Acid-based Deep Eutectic Solvents Research Articles

Molecular interaction between three novel amino acid based deep eutectic solvents with surface active ionic liquid: A comparative study

Interaction between a surface active ionic liquid (IL) viz. 1-decyl-3-methylimidazolium chloride [Dmim][Cl] with three novel amino acid-based deep eutectic solvents (DES, consisting of choline chloride and l-methionine (DES1), l-phenylalanine (DES2), and l-glutamine (DES3) in a 1: 2 mol ratio) is studied. Several techniques, including surface tension, fluorescence, UV–visible spectroscopy, and Fourier transform infrared (FTIR), were used to investigate the key micellar properties and intermolecular interactions between the IL and DESs. All the DESs studied here facilitate the micellization process successfully lowering the critical micelle concentrations (CMC) of [Dmim][Cl] with addition of 5 wt% and 10 wt% of DESs. In decreasing order of DES2 > DES1 > DES3, the affinity to promote IL [Dmim][Cl] aggregation within aqueous DES solutions. Additionally, the CMC values as well as the surface tension at CMC are both noticeably reduced significantly by DES2. The surface tension method determines how three amino acid-based DESs affect the CMC, Гmax, πCMC, Amin and pC20 of micellization. When IL [Dmim][Cl] forms micelles within DES solutions, the solvophobic effect predominates, and the intermolecular hydrogen-bond interaction helps to form micelles. FTIR was used to examine the molecular interactions and structural changes of the ionic liquid self-assemblies in aqueous DESs. The results show that the presence of DESs greatly aids in the micellization of [Dmim][Cl], and to a greater extent for DES2 than for DES1/DES3. The colloidal properties of DES and their mixtures are advantageous for the solubility, micellization, and other features of ionic liquids; further details on this positive observation are provided in the results and discussion. In the areas of micellization, CMC, synthesis, catalysis, and environmental, biological, and pharmaceutical applications, among others, DESs are extremely useful.

Antibacterial and antioxidant activities of Chlorella vulgaris and Scenedesmus incrassatulus using natural deep eutectic solvent under microwave assisted by ultrasound

Microalgae are increasingly recognized as promising sources of natural bioactive compounds. However, traditional extraction methods using volatile organic solvents (VOCs) pose environmental risks. This study explores renewable deep eutectic solvents (DES) as sustainable alternatives for extracting bioactive compounds from microalgae biomass, focusing on Chlorella vulgaris and Scenedesmus incrassatulus. Four DES systems, comprising choline chloride (ChCl) and glycerol, citric acid, urea, and glucose, were compared with three conventional solvents (ethanol, methanol, and water). Extraction efficiency was assessed based on total phenolic content (TPC), flavonoid content, and tannin content, followed by antioxidant activity evaluation using DPPH, CAT, and FRAP assays. Additionally, antibacterial activity of the DES extracts was determined against Escherichia coli (ATCC 25922), Pseudomonas aeruginosa (ATCC 27853), Staphylococcus aureus (ATCC 29213), and Bacillus subtilis (ATCC 3366) using disc diffusion and microplate dilution methods to determine minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC). Results reveal that DES, particularly choline chloride: citric acid, outperform conventional solvents in terms of polyphenol extraction efficiency, antioxidant activity, and antibacterial activity against both Gram-negative and Gram-positive bacteria. For instance, the citric acid-based DES (SIDES2) showed a TPC of 4.98 mg/g, while the conventional solvent ethanol exhibited a TPC of 3.27 mg/g. Additionally, SIDES2 exhibiting the highest DPPH scavenging activity of 75 %, compared to 60 % for ethanol. Furthermore, SIDES2 showed an MIC of 0.5 mg/ml against Staphylococcus aureus. This study underscores the potential of DES for sustainable extraction of natural antioxidants from microalgae biomass, contributing to the development of environmentally friendly extraction processes in various industries.

