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.     

Optimization of heteroatom doped graphene oxide by deep eutectic solvents and the application for pipette‐tip solid‐phase extraction of flavonoids

In order to improve the permeation and adsorption properties of graphene oxide, heteroatoms and deep eutectic solvent were introduced in this study. After being modified, the structural properties of graphene oxide were improved and the materials were applied to the determination of myricetin and rutin in tea sample by pipette‐tip solid‐phase extraction method. The materials were characterized by scanning electron microscopy, Fourier transform infrared spectroscopy, X‐Ray diffractomer, energy dispersive spectroscopy, atomic force microscope, and specific surface area by Brunauer–Emmett–Teller N₂ adsorption desorption analysis. Meanwhile, they were tested by static and dynamic adsorption. The result showed that the materials after modifying had better adsorption amount for myricetin and rutin than graphene oxide. The calibration graphs of myricetin and rutin in MeOH were linear over 0.10–500.00 µg/mL, and the limits of detection and quantification were in the range of 0.00546–0.0182 µg/mL and 0.00741–0.0247 µg/mL, respectively. A reliable analytical method was developed for recognition targets in tea sample by DES modified nitrogen‐doped graphene oxide with satisfactory extraction recoveries (myricetin 99.77%, rutin 98.14%). It was potential for the rapid purification of myricetin and rutin in tea sample combined with the pipette‐tip solid‐phase extraction.     

Advances of responsive deep eutectic solvents and application in extraction and separation of bioactive compounds

In recent years, it has been found that changing ambient conditions (CO₂/N₂, temperature, pH) can trigger a switchable phase transition of deep eutectic solvents, and such solvents are known as responsive deep eutectic solvents. In this work, we present the development history, properties, and preparation of responsive deep eutectic solvents, followed by the application of responsive deep eutectic solvents in the extraction and separation of bioactive compounds are presented. Importantly, the mechanism of responsive deep eutectic solvents in the extraction of bioactive compounds is discussed. Finally, the challenges and prospects of responsive deep eutectic solvents in the extraction and separation of bioactive compounds are proposed. Responsive deep eutectic solvents are considered green and efficient solvents. Some methods for extraction and separation of bioactive compounds by responsive deep eutectic solvents can increase the possibility of recycling the deep eutectic solvents, and provide higher efficiency in the extraction and separation field. It is hoped that this will provide a reference for the green and sustainable extraction and separation of various bioactive compounds.     

低共熔溶剂的应用研究现状

低共熔溶剂是两种或多种固体或液体物质通过氢键相互作用形成的液体溶剂,其熔点明显低于单一组分的熔点。与传统离子液体相比,低共熔溶剂成本更低,制备更容易,可生物降解,具有100%原子利用率和生物相容性及无毒无害等绿色特性,这些优点使其在许多研究领域被广泛研究。本文介绍了低共熔溶剂的最新分类,综述了低共熔溶剂在电化学、气体吸收、有机合成、功能材料合成、萃取分离、药物增溶及生物质预处理中的应用,并对低共熔溶剂的未来发展进行了展望。     

Development of deep eutectic solvents applied in extraction and separation

Deep eutectic solvents, as an alternative to ionic liquids, have greener credentials than ionic liquids, and have attracted considerable attention in related chemical research. Deep eutectic solvents have attracted increasing attention in chemistry for the extraction and separation of various target compounds from natural products. This review highlights the preparation of deep eutectic solvents, unique properties of deep eutectic solvents, and synthesis of deep‐eutectic‐solvent‐based materials. On the other hand, application in the extraction and separation of deep eutectic solvents is also included in this report. In this paper, the available data and references in this field are reviewed to summarize the applications and developments of deep eutectic solvents. Based on the development of deep eutectic solvents, an exploitation of new deep eutectic solvents and deep eutectic solvents‐based materials is expected to diversify into extraction and separation.     

Rapid extraction of bioactive compounds from gardenia fruit using new and recyclable deep eutectic solvents

