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Bulk Liquid Phase and Interfacial Behavior of Cineole – Based Deep Eutectic Solvents with Regard to Carbon Dioxide
Abstract
A theoretical study considering classical molecular dynamics simulations on Natural Deep Eutectic Solvents based on cineole and organic acids (malic, succinic, or lactic acid) and their behavior as a solvent for CO2 capture are reported. The nanoscopic properties of eutectic + CO2 mixtures in a wide composition range are studied, considering intermolecular forces, solvation, and the changes in the solvent properties upon CO2 absorption. Likewise, interfacial properties of the solvent in contact with vacuum and pure CO2 and flue gas–like gas phases were considered. The results on solvent–gas interfaces allowed the characterization of the mechanism of CO2 capture, considered as a two stages procedure started with the gas adsorption at the interphase followed by an interface to bulk solvent diffusion leading to the gas solvation in the fluid. The study probes the suitability of terpenoid–based natural eutectics for carbon capture operations, thus allowing green, low cost, and sustainable solvents.
A eutectic mixture of L‐menthol and malonic acid, Me/MA (4:1), was characterized by calorimetry and other physical measurements. The new deep eutectic solvent (m.p. 6 °C) solvates 338 mg of ibuprofen per mL, and the solution is stable in a wide temperature range. Strategies of NMR titration used in supramolecular chemistry were employed to explore binding forces between the eutectic constituents as well as solute‒solvent interaction in ibuprofen solution. Even in acetonitrile, Me4MA is formed through a hydrogen‐bonding network, where the constituents act as hydrogen donors and acceptors at the same time. The estimated association constant is around 30 M−1; the binding forces are enough to build the eutectic mixture at high concentrations. The aggregate Me4MA forms a molecular complex with ibuprofen in acetonitrile as a result of the cooperative effect of the constituents. In addition, van der Waals interactions are operative between ibuprofen and menthol in the saturated IB‒Me/MA (4:1) solution.
Deep eutectic solvents (DESs) are a new class of green solvents that exhibit unique properties in various process applications. In this regard, this study evaluated imidazole-type DESs as solvents for carbon dioxide (CO2) capture. A series of imidazole-type DESs with different ratios was prepared through one-step synthesis. The absorption capacity of CO2 in imidazole-type DESs was measured through weighing, and the effects of temperature, hydrogen bond acceptors, hydrogen bond donors, and water content were discussed. DESs absorbed the effects of CO2. Im-MEA (1:2) was selected to linearly fit lnη and 1/T using the Arrhenius equation under variable temperature conditions, and a good linear relationship was found. The results show the best absorption effect for Im-MEA (1:4). At 303.15 K and 0.1 MPa, the absorption capacity of Im-MEA (1:4) was as high as 0.323 g CO2/g DES; through five times of absorption-desorption after the cycle, the absorption capacity of DES was almost unchanged. Finally, the mechanism of CO2 absorption was studied using Fourier transform infrared and nuclear magnetic resonance spectroscopy. The absorption mechanism of imidazole-type DESs synthesized using imidazole salt and an amine-based solution was chemical absorption, and the reaction formed carbamate (-NHCOO) to absorb CO2.
Deep eutectic solvents (DESs) are a tunable class of solvents with many advantageous properties including good thermal stability, facile synthesis, low vapor pressure, and low-to-negligible toxicity. DESs are composed of hydrogen bond donors and acceptors that, when combined, significantly decrease the freezing point of the resulting solvent. DESs have distinct interfacial and bulk structural heterogeneity compared to traditional solvents, in part due to various intramolecular and intermolecular interactions. Many of the physiochemical properties observed for DESs are influenced by structure. However, our understanding of the interfacial and bulk structure of DESs is incomplete. To fully exploit these solvents in a range of applications including catalysis, separations, and electrochemistry, a better understanding of DES structure must be obtained. In this Perspective, we provide an overview of the current knowledge of the interfacial and bulk structure of DESs and suggest future research directions to improve our understanding of this important information.
The increasing global levels of anthropogenic greenhouse gases (GHGs), especially CO2 emissions, have caused environmental problems that impact humanity and the ecosystems. Therefore, gas capture and storage are a feasible solution to this global issue. Some aqueous amine solutions, such as monoethanolamine (MEA), have been used to capture GHGs, but they are not environment friendly. Research on greener solvents for this task led to deep eutectic solvents (DESs) as a novel option. This review explores the applications of different DESs; compares the differences between gas solubility methodologies; and studies the interference of the DESs’ molar ratio, the influence of HBA and HBD, and the differences between the solubility of some gases in these solvents. More than 40 DESs have been analyzed; however, some gaps need to be filled, such as data for gas solubility under higher pressures and thermodynamic modeling of experimental data.
Deep eutectic solvent (DES) is regarded as a new generation of green solvent due to its distinctive and tailorable physicochemical properties, such as low volatility, strong solubility, biodegradability, low-cost, environment-friendly, and feasibility of the structural design. As an alternative to traditional organic solvents and ionic liquids (ILs), DESs have been widely applied in many fields, such as organic chemical synthesis, electrochemical deposition, material preparation, biomass catalytic conversion, extraction and separation, detection and analysis, nanotechnology, gas absorption, and drug delivery. In this paper, through in-depth discussion on factors influencing the physicochemical properties of DESs, we summarized the relations between their composition, structure, and performance. Focusing on their solvent performance, we analyzed the latest research results of DESs with different physicochemical properties in various fields. It should be pointed out that designing and synthesizing DESs from the molecular structure aspect to regulate their physicochemical properties is the direction of accurately developing new functional applications of DESs.
