New horizons in the extraction of bioactive compounds using deep eutectic solvents: A review

Desulfurization Performance of Choline Chloride-Based Deep Eutectic Solvents in the Presence of Graphene Oxide

Extractive catalytic oxidative desulfurization (ECODS) is the one of the recent methods used in fuel desulfurization which involved the use of catalyst in the oxidative desulfurization of diesel fuel. This study is aimed to test the effectiveness of synthesized choline chloride (ChCl) based deep eutectic solvent (DES) in fuel desulfurization via ECODS method, with the presence of graphene oxide (GO) as catalyst and hydrogen peroxide (H2O2) as oxidant. In this study, 16 DESs based on choline chloride were synthesized using glycerol (GLY), ethylene glycol (EG), tetraethylene glycol (TEG) and polyethylene glycol (PEG). The characterization of the synthesized DES was carried out via Fourier transform infrared spectroscopy (FTIR) analysis, density, and viscosity determination. According to the screening result, ChCl-PEG (1:4) was found to be the most effective DES for desulfurization using ECODS method, with a removal of up to 47.4% of sulfur containing compounds in model oil in just 10 min per cycle after the optimization of the reaction parameters, and up to 95% desulfurization efficiency could be achieved by six cycles of desulfurization. It is found that the addition of GO as catalyst does not increase the desulfurization performance drastically; hence, future studies for the desulfurization performance of DESs made up from ChCl and PEG and its derivatives can be done simply by using extraction desulfurization (EDS) method instead of ECODS method, for cost reduction purpose and easier regulation of DES waste into environment.

Innovative Extraction Techniques Using Deep Eutectic Solvents and Analytical Methods for the Isolation and Characterization of Natural Bioactive Compounds from Plant Material

The growing interest of the food, pharmaceutical and cosmetics industries in naturally occurring bioactive compounds or secondary plant metabolites also leads to a growing demand for the development of new and more effective analysis and isolation techniques. The extraction of bioactive compounds from plant material has always been a challenge, accompanied by increasingly strict control requirements for the final products and a growing interest in environmental protection. However, great efforts have been made in this direction and today a considerable number of innovative extraction techniques have been developed using green, environmentally friendly solvents. These solvents include the deep eutectic solvents (DES) and their natural equivalents, the natural deep eutectic solvents (NADES). Due to their adjustable physical-chemical properties and their green character, it is expected that DES/NADES could be the most widely used solvents in the future, not only in extraction processes but also in other research areas such as catalysis, electrochemistry or organic synthesis. Consequently, this review provided an up-to-date systematic overview of the use of DES/NADES in combination with innovative extraction techniques for the isolation of bioactive compounds from various plant materials. The topicality of the field was confirmed by a detailed search on the platform WoS (Web of Science), which resulted in more than 100 original research papers on DES/NADES for bioactive compounds in the last three years. Besides the isolation of bioactive compounds from plants, different analytical methods are presented and discussed.

A green extraction design for enhancing flavonoid compounds from Ixora javanica flowers using a deep eutectic solvent

In this study, an environmentally friendly extraction method for flavonoid compound from Ixora javanica, as a new raw material candidate for herbal medicine and cosmetics, was developed. The objectives of the present work were to provide recommendations for the optimal extraction conditions and to investigate the effects of any extraction parameters on flavonoid yields from the I. javanica flower. The extraction process was performed using deep eutectic solvent (DES) (choline chloride and propylene glycol at molar ratio of 1 : 1) and the ultrasound-assisted extraction method. Both single-factor and response surface analyses using three-level and three-factor Box Behnken designs were conducted to obtain the optimum flavonoid concentrations. The results showed that the optimum extraction conditions for total flavonoids featured an extraction time of 40 min, 25% water content in DES and a solid-to-liquid ratio of 1 : 25 g ml-1. An extract obtained under optimum extraction conditions showed higher total flavonoid yields than an ethanolic extract which was used for comparison. Scanning electron microscope images demonstrated that both of the solvents also showed different effects on the outer surface of the I. javanica flower during the extraction process. In summary, our work succeeded in determining the optimum conditions for total flavonoids in the I. javanica flower using a green extraction method.

