Natural Deep Eutectic Solvents Components Research Articles

Hydration is not detrimental for Glycerol:Lactic acid deep eutectic mixtures

Natural deep eutectic solvents (NADES) have been proposed as eco-friendly alternatives to organic solvents. A trace amount of water is frequently unavoidable as a contaminant and may be also purposely added to the mixtures to reduce their problematically high viscosity and costly price. It is critical to understand the different effects of water on the characteristics of NADES, particularly for their use in procedures such as bioactives’ extraction, and enzymatic synthesis, among others. In this work, the effect of water on the physicochemical properties and structural features of glycerol:lactic acid (GLY:LAC) deep eutectic mixture was investigated. The structural changes after water addition were evaluated using FTIR-ATR and 1H NMR spectroscopy. The pH, conductivity, and polarity of the mixtures were also evaluated after the addition of different percentages of water. Molecular dynamics simulations (MD) were applied to assess the role of water on NADES components' distribution and properties, including the number of hydrogen bonds (HB), the radial distribution functions (RDF), and the spatial distribution functions (SDF). The results demonstrated that when water enters the system, the hydrogen bonds between the eutectic components break but new ones are formed creating strong interactions between them and the water. A ternary eutectic combination arises, leading to a melting point lower than the original counterparts, even with 90 % water, caused by the formation of stronger intermolecular interactions. The MD simulations indicate no phase separation regardless of the ratio of the components or the water content in the mixture, showing preservation of the eutectic behavior.Overall, these unprecedented results, in which the rupture of the HB between eutectic mixtures is never observed up to 90 % water, unravel the potential of these novel mixtures for multiple applications.

NaDES as a green technological approach for the solubility improvement of BCS class II APIs: An insight into the molecular interactions

Recently, Natural Deep Eutectic Solvents (NaDES) have emerged as potential solvents for boosting drug bioavailability. In this work, the mechanism of solubility enhancement of some APIs belonging to BCS class II (tolbutamide, nimesulide, domperidone and cinnarizine) in these eutectic bio-solvents was investigated in order to get deeper insights into the molecular interactions between the NaDES components and the selected drugs. Different NaDES formulations based on choline chloride, proline, solid organic acids (citric, tartaric and malic acid), sugars (glucose and xylitol) and water were prepared by mild heating (70 °C). Characterization of unloaded NaDES (pH, Karl Fisher titration, viscosity and FTIR analysis) indicated that the type of Hydrogen Bond Acceptor (HBA) and Hydrogen Bond Donor (HBD), their molar ratio as well as water amount strongly affect the extent of H-bonding interactions. Hard gelatin capsules filled with NaDES maintained their integrity until 6 months, proving that all water molecules participate in H-bond network. APIs’ solubility enhancement was significant in all NaDES with respect to buffer solutions (pH 1.2 and 6.8). Analysing NaDES having Choline as HBA, it was found that the solubility of smaller molecules increased using larger HBD, while higher molecular weight APIs can be better inserted into the network formed by smaller HBD. NOE experiments demonstrated the formation of a robust supramolecular structure among the protons of choline, those of organic acid and water. In addition, 1D ROESY spectra revealed for the first time the crucial role of choline (methyl groups) in establishing hydrophobic interactions with the relative aliphatic or aromatic portion of the drugs. These data suggest the complex structure of the API-NaDES supramolecular assembly and underline that drug solubility is dependent on a balance network of H-bonds and hydrophobic interactions as well. Understanding the type of interactions between the API and NaDES is essential for their use as effective solubilisation aid.

Biocompatible Self-Assembled Hydrogen-Bonded Gels Based on Natural Deep Eutectic Solvents and Hydroxypropyl Cellulose with Strong Antimicrobial Activity.

