Environmentally-Friendly Extraction of Flavonoids from Cyclocarya paliurus (Batal.) Iljinskaja Leaves with Deep Eutectic Solvents and Evaluation of Their Antioxidant Activities

Green and efficient extraction of an anticaner agent N-methylsansalvamide using ultrasound-assisted deep eutectic solvents from mycelia of strain Frusarium sp. R1

N-methylsansalvamide (SA), one of cyclic pentadepsipeptides produced by several Fusarium strains, is a promising therapeutic agent for the treatment of cancer disease. In order to make sufficient amount of SA for drug development, a green and efficient extraction process of SA from the mycelia of strain Fusarium sp. R1 using deep eutectic solvent-assisted ultrasound extraction (DES-UAE) was firstly achieved in this work. Solvent screening results indicated that choline chloride-acetic acid (ChCl-Aa) was shown to be the best DES for SA extraction. Through single-factor trials, Plackett-Burman design (PBD) and BoxBehnken design (BBD) experiments, the optimal conditions for DES-UAE with the highest SA yield of 58.2 ± 1.1 mg/g were obtained as follows: ChCl-Aa ratio of 1:2.0 (M/M), water content of 16.4 %, liquid-solid ratio of 37:1 (mL/g), ultrasonic power of 175 W for 47.4 min at 46.3 °C. Compared to conventional extraction approaches, DES-UAE exhibited better SA yield since it caused more serious damage to the surface of mycelia powder on basis of scanning electron microscopy (SEM) analysis. Furthermore, molecular interaction studies suggested that SA has a variety of interactions with ChCl-Aa, including hydrogen and electrovalent bonds as well as van der Waals forces. Finally, the recovery rate of SA reached up to 99.5 % when the ratio of distilled water and DES extracts was 15:1 (V/V). These findings provide the way for large-scale production of SA.

Recent advances in methods of extraction, pre-concentration, purification, identification, and quantification of kaempferol

As a naturally widely-occurring dietary, cosmetic, and therapeutic flavonoid, kaempferol has gained much consideration for its nutritional and pharmaceutical properties in recent years. Although there have been performed a high number of studies associated with different aspects of kaempferol's analytical investigations, the lack of a comprehensive summary of the various methods and other plant sources that have been reported for this compound is being felt, especially for many biological applications. This study, aimed to provide a detailed compilation consisting of sources (plant species) and analytical information that was precisely related to the natural flavonoid (kaempferol). There is a trend in analytical research that supports the application of modern eco-friendly instruments and methods. In conclusion, ultrasound-assisted extraction (UAE) is the most general advanced method used widely today for the extraction of kaempferol. During recent years, there is an increasing tendency towards the identification of kaempferol by different methods.

Deep eutectic solvent extraction of myricetin and antioxidant properties

In this study, a response surface method (RSM) was used to optimise the ultrasonic-assisted deep eutectic solvent (DES) extraction of myricetin from myricetin leaves. The results demonstrated that the DES-5 (choline chloride-oxalic acid) system exhibited better extraction results than the other seven DESs prepared. The optimum extraction conditions for myricetin were a DES-5 system with 19% water content of DES, a liquid-to-solid ratio of 37 : 1 mL g-1, an extraction time of 45 min, and an extraction temperature of 72 °C. Under these conditions, the extraction amount of myricetin was 22.47 mg g-1. To optimise the extraction process, the crude myricetin extract was purified, and the optimal conditions were as follows: an AB-8 macroporous adsorption resin was used with an anhydrous ethanol desorption agent. The adsorption rate was 1 BV per h (bed volume per hour), the desorption rate was 1 BV per h, and the desorption capacity was 2 BV (bed volume). The antioxidant properties of the myricetin were also investigated. The results demonstrated that, with an increase in concentration, the scavenging rates of DPPH and ˙OH free radicals increased. Compared to Vc, myricetin had a better scavenging ability for DPPH free radicals, whereas purified myricetin had a better antioxidant effect. At the same concentration, the radical-scavenging rate of the ˙OH radical was slightly higher in myricetin purified by the macroporous adsorption resin than in Vc, and that of the unpurified myricetin was the smallest. Myricetin was purified using a macroporous adsorption resin to improve its antioxidant properties.

The circadian rhythm: A new target of natural products that can protect against diseases of the metabolic system, cardiovascular system, and nervous system

BACKGROUND

The treatment of metabolic system, cardiovascular system, and nervous system diseases remains to be explored. In the internal environment of organisms, the metabolism of substances such as carbohydrates, lipids and proteins (including biohormones and enzymes) exhibit a certain circadian rhythm to maintain the energy supply and material cycle needed for the normal activities of organisms. As a key factor for the health of organisms, the circadian rhythm can be disrupted by pathological conditions, and this disruption accelerates the progression of diseases and results in a vicious cycle. The current treatments targeting the circadian rhythm for the treatment of metabolic system, cardiovascular system, and nervous system diseases have certain limitations, and the identification of safer and more effective circadian rhythm regulators is needed.