Beyond the Conventional Leaching: Exploring Pyruvic Acid-Based Deep Eutectic Solvents for Sustainable Recycling of Spent Lithium-Ion Battery Cathode Material

Beyond the Conventional Leaching: Exploring Pyruvic Acid-Based Deep Eutectic Solvents for Sustainable Recycling of Spent Lithium-Ion Battery Cathode Material

Green extraction of carotenoids from canistel (Lucuma nervosa) pulps using ultrasound-assisted fatty acid-based deep eutectic solvents: Optimization and mechanism

This study aimed to develop an eco-friendly and high-efficiency method for extracting carotenoids from canistel pulps (CPs) by ultrasound-assisted natural fatty acids-based deep eutectic solvents (DESs). The DES consisting of menthol and capric acid (Men-CaA, 2:1) resulted in the highest total carotenoids content (TCC) of 614 ± 3 μg β-carotene equivalent (β-CE)/g DW. The conditions of ultrasound-assisted Men-CaA extraction were then further optimized by using response surface methodology (RSM). The maximum extraction yield of TCC (831.0 ± 0.3 μg β-CE/g DW) was achieved under the conditions of ultrasonic power of 320 W, liquid to solid ratio (L/S) of 6:1, temperature of 40℃, and ultrasound time of 18 min. In addition, ultrasound significantly intensified the extraction of carotenoids from CPs. The carotenoids compositions in CPs were also identified using UPLC-QTRAP-MS/MS for the first time. Men-CaA extract exhibited much higher content of lycopene (499 ± 1 μg/g DW) compared to the acetone and corn oil extracts. Molecular dynamic simulation confirmed that more non-covalent bonds were found between Men-CaA and lycopene. Overall, an ultrasound-assisted eco-friendly fatty acids-based eutectic solvent method was successfully developed for highly efficient extraction of carotenoids from agricultural by-products.

Precise recognition for citrus oils deterpenation through multiple interactions with deep eutectic solvents-functionalized porous aromatic frameworks

Citrus oils are widely used in the pharmaceutical and food industries, accounting for 30% of the global essential oils market. Deterpenation, separation between high-value oxyterpenes (5 wt%) and terpenes, is crucial for obtaining higher quality citrus oils and high-purity limonene, a major terpene pharmaceutical intermediate. Despite various treatments, achieving sustainable, mild, yet efficient deterpenation remains challenging because of their structural and property similarities. We designed a hybrid porous aromatic framework (PAF) by integrating lactic acid-based deep eutectic solvents (LaDESs) as functionalized sites. Compared to available adsorbents, PAF functionalized by LaDES (LaDES@PAF) can realize oxyterpenes adsorption gently without citrus oils dilution by volatile solution. Moreover, it exhibited 91.20% citral adsorption efficiency and 13.60 citral selectivity over limonene, an 11-fold selectivity improvement. Finally, 96.38 wt% pure limonene and high-value citrus oil containing 80 wt% oxyterpenes were achieved. Modeling studies revealed the strong induction effect of LaDESs improved H-bonds between citral and the framework, facilitating citral adsorption. Our findings highlight that LaDES@PAF can serve as a competitive deterpenation medium, establishing PAFs as promising platforms for addressing complex separations in the natural essential oil industry.

Precise recognition for citrus oils deterpenation through multiple interactions with deep eutectic solvents-functionalized porous aromatic frameworks

Citrus oils are widely used in the pharmaceutical and food industries, accounting for 30% of the global essential oils market. Deterpenation, separation between high-value oxyterpenes (5 wt%) and terpenes, is crucial for obtaining higher quality citrus oils and high-purity limonene, a major terpene pharmaceutical intermediate. Despite various treatments, achieving sustainable, mild, yet efficient deterpenation remains challenging because of their structural and property similarities. We designed a hybrid porous aromatic framework (PAF) by integrating lactic acid-based deep eutectic solvents (LaDESs) as functionalized sites. Compared to available adsorbents, PAF functionalized by LaDES (LaDES@PAF) can realize oxyterpenes adsorption gently without citrus oils dilution by volatile solution. Moreover, it exhibited 91.20% citral adsorption efficiency and 13.60 citral selectivity over limonene, an 11-fold selectivity improvement. Finally, 96.38 wt% pure limonene and high-value citrus oil containing 80 wt% oxyterpenes were achieved. Modeling studies revealed the strong induction effect of LaDESs improved H-bonds between citral and the framework, facilitating citral adsorption. Our findings highlight that LaDES@PAF can serve as a competitive deterpenation medium, establishing PAFs as promising platforms for addressing complex separations in the natural essential oil industry.

