Ionic liquid-immobilized NaY zeolite-based matrix solid phase dispersion for the extraction of active constituents in Rheum palmatum L

Solid-phase adsorption methodologies of naturally occurring anthraquinones: A review

INTRODUCTION

Solid-phase extraction applied to plant matrices is nowadays a well-validated technique allowing to concentrate and purify different secondary metabolites. Several classes of phytochemicals have been selectively extracted by this methodology. During the last decade attention has been focused on biologically active anthraquinones from numerous sources like edible, healthy, and medicinal plants.

OBJECTIVES

The aim of this review is to provide a detailed literature survey of the solid-phase adsorption methodologies for the extraction of natural anthraquinones reported so far and to discuss and propose future directions in this field of research.

MATERIALS AND METHODS

Substructure search was performed in the SciFinder Scholar, PubMed, Medline, and Scopus databases.

RESULTS

The first report about application of solid-phase adsorption for the purification of anthraquinones appeared in the literature in 2002. From this date, and in particular during recent years, the most notable examples included the use of chitin- and chitosan-based polymers, of molecularly imprinted polymers, of coated magnetic nanoparticles, of miniaturized matrix solid-phase dispersion, of functionalized resins, of differently structured lamellar solids, and finally of vortex-synchronized matrix solid-phase dispersion.

CONCLUSIONS

The herein detailed solid-phase adsorption methodologies are powerful tools to selectively extract natural anthraquinones and/or provide anthraquinone-enriched phytopreparations. Nevertheless, many other important methods have been applied to synthetic anthraquinones (e.g., azo dyes). These could be conveniently employed also for natural anthranoids. Studies in this field are discussed in this review article.

Simultaneous determination of seven anthraquinones in Cassiae semen by natural deep eutectic solvent extraction

INTRODUCTION

Anthraquinones are considered to be an important class of bioactive substances in Cassiae semen, and the content of anthraquinones is an essential indicator of the quality of Cassiae semen raw herbal materials.

OBJECTIVES

The present study aimed to propose a novel, efficient and effective ultra-high-performance liquid chromatography (UHPLC) method for the simultaneous determination of aurantio-obtusin, aloe-emodin, rhein, obtusin, emodin, chrysophanol and physcion, with the help of natural deep eutectic solvents (NADESs) as extraction solvents.

METHODOLOGY

NADESs were introduced to the simultaneous extraction of anthraquinones from Cassiae semen samples. Several NADESs were designed by menthol, choline chloride, d-glucose as hydrogen bond acceptors, with nine different acids and appropriate water as hydrogen bond donors. The parameters affecting the extraction efficiency of seven anthraquinones were demonstrated in detail.

RESULTS

Among the obtained NADESs, the highest extraction efficiency was demonstrated by a solution consisting of d-glucose, lactic acid and water with a molar ratio of 1:5:4. The seven anthraquinones were separated on an ACQUITY UPLC® BEH C₁₈ column (2.1 mm × 100 mm, 1.8 μm) and detected within 12 min by a photodiode array (PDA) detector at 254 and 284 nm. The limits of detection and quantitation were from 1.00 to 7.26 μg/l and 3.29 to 24.22 μg/l, respectively. And Cassiae semen sample-based recoveries ranged from 81.13% to 113.78% with the relative standard deviation (RSD) (n = 6) of 1.4% to 10.1%.

CONCLUSION

The developed method demonstrated that NADESs were applied successfully to analyse the anthraquinones in Cassiae semen samples collected from different regions in China.

Molecular Traits Underlying the Growth Promotion and Metabolite Accumulation in Rheum palmatum Inoculated with Endophytic Trichoderma citrinoviride HT-1

