Choline Chloride-based Deep Eutectic Solvents Research Articles

Probing the interaction mechanism of choline chloride-based deep eutectic solvents with flavonoid and polyphenol systems

Choline chloride-based deep eutectic solvents (DES) have been demonstrated as promising green solvents for the extraction of flavonoids and polyphenols. This study investigates the interaction between six different hydrogen bond donors (HBD) choline chloride-based DES and three types of polyphenolic flavonoid substrates. Density functional theory (DFT) and molecular dynamics (MD) simulations suggest that Cl− dominates the interaction primarily through electrostatic forces. The extraction effect of alcohol DES on rutin was optimized obviously, and the maximum interaction could reach 737.6 kJ/mol. Acid DES has a better extraction effect on anthocyanins, with a maximum interaction of 376.4 kJ/mol. With the increase of the carbon chain of HBA and the increase of the number of functional groups, the interaction between DES and the active substance decreases. As HBD, ethanolamine with both hydroxyl and amino groups showed the best effect in the extraction process of DES, forming the maximum interaction energy of 1575.8 kJ/mol. Additionally, multivariate analysis is employed to establish the relationship between different variables and interaction energy. This study provides micro-theoretical support for the extraction of flavonoids and polyphenols.

Effects of hydrogen bond donors on PVDF membrane modification using choline chloride-based deep eutectic solvents

Deep eutectic solvents (DESs) were investigated as promising candidates in modifications towards hydrophobic polyvinylidene fluoride (PVDF) membranes based on its hydrophilic and hygroscopic properties. Five choline chloride-based DESs with various hydrogen bond donor (HBD) components were investigated as PVDF membrane modifiers by blending it with the membrane dope solution at 2 wt%. The incorporation of DESs appeared to influence the structure and morphology of the membranes, where macrovoid formations were suppressed and the formation of thin, densely porous skin layers were promoted as observed through SEM imaging. DES incorporation showed effects in contact angle reduction of the PVDF membranes from 90.22° to 60.07°, indicating hydrophilic modifications. Additionally, modifications with DESs yielded improvements in membrane flux (62.49 L/m2·h using glycerol-HBD) and protein solute rejection (74.62 % using glucose-HBD), though the overall tensile strength of the membranes were decreased from 4.24 MPa to the lowest value of 2.92 MPa. Ultimately, DESs were shown to be significant pore-forming agents in altering the morphology of PVDF membranes, and improving the thermal stability. Among the five tested DESs, PVDF modified with glycerol-HBD DES yielded the best membrane parameters and performances. DESs were demonstrated as prospective membrane modifiers in inducing hydrophilicity and influencing membrane morphology.

Experimental and Theoretical Insights into the Intermolecular Interactions in Saturated Systems of Dapsone in Conventional and Deep Eutectic Solvents.

Solubility is not only a crucial physicochemical property for laboratory practice but also provides valuable insight into the mechanism of saturated system organization, as a measure of the interplay between various intermolecular interactions. The importance of these data cannot be overstated, particularly when dealing with active pharmaceutical ingredients (APIs), such as dapsone. It is a commonly used anti-inflammatory and antimicrobial agent. However, its low solubility hampers its efficient applications. In this project, deep eutectic solvents (DESs) were used as solubilizing agents for dapsone as an alternative to traditional solvents. DESs were composed of choline chloride and one of six polyols. Additionally, water-DES mixtures were studied as a type of ternary solvents. The solubility of dapsone in these systems was determined spectrophotometrically. This study also analyzed the intermolecular interactions, not only in the studied eutectic systems, but also in a wide range of systems found in the literature, determined using the COSMO-RS framework. The intermolecular interactions were quantified as affinity values, which correspond to the Gibbs free energy of pair formation of dapsone molecules with constituents of regular solvents and choline chloride-based deep eutectic solvents. The patterns of solute-solute, solute-solvent, and solvent-solvent interactions that affect solubility were recognized using Orange data mining software (version 3.36.2). Finally, the computed affinity values were used to provide useful descriptors for machine learning purposes. The impact of intermolecular interactions on dapsone solubility in neat solvents, binary organic solvent mixtures, and deep eutectic solvents was analyzed and highlighted, underscoring the crucial role of dapsone self-association and providing valuable insights into complex solubility phenomena. Also the importance of solvent-solvent diversity was highlighted as a factor determining dapsone solubility. The Non-Linear Support Vector Regression (NuSVR) model, in conjunction with unique molecular descriptors, revealed exceptional predictive accuracy. Overall, this study underscores the potency of computed molecular characteristics and machine learning models in unraveling complex molecular interactions, thereby advancing our understanding of solubility phenomena within the scientific community.