Deep eutectic solvents (DES) are emerging sustainable designer solvents viewed as greener and better alternatives to ionic liquids. Nonionic DESs possess unique properties such as viscosity and hydrophobicity that make them desirable in microextraction applications such as oil-spill remediation. This work builds upon a nonionic DES, NMA-LA DES, previously designed by our group. The NMA-LA DES presents a rich nanoscopic morphology that could be used to allocate solutes of different polarities. In this work, the possibility of solvating different solutes within the nanoscopically heterogeneous molecular structure of the NMA-LA DES is investigated using ionic and molecular solutes. In particular, the localized vibrational transitions in these solutes are used as molecular reporters of the DES molecular structure via vibrational spectroscopy. The FTIR and 2DIR data suggest that the ionic solute is confined in a polar and continuous domain formed by NMA, clearly sensing the direct effect of the change in NMA concentration. In the case of the molecular nonionic and polar solute, the data indicates that the solute resides in the interface between the polar and non-polar domains. Finally, the results for the non-polar and nonionic solute (W(CO)6) are unexpected and less conclusive. Contrary to its polarity, the data suggest that the W(CO)6 resides within the NMA polar domain of the DES, probably by inducing a domain restructuring in the solvent. However, the data are not conclusive enough to discard the possibility that the restructuring comprises not only the polar domain, but also the interface. Overall, our results demonstrate that the NMA-LA DES has nanoscopic domains with affinity to particular molecular properties, such as polarity. Thus, the presented results have direct implication to separation science.
The principles of ‘green chemistry’ are gaining importance in agri-food sector due to the need to reduce pollution from toxic chemicals, make industrial processes safer and more sustainable, and to offer ‘clean-labeled products’ required by the consumers. The application of natural deep eutectic solvents (NADES) – natural product-based green liquids is considered the promising alternative to conventional organic solvents. This review is intended to summarize and discuss recent advances related to physicochemical properties of NADES, their applications, compatibility with analytic techniques and toxicological profile, pointing out the challenges and necessary improvements for their wider utilization in agri-food sector. NADES allow extraction of wide range of food compounds and they are proven to be convenient for food-related applications. However, their potential for industrial scale-up utilization is not completely investigated. Examined NADES are readily biodegradable, but only preliminary studies on NADES toxicity which include limited number of NADES molecules are available. Apart from fundamental research dealing with NADES formation and the nature of the interactions and structure underpinning the liquid phase formation, the question of purity of NADES obtained by different synthetic methodologies need to be addressed in the future. Data on physicochemical properties of synthetized NADES are still needed as they are relevant for industrial applications.
Deep eutectic solvents (DESs) based on terpenes are identified and characterized. 507 combinations of solid components are tested, which results in the identification of 17 new hydrophobic DESs. Four criteria are introduced to assess the sustainability from a chemical engineering point of view of these hydrophobic DESs. These criteria include a viscosity smaller than 100 mPa s, a density difference between DES and water of at least 50 kg m-3 upon mixing of the DES and water, low transfer of the DES to the water phase and minor to no pH change. The results show that five new hydrophobic DESs based on natural components satisfy these; thymol and coumarin (2:1), thymol and menthol (1:1), thymol and coumarin (1:1), thymol and menthol (1:2) and 1-tetradecanol and menthol (1:2), satisfy these criteria and thus are promising DESs. These new DESs can be considered as natural deep eutectic solvents, which have the potential to be environmentally friendly. A selected group of the hydrophobic DESs were used for the extraction of riboflavin from water. They all show higher removal of riboflavin in comparison to decanoic acid:tetraoctylammonium bromide (2:1). The highest extraction efficiency of Riboflavin from water, 81.1 %, was achieved with the hydrophobic DES DecA:Lid (2:1).
Deep eutectic solvents (DESs) are a large family of solvents that show many similarities with ionic liquids. They are distinguished by the presence of large amount of molecular components (typically as hydrogen bond donor). They are more industrially promising than ionic liquids due to their low cost and tolerance to humidity (hydrolysis or hydro-scopicity). As an emerging research field, DESs have already received numerous research efforts from chemistry scientists. The exploration of DESs used for functional materials in energy and environmental applications is in its early stage. This review briefly introduces the basics of DESs and how they could be promising as solvents for material scientists. We summarize the application of DESs for the synthesis of materials used for energy and environmental applications. In this review, DESs are described in view of their three main roles playing in the solution process of functional materials. Besides DESs have been widely known as inert media or reactive reagents for the synthesis of materials, they can also be adopted directly as functional materials, such as, electrolytes for energy storage devices, CO2 adsorbents, and so on. The present review will focus on several categories of functional materials including noble metals, porous carbonaceous materials, transition metal compounds, and DESs themselves, which are synthesized or derived from DESs for potential applications in the energy and environmental fields. DESs will be demonstrated to be effective in guiding the formation of functional materials with unique structures and properties. In particular, we will introduce our work on exploring the DES-thermal synthesis strategy, in which the DES is used as solvent as well as reagent. Recent theoretical and experimental work for understanding the structural basis of DESs would also be summarized. This review article aims to inspire the scientists to use DESs as a powerful tool to push the frontiers in the field of materials, energy and environmental science.
This study was conducted to determine the effectiveness of Natural Deep Eutectic Solvent (NADES), consisting of choline chloride and a hydrogen bonding donor (HBD) compound, in terms of carbon dioxide absorption. Solubility of carbon dioxide in NADES was found to be influenced HBD compound used and choline chloride to HBD ratio, carbon dioxide pressure, and contact time. HBD and choline/HBD ratios used were 1,2-propanediol (1:2), glycerol (1:2), and malic acid (1:1). The carbon dioxide absorption measurement was conducted using an apparatus that utilizes the volumetric method. Absorption curves were obtained up to pressures of 30 bar, showing a linear relationship between the amount absorbed and the final pressure of carbon dioxide. The choline and 1,2-propanediol eutectic mixture absorbs the highest amount of carbon dioxide, approaching 0.1 mole-fraction at 3.0 MPa and 50°C. We found that NADES ability to absorb carbon dioxide correlates with its polarity as tested using Nile Red as a solvatochromic probe.
Several novel applications of Deep Eutectic Solvents (DESs) have emerged recently. With a growing interest in the field, there is an urge to understand formation and functioning of these solvents at molecular level, which in turn would assist in further designing of DESs. We herein performed molecular dynamics simulations on three of the commonly used type III DES, viz, reline, ethaline, and glyceline, which are mixtures of urea, ethylene glycol, and glycerol with choline chloride at eutectic composition. Our results explain the role of inter-molecular and intra-molecular hydrogen bonding and energies on formation of these DESs. Furthermore, the ability of these DESs to be altered in a desired way through a simple addition of water makes it versatile solution for several other applications. Hence, simulations are also performed on the aqueous DES solutions, which reveal the effect of water on intermolecular network of interaction existing within these DESs.