Natural deep eutectic solvents (NADES)-hydroxypropyl cellulose (HPC) self-assembled gels with potential for pharmaceutical applications are prepared. FT-IR, 1HNMR, DSC, TGA and rheology measurements revealed that hydrogen bond acceptor–hydrogen bond donor interactions, concentration of NADES and the water content influence significantly the physico-chemical characteristics of the studied gel systems. HPC-NADES gel compositions have thermal stabilities lower than HPC and higher than NADES components. Thermal transitions reveal multiple glass transitions characteristic of phase separated systems. Flow curves evidence shear thinning (pseudoplastic) behavior. The flow curve shear stress vs. shear rate were assessed by applying Bingham, Herschel–Bulkley, Vocadlo and Casson rheological models. The proposed correlations are in good agreement with experimental data. The studied gels evidence thermothickening behavior due to characteristic LCST (lower critical solution temperature) behavior of HPC in aqueous systems and a good biocompatibility with normal cells (human gingival fibroblasts). The order of antibacterial and antifungal activities (S.aureus, E.coli, P. aeruginosa and C. albicans) is as follows: citric acid >lactic acid > urea > glycerol, revealing the higher antibacterial and antifungal activities of acids.

Enhancing the Thermostability of Engineered Laccases in Aqueous Betaine-Based Natural Deep Eutectic Solvents.

In recent years, natural deep eutectic solvents (NADESs) have gained increasing attention as promising nontoxic solvents for biotechnological applications, due to their compatibility with enzymes and ability to enhance their activity. Betaine-based NADESs at a concentration of 25 wt % in a buffered aqueous solution were used as media to inhibit thermal inactivation of POXA1b laccase and its five variants when incubated at 70 and 90 °C. All the tested laccases showed higher residual activity when incubated in NADES solutions, with a further enhancement achieved also for the most thermostable variant. Furthermore, the residual activity of laccases in the presence of NADESs showed a clear advantage over the use of NADESs’ individual components. Molecular docking simulations were performed to understand the role of NADESs in the stabilization of laccases toward thermal inactivation, evaluating the interaction between each enzyme and NADESs’ individual components. A correlation within the binding energies between laccases and NADES components and the stabilization of the enzymes was demonstrated. These findings establish the possibility of preincubating enzymes in NADESs as a facile and cost-effective solution to inhibit thermal inactivation of enzymes when exposed to high temperatures. This computer-aided approach can assist the tailoring of NADES composition for every enzyme of interest.

Structural analysis of natural deep eutectic solvents. Theoretical and experimental study

A theoretical and experimental study was performed on natural deep eutectic solvents (NADES) formed by lactic acid-glucose (LGH), citric acid-fructose (CFH) and citric acid-glucose (CGH). The presence of nuclear Overhauser effect (NOE) in the proton nuclear magnetic resonance (1H NMR) spectra of the NADES was studied. The spatial proximity between the NADES components was experimentally confirmed by the detection of multiple NOE effects in the dilutions analyzed. LGH showed the best outcome by partially maintaining its supramolecular structure throughout the dilutions. In order to rationalize the intermolecular interactions generated among the components, a theoretical study was performed using a density functional theory (DFT) computational method. A simplified dimeric model of the NADES was selected in order to achieve a rapid screening of the system searching for interactions between their constituents. In agreement with the experimental evidence, the calculations allowed to confirm the spatial proximity, by finding at least two hydrogen bonds between the components of every NADES.

Green solvents from ionic liquids and deep eutectic solvents to natural deep eutectic solvents