AIM OF THE REVIEW

To systematically assess the possibility of using the biological clock as a natural product target for disease intervention, this work reviews a range of evidence on the potential effectiveness of natural products targeting the circadian rhythm to protect against diseases of the metabolic system, cardiovascular system, and nervous system. This manuscript focuses on how natural products restore normal function by affecting the amplitude of the expression of circadian factors, sleep/wake cycles and the structure of the gut microbiota.

KEY SCIENTIFIC CONCEPTS OF THE REVIEW

This work proposes that the circadian rhythm, which is regulated by the amplitude of the expression of circadian rhythm-related factors and the sleep/wake cycle, is crucial for diseases of the metabolic system, cardiovascular system and nervous system and is a new target for slowing the progression of diseases through the use of natural products. This manuscript provides a reference for the molecular modeling of natural products that target the circadian rhythm and provides a new perspective for the time-targeted action of drugs.

Extracting bioactive compounds and proteins from Bacopa monnieri using natural deep eutectic solvents

This study employed novel extraction methods with natural deep eutectic solvents (NADES) to extract bioactive compounds and proteins from Bacopa monnieri leaves. The conditional influence of ultrasonic-assisted extraction (UAE), microwave-assisted extraction (MAE), and enzymatic-assisted extraction (EAE) on the recovery efficiency of phenolics, proteins, flavonoids, and terpenoids was evaluated. The conditions of UAE were 50 mL/g LSR, 600W of ultrasonic power, and 30% water content with 40°C for 1 min to obtain the highest bioactive compounds and protein contents. The conditions of MAE were 40 mL/g LSR, 400W of microwave power with 30% water content for 3 min to reach the highest contents of biological compounds. The conditions of EAE were 30 mL/g of LSR, 20 U/g of enzyme concentration with L-Gly-Na molar ratio at 2:4:1, and 40% water content for 60 min to acquire the highest bioactive compound contents. Scanning electron microscopy (SEM) is employed to analyze the surface of Bacopa monnieri leaves before and after extraction. Comparing seven extraction methods was conducted to find the most favorable ones. The result showed that the UMEAE method was the most effective way to exploit the compounds. The study suggested that UMEAE effectively extracts phenolics, flavonoids, terpenoids, and protein from DBMP.

Extraction optimization of tea saponins from Camellia oleifera seed meal with deep eutectic solvents: Composition identification and properties evaluation

Traditional organic solvent extractions of tea saponins have many drawbacks. This study aimed to establish an environment-friendly and efficient technology based on deep eutectic solvents (DESs) to extract tea saponins from Camellia oleifera seed meal. The solvent consisting of choline chloride and methylurea was screened as optimal DES. Under the optimal extraction conditions obtained by response surface methodology, the extraction yield of tea saponins reached 94.36 mg/g, which increased by 27% compared with ethanol extraction, while the extraction time was reduced by 50%. Analysis of UV, FT-IR, and UPLC-Q/TOF-MS indicated tea saponins did not alter during DES extraction. Surface activity and emulsification evaluation showed that extracted tea saponins could reduce interfacial tension at the oil-water interface with excellent foamability and foam stability, and they could form nanoemulsions (d₃₂ < 200 nm) with excellent stability. This study provides a suitable approach for the efficient extraction of tea saponins.

Extraction and Identification of Antioxidant Ingredients from Cyclocarya paliurus (Batal.) Iljinsk Using UHPLC-Q-Orbitrap-MS/MS-Based Molecular Networking

Cyclocarya paliurus (Batal.) Iljinskaja (LCP) leaves have been widely employed in food and traditional medicine for treating hyperlipidaemia and its complications, possibly owing to their antioxidant properties. The aim of the present study is to identify the chemical ingredients of antioxidant extracts from LCP by using UHPLC-Q-Orbitrap-MS/MS-based molecular networking, a very recent and useful tool for annotation of chemical constituents in mixtures. The extraction conditions of antioxidant extracts from LCP were optimised by single-factor analysis and response surface methodology (RSM). The optimised conditions were a methanol concentration of 32%, a liquid-to-solid ratio of 0.4 ml/mg, an extraction temperature of 25°C, and an extraction time of 32 min. Under these conditions, the antioxidant yield was 516.20 ± 28.52 μmol TE/ml. The main active ingredients in the antioxidants were identified by UHPLC-Q-Exactive Orbitrap-MS-based molecular networking. In total, 42 compounds were identified, including 20 flavonoids, 16 quinic acid derivatives, 4 caffeoyl derivatives, and 2 coumaroyl derivatives. The findings of the present work suggest that LCP could be a suitable source of natural antioxidant compounds, which might be applicable in the development of potential pharmaceutical drugs targeting diseases related to oxidative stress.

