Microwave Irradiation Research Articles

Isolation, Antibacterial Activity and Molecular Identification of Avocado Rhizosphere Actinobacteria as Potential Biocontrol Agents of Xanthomonas sp.

Actinobacteria, especially the genus Streptomyces, have been shown to be potential biocontrol agents for phytopathogenic bacteria. Bacteria spot disease caused by Xanthomonas spp. may severely affect chili pepper (Capsicum annuum) crops with a subsequent decrease in productivity. Therefore, the objective of the study was to isolate rhizospheric actinobacteria from soil samples treated by physical methods and evaluate the inhibitory activity of the isolates over Xanthomonas. Initially, soil samples collected from avocado tree orchards were treated by dry heat air and microwave irradiation; thereafter, isolation was implemented. Then, antibacterial activity (AA) of isolates was evaluated by the double-layer agar method. Furthermore, the positive/negative effect on AA for selected isolates was evaluated on three culture media (potato-dextrose agar, PDA; yeast malt extract agar, YME; and oat agar, OA). Isolates were identified by 16S rRNA sequence analysis. A total of 198 isolates were obtained; 76 (series BVEZ) correspond to samples treated by dry heat and 122 strains (series BVEZMW) were isolated from samples irradiated with microwaves. A total of 19 dry heat and 25 microwave-irradiated isolates showed AA with inhibition zones (IZ, diameter in mm) ranging from 12.7 to 82.3 mm and from 11.4 to 55.4 mm, respectively. An increment for the AA was registered for isolates cultured on PDA and YME, with an IZ from 21.1 to 80.2 mm and 14.1 to 69.6 mm, respectively. A lower AA was detected when isolates were cultured on OA media (15.0 to 38.1 mm). Based on the 16S rRNA gene sequencing analysis, the actinobacteria belong to the Streptomyces (6) and Amycolatopsis (2) genera. Therefore, the study showed that microwave irradiation is a suitable method to increase the isolation of soil bacteria with AA against Xanthomonas sp. In addition, Streptomyces sp. BVEZ 50 was the isolate with the highest IZ (80.2 mm).

Hybrid Pd0.1Cu0.9Co2O4 nano-flakes: a novel, efficient and reusable catalyst for the one-pot heck and Suzuki couplings with simultaneous transesterification reactions under microwave irradiation

We report the fabrication of a novel spinel-type Pd₀.₁Cu₀.₉Co₂O₄ nano-flake material designed for Mizoroki-Heck and Suzuki coupling-cum-transesterification reactions. The Pd₀.₁Cu₀.₉Co₂O₄ material was synthesized using a simple co-precipitation method, and its crystalline phase and morphology were characterized through powder XRD, UV-Vis, FESEM, and EDX studies. This material demonstrated excellent catalytic activity in Mizoroki-Heck and Suzuki cross-coupling reactions, performed in the presence of a mild base (K₂CO₃), ethanol as the solvent, and microwave irradiation under ligand-free conditions. Notably, the Heck coupling of acrylic esters proceeded concurrently with transesterification using various alcohols as solvents. The catalyst exhibited remarkable stability under reaction conditions and could be recycled and reused up to ten times while maintaining its catalytic integrity.

Preheating Characteristics of Magnetite Pellets Under Microwave Irradiation

Preheating Characteristics of Magnetite Pellets Under Microwave Irradiation

A Novel Approach for the Synthesis of 3,3′-((4-Methoxyphenyl)methylene)bis(4-hydroxyfuran-2(5H)-one) Employing Natural Deep Eutectic Solvents and Microwave Irradiation

Tetronic acid, a five-membered heterocyclic moiety present in various natural products, has emerged as a significant building block for many pharmaceutically active compounds. In this study, a novel protocol for the synthesis of the bis-tetronic acid 3,3′-((4-methoxyphenyl)methylene)bis(4-hydroxyfuran-2(5H)-one) (3) via a domino Knoevenagel–Michael reaction is presented. The natural deep eutectic solvent L-proline/glycerol 1:2 molar ratio was utilized as a solvent and catalyst, while the reaction was further promoted via microwave irradiation, providing the desired product in high yield (83%). The solvent was successfully recycled and reused up to three times.

