Choline-based Deep Eutectic Solvents Research Articles

Understanding the interactions between CO[formula omitted] and selected choline-based deep eutectic solvents using density functional theory

The interaction of CO2 with different deep eutectic solvents (DES) has been studied at the molecular level using density functional theory. Choline chloride and choline bromide were selected as the hydrogen bond acceptors (HBA); urea, ethylene glycol and glycerol were selected as the hydrogen bond donors (HBD). The type and intensity of interactions in DES and that between DES and CO2 molecules at various interaction sites as well as the quantification of short-range interactions has been studied using Bader’s quantum theory of atoms in molecules (QTAIM). The distribution of electrostatic potential (ESP) charges during these interactions has been detailed using the Charges from ESP using a grid (CHELPG) scheme. The non-covalent interactions have been identified using the reduced density gradient (RDG) analysis. Strong van der Waals forces were observed to contribute in the formation of DES. The highest interaction energy of −10.65 kcal/mol was found between the DES2 that comprised of choline chloride and ethylene glycol in the molar ratio of 1:2 and the CO2. The results of this study show that both HBA and HBD affect the interaction between CO2 and DES. This study can contribute in designing more specific DES for CO2 capture and utilization.

Choline-based Deep Eutectic Solvent for Extractive Oxidative Desulfurization of Model Oil

One of the hardest processes encountered by petroleum refining is sulfur elimination from fuel oil. There are many traditional methods executed but they caused drawbacks such as poor selectivity of sulfur compounds and toxic raw materials. Extractive oxidative desulfurization (EODS) caught the interest of researchers due to high selectivity of sulfur compounds and great desulfurization. Currently, researchers are investigating the use of ionic liquids (ILs) as green extractant, unfortunately they are expensive. This research is proposing and comparing the use of cheap biodegradable solvents called deep eutectic solvents (DESs), as extractants in removing sulfur from fuel oil. The DESs are synthesized through a combination of choline chloride - orcinol and choline chloride - ethylene glycol, and their structure is confirmed through FTIR. Their thermal properties are characterized by DSC and TGA. Their desulfurization performance is evaluated by type of DESs, different ratios of DES and model oil, different ratios of oxidant and sulfone and various temperatures which these factors are found to influence the result. The optimum conditions are found to be at 1:1 for DES and model oil ratio, 4 for O/S ratio and temperature at 85 °C with the extraction efficiency of 99.98%. In conclusion, this DES has high potential to be the cheap green alternative to the conventional extractant for extractive oxidative desulfurization process.

Local and cooperative structural transitions of double-stranded DNA in choline-based deep eutectic solvents

The possibility of using deep eutectic solvents (DESs) as co-solvents for stabilizing and preserving the native structure of DNA provides an attractive opportunity in the field of DNA biotechnology. The rationale of this work is a systematic investigation of the effect of hydrated choline-based DES on the structural stability of a 30-base-pair double-stranded DNA model via a combination of spectroscopic experiments and MD simulations. UV absorption and CD experiments provide evidence of a significant contribution of DESs to the stabilization of the double-stranded canonical (B-form) DNA structure. Multi-wavelength synchrotron UV Resonance Raman (UVRR) measurements indicate that the hydration shell of adenine-thymine pairs is strongly perturbed in the presence of DESs and that the preferential interaction between H-bond sites of guanine residues and DESs is significantly involved in the stabilization of the dsDNA. Finally, MD calculations show that the minor groove of DNA is significantly selective for the choline part of the investigated DESs compared to the major groove. This finding is likely to have a significant impact not only in terms of thermal stability but also in the modulation of ligand-DNA interactions.

