Properties Of Deep Eutectic Solvents Research Articles

Unlocking the potential of oat straw: Efficient pretreatment methods for enhanced glucose production

The excellent physical and chemical properties of deep eutectic solvents, especially the ability of some of them to dissolve biomass, make them broadly applicable in biomass pretreatment. In this study, oat straw was pretreated with deep eutectic solvents composed of choline chloride and an acid (formic, lactic, or oxalic acid). The highest reducing sugar yield was obtained for the formic acid/choline chloride mixture. Using a pretreatment temperature of 110 °C, a reaction time of 2 h, and a solid-liquid ratio of 1:20, the reducing sugar yield obtained by cellulase hydrolysis was 23.5%, the degradation rate of cellulose reached 76.9%, and hemicellulose was completely degraded. The pretreated oat straw was then analyzed by scanning electron microscopy, Fourier transform infrared spectroscopy, and X-ray diffraction. The changes in its crystallinity and lignin content compared to the untreated specimen were determined. A preliminary mechanism for the pretreatment of oat straw with formic acid/choline chloride was revealed. The study could provide an opportunity to expand the application in biochemicals or biological feed processes.

Research on the effect of DES properties on the preparation of h-BN nanosheets by electrochemical-liquid phase exfoliation method

Hexagonal boron nitride (h-BN) with a large specific surface area and unique optoelectronic properties has good application prospects in many fields. The liquid phase exfoliation method is considered the most promising method for achieving controllable preparation of boron nitride nanosheets (BNNSs), but the low-cost, relatively environmentally friendly and efficient liquid phase exfoliation is still difficult to achieve. Choosing a suitable solvent system is the key to achieving efficient exfoliation. Deep eutectic solvents (DESs) have the advantages of simple synthesis, low cost, high thermal and chemical stability and strong biocompatibility and are expected to be green solvents for preparation of BNNSs. In this paper, it was found that the properties of DESs and its interaction with h-BN had a significant impact on the electrochemical exfoliation of h-BN. The intercalation effect of DES and the compatibility between DES and h-BN were the main factors affecting the yield, while the quality of BNNSs mainly depended on the decomposition and expansion effect of DES. This rule also can be applied to prepare highly conductive and hydrophilic two-dimensional material Ti-MXene. This research explores the structure–activity relationship between two-dimensional materials and DESs, and provides a theoretical basis for the environmentally friendly and efficient preparation of two-dimensional materials using DESs as exfoliation solvents.

Predicting the properties of deep eutectic solvents based on choline chloride and carboxylic acids and their mixtures with water using QSPR approach

Deep eutectic solvents (DES) are increasingly popular materials in various fields of chemistry. The set of properties of a particular DES determines the range of its applicability for a certain task. Tailoring these properties to meet the needs of various applications can be tedious, as it may require a large amount of experimental work. Here we propose the use of quantitative structure-property relationship (QSPR) approach to model DES properties. Using choline chloride and six carboxylic acids as a case study we attempted to construct regression models relating molecular descriptors of carboxylic acids and the properties of corresponding solvents. Statistically meaningful correlations were established between the descriptors of the acids and density, viscosity and conductivity of DES. The impact of different descriptors on these properties was analyzed based on the regression coefficients. Taking into account rather limited dataset a rigorous validation of the regression models was performed using double loop cross-validation.

Probing the interface of choline chloride-based deep eutectic solvent ethaline with gold surfaces: A molecular dynamics simulation study

