Propylene glycol-based deep eutectic solvent as an alternative to Ethaline for electrometallurgy

Deep eutectic solvents (DESs) and ternary deep eutectic solvents (TDESs) and are derived from two or more salts as the hydrogen bond acceptors (HBAs) and hydrogen bond donors (HBDs). In this work, the several DESs and a TDES were prepared. Allyltriphenyl phosphonium bromide and potassium carbonated were selected as HBAs to mix with various HBDs such as glycerol (GL), ethylene glycol (EG), diethylene glycol (DEG) and triethylene glycol (TEG) into different molar ratios. Two different groups of bacteria were selected for investigation of toxicity of species, namely Escherichia coli (EC) as a Gram negative bacterium and Listeria monocytogenes (LM) as a Gram positive bacterium. The results revealed that by increasing alkyl chain length on HBD, the toxicity of DESs increases towards EC bacterium. However, there appears to have no direct relationship between effect of alkyl chain length and toxicity DESs towards LM bacterium. Moreover, by studying the effect of molar ratio the toxicity of DESs, it was observed that there is no direct relationship between them. Furthermore, it was found that the type of HBD has a dominant effect on the toxicity of DESs compared to type of salt. By comparing the toxicity of DESs in this work with that of ILs in literature, it was found that DESs are less toxic than ILs. The last interesting result of this work is that TDES exhibited the lowest toxicity on EC and LM bacteria compared with DESs.

Within the green chemistry area, deep eutectic solvents (DESs) are playing an increasingly prominent role thanks to their intriguing physicochemical properties. However, a comparative study encompassing a wide range of properties as a function of different parameters such as the nature of the hydrogen bond acceptor (HBA) and donor (HBD) and their molar ratio is still missing. In this work, six DESs based on the most used HBAs (choline chloride (ChCl) and betaine (Bet)) and HBDs (ethylene glycol (EG), glycerol (Gly) and levulinic acid (LevA)) combined in three different molar ratio (1:2, 1:3, 1:4) have been prepared and subjected to a series of analysis aimed at measuring different properties such as density, viscosity, refractive index, thermal stability and thermal behaviour. The most striking findings see the EG-based DESs displaying the lowest density and viscosity values, while the Gly-based DESs exhibited the highest. High viscosity and density have been obtained using Bet instead of ChCl as HBA. Increasing the amount of HBD in DESs caused lower viscosity in all cases, while density increased for all Gly-based DESs and decreased for EG and LevA-based DESs. The refractive index also decreased when the HBD portion was increased. However, higher refractive index was obtained using ChCl instead of Bet as HBA. The temperature and wavelength dependence of the refractive index is otherwise described pretty well by a Sellmeier model. The molar refractivity implied by density and refractive index data via the Clausius-Mossotti equation is consistent with that predicted by the empirical but well-established model of Wildman and Crippen.The short thermal stability of all investigated DESs is strictly related to the HBD used. EG-based DESs were less stable than LevA-based ones while Gly-based DESs were the most stable materials. Moreover, for all DESs three characteristic mass loss events have been identified. They can be attributed to the evaporation/degradation of the HBD, of the intimately interacting HBD-HBA and of the HBA, respectively. Finally, DSC analyses showed that all DESs can be used as solvents given that they are liquids at room temperature, and they maintain a liquid state in a broad range of temperatures (Tg < −50 °C or no thermal events are observed).

Hydrogen bond donor and alcohol chain length effect on the physicochemical properties of choline chloride based deep eutectic solvents mixed with alcohols

Using the basic principle of construction between a hydrogen bond acceptor (HBA) and a hydrogen bond donor (HBD), four bio-based deep eutectic solvents (DESs) were prepared in a 1:2 molar ratio of HBA:HBD. 2,3-Dihydroxypropyl-1-triethylammonium chloride ([C9H22N+O2]Cl−) was synthesized from raw glycerol and used as an HBA. Lactic acid, urea, pure glycerol, and ethylene glycol were selected as HBD. Attempts to prepare DESs, using citric acid and benzoic acid as HBDs, were unsuccessful. All these DESs were characterized using FTIR and NMR techniques. Besides, physicochemical parameters such as pH, viscosity, density, and melting point were determined. The behavior of these DES to fractionate olive pomace was studied. Lignin recovery yields spanned between 27% and 39% (w/w) of the available lignin in olive pomace. The best DES, in terms of lignin yield ([C9H22N+O2]Cl− -lactic acid), was selected to perform a scale-up lignin extraction using 40 g of olive pomace. Lignin recovery on the multigram scale was similar to the mg scale (38% w/w). Similarly, for the holocellulose-rich fractions, recovery yields were 34% and 45% for mg and multi-gram scale, respectively. Finally, this DES was used to fractionate four fruit pruning samples. These results show that our novel DESs are alternative approaches to the ionic liquid:triethylammonium hydrogen sulfate and the widely used DES: choline chloride:lactic acid (1:10 molar ratio) for biomass processing.