Potentilloside A, a New Flavonol-bis-Glucuronide from the Leaves of Potentilla chinensis, Inhibits TNF-α-Induced ROS Generation and MMP-1 Secretion

The major contributor to skin aging is UV radiation, which activates pro-inflammatory cytokines including TNF-α. TNF-α is involved in the acceleration of skin aging via ROS generation and MMP-1 secretion. In our preliminary study, a 30% EtOH extract from the leaves of Potentilla chinensis (LPCE) significantly inhibited TNF-α-induced ROS generation in human dermal fibroblasts (HDFs). Therefore, the objective of this study is to identify the active components in LPCE. A new flavonol-bis-glucuronide (potentilloside A, 1) and 14 known compounds (2-15) were isolated from an LPCE by repeated chromatography. The chemical structure of the new compound 1 was determined by analyzing its spectroscopic data (NMR and HRMS) and by acidic hydrolysis. Nine flavonols (2-9 and 11) and two flavone glycosides (12 and 13) from P. chinensis were reported for the first time in this study. Next, we evaluated the effects of the isolates (1-15) on TNF-α-induced ROS generation in HDFs. As a result, all compounds significantly inhibited ROS generation. Furthermore, LPCE and potentilloside A (1) remarkably suppressed MMP-1 secretion in HDFs stimulated by TNF-α. The data suggested that LPCE and potentilloside A (1) are worthy of further experiments for their potential as anti-skin aging agents.

Progress in Research on the Alleviation of Glucose Metabolism Disorders in Type 2 Diabetes Using Cyclocarya paliurus

Globally, the incidence of diabetes is increasing annually, and China has the largest number of patients with diabetes. Patients with type 2 diabetes need lifelong medication, with severe cases requiring surgery. Diabetes treatment may cause complications, side-effects, and postoperative sequelae that could lead to adverse health problems and significant social and economic burdens; thus, more efficient hypoglycemic drugs have become a research hotspot. Glucose metabolism disorders can promote diabetes, a systemic metabolic disease that impairs the function of other organs, including the heart, liver, and kidneys. Cyclocarya paliurus leaves have gathered increasing interest among researchers because of their effectiveness in ameliorating glucose metabolism disorders. At present, various compounds have been isolated from C. paliurus, and the main active components include polysaccharides, triterpenes, flavonoids, and phenolic acids. C. paliurus mainly ameliorates glucose metabolism disorders by reducing glucose uptake, regulating blood lipid levels, regulating the insulin signaling pathway, reducing β-cell apoptosis, increasing insulin synthesis and secretion, regulating abundances of intestinal microorganisms, and exhibiting α-glucosidase inhibitor activity. In this paper, the mechanism of glucose metabolism regulation by C. paliurus was reviewed to provide a reference to prevent and treat diabetes, hyperlipidaemia, obesity, and other metabolic diseases.

Advances on Cyclocarya paliurus polyphenols: Extraction, structures, bioactivities and future perspectives

Cyclocaryapaliurus (C. paliurus) is an edible and medicinal plant, distributed in southern China. As a kind of new food raw material, the leaves of C. paliurus are processed as tea products in daily life. C. paliurus is recognized as a good source to polyphenols, showing excellent bioactivities, which has attracted more and more attention. Polyphenols are important functional bioactive components in C. paliurus. C. paliurus polyphenols perform nutritional functions in anti-diabetes, anti-hyperlipidemic, anti-obesity, anti-oxidant, and other activities. In this review, we summarize the research progress of extraction technologies, structural characteristics, and bioactivities of C. paliurus polyphenols. Other potential functions of C. paliurus polyphenols are prospected. This review provides a reference for further research and applications of C. paliurus polyphenols in a field of functional food and medicines.

The Leaves of Cyclocarya paliurus: A Functional Tea with Preventive and Therapeutic Potential of Type 2 Diabetes

Type 2 diabetes mellitus (T2DM) has become a universal and chronic global public health concern and causes multiple complex complications. In order to meet the rapidly growing demand for T2DM treatment, increased research has been focused on hypoglycemic drugs. Cyclocarya paliurus (Batal.) Iljinsk is the only living species of the genus Cyclocarya Iljinskaja, whose leaves have been extensively used as a functional tea to treat obesity and diabetes in China. An enormous amount of very recent pharmacological research on the leaves of C. paliurus has demonstrated that they carry out numerous biological activities, such as hypoglycemic, anti-inflammatory, and intestinal microbiota regulation. Multiple in vitro and in vivo studies have also shown that the extracts of C. paliurus leaves are innocuous and safe. This study aims to provide an up-to-date review of the botany, traditional uses, phytochemistry, pharmacological effects against diabetes, toxicology, and clinical studies of C. paliurus leaves, in hopes of promoting a better understanding of their role in the prevention and treatment of T2DM.

