Microwave Conditions Research Articles

SmI2 -mediated C-alkylation of Ketones with Alcohols under Microwave Conditions: A Novel Route to Alkylated Ketones.

A novel protocol is developed towards the preparation of alkylated ketones from alcohols in presence of catalytic amount of SmI2 and base with the elimination of water as a single by-product under microwave irradiation conditions. Furthermore, applicability of this methodology to the synthesis of Donepezil and late-stage functionalization in Pregnenolone is also reported. Successful application of this methodology in Friedländer quinolone synthesis using 2-aminobenzyl alcohol and various acetophenones expand the synthetic utility of this protocol.

Simultaneous conventional and microwave heating for the synthesis of adsorbents for CO2 capture: Comparative study to pristine technologies

Microwave has become an attractive technology in the valorisation of renewable biomass and in the mitigation of challenges of climate change. In this work, the synergic effects of coupling microwave and mild conventional heating conditions has been investigated in preparing engineered ultra-micropore carbons from lignocellulosic biomass. The processing conditions were systematically investigated and correlated to the physicochemical properties of activated carbons produced and their performance in post-combustion CO2 capture. The highest CO2 uptake (225 mg g−1) was achieved for the hybrid carbon produced at low temperature (600 °C) and modest microwave intensity. The synergic effect of hybrid heating was confirmed by the significant CO2 uptake increase up to 80 and 60 % for the activated carbons prepared by microwave and conventional heating, respectively. The enhanced adsorption was confirmed by cyclic regeneration up to 99 % after 16 adsorption–desorption cycles, showing a linear correlation between the surface area, micropore volume and CO2 uptake. The Pseudo-first order model accurately describes the adsorption phenomena, indicating that physisorption is the primary mechanism governing the process. The results acquired from this study highlight the process intensification in the synthesis of porous materials with comparable properties that are typically attained in conventional heating using energy intensive conditions. Additionally, this approach reveals the benefits of conventional treatment for increasing the material’s microwave susceptibility and as consequence to reduce the processing time by microwave heating. The synergic effects confirms the potential of hybrid heating for applications where fast and selective heating is paramount.

Microwave biochars produced with activated carbon catalyst: Characterization and sorption of volatile organic compounds (VOCs)

A series of microwave biochars derived from wheat straw in the presence of a granulated activated carbon (GAC) catalyst, using a range of microwave conditions, were produced, characterized and tested as sorbents of three benzene series volatile organic compounds (VOCs). The microwave biochar with the greatest specific surface area (SSA), total pore volume (TPV), and micropore volume (312.62 m2 g−1, 0.2218 cm3 g−1, and 0.1380 cm3 g−1, respectively), were produced with 1:3 biomass:GAC catalyst mass ratio, 10 min microwave irradiation time, and at 500 W power level (WB500). Maximum adsorption capacities of WB500 to benzene, toluene and o-xylene were 53.9 mg g−1, 75.8 mg g−1 and 63.0 mg g−1, respectively, and were directly correlated to microwave biochar properties such as SSA, TPV or micropore volume, but were also influenced by VOC properties such as molecular polarity and boiling point. Kinetic modeling suggested that adsorption was governed by both physical partitioning and chemisorption mechanisms. In addition, microwave biochars maintained 79% to 92% of their initial adsorption capacity after ten adsorption/desorption cycles. These results suggest that microwave biochars produced with an GAC catalyst have excellent potential for efficient use in the removal of VOCs from waste gas.

Microwave-assisted N-alkylation of amines with alcohols catalyzed by MnCl2 : Anticancer, docking, and DFT studies.

A new protocol for the N-alkylation of amines with alcohols for the synthesis of tertiary amines in the presence of MnCl2 as a catalyst, under microwave conditions, is described. The advantages of this protocol include stable reaction profiles, a wide substrate variety, excellent yields, low cost, high yields, and easy workup conditions. The anticancer efficacy of all the synthesized compounds was tested in vitro against various cancer cell lines, such as MCF-7, MDA-MB-231 (human breast), HT-29, HCT 116 (colon cancer), A549 (human lung carcinoma), and Vero cells. Among the screened compounds, 3e, 3h, and 3i demonstrated potent anticancer activity, with compound 3h surpassing the reference drug cisplatin against A549, MCF7, MDA-MB-231, and HCT116 cancer cells. The introduction of an electron-withdrawing group on the phenyl ring resulted in increased anticancer activity. The most potent compounds, 3e, 3h, and 3i, were tested against VEGFR-2, HER2, and EGFR in multikinase inhibition assays, with compounds 3h and 3i showing improved potency against the HER2 kinase. The compounds formed two H-bonds with amino acids, indicating that they had a high affinity for the target HER2 kinase (PDB ID: 3RCD), according to the docking analysis. The absorption, distribution, metabolism, excretion, and toxicity properties of the optimized analogs were also assessed in vitro, enabling the discovery of promising anticancer agents. Finally, the B3LYP level was used to measure density functional theory geometry optimization and the related quantum parameters for the active compounds.

