, from biotechnology to material science. The high viscosity of most DESs is an obstacle that can be circumvented by the addition of water. But how much water is too much water? There is a need to understand the effect of water in the organizational dynamics of DESs, and to clarify the role of water on the physical properties of the DES, and as a functional additive.In this work, NMR spectroscopy was used to study choline chloride:glycerol (at a 1:2 molar ratio) systems with added water, at water contents ranging from 1 wt% (xw = 0.06) to 70 wt% (xw = 0.94). We identified three distinct water behaviour domains. Up to a water content of 11 wt%, water does not disrupt the DES structure; in fact, water has a glue-like effect, acting as a bridge between the DES components. Between water contents of 11 wt% and 35 wt%, the solvation of the DES components starts to occur, but the DES nanostructure is still present. At 35 wt% of water, the DES structure is disrupted, and the system transitions to a DES-in-water solution.

Unveiling the potential of betaine/polyol-based deep eutectic systems for the recovery of bioactive protein derivative-rich extracts from sardine processing residues

In addition to nutritional and functional properties, fish proteins have been consistently associated to different biological activities. In the work reported herein, the application of betaine/polyol-based deep eutectic systems (DES) was explored for the recovery of bioactive protein derivative-rich extracts contained in sardine processing waste streams. Aiming at maximizing the extraction of target compounds, the impact of operating temperature, extraction time, and solid/liquid ratio on the extraction performance was evaluated. Extractions using DES as alternative solvents were compared to a conventional solid/liquid extraction with water. The antioxidant activity of sardine extracts was assessed using the Oxygen Radical Absorbance Capacity assay, while their antimicrobial potential, as well as DES’, was evaluated towards Staphylococcus aureus and Escherichia coli. Results have shown that the protein maximum extraction yields obtained with DES were similar to those achieved with water (162.2 ± 20.4 compared to 145.7 ± 2.9 mgprotein/gdry residue). Nevertheless, most DES extracts obtained at 80 °C were able to surpass the antioxidant and antimicrobial potential of water extracts, with an increase in activity of up to 3-fold and more than 250-fold, respectively, for the most promising extracts. Furthermore, results have also shown that the DES tested present antimicrobial potential, which might have enhanced the bioactivity of the extracts. Therefore, the study reported herein reinforces that DES represent not only a possible alternative extraction media for the recovery of protein derivatives from fish biomass, but also a promising vehicle for the obtained extracts, with potential to be used in industrial applications.

Promising Technological and Industrial Applications of Deep Eutectic Systems.

Deep Eutectic Systems (DESs) are obtained by combining Hydrogen Bond Acceptors (HBAs) and Hydrogen Bond Donors (HBDs) in specific molar ratios. Since their first appearance in the literature in 2003, they have shown a wide range of applications, ranging from the selective extraction of biomass or metals to medicine, as well as from pollution control systems to catalytic active solvents and co-solvents. The very peculiar physical properties of DESs, such as the elevated density and viscosity, reduced conductivity, improved solvent ability and a peculiar optical behavior, can be exploited for engineering modular systems which cannot be obtained with other non-eutectic mixtures. In the present review, selected DESs research fields, as their use in materials synthesis, as solvents for volatile organic compounds, as ingredients in pharmaceutical formulations and as active solvents and cosolvents in organic synthesis, are reported and discussed in terms of application and future perspectives.

Natural deep eutectic systems, an emerging class of cryoprotectant agents

This work aimed at evaluating the potential of using natural deep eutectic systems (NADES) as cryoprotectant agents (CPAs). Several combinations between natural primary metabolites that have been identified in animals that live in extreme cold climates were prepared. All systems showed very little cytoxicity towards L929 cells at concentrations high as 1–2 M. Moreover, this cell line was highly tolerant to 10% (w/v) of NADES when compared to Me2SO. To test NADES as CPAs, two cell lines were used, L929 and HacaT cells. After freeze/thawing cycle, it was possible to observe that for L929 cells, NADES presented similar behaviour to Me2SO. For Hacat cell line a significant improvement on post-thawing recovery was observed. Moreover, the results presented herein showed that NADES do not need to be removed from the freezing media after thawing the cells, which is a great advantage of these materials. Additionally, we have shown that NADES can act as CPA when cells are frozen at −20 °C. In overall, the results demonstrate the high potential of NADES to be used in cryobiology as alternative CPAs.