Plant growth, physiological variation and homological relationship of Cyclocarya species in ex situ conservation

Natural forests of Cyclocarya paliurus have been seriously damaged because of the extreme demand for leaf medicinal uses, making conservation of this valuable, medicinal woody species necessary. Because of geographical differentiation and diverse adaptability, in this study we analysed the variations in plant growth and physiological response to environmental factors at a resource plantation of ex situ conservation and determined the homological relationships between local provenance (from Fujian Province, FJ) and introduced provenances showing high-survival rate and better growth (from Zhejiang, Hubei, Guizhou and Jiangxi Province). Our results suggested the following: (i) Plant growth: FJ had the highest plant height but not the largest basal diameter in comparison to that of other provenances. (ii) Physiological responses during the growth periods: water content in leaf of FJ had similar change with that of other provenances, except for the provenance from Guizhou Province; total soluble sugar content in leaf of FJ was more than that of other provenances; calcium content in leaf of all provenances was higher as compared to K, Mg and Na; the highest activity among four kinds of antioxidant enzymes in all provenances was superoxide dismutase, then was polyphenol oxidase and peroxidase, finally was catalase; and total flavonoid among three kinds of secondary metabolites in all provenances showed the greatest content, followed by polysaccharides and total triterpenoid. (iii) Relation analysis: plant growth and physiological responses related with environmental factors, especially temperature and precipitation. (iv) Homological relationships: leaf characteristics among six provenances varied in colour, area and common petiole length, but not the shape of leaf base or apex. Cyclocarya paliurus distributed in Fujian Province showed a very close homological relationship with that distributed in Zhejiang Province by simple sequence repeat. These findings will provide knowledge on physiological response to environmental factors and aid to select suitable provenances for Cyclocarya cultivation.

Cyclocarya paliurus (Batalin) Iljinskaja: Botany, Ethnopharmacology, phytochemistry and pharmacology

ETHNOPHARMACOLOGICAL RELEVANCE

Cyclocarya paliurus (Batalin) Iljinskaja (C. paliurus) also known as Sweet tea tree, Money tree, Money willow, green money plum, mountain willow and shanhua tree, is a native rare monocotyledonous plant in Southern China. It possesses numerous traditional benefits, including clearing heat, detoxification, producing saliva, slake thirst, anti-inflammatory, insecticidal, dispelling wind and relieving itching. It is also effective in preventing and treating diabetes, hypertension, hyperlipidemia, dizziness and swelling and pain, as well as reducing cholesterol, and modulating the functions of the immune system. The stem, leaves and bark of this plant are all medicinal parts, but the leaves have the highest research value.

AIM OF THE STUDY

This article summarized the plant's botanical description, distribution, ethnopharmacology, phytochemical profiles and pharmacological for the first time, to provide possible directions for future development and research in brief.

MATERIAL AND METHODS

The literature for this current manuscript was obtained from reports published from 1992 to May 2021 in diverse databases such as the China Knowledge Resource Integrated databases (CNKI), SciFinder, Google Scholar, Baidu Scholar, Elsevier and Pub-Med. The domestic and foreign references published about C. paliurus over recent years were collected, analyzed and summarized.

RESULTS

The botanical characteristics of the fruits of C. paliurus are unique in having a central nutlet surrounded by a circular wing to distinguish the living genera of Juglandaceae. In traditional medicine, C. paliurus leaves are used by the local people of Southern China to make tea to prevent diabetes. More than 210 compounds have been isolated from C. paliurus. Among them, the characteristic 3,4-seco-dammaranes accounted for the most. Other compounds include dammarane tetracyclic triterpenoids, various pentacyclic triterpenoids, flavonoids, isosclerones, phenolic derivatives and polysaccharides. The plant extracts and compounds have been reported to exert various pharmacological activities, such as anti-hyperglycemic, anti-hyperlipidemic, anti-cancer, cytotoxic, anti-oxidative, anti-inflammatory, hepatoprotective, and anti-microbial activities.

CONCLUSIONS

Comprehensive literature analysis shows that C. paliurus extract and its compounds have a variety of biological activities for the treatment of various diseases. The current modern pharmacology research is mostly related to the records of ethnic pharmacology, mainly in vitro research, relatively few in vivo research. Therefore, future studies should focus on this aspect. In addition, we also would like to recommend further research should concentrate on toxicity studies and quality control of C. paliurus to fill the study gap, as well as to provide theoretical support for the further development of the potential functions and clinical applications of the plant.