The utilization of deep eutectic solvent as an alternative and environmentally friendly option has gained significant attention. This study first proposed a series of benzylammonium chloride based-deep eutectic systems for the extraction of bioactive compounds from Gardenia jasminoides Ellis. Through the implementation of response surface methodology, the optimal solvent was determined to be dodecyldimethylbenzylammonium chloride–levulinic acid (1:3, mol/mol) with 35% (v/v) water, specifically tailored to extract geniposide, genipin-1-β-d -gentiobioside, crocin-1, and crocin-2 from gardenia fruits with the ratio of solid to liquid of 1:20 at 86°C for 16 min. Their total extraction yields could reach 70.6 mg/g, outperforming those obtained by other solvents and corresponding techniques. Furthermore, the eutectic system was retrieved after first-cycle extraction, and then applied in the subsequent extraction progress, yielding a consistent extraction efficiency of 97.1%. As compared to previous traditional methods, a quick, high-yielding, and green extraction procedure was achieved through simple heating settings that did not constrain the instrument. Therefore, dodecyldimethylbenzylammonium chloride–levulinic acid could serve as a sustainable and reusable solvent for efficient extraction of natural bioactive compounds from plant-based raw materials. The application of deep eutectic solvents has demonstrated their potential as designable solvents with stronger extraction capabilities than traditional organic solvents.     

Synthesis and characterization of novel ternary deep eutectic solvents简

A series of room-temperature ternary deep eutectic solvents(TDESs) were prepared from imidazolium halides, zinc halides and amides. The [BMIM]Cl–ZnCl2 –acetamide(1:1:1) system shows the lowest freezing point( 60 8C) and lowest density in the series. The viscosity and conductivity of TDESs have an exponential relationship with temperature and can be fitted by Arrhenius equation.     

Extraction and determination of bioactive flavonoids from Abelmoschus manihot (Linn.) Medicus flowers using deep eutectic solvents coupled with high‐performance liquid chromatography

A highly efficient and ecofriendly extraction method using deep eutectic solvents was developed to extract bioactive flavonoids from Abelmoschus manihot (Linn.) Medicus flowers. First, a series of deep eutectic solvents using choline chloride as hydrogen bond acceptor with different hydrogen bond donors was successfully synthesized. Then, the types of deep eutectic solvents and the extraction conditions for bioactive flavonoids (hyperoside, isoquercitrin, and myricetin) were optimized based on the flavonoids extraction efficiencies. The optimized deep eutectic solvent for hyperoside and isoquercitrin extraction was composed of choline chloride and acetic acid with a molar ratio of 1:2. The optimized deep eutectic solvent for myricetin extraction was composed of one mole of choline chloride and two moles of methacrylic acid. The optimal extraction conditions were set as: solid to solvent ratio, 35:1 (mg/mL); extraction time, 30 min; extraction temperature, 30°C. Qualitative and quantitative analysis were performed using ultra high performance liquid chromatography with tandem mass spectrometry and high‐performance liquid chromatography. And the extraction efficiencies of hyperoside, isoquercitrin, and myricetin under optimal extraction conditions were calculated as 11.57, 5.64, and 1.11 mg/g, much higher than those extracted by traditional extraction solvents. Therefore, the prepared deep eutectic solvents can be selected as alternative solvent to extract bioactive flavonoids.     

印迹分子聚合物结合低共熔溶剂用于山楂中咖啡酸的固相萃取

在相同的实验条件下,分别合成了以咖啡酸为模板的印迹分子聚合物和无模板分子聚合物。使用场发射扫描电镜法和吸附实验表征这两种聚合物材料的孔状结构和选择性吸附性能。然后利用印迹分子聚合物、无模板分子聚合物、C₁₈萃取小柱这3种材料结合固相萃取法纯化山楂提取物中的咖啡酸,提取率分别为3.46、1.01、1.17 μg/g。为了优化固相萃取过程,实验研究了不同洗脱剂的影响。分别利用用氯化胆碱和甘油、氯化胆碱和尿素(摩尔比均为1:2)合成出两种低共熔溶剂。甲醇与这两种低共熔溶剂分别以不同的体积比混合作为洗脱剂,用于优化咖啡酸的固相萃取过程。实验结果表明,印迹分子聚合物是一种良好的固相萃取材料;当甲醇和甘油基低共熔溶剂在体积比为3:1混合时,表现出最好的洗脱能力,得到咖啡酸的回收率为82.32%。     

Evaluation of green and efficient deep eutectic solvents as media for extracting alkaloids from lotus leaf

Deep eutectic solvents (DESs) were applied as eco-friendly solvents in this study for the extraction of alkaloids from lotus leaf, including O-nornuciferine, N-nornuciferine, nuciferine and roemerine. A series of hydrophilic and hydrophobic DESs with different hydrogen bond donors and a acceptors were synthesized and screened for a suitable DESs for extraction of alkaloids from lotus leaf. The study results showed that the hydrophilic DES with choline chloride and propanediol had the highest extraction yield. The main factors affecting the extraction efficiency—choline chloride–propanediol ratio, water content in deep eutectic solvents, solid–liquid ratio and extraction time—were investigated via a single-factor experiment. The optimized extraction conditions were 30% of water in choline chloride–propanediol (1:4) for heated extraction for 30 min and solid–liquid ratio 1:100 g/ml. Under optimum conditions, the extraction yields of O-nornuciferine, N-nornuciferine, nuciferine and roemerine were 0.069, 0.152, 0.334 and 0.041 g/100 g respectively, which were higher than those of methanol in acidified aqueous solution. This study suggests considerable potential for DESs as promising materials for the green and efficient extraction solvents for bioactive alkaloids from natural sources.     

