Mild Microwave Research Articles

Catalytic Effects of Various Acids on Microwave-assisted Depolymerization of Organosolv Lignin

The catalytic effects of various acids (sulfuric acid, hydrochloric acid, phosphoric acid, and formic acid) on the depolymerization of organosolv lignin under mild microwave heating (approximately 100 W, 160 °C for 30 min) were investigated. The liquid product was separated from the solid residue and analyzed by gel permeation chromatography (GPC) and Fourier transform infrared spectroscopy (FTIR). The solid residue was analyzed with thermogravimetric analysis (TG-DTG) and observed by scanning electron microscopy (SEM). The experimental results showed that sulfuric acid exhibited a better catalytic effect than the other acids. The SEM and TG-DTG results showed that the solid residue from sulfuric acid-catalyzed depolymerization was not only remarkably smaller than that of the other groups, but also presented a faster thermal decomposition rate. The molecular weight (Mw, weight-average) of the liquid product (Mw = 1020) from sulfuric acid-catalyzed depolymerization was also lower than that of the other groups.

Effect of pH on the synthesis of In(OH)3 and In(OH)3:Ce3+/Dy3+ nanocrystals by a fast, mild microwave method

Indium hydroxide nanocrystals were synthesized through a microwave reaction. It is a fast, simple and mild process to get the uniform and monodisperse In(OH)3 nanomaterials without the aid of any surfactants or templates. Size and morphology of the In(OH)3 nanomaterials could be controllably adjusted through the pH value of the reaction mixtures. The formation mechanisms of the nanostructures have been investigated on the basis of a series of SEM studies of the samples obtained at different reaction durations. Ce3+, Dy3+ or Ce3+/Dy3+ doped In(OH)3 were also synthesized by the microwave reaction and optical properties of these materials were evaluated.

Mild microwave activated, chemo-thermal combinational tumor therapy based on a targeted, thermal-sensitive and magnetic micelle.

The development of combinational anti-tumor therapy is of great value. Here, the thermal-sensitive and hepatic tumor cell targeting peptide-A54 modified polymer, A54-poly(ethylene glycol)-g-poly(acrylamide-co-acrylonitrile) (A54-PEG-g-p(AAm-co-AN)) can self-assemble into an 80nm-sized micelle, which shows a thermal-sensitive behavior with an upper critical solution temperature (UCST) of 43°C. This self-assembled and targeted A54-PEG-g-p(AAm-co-AN) micelle can co-encapsulate anti-tumor drug doxorubicin (DOX) and magnetic nanoparticles (MNPs) taking advantage of the hydrophobic core of the core-shell micellar structure, when the temperature is lower than 43°C. A much higher accumulation of the MNPs@A54-PEG-g-p(AAm-co-AN) to the tumor navigated by the A54 targeting peptide is achieved. Due to the thermal-agent effect of the accumulated MNPs in tumor, the mild microwave (8W) applied afterwards specifically elevates the local tumor temperature by 13°C, compared to 6°C without MNPs accumulation in 30min. The greater temperature rise resulted from the thermal-agent effect of MNPs doesn't only activate the drug release inside tumor cells, but also achieve an augmented hyperthermia. A mild microwave activated, chemo-thermal combinational tumor therapy is thus developed.

Multisynergistic Platform for Tumor Therapy by Mild Microwave Irradiation-Activated Chemotherapy and Enhanced Ablation.

Microwave (MW) therapy, as a promising type of thermal therapy, has been attracting more and more attention from scientists. The combination of thermal and chemotherapy is of great significance in the latest studies of synergistic tumor therapy. However, the research on the MW therapy mechanism, especially the nonthermal effect applied in the combined cancer therapy, is not thorough enough. Pleasantly, we have discovered that nonthermal MW irradiation can promote the cellular uptake of nanoparticles and anticancer drugs via experiments in vitro and in vivo. Therefore, multifunctional nanoplatforms have been designed for enhanced tumor inhibition by loading ionic liquids (ILs), doxorubicin hydrochloride (DOX), and phase change materials (PCMs) into ZrO2 hollow nanoparticles. PCMs act as MW switches. The as-made IL-DOX-PCM@ZrO2 nanoplatforms were injected into H22-tumor-bearing mice via the tail vein. Mild microwave irradiation (0.9 W, 450 MHz) was then applied. The thermal effect of MW could cause the temperature of the tumor site to rise (58 °C). On the other hand, it will trigger the MW switch to open and release DOX when the temperature is high enough. At the same time as drug release, a MW nonthermal effect could improve the cellular uptake of nanomaterials and anticancer drugs. The multisynergistic effect can promote the survival rate of the IL-DOX-PCM@ZrO2+MW group to 100%. The results of the tumor therapy experiment in vivo demonstrated that as-made multifunctional IL-DOX-PCM@ZrO2 nanoplatforms could enhance the therapeutic outcome of combined thermal and chemotherapy under mild MW irradiation.