Development of sustainable sugarcane bagasse biorefinery using a greener deep eutectic solvent from hemicellulose-derived acids

Acid-based deep eutectic solvents (ADES) have recently been tested as an emerging technology in biomass deconstruction. In particular, the use of hemicellulose-derived carboxylic acids has attracted great interest as this type of ADES can enable a sustainable closed-loop biorefinery, due to their efficiency and recyclability. Therefore, this study proposed the pretreatment of sugarcane bagasse (SCB) with acetic acid, as a biomass-derived chemical, and choline chloride [ChCl]:AA to perform a complete biomass fractionation to enhance enzymatic digestibility. Thus, this work analyzed the effect of different temperatures and reaction time during pretreatment, studying the impact on biomass composition and digestibility during enzymatic hydrolysis. In addition, the reuse of ADES to produce an environmentally friendly and low-cost SCB biorefinery was explored by studying the physicochemical modifications in polysaccharide-rich material (PRM) and lignin-rich material (LRM) by ATR-FTIR and SEM photography. Furthermore, the ADES content was also characterized by HPLC after each recycling cycle. The results demonstrated efficient polysaccharide conversion, promoting an enrichment in glucan (>60%) and xylan (>20%) content under mild operating conditions (130°C and 90 min) supported by ATR-FTIR and SEM. Furthermore, SCB pretreated under these selected conditions achieved higher digestibility, increasing by 89% for glucan and 73% for xylan, using a simple and competitive process. In contrast, increasing the temperature above 130°C did not improve the enzymatic digestibility of SCB. Thus, ChCl:AA could be recycled and reused. Therefore, this study demonstrated the potential of AA in DES pretreatments as an environmentally friendly and efficient method for the valorization of SCB components.

Combined experimental and computational investigation of tetrabutylammonium bromide-carboxylic acid-based deep eutectic solvents

Aiming at shedding light on the molecular interactions in deep eutectic solvents (DESs), the DESs based on tetrabutylammonium bromide (TBAB) as hydrogen bond acceptor (HBA) and carboxylic acids (CAs) (formic acid (FA), oxalic acid (OA), and malonic acid (MA)) as hydrogen bond donor (HBD) were investigated by both experimental and theoretical techniques. The thermal behaviors of the prepared DESs were investigated by differential scanning calorimetry (DSC) method. In order to study the hydrogen bond formation between the DESs constituents, the FT-IR analysis was carried out. The large positive deviations of the iso solvent activity lines of ternary HBA+HBD + 2-propanol mixtures determined by the isopiestic technique from the semi-ideal behavior indicate that CAs interact strongly with TBAB and therefore they can form DESs. Molecular dynamics (MD) simulations were performed to present an atomic-scale image of the components and describe the microstructure of DESs. From the MD simulations, the radial distribution functions (RDFs), coordination numbers (CNs), combined distribution functions (CDFs), and spatial distribution functions (SDFs) were calculated to investigate the interaction between the components and three-dimensional visualization of the DESs. The obtained results confirmed the importance of hydrogen bonds in the formation of TBAB/CAs DESs.

Completely Inorganic Deep Eutectic Solvents for Efficient and Recyclable Liquid-Liquid Interface Catalysis.

Organic acid-based deep eutectic solvents (DESs) as catalysts always suffer from weak stability and low recyclability due to the accumulation of organic oxidative products in the DES phase. Herein, a completely inorganic deep eutectic solvent (IDES) ZnCl2/PA with zinc chloride (ZnCl2) and phosphoric acid (PA) as precursors is constructed to realize liquid-liquid interface catalysis for desulfurization of fuel and product self-separation for the first time. Owing to the inorganic nature, the organic oxidative products are accumulated at the interface between the IDES and fuel rather than the IDES phase. With this unique feature, the IDES can be reused for at least 15 times without any further treatment in oxidative desulfurization process, showing a state-of-the-art cycle-regeneration stability. Moreover, compared with the reported organic DESs, the IDES also reveals more attractive catalytic oxidative desulfurization performance. Experimental and theoretical studies indicate that the strong coordination Zn···O═P and the strong adsorption energy between IDES and sulfides enhance the activation of H2O2 to reactive oxygen species, leading to the superior catalytic performance in oxidative desulfurization of fuel.

One-pot extraction of nanocellulose from raw durian husk fiber using carboxylic acid-based deep eutectic solvent with in situ ultrasound assistance

Nanocellulose (CNF) has emerged as a promising alternative to synthetic petroleum-based polymers, but the conventional preparation process involves multiple tedious steps, heavily dependent on chemical input, and proves cost-inefficient. This study presented an, in situ ultrasound-assisted extraction using deep eutectic solvent (DES) based on choline chloride and oxalic acid for more facile production of CNF from raw durian husk fibers. FESEM analysis confirmed the successful extraction of web-like nanofibril structure with width size ranging from 18 to 26 nm. Chemical composition analysis and FTIR revealed the selective removal of lignin and hemicellulose from the raw fiber. As compared to post-ultrasound treatment, in situ ultrasound-assisted extraction consistently outperforms, yielding a higher CNF yield with finer fiber width and significantly reduced lignin content. Integrating this eco-friendly in situ ultrasonication-assisted one-pot extraction method with a 7.5 min interval yielded the highest CNF yield of 58.22 % with minimal lignin content. The superior delignification ability achieved through the proposed in situ ultrasound-assisted protocol surpasses the individual efficacy of DES and ultrasonication processes, neither of which yielded CNF in our experimental setup. This single-step fabrication process significantly reduces chemical usage and streamlines the production steps yielding web-structured CNF that is ideal for sustainable application in membrane and separator.