Trichoderma spp. are an important plant-growth-promoting fungi. Trichoderma citrinoviride HT-1 was isolated from Rheum palmatum root, which has beneficial effects on growth and metabolite accumulation. However, the improvement mechanisms for growth and metabolite accumulation of T. citrinoviride HT-1 are unclear. In this study, RNA sequencing (RNA-seq) and high-performance liquid chromatography (HPLC) were used to measure the effect of different concentrations of conidial suspension of the HT-1 strain on the growth promotion and metabolite accumulation of R. palmatum seedlings. The results showed that the highest biomass and metabolites of R. palmatum seedlings were obtained through treatment with the HT-1 strain at a final spore concentration of 107 spores/mL. RNA sequencing indicated that 1662 genes were upregulated and 2155 genes were downregulated after inoculation with 107 spores/mL of the HT-1 strain. This strain induced significant upregulation of related genes in the phenylpropanoid biosynthesis pathway, plant hormone signal transduction pathway, biosynthesis of secondary metabolites pathway, and plant–pathogen interaction pathway in R. palmatum. The gene expression trends were revealed through quantitative real-time polymerase chain reaction (qRT-PCR) and were consistent with those determined by RNA-seq. Our results will help us to understand the growth-promoting mechanisms of the HT-1 strain on R. palmatum and provide a theoretical basis for the application of T. citrinoviride HT-1 as a biological fertilizer.

Ultrasonic Solvent Extraction Followed by Dispersive Solid Phase Extraction (d-SPE) Cleanup for the Simultaneous Determination of Five Anthraquinones in Polygonum multiflorum by UHPLC-PDA

A rapid and effective ultra-high performance liquid chromatography (UHPLC) method was developed for the determination of five anthraquinones (emodin, physcion, aloe-emodin, rhein, and chrysophanol) in Polygonum multiflorum. The target compounds were ultrasonically extracted with 70% methanol, followed by dispersive solid-phase extraction (d-SPE) with HC-C18 and desorption with acetonitrile. The five anthraquinones were separated on an ACQUITY UPLC® HSS T3 column (2.1 × 100 mm, 1.8 μm) and detected by a photodiode array detector (PDA) at 254 nm. Under the optimized conditions, linear relationships were achieved in the range of 0.3~100 mg/L for emodin, 0.3~40 mg/L for physcion, 0.1~20 mg/L for aloe-emodin, and 0.05~20 mg/L for rhein and chrysophanol. The limits of detection of the five analytes ranged from 0.01 to 0.08 mg/L, and the recoveries were within the range of 82.8~118.4% with an RSD (n = 6) of 1.0~10.3%. The intra-day and inter-day precision (n = 5) of the five targets were in the range of 1.0~1.8% and 3.0~3.1%, respectively. Furthermore, this method was applied to analyses of Polygonum multiflorum samples collected from different regions in China with satisfactory results. All the results indicated that this method is suitable for the detection of five anthraquinones in Polygonum multiflorum.

Analysis of Endophyte Diversity of Rheum palmatum from Different Production Areas in Gansu Province of China and the Association with Secondary Metabolite

Investigations of the differences in the metabolites of medicinal plants have typically focused on the effects of external environmental factors. However, little is known about the relationship between endophytes diversity and host metabolites. We used high-throughput sequencing methods to compare the endophyte diversity of Rheum palmatum from eight different production areas in Gansu Province of China and to analyze the association between those areas and five secondary metabolites (aloe-emodin, rhein, emodin, chrysophanol, and physcion). The results show that the diversity and OTUs (Operational taxonomic units) abundance of endophytic fungi and bacteria of R. palmatum differed according to production area. Spearman analysis showed that the five secondary metabolites of R. palmatum were positively correlated with the diversity and abundance of endophytic fungi. Comparing both space and environmental differences to determine influences on community structure, VPA analysis revealed that geographic factors explained more difference in community composition of fungal and bacterial endophytes than climate factors. PICRUSt and FUNGuild predictive analysis indicated that metabolites were the primary components of endophytic bacteria in all samples, while the function of endophytic fungi was composed of dominant trophic modes (saprotroph and pathotroph), and relative abundances were different. Our results help elucidate the correlation of plant-microbe interactions and offer pivotal information to reveal the role of endophytes in the production of R. palmatum and its important secondary metabolite.

