Ionic liquids based simultaneous ultrasonic and microwave assisted extraction of phenolic compounds from burdock leaves

The ionic liquids based simultaneous ultrasonic and microwave assisted extraction (IL-UMAE) technique was first proposed and applied to isolate compounds. The ionic liquids comprising a range of four anions, five 1-alkyl-3-methylimidazolium derivatives were designed and prepared. The results suggested that varying the anion and cation both had apparent effects on the extraction of phenolics. The results also showed that irradiation power, time and solid–liquid ratio significantly affected the yields. The yields of caffeic acid and quercetin obtained by IL-UMAE were higher than those by regular UMAE. Compared with conventional heat-reflux extraction (HRE), the proposed approach exhibited higher efficiency (8–17% enhanced) and shorter extraction time (from 5 h to 30 s). The results indicated ILUMAE to be a fast and efficient extraction technique. Moreover, the proposed method was validated by the reproducibility and recovery experiments. The ILUMAE method provided good recoveries (from 96.1% to 105.3%) with RSD lower than 5.2%, which indicated that the proposed method was credible. Based on the designable nature of ionic liquids, and the rapid and highly efficient performance of the proposed approach, ILUMAE provided a new alternative for preparation of various useful substances from solid samples.     

Ultrasound assisted extraction of phenolic compounds from grapes

A new ultrasound-assisted extraction method was developed for the determination of phenolic compounds present in grapes. Several extraction variables including extraction temperature (0–75 °C), output amplitude (20, 50 and 100%), duty cycle (0.2 s, 0.6 s and 1 s), the quantity of sample (0.5–2 g), and the total extraction time (3–15 min) were evaluated. One of the most widely used extraction methods of polyphenol extraction has been used as reference method. Three parameters were compared: total amount of phenolic compounds, total amount of anthocyanins and total amount of tannic components. The resulting method produced similar or higher recoveries for these three parameters; however a much shorter extraction time was needed: 6 min (ultrasound assisted extraction method) instead of 60 min (reference method).     

Deep eutectic solvents as green media for efficient extraction of terpene trilactones from Ginkgo biloba leaves

Deep eutectic solvents (DESs)-based ultrasonic extraction of terpene trilactones (TTLs) from Ginkgo biloba leaves was efficiently developed. Sixteen DESs were prepared, and DESs composed of choline chloride-urea (ChCl-U) and betaine-ethylene glycol (BE-EG) gave higher TTL extraction yields than the present, most efficient solvent 70% ethanol. The extraction conditions were further optimized, and the optimum conditions were as follows: taking BE-EG containing 40% (w/w) water as the extraction solvent, 1:10 of G. biloba leaves powder-to-solvent ratio, and ultrasonic treatment at 45°C and 100?W for 20?min. A total extraction yield of 1.94?±?0.03?mg/g was obtained under the optimum conditions, which indicated that 99.37% of TTLs could be extracted from the G. biloba leaves powder by a single extraction. Moreover, the polyamide resin was used to recover the TTLs in DES extracting solution, and recovery yield of 95.1% was attained. Therefore, BE-EG containing 40% (w/w) water was a potential alternative solvent for TTLs extraction from G. biloba leaves.     

An efficient microwave assisted synthesis of novel class of Rhodanine derivatives as potential HIV-1 and JSP-1 inhibitors

(Z)-5-(2-(1H-Indol-3-yl)-2-oxoethylidene)-3-phenyl-2-thioxothiazolidin-4-one (7a-q) derivatives have been synthesized by the condensation reaction of 3-phenyl-2-thioxothiazolidin-4-ones (3a-h) with suitably substituted 2-(1H-indol-3-yl)-2-oxoacetaldehyde (6a-d) under microwave condition. The thioxothiazolidine-4-ones were prepared from the corresponding aromatic amines (1a-e) and di-(carboxymethyl)-trithiocarbonyl (2). The aldehydes (6a-h) were synthesized from the corresponding acid chlorides (5a-d) using HSnBu₃.     

Simple and efficient microwave assisted N-alkylation of isatin

We present herein the results of microwave promoted N-alkylations of isatin (1)with different alkyl, benzyl and functionalized alkyl halides. Reactions were carried out under different conditions, always employing methodologies compatible with MW assisted chemistry. Generation of isatin anion employing diverse bases and solvents or using the preformed isatin sodium salt was tested. The best results were achieved using K(2)CO(3) or Cs(2)CO(3) and a few drops of N,N-dimethylformamide or N-methyl-2-pyrrolidinone. These reactions present noteworthy advantages over those carried out employing conventional heating.     