The interest on deep eutectic solvents (DES) has been increasing. However, the ecotoxicological profile of DES is scarcely known. Also, despite previous studies showed that DES components dissociate in water, none assessed DES toxicity using the classical and adequate models for mixture toxicity prediction - concentration addition (CA) and independent action (IA). This study evaluates the ecotoxicological profile of DES based on [N1111]Cl, [N2222]Cl and [N3333]Cl as hydrogen bond acceptors (HBA) combined with hydrogen-bond donors (HBD) vis. ethylene glycol and 1-propanol, through the Microtox® Acute Toxicity Test. CA and IA with deviations describing synergism/antagonism, dose-ratio and dose-level effects were fitted to the toxicity data. Neither the starting materials nor DES were found hazardous to Aliivibrio fischeri, in this specific case agreeing with the claimed “green character” of DES. Among the starting materials, ethylene glycol was the least toxic, whereas [N3333]Cl was the most toxic (30 min-EC50 = 96.49 g L−1 and 0.5456 g L−1, respectively). DES toxicity followed the same trend as observed for the salts: [N1111]Cl-based DES < [N2222]Cl-based DES < [N3333]Cl-based DES. The IA model, with specific deviations, adjusted better in 5 out of 6 DES. Antagonism was observed for [N1111]Cl-based DES, and synergism for [N3333]Cl-based DES and for 1-propanol:[N2222]Cl. The application of the mixture toxicity models represents a breakthrough in the problematic of assessing the toxicity of the countless number of DES that can be created with the same starting materials, since they provide the expected toxicity of any virtual combination between HBA and HBD.

Common solvents used for aromatic extraction from aliphatics typically degrade into toxic compounds, while green alternatives perform poorly compared to the state-of-the-art solvents. Deep eutectic solvents (DES) are a novel solvent type made of hydrogen bond donors (HBD) and hydrogen bond acceptors (HBA). DES have been applied in various applications, including advanced separations. In this study, DES were studied experimentally and using the Conductor-like Screening Model (COSMO) to separate benzene from cyclohexane as model compounds for an aromatic:aliphatic system. Both equilibrium and kinetic studies were performed to determine the liquid liquid equilibrium (LLE) and mass transfer rate for the DES-based separation. Selected HBAs including tetrabutylammonium bromide (N4444Br), tetrahexylammonium bromide (N6666Br), choline chloride (ChCl), and methyltriphenylphosphonium bromide (METPB) were paired with HBDs including ethylene glycol (EG) and glycerol (Gly). COSMO was used, with adjustments to reflect DES specific interactions, to predict the liquid-liquid equilibrium (LLE). COSMO results showed that ChCl and N6666Br-based DES extracted too little benzene or too much cyclohexane, respectively, to be considered for experimental evaluation. Overall, the COSMO model predictions for LLE of EG-based DES were very accurate, with root-mean-square deviations (RMSD) below 1% for both N4444Br:EG and METPB:EG. The glycerol systems were less accurately modeled, with RMSD’s of 4% for N4444Br:Gly and 6% for METPB:Gly. The lower accuracy of glycerol system predictions fmay be due to limitations in COSMO for handling glycerol’s influence on polarizability in the DES that is not seen in EG-based DES. Mass transfer kinetics were determined experimentally for DES and the results were fit to a first order kinetics model. METPB:Gly had the highest mass transfer coefficient at 0.180 min−1, followed by N4444Br:EG at 0.143 min−1. N4444Br:Gly and METPB:EG had the lowest mass transfer coefficients at 0.096 min−1 and 0.084 min−1, respectively. It was found that mass transfer rate was not directly related to maximum benzene solubility, as N4444Br:EG and METPB:Gly had the highest and lowest benzene removal, respectively, but had similar mass transfer coefficients.