Process design for acidic and alcohol based deep eutectic solvent pretreatment and high pressure homogenization of palm bunches for nanocellulose production

This research aimed to study on nanocellulose production from palm bunch using process design and cost analysis. Choline chloride based deep eutectic solvent pretreatment was selected for high-purity cellulose separation at mild condition, followed by nano-fibrillation using mechanical treatment. Three types of choline chloride-based deep eutectic solvents employing different hydrogen-bond donors (HBDs) namely lactic acid, 1,3-butanediol and oxalic acid were studied. The optimal cellulose extraction condition was choline chloride/lactic acid (ChLa80C) pretreatment of palm empty bunch at 80 °C followed by bleaching yielding 94.96%w/w cellulose content in product. Size reduction using ultrasonication and high-pressure homogenization produced nanocellulose at 67.12%w/w based on cellulose in raw material. Different morphologies of nanocellulose were tunable in the forms of nanocrystals, nano-rods and nanofibers by using dissimilar deep eutectic solvents. This work offered a sustainable and environmentally friendly process as well as provided analysis of DES pretreatment and overview operating cost for nanocellulose production. Application of nanocellulose for the fabrication of highly functional and biodegradable material for nanomedicine, electronic, optical, and micromechanical devices is achievable in the near future.

Molecular mechanism and extraction performance evaluation of choline chloride-based deep eutectic solvents for phenol separation from oil: Different glycols as hydrogen bond donors

Highly efficient separation of phenols from coal-to-liquids can enhance the economics of the coal conversion process. The selection of extractants with high extraction efficiency and low neutral oil entrainment is significant for energy development strategy. In this study, four ChCl-based DESs with different glycols as hydrogen bond donors (HBDs) were designed for the separation of phenol/toluene mixtures and the experimental results were analyzed by theoretical calculations. The experimental results showed that ChCl-EG had the highest extraction efficiency (94.02 %) and the least entrainment of toluene (0.449 g). Meanwhile, it could be regenerated and reused four times with no significant change in extraction capacity. The formation of hydrogen bonds between DESs and phenol was elucidated by σ-profile based on COSMO-SAC model. Multi-scale simulations and comparative analyses of the micro-mechanisms of the DESs system were carried out using quantum chemical (QC) and molecular dynamics (MD). It was shown that the attraction of DESs to phenol was mainly due to hydrogen bonds and vdW forces, with hydrogen bond interaction between Cl− in ChCl and H atom in phenol hydroxyl group being dominant. As the chain length of HBDs increased, the interaction of DESs with phenol was enhanced, while the entrainment of toluene also increased. Overall, the effect on the separation of phenol by different chain lengths of glycols as HBDs is elucidated. This study provides a theoretical reference for selecting and designing other DES extractants to separate phenol/toluene systems and similar systems.

Antioxidant and antidiabetic potential of Acanthus mollis L. using choline chloride-based deep eutectic solvents

In recent years, the study of medicinal plants’ therapeutic properties has increased due to their effects and biological activities. The Acanthaceae family consists of 242 genera and 3947 species mainly distributed across tropical and subtropical zones. This family is known to contain a wide range of bioactive compounds, such as, alkaloids, triterpenes steroids glycosides, polyphenols, and polysaccharides. Herein, the antioxidant and anti-diabetic effects of Acanthus mollis (AM) extracted by green alternative technology; ultrasound assisted-deep eutectic solvents extraction (UAE- DES) were determined. The data obtained, showed that AM seeds had the highest Total Phenolic Content, antioxidant activity and anti-diabetic activity compared to AM seeds shell. The presence of antioxidants with anti-diabetic proper- ties in AM could potentially serve as a foundation for innovative drug formulations capable of addressing several diseases. However, it is strongly advised that studies, including toxicity assessments, be conducted with a view to- wards pharmaceutical applications.