A Review of the Use of Eutectic Solvents, Terpenes and Terpenoids in Liquid–liquid Extraction Processes

Diverse and abundant applications of the eutectic solvents have appeared in the last years. Their promising tunable properties, eco-friendly character and the possibility of being prepared from numerous compounds have led to the publication of numerous papers addressing their use in different areas. Terpenes and terpenoids have been employed in the formulation of eutectic solvents, though they also have been applied as solvents in extraction processes. For their hydrophobic nature, renewable character, low environmental impact, cost and being non-hazardous, they have also been proposed as possible substitutes of conventional solvents in the separation of organic compounds from aqueous streams, similarly to hydrophobic eutectic solvents. The present work reviews the application of eutectic solvents in liquid–liquid extraction and terpenes and terpenoids in extraction processes. It has been made a research in the current state-of-the-art in these fields, describing the proposed applications of the solvents. It has been highlighted the scale-up feasibility, solvent regeneration and reuse procedures and the comparison of the performance of eutectic solvents, terpenes and terpenoids in extraction with conventional organic solvents or ionic liquids. Ultimately, it has been also discussed the employ of predictive methods in extraction, the reliability of thermodynamic models in correlation of liquid–liquid equilibria and simulation of liquid–liquid extraction processes.

Understanding the Formation of Deep Eutectic Solvents: Betaine as a Universal Hydrogen Bond Acceptor

The mechanism of formation of betaine-based deep eutectic solvents (DES) is presented for the first time. Due to its polarity unbalance, it was found that betaine displays strong negative deviations from ideality when mixed with a variety of different organic substances. These results pave the way for a comprehensive design of novel deep eutectic solvents. A connection to biologically relevant systems was made using betaine (osmolyte) and urea (protein denaturant), showing that these two compounds formed a DES, the molecular interactions of which were greatly enhanced in the presence of water.

On the Physicochemical Characteristics and Applications of an "Undesirable" Pyrenean Thorny Cushion Dwarf: Echinospartum horridum (Vahl) Roth

Small evergreen shrubs of the family Fabaceae represent a large proportion of current Mediterranean mountain vegetation. Their low pastoral value and tendency for encroachment makes these plants undesirable. In this paper, the thermal and chemical characteristics of Echinospartum horridum, a thorny cushion-shaped dwarf shrub native to the French Central Massif and the Pyrenees (particularly dominant in the shrublands of the Pyrenees), have been analyzed with a view to its valorization. Although the higher and lower heating values of the biomass from E. horridum met the ISO 17225-2:2014 requirements for its use in pellets, the ash content was slightly above the upper limit, so it would not comply with the normative for its acceptable use as a fuel. Nevertheless, the presence of high added-value flavonoids and lignans in its extracts, which are receiving increasing recent interest as efficient anti-tumor drugs and antivirals, may open the door to the valorization of this shrub for pharmacological applications.

A novel sustainable approach for the extraction of value-added compounds from Hibiscus sabdariffa L. calyces by natural deep eutectic solvents

Hibiscus sabdariffa L. is widely acknowledged as an important source of value-added compounds as natural pigments and bioactive compounds whose isolation is of great interest in food industry. Due to the incessant demand of green extraction procedures, NADESs have emerged in the last years as new green solvents alternative to the conventional organic ones. The feasibility of NADESs for the extraction of value-added compounds of H. sabdariffa has been assessed in this work for the first time. An extraction technique based on microwave assisted extraction (MAE) and the use of NADESs was proposed testing different deep eutectic solvents based on choline chloride (ChCl). Among them, oxalic acid based NADES exhibited a great selectivity for anthocyanins in particular as well as higher extraction yields of bioactive compounds was also observed, even greater than those observed by methanol. The effect of extraction variables such as liquid-solid ratio, temperature and water percentage were studied by Box-Behnken design and a response surface methodology. The statistical program pointed out the liquid-solid ratio of 1:30 mL mg^-1, temperature of 75 °C and a water percentage of 55% as the conditions to maximize extraction within the experimental domain. Hence, NADES composed by oxalic acid and choline chloride resulted to be an effective green alternative tailor-made solvent to carry out selective extractions of value-added compounds from H. sabdariffa.

