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.     

Direct from solid natural products to pure compounds in a single step: Coupling online extraction with high‐speed counter‐current chromatography

Extraction is the most important step in the purification of bioactive compounds from natural products. This study introduces a simple online extraction strategy coupled with high‐speed counter‐current chromatography for efficient extraction and purification of bioactive components from solid natural products. For online extraction strategy, 1.0 g of ground Mangnolia officinalis or Piper nigrum was loaded into a guard column, which was then positioned on the manual injection valve instead of the sample loop. Bioactive components were directly extracted by the mobile phase of high‐speed counter‐current chromatography, and then transferred into high‐speed counter‐current chromatography for purification. In addition, the compatibility of the developed methodology for direct purification of bioactive components from fresh M. officinalis was successfully demonstrated. Obviously, in comparison with traditional offline heat‐reflux extraction, online extraction avoided the instrument, time, solvent, and energy consumption, and purified two phenolic compounds (honokiol and magnolol) from M. officinalis and three alkaloids (piperyline, piperine, and piperanine) from P. nigrum with high extraction efficiency. The superiority of the developed methodology is to establish an easy, rapid, and efficient technique for the purification of a wide variety of bioactive components from solid natural products.     

Hydrogen bonding mediated ion pairs of some aprotic ionic liquids and their structural transition in aqueous solution

Ion pair speciation of ionic liquids(ILs) has an important effect on the physical and chemical properties of ILs and recognition of the structure of ion pairs in solution is essential. It has been reported that ion pairs of some ILs can be formed by hydrogen bonding interactions between cations and anions of them. Considering the fact that far-IR(FIR) spectroscopy is a powerful tool in indicating the intermolecular and intramolecular hydrogen bonding, in this work, this spectroscopic technique has been combined with molecular dynamic(MD) simulation and nuclear magnetic resonance hydrogen spectroscopy(~1H NMR) to investigate ion pairs of aprotic ILs [Bmim][NO_3], [BuPy][NO_3], [Pyr_(14)][NO_3], [PP_(14)][NO_3] and [Bu-choline][NO_3] in aqueous IL mixtures. The FIR spectra have been assigned with the aid of density functional theory(DFT) calculations, and the results are used to understand the effect of cationic nature on the structure of ion pairs. It is found that contact ion pairs formed in the neat aprotic ILs by hydrogen bonding interactions between cation and anion, were still maintained in aqueous solutions up to high water mole fraction(say 0.80 for [BuPy][NO3]). When water content was increased to a critical mole fraction of water(say 0.83 for [BuPy][NO3]), the contact ion pairs could be transformed into solvent-separated ion pairs due to the formation of the hydrogen bonding between ions and water. With the further dilution of the aqueous ILs solution, the solvent-separated ion pairs was finally turned into free cations and free anions(fully hydrated cations or anions). The concentrations of the ILs at which the contact ion pairs were transformed into solvent-separated ion pairs and solvent-separated ion pairs were transformed into free ions(fully hydrated ion) were dependent on the cationic structures. These information provides direct spectral evidence for ion pair structures of the aprotic ILs in aqueous solution. MD simulation and ~1H NMR results support the conclusion drawn from FIR spectra investigations.     

Calorimetric Studies and Structural Aspects of Ionic Liquids in Designing Sorption Materials for Thermal Energy Storage

The thermal properties of a series of twenty‐four ionic liquids (ILs) have been determined by isothermal titration calorimetry (ITC) with the aim of simulating processes involving water sorption. For eleven water‐free ILs, the molecular structures have been determined by X‐ray crystallography in the solid state, which have been used to derive the molecular volumes of the ionic components of the ILs. Moreover, the structures reveal a high prevalence of hydrogen bonding in these compounds. A relationship between the molecular volumes and the experimentally determined energies of dilution could be established. The highest energies of dilution observed in this series were obtained for the acetate‐based ILs, which underlines their potential as working fluids in sorption‐based thermal energy storage systems.     

A facile phenol-driven intramolecular diastereoselective thermal/base-catalyzed dipolar [2+2] annulation reactions: an easy access to complex bioactive natural and unnatural benzopyran congeners

The complex bioactive natural and unnatural benzopyran congeners have been synthesized using one-/two-step approaches in very good yields from the reactions of two different dihydroxyphthalides, natural resorcyclic acid derivative, and trihydroxybenzophenone with citral and/or farnesal, via the phenol-driven intramolecular diastereoselective thermal/base-catalyzed dipolar [2+2] cycloaddition reactions and three different thermal intramolecular cyclization reactions. The effects of the nature and the position of phenolic groups in the starting materials on the course of these cycloaddition reactions have also been described. Depending upon the absence or presence of intramolecular hydrogen bonding of the phenolic group with the carbonyl moiety in the starting materials, these phenol-driven intramolecular thermal/base-catalyzed dipolar [2+2] cycloaddition reactions either furnished the kinetically controlled products or directly formed the thermodynamically controlled rearranged products, respectively.     