Physicochemical properties of choline chloride-based deep eutectic solvents and excess properties of their pseudo-binary mixtures with 1-butanol

The effects of a hydrogen bond acceptor and hydrogen bond donor on carbon dioxide absorption via natural deep eutectic solvents were studied in this work. Naturally occurring non-toxic deep eutectic solvent constituents were considered; choline chloride, b-alanine, and betaine were selected as hydrogen bond acceptors; lactic acid, malic acid, and fructose were selected as hydrogen bond donors. Experimental gas absorption data were collected via experimental methods that uses gravimetric principles. Carbon dioxide capture data for an isolated hydrogen bond donor and hydrogen bond acceptor, as well as natural deep eutectic solvents, were collected. In addition to experimental data, a theoretical study using Density Functional Theory was carried out to analyze the properties of these fluids from the nanoscopic viewpoint and their relationship with the macroscopic behavior of the system, and its ability for carbon dioxide absorption. The combined experimental and theoretical reported approach work leads to valuable discussions on what is the effect of each hydrogen bond donor or acceptor, as well as how they influence the strength and stability of the carbon dioxide absorption in deep eutectic solvents. Theoretical calculations explained the experimental findings, and combined results showed the superiority of the hydrogen bond acceptor role in the gas absorption process, with deep eutectic solvents. Specifically, the cases in which choline chloride was used as hydrogen bond acceptor showed the highest absorption performance. Furthermore, it was observed that when malic acid was used as a hydrogen bond donor, it led to low carbon dioxide solubility performance in comparison to other studied deep eutectic solvents. The cases in which lactic acid was used as a hydrogen bond donor showed great absorption performance. In light of this work, more targeted, specific, deep eutectic solvents can be designed for effective and alternative carbon dioxide capture and management.

Effect of water and hydrogen bond acceptor on the density and viscosity of glycol-based eutectic solvents

Background: Hypertension affects 32% of adults worldwide, leading to a significant global consumption of cardiovascular medications. Atenolol, a β-adrenergic receptor blocker, is widely prescribed for cardiovascular diseases such as hypertension, angina pectoris, and myocardial infarction. According to the Biopharmaceutics Classification System (BCS), atenolol belongs to Class III, characterized by high solubility but low permeability. Currently, atenolol is commercially available in oral formulations. Increasing attention is being directed towards developing cost-effective transdermal delivery systems, due to their ease of use and better patient compliance. Eutectogels represent next-generation systems that are attracting great interest in the scientific community. Typically obtained from deep eutectic solvents (DESs) combined with gelling agents, these systems exhibit unique properties due to the intrinsic characteristics of DESs. Methods: In this study, a DES based on choline chloride as a hydrogen bond acceptor (HBA) and propylene glycol as a hydrogen bond donor (HBD) was explored to enhance the topical delivery of atenolol. The solubility of atenolol in the DES was evaluated using spectroscopic and thermodynamic measurements which confirmed the formation of hydrogen bonds between the drug and DES components. Additionally, the safety of the DES was assessed in a cell viability assay. Subsequently, we formulated eutectogels with different concentrations using animal gelatin and Tego Carbomer 140, and characterized these formulations through rheological measurements, swelling percentage, and permeation studies with Franz cells. Results: These novel eutectogels exhibit superior performance over conventional hydrogels, with a release rate of approximately 86% and 51% for Carbomer- and gelatin-based eutectogels, respectively. In contrast, comparable hydrogels released only about 27% and 35%. Conclusions: These findings underscore the promising potential of eutectogels for the transdermal delivery of atenolol.