Secondary Bioactive Metabolites from Plant-Derived Food Byproducts through Ecopharmacognostic Approaches: A Bound Phenolic Case Study

The climate emergency and the risks to biodiversity that the planet is facing nowadays, have made the management of food resources increasingly complex but potentially interesting. According to FAO, one-third of the edible parts of food produced throughout the whole food supply chain gets lost or wasted globally every year. At the same time, demographic growth makes it necessary to change course toward sustainable economic development in order to satisfy market demands. The European Union supported the idea of a Circular Economy from 2015 and arranged annual Action Plans toward a greener, climate-neutral economy. Following the biorefinery concept, food waste becomes byproducts that can be recovered and exploited as high added-value materials for industrial applications. The use of sustainable extraction processes to manage food byproducts is a task that research has to support through the development of low environmental impact strategies. This review, therefore, aims to take stock of the possibilities of extracting molecules from food waste biomass following ecopharmacognostic approaches inspired by green chemistry guidelines. In particular, the use of innovative hybrid techniques to maximize yields and minimize the environmental impact of processes is reviewed, with a focus on bound phenolic extractions.

Structure and properties of two glucose-based deep eutectic systems

Continued industrialization and increasing environmental problems have highlighted the need to research new eco-friendly solvents, also known as deep eutectic solvents (DESs). To implement these solvents in industrial processes, the knowledge of their molecular organization and thermophysical properties must be enhanced. In this work, two DESs have been characterized: d-glucose:choline chloride:water (GCH) and d-glucose:citric acid:water (GCiH). NMR techniques were used to analyse both the supramolecular structure and the role of water and to calculate the diffusion coefficients. Moreover, seven thermophysical properties at several temperatures were evaluated. As a second aim, the solubility of quercetin was determined. NMR studies showed a stronger supramolecular structure of GCH and a high ratio of β-glucose in both DESs. Based on the thermophysical results, the solvent with choline chloride had the most compact fluid structure. Finally, the solubility of quercetin in the DESs was higher than in water, especially for GCH.

Emerging Technologies for the Extraction of Marine Phenolics: Opportunities and Challenges

Natural phenolic compounds are important classes of plant, microorganism, and algal secondary metabolites. They have well-documented beneficial biological activities. The marine environment is less explored than other environments but have huge potential for the discovery of new unique compounds with potential applications in, e.g., food, cosmetics, and pharmaceutical industries. To survive in a very harsh and challenging environment, marine organisms like several seaweed (macroalgae) species produce and accumulate several secondary metabolites, including marine phenolics in the cells. Traditionally, these compounds were extracted from their sample matrix using organic solvents. This conventional extraction method had several drawbacks such as a long extraction time, low extraction yield, co-extraction of other compounds, and usage of a huge volume of one or more organic solvents, which consequently results in environmental pollution. To mitigate these drawbacks, newly emerging technologies, such as enzyme-assisted extraction (EAE), microwave-assisted extraction (MAE), ultrasound-assisted extraction (UAE), pressurized liquid extraction (PLE), and supercritical fluid extraction (SFE) have received huge interest from researchers around the world. Therefore, in this review, the most recent and emerging technologies are discussed for the extraction of marine phenolic compounds of interest for their antioxidant and other bioactivity in, e.g., cosmetic and food industry. Moreover, the opportunities and the bottleneck for upscaling of these technologies are also presented.