Nose has modified Newtonian dynamics so as to reproduce both the canonical and the isothermal-isobaric probability densities in the phase space of an N-body system. He did this by scaling time (with s) and distance (with V¹D/ in D dimensions) through Lagrangian equations of motion. The dynamical equations describe the evolution of these two scaling variables and their two conjugate momenta p/sub s/ and p/sub v/. Here we develop a slightly different set of equations, free of time scaling. We find the dynamical steady-state probability density in an extended phase space with variables x, p/sub x/, V, epsilon-dot, and zeta, where the x are reduced distances and the two variables epsilon-dot and zeta act as thermodynamic friction coefficients. We find that these friction coefficients have Gaussian distributions. From the distributions the extent of small-system non-Newtonian behavior can be estimated. We illustrate the dynamical equations by considering their application to the simplest possible case, a one-dimensional classical harmonic oscillator.
The electroless and electrolytic deposition of nickel from a solution containing nickel chloride in either an ethylene glycol (EG)-choline chloride based or a urea-choline chloride based ionic liquids has been carried out onto copper and steel cathodes under different conditions. It is found that electroless nickel deposits of up to several microns has been obtained by dip coating from only EG based ionic liquids at temperature above 70°C without the use of catalysts. The influences of various experimental conditions on electrodeposition and the morphology of the deposited layers have been investigated by scanning electron microscopy and X-ray diffraction. It is shown that very smooth, shiny and dense with good adherence and bright metallic coloured nickel coatings can be obtained from both EG and urea-based ionic liquids at applied deposition potential of up to -0.50 V and applied deposition current density of up to -5.0 A m-2 between 50°C and 100°C. The cathodic current efficiency for the deposition of Ni is about 97%.
Choline chloride + levulinic acid deep eutectic solvent is studied as a suitable material for CO2 capturing purposes. The most relevant physicochemical properties of this solvent are reported together with the CO2 solubility as a function of temperature. The corrosivity of this solvent is studied showing better performance than amine-based solvents. A theoretical study using both Density Functional Theory and Molecular Dynamics approaches is carried out to analyze the properties of this fluid from the nanoscopic viewpoint and their relationship with the macroscopic behavior of the system and its ability for CO2 capturing. The behavior of liquid – gas interface is also studied and its role on the CO2 absorption mechanism is analyzed. The combined experimental plus theoretical reported approach leads to a complete picture of the behavior of this new sorbent with regard to CO2, which together with its low pricing, and the suitable environmental and toxicological properties of this solvent, lead to a promising candidate for CO2 capturing technological applications. Keywords: Deep eutectic solvents; carbon capture; thermodynamics; molecular simulations.
The research into ionic liquids (IL) has escalated in the last two decades, ever since the potential for new chemical technologies was realized. In the period covered by this review, approximately 6000 journal articles have been published on the topic. Compared to classical ILs, the research into DESs is comparatively in its infancy, with the first paper on the subject only published in 2001. DESs contain large, nonsymmetric ions that have low lattice energy and hence low melting points. They are usually obtained by the complexation of a quaternary ammonium salt with a metal salt or hydrogen bond donor (HBD). A majority of ionic liquids which are fluid at ambient temperatures are formed using an organic cation, generally based around ammonium, phosphonium, and sulfonium moieties. The second generation of ionic liquids are those that are entirely composed of discrete ions, rather than the eutectic mixture of complex ions seen in the first generation ionic liquids.
Tri-reforming is a novel process concept proposed for effective conversion and utilization of CO2 in the flue gases from fossil fuel-based power plants (C. Song, Chemical Innovation, 2001, 31, 21–26). The CO2, H2O, and O2 in the flue gas need not be pre-separated because they will be used as co-reactants for tri-reforming of natural gas. The tri-reforming is a synergetic combination of CO2 reforming, steam reforming, and partial oxidation of natural gas. It can produce synthesis gas (CO+H2) with H2/CO ratios (1.5–2.0) and could eliminate carbon formation which is a serious problem in the CO2 reforming of methane. These two advantages have been demonstrated by a laboratory experimental study of tri-reforming at 850°C. Both thermodynamic analysis and the experimental testing in a fixed-bed flow reactor showed that over 95% CH4 conversion and over 80% CO2 conversion can be achieved by using certain supported transition metal catalysts such as Ni supported on an oxide substrate.
A general purpose, scalable parallel molecular dynamics package for simulations of arbitrary mixtures of flexible or rigid molecules is presented. It allows use of most types of conventional molecular-mechanical force fields and contains a variety of auxiliary terms for inter- and intramolecular interactions, including an harmonic bond-stretchings. It can handle both isotropic or ordered systems. Besides an NVE MD ensemble, the simulations can also be carried out in either NVT or NPT ensembles, by employing the Nosé–Hoover thermostats and barostats, respectively. If required, the NPT ensemble can be generated by maintaining anisotropic pressures. The simulation cell can be either cubic, rectangular, hexagonal or a truncated octahedron, with corresponding periodic boundary conditions and minimum images. In all cases, the optimized Ewald method can be used to treat the Coulombic interactions. Double time-step or constrained dynamics schemes are included. An external electric field can be applied across the simulation cell. The whole program is highly modular and is written in standard Fortran 77. It can be compiled to run efficiently both on parallel and sequential computers. The inherent complexity of the studied system does not affect the scalability of the program. The scaling is good with the size of the system and with the number of processors. The portability of the program is good, it runs regularly on several common single- and multiprocessor platforms, both scalar and vector architectures included.
