Molecular Dynamics Insights and Water Stability of Hydrophobic Deep Eutectic Solvents Aided Extraction of Nitenpyram from an Aqueous Environment

Valorization and protection of anthocyanins from strawberries (Fragaria×ananassa Duch.) by acidified natural deep eutectic solvent based on intermolecular interaction

This study introduces an innovative approach for the valorization and protection of anthocyanins from 'Benihoppe' strawberry (Fragaria × ananassa Duch.) based on acidified natural deep eutectic solvent (NADES). Choline chloride-citric acid (ChCl-CA, 1:1) was selected and acidified to enhance the valorization and protection of anthocyanins through hydrogen bond. The optimal conditions (ultrasonic power of 318 W, extraction temperature of 61 °C, liquid-to-solid ratio of 33 mL/g, ultrasonic time of 19 min), yielded the highest anthocyanins of 1428.34 μg CGE/g DW. UPLC-Triple-TOF/MS identified six anthocyanins in acidified ChCl-CA extract. Stability tests indicated that acidified ChCl-CA significantly increased storage stability of anthocyanins in high temperature and light treatments. Molecular dynamics results showed that acidified ChCl-CA system possessed a larger diffusion coefficient (0.05 m2/s), hydrogen bond number (145) and hydrogen bond lifetime (4.38 ps) with a reduced intermolecular interaction energy (-1329.74 kcal/mol), thereby efficiently valorizing and protecting anthocyanins from strawberries.

Menthol-Based (Deep) Eutectic Solvents: A Review on Properties and Application in Extraction

In the last 10 years the interest in deep eutectic solvents (DESs) as a new class of green solvents has considerably increased. The emergence of numerous of hydrophobic DESs has stimulated intensive research into their application in extraction technologies, including sample preparation. As the properties of such systems are highly dependent on the properties of their components (hydrogen bond donors and acceptors) and can be finely tuned, DESs can be successfully used for the extraction of both metal ions and organic substances, including biomolecules. Despite the rapidly increasing number of publications on the use of DESs as an extraction medium, including review articles, information on the extraction properties of DESs in terms of their chemical composition has not yet been summarized. This review covers available literature data on the physicochemical properties of menthol-based eutectic solvents and the results of their practical application as an extraction medium. Also, the appropriateness of using the term "DES" for all mixtures with melting points lower than the melting points of their components is discussed.

A comparative study of deep eutectic solvents based on fatty acids and the effect of water on their intermolecular interactions

In this work, intermolecular interactions among the species of fatty acids-based DESs with different hydrogen bond acceptors (HBA) in the adjacent water have been investigated using molecular dynamics (MD) simulation. The results of this work provide deep insights into understanding the water stability of the DESs based on thymol and the eutectic mixtures of choline chloride and fatty acids at a temperature of 353.15 K and atmospheric pressure. Stability, hydrogen bond occupancy analysis, and the distribution of the HBA and HBD around each other were attributed to the alkyl chain length of FAs and the type of HBA. Assessed structural properties include the combined distribution functions (CDFs), the radial distribution functions (RDFs), the angular distribution functions (ADFs), and the Hydrogen bonding network between species and Spatial distribution functions (SDF). The reported results show the remarkable role of the strength of the hydrogen bond between THY molecules and fatty acids on the stability of DES in water. The transport properties of molecules in water-eutectic mixtures were analyzed by using the mean square displacement (MSD) of the centers of mass of the species, self-diffusion coefficients, vector reorientation dynamics (VRD) of bonds and the velocity autocorrelation function (VACF) for the center of the mass of species.

