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Special Issue "Deep Eutectic Solvents: Linking Fundamental Properties to Final Applications"

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A special issue of Molecules (ISSN 1420-3049). This special issue belongs to the section "Green Chemistry".

Deadline for manuscript submissions: closed (31 December 2022) | Viewed by 8691

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Dr. Mónia A. R. Martins

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Guest Editor

CICECO—Aveiro Institute of Materials, Department of Chemistry, University of Aveiro, 3810-193 Aveiro, Portugal
Interests: thermodynamics; physicochemical properties; phase equilibria; alternative solvents; terpenes; ionic liquids; deep eutectic solvents; eutectic mixtures; pharmaceuticals

Dr. Nicolas Schaeffer

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Guest Editor

CICECO—Aveiro Institute of Materials, Department of Chemistry, University of Aveiro, 3810-193 Aveiro, Portugal
Interests: hydrometallurgy; alternative solvents; critical metals; recycling; solvent extraction
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Special Issue Information

Dear Colleagues,

Since 2003, research on eutectic mixtures, commonly known as deep eutectic solvents or DES, has grown exponentially. These neoteric and cost-effective solvents are characterized by interesting physicochemical properties and a promising green character, which grants them potential for a wide range of applications including, but not limited to, extraction and separation, biotechnology, electrochemistry, cosmetics, and pharmaceuticals. Naturally, the properties of a given DES depend on the starting materials used that will ultimately determine its final end usage and suitability. Research on DES applications followed by the fundamental understanding of their nature is essential for the efficient design and selection of the best DES for a given application.

This Special Issue focuses on innovative research regarding the link between the description of fundamental DES properties and the impact on their applications. The scope of this Special Issue encompasses the use of eutectic mixtures as solvents in alternative or breakthrough applications in different fields and fundamental properties, namely the description of liquid phase interactions across various size scales and phase equilibria. Both experimental and computational studies are welcome as well as critical analyses of existing and future bottlenecks facing the large-scale application of DES.

With the aim of creating an invaluable resource of knowledge on DES, we warmly invite our colleagues to participate in this Special Issue with both experimental and theoretical contributions toward expanding our knowledge in this emerging and exciting area.

Dr. Mónia A. R. Martins
Dr. Nicolas Schaeffer
Guest Editors

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Keywords

deep eutectic solvents
eutectic systems
sustainability
thermodynamics and phase equilibria
simulations
extraction and separation
drug delivery
bioengineering and biotechnology
cosmetics
electrochemistry

Published Papers (5 papers)

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Research

Open AccessArticle

Enhanced Recovery of Natural Antioxidants from Grape Waste Using Natural Eutectic Solvents-Based Microwave-Assisted Extraction

Raquel Cañadas

Blanca Sáenz de Miera

Paloma Méndez

Emilio J. González

and

María González-Miquel

Molecules 2023, 28(3), 1153; https://doi.org/10.3390/molecules28031153 - 24 Jan 2023

Cited by 1 | Viewed by 1091

Abstract

The evaluation of sustainable solvents as alternatives to more harmful conventional solvents combined with intensification techniques to recover phenolic compounds from agri-food waste is in the spotlight. The wine industry generates large amounts of waste as a consequence of grape processing operations, which can be revalued by solvent extraction of valuable antioxidants for food and fine chemical applications. Therefore, the present study focuses on the use of natural eutectic solvents (NAESs) with benign environmental, health, and safety profiles, for valorization of grape waste in the context of a circular economy. Herein, up to 15 NAESs consisting of combinations of three hydrogen bond acceptors (choline chloride, L-proline, and betaine) and four hydrogen bond donors (1,2-propanediol, glycerol, and 1,2- and 1,3-butanediol) were evaluated for antioxidant recovery. After an initial screening of the performance of NAESs by conventional extraction, the process was intensified by microwave-assisted extraction (MAE). The extracts were analyzed by UV/VIS spectrophotometric and HPLC methods. Promising results were obtained with the solvent betaine, 1,2-butanediol [1:4], using MAE at 100 °C for 3 min. Overall, the proposed NAESs-based MAE method was successfully applied to recover target compounds from grape waste, with great prospects for the antioxidants market and sustainable development for the winery sector. Full article

(This article belongs to the Special Issue Deep Eutectic Solvents: Linking Fundamental Properties to Final Applications)

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Open AccessArticle

Predicting the Surface Tension of Deep Eutectic Solvents: A Step Forward in the Use of Greener Solvents

Amit Kumar Halder

Reza Haghbakhsh

Iuliia V. Voroshylova

Ana Rita C. Duarte

and

Maria Natalia D. S. Cordeiro

Molecules 2022, 27(15), 4896; https://doi.org/10.3390/molecules27154896 - 31 Jul 2022

Cited by 3 | Viewed by 1149

Abstract

Deep eutectic solvents (DES) are an important class of green solvents that have been developed as an alternative to toxic solvents. However, the large-scale industrial application of DESs requires fine-tuning their physicochemical properties. Among others, surface tension is one of such properties that have to be considered while designing novel DESs. In this work, we present the results of a detailed evaluation of Quantitative Structure-Property Relationships (QSPR) modeling efforts designed to predict the surface tension of DESs, following the Organization for Economic Co-operation and Development (OECD) guidelines. The data set used comprises a large number of structurally diverse binary DESs and the models were built systematically through rigorous validation methods, including ‘mixtures-out’- and ‘compounds-out’-based data splitting. The most predictive individual QSPR model found is shown to be statistically robust, besides providing valuable information about the structural and physicochemical features responsible for the surface tension of DESs. Furthermore, the intelligent consensus prediction strategy applied to multiple predictive models led to consensus models with similar statistical robustness to the individual QSPR model. The benefits of the present work stand out also from its reproducibility since it relies on fully specified computational procedures and on publicly available tools. Finally, our results not only guide the future design and screening of novel DESs with a desirable surface tension but also lays out strategies for efficiently setting up silico-based models for binary mixtures. Full article