Developing green solvents with low toxicity and cost is an important issue for the biochemical industry. Synthetic ionic liquids and deep eutectic solvents have received considerable attention due to their negligible volatility at room temperature, high solubilization ability, and tunable selectivity. However, the potential toxicity of the synthetic ionic liquids and the solid state at room temperature of most deep eutectic solvents hamper their application as extraction solvents. In this study, a wide range of recently discovered natural ionic liquids and deep eutectic solvents (NADES) composed of natural compounds were investigated for the extraction of phenolic compounds of diverse polarity. Safflower was selected as a case study because its aromatic pigments cover a wide range of polarities. Many advantageous features of NADES (such as their sustainability, biodegradability combined with acceptable pharmaceutical toxicity profiles, and their high solubilization power of both polar and non-polar compounds) suggest their potential as green solvents for extraction. Experiments with different NADES and multivariate data analysis demonstrated that the extractability of both polar and less polar metabolites was greater with NADES than conventional solvents. The water content in NADES proved to have the biggest effect on the yield of phenolic compounds. Most major phenolic compounds were recovered from NADES with a yield between 75%-97%. This study reveals the potential of NADES for applications involving the extraction of bioactive compounds from natural sources.
Adequate initial configurations for molecular dynamics simulations consist of arrangements of molecules distributed in space in such a way to approximately represent the system's overall structure. In order that the simulations are not disrupted by large van der Waals repulsive interactions, atoms from different molecules must keep safe pairwise distances. Obtaining such a molecular arrangement can be considered a packing problem: Each type molecule must satisfy spatial constraints related to the geometry of the system, and the distance between atoms of different molecules must be greater than some specified tolerance. We have developed a code able to pack millions of atoms, grouped in arbitrarily complex molecules, inside a variety of three-dimensional regions. The regions may be intersections of spheres, ellipses, cylinders, planes, or boxes. The user must provide only the structure of one molecule of each type and the geometrical constraints that each type of molecule must satisfy. Building complex mixtures, interfaces, solvating biomolecules in water, other solvents, or mixtures of solvents, is straightforward. In addition, different atoms belonging to the same molecule may also be restricted to different spatial regions, in such a way that more ordered molecular arrangements can be built, as micelles, lipid double-layers, etc. The packing time for state-of-the-art molecular dynamics systems varies from a few seconds to a few minutes in a personal computer. The input files are simple and currently compatible with PDB, Tinker, Molden, or Moldy coordinate files. The package is distributed as free software and can be downloaded from http://www.ime.unicamp.br/~martinez/packmol/.
The previously developed particle mesh Ewald method is reformulated in terms of efficient B‐spline interpolation of the structure factors. This reformulation allows a natural extension of the method to potentials of the form 1/r p with p≥1. Furthermore, efficient calculation of the virial tensor follows. Use of B‐splines in place of Lagrange interpolation leads to analytic gradients as well as a significant improvement in the accuracy. We demonstrate that arbitrary accuracy can be achieved, independent of system size N, at a cost that scales as N log(N). For biomolecular systems with many thousands of atoms this method permits the use of Ewald summation at a computational cost comparable to that of a simple truncation method of 10 Å or less.
Terpene based natural deep eutectic solvents (NADES) formed by using carvone as hydrogen bond acceptor and series of organic acids including tartaric, succinic, malic, and lactic acids as hydrogen bond donors are studied using a combination molecular simulation methods. Density functional theory (DFT) was used to study small molecular clusters, and the topological characterization of the intermolecular forces by using atoms-in-a-molecule theory (AIM). Close-range interactions between the optimized carvone (CARV) bases eutectic solvents between carbon dioxide (CO2) have been studied for potential utilization of these solvents for gas capture purposes. Furthermore, COSMO-RS calculations have been carried out for CO2 solubilization performance of NADES compounds, and to obtain s-profiles in order to infer on the polarity and H-bond forming ability of the studied solvents. On the other hand, molecular dynamics (MD) simulations were carried out to analyze the bulk liquid properties and their relationship with relevant macroscopic properties (e.g., density or thermal expansion). Last but not least, relevant toxicity properties of the studied systems were predicted and reported in this work. The reported results provide the characterization of environmentally friendly NADES and show the suitability of CARV for advanced applications as CO2 solubilizers.
Bisphenol A (BPA) is a widely used chemical that is found in wastewaters and surface water due to its ineffective removal by conventional water treatment processes. BPA being an endocrine disruptor, regulations and different technologies have been proposed for its treatment. In this work, the use of natural solvents such as terpenoids and eutectic solvents is presented, envisioning a BPA extraction from aqueous solutions based on the hydrophobicity of these sustainable solvents. First, an initial screening of 43 solvents was performed by molecular simulation using the COSMO-RS method. BPA extraction from aqueous solutions was experimentally evaluated with initial BPA concentrations of 5 to 100 mg/L, and several solvent-to-feed ratios at 303.2 K. Extraction yields >99% were obtained with eucalyptol, geraniol, and (menthol + camphor) eutectic solvent outperforming conventional solvents. Eucalyptol, geraniol, and (menthol + camphor) have been used in a scaling-up evaluation and reuse in 6 consecutive cycles observing yields in all stages above 98.5% at solvent-to-feed ratios ranging 0.01-0.05. Besides, the solvents were regenerated using back-extraction with NaOH, providing yields above 99.5%. The regenerated solvents showed similar yields to those obtained with fresh solvent, and their chemical stability was checked through FTIR analysis. BPA was recovered by precipitation from the aqueous back-extraction solution, showing by FTIR that no degradation occurs during the extraction, back-extraction, and precipitation processes. For the first time, the complete cycle of extraction with solvent reuse, back-extraction, and precipitation of BPA using eutectic solvents and terpenoids has been studied.