Deep eutectic systems from betaine and polyols – Physicochemical and toxicological properties

The tailor-made versatility of deep eutectic systems (DES) has opened promising future perspectives for their applications in industry, to complement or even replace some of the already existing processes. Although there has been an active and considerable effort by the scientific community to characterize these systems, their toxicity towards different living organisms has not yet been thoroughly investigated. In this work, different mixtures of betaine with glycerol, propylene glycol, ethylene glycol, and their mixtures with water, were prepared and characterized in terms of density, viscosity, and polarity. Additionally, DES effects were also evaluated on a human intestinal epithelial cell model (Caco-2), towards a Gram-positive (Staphylococcus aureus) and a Gram-negative (Escherichia coli) bacterium, and on wheat (Triticum aestivum) seeds. Results showed that the physicochemical properties of the DES tested, namely density and viscosity, could be tuned not only through the hydrogen bond donor, but also by changing temperature or the water content. Polarity was also considerably affected by the water content of the system. Additionally, although DES presented different responses towards different organisms, generally, the systems presented a low toxicity profile, which could be substantially reduced by increasing their water content. These findings suggest that the DES studied can be minimally toxic, with easily tunable properties, which reinforces the prospect of using this kind of systems in the field of green technologies.

The Role of Hydrogen Bond Donor on the Extraction of Phenolic Compounds from Natural Matrices Using Deep Eutectic Systems.

Recently, deep eutectic systems (DESs) as extraction techniques for bioactive compounds have surfaced as a greener alternative to common organic solvents. In order to study the effect of these systems on the extraction of phenolic compounds from different natural sources, a comprehensive review of the state of the art was carried out. In a first approach, the addition of water to these systems and its effect on DES physicochemical properties such as polarity, viscosity, and acidity was investigated. This review studied the effect of the hydrogen bond donor (HBD) on the nature of the extracted phenolics. The effects of the nature of the HBD, namely carbon chain length as well as the number of hydroxyl, methyl, and carbonyl groups, have shown to play a critical role in the extraction of different phenolic compounds. This review highlights the differences between DES systems and systematizes the results published in the literature, so that a more comprehensive evaluation of the systems can be carried out before any experimental trial.

Influence of natural deep eutectic systems in water thermal behavior and their applications in cryopreservation

Natural deep eutectic systems (NADES), which have applications as solvents for both engineering and life sciences, are mainly composed of sugars, aminoacids or organic acids. In this work NADES composed by glucose, urea and proline (G:U:P in a molar ratio of 1:1:1) and proline and glucose (P:G 5:3) were prepared and added in different mass fractions to water.By differential scanning calorimetry it was verified as the crystallization tendency of water is modified even for low fraction of NADES added. This is also observed by polarized optical microscopy which allowed following the formation of crystals with different crystalline morphologies as bulk water. Calorimetric data also shown as the crystallization temperature decreases for all P:G mixtures and this shift is more accentuated for weight fraction of NADES higher than 0.5. Crystallization is totally suppressed for NADES fraction higher than 0.7.NADES/water mixtures cytotoxicity was evaluated in vitro, revealing that they are less toxic as compared with the commonly used cryoprotective additives as dimethyl sulfoxide (DMSO). Additionally, cell viability tests with cell lines cryopreserved using DMSO and both the prepared NADES showed comparable viability.This work combines thermophysical data on NADES and evaluates it’s in vitro performance, providing cues for their use in cryopreservation applications.

Microwave-Assisted One-Pot Lipid Extraction and Glycolipid Production from Oleaginous Yeast Saitozyma podzolica in Sugar Alcohol-Based Media.

Glycolipids are non-ionic surfactants occurring in numerous products of daily life. Due to their surface-activity, emulsifying properties, and foaming abilities, they can be applied in food, cosmetics, and pharmaceuticals. Enzymatic synthesis of glycolipids based on carbohydrates and free fatty acids or esters is often catalyzed using certain acyltransferases in reaction media of low water activity, e.g., organic solvents or notably Deep Eutectic Systems (DESs). Existing reports describing integrated processes for glycolipid production from renewables use many reaction steps, therefore this study aims at simplifying the procedure. By using microwave dielectric heating, DESs preparation was first accelerated considerably. A comparative study revealed a preparation time on average 16-fold faster than the conventional heating method in an incubator. Furthermore, lipids from robust oleaginous yeast biomass were successfully extracted up to 70% without using the pre-treatment method for cell disruption, limiting logically the energy input necessary for such process. Acidified DESs consisting of either xylitol or sorbitol and choline chloride mediated the one-pot process, allowing subsequent conversion of the lipids into mono-acylated palmitate, oleate, linoleate, and stearate sugar alcohol esters. Thus, we show strong evidence that addition of immobilized Candida antarctica Lipase B (Novozym 435®), in acidified DES mixture, enables a simplified and fast glycolipid synthesis using directly oleaginous yeast biomass.