Zinc Borohydride-Ionic Liquid： Stable and Efficient System for Reductive Reaction of Aldehydes with Primary Amines to Corresponding Secondary Amines

Ionic liquids（ILs） are attracting much attention in various fields of chemical synthesis, electrochemical applications, liquid-liquid extractions, as well as biotransformations. Among those fields, the application of ILs as the potential green solvent for a wide variety of synthetic processes is an area of intense researches. High yield, high selectivity, and good catalytic charac-teristics have usually been achieved. After the isolation of products, ILs can usually be recovered and recycled many times by simple treating procedures, such as, filtration, extraction, and dryness.     

Extraction of coal-tar pitch using NMP/ILs mixed solvents

Coal-tar pitch(CP)is a promising carbon raw material for producing needle coke,carbon fiber etc.During processing,the H/C ratio,ash content,and quinoline insoluble(QI)in the CP are the key factors that influence the material preparation.In this study,NMP was selected to extract CP first;then[BMIM]Cl/NMP mixed solvent was used;and finally a series of ionic liquids(ILs)mixtures with NMP were developed for the extraction of CP to obtain the refined pitch.The extracts were analyzed via elemental analysis,TGA,FT-IR,and 13C-NMR.Results indicate that different NMP/IL mass ratios or different kinds of ILs have impact on the extraction yield.The relationship of the hydrogen to carbon(H/C)ratio changed with different solvents and QI extracts were obtained.Results showed that the H/C ratios changed little between NMP extracts and could be adjusted by changing the NMP/ILs mass ratio or using different ILs.The extracts are suitable for preparation mesophase pitch because of no ash content,low QI,and appropriate H/C ratios.As a result,NMP can be used to refine pitch.In addition,[BMIM]Cl is good mixed with NMP for CP extraction,because it can obtain a relatively high yield under the same extraction conditions.     

Ionic liquids in sample preparation

Due to their unique properties, their good extractabilities for various target analytes, and the fact that many compounds are highly soluble in them, room-temperature ionic liquids (ILs) are used as promising alternatives to the traditional organic solvents employed in sample preparation. ILs have been used as extraction solvents for a wide range of analytes, from environmental contaminates to biomacromolecules and nanomaterials, and as dissolution solvents for various detection techniques. In this paper, the main applications of ILs in sample preparation are reviewed, and the problems and challenges in this area are described.     

基于低共熔溶剂的萃取分离技术及其应用研究进展

随着绿色化学的发展,开发和应用符合绿色化学要求的溶剂和方法备受关注。作为离子液体类似物,低共熔溶剂(deep eutectic solvent, DES)是通过氢键受体(hydrogen bond acceptor, HBA)和氢键供体(hydrogen bond donator, HBD)的氢键作用而形成的一种混合物,具有环境友好、制备简单、成本低、可生物降解等优点,在很多领域均有越来越广泛的应用。DES可以从不同样品中萃取和分离不同的目标化合物,其作为萃取溶剂具有独特的优势,可以获得较高的萃取效率且样品基质对分析过程的影响较小。在分散液液微萃取(dispersive liquid-liquid micro-extraction, DLLME)程序中,DES可以萃取复杂基质中的残留药物、金属离子和生物活性成分;与传统的萃取方法相比,该方法具有对有机试剂需求少,萃取效率更高等明显优势。而且,在DLLME中加入DES作为分散剂,能够加速萃取剂在样品溶液中的扩散,具有小型化、成本低等优点。相比于传统分散剂甲醇、乙腈的高挥发性、易燃性,DES的高稳定性、低毒性使其在绿色化学领域中更具有优势,应用更广。因此,DES与DLLME的结合近年来发展迅速。不仅如此,DES与固相萃取联合应用也具有广泛的应用前景,在与固相萃取小柱和搅拌棒联合应用时,DES可以作为洗脱剂,氢键供体及氢键给体的用量之比是洗脱效率的重要考察因素之一。在与磁性材料联用时,DES能与磁性多壁碳纳米管、磁性氧化石墨烯等纳米复合材料结合,通过氢键、π-π作用力和静电作用力等特异性吸附目标分析物。并且能够参与磁性凝胶和分子印迹聚合物的合成,推动磁性材料向绿色化学的方向发展,进一步拓展DES的应用。作为一类新兴的绿色溶剂,DES在化合物的萃取分离技术方面受到广泛关注,在不同的萃取技术中扮演了不同的角色,并表现出良好的性能,因此逐渐成为绿色化学领域的研究重点。该文整合了DES在萃取分离技术中的研究进展,介绍了DES的制备、性质和分类,对DES在DLLME和固相萃取中的应用进行了总结和归类,并展望了DES在萃取分离技术中的应用前景,为DES未来的应用提供参考。     