At present, oral chemotherapy showing the advantages of non-invasiveness, convenience, and high patient compliance, is gradually replacing traditional intravenous chemotherapy to treat patients with cancer. RA-XII, a unique natural cyclopeptide, exhibits various biological activities, such as anti-tumor, anti-angiogenic, and anti-metastatic activities. Designing an orally available formulation of RA-XII is of great importance in the development of clinically useful anticancer agents. However, RA-XII shows low oral bioavailability in rats due to its poor solubility and low permeability. To overcome these limitations, in this work, a natural deep eutectic solvent (NADES) was designed to efficiently deliver RA-XII by oral administration. A novel NADES composed of betaine and mandelic acid in the molar ratio of 1:1 (Bet-Man NADES) was successfully prepared based on a binary phase diagram of Bet and Man. Acute toxicity studies indicated that Bet-Man NADES was well tolerated with acceptable toxicity. In Bet-Man NADES solutions, the solubility of RA-XII was increased by up to 17.54-fold, and the diffusion and permeability of RA-XII carried out in a Franz cell was also significantly improved 10.35 times. In terms of biopharmaceutical classification this is translated into a change for RA-XII from class IV to class II systems. More importantly, Bet-Man NADES was transferred into the solid formulation by the inclusion of a polymer, and amorphous solid dispersions based on Bet-Man NADES (PVP K30/NADES/RA-XII, ASDs) were successfully prepared to improve uniformity, apparent solubility, dissolution, and cytotoxicity in vitro. Consequently, the oral bioavailability of RA-XII in NADES solutions and ASDs was enhanced by approximately 11.58 and 7.56 times compared with that of pure RA-XII in 0.5% CMC-Na. Thus, it can be seen that a natural deep eutectic solvent and its modified amorphous solid dispersions are appropriate novel strategies for improving dissolution rate and bioavailability of poor soluble natural products such as RA-XII.
Deep eutectic solvents based on cineole as hydrogen bond acceptors and organic acids (succinic, malic, and lactic) as hydrogen bond donors are studied using a theoretical approach. The nature, strength, and extension of hydrogen bonding are analyzed, thus quantifying this prevailing interaction and its role in the fluid properties. Density functional theory was used to study small molecular clusters, and the topological characterization of the intermolecular forces was carried out using atoms in a molecule theory. Classical molecular dynamics simulations were considered to study nanoscopic bulk liquid properties and their relationship with relevant macroscopic properties such as density or thermal expansion. The reported results provide the characterization of environmentally friendly deep eutectic solvents and show the suitability of cineole for developing these sustainable materials.
Sustainable technologies applied to energy-related applications should develop a pivotal role over the next decades. Therefore, the development of new materials for old processes has merged as a central research line lately. Deep eutectic solvents (DESs) have been recently considered alternative and economic task-specific solvents for many chemical and environmental processes. The low-cost production of DESs production from natural sources and their tunable properties, such as neat null toxicity and biodegradability, make these solvents suitable candidates for various processes within the green chemistry framework. Considering the millions of possible DES combinations yet to be explored, a detailed review of DES research's current status that can elaborate on the structure-property relationship is an essential task to identify the missing links and strong points on DES research. Thus, this review work focuses on the recent research efforts on the utilization of DES on chemical processes, with the purpose of elucidation on gas capture/separation, fuel desulfurization, biodiesel production, and water treatment processes and provides a deeper understanding on outstanding scientific questions and identifies promising new research directions that involve DESs.
Deep eutectic solvents show great potential as CO2 absorbents, which is highly desirable for the sustainable development of CO2 reduction and prevention of global climate changes. Ab initio molecular dynamics simulations in the isothermal-isobaric ensemble at pressures of 1 MPa and 5 MPa and at the corresponding experimental density are carried out to investigate the CO2 absorption in choline chloride: ethylene glycol deep eutectic solvent. Based on the structural analysis, there is a strong anion and hydrogen bond donor effect and a minor cation effect on CO2 solvation in the solvent. Instead of cooperation, a competition between the anion and the hydrogen bond donor (ethylene glycol) for the interaction with CO2 is indicated. While at a lower pressure, the ethylene glycol-CO2 interaction dominates, at a higher pressure, it is the chloride-CO2 interaction. Thus, it is possible to use the same advantages within the deep eutectic solvent as the CO2 absorbent as in ionic liquids, but in the hydrogen bond, a donor can be exploited.
Deep eutectic solvents (DESs) are an emerging class of mixtures characterized by significant depressions in melting points compared to those of the neat constituent components. These materials are promising for applications as inexpensive "designer" solvents exhibiting a host of tunable physicochemical properties. A detailed review of the current literature reveals the lack of predictive understanding of the microscopic mechanisms that govern the structure-property relationships in this class of solvents. Complex hydrogen bonding is postulated as the root cause of their melting point depressions and physicochemical properties; to understand these hydrogen bonded networks, it is imperative to study these systems as dynamic entities using both simulations and experiments. This review emphasizes recent research efforts in order to elucidate the next steps needed to develop a fundamental framework needed for a deeper understanding of DESs. It covers recent developments in DES research, frames outstanding scientific questions, and identifies promising research thrusts aligned with the advancement of the field toward predictive models and fundamental understanding of these solvents.
In the design of greener chemicals, deep eutectic solvents (DESs) are considered as one of the most versatile alternative media with widespread applications. DESs have the advantages of being nonflammable with negligible vapor pressure compared to the traditional solvents. They share many characteristics of ionic liquids, but DESs are cheaper to formulate, typically nontoxic, highly pure, recyclable, biodegradable, and are suitable for use with biological systems. In this article, the two emerging and unconventional types of DESs, therapeutic DES (THEDES) and amino acid-based DES (AADES) are reviewed. Based on the published literature, choline chloride and menthol are the two most common constituents to formulate THEDESs, while proline is the most common component to formulate AADESs. THEDESs have primarily been developed to enhance the efficacy of drugs, whereas AADESs have been explored for pharmaceuticals as well as for the extraction of phytochemicals, radioactive iodine capture, oil separation from ores, and to synthesize bioactive compounds. Since detailed knowledge of their structures, nonbonding interactions, formulations, and applications are yet to be explored, the aim of this review is to compile these details and provide a solid background for the future research.
In this work, the theoretical solubility of CO2 into different choline chloride and phosphonium based deep eutectic solvents (DESs) was successfully calculated using COSMO-RS method. FTIR spectrums of the seven DESs were calculated in order to investigate and check out their structure. There was a good agreement between the predicted values and the experimental results reported in the literature. The Sigma profiles analysis showed the possibility of formation of H-bonding between CO2 and the DESs which favors increasing the solubility of CO2. Molecular dynamics simulation was performed to investigate the molecular interaction between the different DESs and CO2. The actual approach can be used in the estimation of different physicochemical properties of DESs especially the capture of undesirable molecules like H2S, NOx, H2O and CO2.