[Research progress in application of immobilized ionic liquid materials to separation by solid-phase extraction]

Ionic liquids are low-temperature molten salts with almost no vapor pressure, and they are composed of organic cations and inorganic anions. Ionic liquids are characterized by the properties of good chemical stability, high solubility, designable structure, high conductivity and so on. The physicochemical properties of an ionic liquid depend on the nature and size of the cation and anion, which confer unique characteristics; hence, these reagents are also termed "designed extractants." As a new class of green solvents, ionic liquids are potential replacements to traditional volatile organic solvents used for extraction; for this reason, ionic liquids have attracted the attention of scientists. Research on the methods of preparation and applications of ionic liquids is being diversified, and they are extensively used in catalytic chemistry, photoelectron chemistry, materials chemistry, analytical chemistry, etc. By functional guiding design, the structures of ionic liquids, especially the imidazole ring cations, can be easily grafted with active groups such as hydroxyl, amino, carboxyl, and cyano groups, so that interactions between the ionic liquids and target molecules can be promoted via the formation of π-π bonds, hydrogen bonds, ionic bonds, and van der Waals forces. In addition, ionic liquids can be readily immobilized on solid carriers by physical or chemical means in order to obtain a new solid material with ionic liquids embedded internally or decorated on the surface. Furthermore, ionic liquids could be converted into ionic liquid-immobilized composite materials by impregnation, grafting, etc. The resulting composites not only suffer minimal loss of ionic liquids but also retain the typical characteristics of the ionic liquids and solid materials, thus showing improved mass transfer performance and better adsorption performance. Immobilized materials are characterized by high enrichment efficiency, high adsorption capacity, good stability, and strong extraction selectivity, as well as the presence of numerous recognition sites and high utilization rate of ionic liquids. In recent years, they have been widely used as solid-phase extraction adsorption materials for the separation of small organic molecules. This review introduces common immobilization methods and the characteristics of ionic liquid-immobilized materials, as well as their application in solid-phase extraction. In this paper, methods for the immobilization of ionic liquids with solid carriers such as silica gel, molecular sieves, molecularly imprinted polymers, graphene oxide, and magnetic nanomaterials are summarized, and the application of ionic liquid-immobilized materials in solid-phase extraction is reviewed. The target substances include alkaloids, flavonoids, polyphenols, and other natural active components as well as common drug molecules, organic pesticides, and other organic small molecular compounds. The properties, applications, and separation mechanisms of ionic liquids immobilized with various carriers are systematically introduced. Literature survey shows that the distribution of the binding active sites of ionic liquid-immobilized materials to the target molecules is more uniform, which increases the adsorption capacity of the materials. The adsorption efficiency of ionic liquid-immobilized materials is related to the type of ionic liquid, amount of adsorption material, concentration of the sample solution, adsorption temperature, solution pH, flow rate of the eluent, and type and amount of the eluting solvent. The existing disadvantages of ionic liquids, such as simple structures, insufficient basic theoretical research, and unsatisfactory extraction degree in complex matrixes would also be discussed. The corresponding solutions would be presented with the aim of providing guidance for the application of ionic liquid-immobilized materials in the separation and analysis of targets in complex matrices, thus paving the way for a new direction in the field of extraction and separation.

Cucurbituril and zwitterionic surfactant-based matrix solid-phase dispersion microextraction to simultaneously determine terpenoids from Radix Curcumae

A rapid, efficient, and environmentally friendly matrix solid-phase dispersion microextraction was established to determine and quantify terpenoids in Radix Curcumae using ultra-high-performance liquid chromatography with a diode array detector. Various parameters affecting the extraction were investigated in detail, such as the grinding time, amount of adsorbent, type and concentration of elution solvent, and pH. The optimization of single-factor and response surface methodology was performed to confirm the best conditions in this procedure. The final optimized conditions were obtained by applying 70 mg of cucurbituril as adsorbent, 149 s as the optimum grinding time, and 228 mM of 3-(N,N-dimethylpalmitylammonio)propanesulfonate aqueous solution (pH 6.5) as the optimal elution solvent. The validated method showed a satisfactory linear range of 0.10-10 µg/mL for curdione and furanodiene, 0.01-10 µg/mL for isocurcumenol and germacrone, and 0.05-10 µg/mL for furanodienone, while the correlation coefficients ranged from 0.9945 to 0.9970. The recoveries of the investigated analytes at two spiked concentration levels (0.1 and 1.0 µg/mL) ranged from 96.53 to 104.60%. In addition, this method displayed acceptable reproducibility (relative standard deviation ≤ 3.66%). The results showed that the newly proposed matrix solid-phase dispersion microextraction method was successfully applied to analyze curdione, isocurcumenol, furanodienone, germacrone and furanodiene in Radix Curcumae samples.