Unravelling the nature of citric acid:L-arginine:water mixtures: the bifunctional role of water.

The use of water as a component of deep eutectic systems (DES) has raised some questions regarding its influence on the nature of the mixture. Does it form a DES or an aqueous solution and what is the role of water? In this work, the nature of citric acid:l-arginine:water mixtures was explored through phase equilibria studies and spectroscopic analysis. In a first step, PC-SAFT was validated as a predictive tool to model the water influence on the solid liquid equilibria (SLE) of the DES reline using the individual-component approach. Hence, activity coefficients in the ternary systems citric acid:l-arginine:water and respective binary combinations were studied and compared using ePC-SAFT. It was observed that the water-free mixtures citric acid:l-arginine showed positive deviation from Raoult's law, while upon addition of water strong negative deviation from Raoult's law was found, yielding melting depressions around 100 K. Besides these strong interactions, pH was found to become acidic (pH = 3.5) upon water addition, which yields the formation of charged species ([H2Cit]- and [l-arg]+). Thus, the increased interactions between the molecules upon water addition might be caused by several mechanisms such as hydrogen bonding or ionic forces, both being induced by water. For further investigation, the liquid mixtures citric acid:l-arginine:water were studied by FTIR and NMR spectroscopy. FTIR spectra disproved a possible solubility enhancement caused by salt formation between citric acid and l-arginine, while NMR spectra supported the formation of a hydrogen bonding network different from the binary systems citric acid:water and l-arginine:water. Either being a DES or other type of non-ideal solution, the liquefaction of the studied systems is certainly caused by a water-mediator effect based on the formation of charged species and cross interactions between the mixture constituents.

Untangling the bioactive properties of therapeutic deep eutectic solvents based on natural terpenes

Abstract Treatment of microbial-related infections remains a clinical challenge that has been slowly aggravating over recent years, due to the dissemination of resistance against currently applied treatment protocols. In this current scenario, the design of novel treatment approaches is of great importance, being a prominent focus of the scientific community. In recent years deep eutectic systems (DES) have gained the attention of the scientific community due to their remarkable physicochemical and biological properties, versatility, and compliance with the green chemistry metrics. In this work, DES containing a monoterpenoid (thymol (THY) and menthol (ME)) in combination with ibuprofen (IBU) were formulated and characterized via thermal analyses and NMR spectroscopy. The biological activity of the most promising formulations was then explored, with focus on its antimicrobial and anticancer activity. Both ME and THY-based formulations presented relevant antibacterial activity against the panel of microorganisms tested. Among the THY-based formulation tested, THY:IBU 3:1 M ratio, showed the highest antibacterial activity, affecting all tested microorganisms, while ME:IBU 3:1 M ratio was only effective against Gram-positive bacteria and Candida albicans. Furthermore, both ME and THY-based formulations revealed cytotoxic effect towards the cancer cell model used (HT29), where ME:IBU 3:1 stood out as the most selective towards cancer cells without compromising normal cells viability. Overall, the results obtained highlight the potential use of terpene-based THEDES formulations that, due to their enhanced thermal properties, may represent a versatile alternative in several biomedical applications where an effective antimicrobial or anticancer therapeutic action remains a challenge.

Connecting chloride solvation with hydration in deep eutectic systems.

The Deep Eutectic Solvents/Systems (DESs) choline chloride:urea (xChCl = 0.33) and choline chloride:glycolic acid (xChCl = 0.5) were investigated using viscosity-corrected 35Cl NMR spectroscopy and molecular dynamics simulations to probe the role of chloride as a function of water content. Three Cl- solvation regimes are revealed, with high-symmetry environments for pure and highly dilute DES, and an unusual low-symmetry interstitial region where the primary coordination sphere is most disordered.

Heterogeneous dynamics, correlated time and length scales in ionic deep eutectics: Anion and temperature dependence.