Potential use of deep eutectic solvents (DESs) to enhance anhydrous proton conductivity of Nafion 115® membrane for fuel cell applications

Deep eutectic solvents (DES) are a novel category of environmentally friendly solvents created by the interaction of hydrogen bond donors (HBDs) and acceptors (HBAs) in precise molar ratios, exhibiting unique physicochemical characteristics. DES have low volatility, non-flammability, and great stability, making them ecologically benign substitutes for traditional solvents. The essential physical qualities of DES, including density, viscosity, and thermal stability, are pivotal to its operation. These characteristics are affected by parameters like as temperature, component mix, and molar ratios, enabling customisation for particular purposes. DES have shown considerable promise in several domains, including electrochemistry, material synthesis, and environmentally friendly chemical processes, owing to their adaptability and safety. In the realm of polyurethane (PU) solubilisation, deep eutectic solvents (DES) have notable potential. The solubilization process is ascribed to the breakdown of the polymer’s hydrogen bonds and the dissolving of urethane connections by the DES components, helped by their strong hydrogen bond network. By customising DES characteristics, researchers may enhance the breakdown process for PU, offering a sustainable solution to plastic waste issues. The basic features, physical and chemical properties, wide range of uses, and potential for developing PU solubilisation technologies of DES are highlighted in this paper.

Therapeutic deep eutectic solvents are a new class of deep eutectic solvents (DESs), which include at least an active pharmaceutical ingredient (API) as one of the components. Therapeutic DESs are emerging alternatives that improve the bioavailability, solubility, delivery, and pharmacokinetics properties of drugs. DESs comprise two components, generally a hydrogen bond acceptor (HBA) and a hydrogen bond donor (HBD), with varying ratios. The interaction chemistry between HBA : HBD components in DESs is complex. Moreover, stoichiometry and cluster formation of DESs at the molecular level have received little attention. Mass spectrometry (MS) is an attractive technique for studying isolated gas phase molecules; however, such investigations have not been implemented for DESs. Compared to other techniques, MS is unique in providing information on the gas phase stoichiometry, cluster formation, and interaction network between the two components of DESs. In addition, computational modeling assists in visualizing the isolated DES clusters and unraveling a deeper understanding of the structure-property relationship. In this study, multi-technique approaches, including thermogravimetric (TGA), calorimetric (DSC), spectroscopic (IR and Raman), emerging mass spectrometry, and computational, were employed to characterize the menthol : ibuprofen-based therapeutic DES. The thermal, calorimetric, and spectroscopic studies showed that hydrogen bonding is the primary factor contributing to DES formation. This study also reported the stable gas phase cluster structure of a menthol : ibuprofen DES using electrospray ionization (ESI) and direct analysis in real time (DART) coupled with mass spectrometry. Subsequently, a temperature-dependent DART-MS investigation shows that different-temperature conditions impact the formation and intensity of clusters, and the presence of ester impurities. The most intense peak in the ESI-MS and DART-MS spectra was detected at m/z 363.1, corresponding to the hetero-molecular cluster of a 1 : 1 menthol : ibuprofen complex. In addition to the hetero-cluster, homo-clusters of a two-menthol molecule and a two-ibuprofen molecule were also detected. Density functional theory (DFT) was employed to investigate the possible gas phase structures of the selected clusters obtained from MS. The DFT results show that hydrogen bonds between the constituents stabilize most of the clusters. An MS-guided computational model visualized detailed microstructures and provided insights into the formation mechanism and intermolecular interaction of therapeutic DES.

Mixtures of tetrabutylammonium chloride salt with different glycol structures: Thermal stability and functional groups characterizations

The design of environmentally friendlier solvents has gained increasing relevance in the last decade. Deep eutectic solvents (DES) have recently emerged, with advantages like low-cost and putative lower environmental impact. However, information about DES toxicity is still scarce. This work aims to contribute to profiling the ecotoxicity of DES based on cholinium chloride ([Chol]Cl). Six DES were addressed, combining [Chol]Cl (as hydrogen bond acceptor – HBA) with ethylene glycol, glycerol, 1,2-propanediol, propionic acid, 1-propanol, and urea as hydrogen bond donors (HBD), in different molar ratios. The Microtox® Acute Toxicity Test, was used for assessing their toxicity towards the marine bacteria Allivibrio fischeri . Because the dissociation of DES in water is expected, analysis appraising the mixtures toxicity theory should be considered, which is a step forward in this field. This analysis suggested that [Chol]Cl and all HBD with the exception of propionic acid:[Chol]Cl 1:2 and 4:1 behave antagonistically, which is contrary to what has been suggested previously. The most extreme cases are Urea:[Chol]Cl and 1-Propanol:[Chol]Cl, with EC50 values higher than their starting materials dosed singly, configuring very promising and biocompatible alternative solvents. Toxicity was found to be dependent on DES composition, as well as on molar proportions of the starting materials.