Technologies involving a solvent|surface interface, such as nanotechnology, electrochemistry, and energy storage applications, are actively pursuing ecologically responsible and sustainable development practices. In response to this pressing need, deep eutectic solvents have emerged as a promising solution to bridge the gap between technological requirements and environmental concerns. In this work, we present the results of a molecular dynamics simulation study of the interface between a monocrystalline gold surface and the deep eutectic solvent ethaline, where a molar ratio of 1:2 choline chloride:ethylene glycol was used for ethaline. The simulations covered a range of temperatures from 313 K to 343 K and applied charge values ranging from 0 to ± 24 μC cm‒2. Several key interfacial properties were thoroughly analyzed, including among others, charge density profiles, radial distribution functions, hydrogen bond close contacts, and molecular orientation. Additionally, we examined how the differential capacitance varied upon the applied potential. Our findings reveal that, at neutral surfaces, all components of the solvent are present in the innermost layer, with ethylene glycol molecules being the most prevalent, followed by choline cations and a residual amount of chloride anions. For lower applied charges, this mixed composition at the boundary layer persists, despite the growing accumulation of ionic species with charges opposite to that of the electrode. As surface polarization increases, unique innermost boundary layers composed exclusively of one of the ionic species and the hydrogen bond donor molecules are observed, forming a multilayer structure, with subsequent layers enriched of paired counterions. Interestingly, even at higher applied charges, choline cations and ethylene glycol molecules tended to orient themselves in a parallel fashion toward the electrodes. Differential capacitance curves exhibited a camel-shaped behavior, suggesting a complex interplay of electrochemical processes at the DES|Au(100) interface. In summary, our study provides valuable insights into the interfacial properties of deep eutectic solvents on gold surfaces and their response to changes in temperature and potential, which are crucial for understanding and optimizing deep eutectic solvent-based electrochemical systems.

Computational insight into the effect of alkyl chain length in tetraalkylammonium-based deep eutectic solvents

The effect of the increase in the alkyl chain length of cation on the properties of deep eutectic solvents based on ethylene glycol has been investigated employing classical molecular dynamics simulations. The change in the structural and dynamic properties in both the bulk and liquid–vapor interface is explored through various analyses. The interaction between the anion and the ethylene glycol increases with an increase in the alkyl chain length of the cation, as observed in the increase of the lifetime of the hydrogen bond formed between the two. The terminal carbon atoms are found to be closer to each other when the cation changes from tetraethylammonium to tetrabutylammonium. The cations are located closer to the interface, and the association of the alkyl chains becomes more significant with increased alkyl chain length, decreasing the surface tension values.

DESignSolvents: an open platform for the search and prediction of the physicochemical properties of deep eutectic solvents

A web-resource, DESignSolvents, to provide users worldwide with the database of DES properties and the corresponding prediction models.

Cationic micelles in deep eutectic solvents: effects of solvent composition.

Deep eutectic solvents (DES) are mixtures of hydrogen bond donors and acceptors that form strongly hydrogen-bonded room temperature liquids. Changing the H-bonding components and their ratios can alter the physicochemical properties of deep eutectic solvents. Recent studies have shown p-toluenesulfonic acid (pTSA) forms room temperature liquids with choline chloride (ChCl) at different molar ratios: 1 : 1, 1 : 2 and 2 : 1 [Rodriguez Rodriguez et al., ACS Sustain. Chem. Eng., 2019, 7(4), 3940]. They also showed that the composition affects the physical properties of these liquids and their ability to dissolve metal oxides. In this work we evaluate the solubility and self-assembly of cationic surfactants alkyltrimethyl ammonium bromides (CnTAB) in these pTSA/ChCl based liquids. CnTABs are insoluble in 1pTSA : 2ChCl, whereas in 1pTSA : 1ChCl and 2pTSA : 1ChCl they form micelles. We characterise CnTAB (n = 12, 14, 16) micelles using small angle neutron scattering and also look at interaction of water with the micelles. These studies help determine the interaction of DES components with the surfactant and the influence of varying pTSA and water ratios on these interactions. This provides potential for controlled surfactant templating and for tuning rheology modification in such systems.