Vortex-assisted dispersive liquid-liquid microextraction based on the hydrophobic deep eutectic solvent-based ferrofluid for extraction and detection of myclobutanil

A vortex-assisted dispersive liquid-liquid microextraction (VA-DLLME) procedure using hydrophobic deep eutectic solvent-based ferrofluid (HDES-FF) as an extractant was established. The developed sample preparation method coupled with high-performance liquid chromatography-diode array detector (HPLC-DAD) was applied to the pretreatment and determination of myclobutanil (MYC) in fruit juice. Hydrophobic deep eutectic solvent, synthesized by n-decanoic acid and DL-menthol, was as a carrier and combined with magnetic nanoparticles (Fe3O4@OA) to form HDES-FF as an extractant with high extraction capacity. The synthesized materials were characterized by Fourier transform infrared (FT-IR) spectroscopy, X-ray diffraction (XRD), and vibrating sample magnetometer (VSM). Parameters affecting extraction efficiency were optimized using single-factor experiments and Box-Behnken design via response surface methodology (BBD-RSM). Parallel tests were performed three times under the optimal conditions predicted by the model, yielding an actual mean recovery of 94.77% with RSD of 2.7% (n = 3) and an enrichment factor of 41.8 ± 0.98 (mean value ± SD, n = 3). Under the optimal conditions, the linear range was 1.0-100.0 µg·mL-1; the limit of detection (LOD) and limit of quantification (LOQ) were 0.25 and 0.80 µg·mL-1, respectively. The average spiked recoveries in the samples ranged from 98.2 to 100.5% with intra-day relative standard deviations (RSDs) of 1.2-3.5% (n = 3) and inter-day RSDs of 1.1-3.8% (n = 3). Finally, the method was successfully applied to the determination of MYC antimicrobial agent in different fruit juice samples. The proposed HDES-FF-VA-DLLME/HPLC-DAD method was verified to widely apply to the extraction of triazole fungicides.

Can deep eutectic solvents be the best alternatives to ionic liquids and organic solvents: A perspective in enzyme catalytic reactions

As a new generation of green solvents, deep eutectic solvents (DESs) have been considered as a promising alternative to classical organic solvents and ionic liquids (ILs). DESs are normally formed by two or more components via various h-bonds interactions. Up to date, four types of DESs are found, namely, type I DESs (formed by MClx, namely FeCl₂, AlCl₃, ZnCl₂, CuCl₂ and AgCl et al., and quaternary ammonium salts); type II DESs (formed by metal chloride hydrates and quaternary ammonium salts); type III DESs (formed by choline chlorides and different kinds of HBDs) and type IV DESs (formed by salts of transition metals and urea). DESs share many advantages, such as low vapor pressure, good substrate solubility and thermal stability, with ILs, and offering a high potential to be the medium of biocatalysis reactions. In this case, this paper reviews the applications of DESs in enzymatic reactions. Lipases are the most widely used enzyme in DESs systems as their versatile applications in various reactions and robustness. Interestingly, DESs can improve the efficiency of these reactions via enhancing the substrates solubility and the activity and stability of enzymes. Therefore, the directed engineering of DESs for special reactions such as degradation of polymers in high temperature or strong acid-base conditions will be one of the future perspectives of the investigation DESs.

An Overview of Structure and Dynamics Associated with Hydrophobic Deep Eutectic Solvents and Their Applications in Extraction Processes

Recent development of novel water-immiscible green solvents known as hydrophobic deep eutectic solvents (HDESs) has opened the gates for applications requiring media where presence of water is undesirable. Ever since they were prepared, researchers have used HDESs in diverse fields such as extraction processes, CO 2 sequestration, membrane formation, and catalysis. The microstructure and dynamics associated with the species comprising HDESs guide their suitability for specific applications. For example, varying the alkyl tail length of HDES components significantly affects the dynamics of the components and thus helps in tuning the efficiency of extraction processes. The development of HDESs is still in infancy and very few theoretical studies are available in the literature that help in understanding the structure and dynamics of HDESs. This review highlights the recent work focused on the microscopic structure and dynamics of HDESs and their potential applications, particularly in extraction processes. We have also provided a glimpse of how the integration of experiments and computational techniques can help understand the mechanism of extraction processes.