Heterogeneous relaxation dynamics often characterizes deep eutectic solvents. Extensive and molecular dynamics simulations have been carried out in the temperature range, 303 ≤ T/K ≤ 370, for studying the anion and temperature dependencies of heterogeneous dynamics of three different ionic acetamide deep eutectics: acetamide + LiX, X being bromide (Br-), nitrate (NO3 -), and perchlorate (ClO4 -). These systems are chosen because the fractional viscosity dependence of average relaxation rates reported by various measurements has been attributed to the heterogeneous dynamics of these systems. Simulations performed here attempt to characterize the heterogeneous relaxation dynamics in terms of correlated time and length scales and understand the solution inhomogeneity in microscopic terms. Additionally, simulation studies for pure molten acetamide have been performed to understand the impact of ions on motional features of acetamide in these ionic deep eutectic systems. The computed radial distribution functions suggest microheterogeneous solution structure and dependence upon anion identity and temperature. A significant plateau in the simulated time dependent mean squared displacements indicates pronounced cage-rattling and inhomogeneity in relaxation dynamics. Simulated diffusion coefficients for acetamide and ions show decoupling from the simulated viscosities of these deep eutectics. Calculated two- and four-point correlation functions reveal the presence of dynamic heterogeneity even at ∼180 K above the measured thermodynamic glass transition temperature (Tg). Further analyses reveal the existence of multiple timescales that respond strongly to the rise in solution temperature. The simulated dynamic structure factor and overlap function relaxations show strong stretched exponential relaxations. The simulation results support the experimental observation that the bromide system is the most dynamically heterogeneous among these three systems. Correlated length scales show much weaker anion and temperature dependencies with an estimated length of ∼1 nm, suggesting formation of clusters at the local level as the origin for the micro-heterogeneous nature of these ionic deep eutectics.

Natural deep eutectic systems for improved cryopreservation of cells

Natural deep eutectic systems for improved cryopreservation of cells

Optimal Design of THEDES Based on Perillyl Alcohol and Ibuprofen.

Therapeutic deep eutectic systems (THEDES) have dramatically expanded their popularity in the pharmaceutical field due to their ability to increase active pharmaceutical ingredients (APIs) bioavailability. However, their biological performance has not yet been carefully scrutinized. Herein, THEDES based on the binary mixture of perillyl alcohol (POH) and ibuprofen (IBU) were prepared using different molar ratios. Our comprehensive strategy includes the characterization of their thermal and structural behavior to identify the molar ratios that successfully form deep eutectic systems. The in vitro solubility of the different systems prepared has demonstrated that, unlike other reported examples, the presence of the terpene did not affect the solubility of the anti-inflammatory agent in a physiological simulated media. The biological performance of the systems was studied in terms of their antimicrobial activity against a wide panel of microorganisms. The examined THEDES showed relevant antimicrobial activity against all tested microbial strains, with the exception of P. aeruginosa. A synergistic effect from the combination of POH and IBU as a eutectic system was verified. Furthermore, the cytotoxic profile of these eutectic systems towards colorectal cancer (CRC) in vitro cell models was also evaluated. The results provide the indication that the cell viability varies in a dose-dependent manner, with a selective THEDES action towards CRC cells. With tunable bioactivities in a ratio-dependent manner, THEDES enhanced the antimicrobial and anticancer properties, representing a possible alternative to conventional therapies. Therefore, this study provides foreseeable indications about the utility of THEDES based on POH and IBU as strong candidates for novel active pharmaceutical systems.

Natural deep eutectic systems for nature‐inspired cryopreservation of cells

AbstractNatural deep eutectic systems (NADES) are emerging as potential cryoprotective agents (CPA) for cell preservation. In this investigation, we develop an optimized CPA formulation using trehalose‐glycerol NADES (T:G) diluted in Normosol‐R and supplemented with isoleucine. Differential scanning calorimetry (DSC) is used to define the thermophysical properties of NADES‐based solutions, and Raman spectroscopy is used to characterize the effect of NADES on ice formation and hydrogen bonding. Jurkat cells are cryopreserved in each solution, and post‐thaw cell recovery, apoptosis, and growth are quantified. Raman spectra and heat maps show that NADES suppresses both ice formation and dehydration of the nonfrozen region. Supplementing NADES with isoleucine does not affect the solution's thermophysical properties but significantly improves the cells' survival and proliferation post‐thaw. The study indicates that thermophysical properties of CPA solutions alone cannot predict optimal cell survival, suggesting that stabilization of biological structures by CPAs may play a role in successful cryopreservation.