Physical properties of deep eutectic solvents with efficient nitrogen removal capability

The efficient separation of N-compounds from fuel oil is of great significance for environmental protection and the development of sustainable chemical processes. In this work, eight quaternary acidic deep eutectic solvents (DESs) were prepared for the removal of basic N-compounds (pyridine) from simulated oils. Initially, the density, viscosity, conductivity, surface tension and refractive index values of the DESs were determined at 293.15–333.15 K. Based on these data, physical quantities such as molecular volume, standard entropy, lattice energy, activation energy of viscous flow, activation energy of conductivity, surface entropy, surface energy, speed of sound, molar Gibbs free energy, molar polarizability, molar polarizability, and free molar volume have been calculated. The effects of temperature, alkyl chain length of hydrogen bond acceptors (HBAs)/hydrogen bond donors (HBDs), structure of HBDs, and HBAs anion on the physical properties of DESs were systematically investigated. The internal interaction and property change of DESs are further studied. Finally, pyridine was extracted from the simulated oil using the prepared DESs. DESs consisting of tetrabutylammonium bromide and lactic acid had the highest extraction capacity under the same conditions. The extraction efficiency was found to be strongly correlated with the alkyl chain length and the acidity of the HBDs. This work is expected to provide information on the removal of N-compounds from both theoretical and industrial perspectives.

Deep eutectic solvent-treated palm oil mill sludge adsorbents for methylene blue adsorption.

This study evaluated the adsorptive properties of deep eutectic solvent (DES)-treated palm oil mill sludge adsorbents for methylene blue removal. The adsorbents were prepared at a ratio of 1:2 at 80°C to form P1:D2@80°C, at 25°C to form P1:D2@25°C and without DES to form dry sludge (DS). The adsorbent samples were characterized for surface functional groups, textural properties and surface morphology. The values of specific area were 534, 236 and 184 m2/g, respectively. Batch adsorption of methylene blue at varying concentration, adsorbent dosage, pH, contact time and temperature was performed. The maximum adsorption capacities by Sips model were recorded as 72.07, 56.18 and 48.33 mg/g for P1:D2@80°C, P1:D2@25°C and DS, respectively. P1:D2@80°C displayed the highest rate constant (Ks = 0.0037 g/mg.min). The adsorption data were well fitted into Sips isotherm and pseudo-second-order kinetic models, suggesting that the adsorption is a physical process onto heterogeneous adsorbent surface via pore filling and electrostatic attraction. The adsorption was spontaneous, feasible and exothermic with decreased disorderliness in the solid-bulk solution interface. The DES-treated palm oil mill sludge adsorbent is a promising alternative adsorbent for dye removal from wastewater.

Structural Characterization and Properties of Deep Eutectic Solvents Plasticized Chitosan Films

In this study chitosan (CS) films were prepared from a deep eutectic solvent (DES) composed of choline chloride and malonic acid by solvent casting, and the influence of DES content on the structure and properties of the CS films was investigated in detail. It was confirmed by the spectral data that hydrogen bonds and ionic bonds were formed between the CS chains and DES. Structural analysis demonstrated that the crystallization of the CS was greatly hampered and the CS chains were stacked disorderly in films with high DES content. Differential scanning calorimetry (DSC) results indicated that DES exerted a significant plasticizing effect. In the case of the plasticized film containing 80 wt% of DES it showed a low glass transition temperature (Tg) of 20 °C. With increasing DES content, the water content of the plasticized films also increased, evidenced by the TGA results. Meanwhile, a structural change from granular to lamellar structure was observed by SEM. In addition, compared with pure CS film, the DES plasticized CS films possessed good fracture toughness and hydrophilicity. These observations suggest that the structure and properties of the CS films can be controlled by changing their DES content.

A surfactant-based quasi-hydrophobic deep eutectic solvent for dispersive liquid-liquid microextraction of gliflozins from environmental water samples using UHPLC/fluorescence detection