Optimisation and characterisation of various extraction conditions of phenolic compounds and antioxidant activity in olive seeds

This study was conducted to optimise the extraction conditions of phenolic compounds to evaluate antioxidant extraction parameters and to identify the major free and bound phenolic compounds in olive seeds. The results obtained using methanol as an extraction solvent for olive seeds indicated that the optimised total phenolic content and antioxidant activity were obtained at an extraction time of 12 h, an extraction temperature of 70°C and an extraction cycle of three stages. The correlation coefficient between total phenolic compounds and antioxidant activities was positive (R2 = 0.83). The major finding is that the predominant phenolic compounds in olive seeds were present in free form. However, a small percentage of the bound phenolic compounds was found in olive seeds compared to that of the free phenolic compounds. This study recommends that olive seeds with optimised extraction conditions (i.e. optimised correlation between phenolic compound contents and antioxidant activities) can be used as potential food additive candidates in functional, nutraceutical and pharmaceutical industries.     

An efficient palladium catalytic system for microwave assisted cyanation of aryl halides

Application of a new catalytic system for cyanation reaction of various aryl halides using K₄[Fe(CN)₆] as cyanating source was examined. The reactions were performed under microwave irradiation and results showed that application of this catalytic system and DMF at 130 °C minimized the reaction times from hours to minutes in good to excellent yields.     

An efficient transformation of cellulose into cellulose carbamates assisted by microwave irradiation

Cellulose carbamates (CCs) were microwave-assisted synthesized from the native cellulose and urea under solvent-free and catalyst-free conditions. Types of raw materials, the effects of the reaction condition on the nitrogen content of CCs were investigated. CCs were characterized with infrared spectroscopy (FT-IR), ¹³C NMR spectrometry, X-ray diffraction, scanning electron microscopy and thermogravimetry. The results indicated that various source of native celluloses such as cotton linter, reed, bagasse and wood pulps with different degree of polymerization could be successfully converted to CCs by the efficient and environmentally friendly procedure. The nitrogen content of CCs increased with an increase of the urea content and the mass of the mixtures, as well as the pulsed times of microwave irradiation. CCs retained the cellulose I crystalline form of the native cellulose and the degree of crystallinity decreased with the incorporation of carbamates. This work provided a novel pathway for the preparation of cellulose carbamate, which is expected to be useful for the CarbaCell process.     

Two compounds from the endophytic Colletotrichum sp. of Ginkgo biloba

Two compounds, apigenin-8-C-beta-D-glucopyranoside and 2-(hydroxymethylthio)ethanol, were extracted from the fermentation products of a strain of endophytic fungus, Colletotrichum sp. NTB-2, isolated from the leafstalk of Ginkgo biloba. The structures of the two compounds were determined on the basis of extensive spectroscopic analysis, including 1D and 2D NMR spectral data. The compounds wereobtained from microorganisms for the first time.     

Improved extraction of ginkgotoxin (4'-O-methylpyridoxine) from Ginkgo biloba products

A simple extraction procedure was applied to the analysis of canned/packaged white nuts and Ginkgo biloba extracts. Extraction by shaking with water at room temperature was more convenient to use than a previously published Soxhlet procedure for analysis of packaged Ginkgo biloba seeds (white nuts) for ginkgotoxin; recoveries from spiked dried seeds by the simple extraction procedure averaged 76%. Determination was by liquid chromatography with UV or fluorescence detection. Recoveries of ginkgotoxin from a spiked and unspiked natural health product (powder from Ginkgo biloba capsules) were equivalent by both procedures; recovery from spiked powder by the simple extraction procedure was 81%. Application of this extraction procedure in the analysis of 6 samples of white nuts (vacuum packaged and canned products) showed that free ginkgotoxin was present in 5 samples at concentrations up to 25 microg/g dry weight. Total ginkgotoxin was determined after hydrolysis with beta-glucosidase of sample extracts in which a peak corresponding to the 5'-O-glucoside was detected. Ginkgotoxin was determined in 10 Ginkgo biloba natural health products by the same method at levels up to 181 microg/g.     

