Role of the hydrogen bond donor component for a proper development of novel hydrophobic deep eutectic solvents

Star anise (Illicium verum Hook. F.) polysaccharides: Potential therapeutic management for obesity, hypertension, and diabetes

This study explores the extraction of polysaccharides from star anise (Illicium verum Hook. f.) with its anti-obesity, antihypertensive, antidiabetic, and antioxidant properties. The aim is to optimize the extraction conditions of star anise polysaccharides (SAP) utilizing propane alcohols-based deep eutectic solvents and microwave-assisted methods. The optimized conditions resulted in an extraction yield of 5.14%. The characteristics of acidic pectin-like SAP, including high viscosity (44.86 mPa s), high oil-holding capacity (14.39%), a high degree of esterification (72.53%), gel-like properties, highly amorphous, a high galacturonic acid concentration, and a highly branching size polysaccharide structure, significantly contribute to their potent inhibition of pancreatic lipase (86.67%), angiotensin-converting enzyme (73.47%), and α-glucosidase (82.33%) activities as well as to their antioxidant properties of azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) diammonium salt (ABTS, 34.94%) and ferric ion reducing antioxidant power (FRAP, 0.56 mM FeSO4). Therefore, SAP could be used as a potential therapeutic agent for obesity, hypertension, and diabetes mellitus management.

Interfacial Nanostructure and Hydrogen Bond Networks of Choline Chloride and Glycerol Mixtures Probed with X-ray and Vibrational Spectroscopies

The molecular distribution at the liquid-vapor interface and evolution of the hydrogen bond interactions in mixtures of glycerol and choline chloride are investigated using X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy. Nanoscale depth profiles of supersaturated deep eutectic solvent (DES) mixtures up to ∼2 nm measured by ambient-pressure XPS show the enhancement of choline cation (Ch+) concentration by a factor of 2 at the liquid-vapor interface compared to the bulk. In addition, Raman spectral analysis of a wide range of DES mixtures reveals the conversion of gauche-conformer Ch+ into the anti-conformer in relatively lower ChCl concentrations. Finally, the depletion of Ch+ from the interface (probing depth = 0.4 nm) is demonstrated by aerosol-based velocity map imaging XPS measurements of glyceline and water mixtures. The nanostructure of liquid-vapor interfaces and structural rearrangement by hydration can provide critical insight into the molecular origin of the deep eutectic behavior and gas-capturing application of DESs.

Toxicity test profile for deep eutectic solvents: A detailed review and future prospects

Deep eutectic solvents (DESs) are preferable in terms of starting materials, storage and synthesis, simplicity, and component material affordability. In several industries ranging from chemical, electrochemical, biological, biotechnology, material science, etc., DES has demonstrated remarkable potential. Despite all these accomplishments, the safety issue with DES must be adequately addressed. Different DES interacts with the cellular membranes differently. It is not possible to classify all DES as easily biodegradable. By expanding the current understanding of the toxicity and biodegradation of DES, interactions between organisms and cellular membranes can be linked. The DES toxicity profile varies according to their concentration, the nature of the individual components, and how they interact with living things. Therefore, the results of this review can serve as a baseline for DES development in the future.

Recyclable water-modified deep eutectic solvents for removal of multiple heavy metals from soil

Removing heavy metals from soil has always been a challenge in terms of safety and effectiveness. Deep eutectic solvents (DESs) are recognized as environmentally friendly reagents with great potential in the removal of heavy metals from soil. In this study, water was introduced as a third component to form new ternary deep eutectic water solvents (DEWSs) to improve their performance. The removal capacity, applicable conditions and mechanisms of sixteen DEWSs for heavy metals were systematically investigated. Experimental results showed that the presence of water significantly enhanced the removal efficiency of three DESs (Choline chloride plus Urea, DEU; Choline chloride plus l-lactic acid, DELA; and Choline chloride plus Ethylene glycol, DEEG) for heavy metals. However, as the molar ratio of water increased, the eutectic systems in the DEWSs weakened and eventually disappeared. Under optimum conditions, DEWLA7 (DELA : H2O = 2 : 8) showed the highest removal rate for cadmium, lead, copper and zinc, which were 43.42%, 94.73%, 90.72% and 96.44%, respectively. Hydrogen bonding, adsorption of oxygen functional groups, exchangeable hydrogen substitution, changes in viscosity properties and co-precipitation all contributed to the removal of heavy metals by DEWLA7. Notably, DEWLA7 had no significant effect on the content of major minerals and nutrients in the soil. Furthermore, DEWLA7 proved to be reusable for soil washing, and still retains a high removal rate of 37.32%-83.66% after multi-stage filtration treatment. Therefore, DEWLA7 was an unexplored and excellent soil washing agent with great potential in economic and social benefits.