Despite the anticipated exceptional properties of deep eutectic solvents (DES) in microextraction techniques, their self-aggregation behaviour has only been sporadically studied in the previous literature. In the presented study, a novel surfactant-based quasi-hydrophobic deep eutectic solvent (DES) is synthesized and utilized in dispersive liquid-liquid microextraction (DLLME) of three gliflozins in environmental water samples as a proof-of-concept examples. The synthesized DES is composed of benzalkonium chloride (BZKCl) as a hydrogen bond acceptor and octanol (Oct) as a hydrogen bond donor. A full optimization of the extraction conditions was carried out including molar ratio and composition of DES, volume of DES, volume of water samples, extraction time and type of diluting solvent. Moreover, the extraction mechanism was thoroughly investigated, and it was established that the extraction of the target analytes is attributed to the analytes' incorporation into the micelles’ cores that facilitates mass transfer from the aqueous layer into DES layer. Furthermore, micelles formed by surfactant-based DES will provide adequate dispersion of extractant phase within water samples, which consequently improves the extraction efficiency. Micelles formation was confirmed by transmission electron microscopy (TEM). Furthermore, 1H NMR spectra verifies that the synthesized DES keeps its integrity even after extraction, which excludes any decomposition of DES after DLLME procedure. The extraction recovery is in an excellent agreement with the hydrophobicity of the investigated drugs, being the highest for the most hydrophobic one. The extracted analytes were separated by UHPLC coupled with fluorescence detection. Under the optimized experimental conditions, the method exhibits excellent linearity and a high detection sensitivity with a limit of detection of 0.5, 2.0 and 0.1 ng mL−1 for EMP (empagliflozin), DAP (dapagliflozin) and CAN (canagliflozin), respectively. The greenness of the developed microextraction approach was assessed by different greenness metrics such as Complex GAPI and AGREE tools. The developed method shows excellent greenness of synthetic procedure for preparation of DES, the environmentally benign nature of DLLME procedure as well as the greenness of the developed UHPLC approach.

Generative discovery of de novo chemical designs using diffusion modeling and transformer deep neural networks with application to deep eutectic solvents

We report a series of deep learning models to solve complex forward and inverse design problems in molecular modeling and design. Using both diffusion models inspired by nonequilibrium thermodynamics and attention-based transformer architectures, we demonstrate a flexible framework to capture complex chemical structures. First trained on the Quantum Machines 9 (QM9) dataset and a series of quantum mechanical properties (e.g., homo, lumo, free energy, and heat capacity), we then generalize the model to study and design key properties of deep eutectic solvents (DESs). In addition to separate forward and inverse models, we also report an integrated fully prompt-based multi-task generative pretrained transformer model that solves multiple forward, inverse design, and prediction tasks, flexibly and within one model. We show that the multi-task generative model has the overall best performance and allows for flexible integration of multiple objectives, within one model, and for distinct chemistries, suggesting that synergies emerge during training of this large language model. Trained jointly in tasks related to the QM9 dataset and DESs, the model can predict various quantum mechanical properties and critical properties to achieve deep eutectic solvent behavior. Several combinations of DESs are proposed based on this framework.

Group contribution models for densities and heat capacities of deep eutectic solvents

The most recent database regrouping two key properties for the use of deep eutectic solvents in chemical processes, namely the density and the heat capacity, was used to develop simple group contribution models for predicting these properties. The databank contains a total of 3266 data points for 231 systems and 573 data points for 27 systems for density and heat capacity, respectively. These models only require the temperature and the number of each group in the molecules with no limitation on the number of molecules composing the studied deep eutectic solvent. The resulting average deviations are of 1.95% for density with 42.8% of the data having an average deviation under 1%, and 3.09% for heat capacity, with 55.5% of the data with a deviation under 1%. Both binary and ternary deep eutectic solvents have been investigated, with the deviation for ternary systems being of 1.05% in the case of the density model. Several families of DESs have been examined, with the best results obtained for DESs based on choline chloride, betaine and the benzyltrialkylammonium cation. These models are compared to more complex group contribution models from the literature. The models from this work are easy to implement and to modify when new data are available and are a step in the direction of the general prediction of properties of deep eutectic solvents.