Acid-based deep eutectic solvents followed by GFAAS for the speciation of As(III), As(V), total inorganic arsenic and total arsenic in rice samples

In the present study, an efficacious, safe, inexpensive and eco-friendly microextraction was provided by deep eutectic solvents based on dispersive liquid–liquid microextraction (DLLME − DES) followed by GFAAS. A series of DESs were synthesised using l-menthol as hydrogen bond acceptor (HBA) and carboxylic acids with 4, 6, 8 and 10 carbon atoms as hydrogen bond donors (HBD). The synthesised DESs were used as extractants of arsenic ions. Under optimised conditions, good linearity with coefficient of determination (r 2) 0.992 and an acceptable linear range of 0.3–100 µg kg−1 was obtained. The limit of detection was 0.1 µg kg−1 (S/N = 3) for arsenite (As(III)) ions, and a high enrichment factor (EF = 200) was obtained. The enhancement factor and extraction recovery (ER%) of the method were 340 and 60%, respectively. RSDs including inter- and intra-day ranged from 3.2% to 5.8% in three examined concentrations. After a specific digestion, the capability of the synthesised DES in the extraction of As(III) from rice was tested. Total inorganic arsenic was separated similarly after reduction of arsenate (As(V)) to As(III), and As(V) concentration was calculated by difference. Using a second digestion method, total arsenic concentration (sum of organic and inorganic arsenic) in the samples was determined.

Translational and reorientational dynamics in carboxylic acid-based deep eutectic solvents.

The glass formation and the dipolar reorientational motions in deep eutectic solvents (DESs) are frequently overlooked, despite their crucial role in defining the room-temperature physiochemical properties. To understand the effects of these dynamics on the ionic conductivity and their relation to the mechanical properties of the DES, we conducted broadband dielectric and rheological spectroscopy over a wide temperature range on three well-established carboxylic acid-based natural DESs. These are the eutectic mixtures of choline chloride with oxalic acid (oxaline), malonic acid (maline), and phenylacetic acid (phenylaceline). In all three DESs, we observe signs of a glass transition in the temperature dependence of their dipolar reorientational and structural dynamics, as well as varying degrees of motional decoupling between the different observed dynamics. Maline and oxaline display a breaking of the Walden rule near the glass-transition temperature, while the relation between the dc conductivity and dipolar relaxation time in both maline and phenylaceline is best described by a power law. The glass-forming properties of the investigated systems not only govern the orientational dipolar motions and rheological properties, which are of interest from a fundamental point of view, but they also affect the dc conductivity, even at room temperature, which is of high technical relevance.

Dissolving and Efficient Fractionation of Chitin and Synchronous Preparation of Calcium Lactate from Crayfish Shell Waste Using Amino Acid-Based Deep Eutectic Solvents

Dissolving and Efficient Fractionation of Chitin and Synchronous Preparation of Calcium Lactate from Crayfish Shell Waste Using Amino Acid-Based Deep Eutectic Solvents

Efficient synthesis of novel thiadiazolo[2,3-b]quinazolin-6-ones catalyzed by diphenhydramine hydrochloride-CoCl2⋅6H2O deep eutectic solvent

In this research, a new Lewis acid-based deep eutectic solvent (LA-DES) was synthesized using diphenhydramine hydrochloride and CoCl2·6H2O, (2[HDPH]:CoCl42−), and identified by FT-IR and 1HNMR techniques. The physicochemical properties of this LA-DES, such as thermal behavior, thermal stability, and solubility in common solvents were also investigated. The catalytic ability of 2[HDPH]:CoCl42− was ascertained in the efficient synthesis of a novel array of thiadiazolo[2,3-b]quinazolin-6-one scaffolds via a one-pot three-component reaction of dimedone/1,3-cyclohexanedione, aldehydes, and 5-aryl-1,3,4-thiadiazol-2-amines/3-(5-amino-1,3,4-thiadiazol-2-yl)-2H-chromen-2-one under solvent-free conditions. This catalyst was also successfully utilized for the synthesis of mono- and bis-thiadiazolo[2,3-b]quinazolin-6-ones from dialdehydes or bis-1,3,4-thiadiazol-2-amine. The simplicity of enforcement, short reaction time, avoidance of toxic organic solvents, scalability of the synthesis procedure, excellent atom economy, high reaction mass efficiency, and low E-factor are other outstanding advantages of this newly developed method. Furthermore, due to the convenient recovery and reuse of LA-DES, this protocol is economically justified and environmentally friendly.