Microwaves as a pretreatment for enhancing enzymatic hydrolysis of pineapple industrial waste for bioethanol production

The pineapple industry generates significant amounts of residues which are classified as lignocellulosic residual biomass. In the present paper, microwaves are studied as a pretreatment to improve pineapple waste saccharification. Different microwave (MW) powers (10.625, 8.5, 6.375, 4.25 and 2.125W/g) and exposure times (1–20min) were applied to the solid part of the waste before enzymatic hydrolysis. Infrared thermography was used to assess temperature evolution and structural modifications were evaluated by Cryo-SEM. Sugar content and fermentation inhibitors (phenols, furfural and hydroxymethylfurfural) were also determined. MW increased sugar yield as long as intermediate powers were used (up to 6.375W/g). However, high powers and longer treatments resulted in sugar degradation and/or a decrease in the efficiency of the enzymatic hydrolysis process. Temperature records indicated that thermal sugar degradation may occur in those cases. The presence of fermentation inhibitors have been confirmed and related to prolonged MW treatments. Microscopic observations suggested that mild microwave pretreatments may promote microstructural changes that enhance enzyme performance, whereas harsher treatments could increase tissue compactness and reduce the effectiveness of the enzymatic treatment. It is concluded that microwave pretreatments using the appropriate energy supply and exposure time enhances saccharification efficiency, potentially improving further bioethanol yield.

Effect Of Drying Methods And Extraction Time-Temperature Regime On Mango Kernel Lipids

In this study, effect of drying method and time temperature regime of extraction on quality of mango kernel lipid was evaluated. Hot air drying required drying of seeds for long intervals and exposure to higher temperature, where as microwave drying was found to be quick due to heating induced at the molecular level. The drying time under optimized conditions for microwave was reduced by 34 folds when compared with hot air drying. Parameters including drying temperature, extraction time, lipid yield and fatty acid profile were evaluated. The study shows that modification of extraction method for lower temperature and lesser time does not alter the quality and quantity of lipids from mango kernel (10.8%). Structural changes induced due to drying were studied using scanning electron microscopy. Statistical analysis showed that drying conditions and extraction conditions affected the lipid yield. The further comparison between two methods was done in terms of fatty acid profiles and oxidative stability. The stability of lipid was estimated by measuring the ratio of linoleic acid to palmitic acid for all extraction conditions. The ratio of C18:2/C16 was similar for microwave irradiation when compared to hot air dried samples (1.0 - 1.2). It was concluded that mild microwave power level (180W) helps in quick drying of kernels. The structure was found to be intact with minimal damage to starch granules. Lower microwave power level helped in retention of the lipid yield and quality while higher microwave power levels significantly affected the unsaturated fatty acids.

Potential use of microwave treatment on fresh-cut carrots: physical, chemical and microbiological aspects.

The effect of microwave treatments (900 and 750 W for 45 and 60 s) on the microbial, physicochemical and sensory properties of fresh-cut carrot slices and the contents of several bioactive compounds was studied. Carrot samples were stored for 7 days at 5 °C. The microwaving of fresh-cut carrots reduced the initial respiration rate (8.6 CO2 mL kg(-1) h(-1)) by 55-74% compared with untreated samples, although the rates then increased during storage. The initial pH (6.7), titratable acidity (0.036%), soluble solid content (8.2 °Brix) and shelf-life of the samples did not differ greatly from those of the untreated samples. Microwaving prevented the incipient whitening and surface dryness during storage. In general, no significant changes in phenylalanine ammonia lyase activity (5.5 µmol t-cinnamic acid kg(-1) h(-1)), total phenolics (TP, 81.3 mg chlorogenic acid equivalent kg(-1) fresh weight (FW)) or total antioxidant capacity (TAC, 74.2 µmol Trolox equivalent kg(-1) FW) were observed on the processing day or over storage. However, the mildest treatment (750 W for 45 s) caused TP and TAC enhancements of 118 and 394% respectively after 7 days of shelf-life. Microwave treatments reduced the initial microbial loads of the samples by up to 1.8 log units, although their microbial growth was greater than that of the untreated samples throughout storage. Mild microwave treatments such as 750 W/45 s and 750 W/60 s are a good sustainable alternative to the use of NaOCl; however, combining them with other sanitizing techniques is needed to control microbial growth throughout the shelf-life of fresh-cut carrot slices.