N-Heterocycle-Substituted Hexa-peri-hexabenzocoronenes with Windmill Architectures.

We describe the synthesis and computational investigation of N-heterocycle-substituted hexa-peri-hexabenzocoronenes (HBCs). Following our method for the preparation of thioether-substituted HBCs, we prepared pyrrole-, indole-, carbazole-, and 1H-benz[g]indole-substituted HBCs from the corresponding fluorinated precursors under microwave irradiation. A series of polysubstituted benzoindole-HBCs with windmill architectures was also synthesized using the polyfluorinated HBC analogs. Due to the circular arrangement of the benzoindole moiety, the attachment of multiple substituents results in the presence of multiple conformers at room temperature. The rotation barrier can be overcome by heating the compounds to 323-333 K. Additionally, the investigation of the relaxed geometries shows two π-stacking motifs within the conformers. Similar to the thioether substituted HBCs, the nature of the heterocycle does not influence the optoelectronic properties of the HBC core. The attachment of multiple benzoindole substituents leads to a bathochromic shift of the absorption and emission spectra, comparable to our previous studies.

CuI–Zn(OAc)2 Catalyzed Selective CC Bond Cleavage of 1,3‐Diketones/β‐Ketoester for the Formation of Quinazolin‐4(3H)‐Ones: A Fast, Solvent‐Free, Synthetic Strategy Under Microwave Irradiation

ABSTRACTCuI–Zn(OAc)2 catalyzed a new, fast, solvent‐free strategy for the synthesis of quinazolin‐4(3H)‐ones via selective scission of CC bond of the 1,3‐diketone (both cyclic and acyclic) and β‐ketoester was achieved under microwave irradiation. In contrast to the frequently applied synthetic strategy that involves cyclization‐oxidation sequence of anthranilamides (2‐aminobenzamides) with various aldehydes or benzyl alcohols, here, anthranilamide reacts with β‐ketoester/1,3‐diketo compounds in presence of CuI‐Zn(OAc)2 catalyst to form quinazolin‐4(3H)‐ones scaffold through an uncommon CC bond cleavage under solvent‐free mild conditions with excellent yields. Besides, this method displays its capacity for gram‐scale reactions.

Effects of microwave treatment on structural and functional properties of germinated corn starch.

Measuring the germination index of corn, and gelatinization index, thermodynamic properties, long-range structure, short-range structure and particle morphology of corn starch, the study aimed to investigate the effects of different microwave (MW) treatment on the structural and functional properties of germinated corn starch. The results indicated that after appropriate MW treatment, the germination indices (germination rate, germination potential, sprout length and sprout weight) of germinated corn starch were improved after 7 days of germination. In addition, MW treatment also affected the structure of germinated corn starch. MW treatment could reduce the relative crystallinity of starch, but did not change the crystal type and the peak position of each absorption peak in Fourier transform infrared spectra. In addition, rapid visco-analysis and differential scanning calorimetry results showed, respectively, that MW treatment decreased the peak viscosity of germinated corn starch and increased the gelatinization temperature. Finally, MW treatment made the starch surface become rough, destroyed the starch particle structure and produced random cracks and voids. Overall, the present study proves that appropriate MW treatment is an effective measure for the modification of germinated corn starch, and provides a theoretical basis for the application of MW technology in germinated corn products. © 2024 Society of Chemical Industry.

Cs2CO3-Catalyzed Rauhut-Currier-Type Reaction for the Synthesis of 2,3-Dihydrobenzo[b]oxepin Derivatives.

The synthesis of fused benzoxepines relies on the use of complex substrates and methodologies. Herein, we report our experimental and theoretical findings about an unprecedented Rauhut-Currier-type reaction catalyzed by Cs2CO3 to access these important compounds. The developed methodology avoids the use of phosphine- or amine-based catalysts and additives. The reaction can be performed under microwave irradiation and proceeds with complete chemoselectivity.