Eco-friendly Functionalization of MWCNTs with Deep Eutectic Solvents

The unique features of deep eutectic solvents (DESs) have sparked interest in their use for various applications due to their capacity to introduce new functional groups and other surface alterations. In this study, DESs were employed for the surface modification of MWCNTs. Twelve distinct varieties of Choline chloride-based DESs were prepared and characterized. Prior to the MWCNTs functionalization process, further tests, including viscosity, density, and TGA analysis, were carried out to evaluate the stability of the prepared solvents. The surface functionalization of MWCNTs was then carried out using the most stable solvent. The DESs-functionalized samples were tested for dispersibility and solubility, and FTIR was used to confirm the functional groups present. In comparison to the pristine MWCNTs, the result showed that samples D1, D2, and D4 had several functional groups on their surfaces. Also, in comparison to other DESs-functionalized samples, D1, D2, and D4 had more oxygen-containing groups, as further corroborated by CHNS analysis.As a result, DESs comprising glycerol and ethylene glycol provide an environmentally benign route to alter the surface of MWCNTs, making them suitable functional materials for a range of uses such as Adsorbents, Catalysts, Li batteries, EMI shielding materials, and Supercapacitor electrolytes.

Ultrasound-assisted oxidative desulphurization of coal using choline chloride-based deep eutectic solvents

Ultrasound-assisted oxidative desulphurization of coal using choline chloride-based deep eutectic solvents

Ultrasound assisted choline chloride-based deep eutectic solvent extraction of bioactive compounds from salsify (Tragopogon buphthalmoides (DC.) boiss. Var. Latifolius Boiss.): A Box–Behnken design approach for optimization

This study aimed to investigate the ultrasound-assisted extraction of bioactive compounds from salsify using deep eutectic solvents (DESs) with different molar ratios. For this reason, total phenolic (TPC), total flavonoid (TFC) compounds, and antioxidant activities (1,1-diphenyl-2-picrilhydrazyl radical scavenging activity (DPPH•), and ferric reducing antioxidant power (FRAP)) of extracts prepared with DES were investigated with an experimental design and optimization study conducted for this purpose. An extraction time of 40.15 min was determined as the optimal condition. Under these conditions, a molar ratio of 3:1 (acetic acid:choline chloride) and a water ratio of 42.17 % provided the highest phenolic/flavonoid compounds and antioxidant activity. Correlations between water ratio, molar ratio, and sonication extraction time were determined using principal component analysis (PCA). In conditions where TPC, FRAP, and DPPH• were high according to PCA, it can be concluded that the extraction time, water ratio, and molar ratio are at high levels; contrarily, TFC is at a low level. In conclusion, ultrasound-assisted extraction using DES proved effective for salsify. Therefore, choline chloride-based DESs, can be recommended as environmentally friendly green solvents and an alternative to organic solvents for the extraction of bioactive compounds from salsify.

Effectiveness of ammonium-based deep eutectic solvents in extracting polyphenol from Chlorella vulgaris

This study investigated the extraction of polyphenols from Chlorella vulgaris microalgae using environmentally friendly choline chloride-based deep eutectic solvents (DESs), specifically DES 1 (choline chloride: ethylene glycol, 1:2) and DES 2 (choline chloride: glycerol, 1:2). Thermal characterization of DESs through DSC analysis confirmed their formation as a glass former, while through density and viscosity analysis reveals their influence on extraction efficiency. Both DESs and methanol were employed in solid-liquid extraction combined with centrifugation. The Folin-Ciocalteu method quantified total phenolic content, showing DES 1 and DES 2 to outperform methanol (80.04, 68.63, and 60.15 mg GAE/g, respectively). High performance liquid chromatography (HPLC) was used in order to confirm these results. The HPLC result revealed that DES 1 exhibited the highest extraction efficiency at 198.00 ± 4.45 mg/L of Gallic acid yielded, followed by DES 2 at 189.83 ± 4.84 mg/L and the lowest is MeOH at 138.47 ± 5.36 mg/L. DPPH Radical Scavenging assay indicated both DES 1 and DES 2 extracts with significant radical scavenging activity (88.45 ± 0.17) % and (66.13 ± 1.62) %, respectively, compared to MeOH extracts that showed the lowest antioxidant activity at (30.41 ± 1.70) %. Overall, this study highlighted the potential of DESs in enchancing polyphenol extraction from Chlorella vulgaris, with room for further optimization and exploration of DES-polyphenol interactions.