An ultrasound-based technique for the analytical extraction of phenolic compounds in red algae

Phenolic compounds are bioactive compounds that are also naturally found in red algae. To determine the level of these compounds in the red algae, spectroscopic or chromatographic determination was applied over the liquid extracts. Therefore, a prior extraction method is needed. The presented study aimed to develop the analytical ultrasound-assisted extraction (UAE) method to extract phenolic compounds from red algae. A Box–Behnken design (BBD) based on five factors included solvent composition (50–90% ethanol in water), extraction temperature (10–60 °C), ultrasonic power (20–100%), pulse duty-cycle (0.2–1.0 s^?1), and solvent-to-sample ratio (10:1 to 30:1) was used to evaluate the effects of the studied factors. Subsequently, response surface methodology (RSM) was performed to define the optimum extraction condition to recover phenolic compounds from the alga matrices. The UAE condition suggested by RSM was: ultrasonic power 100%, pulse duty-cycle 1 s^?1, temperature 52.5 °C, extraction solvent 50% ethanol in water, and solvent-to-sample ratio 30:1. Kinetic studies confirmed 10 min to provide comparable recovery (p > 0.05) than any longer extraction time. The acceptable values validated the developed method for repeatability (CV, 4.8%) and intermediate precision (CV, 5.7%). In addition, the accuracy of the method suggested a complete recovery for two extraction cycles. Furthermore, the method has successfully been applied for a number of samples covering three different red algae species. Fingerprints of each sample based on phenolic composition and levels characterize the type and origin of different red algae species.     

Microwave-assisted extraction of phenolic compounds from grape seed

A microwave-assisted extraction technique was developed to optimize the extraction of phenolic compounds from grape seeds. The microwave power (300-150W) and time of extraction (20-200s) were varied during the optimization process. The polyphenol content of the resulting extracts were measured as mg of tannic acid equivalent per gram of crude extract (mg TAE/g of crude extract), using a Folin-Ciocalteau reagent. In general, neither the time nor the power had a significant effect on the overall % yield (average of 13.5%) and on the polyphenol content (392 mg TAE/g of crude extract) of the extracts. However, when the solvent polarity was changed by the addition of 10% water, the yield increased to 15.2% and the polyphenol content increased to 429 mg TAE/g of crude extract.     

Membrane solid-phase extraction with closed vessel microwave elution for the determination of phenolic compounds in aqueous matrices

Preconcentration of phenolic compounds was carried out with Empore C₁₈ membrane disks, which were eluted with a closed-vessel microwave extraction system. The optimum microwave-elution conditions were obtained by optimizing the elution solvent, elution temperature, duration of elution and volume of elution solvent. The recoveries of eleven phenolic compounds spiked at 10 and 500 g/L levels into water, using the optimum conditions, were all above 85% with relative standard deviations between 4.0 and 10.0%, except for phenol and 4-nitrophenol. Extraction of an industrial waste water sample suspected of containing phenolic compounds by SPE-CVME showed similar recoveries of phenol (the only phenolic compound detected) when compared with LLE and C₁₈ SPE cartridge techniques. Analysis of phenolic compounds was carried out using liquid chromatography coupled to a UV detection system.     

Thermal stability of total phenolic compounds and antioxidant activities of jaboticaba peel: Effect of solvents and extraction methods

The objective was to evaluate the effect of temperature on the degradation of total phenolic compounds (TPC) and antioxidant activities (AA), in addition to the effects of solvents (water, ethanol and methanol) and methods of maceration and ultrasound in the extraction of polyphenols from the jaboticaba peel powder (JPP). The thermal stability of the TPC and AA (DPPH, FRAP and ABTS) from JPP at different temperatures (90, 110 and 130 °C) was monitored over time (0–360 min). The effect of solvents (water, ethanol and methanol) and methods of maceration and ultrasound on the extraction of polyphenols from JPP was also evaluated. The best conditions for extracting polyphenols were quantified by HPLC. After extraction, the morphology of the powders was evaluated by scanning electron microscopy (SEM). The study of thermal stability showed that the ABTS radical presented a lower stability with time when compared to the other radicals. In addition, it was observed that the thermal degradation of TPC at the studied temperatures and that there is a positive correlation between TPC and AA. In the ultrasonic extraction using ethanol and methanol in the mass ratio of JPP/volume of solvent 1:20, the maximum TPC amounts were obtained. In the analysis by HPLC, a content of gallic acid (16.28 mg L⁻¹) and hesperidin (9.26 mg L⁻¹) were found for ethanol and methanol, respectively. The SEM images indicated that the changes in the structure favored the formation of pores contributing to the solubilization of TPC and consequently AA.     