Synthesis and Docking Studies of Novel Spiro[5,8-methanoquinazoline-2,3′-indoline]-2′,4-dione Derivatives

In this study, a set of spiro[5,8-methanoquinazoline-2,3′-indoline]-2′,4-dione derivatives 3a–p were synthesized starting from unsubstituted and N-methyl-substituted diendo- and diexo-2-aminonorbornene carboxamides, as well as various substituted isatins. The typical method involves a condensation reaction of alicyclic aminocarboxamide and isatin in the presence of a catalyst, using a solvent and an acceptable temperature. We developed a cost-effective and ecologically benign high-speed ball milling (HSBM), microwave irradiation (MW), and continuous flow (CF) technique to synthesize spiroquinazolinone molecule 3a. The structures of the synthesized compounds 3a–p were determined using 1D and 2D NMR spectroscopies. Furthermore, docking studies and absorption, distribution, metabolism, and toxicity (ADMET) predictions were used in this work. In agreement with the corresponding features found in the case of both the SARS-CoV-2 main protease (RCSB Protein Data Bank: 6LU7) and human mast cell tryptase (RCSB Protein Data Bank: 2ZA5) based on the estimated total energy and binding affinity, H bonds, and hydrophobicity in silico, compound 3d among our 3a–g, 3i–k, and 3m derivatives was found to be our top-rated compound.

Electric properties for thin films of microwave treated hydrophilic graphite fabricated by liquid-liquid interface

Abstract This paper reports the results of an attempt to combine microwave treated hydrophilic graphite (MwHG), a new carbon material that is both hydrophilic and electrically conductive, with a new deposition method using the interface between the aqueous and organic phases, the liquid-liquid interface deposition method (L-L method). The synthesized MwHG was characterized by X-ray diffraction (XRD) and Raman spectroscopy, and the deposited MwHG films were characterized by scanning electron microscopy (SEM) and electrical properties. It was found that the crystallinity of MwHG was changed by changing the microwave irradiation time during the synthesis of MwHG. It was also found that the high electrical conductivity was related to the microwave irradiation time or the order in which the films were deposited. Furthermore, the surface morphology of the films consisted of agglomerations of particles of different sizes with pores, and the size of the particles decreased with the number of depositions.

One‐Pot Synthesis of C‐Substituted bis‐Benzimidazoles and Benzobisimidazoles via Reductive Cyclization of o‐Nitroaniline Derivatives and Aldehydes using Sodium Metabisulfite in a Microwave Reactor

AbstractHerein, we report a simple and an economical method to synthesize C‐substituted bis‐benzimidazole and C‐substituted benzobisimidazole derivatives in moderate to excellent yields using sodium metabisulfite, under microwave irradiation conditions. The most attractive feature of the methodology is the three‐step yet one‐pot condensation of nitroarenes with various benzaldehyde derivatives to synthesize useful benzimidazoles, and an easy product isolation method by simple solvent trituration techniques. The methodology can be fine‐tuned to synthesize selectively the mono C‐substituted benzimidazoles, leaving a nitroaniline functionality intact for preparing a variety of unsymmetrical C‐substituted bis‐benzimidazoles.

Rapid Generation of Microplastics and Plastic-Derived Dissolved Organic Matter from Food Packaging Films under Simulated Aging Conditions.

In this study, we show that low-density polyethylene films, a prevalent choice for food packaging in everyday life, generated high numbers of microplastics (MPs) and hundreds to thousands of plastic-derived dissolved organic matter (DOM) substances under simulated food preparation and storage conditions. Specifically, the plastic film generated 66-2034 MPs/cm2 (size range 10-5000 μm) under simulated aging conditions involving microwave irradiation, heating, steaming, UV irradiation, refrigeration, freezing, and freeze-thaw cycling alongside contact with water, which were 15-453 times that of the control (plastic film immersed in water without aging). We also noticed a substantial release of plastic-derived DOM. Using ultrahigh-resolution mass spectrometry, we identified 321-1414 analytes with molecular weights ranging from 200 to 800 Da, representing plastic-derived DOM containing C, H, and O. The DOM substances included both degradation products of polyethylene (including oxidized forms of oligomers) and toxic plastic additives. Interestingly, although no apparent oxidation was observed for the plastic film under aging conditions, plastic-derived DOM was more oxidized (average O/C increased by 27-46%) following aging with a higher state of carbon saturation and higher polarity. These findings highlight the future need to assess risks associated with MP and DOM release from plastic wraps.