Influence of Steric Effect on the Pseudo-Multicomponent Synthesis of N-Aroylmethyl-4-Arylimidazoles.

A pseudo-three-component synthesis of N-aroylmethylimidazoles 3 with three new C–N bonds formed regioselectively under microwave conditions was developed. Products were obtained by reacting two equivalents of aroylmethyl bromide (ArCOCH2Br, 1) with the appropriate amidine salt (RCN2H3.HX, 2) and with K2CO3 as a base in acetonitrile. The bicomponent reaction also occurred, giving the expected 4(5)-aryl-1H-imidazoles 4. Notably, the ratio of products 3 and 4 is governed by steric factors of the amidine 2 (i.e., R = H, CH3, Ph). Therefore, a computational study was carried out to understand the reaction course regarding product ratio (3/4), regioselectivity, and the steric effects of the amidine substituent group.

MW-assisted hydrolysis of phosphinates in the presence of PTSA as the catalyst, and as a MW absorber

Abstract The hydrolysis of phosphinic esters is an important transformation that may be performed under acidic or basic conditions on conventional heating. A series of cyclic phosphinates, 1-alkoxy-3-methyl or 3,4-dimethylphospholane oxides, has now been hydrolyzed under microwave (MW) conditions in the presence of 0.1 or 0.5 equivalents of p-toluenesulfonic acid that served not only as the catalyst but also as a MW absorber. The later phenomenon was proved separately. The pseudo-first-order rate constants for the hydrolyses performed by the new approach were determined and a reactivity order was setup. The model reactions investigated were transplanted into flow MW accomplishment.

Vitamin C-Catalyzed Hantzsch reaction under microwave condition: A greener access to 1,4-Dihydropyridines

A cost effective, operationally simple and environmentally benign one-pot access to 1,4-dihydropyridine (DHP) derivatives was achieved through the successful utilization of vitamin C as catalyst under microwave irradiation. The applicability of this method was fairly demonstrated through implementation of reaction conditions on diversified substrates. A plausible mechanistic interpretation for this reaction has been outlined based on Hantzsch reaction.

Guerbet-type β-alkylation of secondary alcohols catalyzed by chromium chloride and its corresponding NNN pincer complex

β-Alkylation of alcohols has been efficiently accomplished using readily available 3d metal Cr under microwave conditions in air. Well-defined molecular Cr is involved with a KIE of 7.33 and insertion of α-alkylated ketone into Cr–H bond as the RDS.

Synthesis of benzimidazole derivatives in an aqueous media and reflux conditions catalyzed by glycine at pH 5.2 under microwave approach

A versatile organic amino acid catalyst like Glycine was used to prepare an effective synthesis of Benzimidazole derivatives from a wide variety of aldehydes and substituted phenylenediamine in an aqueous environment under microwave conditions. this process produced the required compounds in good to outstanding yields. The synthesis of benzimidazole derivatives via a Glycine catalyzed process is both environmentally friendly, cost effective, easy to carry method and under microwave approach.

A Facile Synthesis of (N-Heterocyclic Carbene)-Cu(I) Complexes Under Microwave Conditions and Their Application in A3 Reaction

A Facile Synthesis of (N-Heterocyclic Carbene)-Cu(I) Complexes Under Microwave Conditions and Their Application in A3 Reaction

Access to hexahydroazepinone heterocycles via palladium-catalysed C(sp3)-H alkenylation/ring-opening of cyclopropanes.

In this communication, we describe the synthesis of novel hexahydroazepinone derivatives starting from two simple building blocks in presence of a readily available palladium catalyst. The reaction proceeds through a selective C(sp3)-H alkenylation/ring-opening process to obtain the seven-membered ring products in good to excellent yields on a wide variety of substrates under batch, microwave, and continuous flow conditions.