Green extraction of apigenin and luteolin from celery seed using deep eutectic solvent

In recent years, deep eutectic solvent (DES) has attracted a great deal of attention as an environmentally friendly solvent and could be used as an alternative to conventional solvents. In this study, 34 choline and betaine-based deep eutectic solvents were prepared and investigated the ability to extract apigenin and luteolin from the celery seed. The results showed that DES composed of betaine hydrochloride and propylene glycol had the best extraction efficiency. Using one factor at a time combined with response surface methodology, the optimal conditions of extraction were determined as follows: time of extraction: 19 min, extraction temperature: 75 °C, the water content in solvent: 40% (w/w). Antisolvent (water) combined with distillation was proposed as an efficient method to recover apigenin and luteolin from the DES extract. The relationship between components of DES and solubility of apigenin, luteolin was also established which was the starting point for the prediction of extractability of DES. Molecular dynamics revealed that betaine hydrochloride and propylene glycol could interact with each other by the formation of two types of hydrogen bond while water molecules might play an important role in the ability to dissolve apigenin and luteolin of DES.

Natural deep eutectic solvents as tailored and sustainable media for the extraction of five compounds from compound liquorice tablets and their comparison with conventional organic solvents

An efficient and environmentally friendly ultrasound-assisted (UAE) natural deep eutectic solvent (NADES) extraction method was applied for the extraction of five bioactive compounds (liquiritin, isoliquiritin, liquiritigenin, glycyrrhizic acid and isoliquiritigenin) from compound liquorice tablets (CPLTs), and the antioxidant activities of these compounds were evaluated. In this study, eighteen different NADES systems based on either two or three components were tested and a 1,4-butanediol–levulinic acid system (1 : 3 molar ratio) was selected as a topgallant solvent for maximizing analyte extraction yields. Various extraction parameters, such as water content, liquid/solid ratio, extraction time and temperature, were systematically optimized by single-factor and response surface methodology (RSM) experiments. The results indicated that the optimum extraction conditions for the analytes featured a water content of 17%, a liquid/solid ratio of 42 mL g⁻¹ and an extraction time of 30 min. The extracted amounts of liquiritin, isoliquiritin, liquiritigenin, glycyrrhizic acid and isoliquiritigenin reached 5.60, 3.17, 1.27, 74.62 and 1.34 mg g⁻¹, respectively, under optimized conditions, which were much higher than those extracted using conventional organic solvents. In addition, antioxidant tests revealed that the NADES extracts showed higher DPPH and hydroxyl radical-scavenging capacity than the conventional solvent extracts used for comparison. This study provides a suitable approach for efficiently extracting the bioactive compounds of CPLTs. Meanwhile, NADESs can be extended to other natural products as green extraction media.

A 1,4-butanediol–levulinic acid system was selected as a topgallant solvent and extraction parameters were optimized. NADES extracts exhibited higher extraction efficiency and in vitro antioxidant activities than conventional solvent extracts.

Greener Is Better: First Approach for the Use of Natural Deep Eutectic Solvents (NADES) to Extract Antioxidants from the Medicinal Halophyte Polygonum maritimum L

In this study, natural deep eutectic solvents (NADES) formed by choline chloride (ChCl), sucrose, fructose, glucose, and xylose, were used to extract antioxidants from the halophyte Polygonum maritimum L. (sea knotgrass) and compared with conventional solvents (ethanol and acetone). NADES and conventional extracts were made by an ultrasound-assisted procedure and evaluated for in vitro antioxidant properties by the radical scavenging activity (RSA) on the 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical, oxygen radical absorbance capacity (ORAC), and copper chelating activity (CCA). Samples were profiled by liquid chromatography (LC)-electrospray ionization (ESI)-QTOF-MS analysis. ChCl:fructose was more efficient in the DPPH assay, than the acetone extract. ChCl:sucrose and ChCl:fructose extracts had the highest ORAC when compared with the acetone extract. NADES extracts had higher CCA, than the acetone extract. The phenolic composition of the NADES extracts was less complex than the conventional extracts, but the proportions of major antioxidants, such as flavonols and flavan-3-ols, were similar in all the solvents. Myricitrin was the major flavonoid in all of the samples, while gallic acid was the main phenolic acid in the conventional extracts and present in a greater amount in ChCl:fructose. Results suggest that NADES containing ChCl and sucrose/fructose can replace conventional solvents, especially acetone, in the extraction of antioxidants from sea knotgrass.