Design, Synthesis, Molecular Docking, and ADME-Tox Investigations of Imidazo[1,2-a]Pyrimidines Derivatives as Antimicrobial Agents

A convenient and effective synthesis of imidazo[1,2-a]pyrimidine derivatives has been developed under microwave irradiations using Al2O3 as a catalyst in solvent-free conditions. The functionalized imidazo[1,2-a]pyrimidine derivatives are useful in biochemistry and medical science. In our investigation, the antimicrobial activity of the synthesized compounds was evaluated against 13 microorganisms, including 6 Gram-positive bacteria, 4 Gram-negative bacteria, and 3 pathogenic fungi. Bioactivity tests revealed that the majority of the compounds exhibited good antimicrobial activity. Finally, molecular docking simulations and ADME-T predictions were performed, showing that the most active compounds have good binding modes with microbial targets and promising pharmacokinetic safety profiles.

Hydrothermal pretreatment with microwaves: A new strategy for ensuring the sustainability of biorefineries

Lignocellulosic biomass (LCB) includes agricultural residues, crop wastes, and food wastes that are ubiquitously present and can be used as renewable resources to generate bioenergy or biofuels. Still, direct utilization of LCB to produce biofuel is not an easy task due to the recalcitrance property of LCB. The pretreatment strategy is an important step in a biorefinery to reduce biomass recalcitrance and to use it for bioenergy including value-added product generation. Microwave irradiation is procuring interest regarding LCB and waste material pretreatment over time before moving to biological transformation to biofuels. The coupling of microwave heating with water has made it the most effective treatment for biomass valorization to generate biofuel and other value-added products, turning it into the most cost-effective and eco-friendly approach. Despite its numerous advantages, scaling up microwave pretreatment from laboratory experiments to industrial applications faces several challenges. These limitations become significant hurdles in scaling up. As a result, it is necessary to focus research on cost evaluations and life cycle assessment (LCA) studies for commercialization that will benefit the bioeconomy and the environment. This review discusses microwave-assisted pretreatment significance in valorizing LCB for biofuel generation including the cost evaluation and LCA studies that have the most important role in commercializing the microwave-assisted pretreatment from lab scale to industrial scale.

Rapid and Efficient Dual Detection Of Zn2+ Ions and Oxytetracycline Hydrochloride Using a Responsive Fluorescent "On-Off" Sensor Based on Simple Salen-Type Schiff Base Ligand.

This research has progressed to an effective detection chemosensor of zinc, aluminum ions and oxytetracycline hydrochloride antibiotic based on the fluorescence technique. A straightforward method utilizing microwave irradiation was employed to synthesize the salen-type Schiff base ligand N,N'-bis(salicylaldehyde)4,5-dichloro-1,2-phenylenediamine (H2I), providing a good 70 % yield. In ethanol, the H2I sensor demonstrated remarkable rapidity, selectivity, and sensitivity in detecting zinc ions. The fluorescence spectrum exhibited a 44-fold substantial enhancement at 522 nm and achieved a low limit of detection (LOD) of 1.47 μM. Furthermore, the H2I probe's emission intensity increased by 124 times when compared to the ligand's ability to detect Al3+ ions at 494 nm with a LOD value of 7.4 μM. Additional research was done using the H2I probe's effective Zn2+ detection capability. The ability to recognize zinc ions in different real water samples demonstrated a recovery rate of 98.67 % to 103.31 %. Interestingly, a naked-eye visible fluorescence color of H2I solution impregnated filter papers turned colorless into yell ow under UV irradiation by adding Zn2+ ions, renders it suitable for developing a practical zinc ion detection kit test. In particular, the I-Zn2+ complex effectively quenched the fluorescence toward oxytetracycline hydrochloride (OTC) with a LOD value of 1.49×10-2 μM in DMSO:H2O (6 : 4, v/v). This is a novel and effective procedure for sensing OTC antibiotic by the I-Zn2+ complex. These findings hold immense potential for the development of dual fluorescent probes, thereby enhancing sensitivity and specificity in identifying metal ions and antibiotics in a wide range of applications.