Improvement of solubility, stability and antioxidant activity of carotenoids using deep eutectic solvent-based microemulsions

Natural carotenoids have been widely used as colorants and antioxidants in process of food, medicine, and cosmetic. However, the carotenoids have low bioactivity in vivo due to poor water-solubility. To enhance the solubility, stability and antioxidant activity of carotenoids, novel microemulsions (MEs) composed with deep eutectic solvents (DESs), tween 80 and water were developed as alternatives to organic solvents. The phase diagrams and physicochemical properties (viscosity, pH, and diameter) of the DES-based MEs were investigated at different temperatures. Then the solubility distribution, storage stability and DPPH free radical-scavenging activity of three carotenoids (astaxanthin, astaxanthin ester and lutein) in the MEs were evaluated. Compared with ethanol, methanol, and acetone, all the DES-based MEs studied significantly enhanced the solubility of the carotenoids due to the stronger hydrogen bonding and Van der Waals interactions. The highest solubilities of 0.27, 473.63, and 12.50 mg/mL for astaxanthin, astaxanthin ester and lutein, respectively, were observed in the MEs containing DES (DL-menthol:acetic acid = 1:2) at 35 ℃. Moreover, astaxanthin ester can be well preserved in the MEs containing DES (DL-menthol:octanoic acid = 1:2) with a half-life of more than 69 days. In addition, the DPPH scavenging capacities of the three carotenoids in all the MEs were higher than the organic solvents. The results revealed that the DES-based MEs with low viscosity (<0.2 Pa•s) and mild acidic pH (4-5) are potential solvents for natural carotenoids in food processing and storage, medicine making, as well as biomaterials processing.

Effect of Water on a Hydrophobic Deep Eutectic Solvent

Deep eutectic solvents (DESs) formed by hydrogen bond donors and acceptors are a promising new class of solvents. Both hydrophilic and hydrophobic binary DESs readily absorb water, making them ternary mixtures, and a small water content is always inevitable under ambient conditions. We present a thorough study of a typical hydrophobic DES formed by a 1:2 mole ratio of tetrabutyl ammonium chloride and decanoic acid, focusing on the effects of a low water content caused by absorbed water vapor, using multinuclear NMR techniques, molecular modeling, and several other physicochemical techniques. Already very low water contents cause dynamic nanoscale phase segregation, reduce solvent viscosity and fragility, increase self-diffusion coefficients and conductivity, and enhance local dynamics. Water interferes with the hydrogen-bonding network between the chloride ions and carboxylic acid groups by solvating them, which enhances carboxylic acid self-correlation and ion pair formation between tetrabutyl ammonium and chloride. Simulations show that the component molar ratio can be varied, with an effect on the internal structure. The water-induced changes in the physical properties are beneficial for most prospective applications but water creates an acidic aqueous nanophase with a high halide ion concentration, which may have chemically adverse effects.

Computer Simulations of Deep Eutectic Solvents: Challenges, Solutions, and Perspectives

Deep eutectic solvents (DESs) are one of the most rapidly evolving types of solvents, appearing in a broad range of applications, such as nanotechnology, electrochemistry, biomass transformation, pharmaceuticals, membrane technology, biocomposite development, modern 3D-printing, and many others. The range of their applicability continues to expand, which demands the development of new DESs with improved properties. To do so requires an understanding of the fundamental relationship between the structure and properties of DESs. Computer simulation and machine learning techniques provide a fruitful approach as they can predict and reveal physical mechanisms and readily be linked to experiments. This review is devoted to the computational research of DESs and describes technical features of DES simulations and the corresponding perspectives on various DES applications. The aim is to demonstrate the current frontiers of computational research of DESs and discuss future perspectives.

Application of Extraction and Determination Based on Deep Eutectic Solvents in Different Types of Environmental Samples

Water sources are an indispensable resource for human survival. Monitoring the pollution status of the surrounding environment is necessary to protect water sources. Research on the environmental matrix of deep eutectic solvents (DESs) has expanded rapidly because of their high extraction efficiency for various target analytes, controllable synthesis, and versatile structure. Following the synthesis of hydrophobic deep eutectic solvents (HDESs), their application in aqueous matrices broadened greatly. The present review conducted a survey on the pollutant extraction methods based DESs in environmental matrices from two aspects, application methods and matrix types; discussed the potential risk of DESs to the environment and future development trends; and provided some references for researchers to choose DES-based extraction methods for environmental research.