Developing amino acid-citric acid-based deep eutectic solvent for food applications: Preparation, characterization, antibacterial activity, biosafety, and formation mechanism exploration

The deep eutectic solvent (DES) is a novel environmentally-friendly solvent that shows promising potential for applications in the field of functional food. However, the current development of choline-based DESs faces limitations due to their toxicity levels, which restrict their application in the food industry. Therefore, in this study, amino acid (AA)-citric acid (CA) DESs suitable for functional food applications were developed using natural food additives as raw materials. The purity and thermodynamic properties of the AA-CA DESs were characterized by simultaneous thermogravimetry/differential scanning calorimetry (TG-DSC) and DSC analysis. The molecular interactions within the AA-CA DESs were investigated using FT-IR, NMR, and molecular dynamics (MD) simulations. The rheometer was used to study the viscosity of AA-CA DESs. The density of the AA-CA DESs was tested using a pycnometer and mutually verified with MD simulations. The antibacterial activity and biological safety of DESs were investigated by bacteriostatic and cell experiments. FT-IR, NMR, and MD simulations studies indicated that AA-CA DESs primarily form through hydrogen bonding interactions. Antibacterial experiments demonstrated that AA-CA DESs exhibited significantly enhanced antibacterial activity against P. aeruginosa and E. coli compared to pure substrates Gly, Ala, and Arg, respectively, indicating improved antibacterial properties. The cell experiments showed that AA-CA DESs possess good biological safety. In conclusion, this study successfully developed a class of AA-CA DESs and found that AA-CA DESs have good antibacterial activity and biosafety. This finding provides theoretical guidance for the sustainable development and application of DESs in the field of functional foods.

Eutectic solvent-based bioactive films functionalized with microbial astaxanthin extends shelf life of fresh strawberries

Food waste and consumers safety are critical concerns that necessitate the development of improved packaging systems, such as those involving the use of edible films and coatings, which may act as primary packaging, helping the external (secondary) packaging in its protecting role. However, current options of films/coatings have limitations, such as inefficient plasticizer agents and the need for high levels of active ingredients. To address these challenges, we have created a new packaging material formulated with bio-based sodium alginate (SA) and choline-based deep eutectic solvents (DES), which are eco-friendly and capable of packaging food substrates to enhance their safety and longevity. Using a SA-DES materials we incorporated naturally derived microbial products (astaxanthin - AXT) with antioxidant and antimicrobial properties and evaluated the mechanisms behind the formation of coatings. Our results demonstrate that strawberries coated with alginate-choline chloride:glycerol (SA-[Ch]Cl:Gly) had a longer shelf life, inhibited natural microbial proliferation, and lost less weight than uncoated controls at room temperature. This study demonstrated that DES are a promising and sustainable solution for cost-effective, and biodegradable environmentally friendly packaging systems.

A Systematic Study on the Role of Hydrogen Bond Donors in Dictating the Dynamics of Choline-Based Deep Eutectic Solvents.

Deep eutectic solvents, promising green alternatives to conventional solvents, consist of a hydrogen bond donor and a hydrogen bond acceptor. The hydrogen bonding components in deep eutectic solvents form an extended hydrogen bonding network, which can be tuned to specific applications by changing the hydrogen bond donors. In this work, we have changed the hydrogen bond donor from a diol to a dicarboxylic acid by systematically replacing a hydroxyl group with an acid group one at a time to investigate the solvation structure and dynamics of the deep eutectic systems. Using a combination of ultrafast vibrational spectroscopy and molecular dynamics simulations, we compared the spectral diffusion and orientational relaxation dynamics of three deep eutectic systems using the vibrational responses of a dissolved anion. Our results indicate that although the solvation structures are marginally different across the systems, distinct differences are present in the solvent fluctuation and solute reorientation dynamics. This work provides a detailed molecular understanding of carboxylic-acid-based deep eutectic systems and how they differ from alcohol-based deep eutectic systems.

Assessing the compatibility of choline-based deep eutectic solvents for the structural stability and activity of cellulase: Enzyme sustain at high temperature