A Tumor-Homing Nanoframework for Synergistic Microwave Tumor Ablation and Provoking Strong Anticancer Immunity Against Metastasis.

Microwave thermotherapy (MT) is a clinical local tumor ablation modality, but its applications are limited by its therapeutic efficacy and safety. Therefore, developing sensitizers to optimize the outcomes of MT is in demand in clinical practice. Herein, we engineered a special nanoframework (i.e., FdMI) based on a fucoidan-decorated zirconium metal-organic framework incorporating manganese ions and liquid physisorption for microwave tumor ablation. The monodisperse nanoframework exhibited both microwave thermal effects and microwave dynamic effects, which could effectively kill cancer cells by efficient intracellular drug delivery. Through fucoidan-mediated targeting of P-selectin in the tumor microenvironment (TME), the FdMI effectively accumulated in tumor regions, leading to significant eradication of orthotropic triple-negative breast cancer (TNBC) and aggressive Hepa1-6 liver tumors by the synergistic effects of microwave thermotherapy/dynamic therapy (MT/MDT). The eradication of primary tumors could activate systemic immune responses, which effectively inhibited distant TNBC tumors and lung metastasis of Hepa1-6 liver tumors, respectively. This work not only engineered nanoparticle sensitizers for tumor-targeted synergistic MT/MDT but also demonstrated that nanocarrier-based microwave tumor ablation could stimulate antitumor immunity to effectively inhibit distant and metastatic tumors, demonstrating the high potential for effectively managing advanced malignant tumors.

Characterisation of fibre distribution uniformity in steel fibre-reinforced concrete under microwave-induced heating during casting

Traditional active microwave thermography (AMT) tests for hardened steel fibre-reinforced concrete (SFRC). The surface temperature of SFRC derived from AMT cannot fully characterise the distribution of steel fibres in the SFRC. This study proposes a microwave-induced heating method combined with temperature sensors (MI-TS) to estimate the fibre dispersion of an SFRC mixture during casting. The principles and testing process are discussed, and a numerical model is developed to evaluate the temperature distribution of the SFRC mixture following microwave exposure. Through MI-TS and numerical models, the temperature in the SFRC mixture with uniform fibre distribution, fibre clustering and fibre sinking is investigated, and the results are compared with those obtained by AMT and destruction technology to evaluate the feasibility of the proposed method. The results show that in the same specimen, the temperature difference between areas with similar fibre content falls in a very narrow range (e.g., 3.5–4.5 °C for a 100 × 100 × 100 mm specimen exposed to 600 W of microwave irradiation for 180 s). When the fibre content in a given area is more than 0.5 vol%, a large temperature difference forms between this and other areas. When the equivalent fibre content of the specimen is ignored, the temperature difference between the two areas is directly proportional to the difference in fibre content. Therefore, the area that shows differences in fibre clustering and fibre content can be easily determined found based on the temperature difference derived from MI-TS.

Synthesis of Zinc Sulfide Luminescent Nanoparticles Using Zinc Metal Complexes of S-benzyl Dithiocarbonate via Microwave Irradiation Route