Application of deep eutectic solvents in the extraction and separation of target compounds from various samples

Deep eutectic solvents, as a new type of eco‐friendly solvent, have attracted increasing attention in chemistry for the extraction and separation of target compounds from various samples. To summarize the application of deep eutectic solvents, this review highlights some of the unique properties of deep eutectic solvents and deep‐eutectic‐solvent‐based materials, as well as their applications in extraction and separation. In this paper, the available data and references in this field are reviewed to summarize the application developments of deep eutectic solvents. Based on the development of deep eutectic solvents, the exploitation of new deep eutectic solvents and deep‐eutectic‐solvent‐based materials are expected to diversify into extraction and separation.     

Optimized extraction of bioactive compounds from Herba Artemisiae Scopariae with ionic liquids and deep eutectic solvents

Ionic liquids with length of alkyl chain and different anions, deep eutectic solvents with choline chloride and 7 different hydrogen bond donors were applied as extraction additives after optimizing the extraction conditions to increase the extraction amounts of rutin, quercetin, and scoparone from Herba Artemisiae Scopariae. The extraction conditions were optimized as follows: refluxing with methanol with a solid/liquid ratio of 1:120 under 60°C for 60 min after changing the different extraction conditions of: extraction methods (dipping, ultrasonic, reflux and soxlet), extraction solvents (methanol, water and ethanol), extraction temperature (30, 40, 50, 60, 70 and 80°C), extraction time (30, 60, 80, 100 and 120 min), extraction ratio of solid to liquid (1:5, 1:10, 1:20, 1:50, 1:100, 1:120 and 1:150). Under these optimal conditions, the best preformed extraction additive among the 7 kinds of ionic liquids and 7 kinds of deep eutectic solvents extraction additives were selected and optimized with its contraction of 0.5mg/mL. Using the most effective extraction additive, [BMIM][Br], 10275.92 µg/g rutin, 899.73 µg/g quercetin, and 554.32 µg/g scoparone were obtained. Overall, ionic liquids and deep eutectic solvents have potential applications as extraction additives for the extraction of bioactive compounds from nature plants.     

Natural deep eutectic solvents as new potential media for green technology

Developing new green solvents is one of the key subjects in Green Chemistry. Ionic liquids (ILs) and deep eutectic solvents, thus, have been paid great attention to replace current harsh organic solvents and have been applied to many chemical processing such as extraction and synthesis. However, current ionic liquids and deep eutectic solvents have still limitations to be applied to a real chemical industry due to toxicity against human and environment and high cost of ILs and solid state of most deep eutectic solvents at room temperature. Recently we discovered that many plant abundant primary metabolites changed their state from solid to liquid when they were mixed in proper ratio. This finding made us hypothesize that natural deep eutectic solvents (NADES) play a role as alternative media to water in living organisms and tested a wide range of natural products, which resulted in discovery of over 100 NADES from nature. In order to prove deep eutectic feature the interaction between the molecules was investigated by nuclear magnetic resonance spectroscopy. All the tested NADES show clear hydrogen bonding between components. As next step physical properties of NADES such as water activity, density, viscosity, polarity and thermal properties were measured as well as the effect of water on the physical properties. In the last stage the novel NADES were applied to the solubilization of wide range of biomolecules such as non-water soluble bioactive natural products, gluten, starch, and DNA. In most cases the solubility of the biomolecules evaluated in this study was greatly higher than water. Based on the results the novel NADES may be expected as potential green solvents at room temperature in diverse fields of chemistry.     