Investigation of pretreatment parameters in the delignification of paddy husks with deep eutectic solvents

In the present study, the delignification of paddy husks was carried out with ethylene glycol (EG)/citric acid (CA) deep eutectic systems (DES). The effects of the molar ratio of DES components, pretreatment temperature and pretreatment time on the lignin removal efficiency were investigated. The approximate quantitative analysis, ATR/FT-IR spectra and SEM-EDS analysis of untreated and pretreated samples were used to determine the lignin removal from paddy husks. The results obtained with ATR/FT-IR spectra and approximate analysis were determined to be consistent and supported the removal of lignin from the structure. The analysis results showed that the silica, which gives chemical strength to the structure, was also removed from the structure. Using DES systems with EG/CA molar ratios of 1:1, 1:2 and 2:1, lignin removal percentages at 90 °C were found to be 47.10%, 52.35% and 51.17%, respectively. The obtained results showed that two important parameters affecting the removal of lignin from the paddy husk are the pretreatment temperature and time. It was concluded that at high temperatures, intermolecular hydrogen bonds are weakened, the viscosity of the DES solution decreases, DES penetrates the lignocellulosic structure easily and thus the lignin removal efficiency is increased. The highest lignin removal percentage was found as 57.33% after 4 h of pretreatment time at 120 °C. The results showed that efficient delignification of paddy husks is possible using EG/CA DES systems.

Structure and properties of two glucose-based deep eutectic systems

Continued industrialization and increasing environmental problems have highlighted the need to research new eco-friendly solvents, also known as deep eutectic solvents (DESs). To implement these solvents in industrial processes, the knowledge of their molecular organization and thermophysical properties must be enhanced. In this work, two DESs have been characterized: d-glucose:choline chloride:water (GCH) and d-glucose:citric acid:water (GCiH). NMR techniques were used to analyse both the supramolecular structure and the role of water and to calculate the diffusion coefficients. Moreover, seven thermophysical properties at several temperatures were evaluated. As a second aim, the solubility of quercetin was determined. NMR studies showed a stronger supramolecular structure of GCH and a high ratio of β-glucose in both DESs. Based on the thermophysical results, the solvent with choline chloride had the most compact fluid structure. Finally, the solubility of quercetin in the DESs was higher than in water, especially for GCH.

Design of Nonideal Eutectic Mixtures Based on Correlations with Molecular Properties.

In this work, a statistical analysis was performed to reveal how the molecular properties are correlated with the nonideal behavior observed in eutectic mixtures. From this, a statistical model, combined with theory and experimental results, was developed to predict the nonideal behavior of a specific set of eutectic mixtures, consisting of quaternary ammonium bromides with dicarboxylic acids and polyols. The combination of this analysis and this model can be considered as a first step toward the a priori design of eutectic mixtures. The analysis performed is based on principal components. The descriptors used for this are molecular properties of the constituents of these mixtures. The molecular properties are a combination of experimental, theoretical, and computed properties. The analysis reveals that there are strong correlations between the nonideality of the mixtures and a measure of the acidity of the hydrogen bond donating protons, the displacement of the bromide anion, and the bulkiness of the quaternary ammonium salt. Our analysis highlights the design rules of deep eutectic systems (DES), enabling control over the extent of the liquid window. Our model enables prediction of the eutectic temperature for a range of related mixtures.

Macroporous Polyacrylamide γ-Fe2O3 Nanoparticle Composites as Methylene Blue Dye Adsorbents

In this work, we have explored the use of hydrophobic deep eutectic systems (DESs) composed of D-L-menthol and different naturally occurring acids (acetic acid, lauric acid, lactic acid and pyruvic...

Aqueous solutions of deep eutectic systems as reaction media for the saccharification and fermentation of hardwood xylan into xylitol

The aim of this study was to evaluate the effect of aqueous solutions of deep eutectic solvent, Cholinium Chloride:Urea ([Ch]Cl:U) at 50 wt% and 20 wt%, using different molar ratios (1:1, 2:1 and 1:2) on the enzymatic hydrolysis of xylan for xylose production and its subsequent bioconversion into xylitol using a recombinant yeast strain. The lowest xylan conversion into xylose (45%) was obtained using 1:2 [Ch]Cl:U molar ratio. On the other hand, the 1:1 [Ch]Cl:U molar ratio, at 20 wt% in water, improved this conversion, achieving the highest xylose yield (81.4%). The xylitol production was then optimized with [Ch]Cl:U (1:1) at 20 wt% by simultaneous saccharification and fermentation process, attaining 23.67 g/L, corresponding to 66.04% of xylitol yield. This study reveals the possibility of using xylan solubilized in DES aqueous solutions directly for xylitol production, thus assembling a one-step process.