Deep Eutectic Solvents (DESs) as Green Extraction Media of Beneficial Bioactive Phytochemicals

Deep eutectic solvents (DES) are a mixture of two or more components and are classified as ionic solvents with special properties such as low volatility, high solubility, low melting points, low-cost materials and are less toxic to humans. Using DES has been suggested as an eco-friendly, green method for extraction of bioactive compounds from medicinal plants and are a safe alternative for nutritional, pharmaceutical and various sector applications. Conventional solvent extraction methods present drawbacks such as long extraction period, safety issues, harmful to the environment, costly and large volume of solvents required. The extraction method with DES leads to higher extraction yield and better bioactivity results as compared to the conventional solvents. This review provides a summary of research progress regarding the advantages of using DES to extract bioactive compounds such as phenolic acid, flavonoids, isoflavones, catechins, polysaccharides, curcuminoids, proanthocyanidin, phycocyanin, gingerols, ginsenosides, anthocyanin, xanthone, volatile monoterpenes, tannins, lignin, pectin, rutin, tert-butyl hydroquinone, chlorogenic acids, resveratrol and others, as opposed to using conventional solvents. The bioactivity of the extracts is determined using antioxidant, antibacterial and antitumor activities. Hence, DESs are considered potential green media with selective and efficient properties for extracting bioactive ingredients from medicinal plants.

Study on Adsorption Performance of Benzoic Acid in Cyclocarya paliurus Extract by Ethyl Cellulose Microspheres

Polymer microspheres with inter-connecting pores are widely used as microsphere materials. In the study, the ethyl cellulose microspheres (ECM) were prepared by using the solvent-evaporation method. Based on that, a method for the separation and purification of benzoic acid from crude extract of Cyclocarya paliurus was established by the ECM and high performance liquid chromatography (HPLC). The ECM after the sorption equilibrium was desorbed by using 40% methanol as the analytical solvent. The content of benzoic acid in eluent is up to 0.0216 mg/mL, and the benzoic acid can be obtained with a high purity of 82.22%. Furthermore, the adsorption-desorption behavior of benzoic acid onto ECM was investigated. The results of adsorption kinetics of benzoic acid showed that the adsorption followed the pseudo-first-order kinetic model. The ECM was characterized by using Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), scanning electron microscope (SEM), and X-ray diffraction (XRD). The results showed that the ECM has a high adsorption property due to its more porous structure, phenolic hydroxyl group, and other oxygen-containing functional groups. This method and the ECM can be used stably, continuously, and efficiently to purify the benzoic acid from the methanol extract of C. paliurus on a large scale.

Current Progress in Natural Deep Eutectic Solvents for the Extraction of Active Components from Plants

In the last decade, natural deep eutectic solvents (NADESs) have gained more and more attention due to their green, convenient preparation, low toxicity and biodegradability. It is widely used in various fields, especially in the extraction of active components from plants, formed by the combination of hydrogen bond donors (HBDs) and hydrogen bond acceptors (HBAs) at a certain condition. In this article, six preparation methods of NADESs were summarized and the interactions that occur in the eutectic behavior of NADES including hydrogen bonding, electrostatic interaction and van der Waals force were also reviewed. What is more, its significant extraction capacity on flavonoids, phenols, alkaloids and plant pigments endows its extensive applications in the extraction of active components from medicinal plants. Extraction factors including solvents properties (viscosity, carbon chain length, number of hydroxyl groups), extraction condition (water content, extraction temperature, extraction time, solid-liquid ratio), extraction method and recycling method were discussed. In addition, NADESs can also be combined with other technologies, like molecular imprinting, monolithic column, to achieve efficient and specific extraction of active ingredients. Further systematic studies on the biodegradability and biotoxicity are put forward to be urgent.

The evaluation of phenolic content, in vitro antioxidant and antibacterial activity of Mentha piperita extracts obtained by natural deep eutectic solvents

The focus of this study was to evaluate whether six choline chloride-based natural deep eutectic solvents (NADES) could serve as solvents for the extraction of bioactives from the leaves of Mentha piperita. NADES extracted significantly higher amounts of phenols from peppermint than 70% ethanol and may be useful in the extraction of targeted major compounds from peppermint, like rosmarinic acid, at a similar level as 70% ethanol. The microdilution method for in vitro antibacterial activity showed that all NADES exhibit bacterial growth inhibition at a lower concentration than 70% ethanol, especially NADESs containing organic acids. The majority of NADES extracts neutralize DPPH radical at a lower concentration than conventional solvent and showed similar ability to reduce Fe³⁺ to Fe²⁺ ions in FRAP assay. NADES can be useful in the isolation of phenolic compounds from plant sources and should be considered as novel, sustainable, and low-cost solvents with a variety of applications.

Structure, Biological Activities and Metabolism of Flavonoid Glucuronides

BACKGROUND

Flavonoid glucuronides are a kind of natural products which present a flavone linked directly with one or several glucuronides through O-glycoside bond. They had become of interest in natural product research in the past decades for their antioxidant, anti-inflammatory, and anti-bacteria activities. In particular, the compound breviscapine has a notable effect on cardio-cerebrovascular diseases. Several other compounds even have antitumor activity.