F. R. Ferreira I, Ferreira O. Insights on the Extraction Performance of Alkanediols and Glycerol: Using Juglans regia L. Leaves as a Source of Bioactive Compounds

Glycerol and alkanediols are being studied as alternative solvents to extract phytochemicals from plant material, often as hydrogen bond donors in deep eutectic solvents (DESs). Many of those alcohols are liquid at room temperature, yet studies of their use as extraction solvents are scarce. In this work, glycerol and a series of alkanediols (1,2-ethanediol, 1,2-propanediol, 1,3-propanediol, 1,3-butanediol, 1,2-pentanediol, 1,5-pentanediol, and 1,2-hexanediol) were studied for the extraction of phenolic compounds from Juglans regia L. leaves, a rich source of this class of bioactive compounds. The extraction yield was quantified, and the bioactivity of both extracts and pure solvents was evaluated by measuring the anti-inflammatory and cytotoxic activities. The solvents showing the best combined results were 1,2 and 1,3-propanediol, as their extracts presented a high amount of phenolic compounds, close to the results of ethanol, and similar cytotoxicity against cervical carcinoma cells, with no impact on non-tumor porcine liver cells in the studied concentration range. On the other hand, none of the extracts (and solvents) presented anti-inflammatory activity. Overall, the results obtained in this work contribute to the study of alternative solvents that could potentially be used also as formulation media, highlighting the importance of walnut leaves as a source of bioactive compounds.

Investigation of Total Phenolic Content and Antioxidant Activities of Spruce Bark Extracts Isolated by Deep Eutectic Solvents

Extracts from spruce bark obtained using different deep eutectic solvents were screened for their total phenolic content (TPC) and antioxidant activities. Water containing choline chloride-based deep eutectic solvents (DESs) with lactic acid and 1,3-propanediol, 1,3-butanediol, 1,4-butanediol, and 1,5-pentanediol, with different molar ratios, were used as extractants. Basic characteristics of the DESs (density, viscosity, conductivity, and refractive index) were determined. All the DESs used behave as Newtonian liquids. The extractions were performed for 2 h at 60 °C under continuous stirring. TPC was determined spectrophotometrically, using the Folin-Ciocalteu reagent, and expressed as gallic acid equivalent (GAE). The antioxidant activity was determined spectrophotometrically by 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging assay. The TPC varied from 233.6 to 596.2 mg GAE/100 g dry bark; radical scavenging activity (RSA) ranged between 81.4% and 95%. This study demonstrated that deep eutectic solvents are suitable solvents for extracting phenolic compounds from spruce bark.

Bioactive Phenolic Compounds From Agri-Food Wastes: An Update on Green and Sustainable Extraction Methodologies

Phenolic compounds are broadly represented in plant kingdom, and their occurrence in easily accessible low-cost sources like wastes from agri-food processing have led in the last decade to an increase of interest in their recovery and further exploitation. Indeed, most of these compounds are endowed with beneficial properties to human health (e.g., in the prevention of cancer and cardiovascular diseases), that may be largely ascribed to their potent antioxidant and scavenging activity against reactive oxygen species generated in settings of oxidative stress and responsible for the onset of several inflammatory and degenerative diseases. Apart from their use as food supplements or as additives in functional foods, natural phenolic compounds have become increasingly attractive also from a technological point of view, due to their possible exploitation in materials science. Several extraction methodologies have been reported for the recovery of phenolic compounds from agri-food wastes mostly based on the use of organic solvents such as methanol, ethanol, or acetone. However, there is an increasing need for green and sustainable approaches leading to phenolic-rich extracts with low environmental impact. This review addresses the most promising and innovative methodologies for the recovery of functional phenolic compounds from waste materials that have appeared in the recent literature. In particular, extraction procedures based on the use of green technologies (supercritical fluid, microwaves, ultrasounds) as well as of green solvents such as deep eutectic solvents (DES) are surveyed.