Ternary deep eutectic solvents: Evaluations based on how their physical properties affect energy consumption during post-combustion CO2 capture

In this work, an inverse design method for absorbent development was proposed to reduce the energy requirement of post-combustion CO2 capture (PCC) with 4 steps. 1. Four physical solvents were modeled for PCC and the artificial neural network (ANN)-simulated annealing (SA) models were developed for fast and accurate multi-objective optimization. 2. The optimization results shows that the physical properties of absorbents are important for energy savings. Further analysis on liquid pump energy demand and optimal operating parameters of each absorbent identified absorbents with low viscosity, small average molecular weight, and high CO2 capture ability from flue gas are desirable for PCC. 3. A new strategy was proposed to adjust the physical properties of deep eutectic solvents (DESs) and overcome the disadvantages of aqueous DESs—low thermal stability—by using two ingredients as hydrogen bond donors. 4. Through experimental tests and computer modeling, a DES (TEAC/2Gly/PDO) consisting of tetraethylammonium chloride, glycerol, and 1,3-propanediol in a mole ratio of 1:2:1 was identified as a promising CO2 absorbent with energy demand of 1.06 MJ/kg CO2.

Fine-tuning the Basicity of Deep Eutectic Solvents by Substituting Guanidine for Urea in Reline.

The physicochemical properties of deep eutectic solvents (DESs) depend on the combination of hydrogen bond acceptors and hydrogen bond donors used. The basicity of a DES significantly influences its performance in CO2 chemical absorption, biomass and protein dissolution, and catalytic reactions. To the best of our knowledge, a strategy for fine-tuning the basicity of DESs has not yet been reported. Therefore, in this study, we substituted the base urea (Ur) in reline, which is a 1:2 mixture of choline chloride (ChCl) and Ur, with the superbase guanidine (Gu) to fine-tune its basicity. Binary (2Gu-ChCl) and ternary (Gu-Ur-ChCl) DESs were prepared, and their CO2 absorption capacities were investigated at 313.2 K. The equimolar mixture Gu-Ur-ChCl absorbed CO2 gas up to the molar ratio [CO2]/[ChCl] ≈ 1.0. Therefore, the basicity of ChCl-based DES can be continuously varied by substituting more molecules of Ur with Gu. Our strategy of combining functional and non-functional molecules with similar structures to vary the basicity of DESs has potentially wide applications that utilize DESs in the future.

Antiamoebic properties of Methyltrioctylammonium chloride based deep eutectic solvents.

This aim of this study was to assess anti-parasitic properties of deep eutectic solvents against eye pathogen, Acanthamoeba, often associated with the use of contact lens. Assays were performed to investigate the effects of various Methyltrioctylammonium chloride-based deep eutectic solvents on Acanthamoeba castellanii, comprising amoebicidal assays, encystment assays, excystment assays, cytotoxicity assays by measuring lactate dehydrogenase release from human cells, and cytopathogenicity assays to determine parasite-mediated host cell death. In a 2h incubation period, DES-B, DES-C, DES-D, and DES-E exhibited up to 85% amoebicidal activity at micromolar doses, which was enhanced further following 24h incubation. When tested in encystment assays, selected deep eutectic solvents abolished cyst formation and were able to block excystment of A. castellanii. All solvents exhibited minimal human cell cytotoxicity except DES-D. Finally, all tested deep eutectic solvents inhibited amoeba-mediated cytopathogenicity, except DES-B. Deep eutectic solvents show potent antiamoebic effects. These findings are promising and could lead to the development of novel contact lens disinfectants, as well as opening several avenues to explore the molecular mechanisms, various doses and incubation periods, and use of different bases against Acanthamoeba castellanii.

A novel approach to mineral carbonation using deep eutectic solvents for the synthesis of nano-sized amorphous CaCO3

This paper proposes a novel synthesis method for nanosized amorphous CaCO3 based on advanced mineral carbonation using the macromolecular properties of deep eutectic solvents (DESs). DESs are generally synthesized by mixing hydrogen bond acceptors (HBAs) and hydrogen bond donors (HBDs), and their properties vary depending on the HBDs and HBAs used for the synthesis. To synthesize DESs with CO2-philic properties, monoethanolamine (MEA) was selected as the HBD because it possesses a CO2-active site. However, alkanolamine-based DESs are difficult to use in practical applications because of their high viscosity following CO2 absorption. To mitigate the onset of high viscosity, H2O was added to the synthesized DESs, with the molar ratio HBA:HBD:H2O as 1:5:10 and 1:5:15. In the proposed process, CO2 was captured by the DESs-H2O system and converted into particle-size- and morphology-controlled CaCO3. Nanosized amorphous CaCO3 (ACC) with average particle sizes of 38.1 and 48.0 nm was formed by DESs based on the molar ratio of 1:5:10. The results demonstrated the need for an adequate ratio of H2O to DES to form nanosized ACC, implying that the strength of hydrogen bonding in DES-H2O systems is the primary factor affecting the performance of the solvent. The DES-H2O systems with inter- and intramolecular hydrogen bonding inhibited the crystallization of CaCO3. The findings of this study are applicable to CO2 utilization processes designed for the production of nanosized ACC.

