Molecular dynamics study on water confinement in deep eutectic solvents

Enhanced oil recovery promoted by aqueous deep eutectic solvents on silica and calcite surfaces: a molecular dynamics study

Enhanced oil recovery (EOR) plays a critical role in optimizing oil extraction from existing fields to satisfy global energy demands while mitigating environmental impact. One promising EOR technique involves injecting water with reduced surface tension utilizing deep eutectic solvents (DESs). Despite early experimental support, the efficacy of aqueous-DES EOR varies and depends on factors such as connate water saturation, water salinity, and reservoir wettability. The recovery mechanisms for aqueous DESs are poorly understood due to the intricate nature of oil components and reservoir formation. In this paper, we investigate the role of DESs in the EOR process through molecular dynamics (MD) simulations. Three different types of DES molecules, such as choline chloride : urea (ChCl : U), choline chloride : ethylene glycol (ChCl : EG), and menthol : salicylic acid (M : SA) are used, for the recovery of dodecane (C12H26) oil from silica and calcite confined surfaces. We have demonstrated the structural characteristics of these systems by examining various physical properties, including interaction energies, density profiles, hydrogen bonds, and interfacial tension (IFT). Different concentrations (10 and 25 wt%) of DESs have been considered to unravel the effect of concentration on oil removal. The wettability of the substrate and the IFT between oil and aqueous DESs are critical physical properties that play a crucial role in influencing EOR phenomena. The IFT between water and oil decreases with the addition of DESs for all DES molecules, leading to a shift in surface behavior from oleophilic to oleophobic and ultimately facilitating the removal of oil from the substrate. Additionally, hydrogen bond formation between DESs and water has been calculated to elucidate its influence on the water/oil interface and substrate wettability. The study provides insights into the fundamental aspects of EOR processes for more effective and sustainable oil extraction.

Based on theoretical design simultaneous analysis of multiple neonicotinoid pesticides in beeswax by deep eutectic solvents extraction combined with UHPLC-MS/MS

Beeswax, an FDA-approved component, has been extensively applied in feed, pharmaceutical, and food industries. The occurrence of neonicotinoid pesticides in beehive systems and their residues in beeswax have caused safety risks. Therefore, establishing a detection method for neonicotinoid pesticide residues in beeswax is crucial for ensuring its quality. The superhydrophobic property of beeswax makes it a challenge to develop suitable determination methods. In this work, we determined Proline and Oxalic acid as a suitable deep eutectic solvent (DES) to extract neonicotinoids from beeswax through theoretical design and verification tests. Systematic molecular dynamics simulations confirmed that hydrogen bonding and van der Waals forces facilitate the migration of neonicotinoid pesticides from beeswax into the DES. Performance analysis of the method revealed that the DES extraction combined with UHPLC-MS/MS approach exhibited excellent detection capabilities. It was applied to real beeswax sample analysis with the characteristics of simpleness, quickness, environmental friendliness, and high throughput.

Peculiar Effect of Water on Tribological Properties of Natural Deep Eutectic Solvent

Deep eutectic solvents (DESs) have emerged as promising green liquid lubricants for solving tribological problems due to their economic and excellent physicochemical and lubrication properties. However, a trace amount of water would affect their structure, physicochemical properties, and tribological properties. The effect of water on the tribological properties of DES is still unclear and needs further investigate. Herein, we carried out a systematic investigation into the chemical structure, rheological properties, and tribological performance of DES-water (DES-W) binary systems constructed by combining DES with varying contents of water. The results revealed that low levels of water in DES had a minimal impact on its chemical structure but affected its fluidity and viscosity. Frictional experiments demonstrated that DES-W binary systems displayed a reduced coefficient of friction from 0.094 to 0.025 compared to pure DESs and manifested outstanding antiwear properties under a high-load condition. This was attributed to the formation of hydration layers, adsorption layers, and tribochemical films at the tribointerface through physicochemical adsorption and tribochemical reactions. Our findings not only foster the design and development of green lubricating materials but also expand the engineering applications of DESs to solve wear-related mechanical failures in practical application.