As a new generation of ‘green solvents’ deep eutectic solvents (DESs) represents a promising alternative to the conventional solvents. Their environmental-benign nature and designer properties promote their utility in biocatalysis. Enzymes are marginally stable when exposed to physical/chemical disturbances. One such enzyme is cellulase which is a propitious catalyst for the depolymerization of cellulose under mild conditions. Therefore, their stability is a prerequisite condition to match demands of biorefineries. To address this issue of low stability, activity and thermal denaturation of cellulase, there is a need to find a sustainable and suitable co-solvent that is biocompatible with enzymes ultimately to facilitate their application in bio-industries. In this regard, we synthesized three choline-based DESs, choline chloride (ChCl)-glycerol, ChCl-ethylene glycol and ChCl-lactic acid and employed them to analyze their suitability for cellulase. The present study systematically evaluates the influence of the mentioned DESs on stability, activity and thermal stability of cellulase with the help of various spectroscopic techniques. The spectroscopic analysis revealed that the structural stability and activity of the enzyme were improved in presence of ChCl-glycerol and ChCl-ethylene glycol. The thermal stability was also very well maintained in both the DESs. Interestingly, the relative activity of cellulase was >80 % even after incubation at 50 °C after 48 h for both the DESs. This activity preservation behaviour was more pronounced for ChCl-ethylene glycol than ChCl-glycerol. Moreover, temperature variations studies also reveal promising results by maintain conformational intactness. On the other side, ChCl-lactic acid showed a deleterious effect on the enzyme both structurally as well as thermally. The dynamic light scattering (DLS) analysis provides more specific information about the negative influence of ChCl-lactic acid towards cellulase native structure. This DES induces unavoidable alterations in the enzyme structure which leads to the unfolding of enzyme, ultimately, destabilizing it. Overall, our results present a physical insight into how the enzyme stability and activity depend on the nature of DES. Also, the findings will help to facilitate the development and application of DESs as biocatalytic process.

Volumetricand ultrasonic properties of thiamine hydrochloride drug in aqueous solutions of choline-based deep eutectic solvents at different temperatures

Important efforts have been made over the past years to improve the drug acts, which leads to the discovery of novel drug preparations and delivery systems. The optimal design of such processes requires a molecular-level understanding of the interactions between drug molecules and biological membranes. The thermodynamic investigation provides deep and complete knowledge of interactions and the choice of appropriate and suitable production compounds in pharmaceutical fields. Particularly, the analysis of drugs + co-solvents in aqueous media is the central issue in many types of research because they exert their impact by interacting with biological membranes. This work is aimed to measure the density and speed of sound for the thiamine hydrochloride in water + deep eutectic solvents (DESs) mixtures (choline chloride/urea, choline chloride/ethylene glycol and choline chloride/glycerol) at temperature range (293.15–308.15) K. By correlation of the evaluated parameters in some standard relations, the partial molar parameters i.e. apparent molar volumes, Vφ,m, and apparent molar isentropic compression, κs,φ,m, are calculated. In addition, apparent molar isobaric expansion, Eφ,m0, and Hepler’s constant are computed from the density and speed of sound data. For fitting the experimental Vφ,m and κs,φ,m the Redlich-Meyer equation was employed that the important quantities; standard partial molar volume, Vm0, and partial molar isentropic compression, κs,m0, were obtained. The thermodynamic analysis of the studied system also plays a crucial role in the pharmaceutical industry.

Chitosan films plasticized with choline-based deep eutectic solvents: UV shielding, antioxidant, and antibacterial properties

Deep eutectic solvents (DES) as plasticizers of chitosan film show great potential for food packaging. This paper introduced some novel antioxidant and antibacterial films based on chitosan and DES consisting of choline chloride (ChCl) and organic acids. The effects of the composition and contents of choline-based DES on structures, mechanical properties, thermal stability, contact angle, optical, antioxidant and antibacterial properties of chitosan films were studied. FTIR analysis showed that choline-based DES did exist in the chitosan film with good polymer matrix compatibility. Most of the films exhibited uniform, flat surfaces and cross sections. The Young's modulus of the films decreased inversely to the level of choline-based DES, and maximal mechanical characteristics were achieved for films plasticized with ChCl and acetylsalicylic acid. The addition of choline-based DES apparently reduced water contact angles, decreased the decomposition temperature and the thermal stability of chitosan films. In terms of antioxidant capacities and ultraviolet (UV) shielding, chitosan films plasticized with choline-based DES containing acetylsalicylic acid and vitamin C had strong UV shielding and antioxidant properties. Chitosan films plasticized with choline-based DES containing acetylsalicylic acid, malonic acid and lactic acid showed excellent antibacterial properties against Escherichia coli and Staphylococcus aureus . In conclusion, the chitosan film with the choline-based DES, especially for ChCl and acetylsalicylic acid showed a good application prospect in food active packaging. Chitosan films plasticized with choline-based deep eutectic solvents: UV shielding, antioxidant, and antibacterial properties. • Novel chitosan films plasticized with 6 kind of deep eutectic solvents (DES) and 2 different levels addition were studied. • Chitosan films plasticized with choline-based DES containing acetylsalicylic acid or vitamin C had strong ultraviolet shielding and antioxidant activities. • Chitosan films plasticized with choline-based DES containing acetylsalicylic acid, malonic acid or lactic acid showed excellent antibacterial properties.