Deep-eutectic-solvents (DESs) are a new class of green solvents. Here we report the hydrogen bonding and structural properties of the archetypal DES ethaline, a mixture of choline chloride (ChCl) and ethylene glycol (EG) of 1:2 molar ratio, and its pseudo-binary mixtures with acetonitrile. The investigations were carried out employing FTIR combined with quantum chemical calculations. Excess and 2D-correlation spectroscopies were used to identify favorable species in the solutions and to explore the heterogeneity. The results show that the mixing process is the transformation from ethaline, EG tetramer, and CH3CN dimer to the complexes of ethaline-1CH3CN and ethaline-2CH3CN, together with the increased percentages of EG dimer, EG trimer, and CH3CN monomer with respect to their total amounts in the mixtures. Theoretical calculations show that, for ChCl, the positive charge is located at the methyl groups and methylenes, rendering their ability to form hydrogen bonds. Adding CH3CN to ethaline can hardly break apart the doubly ionic hydrogen-bonds between Ch⁺ and Cl⁻. The co-solvent molecules mainly surround the core-structure of ethaline, forming non-covalent hydrogen bonds with hydroxyl groups of EG/Ch⁺, but not Cl⁻. These in-depth studies on the properties of ethaline and CH3CN/CD3CN mixed solvents may shed light on exploring their applications.
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Considering the great potential of deep eutectic solvent (DES) for CO2 capture, this work studies the CO2 solubility in DESs by combining experimental measurement and molecular dynamics (MD) simulation. First, four phosphonium-based DESs are prepared in laboratory, involving two types of hydrogen bond acceptors (HBAs), namely tetrabutylphosphonium bromide (TBPB) and allyltriphenylphosphonium bromide (ATPPB), and two types of hydrogen bond donors (HBDs), namely phenol (PhOH) and diethylene glycol (DEG). The CO2 solubility in the obtained DESs is measured under 313.15 K – 333.15 K and pressure below 2000 kPa, and compared with that of previously reported DESs and ionic liquids. Second, MD simulations are performed to study the microscopic behaviors of the involved DESs and mixtures. Through the analyses of radial distribution functions (RDFs), spatial distribution functions (SDFs) and intermolecular interaction energy, the eutectic formation and CO2 absorption mechanisms, as well as the effect of HBA/HBD type and molar ratio are interpreted.
Mixtures of non-ionic compounds have been reported as DES but most are just ideal mixtures. In the thymol–menthol system, an abnormal strong interaction was identified stemming from the acidity difference of the phenolic and aliphatic hydroxyl groups. This type of interaction is found to be the key to prepare non-ionic DES, that may be classified as type V.
New-generation solvents termed deep eutectic solvents (DESs) are attracting increasing attention as eco-friendly solvents in analytical chemistry. Recently, a new subclass of DESs called hydrophobic DESs (hDESs) has been reported. hDESs are generally immiscible with water and have high extraction efficiency for nonpolar analytes; thus, they have been suggested as potential extraction media to replace toxic organic solvents or expensive hydrophobic ionic liquids. Since the first introduction of hDESs in 2015, a growing number of studies on the application of hDESs in sample preparation methods have been reported. The present review provides an overview on the preparation and physicochemical properties of hDESs, followed by applications of hDESs in the extraction of organic and inorganic analytes from aqueous environments. In this review, up-to-date studies of conventional (liquid–liquid extraction) and miniaturized (liquid-phase microextraction) scale processes will be discussed with a focus on work up to January 2019.
Deep eutectic solvents (DESs) consist of a mixture of two or more solid components leading to a drop of the melting point of the mixture when compared to the starting materials. Until recently, only hydrophilic DESs were available, and despite their revolutionary role in the alternative solvents scenario, important issues in chemistry and chemical engineering, such as water related problems or the replacement of toxic volatile organic compounds, could not be tackled. Hydrophobic (Deep) ‐ here in parenthesis due to the different depths of the eutectic´s melting points ‐ Eutectic Solvents are a sub‐class of DESs where both components are hydrophobic. The choice of low cost, naturally occurring compounds, with low toxicity and high biodegradability and straightforward preparation without purification steps, are among the key advantages that distinguish them as innovative solvents. Although research on hydrophobic DESs is scarce, since the first paper on the subject was only published in 2015, some interesting features and applications have been published and deserve to be reviewed and comparisons established. The current review is divided into two parts: first, a brief general introduction to DESs and the second part details on nomenclature using solid‐liquid phase diagram analysis, chemical stability, thermophysical properties comparison and finally the most important emerging fields of application.
Dimethyl carbonate (DMC) is an excellent gasoline and diesel additive in the field of fuel. However, it can form azeotrope with ethanol, so separation of DMC with high purity from the azeotrope is of significance. To separate the azeotrope of DMC and ethanol, the σ-profiles were calculated by the COSMO-SAC model to determine suitable deep eutectic solvents (DESs). On the basis of σ-profiles analysis, four choline chloride based DESs were selected and evaluated as extractant. The liquid−liquid equilibrium (LLE) data for the ternary systems DMC + ethanol + DESs were determined at T/K = 298.15 and 308.15 K under 101.3 kPa. The distribution coefficient and selectivity were calculated to evaluate the extraction ability of the DESs. And the influence of different temperature on phase behavior was explored. In addition, the ¹H NMR spectrums of the DESs distributed in the upper and lower phases were obtained to check the integrity of the DESs. Meanwhile, the LLE experimental data were correlated by the NRTL model, the correlation results show an agreement with the experimental data.
Anthropogenic CO2 emissions into the atmosphere are responsible for the global warming, therefore, it is essential to reduce these emissions at the source. Recently, deep eutectic solvents (DESs) have shown great potential to absorb the CO2. In the current study, 15 different types of amine- and glycol-based deep eutectic solvents were synthesized and investigated for CO2 absorption. In general, amine-based solvents have shown higher CO2 absorption as compared to glycol based solvents. In particular, the highest CO2 absorption was observed for the tetrabutyl ammonium bromide and methyldiethanol amine (TBAB/4MDEA) system having a CO2 solubility of 0.29 (mol CO2/mol solvent) at 1 MPa and 303.15 K. Thermophysical properties of all synthesized DESs were estimated using the modified Lydersen–Joback–Reid method and Lee–Kesler mixing rule. Experimental CO2 solubility data were well fitted using the nonrandom two liquid and the Peng–Robinson thermodynamic models. Apart, CO2 solubility data were correlated with Henry’s law, and Henry’s constant was calculated for all DESs. The kinetic modeling of CO2 absorption in DESs was also studied and rate constants were evaluated.