Corrosion inhibition activity of a natural polysaccharide from Dysosma versipellis using tailor-made deep eutectic solvents

In this work, a total of 18 types of choline chloride, betaine, and L-proline-based deep eutectic solvents (DESs) were synthesized to determine the extraction yield of a natural polysaccharide (PSA) from Dysosma versipellis using an ultrasound-assisted extraction method. Results indicate that the choline-oxalic acid-based DES has the best extraction yield for PSA due to the proper physical-chemical properties between PSA and DES. To evaluate the optimal extraction conditions, a response surface methodology was carried out. Under the optimal conditions, the extraction yield of PSA reaches 10.37 % (± 0.03 %), higher than the conventional extraction methods. Findings from FT-IR and NMR suggest that the extracted PSA belongs to a neutral polysaccharide with (1 → 6)-linked α-d-glucopyranose in the main chain. Interestingly, results from various electrochemical measurements show the extracted PSA exhibits excellent corrosion inhibition performance for mild steel (MS) in a 0.5 M HCl solution, with 90.8 % of maximum corrosion inhibition efficiency at 210 mg L−1. SEM and XPS measurements reveal the formation of a protective layer on the MS surface. The adsorption behaviour of extracted PSA well obeys the Langmuir adsorption isotherm containing the chemisorption and physisorption. Additionally, theoretical calculations validate the experimental findings.

The protocatechuic acid-based deep eutectic solvent-mediated green synthesis of 1,2,4,5-tetrasubstituted imidazoles.

A novel protocatechuic acid-based deep eutectic solvent (ETPPBr/PCA-DES) was prepared by mixing ethyltriphenylphosphonium bromide (ETPPBr) and protocatechuic acid (PCA = 3,4-dihydroxybenzoic acid), and its structure was fully investigated by using the FT-IR, TGA/DTA, densitometer, eutectic point and 1H NMR techniques. Different molar ratios of ETPPBr to PCA were examined and the eutectic point phase diagram showed that the best ratio for the synthesis of the new DES is the one-to-one ratio of the two starting materials (ETPPBr and PCA). Then, the novel DES was used as a new and capable catalyst for the green synthesis of diverse 1,2,4,5-tetrasubstituted imidazoles a1-a12 from the four-component condensation reaction of phenanthrene-9,10-dione, aromatic amine, aromatic aldehyde, and ammonium acetate with high yields and very short reaction times. High yields and very short reaction times are two advantages of our proposed method compared with the previous reported methods.

Green synthesis approach using deep eutectic solvents to enhance the surface functional groups on porous carbon for CO2 capture

This study explores the potential of green solvents using amino acids-based deep eutectic solvents to alter surface functionality of activated carbon thus enhancing the carbon dioxide (CO2) adsorption capacity. Green solvent is prepared by mixing an amino acid (L-Arginine) with ethylene glycol to form amino acid-based deep eutectic solvents. Amino acid-based deep eutectic solvents were used to modify the surface functionalities of activated carbon derived from palm shell waste. The change in surface functional groups and surface morphology of the modified activated carbon samples were characterized by Fourier-transform infrared spectroscopy and Scanning electron microscopy-energy dispersive X-ray analysis. Then, CO2 removal performance was performed using a packed-bed CO2 adsorption reactor to evaluate CO2 breakthrough time and adsorption capacity. CO2 adsorption experiments were measured at a certain temperature (25–45°C), at a fixed feed flow rate and CO2 concentration of 200 mL/min and 15%. It was observed that modified activated carbon showed the highest breakthrough time (15.2 min) compared to raw palm shell (5.2 min) at an adsorption temperature of 25°C. CO2 breakthrough times significantly decreased with increasing adsorption temperature because of physical adsorption.

Ultrasonic-Assisted Extraction of Antioxidants from Perilla frutescens Leaves Based on Tailor-Made Deep Eutectic Solvents: Optimization and Antioxidant Activity.