Determination of 18 Intact Glucosinolates in Brassicaceae Vegetables by UHPLC-MS/MS: Comparing Tissue Disruption Methods for Sample Preparation.

Glucosinolates (GSLs) are important precursor compounds with anticancer activities in Brassicaceae vegetables and are readily hydrolyzed by myrosinase. Given the diversity of these species, establishing an accurate and universal method to quantify intact GSLs in different plant tissues is necessary. Here, we compared and optimized three tissue disruption methods for sample preparation. After microwave treatment for 90 s, 13 GSLs in homogenized Chinese cabbage samples were recovered at 73–124%. However, a limitation of this method was that different tissues could not be processed under the same microwave conditions. Regarding universality, GSLs in Brassicaceae vegetables could be extracted from freeze-dried sample powder with 70% methanol (v/v) or frozen-fresh sample powder with 80% methanol (v/v). Moreover, heating extraction is necessary for GSLs extracted from frozen-fresh sample powder. Average recoveries of the two optimized methods were 74–119% with relative standard deviations ≤ 15%, with the limits of quantification 5.72–17.40 nmol/g dry weight and 0.80–1.43 nmol/g fresh weight, respectively. Notably, the method for analyzing intact GSLs was more efficient than that for desulfo-GSLs regarding operational complexity, detection speed and quantification accuracy. The developed method was applied to identify the characteristic GSLs in 15 Brassicaceae vegetables, providing a foundation for further research on GSLs.

Development of Efficient One-Pot Methods for the Synthesis of Luminescent Dyes and Sol-Gel Hybrid Materials.

This paper presents a comparison of the simultaneous preparation of di-O-alkylated and ether–ester derivatives of fluorescein using different methods (conventional or microwave heating). Shortening of the reaction time and increased efficiency were observed when using a microwave reactor. Moreover, described here for the first time is the application of a fast, simple, and eco-friendly ball-assisted method to exclusively obtain ether–ester derivatives. We also demonstrate that fluorescein can be effectively functionalized by O-alkylation carried out under microwave or ball-milling conditions, saving time and energy and affording the desired products with good yields and minimal byproduct formation. All the synthesized products as well as pH-dependent (prototropic) forms trapped in the SiO2 matrix were examined using UV–Vis and fluorescence spectroscopy.

Design, Synthesis, and Biological Evaluation of Tryptanthrin Alkaloids as Potential anti-Diabetic and Anticancer Agents

An efficient green chemical approach has been reported to synthesize tryptanthrin alkaloids, utilizing isatin and isatoic anhydride as a substrate in the presence of tetrabutylammonium salt-based ionic liquids (TBA-ILs) as catalyst and reaction medium under microwave conditions (MWs). The reaction proceeds evenly under mild conditions to provide the bioactive natural product tryptanthrins in excellent yields. Besides, the molecular docking studies show that all the synthesized scaffolds exhibit potential binding affinities toward α-amylase, α-glucosidase ligands, GLP-1, and EGFR receptors; the in-vitro α-amylase and α-glucosidase assays show positive inhibition. In addition, the in vitro anticancer activity against A-549 non-small lung cancer (NSLC) cell lines leads to excellent inhibition. The present findings show the therapeutic potential of the tryptanthrins for targeting antidiabetic and anticancer activities.

Method modified AOAC 2015.01 in the microwave conditions and the addition of HCl during sample digestion for simultaneous Pb, Cd, Hg, and As in infant formula using ICP-MS: a method validation

The presence of heavy metals in infant formula has become a global concern. The most common method to determine heavy metals is AAS. However, as this technique is lacking in several aspects, including the instrument’s low sensitivity, a more sensitive instrument such as ICP-MS is necessary. The Inductively Coupled Plasma Mass Spectrometry (ICPMS) was used in accordance with the standard method AOAC 2015.01 with modifications on the microwave condition and the addition of hydrochloric acid (HCl) during the sample digestion process. The modified standard method requires a validation process. This research aimed to validate the method of analysis for the determination of Pb, Cd, Hg, As in infant formula using ICP-MS and its application in formula milk. This research consists of five stages: 1) instrumental performance; 2) homogeneity test; 3) method orientation; 4) method validation; and 5) the application of the validated method to other products. The findings in the research were: the method linearity was confirmed at working concentration 5-30 µg/kg for all the heavy metals with R2 value of nearly 1,000; the method limits of detection (LOD) were 0.74 µg/kg (Pb), 0.41 µg/kg (Cd), 0.08 µg/kg (Hg), 0.50 µg/kg (As), while the method’s limits of quantification (LOQ) were 2.48 µg/kg (Pb), 1.36 µg/kg (Cd), 0.27 µg/kg (Hg), 1.67 µg/kg (As); the method was found precise with Relative Standard Deviation (RSD) below 2/3 RSD Horwitz and all the recovery values were found to fall within the acceptable range (60–115%); the % RSD intra-lab reproducibility was below RSD Horwitz; and the method was robust, indicating that it was unaffected by small changes in its variables. The validated method can be applied routinely to determine heavy metals in infant formula and formula milk.