METHODS

Through searching the database and reading a large number of documents, we summarized the related findings of flavonoid glucuronides.

RESULTS

We summarized 211 naturally occurring flavonoid glucuronides in 119 references with their chemical structures, biological activities, and metabolism. A total of 220 references from 1953 to 2020 were cited in this paper according to literature databases such as CNKI, Weipu, Wanfang data, Elsevier, Springer, Wiley, NCBI, PubMed, EmBase, etc..

CONCLUSION

Flavonoid glucuronides are a class of compounds with various chemical structures and a diverse range of biological activities. And they are thought to be potential candidates for drug discovery, but the specific study on their mechanisms is still limited until now. We hope this article can provide references for natural product researchers and draw more attention to flavonoid glucuronides' biological activities and mechanisms.

Kaempferol-3-O-Glucuronide Ameliorates Non-Alcoholic Steatohepatitis in High-Cholesterol-Diet-Induced Larval Zebrafish and HepG2 Cell Models via Regulating Oxidation Stress

NAFLD (non-alcoholic fatty liver disease) is one of the most prominent liver diseases in the world. As a metabolic-related disease, the development of NAFLD is closely associated with various degrees of lipid accumulation, oxidation, inflammation, and fibrosis. Ilex chinensis Sims is a form of traditional Chinese medicine which is used to treat bronchitis, burns, pneumonia, ulceration, and chilblains. Kaempferol-3-O-glucuronide (K3O) is a natural chemical present in Ilex chinensis Sims. This study was designed to investigate the antioxidative, fat metabolism-regulating, and anti-inflammatory potential of K3O. A high-cholesterol diet (HCD) was used to establish steatosis in larval zebrafish, whereby 1mM free fatty acid (FFA) was used to induce lipid accumulation in HepG2 cells, while H₂O₂ was used to induce oxidative stress in HepG2. The results of this experiment showed that K3O reduced lipid accumulation and the level of reactive oxygen species (ROS) both in vivo (K3O, 40 μM) and in vitro (K3O, 20 μM). Additionally, K3O (40 μM) reduced neutrophil aggregation in vivo. K3O (20 μM) also decreased the level of malondialdehyde (MDA) and significantly increased the level of glutathione peroxidase (GSH-px) in both the HCD-induced larval zebrafish model and H₂O₂-exposed HepG2 cells. In the mechanism study, keap1, nrf2, tnf-α, and il-6 mRNA were all significantly reversed by K3O (20 μM) in zebrafish. Changes in Keap1 and Nrf2 mRNA expression were also detected in H₂O₂-exposed HepG2 cells after they were treated with K3O (20 μM). In conclusion, K3O exhibited a reduction in oxidative stress and lipid peroxidation, and this may be related to the Nrf2/Keap1 pathway in the NAFLD larval zebrafish model.

Editorial for the “Green Chemistry” Section in the Journal Molecules: Focus on Solvents

It is a pleasure to write this editorial highlighting some of the recent papers discussing solvents in the Green Chemistry section of Molecules [...]

Morphological and physiological variations of Cyclocarya paliurus under different soil water capacities

Soil water capacity (SWC) is a very important factor for the artificial cultivation and production of seedling in Cyclocarya paliurus. To understand SWC requirement for seedling cultivation and to investigate morphological and physiological changes under different SWCs, a 100-day SWC treatment was conducted during artificial cultivation; four treatments were 10-20 wt% SWC (W1), 30-40 wt% SWC (W2), 50-60 wt% SWC (W3), and 70-80 wt% SWC (W4). The result showed that W3 was suitable for seedling cultivation. Compared with W3, growth biomass decreased and water content increased at W1, W2 and W4; K, Ca, and Mg content increased under W1, while Na content increased under W4; SOD, PPO, POD, and CAT activity in leaf significantly increased under W1 and W4, of which SOD activity was the highest, and MDA content reached its maximum under W1. W1 and W4 had negative effects on seedling growth, and seedlings adapt to unfavorable water condition by morphological and physiological responses. Our research would be useful for artificial cultivation and management of Cyclocarya species.

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.

Deep Eutectic Solvents for Pretreatment, Extraction, and Catalysis of Biomass and Food Waste

Valorization of lignocellulosic biomass and food residues to obtain valuable chemicals is essential to the establishment of a sustainable and biobased economy in the modern world. The latest and greenest generation of ionic liquids (ILs) are deep eutectic solvents (DESs) and natural deep eutectic solvents (NADESs); these have shown great promise for various applications and have attracted considerable attention from researchers who seek versatile solvents with pretreatment, extraction, and catalysis capabilities in biomass- and biowaste-to-bioenergy conversion processes. The present work aimed to review the use of DESs and NADESs in the valorization of biomass and biowaste as pretreatment or extraction solvents or catalysis agents.