Deep Eutectic Solvents Based on Natural Ascorbic Acid Analogues and Choline Chloride

Deep eutectic solvents (DES) are one of the most promising green technologies to emerge in recent years given their combination of environmentally friendly credentials and useful functionalities. Considering the continued search for new DES - especially those that exemplify the aforementioned characteristics, we report the preparation of DES based on natural analogues of l-ascorbic acid for the first time. The onset of eutectic melting occurred at temperatures far below the melting point of the individual components and resulted in the generation of glass forming fluids with glass transition temperatures, viscosities and flow behavior that are comparable to similar systems. This work expands the current array of DES that can be produced using naturally occurring components, which given their potential to be bio-derived, interesting physicochemical properties (e. g. propensity to supercool and vitrify) and apparent antibacterial nature, may provide utility within a range of applications.

Natural Deep Eutectic Solvents for the Extraction of Phenyletanes and Phenylpropanoids of Rhodiola rosea L

The extraction of Rhodiola rosea rhizomes using natural deep eutectic solvent (NADES) consisting of lactic acid, glucose, fructose, and water was investigated. A two-level Plackett-Burman design with five variables, followed by the steepest ascent method, was undertaken to determine the optimal extraction conditions. Among the five parameters tested, particle size, extraction modulus, and water content were found to have the highest impact on the extrability of phenyletanes and phenylpropanoids. The concentration of active compounds was analyzed by HPLC. The predicted results showed that the extraction yield of the total phenyletanes and phenylpropanoids (25.62 mg/g) could be obtained under the following conditions: extraction time of 154 min, extraction temperature of 22 °C, extraction modulus of 40, molar water content of 5:1:11 (L-lactic acid:fructose:water, mol/mol), and a particle size of rhizomes of 0.5-1 mm. These predicted values were further verified by validation experiments in predicted conditions. The experimental yields of salidroside, tyrosol, rosavin, rosin, cinnamyl alcohol and total markers (sum of phenyletanes and phenylpropanoids in mg/g) were 11.90 ± 0.02, 0.36 ± 0.02, 12.23 ± 0.21, 1.41 ± 0.01, 0.20 ± 0.01, and 26.10 ± 0.27 mg/g, respectively, which corresponded well with the predicted values from the models.

Extraction for profiling free and bound phenolic compounds in tea seed oil by deep eutectic solvents

Bound phenolic compounds have rarely been reported in vegetable oils and this may be due to little research about the extraction. Deep eutectic solvents (DESs), recently applied in the extraction of phenolic compounds as alternatives to organic solvents, were adopted in the extraction of free and bound phenolic compounds from tea seed oil in this work. First, the phenolic compounds were analyzed by ultra-high-performance liquid chromatography with quadrupole-time-of-flight and triple-quadrupole tandem mass spectrometry (UHPLC-Q-TOF-MS/MS) for characterization and UHPLC-QqQ-MS/MS for quantification and 25 phenolic compounds were found to exist in both free and bound forms. Then, DESs were screened for extraction of free and bound phenolic compounds from tea seed oil as the pretreatment for analysis and the results showed that hydrogen bond donors (HBDs) and temperature significantly affected the extraction efficiency of DESs. Finally, free phenolic compounds (83.91 µg/g) and bound phenolic compounds (25.71 µg/g), extracted by the DES with glycerol as HBD at 50 °C, were 51.0% and 93.2% higher than those extracted by methanol/water (60%, v/v), respectively. This work not only advanced the basic data of phenolic compounds in tea seed oil but also explored an efficient extraction method for scientific analysis of free and bound phenolic compounds.

A Global Model for the Estimation of Speeds of Sound in Deep Eutectic Solvents

Deep eutectic solvents (DESs) are newly introduced green solvents that have attracted much attention regarding fundamentals and applications. Of the problems along the way of replacing a common solvent by a DES, is the lack of information on the thermophysical properties of DESs. This is even more accentuated by considering the dramatically growing number of DESs, being made by the combination of vast numbers of the constituting substances, and at their various molar ratios. The speed of sound is among the properties that can be used to estimate other important thermodynamic properties. In this work, a global and accurate model is proposed and used to estimate the speed of sound in 39 different DESs. This is the first general speed of sound model for DESs. The model does not require any thermodynamic properties other than the critical properties of the DESs, which are themselves calculated by group contribution methods, and in doing so, make the proposed method entirely independent of any experimental data as input. The results indicated that the average absolute relative deviation percentages (AARD%) of this model for 420 experimental data is only 5.4%. Accordingly, based on the achieved results, the proposed model can be used to predict the speeds of sound of DESs.