The development of natural antioxidants to replace synthetic compounds is attractive. Perilla frutescens leaves were proven to be rich in antioxidants. The extraction of antioxidants from Perilla leaves via ultrasonic-assisted extraction (UAE) based on choline chloride-based deep eutectic solvents (DESs) was studied. Firstly, several DESs were prepared, and their extraction effects were compared. Secondly, the extraction process was optimized by single-factor experiments and response surface methodology (RSM). Finally, the optimization results were verified and compared with the results of traditional solvent-based UAE. The effects of solvents on the surface cell morphology of Perilla frutescens leaves were characterized by scanning electron microscopy (SEM). Choline chloride-acetic acid-based DES (ChCl-AcA) extract showed a relatively high ferric-reducing antioxidant activity (FRAP) and 2,2-diphenyl-1-picrylhyldrazyl radical scavenging rate (DPPH). Under the optimal operating conditions (temperature 41 °C, liquid-solid ratio 33:1, ultrasonic time 30 min, water content 25%, ultrasonic power 219 W), the experimental results are as follows: DPPH64.40% and FRAP0.40 mM Fe(II)SE/g DW. The experimental and predicted results were highly consistent with a low error (<3.38%). The values of the DPPH and FRAP were significantly higher than that for the water, ethanol, and butanol-based UAE. SEM analysis confirmed that ChCl-AcA enhanced the destruction of the cell wall, so that more antioxidants were released. This study provides an eco-friendly technology for the efficient extraction of antioxidants from Perilla frutescens leaves. The cytotoxicity and biodegradability of the extract will be further verified in a future work.

Developing amino acid-citric acid-based deep eutectic solvent for food applications: Preparation, characterization, antibacterial activity, biosafety, and formation mechanism exploration

The deep eutectic solvent (DES) is a novel environmentally-friendly solvent that shows promising potential for applications in the field of functional food. However, the current development of choline-based DESs faces limitations due to their toxicity levels, which restrict their application in the food industry. Therefore, in this study, amino acid (AA)-citric acid (CA) DESs suitable for functional food applications were developed using natural food additives as raw materials. The purity and thermodynamic properties of the AA-CA DESs were characterized by simultaneous thermogravimetry/differential scanning calorimetry (TG-DSC) and DSC analysis. The molecular interactions within the AA-CA DESs were investigated using FT-IR, NMR, and molecular dynamics (MD) simulations. The rheometer was used to study the viscosity of AA-CA DESs. The density of the AA-CA DESs was tested using a pycnometer and mutually verified with MD simulations. The antibacterial activity and biological safety of DESs were investigated by bacteriostatic and cell experiments. FT-IR, NMR, and MD simulations studies indicated that AA-CA DESs primarily form through hydrogen bonding interactions. Antibacterial experiments demonstrated that AA-CA DESs exhibited significantly enhanced antibacterial activity against P. aeruginosa and E. coli compared to pure substrates Gly, Ala, and Arg, respectively, indicating improved antibacterial properties. The cell experiments showed that AA-CA DESs possess good biological safety. In conclusion, this study successfully developed a class of AA-CA DESs and found that AA-CA DESs have good antibacterial activity and biosafety. This finding provides theoretical guidance for the sustainable development and application of DESs in the field of functional foods.

Malic acid-based deep eutectic solvent and its application in Insulin's structural stability

Deep eutectic solvents (DESs) and Ionic Liquids (ILs) have been recently used as a solvent for insulin delivery via subcutaneous, transdermal, oral, and nasal ways. However, due to their high viscosity, DESs are usually impractical for delivery applications in their pure solution. The addition of water decreases the viscosity of DESs, but it can also influence the structural stability of the proteins. Hence, DES-water solutions and their effect on insulin's structural stability need to be investigated. In this study, molecular dynamics simulations on insulin dimer in DES consisting of malic acid and choline chloride (MA-ChCl) with varying amounts of water were performed. Insulin is strongly stabilized in the DES and its aqueous solutions as compared to water. However, in the DES solutions with 50 % and 75 % water content, malic acid was observed to interact readily with insulin dimer and its binding site, causing the separation of the two monomers. Therefore, while the insulin dimer is stable in the DES with low water content, in the presence of higher amounts of water it is destabilized and the monomers are separated. Considering that insulin's active form is monomeric, and the decomposition of insulin into monomers before reaching the bloodstream can increase the pharmacokinetics of insulin delivery, the use of the aqueous DES for rapid insulin delivery is highly relevant.