In-silicoPharmacokinetic and Affinity Studies of Piperazine/Morpholine Substituted Quinolines in Complex with GAK as Promising Anti-HCV Agent

Piperazine/morpholine derivatives of quinoline substituted at positions C-3, C-6 and C-8 has been previously prepared by SNAr reactions of 3,6,8-tribromoquinoline (1) under microwave or conventional heating reaction conditions. In this study, we evaluated binding interactions between the piperazine/morpholine substituted quinolines and its highly-likely receptor, Cyclin G associated kinase (GAK) involved in hepatitis C virus (HCV) entry into host cells, via docking, molecular dynamics (MD), thermodynamic and pharmacokinetics computations in order to select a possible lead compound, which may be used for lead-optimization in our future studies to develop novel drug candidates against HCV infections. 372 nsec MD simulations followed by MM-PBSA thermodynamic computations revealed that compound 23 ([Formula: see text]= 0.08[Formula: see text]nM) possesses the greatest potential to inhibit GAK. Pharmacokinetics computations suggest that compound 23 is a drug-like molecule as it conforms to the Lipinski filter. We determined that compound 23 could be a lead-like molecule for peripheric and cerebral HCV infections.

Effect of microwave/hydrothermal combined ionic liquid pretreatment on straw: Rumen anaerobic fermentation and enzyme hydrolysis

To explore green technology for wheat straw pretreatment, this study combined the microwave or hydrothermal with ionic liquid ([Bmim][OAc]) on wheat straw followed by rumen fermentation. The optimal conditions of microwave assisted ionic liquids pretreatment (M-I) and hydrothermal assisted ionic liquids pretreatment (H–I) treatment were 360 W and 200 °C, and the corresponding lignin removal rates reached 35.3% and 25.4%, respectively. Rumen fermentation showed that the highest volatile fatty acid (VFA) yield was found in M-I group, followed by H–I group at 234 and 180 mg/g, respectively. As for enzymatic hydrolysis, the saccharification rates at 3 days of M-I (360 W) and H–I (200 °C) were determined to be 393 and 320 mg/g. The optimal ionic liquid dosage was determined to be 30% in consideration of cost and VFA conversion rate. M-I pretreatment plus the rumen fermentation enjoyed the benefit of no enzyme addition and high product recovery, which was worth further investigating.

Synthesis and Antimicrobial Evaluation of Amino Acid Naphthoquinone Derivatives as Potential Antibacterial Agents

Background: The synthesis and biological evaluation of 1,4-naphthoquinone derivatives are of great interest since these compounds exhibit strong antibacterial, antifungal, antimalarial, and anticancer activities. The electronic properties of naphthoquinones are usually modulated by attaching functional groups containing nitrogen, oxygen, and sulfur atoms, which tune their biological potency and selectivity. Methods: A series of 13 amino acid 1,4-naphthoquinone derivatives was synthesized under assisted microwave and ultrasound conditions. The antibacterial activity of compounds was tested against American Type Culture Collection (ATCC): Escherichia coli, Pseudomonas aeruginosa, Staphylococcus aureus, and Enterococcus faecalis, as well as 2 multidrug resistant pathogens: E. coli and S. aureus from clinical isolated. Minimal inhibitory concentration (MIC) was determined using the broth microdilution method. Results: MIC of derivatives 4–11, 14, and 16 showed antimicrobial activity against Gram-positive and Gram-negative bacteria. Antimicrobial activities of the compounds 4–8 and 14 were ≤MIC 24.7 μg mL⁻¹ against all the reference strains; even more, compound 6 showed the most potent activity with an MIC of 3.9 μg mL⁻¹ on S. aureus. On the clinical isolated, the compounds 7, 8, and 14 showed an MIC of 49.7 and 24.7 μg mL⁻¹ against S. aureus and E. coli, respectively. About ADME properties and Osiris analysis, the compounds 4–16 presented high gastrointestinal absorption and good characteristics for oral bioavailability, and compound 14 was the less toxic. Conclusion: Amino acid 1,4-naphthoquinone derivatives showed good in vitro antibacterial activity against clinical strains, and modifications on C-3 with a chloride atom enhanced the efficiency against the same pathogens.