Natural deep eutectic solvents (NADESs) are defined as mixtures of certain molar ratios of natural compounds such as sugars, organic acids, amino acids, and organic bases that are abundant in organisms. The melting points of these mixtures are considerably lower than those of their individual ingredients and far below ambient temperature. The first publications on the NADES concept in 2011 created a great expectation regarding their potential as green solvents that could replace conventional organic solvents in a wide range of applications. This was largely because many of the drawbacks of conventional synthetic ionic liquids (ILs) and deep eutectic solvents (DESs), particularly their toxicity and environmental hazards, could be solved using NADESs. Throughout the last 7 years, the interest in NADESs has increased enormously as reflected by the exponential growth of the number of related publications. The research on NADESs has rapidly expanded particularly into the evaluation of the feasibility of their application in diverse fields such as the extraction of (targeted) bioactive compounds from natural sources, as media for enzymatic or chemical reactions, preservatives of labile compounds, or as vehicles of non–water-soluble compounds for pharmaceutical purposes. Along with the exploration of these potential applications, there have been a large number of other studies related to their physicochemical features, the search for new NADESs, the research into the interactions between NADES components or with solutes, the recovery of solutes from NADES solutions, and the ways of circumventing inherent problems of NADESs such as their high viscosity and the consequent difficulties in handling them. This article contains a review of the applications of NADESs as extraction solvents, reaction media, and preservative, providing also a perspective of their future.

Natural deep eutectic solvents as beneficial extractants for enhancement of plant extracts bioactivity

In the present study phenolic grape skin extracts were prepared by using five choline chloride based natural deep eutectic solvents (NADESs) containing glucose, fructose, xylose, glycerol, malic acid and valorised by testing their biological activity in vitro using two human tumour cell lines (HeLa and MCF-7). Initially, used NADESs were investigated regard to their toxicity and low cytotoxicity of solvents was observed toward HeLa and MCF-7 cells (EC50 values > 2000 mg/L). Among used choline chloride based NADESs, the one containing malic acid showed the best performance concerning extraction efficiency (total phenolic and total anthocyanin were 91 and 24 mg/g dw), as well as antioxidant (ORAC values were 371 μmol TE/g dw) and antiproliferative activity (percentage of cell viability were about 20%). Herein, for the first time it was showed that NADES components could be chosen not only to fine-tune solvent physicochemical characteristics but also to enhance biological activity of extracts prepared in NADESs. Therefore, our research confirmed that NADESs are excellent and promising choice of solvents for sustainable and green extraction, which will lead to its novel application in food and pharmaceutical industry.

Recovery of metabolites from natural deep eutectic solvent matrices by countercurrent separation

NAtural Deep Eutectic Solvents (NADES) were discovered in 2011 as being mixtures of polar “primary metabolites” that exhibit unexpected solubilizing and stabilizing abilities for hydrophobic and/or bioactive ingredients. However, due to the inherent low vapor pressure of NADES, it is challenging to recover analytes such as “secondary” metabolites from a NADES-analyte(s) matrix by conventional liquid chromatography. The present study shows that countercurrent separation (CCS) can perform this task successfully. The resolution capability of CCS depends on the differential distribution coefficients (K values) of the analytes. Compared to most bioactive constituents, the NADES components have extreme K values (close to 0 or ∞, in RP or NP, resp.) because of their high polarity. Glucose-choline chloride-water (2:5:5, mole/mole) with rutin, quercetin, kaempferol, or daidzein were chosen as the test matrices. The CCS fraction analysis by UV-UHPLC and qHNMR showed that CCS can recover the target analyte completely from the NADES-analyte matrix, and at the same time yield the NADES quantitatively, allowing further study of “primary” NADES vs. bioactive “secondary” metabolites in botanical extracts. *represents equal contribution to this work

Tailoring properties of natural deep eutectic solvents with water to facilitate their applications

Previously it was demonstrated that natural deep eutectic solvents (NADES) are promising green solvents for the extraction of natural products. However, despite their potential, an obvious disadvantage of NADES is the high viscosity. Here we explored the dilution effect on the structures and physicochemical properties of NADES and their improvements of applications using quercetin and carthamin. The results of FT-IR and 1H NMR experiments demonstrated that there are intensive H-bonding interactions between the two components of NADES and dilution with water caused the interactions weaken gradually and even disappeared completely at around 50% (v/v) water addition. A small amount of water could reduce the viscosity of NADES to the range of water and increase the conductivity by up to 100 times for some NADES. This study provides the basis for modulating NADES in a controllable way for their applications in food processing, enzyme reactions, pharmaceuticals and cosmetics.