As the demand for medical cannabis preparations increases, so does the use of the common organic solvents that are used in the extraction and quantification of phytocannabinoids. Since common organic solvents are typically hazardous to the environment and to human health, it is vital to identify safer, greener, and more efficient alternatives. The aim of the present research was to develop a series of hydrophobic deep eutectic solvents (DESs) based on terpenes and natural organic acids and to establish whether these might be potential substitutes for the extraction of phytocannabinoids (tetrahydrocannabinol, cannabidiol, and their carboxylated homologues) from raw cannabis plant material. Data were obtained using capillary electrophoresis with diode array detection (DAD). Initial screening showed that the DES composed of a menthol: acetic acid (1:1 M ratio) mixture showed the greatest extraction efficiency (of all the DESs that were tested), with yields ranging from 118.6% to 132.6% (compared to a methanol: chloroform mixture). In conclusion, menthol: acetic acid DES extraction is efficient, as well as non-toxic and biodegradable. As such it has applications within the pharmaceutical industry and represents a greener alternative organic solvent for the extraction of phytocannabinoids.
As functional liquid media, natural deep eutectic solvent (NADES) species can dissolve natural or synthetic chemicals of low water solubility. Moreover, the special properties of NADES, such as biodegradability and biocompatibility, suggest that they are alternative candidates for concepts and applications involving some organic solvents and ionic liquids. Owing to the growing comprehension of the eutectic mechanisms and the advancing interest in the natural eutectic phenomenon, many NADES applications have been developed in the past several years. However, unlike organic solvents, the basic structural unit of NADES media primarily depends on the intermolecular interactions among their components. This makes NADES matrices readily influenced by various factors, such as water content, temperature, and component ratio and, thus, extends the metabolomic challenge of natural products (NPs). To enhance the understanding of the importance of NADES in biological systems, this review focuses on NADES properties and applications in NP research. The present thorough chronological and statistical analysis of existing report adds to the recognition of the distinctiveness of (NA)DES, involves a discussion of NADES-related observations in NP research, and reportes applications of these eutectic mixtures. The work identifies potential areas for future studies of (NA)DES by evaluating relevant applications, including their use as extraction and chromatographic media as well as their biomedical relevance. The chemical diversity of natural metabolites that generate or participate in NADES formation highlights the growing insight that biosynthetically primordial metabolites (PRIMs) are as essential to the biological function and bioactivity of unrefined natural products as the biosynthetically more highly evolutionary metabolites (HEVOs) that can be isolated from crude mixtures.
The search for both new and sophisticated materials that meet the needs of the modern era, and for sustainable eco-efficient processes, has raised deep eutectic solvents (DES) to a prominent position. Research focused on the use of these solvents – highly advantageous in economic, practical, and environmental terms – for the creation of innovative materials has been growing fast, and a very large number of publications reporting the use of DES as valuable alternatives to overcome the limitations of conventional solvents, and even ionic liquids, has been published. DES have proved to offer tremendous opportunities and have opened new perspectives to produce novel and refined materials.
This review focuses on recent advances concerning these new materials and on the practices that have been developed employing DES as solvents. The definition, preparation and unique properties of DES are first addressed, followed by a more extensive description of their applications in polymer, metal deposition and nanomaterial science and sensing technologies. Their impact in the production processes and in the properties of the materials obtained, as well as their key role as designer solvents, is highlighted.
The deep eutectic solvent glyceline formed by choline chloride and glycerol in 1:2 molar ratio is much less viscous compared to glycerol, which facilitates its use in many applications where high viscosity is undesirable. Despite the large difference in viscosity, we have found that the structural network of glyceline is completely defined by its glycerol constituent, which exhibits complex microscopic dynamic behavior, as expected from a highly correlated hydrogen-bonding network. Choline ions occupy interstitial voids in the glycerol network and show little structural or dynamic correlations with glycerol molecules. Despite the known higher long-range diffusivity of the smaller glycerol species in glyceline, in applications where localized dynamics is essential (e.g., in microporous media), the local transport and dynamic properties must be dominated by the relatively loosely bound choline ions.
Deep eutectic solvents (DESs) as ionic liquid (IL) analogues show great potential for CO2 capture. They exhibit favorable solvent properties and are considered to be economical alternatives to conventional ILs. In this study, we prepare 35 DESs and screen them in terms of their CO2 solubility and viscosity, both crucial factors to be considered when designing efficient CO2 sorbents. The influence of salt and HBD type and structure, as well their molar ratio on the CO2 solubility and viscosity of the DESs is investigated. The viscosity and CO2 solubility of the DESs are compared with those of other DESs and conventional ILs. 15 DESs, which exhibit comparable CO2 absorption capacity to choline chloride–urea DESs, glycerol DESs and fluorinated ILs, are chosen as the promising ones. The viscosities of the selected DESs are below 200 mPa s and are lower than those of choline chloride-based DESs. Since the viscosity of the DESs is relatively high, on a par with those of conventional ILs, the effect of water as a co-solvent is investigated in order to decrease the viscosity. The addition of water to the glycerol-based DESs improves the kinetics of absorption by decreasing the viscosity, thus increasing the CO2 absorption capacity. Dry or aqueous DESs that demonstrate a high sorption capacity and low viscosity are chosen for additional analysis and characterization, and further functionalization will be carried out in the future to improve their sorption capacity.
The properties of choline chloride plus phenylacetic acid deep eutectic solvents in neat liquid state and upon absorption of CO2 are analyzed using a theoretical approach combining quantum chemistry using Density Functional Theory and classic molecular dynamics methods. This study investigates the physicochemical properties, structuring, dynamics and interfacial behavior of the selected deep eutectic solvent from the nano-size point of view to infer its viability for effective CO2 capture. DFT results provided information on the mechanism of short-range interactions between CO2 and the studied DES, showing a better performance than previously studied DES. The mechanism of CO2 capture is analyzed considering model flue gas, showing a two-stage process with water, CO2 and N2 molecules developing adsorbed layers at the interface but in different regions. Water adsorbed layers would delay the migration of CO2 molecules toward bulk liquid regions, which should be considered for developing large-scale applications.