The attenuating ability of deep eutectic solvents towards the carboxylated multiwalled carbon nanotubes induced denatured β-lactoglobulin structure.

The stabilization of proteins has been a major challenge for their practical utilization in industrial applications. Proteins can easily lose their native conformation in the presence of denaturants, which unfolds the protein structure. Since the introduction of deep eutectic solvents (DESs), there are numerous studies in which DESs act as promising co-solvents that are biocompatible with biomolecules. DESs have emerged as sustainable biocatalytic media and an alternative to conventional organic solvents and ionic liquids (ILs). However, the superiority of DESs over the deleterious influence of denaturants on proteins is often neglected. To address this, we present the counteracting ability of biocompatible DESs, namely, choline chloride-glycerol (DES-1) and choline chloride-urea (DES-2), against the structural changes induced in β-lactoglobulin (Blg) by carboxylated multiwalled carbon nanotubes (CA-MWCNTs). The work is substantiated with various spectroscopic and thermal studies. The spectroscopic results revealed that the fluorescence emission intensity enhances for the protein in DESs. Contrary to this, the emission intensity extremely quenches in the presence of CA-MWCNTs. However, in the mixture of DESs and CA-MWCNTs, there was a slight increase in the fluorescence intensity. Circular dichroism spectral studies reflect the reappearance of the native band that was lost in the presence of CA-MWCNTs, which is a good indicator of the counteraction ability of DESs. Further, thermal fluorescence studies showed that the protein exhibited extremely great thermal stability in both DESs as well as in the mixture of DES-CA-MWCNTs compared to the protein in buffer. This study is also supported by dynamic light scattering and zeta potential measurements; the results reveal that DESs were successfully able to maintain the protein structure. The addition of CA-MWCNTs results in complex formation with the protein, which is indicated by the increased hydrodynamic size of the protein. The presence of DESs in the mixture of CA-MWCNTs and DESs was quite successful in eliminating the negative impact of CA-MWCNTs on protein structural alteration. DES-1 proved to be superior to DES-2 over counteraction against CA-MWCNTs and maintained the native conformation of the protein. Overall, both DESs act as recoiling media for both native and unfolded (denatured by CA-MWCNTs) Blg structures. Both the DESs can be described as potential co-solvents for Blg with increased structural and thermal stability of the protein. To the best of our knowledge, this study for the first time has demonstrated the role of choline-based DESs in the mixture with CA-MWCNTs in the structural transition of Blg. The DESs in the mixture successfully enhance the stability of the protein by reducing the perturbation caused by CA-MWCNTs and then amplifying the advantages of the DESs present in the mixture. Overall, these results might find implications for understanding the role of DES-CA-MWCNT mixtures in protein folding/unfolding and pave a new direction for the development of eco-friendly protein-protective solvents.

Carbon Dioxide Capture with Choline-Based DESs Solvents

Deep eutectic solvents (DES) are an interesting alternative to conventional amines. Due to their biodegradability, lower toxicity and lower prices, DES are considered “more benign” sorbents for CO2 capture than ionic liquids. To study the effect of water on the properties of choline chloride (ChCl)/glycerol mixtures (1:3 on a molar basis), the density and viscosity of ChCl/Gly with different water content (30%, 40% and 50%) were measured at temperature from 293.15 K to 333.15 K at atmospheric pressure, the CO2 solubility in (ChCl/Gly) with water was determined from 293.15 K to 373.15 K and at pressure from 0.5 MPa to 3 MPa. The result shows the dramatically influence of water in the viscosity but not in the CO2 solubility and Absorption.