Choline chloride-based deep eutectic solvents (NADES): Potential use as green extraction media for polyphenols from Mentha pulegium, antioxidant activity, and antifungal activity

With the introduction of the concept of green chemistry, eco-friendly extraction processes are moving from an option to a must. Combined with ultrasound-assisted extraction (UAE), 9 choline chloride deep eutectic solvents were screened for the extraction of antioxidant polyphenolic compounds from Mentha pulegium (Lamiaceae). Data indicated that among the 9 types of choline chloride-based solvents tested, Choline Chloride: Lactic acid (1:2) and Choline Chloride: Glycerol (1:2) were selected as the most promising solvent compared to 80 % methanol. The extraction conditions were statistically investigated using Response surface methodology conducted by Boc-Behnken design (BBD). The optimal operational conditions were: temperature of extraction 80 °C, extraction time of 30 and 51 min with 44 and 20 % water content in Choline Chloride: Glycerol (1:2) and Choline Chloride: Lactic acid (1:2), respectively. The selected NADES extracts recorded excellent scavenging activity at a concentration of 1,9 mg/ml higher than 93 %. HPLC–MS/MS analysis revealed that Phenolic acids mainly hydroxycinnamic acids, such as rosmarinic acid, chlorogenic acid, salvianolic acid, caffeoyl glucose, lithospermic acid, and its derivatives, dominated the extracts tested. Otherwise, our results support that the proposed eutectic solvents are able to provide a higher selectivity toward flavonoids such as apigenin derivative, kaempferol coumaroyl hexoside, epi gallocatechin and quercetin o glucopyranoside gallate. The antifungal activity of the optimized extracts revealed inhibition of over than 88 % against the postharvest citrus fungal: Phytophthora citrophthora. In light of the presented results and considering the nature of components constituting Natural deep eutectic solvents (NADES), make these green, novel, sustainable, and low-cost extracts fresh samples for further investigation.

Isolation and quantification of alginate in choline chloride-based deep eutectic solvents

Extraction of seaweed compounds using Deep Eutectic Solvents (DES) has shown high interest. Quantification, however, is challenging due to interactions with DES components. In this research work, three chemical separation techniques were investigated to isolate and quantify alginate from a set of choline chloride-based DES. While choline chloride served as the hydrogen bond acceptor (HBA); Urea, Ethylene Glycol, Propylene Glycol, Glycerol, Sorbitol, Xylitol and Glucose were used as hydrogen bond donors (HBD). DES containing sodium alginate were subjected to precipitation with sulfuric acid 0.2 M (pH 1.6), ethanol-water mixture (80 % v/v) and calcium chloride (1 % w/v CaCl2·2H2O). Alginate in precipitates was quantified and used to evaluate the performance of each separation technique. The highest recovery yields (51.2 ± 1.3 %) were obtained using the ethanol-water mixture followed by calcium chloride (45.7 ± 1.2 %), except for polyols (e.g. sorbitol). The lowest recovery yields were obtained with acid, with a particularly low recovery yield when urea was used as HBD (9.6 ± 1.3 %). Estimations of ManA/GulA ratios showed lower values for precipitates from DES compared to the ones obtained from water. This research shows ethanolic precipitation as a suitable method for alginate separation from the studied set of choline chloride-based DES.

Probing the interface of choline chloride-based deep eutectic solvent ethaline with gold surfaces: A molecular dynamics simulation study