This paper reported highly luminous zinc sulfide (ZnS) nanoparticles grown by microwave-irradiated single molecular precursors. The precursor was obtained by Schiff bases of S-benzyl dithiocarbazate (SBDTC) ligand using 5-Bromo-4-hydroxy-3-methoxy-2-nitro Benzaldehyde; 4NNbiscyno diethylamino benzaldehyde and p-amino acetophenone. The nanoparticles obtained were characterized by X-ray diffraction studies for structural analysis, transmission electron micrographs (TEM) for morphological analysis, and UV-Vis spectra for optical analysis. X-ray diffractograms exhibit mixed structures analysis (wurtzite and cubic) for particles obtained using 5-Bromo-4-hydroxy-3-methoxy-2-nitro benzaldehyde and 4NNbiscyno diethylamino benzaldehyde. However, the particles obtained by p-amino acetophenone Schiff bases of SBDTC exhibit only wurtzite structure. Variation in optical properties is also observed with the precursors used. The excellent optical properties of ZnS nanoparticles signify the role of microwave irradiation in synthesis. The Photoluminescence (PL) study shows the luminescence in the visible region and the maximum intensity for ZnS particles obtained by zinc complex of p-amino acetophenone Schiff base of S-benzyl dithiocarbazate. The microwave-assisted process can be used for large-scale production of nanoparticles for emitting light in the visible region in various detecting and sensing applications.

DABCO‐Saccharin Acetate as a Novel, Recyclable and Metal‐Free Catalyst for Eco‐Friendly Synthesis of Various Pyridazino[1,2‐a]indazole and 1H‐indazolo[1,2‐b]phthalazine Heterocycles Under Solvent‐Free Conditions

AbstractIn this research various pyridazino[1,2‐a]indazole and 1H‐indazolo[1,2‐b]phthalazine and 1H‐indazolo[1,2‐b]phthalazine derivatives were produced with a high yield via a multi‐component reaction of dimedone, aldehyde, hydrazine and anhydride compounds in the presence of a novel DABCO‐Saccharin acetate ([DABCOH][Sac‐CH3CO2]) ionic liquid under microwave irradiation. The applied method for producing these heterocyclic compounds demonstrated a number of desirable traits, including quick reactions, high yields of the final product, and straightforward separation of the product and catalyst from the reaction mixture.

Producing aromatic‐rich oil through microwave‐assisted catalytic pyrolysis of low‐density polyethylene over Ni/Co/Cu‐doped Ga/ZSM‐5 catalysts

AbstractMicrowave (MW)‐assisted catalytic pyrolysis represents a promising method for transforming petroleum‐based plastic waste into valuable chemicals, offering a pathway towards more sustainable circular economy. In this study, catalytic pyrolysis of low‐density polyethylene (LDPE) was conducted under MW irradiation. The influence of various catalyst types (HZSM‐5, Ga/ZSM‐5, Ga/Ni/ZSM‐5, Ga/Co/ZSM‐5, and Ga/Cu/ZSM‐5) on product yield and distribution was examined. The results revealed that the Ga/ZSM‐5 catalyst yielded the maximum liquid oil, approximately 41%. Ga/Ni/ZSM‐5 performed excellently in the production of long‐chain olefins, constituting about 27% of the liquid fraction. However, Ga/Co/ZSM‐5 led to the production of heavy pyrolysis oil containing nearly 25% long‐chain paraffins, rendering it unsuitable for producing high‐value chemicals. Conversely, the Ga/Cu/ZSM‐5 catalyst yielded an aromatic‐rich pyrolysis oil, with benzene derivatives constituting approximately 90% of the liquid oil fraction, thus proving to be a suitable catalyst for the intended application. The liquid product distribution was compared with a petroleum assay by SimDist, and this suggested that utilizing the HZSM‐5 catalyst could yield an 86.4% naphtha fraction. The study also revealed that the Ga/Cu/ZSM‐5 catalyst generated the largest amounts of hydrogen and syngas, as determined by a MicroGC analysis of the gas products. This catalyst also exhibited the maximum coke deposition (1.35%) postreaction, which was attributed to its high aromatic hydrocarbon content in the pyrolysis oil and maximal hydrogen release. A comparison of fresh and spent catalyst properties was conducted to gain insights into catalyst activity and to correlate the effects of metal doping on product distribution. These findings underscore the potential of MW‐assisted catalytic pyrolysis, particularly with the Ga/Cu/ZSM‐5 catalyst, for the efficient conversion of plastic waste into valuable chemicals, thereby contributing to sustainable resource utilization and environmental conservation.