Phase Equilibria and Mechanism Insights into the Separation of Isopropyl Acetate and Methanol by Deep Eutectic Solvents

Separation of methanol–isopropyl acetate (IPAC) obtained via isopropanol synthesis is essential. Deep eutectic solvents (DESs) have garnered extensive attention in the field of azeotropic separation owing to their advantages such as biodegradability, ecofriendliness, and cost-effectiveness. In this work, three choline-based DESs were prepared. Then, the experimental data of the synthesized DESs with methanol and IPAC were measured, which were linearly correlated with Hand and Othmer–Tobias equations. The GM/RT surface obtained using GUI-MATLAB software was used to determine the reliability of the fitting data based on the NRTL model. Choline chloride and ethylene glycol DES with a molar ratio of 1:2 exhibited the best methanol affinity. The effect of the solvent structure was studied using a combination of experimental and quantum chemistry and molecular dynamics (MD) calculations. Through electrostatic potential distribution, atoms-in-molecules, and independent gradient model analytical methods, the three DEEs were primarily extracted via a hydrogen bond interaction and van der Waals interaction, wherein the former played a dominant role in separation. MD simulation was used to reveal the effect of the structures of hydrogen bond acceptors (HBAs) and hydrogen bond donors (HBDs) on the extraction process at the molecular level. The analysis results indicated that HBA was the main influencing factor in the separation, and the electrostatic interaction of Cl– and methanol was dominant in the separation. Additionally, HBDs were the secondary factor during the separation process. In this work, the reasons for the differences in the separation performances of different DESs were analyzed from a microscopic perspective, offering theoretical support for selecting suitable DESs for separating alcohol-containing azeotropic systems.

Mechanism analysis of liquid-liquid extraction separation for dimethyl carbonate and methanol by choline-based DESs as extractants

Dimethyl carbonate (DMC) is a widely used chemical raw material and chemical product with excellent performance. In this manuscript, based on electrostatic potential (ESP), reduced density gradient (RDG) function, non-bond interaction energy, radial distribution function (RDF), spatial distribution function (SDF) and self-diffusion coefficient, the separation of DMC / methanol (MeOH) by four deep eutectic solvents (DESs) was studied. The results of ESP analysis showed that the hydrogen bond receptor played a leading role in the separation process, and the urea in the four hydrogen bond donors was more likely to form a stable structure with MeOH. The weak interaction region between different DESs and azeotropes was studied by RDG function. Based on the non-bond interaction energy, it can be seen that Cl− can form a very strong interaction with MeOH, and Electrostatic energy (Eelec) plays a leading role in the separation process. The charge density around the central atom can be observed by RDF and SDF, so as to determine the interaction between azeotrope and DESs. The diffusion rate of azeotrope in different DESs was studied by self-diffusion coefficient. The results showed that MeOH moved the slowest in the DES composed of urea and choline chloride (CHCl). The effect of DES structure on the liquid level of methanol dimethyl carbonate system was clarified by analyzing the experimental liquid-liquid equilibrium data. In this study, based on quantum chemistry (QC) calculation and molecular dynamics (MD) simulation, this study analyzed the liquid-liquid extraction and separation mechanism of DMC and MeOH. The extraction effect of DES composed of CHCl+urea is the best, which has certain theoretical guiding significance for liquid-liquid extraction to realize the green and efficient separation of DMC and MeOH.

Selective Separation of Tocol Homologues by Liquid-Liquid Extraction Using Choline-Based Deep Eutectic Solvents

In this paper we examined the potential of choline-based deep eutectic solvents (DESs) for selective extraction of tocol homologues from crude palm oil (CPO) through liquid-liquid extraction (LLE). Distribution of tocol homologues (α-tocopherol, α-, β, γ-, and δ-tocotrienol) presence in CPO when subjected to DES-assisted LLE has not been fully understood in the past. The effect of increasing the amount of DES on the distribution and selectivity of were investigated. It was found that tocol homologues were distributed in the order of their hydrophilic power, with tocols of higher polarity distributed more into the stripping phase compared to the less polar tocols. Distribution coefficients for α-tocopherol, α-, β, γ-, and δ-tocotrienol were 7.8, 13.1, 19.8, 22.1 and 29.6, respectively, when equal weight of CPO and choline chloride-malonic acid eutectic mixture (DES1) were used. The distribution of each tocol homologues also increased with increasing DES1, due to the increase in polarity of the stripping phase that attracted more tocols. Selectivity of δ-tocotrienol, which is the most polar tocol, was always higher than other homologues (α-tocopherol: 3.81, α-tocotrienol: 2.22, β-tocotrienol: 1.50, γ-tocotrienol: 1.34). Role of hydrophilic power of the tocols using selected DESs to selectively separate tocol homologues established in this paper has a potential for palm oil industry as tocotrienols are better antioxidants, thus more favorable, than α-tocopherol.
 HIGHLIGHTS
 