Interfacial Properties of Hydrophobic Deep Eutectic Solvents with Water

Hydrophobic deep eutectic solvents (DESs) have recently gained much attention as water-immiscible solvents for a wide range of applications. However, very few studies exist in which the hydrophobicity of these DESs is quantified. In this work, the interfacial properties of hydrophobic DESs with water were computed at various temperatures using molecular dynamics simulations. The considered DESs were tetrabutylammonium chloride–decanoic acid (TBAC–dec) with a molar ratio of 1:2, thymol–decanoic acid (Thy–dec) with a molar ratio of 1:2, and dl-menthol–decanoic acid (Men–dec) with a molar ratio of 2:1. The following properties were investigated in detail: interfacial tensions, water-in-DES solubilities (and salt-in-water solubilities for TBAC–dec/water), density profiles, and the number densities of hydrogen bonds. Different ionic charge scaling factors were used for TBAC–dec. Thy–dec and Men–dec showed a high level of hydrophobicity with negligible computed water-in-DES solubilities. For charge scaling factors of 0.7 and 1 for the thymol and decanoic acid components of Thy–dec, the computed interfacial tensions of the DESs are in the following order: TBAC–dec (ca. 4 mN m^–1) < Thy–dec (20 mN m^–1) < Men–dec (26 mN m^–1). The two sets of charge scaling factors for Thy–dec did not lead to different density profiles but resulted in considerable differences in the DES/water interfacial tensions due to different numbers of decanoic acid–water hydrogen bonds at the interfaces. Large peaks were observed for the density profiles of (the hydroxyl oxygen of) decanoic acid at the interfaces of all DES/water mixtures, indicating a preferential alignment of the oxygen atoms of decanoic acid toward the aqueous phase.

Ultrasound-assisted dispersive liquid-phase microextraction by solidifying L-menthol-decanoic acid hydrophobic deep eutectic solvents for detection of five fungicides in fruit juices and tea drinks

An ecofriendly and efficient ultrasound-assisted deep eutectic solvents dispersive liquid-phase microextraction by solidifying the deep eutectic solvents-rich phase was developed to determine azoxystrobin, fludioxonil, epoxiconazole, cyprodinil, and prochloraz in fruit juices and tea drinks by high-performance liquid chromatography. A varieties of environmental hydrophobic deep eutectic solvents serving as extraction agents were prepared using L-menthol and decanoic acid as hydrogen-bond acceptor and hydrogen-bond donor, respectively. The deep eutectic solvents were ultrasonically dispersed in sample solutions, solidified in a freezer and easily harvested. The main variables were optimized by one-factor-at-a-time and response surface test. The new method performs well with relative recovery of 71.75-109.40%, linear range of 2.5-5000 μg/L (r ≥ 0.9968), detection limit of 0.75-8.45 μg/L, quantification limit of 2.5-25 μg/L,_, and inter- and intraday relative standard deviations below 13.53 and 14.84%, respectively. As for the extraction mechanism, deep eutectic solvents were disposed into many fine particles in the solution and captured the analytes based on the changes of particle size and quantity in deep eutectic solvents droplets after extraction. The environmental method can successfully detect fungicide residues in real fruit juices and tea drinks.

Multiple evidences of dynamic heterogeneity in hydrophobic deep eutectic solvents

Hydrophobic deep eutectic solvents (HDESs) have gained immense popularity because of their promising applications in extraction processes. Herein, we employ atomistic molecular dynamics simulations to unveil the dynamics of DL-menthol (DLM) based HDESs with hexanoic (C6), octanoic (C8), and decanoic (C10) acids as hydrogen bond donors. The particular focus is on understanding the nature of dynamics with changing acid tail length. For all three HDESs, two modes of hydrogen bond relaxations are observed. We observe longer hydrogen bond lifetimes of the inter-molecular hydrogen bonding interactions between the carbonyl oxygen of the acid and hydroxyl oxygen of menthol with hydroxyl hydrogen of both acids and menthol. We infer strong hydrogen bonding between them compared to that between hydroxyl oxygen of acids and hydroxyl hydrogens of menthol and acids, marked by a faster decay rate and shorter hydrogen bond lifetime. The translational dynamics of the species in the HDES becomes slower with increasing tail length of the organic acid. Slightly enhanced caging is also observed for the HDES with a longer tail length of the acids. The evidence of dynamic heterogeneity in the displacements of the component molecules is observed in all the HDESs. From the values of the α-relaxation time scale, we observe that the molecular displacements become random in a shorter time scale for DLM-C6. The analysis of the self-van Hove function reveals that the overall distance covered by DLM and acid molecules in the respective HDES is more than what is expected from ideal diffusion. As marked by the shorter time scale associated with hole filling, the diffusion of the oxygen atom of menthol and the carbonyl oxygen of acid from one site to the other is fastest for hexanoic acid containing HDES.