Deep Eutectic Solvents as Extraction Media for Valuable Flavonoids from Natural Sources

The present review article attempts to summarize the use of deep eutectic solvents in the extraction of flavonoids, one of the most important classes of plant secondary metabolites. All of the applications reviewed have reported success in isolation and extraction of the target compounds; competitive, if not superior, extraction rates compared with conventional solvents; and satisfactory behavior of the extract in the latter applications (such as direct analysis, synthesis, or catalysis), wherever attempted.

Green Extraction of Phenolic Acids from Artemisia argyi Leaves by Tailor-Made Ternary Deep Eutectic Solvents

The Artemisia argyi leaf (AL) has been used as a traditional medicine and food supplement in China and other Asian countries for hundreds of years. Phytochemical studies disclosed that AL contains various bioactive constituents. Among bioactive constituents, phenolic acids have been recognized as the main active compounds in AL. To the best of our knowledge, no research has been focused on extraction method for the bioactive phenolic acids from AL. Nowadays, deep eutectic solvents (DESs) are emerging as a new type of green and sustainable solvent for efficient extraction of bioactive compounds from natural products. In the present study, an environmentally friendly extraction method based on DESs was established to extract bioactive phenolic acids from ALs. Diverse tailor-made solvents, including binary and ternary DESs, were explored for simultaneous extraction of four phenolic acids (3-caffeoylquinic acid, 3,4-di-O-caffeoylquinic acid, 3,5-di-O-caffeoylquinic acid, and 4,5-di-O-caffeoylquinic acid) from AL. The results indicated that the ternary DES composed of a 2:1:2 molar ratio of choline chloride, malic acid, and urea showed enhanced extraction yields for phenolic acids compared with conventional organic solvents and other DESs. Subsequently, the extraction parameters for the four phenolic acids by selected tailor-made DESs, including liquid-solid ratios, water content (%) in the DESs, and extraction time, were optimized using response surface methodology and the optimal extraction conditions were: extraction time, 23.5 min; liquid-solid ratio, 57.5 mL/g (mL of DES/g dry weight of plant material); water content, 54%. The research indicated that DESs were efficient and sustainable green extraction solvents for extraction of bioactive phenolic acids from natural products. Compared to the conventional organic solvents, the DESs have a great potential as possible alternatives to those organic solvents in health-related areas such as food and pharmaceuticals.

Optimizing Ultrasound-Assisted Deep Eutectic Solvent Extraction of Bioactive Compounds from Chinese Wild Rice

In this study, deep eutectic solvents (DESs) were used for the ultrasound-assisted extraction (UAE) of valuable bioactive compounds from Chinese wild rice (Zizania spp.). To this end, 7 different choline chloride (CC)-based DESs were tested as green extraction solvents. Choline chloride/1,4-butanediol (DES-2) exhibited the best extraction efficiency in terms of parameters such as the total flavonoid content (TFC), total phenolic content (TPC), and free radical scavenging capacity (DPPH^● and ABTS^●+). Subsequently, the UAE procedure using 76.6% DES-2 was also optimized: An extraction temperature of 51.2 °C and a solid–liquid ratio of 37.0 mg/mL were considered optimal by a Box–Behnken experiment. The optimized extraction procedure proved efficient for the extraction of 9 phenolic and 3 flavonoid compounds from Chinese wild rice as determined by quantification based on ultra-performance liquid chromatography–triple quadrupole tandem mass spectrometry (UPLC-QqQ-MS). This work, thus, demonstrates the possibility of customizing green solvents that offer greater extraction capacity than that of organic solvents.

Ionic deep eutectic solvents for the extraction and separation of natural products

Room ionic liquids (ILs) used as green solvents have received considerable attention and wide application in different research and industrial fields, such as chemistry, biology, catalysis, energy, and even environmental sciences. Recently, a new class of sustainable solvents named deep eutectic solvents (DESs) have been developed, which share the promising solvent characteristics of ILs, such as thermal and chemical stability, low vapor pressure and design ability. In addition, the major advantages of DESs over ILs are their lower prices and easier preparation. Therefore, DESs have been considered to be a potential alternative to replace conventional organic solvents and ILs. Currently, the developed DESs may be classified into ionic and nonionic liquids. Typically, choline chloride (ChCl)/urea (1:2) is an ionic DES, while glucose/sucrose (1:1) is a nonionic DES. Although several reviews have covered advancements in DESs, in this review, we aim to provide a general insight into DESs, particularly ionic DESs, like choline-based DES, in terms of their preparation and application in the extraction of natural products (NPs) mainly from traditional Chinese medicines and the recovery of extracted compounds from their extracts. Additionally, various factors affecting the extraction efficiency of DESs are discussed.