ChemInform Abstract: Solid Supported Rhodium(0) Nanoparticles: An Efficient Catalyst for Chemo‐ and Regio‐Selective Transfer Hydrogenation of Nitroarenes to Anilines under Microwave Irradiation.

Abstract A Solid-supported rhodium(0) (SS-Rh) catalyst has been developed and applied for the chemo- and regio-selective reduction of nitroarenes functionalized with C C multiple bonds and dinitroarenes to their corresponding amines respectively using hydrazine hydrate (N 2 H 4 ·H 2 O) as a reducing source under mild microwave irradiation (MWI) conditions. The present methodology also shows excellent compatibility with a broad range of structurally diverse reducible functional groups. The catalyst can be recovered by simple filtration and reused for 13 cycles with consistent activity hence reduces the cost of the catalyst assertively.

Solid supported rhodium(0) nanoparticles: an efficient catalyst for chemo- and regio-selective transfer hydrogenation of nitroarenes to anilines under microwave irradiation

A Solid-supported rhodium(0) (SS-Rh) catalyst has been developed and applied for the chemo- and regio-selective reduction of nitroarenes functionalized with CC multiple bonds and dinitroarenes to their corresponding amines respectively using hydrazine hydrate (N2H4·H2O) as a reducing source under mild microwave irradiation (MWI) conditions. The present methodology also shows excellent compatibility with a broad range of structurally diverse reducible functional groups. The catalyst can be recovered by simple filtration and reused for 13 cycles with consistent activity hence reduces the cost of the catalyst assertively.

Optimization of mild microwave hyperthermia interconnection with targeted delivery of nanoparticles

The paper deals with interconnection of microwave hyperthermia with controlled biodistribution of nanoparticles in order to maximize the exposure tumorous tissue and minimize heating the neighbouring healthy tissue. We investigated in our research the delivering nanoparticles to the tumorous tissue as a function of time in order to optimize the beginning time of microwave hyperthermia treatment. We also follow the other parameters which could affect the effect process of microwave hyperthermia – the value of dielectric parameters of treated tissues. Streszczenie. W artykule rozwazany jest problem polączenia mikrofalowej hipertermii ze sterowaną biodystrybucją nanocząstek. Celem tego wspoldzialania jest maksymalizacja ekspozycji tkanki guza przy jednoczesnej minimalizacji nagrzewania sie zdrowych tkanek sąsiednich. Zbadana zostala zaleznośc wprowadzania nanocząstek od czasu w celu optymalizacji rozpoczecia procesu hipertermii. Zbadano rowniez inny parametr, mogący wplywac na efekty hipertermii, mianowicie wartośc parametrow dielektrycznych leczonej tkanki. (Optymalizacja lagodnej hipertermii mikrofalowej w powiązaniu z dystrybucją nanocząstek).

Cobalt carbonyl as an effective CO source in one-pot synthesis of esters from aryl halides

For the first time, we have successfully applied Co2(CO)8 as an effective carbonyl source for the Pd catalysed alkoxycarbonylation of aryl halides affording the corresponding aryl esters under mild microwave conditions. A wide variety of esters and carbonyl derivatives were prepared using this protocol.

Microwave-Promoted Synthesis of 3,4-Dihydropyrimidin-2(1H)-(thio)ones Using IL-ONO as Recyclable Base Catalyst Under Solvent-Free Conditions

A mild, efficient, and solvent-free microwave (MW)–promoted Biginelli reaction for the synthesis of 3,4-dihydropyrimidin-2(1H)-(thio)ones in nitrite ionic liquid (IL-ONO) is described. This ionic liquid is a weak Lewis base catalyst, which can be easily recovered and reused in several runs. The satisfactory results were obtained with good yields and short reaction time, using a simple experimental procedure.