Optimized preparation, thermal characterization and microwave absorption properties of deep eutectic solvents made by choline chloride and hydrated salts of alkali earth metals

In this manuscript, we provided insights into the preparation of Deep Eutectic Solvents (DESs) made by choline chloride and MgCl2·6H2O or CaCl2·6H2O, proposed as green solvents for the valorization of biomasses, and we performed an extensive evaluation of their thermal properties. In particular, we highlighted the use of a microwave (MW) coaxial antenna as a rapid, efficient, and eco-friendly heating probe, which can reduce the preparation time up to 40 times with respect to conventional heating without altering the final properties of the product. The thermal properties of the DESs were extensively studied by Differential Scanning Calorimetry and High-Resolution Thermogravimetry with analysis of the evolved gas by Fourier Transformed Infra-Red spectroscopy, with the aim to obtain important information on their thermal stability and thermal degradation mechanism. The experimental data also allowed us to obtain indirect evidence of the hydrogen bonding network formed in DES nanostructures. Finally, the evaluation of the samples’ capability to absorb MWs allowed us to classify them as good MW absorbers, highlighting their potential for future applications in MW-assisted processes.

Study of the Liquid–Liquid Equilibrium and Extraction Properties of Deep Eutectic Solvents Based on Choline Chloride for the Separation of the Ethanol–Ethyl Formate System for Potential Use in Biofuel Production

Study of the Liquid–Liquid Equilibrium and Extraction Properties of Deep Eutectic Solvents Based on Choline Chloride for the Separation of the Ethanol–Ethyl Formate System for Potential Use in Biofuel Production

Effect of temperature and composition on physical properties of deep eutectic solvents based on 2-(methylamino)ethanol – measurement and prediction

Novel deep eutectic solvents were synthesized using 2-(methylamino)ethanol as hydrogen bond donor with tetrabutylammonium bromide or tetrabutylammonium chloride or tetraethylammonium chloride as hydrogen bond acceptors. Mixtures were prepared at different molar ratios of 1:6, 1:8 and 1:10 salt to alkanolamine and then Fourier Transform Infrared Spectroscopy measurements were performed to confirm hydrogen bonds interactions between components. Moreover, thermal properties such as melting points and thermal stability of deep eutectic solvents were determined and described. Each of important physical properties, including densities, viscosities, refractive indices and sound velocities at the temperature range of 293.15–333.15 K and the pressure of 0.1 MPa, were measured and discussed. The effect of hydrogen bond acceptor to hydrogen bond donor molar ratio, anion and length of alkyl chain for each synthesized salt according to their properties was evaluated. Additionally, the experimental values of each physicochemical parameter were compared with the predicted ones calculated using models recommended in literature. The main aim of this work was to assess the suitability of existing mathematical models for predicting the physicochemical properties of novel alkanolamine-based DESs. Empirical correlations for approximating phase behaviour or flow properties for DES systems are used in many procedures for design materials used of carbon-dioxide capture purposes. The obtained results indicate that in the case of deep eutectic solvents based on 2-(methylamino)ethanol, in the absence of any experimental data, the best models for density prediction are the bonding group interaction contribution method and the group contribution model. For modelling of the refractive index it has been confirmed that a method based on the critical properties is the most satisfying. However, for the viscosity and speed of sound, the absolute average relative deviations for the methods based on critical properties exceed the measurement uncertainties found in practice. Therefore, they do not seem suitable for an accurate estimation of these properties for deep eutectic solvents based on 2-(methylamino)ethanol.