Drying characteristics and processing optimization of combined microwave drying and hot air drying of Termitomyces albuminosus mushroom

Termitomyces albuminosus (termite mushroom) is an edible fungus growing from termitaries in certain parts of China. Recently, the mushroom has gained in popularity, but due to rapid post-harvest quality decay, novel processing techniques including drying are required. This study aimed to optimize the conditions of combined microwave and hot air drying for T. albuminosus. Factors including microwave density, air temperature, and moisture content at conversion point were investigated and optimized using the drying rate, protein content, color L*, DPPH scavenging ability, rehydration ratio (RR), texture, sensory, and overall score as responses. The results showed that the overall score dried at 1.83 W/g microwave density, 60°C hot air, and 50% moisture content at conversion point were 0.675, 0.575, 0.530, respectively. The optimum conditions of combined microwave and hot air drying were microwave density 2.0 W/g, moisture content 52% at conversion point, and hot air temperature 57 respectively. The optimum conditions of combined microwave and hot air drying L* was 54.16, DPPH clearance was 91.87%, RR was 2.41, pileus chewiness was 1,587.19 g, stipe chewiness was 4,457.28 g, sensory score was 7.3, and overall score was 0.793, while the sensory quality was very high. Therefore, microwave drying followed by hot air drying is an effective, suitable method to obtain dried T. albuminosus. Practical applications Termitomyces albuminosus is also known as Termitomyces and has a similar internal fiber structure, color, and flavor as chicken. Drying is one of the most important methods for edible fungi processing and the major aim is to decrease water activity, which in turn minimizes the chemical and physical modifications during storage. The conditions of combined microwave and hot air drying for T. albuminosus were investigated and optimized using the drying rate, protein content, color L*, DPPH scavenging ability, rehydration ratio, texture, sensory, and overall score as responses. The obtained process parameters were helpful, effective, and suitable for the application of combined microwave and hot air drying technology to preserve good quality, especially for T. albuminosus.

Synthesis of β-Enaminonitrile-Linked 8-Methoxy-1H-Benzo[f]Chromene Moieties and Analysis of Their Antitumor Mechanisms.

A series of aryl-substituted 3-amino-1-aryl-8-methoxy-1H-benzo[f]chromene-2-carbonitriles (4a–4q) were designed and synthesized via reaction of 6-methoxy-2-naphthol with a mixture of appropriate aromatic aldehydes and malononitrile under microwave conditions. The structures of the novel compounds 4b, 4c, 4f, 4g, 4i, 4l, 4m, and 4o–4q were established according to IR, 1H-NMR, 13C-NMR/13C-NMR-DEPT, and MS. The benzochromene derivative 4c with a single chlorine at the meta position of the phenyl ring and, to a lesser extent, other benzochromenes with monohalogenated phenyl ring (4a, 4c–4f) exhibited the highest cytotoxicity against six human cancer cell lines MDA-MB-231, A549, HeLa, MIA PaCa-2, 5,637, and Hep G2. The mechanisms of the cytotoxic activities of benzochromenes with monohalogenated phenyl ring (4a, 4c–4f) were further analyzed using triple-negative breast cancer cell line MDA-MB-231. Cell cycle analysis showed accumulation of the treated cells in S phase for 4a, 4d–4f, and S-G2/M phases for 4c. In vivo, 4a and 4c–4f inhibited growth, proliferation, and triggered apoptosis in preestablished breast cancer xenografts grown on the chick chorioallantoic membranes while exhibiting low systemic toxicity. Compounds 4a and 4c–4f increased levels of mitochondrial superoxide and decreased mitochondrial membrane potential resulting in initiation of apoptosis as demonstrated by caspase 3/7 activation. In addition, 4c induced general oxidative stress in cancer cells. The SAR study confirmed that halogens of moderate size at meta or para positions of the pendant phenyl ring enhance the cytotoxic activity of 3-amino-1-aryl-8-methoxy-1H-benzo[f]chromene-2-carbonitriles, and these compounds could serve as leads for the development of novel anticancer therapies.