Dye-sensitized solar cells (DSSCs) using an aqueous (40% w w-1 water content) choline chloride-based deep eutectic solvent as an electrolyte medium have been investigated. The joint combination of the above eutectic mixture and proper hydrophilic sensitizer afforded DSSC with power conversion efficiencies comparable to that using the same electrolyte composition but with conventional, toxic and volatile solvents as media, thereby paving the way to a new generation of eco-friendly, nature-inspired, low-cost solar devices.
Deep eutectic solvents (DESs) are a new class of green solvents used to dissolve the non-steroidal anti-inflammatory drugs (NSAIDs) for potential nonaqueous liquid administration applications. Several NSAIDs are readily soluble in various DESs to a high concentration. Aspirin, a hydrolabile NSAID was 8.2-fold more stable against cleavage in DES than in water.
A novel and green method based on precipitation of calcium phosphate reactants in a deep eutectic solvent (DES) was devised for the synthesis of calcium phosphate nanoparticles. The DES was prepared by simple mixing-heating of choline chloride and urea. The effect of synthesis temperature on particulate and structural properties of the synthesized calcium phosphate nanoparticles was examined by X-ray diffractometry, field emission scanning electron microscopy, energy dispersive X-ray spectroscopy, Fourier transform infrared spectroscopy and nitrogen adsorption techniques. Based on the results, increase of synthesis temperature from 25 to 150. °C was associated with the gradual evolution of calcium-deficient apatite phase, however with a poor degree of crystallinity. The particle size and Ca/P molar ratio of precipitated calcium phosphate particles were also dependent of temperature so that they increased from 25 to 85. nm and 1.10 to 1.27 when the synthesis temperature increased from 25 to 150. °C. The synthesized particles were mesoporous regardless of the synthesis temperature. Given the advantages of DESs from both environmental and chemical points of view, the present study can provide a new direction for DES-assisted synthesis of inorganic nanomaterials and particularly nanobiomaterials.
The interfacial properties of deep eutectic solvents based on choline cloride plus urea, glycerol, or malonic acid in contact with gas phases composed by pure CO2, pure SO2, and a model flue gas, along with the liquid-vacuum interface, were studied using molecular dynamics simulations. The works provide insights on the mechanisms of acid gases capture at relevant interfaces and at atomistic level. The structural rearrangements on the molecules and ions composing the solvents at the solvent upon contact with the studied gas phases is studied together with the adsorption of gas molecules at the surface, the diffusion rates across the surface boundary, and the strength of intermolecular forces in the surface. This work provides a detailed analysis on the interfacial mechanism controlling acid gases captured by deep eutectic solvents.
The recrystallization of nitroguanidine from N-methyl pyrrolidone and N,N-dimethyl formamide using supercritical fluids and gases near their vapor pressures as anti-solvents was investigated. The nitroguanidine used for the recrystallization study consisted of high aspect ratio needles, 5 x 100 microns; because of its low bulk density the as-produced nitroguanidine is not satisfactorily incorporated into explosives formulations at high solids loading. Depending upon the specific combinations of parameters, the particle size and size distribution could be varied over a wide range, e.g., spherical particles of 100 microns diameter (the desired shape and size), low aspect ratio crystals, unusual star-shaped clusters, loose spherical agglomerates, or monodisperse particles of one micron or less. The results presented for nitroguanidine define a quite general recrystallization concept for processing difficult-to-comminute solids.
Sustainable technologies applied to energy related applications should develop a pivotal role along the next decades. In particular, carbon dioxide capture from flue gases emitted by fossil fuelled power plants would develop a pivotal role for controlling and reducing greenhouse effect. Therefore, the development of new materials for carbon capture purposes has merged as central research line for which many alternatives have been proposed. ILs have emerged as one of the most promising choices for carbon capture but in spite of their promising properties some serious drawbacks have also appeared. Deep eutectic solvents (DES) have been recently considered as alternatives to ILs that maintain most of their relevant properties, such as task-specific character, and at the same time avoid some of their problems, mainly from economic and environmental viewpoints. DES production from low cost and natural sources, together with their almost null toxicity and total biodegradability, makes these solvents as a suitable platform for developing gas separation agents within the green chemistry framework. Therefore, considering the promising characteristics of DES as CO2 absorbents, and in general as gas separating agents, the state-of-the-art on physicochemical properties of DES, in relationship with their influence on gas separation mechanisms, and on the studies of gas solubility in DES are discussed. The objective of this review work is to analyse the current knowledge on gas separation using DES, comparing the capturing abilities and properties of DES with those for ILs, inferring the weaknesses and strengths of DES and proposing future research directions on this subject.
In this study, we introduced choline-based deep eutectic solvents (such as choline chloride/glycerol at 1:2 molar ratio) as inexpensive, non-toxic, biodegradable and lipase-compatible solvents for the enzymatic preparation of biodiesel from soybean oil. Through the evaluation of different eutectic solvents and different lipases, as well as the study of reaction parameters (i.e. methanol concentration, Novozym 435 loading and reaction time), we were able to achieve up to 88% triglyceride conversions in 24 h. The enzyme could be reused for at least four times without losing much activity. Our results indicate that new benign eutectic solvents can be used as substitutes of toxic and volatile organic solvents in the enzymatic production of biodiesel from real triglycerides (such as soybean oil).
Choline-based ionic liquids show very adequate environmental, toxicological, and economical profiles for their application in many different technological areas. We report in this work a computational study on the properties of choline benzoate and choline salicylate ionic liquids, as representatives of this family of compounds, in the pure state and after CO(2) adsorption. Quantum chemistry calculations using the density functional theory approach for ionic pairs and ions, CO(2) pairs, were carried out, and the results analyzed using natural bond orbital and atoms in a molecule approaches. Classical molecular dynamics simulations of ionic liquids were done as a function of pressure, temperature, and CO(2) concentration. Microscopic structuring and intermolecular forces are analyzed together with the dynamic behavior of the studied fluids.