Ionic liquid-assisted carboxylation of amines by CO2: a mechanistic consideration

The catalytic roles of ionic liquids (ILs) in the syntheses of 1,3-disubstituted ureas from the carboxylation of amines by CO(2) were experimentally and theoretically investigated. The carboxylation reaction of n-butylamine was greatly facilitated by the presence of an IL and the catalytic activity of the IL was strongly affected by the nucleophilicity of the anion. Computational study on the mechanistic aspects of the carboxylation with methylamine with or without the presence of an IL, 1-ethyl-3-methylimidazolium chloride, implies that the activation energies of the transition states and the intermediate ionic species could be lowered significantly through the multi-interactions of the carbonyl group of CO(2) with both cations and anions of the ILs.     

Dissecting the Vaporization Enthalpies of Ionic Liquids by Exclusively Experimental Methods: Coulomb Interaction,Hydrogen Bonding,and Dispersion Forces

The quantification of hydrogen bonding and dispersion energies from vaporization enthalpies is a great challenge. Dissecting interaction energies is particularly difficult for ionic liquids (ILs), for which the composition of the different types of interactions is known neither for the liquid nor for the gas phase. In this study, we demonstrate the existence of ion pairs in the gas phase and dissect the interaction energies exclusively from measured vaporization enthalpies of different alkylated protic ILs (PILs) and aprotic ILs (AILs) and the molecular analogues of their cations. We demonstrate that the evaporated ion pairs are characterized by H‐bond‐enhanced Coulomb interaction. The overall interaction energy for the ILs in the bulk phase is composed of Coulomb interaction (76 kJ mol^?1), hydrogen bonding (38 kJ mol^?1), and minor dispersion interaction (10 kJ mol^?1). Thus, hydrogen bonding prominently contributes to the overall interaction energy of PILs, which is reflected in the properties of this class of liquids.     

汽爆技术促进中药资源高值化利用

汽爆技术在中药资源高值化利用中发挥的作用正在逐渐体现:汽爆处理打破中药植物细胞壁的屏障结构,有利于有效成分的分离提取;汽爆过程物料自体水解发生去糖苷化作用使天然植物中的苷元与糖基分离,提高苷类物质提取和分离效率;汽爆应用于中药炮制和中药脱毒有高效、快速和避免有效成分流失等优点;汽爆处理有利于中药非药用组分如纤维素、半纤维素等的有效分离和利用,联产乙醇、丁醇等能源和化工产品。本文对汽爆技术在中药资源高值化利用中的研究进展进行了综述。     

Characterization of essential oil recovered from fennel horticultural wastes

Fennel crop has been traditionally used as spice in cooking and fragrances, and in folk medicine for its spectrum of useful properties. Mediterranean is the elective natural cultivation area for this plant with Italy being a leader producer. A limit of this production is due to the high amount of wastes derived still rich of phytochemicals, which are usually underused. Hence, the extraction and characterization of essential oil from residues of fennel horticultural market was investigated to understand the potential profit of their recycling. Forty-eight compounds resulted for fennel oil waste, analysed by GC-FID-MS, with the most abundant among components was anethole. Other constituents contributing to fennel flavour were the monoterpenes limonene and nerol. The exploitation of this oil as a good source of bioactive compounds was assessed by means of its antioxidant power measured with DPPH test.     

Effect of water on the molecular structure and arrangement of nitrile-functionalized ionic liquids

Water changes the physical properties of ionic liquids (ILs). In this paper, the effect of water on ILs is investigated at the molecular level. The molecular structure and arrangement of 1-butyronitrile-3-methylimidazolium halide, in the presence and absence of the intruded water molecule, have been elucidated by single-crystal X-ray crystallography and near-infrared Raman spectroscopy. Water molecule is found to change the conformation of the n-butyronitrile chain of the cation. The hydrogen bonding interaction between the anion and water molecule, leading to loose molecular packing, is most likely to be responsible for the change. Distinct molecular structures and arrangements of ILs with and without water molecule have been presented here for the first time. As the unique properties of ILs are related to their structures and molecular arrangements, the presence of water, wanted or unwanted, must be carefully examined in any kind of IL research and applications.     