Technologies involving a solvent|surface interface, such as nanotechnology, electrochemistry, and energy storage applications, are actively pursuing ecologically responsible and sustainable development practices. In response to this pressing need, deep eutectic solvents have emerged as a promising solution to bridge the gap between technological requirements and environmental concerns. In this work, we present the results of a molecular dynamics simulation study of the interface between a monocrystalline gold surface and the deep eutectic solvent ethaline, where a molar ratio of 1:2 choline chloride:ethylene glycol was used for ethaline. The simulations covered a range of temperatures from 313 K to 343 K and applied charge values ranging from 0 to ± 24 μC cm‒2. Several key interfacial properties were thoroughly analyzed, including among others, charge density profiles, radial distribution functions, hydrogen bond close contacts, and molecular orientation. Additionally, we examined how the differential capacitance varied upon the applied potential. Our findings reveal that, at neutral surfaces, all components of the solvent are present in the innermost layer, with ethylene glycol molecules being the most prevalent, followed by choline cations and a residual amount of chloride anions. For lower applied charges, this mixed composition at the boundary layer persists, despite the growing accumulation of ionic species with charges opposite to that of the electrode. As surface polarization increases, unique innermost boundary layers composed exclusively of one of the ionic species and the hydrogen bond donor molecules are observed, forming a multilayer structure, with subsequent layers enriched of paired counterions. Interestingly, even at higher applied charges, choline cations and ethylene glycol molecules tended to orient themselves in a parallel fashion toward the electrodes. Differential capacitance curves exhibited a camel-shaped behavior, suggesting a complex interplay of electrochemical processes at the DES|Au(100) interface. In summary, our study provides valuable insights into the interfacial properties of deep eutectic solvents on gold surfaces and their response to changes in temperature and potential, which are crucial for understanding and optimizing deep eutectic solvent-based electrochemical systems.

Choline chloride-based deep eutectic solvents as plasticizer and active agent in chitosan films

The growing concern over extending the shelf life of food products, coupled with the escalating environmental impact of synthetic plastic waste, has fuelled a quest for bio-based alternatives in packaging research. In response to this pressing need, our study delves into the synthesis of chitosan-based films incorporating a deep eutectic solvents (DES). Choline chloride and diverse hydrogen bond donors were used as plasticizers, we also explored the active properties of DES integrated into the chitosan (Ch) matrix. The Ch-based films with chlorine chloride: citric acid can prevent the mold spotting up to 29 days longer in comparison to bread wrapped in polyethylene films (PE). The obtained Ch/DES films exhibited mechanical properties comparable to conventional PE (e.g., up to tensile strength of 26 MPa and up to 210% in case of elongation at break). This synthesis approach represents a significant stride towards environmentally friendly packaging materials, aligning with the principles of green chemistry.

Synthesis of furfural from xylose using a choline chloride-based deep eutectic solvent and mechanistic insights

Choline chloride-based deep eutectic solvents can be used in the green synthesis of furfural, a platform molecule derived from biomass.

Citrus Peel Extracts: Effective Inhibitors of Heterocyclic Amines and Advanced Glycation End Products in Grilled Pork Meat Patties.

In the present study, citrus peels were extracted using various conventional and deep eutectic solvents (DESs). Compared to other citrus peel extracts, the DES extract based on choline chloride showed notably higher total phenolic and flavonoid content levels, along with superior antioxidant activity, among these extracts. Consequently, this study aimed to further investigate the inhibitory effects of the choline chloride based DES extract on the production of both free and bound heterocyclic amines (HAs) and advanced glycation end products (AGEs) in roast pork meat patties. The results indicated that the addition of choline chloride-based DES extracts, particularly the choline chloride-carbamide based DES extract, can effectively reduce the oxidation of lipids and proteins by quenching free radicals. This approach proves to be the most efficient in reducing the formation of both HAs and AGEs, leading to a significant reduction of 19.1-68.3% and 11.5-66.5% in free and protein-bound HAs, respectively. Moreover, the levels of free and protein-bound AGEs were reduced by 50.8-50.8% and 30.5-39.8%, respectively, compared to the control group. Furthermore, the major phenolics of citrus peel extract identified by UHPLC-MS were polymethoxylated flavonoids (PMFs) including hesperidin, isosinensetin, sinensetin, tetramethoxyflavone, tangeretin, and hexamethoxyflavone, which inferring that these compounds may be the main active ingredients responsible for the antioxidant activity and inhibition effects on the formation of HAs and AGEs. Further research is needed to explore the inhibitory effects and mechanisms of PMFs with different chemical structures on the formation of HAs and AGEs.