Application of deep eutectic solvents for the extraction of phenolic compounds from extra-virgin olive oil

A HPLC–DAD/ESI–MS method has been developed and validated for the analysis of the most representative phenolic compounds in extra-virgin olive oil (EVOO) samples using a green extraction approach based on deep eutectic solvents (DESs) at room temperature. We examined ten DESs based on choline chloride and betaine in combination with different hydrogen bond donors comprising six alcohols, two organic acids, and one urea. Five phenolic compounds, belonging to the classes of secoiridoids and phenolic alcohols, were selected for the evaluation of extraction efficiency. A betaine-based DES with glycerol (molar ratio 1:2) was found to be the most effective for extracting phenolic compounds as compared to a conventional solvent. The optimization of the extraction method involved the study of the quantity of water to be added to the DES and evaluation of the sample-to-solvent ratio optimal condition. Thirty percent of water added to DES and sample to solvent ratio 1:1 (w/v) were selected as the best conditions. The chromatographic method was validated by studying LOD, LOQ, intraday and interday retention time precision, and linearity range. Recovery values obtained spiking seed oil sample aliquots with standard compounds at 5 and 100 μg/g concentration were in the range between 75.2% and 98.7%.     

Green and enhanced extraction of coumarins from Cortex Fraxini by ultrasound‐assisted deep eutectic solvent extraction

Green and enhanced extraction of bioactive ingredients from medicinal plants has become a hot research field, and deep eutectic solvents have been considered as a novel kind of sustainable solvents in the extraction process. In this study, hydrogen bond acceptor (choline chloride, etc.) and hydrogen bond donor (l ‐malic acid, etc.) were used to prepare different kinds of deep eutectic solvents to extract coumarins from Cortex Fraxini. The extraction conditions, including the composition and moisture content of deep eutectic solvents, extraction time, and liquid‐solid ratio, were systematically optimized basing on the extraction yield of coumarins. To further investigate the extraction mechanism, Fourier transform infrared spectroscopy was performed, and the microstructures of Cortex Fraxini powders were observed before and after extraction using scanning electron microscope. Results showed that the novel ultrasound‐assisted extraction with conditions of deep eutectic solvent containing betaine/glycerin (1:3), aqueous solution (20%), solid‐liquid ratio (15 mg/mL), and extraction time (30 min) exhibited the best extraction yields for the four target coumarins and much better extraction efficiency than with conventional solvent extractions. This suggests that the new ultrasound‐assisted deep eutectic solvent extraction could be used as a green and high‐efficient approach for extraction of the main coumarins from Cortex Fraxini.     

Development of a stir bar sorptive extraction method coupled to solidification of floating droplets dispersive liquid–liquid microextraction based on deep eutectic solvents for the extraction of acidic pesticides from tomato samples

A stir bar sorptive extraction method coupled with deep eutectic solvent based solidification of floating organic droplets–dispersive liquid–liquid microextraction has been used for the simultaneous derivatization and extraction of some acidic pesticides in tomato samples. In this method, initially the analytes are adsorbed on a coated stir bar from tomato juice filled in a narrow tube. After extraction, the stir bar is removed and a water–miscible deep eutectic solvent is used to elute the analytes. Afterward, a derivatization agent and a water–immiscible deep eutectic solvent (as an extraction solvent) with melting point near to room temperature are added to the obtained eluant at µL–levels and the obtained mixture is rapidly injected into deionized water. Under the optimum conditions, the introduced method indicated high enhancement (1543–3353) and enrichment (2530–2999) factors, low limits of detection (7–14 ng/L) and quantification (23–47 ng/L), good linearity (r² ≥ 0.9982), and satisfactory repeatabilities (relative standard deviation ≤12% for intra– and inter–day precisions at a concentration of 100 ng/L of each analyte). Finally, the proposed method was applied in analysis of the analytes in tomato samples.     

Using natural deep eutectic solvents for the extraction of metabolites in Byrsonima intermedia leaves

Natural deep eutectic solvents have been used as an alternative to organic solvents for the extraction of plants metabolites, allowing for the extraction of compounds of different polarities, while being inexpensive, non‐toxic, and easy to prepare. This work presents the comparison of the chromatographic profiles by high‐performance liquid chromatography with diode‐array detection obtained from Byrsonima intermedia (Malpighiaceae) using five choline chloride‐based natural deep eutectic solvents, in addition to the most used traditional extraction solvents, methanol/water 7:3 and ethanol/water 7:3 v/v. A reference extract was used to tentatively identify compounds by high‐performance liquid chromatography with tandem mass spectrometry. The water content appeared to be important for the extraction efficiency and the mixture choline chloride/glycerol was shown to be the best candidate for efficiently extracting this matrix when compared with the traditional extraction media in addition to being far greener as shown by the environmental analysis tool. Seven phenolic compounds (digalloyl quinic acid, proanthocyanidin dimer, galloylproanthocyanidin dimer, quercetin‐O‐hexoside, galloyl quercetin hexoside, quercetin‐O‐pentoside, and galloyl quercetin pentoside) were tentatively identified in all extracts. Moreover, the influence of these solvents on the antioxidant activity of the extracts was studied and the results for choline chloride/glycerol extracts were very similar to that of the traditional extraction solvents.     