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 Extraction of Alkaloids and Polyphenols from Peumus boldus Leaves with Natural Deep Eutectic Solvents and Profiling by HPLC-PDA-IT-MS/MS and HPLC-QTOF-MS/MS

Peumus boldus Mol., is a Chilean medicinal tree used for gastrointestinal and liver diseases. Such medicinal properties are associated with the presence of bioactive flavonoids and aporphine alkaloids. In this study, a new green and efficient extraction method used seven natural deep eutectic solvents (NADES) as extraction media. The extraction efficiency of these NADES was assessed, determining the contents of boldine and total phenolic compounds (TPC). Chemical profiling of P. boldus was done by high-performance liquid chromatography coupled to photo diode array detector and electrospray ion-trap mass spectrometry (HPLC-PDA-ESI-IT/MS) and electrospray ionization quadrupole time-of-flight high-resolution mass spectrometry (HPLC-ESI-QTOF-MS). Among the NADES tested, NADES4 (choline chloride-lactic acid) and NADES6 (proline-oxalic acid) enable better extraction of boldine with 0.427 ± 0.018 and 2.362 ± 0.055 mg of boldine g^-1 of plant, respectively. Extraction of boldine with NADES4 and NADES6 was more efficient than extractions performed with methanol and water. On the other hand, the highest TPC were obtained using NADES6, 179.442 ± 3.79 mg of gallic acid equivalents (GAE g^-1). Moreover, TPC in extracts obtained with methanol does not show significant differences with NADES6. The HPLC-PAD-MS/MS analysis enable the tentative identification of 9 alkaloids and 22 phenolic compounds. The results of this study demonstrate that NADES are a promising green extraction media to extract P. boldus bioactive compounds and could be a valuable alternative to classic organic solvents.

Doxorubicin Loading on Functional Graphene as a Promising Nanocarrier Using Ternary Deep Eutectic Solvent Systems

The application of graphene in the field of drug delivery has attracted massive interest among researchers. However, the high toxicity of graphene has been a drawback for its use in drug delivery. Therefore, to enhance the biocompatibility of graphene, a new route was developed using ternary natural deep eutectic solvents (DESs) as functionalizing agents, which have the capability to incorporate various functional groups and surface modifications. Physicochemical characterization analyses, including field emission scanning electron microscope, fourier-transform infrared spectroscopy, Raman spectroscopy, Brunauer-Emmett-Teller, X-ray diffraction, and energy dispersive X-ray, were used to verify the surface modifications introduced by the functionalization process. Doxorubicin was loaded onto the DES-functionalized graphene. The results exhibited significantly improved drug entrapment efficiency (EE) and drug loading capacity (DLC) compared with pristine graphene and oxidized graphene. Compared with unfunctionalized graphene, functionalization with DES choline chloride (ChCl):sucrose:water (4:1:4) resulted in the highest drug loading capacity (EE of 51.84% and DLC of 25.92%) followed by DES ChCl:glycerol:water (1:2:1) (EE of 51.04% and DLC of 25.52%). Following doxorubicin loading, graphene damaged human breast cancer cell line (MCF-7) through the generation of intracellular reactive oxygen species (>95%) and cell cycle disruption by increase in the cell population at S phase and G2/M phase. Thus, DESs represent promising green functionalizing agents for nanodrug carriers. To the best of our knowledge, this is the first time that DES-functionalized graphene has been used as a nanocarrier for doxorubicin, illustrating the potential application of DESs as functionalizing agents in drug delivery systems.