 Tocopherols and tocotrienols in palm oil products are usually extracted for nutritional capsules and dietary products formulations using high-end techniques which are costly. Liquid-liquid extraction is a cheap technique which can be carried out at ambient conditions but with low selectivity
 A series of choline-based eutectic solvents, a new generation of green chemicals, were formulated for targeted separation of, specifically five tocol homologues present in crude palm oil; α-tocopherol, α-, β-, γ-, and δ-tocotrienol
 Unique combination of the eutectic solvents and liquid-liquid extraction resulted in selective separation of tocol homologues depending on the polarity of the tocols. Tocotrienols, having higher polarity and better antioxidative power than tocopherols, can be selectively extracted with the right deep eutectic solvents made from choline chloride, malonic acid, and citric acid
 
 GRAPHICAL ABSTRACT

Insights into the Effect of Lithium Doping on the Deep Eutectic Solvent Choline Chloride:Urea.

Choline-based deep eutectic solvents (DESs) are potential candidates to replace flammable organic solvent electrolytes in lithium-ion batteries (LIBs). The effect of the addition of a lithium salt on the structure and dynamics of the material needs to be clarified before it enters the battery. Here, the archetypical DES choline chloride:urea at 1:2 mole fraction has been added with lithium chloride at two different concentrations and the effect of the additional cation has been evaluated with respect to the non-doped system via multinuclear NMR techniques. 1H and 7Li spin-lattice relaxation times and diffusion coefficients have been measured between 298 K and 373 K and revealed a decrease in both rotational and translational mobility of the species after LiCl doping at a given temperature. Temperature dependent 35Cl linewidths reflect the viscosity increase upon LiCl addition, yet keep track of the lithium complexation. Quantitative indicators such as correlation times and activation energies give indirect insights into the intermolecular interactions of the mixtures, while lithium single-jump distance and transference number shed light into the lithium transport, being then of help in the design of future DES electrolytes.

Understanding Structure-Property Relationships in Deep Eutectic Solvents (DESs)

Deep eutectic solvents (DESs) are an emerging class of highly tunable solvents with unique properties such as high solvent strength, wide electrochemical and thermal stability windows, nonflammability, and biodegradability/nontoxicity. These have given them potential as in many areas, including electrochemical technology applications like redox flow batteries and solar cells. However, they are held back by their relatively high viscosities and low conductivities. For this reason, it would be useful to understand how to improve these materials for target applications based off their molecular identity. Here, we use a variety of experimental techniques to study a series of choline-based DESs which are systematically varied by functional group and its position to examine the changes in local structure and dynamics and that effect on macroscopic properties. Generally, we observe that slight structural changes result in significant changes in the eutectic composition, viscosity, and dc ionic conductivity.

Solubility enhancement and intermolecular interactions of salicylic acid in aqueous solutions of choline chloride based deep eutectic solvents

Novel categories of solvents, deep eutectic solvents (DESs) as greener alternative media to hazardous organic solvents, have received great attention in numerous fields of science and technology. The poor aqueous solubility of many drugs with adequate bioavailability is still one of the main challenges in pharmaceutical sciences. In this regard, the aim of the present study is to measure the solubility and investigate the molecular interactions between salicylic acid (SA) and some choline-based DESs containing choline chloride (ChCl) with urea (U), ethylene glycol (EG), and glycerol (G). The experimental solubility of SA was measured in water, and aqueous solutions of DESs at several temperatures, and the computational studies have been used to get a deep insight into the molecular interactions among DESs and SA. The results indicate that the experimenral ant theoretical results are consistent and also the solubility of SA in DESs was increased significantly. The DESs can also alter the pH of the solution and cause the increase of SA solubility.