Sustainable recovery of phenolic antioxidants from real olive vegetation water with natural hydrophobic eutectic solvents and terpenoids

Olive oil production leads to the generation of olive mill wastewater (OMWW). Due to the presence of phenolic compounds, they are difficult to process, but they represent a source of high-added value chemicals since they have antioxidant and therapeutic properties. This work has studied the extraction of phenolic compounds from a type of OMWW, olive vegetation water, which presents these compounds in a more diluted dosage than in other studied to date, to revalue this waste stream. A real olive vegetation water from a Spanish olive oil producer was used, and liquid-liquid extraction was applied. Terpenoids and terpene-based hydrophobic eutectic solvents were systematically used to extract phenolic compounds following the concentrations of tyrosol, catechol, caffeic acid, and total phenolic content. By molecular simulation with the COSMO-RS method, 4 terpenoids, and 2 eutectic solvents were selected and compared with 2 conventional solvents. The Solvent/Feed ratio in the extraction of phenolic compounds was studied, showing that the solvents with the highest extraction results were geraniol, eucalyptol, and eutectic solvent menthol + camphor, which outperformed conventional solvents methyl isobutyl ketone and diisopropyl ether. Menthol + camphor gave total phenol extraction yields of 88.73% at a Solvent/Feed ratio in volume of 0.50, surpassing all solvents tested. A solvent reuse and regeneration process was applied by back-extraction of the 4 solvents: FTIR results showed the stability of the solvents while maintaining yields in the solvent reuse process. The phenolic compounds could be concentrated in the alkaline phase to factors up to 49.3 to the initial concentration in olive vegetation water. The alkaline phases were neutralized to obtain a precipitate with a caffeic acid content of up to 26 % wt%, and a tyrosol-rich supernatant with a concentration of up to 6.54 g/L. This work proposes a process using natural solvents to extract phenolic compounds from olive vegetation water.

Sustainable solutions for removing aged wax-based coatings from cultural heritage: exploiting hydrophobic deep eutectic solvents (DESs)

Hydrophobic deep eutectic solvents as suitable alternatives to toxic solvents used in the conservation of Cultural Heritage sector.

Liquefying Flavonoids with Terpenoids through Deep Eutectic Solvent Formation

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.

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.

Effective and Selective Extraction of Quercetin from Onion (Allium cepa L.) Skin Waste Using Water Dilutions of Acid-Based Deep Eutectic Solvents

Deep Eutectic Solvents (DESs) are experiencing growing interest as substitutes of polluting organic solvents for their low or absent toxicity and volatility. Moreover, they can be formed with natural bioavailable and biodegradable molecules; they are synthesized in absence of hazardous solvents. DESs are, inter alia, successfully used for the extraction/preconcentration of biofunctional molecules from complex vegetal matrices. Onion skin is a highly abundant waste material which represents a reservoir of molecules endowed with valuable biological properties such as quercetin and its glycosylated forms. An efficient extraction of these molecules from dry onion skin from "Dorata di Parma" cultivar was obtained with water dilution of acid-based DESs. Glycolic acid (with betaine 2/1 molar ratio and L-Proline 3/1 molar ratio as counterparts) and of p-toluensulphonic acid (with benzyltrimethylammonium methanesulfonate 1/1 molar ratio)-based DESs exhibited more than 3-fold higher extraction efficiency than methanol (14.79 µg/mL, 18.56 µg/mL, 14.83 µg/mL vs. 5.84 µg/mL, respectively). The extracted quercetin was also recovered efficaciously (81% of recovery) from the original extraction mixture. The proposed extraction protocol revealed to be green, efficacious and selective for the extraction of quercetin from onion skin and it could be useful for the development of other extraction procedures from other biological matrixes.