Optimization of the extraction process of flavonoids from Trollius ledebouri with natural deep eutectic solvents

In recent years, natural deep eutectic solvents have been favored greatly due to their environment friendly, mild biological toxicity and simple biodegradability. Natural deep eutectic solvents gradually applied for the extracting bioactive compounds from natural products efficiently. In this study, 20 natural deep eutectic solvents were prepared and their physical and chemical properties were tested. The ultrasonic-assisted extraction method was used to extract flavonoids from Trollius ledebouri and high-performance liquid chromatography-ultraviolet was applied to examine two main bioactive flavonoids (orientin and vitexin). Compared with traditional solvents (water and 60% ethanol solution), natural deep eutectic solvents composed of L(-)-proline and levulinic acid (molar ratio 1:2) show a super extraction efficiency. On this basis, the response surface method was used to optimize the extraction temperature, extraction time, water contents, and solid–liquid ratio. As a consequence, the extraction temperature 60℃, extraction time 18 min, water content 14% (v/v), and the solid–liquid ratio 48 mL·g⁻¹ were chosen as the best extraction process. This study shows that natural deep eutectic solvents can effectively extract flavonoids from T. ledebouri, laying a foundation for the further application of natural deep eutectic solvents to extract bioactive compounds from natural products.     

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.     

Hydrogen bonds: a structural insight into ionic liquids

Ionic liquids (ILs) have attracted intensive attention in academia and industry due to their unique properties and potential applications. Nowadays, much interest is focused on finding out what is the main force that determines the properties of ionic liquids. Intuitively like NaCl, in high-temperature molten salt (HTMS) the electrostatic Coulomb force is regarded as the dominant factor that determines the behaviors of ILs. However, a large amount of evidence indicates that such a molten-salt-based simplified explanation is not consistent with the corresponding experimental results. Besides the Coulomb force, the hydrogen bond is another important noncovalent interaction in the IL and is closely related to some important properties and applications, as suggested in some new research results. Therefore in this review, we present results concerning the hydrogen bond in ILs, from the perspective of experiment and calculation, to shed light on its effects and roles. The deep insights into structure, in particular the hydrogen bonds, can provide us with a rational design for the new ILs to fulfill the demands in some complicated chemical processes.     

Sulfur and sulfur compounds in plant defence

The multiplicity of chemical structures of sulfur containing compounds, influenced in part by the element's several oxidation states, directly results in diverse modes of action for sulfur-containing natural products synthesized as secondary metabolites in plants. Sulfur-containing natural products constitute a formidable wall of defence against a wide range of pathogens and pests. Steady progress in the development of new technologies have advanced research in this area, helping to uncover the role of such important plant defence molecules like endogenously-released elemental sulphur, but also deepening current understanding of other better-studied compounds like the glucosinolates. As studies continue in this area, it is becoming increasingly evident that sulfur and sulfur compounds play far more important roles in plant defence than perhaps previously suspected.     

Ionic liquids: solvents and sorbents in sample preparation

The applications of ionic liquids (ILs) and IL‐derived sorbents are rapidly expanding. By careful selection of the cation and anion components, the physicochemical properties of ILs can be altered to meet the requirements of specific applications. Reports of IL solvents possessing high selectivity for specific analytes are numerous and continue to motivate the development of new IL‐based sample preparation methods that are faster, more selective, and environmentally benign compared to conventional organic solvents. The advantages of ILs have also been exploited in solid/polymer formats in which ordinarily nonspecific sorbents are functionalized with IL moieties in order to impart selectivity for an analyte or analyte class. Furthermore, new ILs that incorporate a paramagnetic component into the IL structure, known as magnetic ionic liquids (MILs), have emerged as useful solvents for bioanalytical applications. In this rapidly changing field, this Review focuses on the applications of ILs and IL‐based sorbents in sample preparation with a special emphasis on liquid phase extraction techniques using ILs and MILs, IL‐based solid‐phase extraction, ILs in mass spectrometry, and biological applications.     

Understanding the mechanism of cellulose dissolution in 1-butyl-3-methylimidazolium chloride ionic liquid via quantum chemistry calculations and molecular dynamics simulations

While N,N′-dialkylimidazolium ionic liquids (ILs) have been well-established as effective solvents for dissolution and processing of cellulose, the detailed mechanism at the molecular level still remains unclear. In this work, we present a combined quantum chemistry and molecular dynamics simulation study on how the ILs dissolve cellulose. On the basis of calculations on 1-butyl-3-methylimidazolium chloride, one of the most effective ILs dissolving cellulose, we further studied the molecular behavior of cellulose models (i.e. cellulose oligomers with degrees of polymerization n = 2, 4, and 6) in the IL, including the structural features and hydrogen bonding patterns. The collected data indicate that both chloride anions and imidazolium cations of the IL interact with the oligomer via hydrogen bonds. However, the anions occupy the first coordination shell of the oligomer, and the strength and number of hydrogen bonds and the interaction energy between anions and the oligomer are much larger than those between cations and the oligomer. It is observed that the intramolecular hydrogen bond in the oligomer is broken under the combined effect of anions and cations. The present results emphasize that the chloride anions play a critically important role and the imidazolium cations also present a remarkable contribution in the cellulose dissolution. This point of view is different from previous one that only underlines the importance of the chloride anions in the cellulose dissolution. The present results improve our understanding for the cellulose dissolution in imidazolium chloride ILs.