Thermodynamic, transport, and structural properties of hydrophobic deep eutectic solvents composed of tetraalkylammonium chloride and decanoic acid

With the emergence of hydrophobic deep eutectic solvents (DESs), the scope of applications of DESs has been expanded to include situations in which miscibility with water is undesirable. Whereas most studies have focused on the applications of hydrophobic DESs from a practical standpoint, few theoretical works exist that investigate the structural and thermodynamic properties at the nanoscale. In this study, Molecular Dynamics (MD) simulations have been performed to model DESs composed of tetraalkylammonium chloride hydrogen bond acceptor and decanoic acid hydrogen bond donor (HBD) at a molar ratio of 1:2, with three different cation chain lengths (4, 7, and 8). After fine-tuning force field parameters, densities, viscosities, self-diffusivities, and ionic conductivities of the DESs were computed over a wide temperature range. The liquid structure was examined using radial distribution functions (RDFs) and hydrogen bond analysis. The MD simulations reproduced the experimental density and viscosity data from the literature reasonably well and were used to predict diffusivities and ionic conductivities, for which experimental data are scarce or unavailable. It was found that although an increase in the cation chain length considerably affected the density and transport properties of the DESs (i.e., yielding smaller densities and slower dynamics), no significant influence was observed on the RDFs and the hydrogen bonds. The self-diffusivities showed the following order for the mobility of the various components: HBD > anion > cation. Strong hydrogen bonds between the hydroxyl and carbonyl groups of decanoic acid and between the hydroxyl group of decanoic acid and chloride were observed to dominate the intermolecular interactions.

Using coarse-grained molecular dynamics to understand the effect of ionic liquids on the aggregation of Pluronic copolymer solutions

This study is aimed to enhance the understanding of the interaction between ionic liquids (ILs) and non-ionic Pluronic triblock copolymers in aqueous two-phase micellar systems (ATPMS) used for the selective separation/purification of hydrophobic biomolecules. The ILs allow a precise control of the cloud point phase separation temperature (CPT), particularly important when the stability of the molecule is highly dependent on temperature. The effect of choline-based ILs, with two different counter-anions, chloride and hexanoate, was evaluated using molecular dynamics simulations (MD) for F-68 and L-35 Pluronic aqueous solutions. The simulations revealed the role played by the anions during the Pluronic self-assembly, with choline chloride hindering Pluronic aggregation and the choline hexanoate favouring micelle formation and coalescence, in agreement with the experimental data. A detailed study of the accessible surface area of Pluronic showed a progressive dehydration of the Pluronic hydrophilic micelle corona in choline hexanoate mixtures promoting inter-micelle interactions and, consequently, micelle coalescence. With the addition of choline hexanoate, it was observed that the hydrophilic segments, which form the micelle corona, twisted towards the Pluronic micelle core. The electrostatic interaction is also shown to play a key role in this IL-Pluronic aqueous solution, as the hexanoate anions are accommodated in the Pluronic micelle core, while the choline cations are hosted by the Pluronic micelle corona, with the ions interacting with each other during the self-assembly process. In addition, a comparison study of F-68 and L-35 aqueous solutions shows that the IL impact depends on the length of the Pluronic hydrophilic segment. This work provides a realistic microscopic scenario of the complex interactions between Pluronic copolymers and ILs.