The evaluation of phenolic content, in vitro antioxidant and antibacterial activity of Mentha piperita extracts obtained by natural deep eutectic solvents

The focus of this study was to evaluate whether six choline chloride-based natural deep eutectic solvents (NADES) could serve as solvents for the extraction of bioactives from the leaves of Mentha piperita. NADES extracted significantly higher amounts of phenols from peppermint than 70% ethanol and may be useful in the extraction of targeted major compounds from peppermint, like rosmarinic acid, at a similar level as 70% ethanol. The microdilution method for in vitro antibacterial activity showed that all NADES exhibit bacterial growth inhibition at a lower concentration than 70% ethanol, especially NADESs containing organic acids. The majority of NADES extracts neutralize DPPH radical at a lower concentration than conventional solvent and showed similar ability to reduce Fe³⁺ to Fe²⁺ ions in FRAP assay. NADES can be useful in the isolation of phenolic compounds from plant sources and should be considered as novel, sustainable, and low-cost solvents with a variety of applications.

Review on Extraction of Phenolic Compounds from Natural Sources Using Green Deep Eutectic Solvents

For more sustainable and environmentally friendly scientific research, it is essential to apply green chemistry principles in all areas of science. A possible area in which green chemistry principles can significantly influence the productivity and the quality of the outcome is extraction of natural products. The conventional toxic solvents can be replaced by environmentally friendly solvents known as deep eutectic solvents, which fortunately, due to their unique properties, can significantly improve extraction efficiency. In this literature review, the extraction of a specific class of natural products, phenolic compounds, using different types of green deep eutectic solvents has been reviewed. Within this review, the composition of those solvents used to extract different types of phenolic compounds has been discussed. In addition, the factors affecting their extraction, extracting solvent component structure, molar ratio of extracting solvent components, extraction temperature, solid to extraction solvent ratio, and water content, have been evaluated.

Eco-Friendly 1,3-Dipolar Cycloaddition Reactions on Graphene Quantum Dots in Natural Deep Eutectic Solvent

Due to their outstanding physicochemical properties, the next generation of the graphene family-graphene quantum dots (GQDs)-are at the cutting edge of nanotechnology development. GQDs generally possess many hydrophilic functionalities which allow their dispersibility in water but, on the other hand, could interfere with reactions that are mainly performed in organic solvents, as for cycloaddition reactions. We investigated the 1,3-dipolar cycloaddition (1,3-DCA) reactions of the C-ethoxycarbonyl N-methyl nitrone 1a and the newly synthesized C-diethoxyphosphorylpropilidene N-benzyl nitrone 1b with the surface of GQDs, affording the isoxazolidine cycloadducts isox-GQDs 2a and isox-GQDs 2b. Reactions were performed in mild and eco-friendly conditions, through the use of a natural deep eutectic solvent (NADES), free of chloride or any metal ions in its composition, and formed by the zwitterionic trimethylglycine as the -bond acceptor, and glycolic acid as the hydrogen-bond donor. The results reported in this study have for the first time proved the possibility of performing cycloaddition reactions directly to the p-cloud of the GQDs surface. The use of DES for the cycloaddition reactions on GQDs, other than to improve the solubility of reactants, has been shown to bring additional advantages because of the great affinity of these green solvents with aromatic systems.

Processing of Functional Composite Resins Using Deep Eutectic Solvent

Deep eutectic solvents (DESs)—a promising class of alternatives to conventional ionic liquids (ILs) that have freezing points lower than the individual components—are typically formed from two or more components through hydrogen bond interactions. Due to the remarkable advantages of biocompatibility, economical feasibility and environmental hospitality, DESs show great potentials for green production and manufacturing. In terms of the processing of functional composite resins, DESs have been applied for property modifications, recyclability enhancement and functionality endowment. In this review, the applications of DESs in the processing of multiple functional composite resins such as epoxy, phenolic, acrylic, polyester and imprinted resins, are covered. Functional composite resins processed with DESs have attracted much attention of researchers in both academic and industrial communities. The tailored properties of DESs for the design of functional composite resins—as well as the effects of hydrogen bond on the current polymeric systems—are highlighted. In addition to the review of current works, the future perspectives of applying DESs in the processing of functional composite resins are also presented.

Understanding the Formation of Deep Eutectic Solvents: Betaine as a Universal Hydrogen Bond Acceptor

The mechanism of formation of betaine-based deep eutectic solvents (DES) is presented for the first time. Due to its polarity unbalance, it was found that betaine displays strong negative deviations from ideality when mixed with a variety of different organic substances. These results pave the way for a comprehensive design of novel deep eutectic solvents. A connection to biologically relevant systems was made using betaine (osmolyte) and urea (protein denaturant), showing that these two compounds formed a DES, the molecular interactions of which were greatly enhanced in the presence of water.