Highly efficient nitration of phenolic compounds by zirconyl nitrate

Zirconyl nitrate was found to be an excellent reagent in the nitration of phenol and substituted phenols to give nitrated phenols. This procedure works efficiently on most of the examples at room temperature yielding nitro derivatives in fair to good yields with high regioselectivity.     

Determination of Pt from coke samples by ICP-MS after microwave assisted digestion and microwave assisted cloud point extraction

Platinum in coke samples was determined by inductively coupled plasma mass spectrometry (ICP-MS) after microwave-assisted sample digestion and temperature controlled microwave assisted cloud point extraction (MW-CPE). Interferences due to hafnium (¹⁷⁹Hf¹⁶O) were successfully eliminated using MW-CPE with 2-MBT prior to the determination of platinum by ICP-MS. The validity of the method was studied by spike recovery tests and by analyzing certified reference material (BCR-723 street dust). The results obtained for platinum in the BCR-723 were generally in good agreement with the certified values. Furthermore, the preliminary platinum results obtained for coke sample by ICP-MS after MW-CPE were compared to those obtained by a reference method (NiS-Fire Assay preconcentration/Te coprecipitation and ICP-MS determination).     

Investigation on phenolic compounds stability during microwave-assisted extraction

The stability of 22 phenolic compounds of different families (benzoic acids, benzoic aldehydes, cinnamic acids, catechins, coumarins, stilbens and flavonols) has been studied under conditions of microwave-assisted extraction. The influence on the stability affected by the working temperature between 50 and 175 degrees C has been evaluated, and it has been concluded that all the compounds studied are stable up to 100 degrees C, whereas at 125 degrees C there is significant degradation of epicatechin, resveratrol and myricetin. Conclusions have been drawn on the relationship between the chemical structure and the stability of the compounds; it has been found that those that have a greater number of hydroxyl-type substituents are more easily degraded under the extraction conditions.     

Qualitative and quantitative analysis of phenolic acid glycosides in Ginkgo biloba L. leaf,G. biloba leaf extract and its injection

Ginkgo biloba L. leaf (GBL) is one of the most commonly used medicinal plants in the world. Phenolic acids with biological activities have a relatively high content in G. biloba leaf extracts (GBE); therefore they are of great significance for the quality control of GBL, GBE and its preparations. However, there have been few studies focused on their analysis. In this work, 12 phenolic acids, including 11 phenolic acid glycosides, were identified by liquid chromatography coupled with quadrupole time-of-flight mass spectrometry (LC–Q-TOF/MS). Then, a method combining enzymolysis with HPLC was established for quantification of phenolic acid glycosides. It was found that the aglycones of phenolic acid glycosides mainly comprised five phenolic acids: 2,4,6-trihydroxybenzoic acid, protocatechuic acid, p-hydroxybenzoic acid, vanillic acid and p-coumaric acid. The quantitative method was validated, and the correlation coefficient (0.9993–0.9999), recovery (≥88.4%), repeatability (≤0.8%), and inter-day precision (≤5.5%) were satisfactory. Finally, the contents of glycosides of five phenolic acids in GBL, GBE and GBE injection from different sources were determined by the developed method. The method was accurate, repeatable and practicable, which could be helpful for the quantification of phenolic acid glycosides in other products containing GBL or GBE.     

Microwave‐assisted preparation of magnetic nanoparticles modified with graphene oxide for the extraction and analysis of phenolic compounds

Here in, magnetic nanoparticles combined with graphene oxide adsorbent were fabricated via a microwave‐assisted synthesis method, and used in the solid‐phase extraction of three phenolic compounds (phenol, 4‐nitrophenol, and m‐methylphenol) in environmental water samples. Various instrumental methods were employed to characterize the magnetic nanoparticles modified with graphene oxide. The influence of experimental parameters, such as desorption conditions, amount of adsorbent, extraction time, and pH, on the extraction efficiency was investigated. Owing to the high surface area and excellent adsorption capacity of the prepared material, satisfactory extraction was achieved. Under optimum conditions, a linear response was observed in the concentration range of 1.000–100.0 μg/L for phenol, 0.996–99.6 μg/L for 4‐nitrophenol, and 0.975–97.5 μg/L for m‐methylphenol, with correlation coefficients in the range of 0.9995–0.9997. The limit of detection (signal‐to‐noise ratio of 3) of the method varied between 0.5 and 0.8 μg/L. The relative standard deviations were <5.2%. The recovery percentages of the method were in the range of 89.1–104.3%. The results indicate that the graphene oxide‐modified magnetic nanoparticles possess high adsorptive abilities toward phenolic compounds in environmental water samples.