己内酰胺基酸性低共熔剂对柴油的氧化脱硫:低共熔剂组成与催化反应活性（英文）

汽车尾气中硫化物的排放所导致的酸雨和PM2.5等环境污染问题广受关注.各个国家和地区也相继制定了严格的标准来控制柴油中的含硫量.加氢脱硫工艺成熟,但是需要在高温高压下进行,并且柴油中二苯并噻吩及其衍生物的位阻效应使得加氢脱硫难以将其脱除.氧化脱硫作为加氢脱硫的补充技术,以其反应条件温和等优点成为脱硫研究的重要课题.作为离子液体类似物,低共熔剂不仅具有离子液体的优点,而且无毒、生物可降解、价格低廉,且制备过程简单,是一种绿色溶剂.低共熔剂作为萃取剂和催化剂用于柴油的氧化脱硫中,展现出非常好的应用前景.尽管在低共熔剂氧化脱硫体系中氢键发挥着重要的作用,但是关于低共熔剂组成,氢键强度与氧化脱硫反应活性三者之间关系的探究相对缺乏.本文以己内酰胺和草酸为原料,调节二者配比制备了一系列己内酰胺基低共熔剂.通过差示扫描量热法、傅里叶变换红外光谱、核磁共振氢谱以及热重分析对制备的低共熔剂进行表征,从而确定组成与氢键之间的关系.将制备的低共熔剂应用于氧化脱硫体系中,发现氧化脱硫率随着低共熔剂组成的变化而规律变化.此外,系统地研究了影响氧化脱硫效率的反应参数.结果表明,在优化的反应条件下,己内酰胺基酸性低共熔剂的脱硫率可以达到98%.该反应体系下,三种不同硫化物的脱除率按照以下顺序依次递减:二苯并噻吩4,6-二甲基二苯并噻吩苯并噻吩.实验数据与表征结果表明,在低共熔剂氧化脱硫体系中氢键相互作用影响脱硫效率,而氢键相互作用则可以通过调节低共熔剂的组成来改变.该结果为了解柴油深度脱硫机理提供了新的思路.     

Basic deep eutectic solvents as reactant,template and solvents for ultra-fast preparation of transition metal oxide nanomaterials

Developing a new type of deep eutectic solvents(DESs) is indispensable for expanding their application in various fields.Here,we report a series of new highly basic DESs.FT-IR,quantitative ~1 H NMR,MD simulation and physical properties show that these basic liquids are made up of hydroxide acceptor of alkali metal hydroxides in which the hydrogen bonding interactions coordinate the donor.These DESs can be played three roles as new solvents,template and reactant for facile and ultra-fast preparation of transition metal oxide nanomaterials such as NiCo_2 O_4,MnCo_2 O_4,NiMn_2 O_4,CoCu_2 O_4 and Co_3 O_4 under mild condition.This work shows one of the low energy-intensive methods for nanomaterial preparation.These initial findings of basic deep eutectic solvents provide a potential applicability around the systematic development of transition metal oxide nanosheets.     

Metal-organic framework functionalized with deep eutectic solvent for solid-phase extraction of Rhodamine 6G in water and cosmetic products

An NH₂-MIL-53(Al)-DES(ChCl-Urea) nanocomposite was synthesized for extraction and determination of Rhodamine (Rh) 6G from environmental and cosmetic samples. The deep eutectic solvent (DES) was prepared by mixing choline chloride and urea in a mole ratio of 1:2. NH₂-MIL-53(Al)-DES(ChCl-Urea) nanocomposite was synthesized using the impregnation method at a ratio of 60:40 (w/w). The optimum conditions were determined after NH₂-MIL-53(Al)-DES(ChCl-Urea) characterization was performed. The optimum conditions were determined as pH 8, adsorbent amount of 15 mg, total adsorption-desorption time of 6 min, and enrichment factor of 20. The recovery values of the solid-phase extraction method for water and cosmetic samples under optimum conditions were between 95% and 106%. NH₂-MIL-53(Al)-DES(ChCl-Urea) nanocomposite was an economically advantageous adsorbent because of its reusability of 15 times. All analyses were performed using the ultraviolet-visible spectrophotometer. The linear range, limit of detection, and limit of quantification of the method were 100–1000, 9.80, and 32.68 μg/L, respectively. The obtained results showed that the synthesized nanocomposite is a suitable adsorbent for the determination of Rh 6G in water and cosmetic samples. The real sample applications were verified with the high-performance liquid chromatography system.