Application of Deep Eutectic Solvents for the Extraction of Rutin and Rosmarinic Acid from Satureja montana L. and Evaluation of the Extracts Antiradical Activity

Satureja montana L. was used in the current research as the plant exhibits numerous health-promoting benefits due to its specific chemical composition. The extraction method based on deep eutectic solvents (DESs) was used for the extraction of rutin and rosmarinic acid from this plant. Five different choline chloride-based DESs with different volumes of water (10%, 30%, and 50% (v/v)) were used for the extraction at different temperatures (30, 50, and 70 °C) to investigate the influence on rosmarinic acid and rutin content obtained by high-performance liquid chromatography with diode-array detector (HPLC-DAD) in the obtained extracts. A principal component analysis was employed to explore and visualize the influence of applied parameters on the efficiency of the extraction procedure of rutin and rosmarinic acid. Among the tested DESs, choline chloride:lactic acid (mole ratio 1:2) and choline chloride:levulinic acid (mole ratio 1:2) were the most suitable for the extraction of rutin, while for rosmarinic acid choline chloride:urea (mole ratio 1:2) was the most effective solvent. The extract showing the best antiradical activity was obtained with choline chloride:urea (mole ratio 1:1) at 30 °C and 50% H₂O (v/v).

Innovative Approaches for Recovery of Phytoconstituents from Medicinal/Aromatic Plants and Biotechnological Production

Continuously growing demand for plant derived therapeutic molecules obtained in a sustainable and eco-friendly manner favors biotechnological production and development of innovative extraction techniques to obtain phytoconstituents. What is more, improving and optimization of alternative techniques for the isolation of high value natural compounds are issues having both social and economic importance. In this critical review, the aspects regarding plant biotechnology and green downstream processing, leading to the production and extraction of increased levels of fine chemicals from both plant cell, tissue, and organ culture or fresh plant materials and the remaining by-products, are discussed.

Deep eutectic solvents for biocatalytic transformations: focused lipase-catalyzed organic reactions

Biocatalysis is a green and sustainable technology for which the ideal solvent should be nontoxic, biocompatible, biodegradable, and sustainable, in addition to supporting high enzyme activity and stability. Deep eutectic solvents (DESs), a novel class of green solvents, have recently emerged as excellent alternatives for use in various biocatalytic reactions and, in particular, in lipase-catalyzed reactions with enzymes. This review discusses the achievements that have been made so far in the use of DESs as reaction media for lipase-catalyzed reactions. In addition, the application of DESs in esterification, transesterification, and amidation reactions with isolated or immobilized biocatalysts, toward enabling the synthesis of biodiesels, sugar esters, phenolipids, and fatty acyl ethanolamides, is summarized, while advances in lipase-catalyzed chemoenzymatic epoxidation reactions, C-C bond-forming Aldol reactions, and hydrolysis reactions in DESs are also discussed. This review also summarize some remaining questions concerning the use of DESs, including the intriguing role of water as a cosolvent in biocatalytic reactions carried out in DESs, and the relationship between the nature of the DESs and their influence on the enzyme stability and activity at the molecular level.

Ultrasound-assisted extraction of bioactive alkaloids from Phellodendri amurensis cortex using deep eutectic solvent aqueous solutions

ChCl/citric acid-based DESs are demonstrated to be effective green solvents for the ultrasound-assisted extraction of bioactive alkaloids from herbs.