Rational design of deep eutectic solvents for the stabilization of dehydrogenases: an artificial neural network prediction approach

Stabilized enzymes are crucial for the industrial application of biocatalysis due to their enhanced operational stability, which leads to prolonged enzyme activity, cost-efficiency and consequently scalability of biocatalytic processes. Over the past decade, numerous studies have demonstrated that deep eutectic solvents (DES) are excellent enzyme stabilizers. However, the search for an optimal DES has primarily relied on trial-and-error methods, lacking systematic exploration of DES structure-activity relationships. Therefore, this study aims to rationally design DES to stabilize various dehydrogenases through extensive experimental screening, followed by the development of a straightforward and reliable mathematical model to predict the efficacy of DES in enzyme stabilization. A total of 28 DES were tested for their ability to stabilize three dehydrogenases at 30°C: (S)-alcohol dehydrogenase from Rhodococcus ruber (ADH-A), (R)-alcohol dehydrogenase from Lactobacillus kefir (Lk-ADH) and glucose dehydrogenase from Bacillus megaterium (GDH). The residual activity of these enzymes in the presence of DES was quantified using first-order kinetic models. The screening revealed that DES based on polyols serve as promising stabilizing environments for the three tested dehydrogenases, particularly for the enzymes Lk-ADH and GDH, which are intrinsically unstable in aqueous environments. In glycerol-based DES, increases in enzyme half-life of up to 175-fold for Lk-ADH and 60-fold for GDH were observed compared to reference buffers. Furthermore, to establish the relationship between the enzyme inactivation rate constants and DES descriptors generated by the Conductor-like Screening Model for Real Solvents, artificial neural network models were developed. The models for ADH-A and GDH showed high efficiency and reliability (R2 > 0.75) for in silico screening of the enzyme inactivation rate constants based on DES descriptors. In conclusion, these results highlight the significant potential of the integrated experimental and in silico approach for the rational design of DES tailored to stabilize enzymes.

Bulk nanostructure of a deep eutectic solvent with an amphiphilic hydrogen bond donor

Neutron diffraction with empirical potential structure refinement (EPSR) show the deep eutectic solvent (DES) 1 : 4 choline chloride : butyric acid is amphiphilically nanostructured. Nanostructure results from solvophobic interactions between the alkyl chains of the butyric acid hydrogen bond donor (HBD) and is retained with addition of 10 wt% water. EPSR fits to the diffraction data is used to produce a three-dimensional model of the liquid which is interrogated to reveal the interactions leading to the solvophobic effect, and therefore nanostructure, in this DES at atomic resolution. The model shows electrostatic and hydrogen bond interactions cause the cation, anion and HBD acid group to cluster into a polar domain, from which the acid alkyl chains are solvophobically excluded into theapolar domain. The polar and apolar domains percolate through the liquid in a bicontinuous sponge-like structure. The effect of adding 10 wt% water is probed, revealing that water molecules are sequestered around the cation and anion within the polar domain, while the neat bulk structure is retained. Alkyl chain packing in the apolar domain becomes slightly better-defined indicating water marginally strengthens solvophobic segregation. These findings reveal bulk self-assembled nanostructure can be produced in DESs via an amphiphilic HBD.

Laccase-catalyzed lignin depolymerization in deep eutectic solvents: challenges and prospects

Lignin has enormous potential as a renewable feedstock for depolymerizing to numerous high-value chemicals. However, lignin depolymerization is challenging owing to its recalcitrant, heterogenous, and limited water-soluble nature. From the standpoint of environmental friendliness and sustainability, enzymatic depolymerization of lignin is of great significance. Notably, laccases play an essential role in the enzymatic depolymerization of lignin and are considered the ultimate green catalysts. Deep eutectic solvent (DES), an efficient media in biocatalysis, are increasingly recognized as the newest and utmost green solvent that highly dissolves lignin. This review centers on a lignin depolymerization strategy by harnessing the good lignin fractionating capability of DES and the high substrate and product selectivity of laccase. Recent progress and insights into the laccase-DES interactions, protein engineering strategies for improving DES compatibility with laccase, and controlling the product selectivity of lignin degradation by laccase or in DES systems are extensively provided. Lastly, the challenges and prospects of the alliance between DES and laccase for lignin depolymerization are discussed. The collaboration of laccase and DES provides a great opportunity to develop an enzymatic route for lignin depolymerization.

A feasibility study on the use of hydrophobic eutectic solvents as pseudo-stationary phases in capillary electrophoresis for chiral separations

A critical challenge in using deep eutectic solvents (DESs) in capillary electrophoresis (CE) is to develop separation systems in which a DES can really work as a single entity. To achieve this, the authors recently demonstrated a novel strategy that takes advantage of the aqueous dispersibility of hydrophobic DESs (or more accurately hydrophobic eutectic solvents (HESs)). However, the previous work was limited only to the separation of achiral analytes, e.g., analogues, homologues, and isomers. The present study was designed as a follow-up study in order to explore the feasibility of employing HES-type pseudo-stationary phases (PSPs) in CE for chiral separations. By using carboxymethyl-β-cyclodextrin (CM-β-CD) as a model chiral selector, we provide the first evidence that there is a potential synergistic effect between HESs and traditional chiral selectors. Specifically, the combined use of HES (-)-menthol:octanoic acid and CM-β-CD allowed excellent enantioseparations of several basic drugs which were not able to be resolved in the single CM-β-CD system. The enantioresolutions were significantly improved while the migration times of the enantiomers were also shortened due to the hydrophobic mechanism of the HES-type PSP. Critical factors influencing the novel chiral CE system were systematically investigated. Since HESs are considered as "designer" solvents with highly tunable properties, this study demonstrates the potential of employing HESs (or HDES)-type PSPs in CE for chiral separations.