(This article belongs to the Special Issue Deep Eutectic Solvents: Linking Fundamental Properties to Final Applications)

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Open AccessArticle

Liquefying Flavonoids with Terpenoids through Deep Eutectic Solvent Formation

Ana I. M. C. L. Ferreira

Luís M. N. B. F. Santos

Olga Ferreira

and

João A. P. Coutinho

Molecules 2022, 27(9), 2649; https://doi.org/10.3390/molecules27092649 - 20 Apr 2022

Cited by 6 | Viewed by 2181

Abstract

The formation of deep eutectic solvents (DES) is tied to negative deviations to ideality caused by the establishment of stronger interactions in the mixture than in the pure DES precursors. This work tested thymol and menthol as hydrogen bond donors when combined with different flavonoids. Negative deviations from ideality were observed upon mixing thymol with either flavone or flavanone, two parent flavonoids that only have hydrogen bond acceptor (HBA) groups, thus forming non-ionic DES (Type V). On the other hand, the menthol systems with the same compounds generally showed positive deviations from ideality. That was also the case with the mixtures containing the more complex hydroxylated flavonoid, hesperetin, which resulted in positive deviations when mixed with either thymol or menthol. COSMO-RS successfully predicted the behavior of the solid-liquid phase diagram of the studied systems, allowing for evaluation of the impact of the different contributions to the intermolecular interactions, and proving to be a good tool for the design of DES. Full article

(This article belongs to the Special Issue Deep Eutectic Solvents: Linking Fundamental Properties to Final Applications)

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Open AccessArticle

Efficient Extraction of Fermentation Inhibitors by Means of Green Hydrophobic Deep Eutectic Solvents

Patrycja Makoś-Chełstowska

and

Molecules 2022, 27(1), 157; https://doi.org/10.3390/molecules27010157 - 28 Dec 2021

Cited by 5 | Viewed by 1631

Abstract

The methods for hydrogen yield efficiency improvements, the gaseous stream purification in gaseous biofuels generation, and the biomass pretreatment are considered as the main trends in research devoted to gaseous biofuel production. The environmental aspect related to the liquid stream purification arises. Moreover, the management of post-fermentation broth with the application of various biorefining techniques gains importance. Chemical compounds occurring in the exhausted liquid phase after biomass pretreatment and subsequent dark and photo fermentation processes are considered as value-added by products. The most valuable are furfural (FF), 5-hydroxymethylfurfural (HMF), and levulinic acid (LA). Enriching their solutions can be carried with the application of liquid–liquid extraction with the use of a suitable solvent. In these studies, hydrophobic deep eutectic solvents (DESs) were tested as extractants. The screening of 56 DESs was carried out using the Conductor-like Screening Model for Real Solvents (COSMO-RS). DESs which exposed the highest inhibitory effect on fermentation and negligible water solubility were prepared. The LA, FF, and HMF were analyzed using FT-IR and NMR spectroscopy. In addition, the basic physicochemical properties of DES were carefully studied. In the second part of the paper, deep eutectic solvents were used for the extraction of FF, LA, and HMF from post-fermentation broth (PFB). The main extraction parameters, i.e., temperature, pH, and DES: PFB volume ratio (V_DES:V_PFB), were optimized by means of a Box–Behnken design model. Two approaches have been proposed for extraction process. In the first approach, DES was used as a solvent. In the second, one of the DES components was added to the sample, and DES was generated in situ. To enhance the post-fermentation broth management, optimization of the parameters promoting HMF, FF, and LA extraction was carried under real conditions. Moreover, the antimicrobial effect of the extraction of FF, HMF, and LA was investigated to define the possibility of simultaneous separation of microbial parts and denatured peptides via precipitation. Full article

(This article belongs to the Special Issue Deep Eutectic Solvents: Linking Fundamental Properties to Final Applications)

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Open AccessArticle

Enhanced Furfural Production in Deep Eutectic Solvents Comprising Alkali Metal Halides as Additives

Eduarda S. Morais

Mara G. Freire

Carmen S. R. Freire

and

Armando J. D. Silvestre

Molecules 2021, 26(23), 7374; https://doi.org/10.3390/molecules26237374 - 04 Dec 2021

Cited by 5 | Viewed by 1925

Abstract

The addition of alkali metal halide salts to acidic deep eutectic solvents is here reported as an effective way of boosting xylan conversion into furfural. These salts promote an increase in xylose dehydration due to the cation and anion interactions with the solvent being a promising alternative to the use of harsh operational conditions. Several alkali metal halides were used as additives in the DES composed of cholinium chloride and malic acid ([Ch]Cl:Mal) in a molar ratio of 1:3, with 5 wt.% of water. These mixtures were then used as both solvent and catalyst to produce furfural directly from xylan through microwave-assisted reactions. Preliminary assays were carried out at 150 and 130 °C to gauge the effect of the different salts in furfural yields. A Response Surface Methodology was then applied to optimize the operational conditions. After an optimization of the different operating conditions, a maximum furfural yield of 89.46 ± 0.33% was achieved using 8.19% of lithium bromide in [Ch]Cl:Mal, 1:3; 5 wt.% water, at 157.3 °C and 1.74 min of reaction time. The used deep eutectic solvent and salt were recovered and reused three times, with 79.7% yield in the third cycle, and the furfural and solvent integrity confirmed. Full article

(This article belongs to the Special Issue Deep Eutectic Solvents: Linking Fundamental Properties to Final Applications)

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