Application and optimization of ultrasound-assisted deep eutectic solvent for the extraction of new skin-lightening cosmetic materials from Ixora javanica flower

The high demand for cosmetics has had a great impact on the development of innovative products in the cosmetic industry. The availability of raw materials has become a common problem in the cosmetic industry. Materials from nature can act as alternative sources, such as Ixora javanica. Several studies have shown the potential of I. javanica as an antioxidant and skin lightening agent. The objectives of the present study were to develop and optimize a green ultrasound-assisted deep eutectic solvent extraction of I. javanica. Eleven deep eutectic solvents were evaluated based on extraction efficiency parameters; that is, flavonoid and anthocyanin yields; the antioxidant and tyrosinase inhibitory activities of the extracts. The combination of choline chloride and propylene glycol (1:1) was shown to be the optimal deep eutectic solvent for I. javanica extraction. The extraction parameters of temperature, extraction time, and solid-to-liquid ratio were also optimized using response surface methodology. The total flavonoid compound obtained was 33 mg quercetin equivalent/g dried sample under the optimum extraction condition (extraction time of 5 min, temperature of 57 °C, solid-to-liquid ratio of 0.02 g/mL). In sum, this work demonstrates the potential of natural deep eutectic solvent as an organic solvent replacement to obtain high quality Ixora javanica extract, which is a potential new source of skin-lightening cosmetic materials.

Sequential ultrasonication and deep eutectic solvent pretreatment to remove lignin and recover xylose from oil palm fronds

This study demonstrated the effect of two-pot sequential pretreatment, comprising of ultrasound assisted deep eutectic solvent (DES) with the aim to investigate the effects of ultrasound amplitude and duration in enhancing delignification. Oil palm fronds (OPF) were ultrasonicated in a water medium, followed by a pretreatment using DES (choline chloride:urea). Fourier transform infra-red spectroscopy, X-ray diffraction, field emission scanning electron microscope, Brunauer-Emmet-Teller and solubilised lignin concentration were conducted to confirm the effectiveness of ultrasound assisted DES on the pretreatment of OPF. The recommended ultrasound conditions were determined to be 70% amplitude and duration of 30 min, where the sequential DES pretreatment was able to reduce lignin content of OPF to 14.01%, while improving xylose recovery by 58%.

Interaction and Dynamics in a Fully Biodegradable Glucose-Containing Naturally Abundant Deep Eutectic Solvent: Temperature-Dependent Time-Resolved Fluorescence Measurements

A new room-temperature deep eutectic solvent (DES) composed of glucose, urea, and water has been prepared and its relaxation dynamics explored via temperature-dependent time-resolved fluorescence measurements employing hydrophilic and hydrophobic solute probes. Differential scanning calorimetry measurements indicate a glass transition temperature (T_g) of ∼236 K. Measured viscosity coefficients (η) vary from ∼600 to ∼100 cP in the temperature range 318 ≤ T/K ≤ 343 and exhibit Arrhenius-type temperature dependence with an activation energy of ∼65 kJ mol^-1. Interestingly, this DES forms a stable liquid at ∼300 K but is too viscous to be accurately measured by us below 318 K. Temperature-dependent dynamic fluorescence anisotropy measurements using hydrophobic and hydrophilic solutes of similar sizes reveal bi-exponential kinetics and Arrhenius-type temperature dependence for solute rotation times (⟨τ_r⟩) but with significantly decreased activation energies, ∼31 kJ mol^-1 (hydrophobic) and ∼21 kJ mol^-1 (hydrophilic). Deviation from hydrodynamics is further reflected in the strong fractional viscosity dependence of ⟨τ_r⟩: ⟨τ_r⟩ ∝ (η/T)^p with p ≈ 0.3-0.5, indicating pronounced temporal heterogeneity in the relaxation dynamics. Dynamic fluorescence Stokes shift measurements (temporal resolution ∼85 ps) produce dynamic shifts of ∼500-700 cm^-1, bi-exponential solvation energy relaxation with time constants in the range ∼0.2 ns and ∼4 ns, and estimated missing amplitudes of ∼65-75%. Impact of the density difference between a nonpolar solvent and this DES on the estimated missing amplitudes is explored via measuring the temperature-dependent densities and refractive indices of this DES. Lifetime measurements suggest considerable temperature dependence for the hydrophobic solute but no such dependence for the hydrophilic one. Excitation energy dependence of fluorescence emission of various solutes with widely different lifetimes indicates mild spatial heterogeneity for this DES.