Preparation mechanism and performance evaluation of deep eutectic solvent-lignin/ZnO composites by one-pot

Lignin, as the aromatic polymer in the world, has attracted more attention because of rich functional groups. In this study, lignin/ZnO composites was prepared by a simple one-pot method rely on urea and ZnCl₂-deep eutectic solvent (U/ZnCl₂-DES) as solvent and raw material. Through molecular dynamics simulation, the interaction mechanism between lignin functional groups and DES was clarified, and it was blended with waterborne polyurethane (WPU) to form a film, while the feasibility of its application in ultraviolet shielding was evaluated. The results showed that lignin /ZnO composites with excellent ultraviolet shielding properties were successfully prepared. Compared with lignosulfonate (SL), enzymatic hydrolysis lignin (EHL) was easier to combine with ZnO, which was benefit to prepare lignin/ZnO composites. When the addition of EHL/ZnO-N_12.5 complex was 1.5 %, the WPU film prepared has good mechanical properties (elongation at break was 25.53 %, tensile strength was 1422 kPa), good light transmission and ultraviolet shielding.

Mechanism study of ternary deep eutectic solvents with protonic acid for lignin fractionation

This paper investigated the fractionation of lignin by ternary DES of different polyols using simulation calculation. ChCl-EG-PTSA showed the highest degradability of lignin with the absolute value of total interaction energy of -8023.80 kJ/mol, and the total number of hydrogen bonds was 91.4. The highest degradability was observed for ChCl:EG: PTSA = 2:4:1. The results show that CL^- plays a dominant role in lignin fractionation and readily forms hydrogen bonds with γ-OH. The difference is that the polyol preferred to form hydrogen bonds with α-OH in lignin. The addition of PTSA provided protons to the original system. It formed a new π-π stacking interaction with the lignin benzene ring, which destroyed the π-π stacking interaction between the original lignin. And increased the interaction of DES on lignin from -39.73 kcal/mol to -58.15 kcal/mol based on DFT.

Molecular Dynamic Insights into the Distinct Solvation Structures of Aromatic and Aliphatic Compounds in Monoethanolamine-Based Deep Eutectic Solvents

Deep eutectic solvents (DESs) are developing as an alternate medium for aromatic extraction, especially benzene and thiophene from aliphatic hydrocarbon mixtures. In this work, molecular dynamics (MD) simulations were first used to investigate the solvation structure of benzene, thiophene, and n-hexane in monoethanolamine-based DESs. It reveals the liquid structures in the adjacent neighbor shells, which is a function of electron-withdrawing sulfur attached to thiophene and the π-electron cloud of benzene. The intermolecular forces between aromatic, aliphatic, and DES components are analyzed in van der Waals and hydrogen bond interactions. The chloride ions serve as a charge carrier bridge between choline and monoethanolamine precursors. The solvation of benzene, thiophene, and n-hexane in the DESs depends on volume expansion and minor solvent structural changes. Density functional theory results provided information on the mechanism of short-range interactions between organic solutes and studied DES. It aids in understanding the structural orientations of a DES with the addition of solutes, essential to the formation of DES. The solvation shell structure and characteristics were investigated in tandem with the possibility of benzene and thiophene clustering. The ¹H NMR and 2D ¹H-¹H-NOESY were used to investigate the intermolecular interactions between benzene, thiophene, and n-hexane with monoethanolamine-based solvents. It concludes that high-ordered DES1 is more inclined to higher solubility than lower-ordered ones with a higher molar ratio of monoethanolamine. The solvation was reduced because the entropy gain was not maximized in the lower ordered DESs.

Deep eutectic solvents: Recent advances in fabrication approaches and pharmaceutical applications

Deep eutectic solvents (DESs) have received increasing attention in the past decade owing to their distinguished properties including biocompatibility, tunability, thermal and chemical stability. Particularly, DESs have joined forces in pharmaceutical industry, not only to efficiently separate actives from natural products, but also to dramatically increase solubility and permeability of drugs, both are critical for the drug absorption and efficacy. As a result, lately DESs have been extensively and practically adopted as versatile drug delivery systems for different routes such as nasal, transdermal and oral administration with enhanced bioavailability. This review summarizes the emerging progress of DESs by introducing applied fabrication approaches with advantages and limitations thereof, and by highlighting the pharmaceutical applications of DESs.