Liquid-liquid extraction and mechanism analysis of extracting fuel additive isopropanol from mixture with choline-based deep eutectic solvents as efficient extractants

• Choline-based DESs was prepared for the separation of IPA- n -heptane. • The extraction performance of three kinds of DESs was compared by LLE experiment. • MD simulation was used to explore the mechanism of extraction process. • The effect of azeotrope ratio on extraction was studied. Deep eutectic solvents (DESs) have wide application prospects in azeotropic separation since of their advantages of good thermal stability, non harmfulness and low raw material price. As a green solvent, DESs has attracted more and more attention in recent years. As a high-quality fuel additive, isopropanol (IPA) has high chemical added value because of its high energy density, low volatile and small corrosive. Therefore, extracting high alcohols such as IPA from azeotropes can effectively improve the combustion efficiency of fossil fuels and reduce tail gas emissions. In this work, ethylene glycol and other hydrogen bond receptors were selected to synthesize three choline-based DESs to extract IPA from n -heptane. The selectivity of DESs to IPA was obtained by liquid–liquid equilibrium (LLE) experiment and the separate efficiency of diverse DESs was compared. To profoundly investigate the intrinsic principle of extracting IPA from DESs, molecular dynamics (MD) simulation method was utilized to acquire the interaction energy between DESs and IPA/ n -heptane, as well as the radial distribution function between DESs and IPA and other kinetic analysis data. The data showed that the experiment is in great assertion with the simulation, DESs synthesized from choline chloride and ethylene glycol has the leading extraction impact of IPA among three kinds of DESs, and Cl - played an imperative part in LLE. In addition, the effect of azeotrope ratio on separation efficiency was explored by simulating LLE with different azeotrope composition.

Theoretical investigation on the structure and physicochemical properties of choline chloride-based deep eutectic solvents

Deep eutectic solvents (DESs) are analogous to ionic liquids that have been widely employed in scientific research and engineering applications. The physicochemical properties of DESs, including the density, viscosity, and nanostructure, serve as the foundation for green solvent development. In the present work, the density and viscosity of choline-based DESs at 293.15–353.15 K were simulated using molecular dynamics (MD) simulation under the Generation Amber Force Field. The radial distribution function (RDF) and number of hydrogen bonds of the selected systems were analysed. It was found that a large amount of the hydrogen bonding network was formulated between chlorine and hydrogen atoms in hydroxyl groups, which greatly decreased the melting temperature of the solvent in comparison with the pure components. The intermolecular interaction decreased with increasing temperature as well as the length of the alkyl chain on the hydrogen bond donor (HBD). Furthermore, an increase in the number of hydroxyl groups in HBD molecules leads to the formation of a more complex and extensive hydrogen bond network, which results in a higher viscosity of the DES.

Hydrogen bonds in aqueous choline chloride solutions by DFT calculations and X-ray scattering

Choline chloride (ChCl) is a common hydrogen bond acceptor (HBA) for deep eutectic solvents (DESs), and the hydrogen bonds between ChCl and H2O impact the physicochemical properties of DES-water mixtures. In the present work, the hydrogen bonds in aqueous ChCl solutions were investigated combining with Raman spectroscopy, density functional theory (DFT) calculations, X-ray scattering and empirical potential structure refinement (EPSR). The Ch+ in aqueous ChCl solutions mainly exists as the gauche conformation. The aqueous ChCl solutions were found to be stabilized by both classical hydrogen bonds (O-H⋯Y, Y = Cl, OW) and carbon-hydrogen bonds (C-H⋯Y, Y = OW) between the components. The orientation of the hydrogen bonds is close to linear (∼180°), while the orientation of the carbon-hydrogen bonds is relatively weak (150°∼176°). The existence of carbon-hydrogen bonds elucidates the high coordination of quaternary ammonium group with H2O. Carbon-hydrogen bonds are found in the partial radial distribution functions, the angle distribution functions and the atoms in molecules analysis. Hydrogen bonds and carbon-hydrogen bonds can affect the physicochemical properties of aqueous ChCl solutions and DES-H2O mixtures. This fundamental understanding of the aqueous ChCl solutions will enable future developments in functional design and application of choline-based DESs.