A comparative study of thermophysical properties between choline chloride-based deep eutectic solvents and imidazolium-based ionic liquids

In respond to the queries of deep eutectic solvent (DES) as a better analogue over ionic liquid (IL), this research aims in contributing a comparative study on the thermophysical properties of choline chloride-based DESs and imidazolium-based ILs to provide a general understanding on the similarities and differences of their properties. The thermal conductivity, viscosity and ionic conductivity of choline chloride-based DESs with glycerol (Gly) and ethylene glycol (EG) as hydrogen bond donors (HBDs) are characterized and compared with those of 1-ethyl-3-methylimidazolium chloride (EmimCl) and 1-hexyl-3-methylimidazolium chloride (HmimCl). It is observed that the thermal conductivity of DESs increases with salt: HBD molar ratio while that of ILs increases with alkyl chain length. Meanwhile, the viscosity of DESs is depending on the nature of HBD. DESs with glycerol as HBD show an incremental trend in viscosity with increasing molar ratio, while DESs with ethylene glycol as HBD depict an opposite trend. For ILs, longer alkyl chain length results in greater viscosity. The ionic conductivity of both DESs and ILs increase as their viscosity decrease. The effect of temperature is insignificant on the thermal conductivity of DESs and ILs. The viscosity of both DESs and ILs is reduced while their ionic conductivity is enhanced with increase of temperatures. When aqueous form of DESs and ILs is considered, water has greatly enhanced the thermal conductivity and ionic conductivity of DESs and ILs. However, the viscosity of DESs and ILs is drastically reduced with the presence of water content. In general, the thermophysical properties of both DESs and ILs are comparable, including in their aqueous forms. A prefeasibility study is conducted to further evaluate the potential and practicality of DESs and ILs in comparison with the conventional lubricant and battery electrolyte.

Thermodynamic study of choline chloride-based deep eutectic solvents with dimethyl sulfoxide and isopropanol

The thermodynamic properties of four binary mixtures of deep eutectic solvent (DES), i.e., ChCl/Gly (choline chloride + glycerol at a molar ratio of 1:2) and ChCl/EG (choline chloride + ethylene glycol at a molar ratio of 1:2) with two common co-solvents, i.e., dimethyl sulfoxide (DMSO) and isopropanol (IPA), were studied. Density and viscosity were determined at temperatures from 288.15 to 323.15 K, while measuring the enthalpy of mixing was performed at 308.15 and 318.15 K. The volumetric properties (i.e., excess molar volume and excess partial molar volume) and excess viscosities (i.e., viscosity deviation and logarithmic excess viscosity) were further calculated to investigate the effects of temperature, types of co-solvent and DES, and their contents on the non-ideal behavior of these systems, where the influence of treating the DES as a mixture of two components or a pseudo-component was discussed. The results of volumetric properties indicate that the combined influence of packing effects and H-bonding interactions between the DES and co-solvents led to the contraction of mixture volume, and the results of excess viscosities show H-bonding interactions play an important role in their variations. The results of enthalpy of mixing show that the mixing of DES with IPA is endothermic, while the mixing of DES with DMSO is exothermic. Furthermore, the nonrandom two-liquid (NRTL) model and Gibbs-Helmholtz equation were combined to represent the experimental results of the enthalpy of mixing, and the total average relative deviation (ARD) of all studied systems is 5.43%.

Chemical recycling of Polylactic acid to methyl lactate catalyzed by choline chloride/ZnCl2 deep eutectic solvents

Methyl lactate (ML) is a green and biodegradable chemical product, which can be used as a solvent for cellulose, paints and dyes. Although several kinds of catalysts have been reported for the methanolysis of Polylactic acid (PLA) into ML, low catalytic activity and high cost and complicated operation are still problems. Renewable, environmentally friendly, and non-toxic choline chloride-based Deep eutectic solvents (DESs) are the newest alternatives to conventional catalysts for the methanolysis of PLA to obtain the valuable product ML. In this study, the methanolysis of PLA into ML using DESs composed of choline chloride (ChCl) and Zinc chloride (ZnCl2) was investigated by experiments and calculations. Experimental results reveal that ChCl-2ZnCl2 can catalyze the methanolysis of PLA to produce ML, more importantly, ML is easily obtained by vacuum distillation, and the catalyst can be reused for 5 times without significant loss of activity. Moreover, the possible reaction mechanism was derived from experimental data and density functional theory (DFT) calculations. And the kinetics of the methanolysis of PLA catalyzed by ChCl-2ZnCl2 was studied and the activation energy was obtained. This work reveals that ChCl/ZnCl2 DESs are conducive to the methanolysis of PLA to ML under moderate conditions, which can also provide strategies for other polymer degradation.

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.