Microwave-assisted synthesis of symmetrical and unsymmetrical N,N′-disubstituted thioureas and ureas over MgO in dry media

Under mild microwave irradiation conditions a variety of symmetrical and unsymmetrical N,N′-disubstituted thioureas and ureas were prepared via the reaction of N-monosubstituted hydroxylamines with isocyanate and isothiocyanate derivatives over MgO under solvent-free conditions. This new method afforded satisfactory results with good yields, short reaction time, and simplicity in the experimental procedure.

Detailed investigations of phase transitions and magnetic structure in Fe(iii), Mn(ii), Co(ii) and Ni(ii) 3,4,5-trihydroxybenzoate (gallate) dihydrates by neutron and X-ray diffraction

The effect of cation valency on the complex structures of divalent and trivalent transition metal gallates has been examined using a combination of neutron and synchrotron X-ray powder diffraction, single-crystal X-ray diffraction and XANES spectroscopy. In the divalent frameworks, M(C(7)H(4)O(5))·2H(2)O (M = Mn, Co and Ni), it was found that charge balance was achieved via the presence of protons on the meta-hydroxyl groups. It was also established that these compounds undergo a discontinuous phase transition at lower temperatures, which is driven by the position of the extra-framework water molecules in these materials. By contrast, in the trivalent Fe gallate, Fe(C(7)H(3)O(5))·2H(2)O, it was found that the stronger bonding between the meta-hydroxy oxygen and the cations leads to a weakening of the bond between this oxygen and its proton. This is turn is thought to lead to stronger hydrogen bonding with the extra-framework water. The lattice water is disordered in the Fe(III) case, which prevents the phase transition found in the M(II) gallates. Refinement against the neutron diffraction patterns also revealed that the relatively mild microwave synthesis of gallate frameworks in D(2)O led to an extensive deuteration of the ortho-hydrogen sites on the aromatic ring, which may suggest a more versatile method of deuterating aromatic organics. The antiferromagnetic structure of Co gallate has also been determined.

ChemInform Abstract: Mild, Versatile, and Chemoselective Indium(III) Triflate‐Catalyzed Deprotection of Acetonides under Microwave Heating Conditions.

AbstractThe method allows the presence of acid‐labile functional groups.

Mild, versatile, and chemoselective indium(III) triflate-catalyzed deprotection of acetonides under microwave heating conditions

A series of acetonides (both terminal and internal isopropylidene acetals) have been deprotected under catalytic, neutral conditions to give their corresponding 1,2-diols. The reactions utilize indium(III) triflate in the presence of water and an organic solvent with mild microwave heating. Terminal acetonides are chemoselectivley removed in the presence of internal acetonides; acid labile functional groups remain intact under these conditions, thereby greatly enhancing the scope of the reaction substrates that can be utilized with this approach.

Efficient combination of task‐specific ionic liquid and microwave dielectric heating applied to synthesis of a large variety of nitrones

AbstractUnder mild microwave irradiation conditions and without any additional organic solvents, a large variety of nitrones were prepared in a weak Lewis base phosphinite task‐specific ionic liquid (TSIL‐OPPh2) in excellent yields. This catalytic TSIL was also recyclable. Under optimized microwave irradiation conditions, the reaction occurred at very shorter reaction time and higher yields in comparison with conventional heating conditions. © 2010 Wiley Periodicals, Inc. Heteroatom Chem 21:78–83, 2010; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/hc.20581

Synthesis of CuS thin films by microwave assisted chemical bath deposition

In this study, oriented CuS nanoplates standing perpendicularly on F: SnO 2 (FTO) coated glass substrates have been prepared through a mild microwave assisted chemical bath deposition process in which copper acetate reacted with ethylenediamine tetraacetate acid disodium and thioacetamide in aqueous solution within 40 min. The effects of reaction time and microwave radiation on the treatment process were investigated. The morphology, structure, and composition of the yielded nanostructures have been confirmed by X-ray diffraction (XRD), energy-dispersive X-ray analysis (EDX), and scanning electron microscope (SEM). Also, the correlation between the reflectance, transmittance coefficient in the UV and the thickness of films was established. Furthermore, a two-point probe was used for resistivity measurements. We believe this simple chemical conversion technique can be further extended to the synthesis of other semiconductors with various morphologies.

Facile, environmentally friendly fabrication of porous silver monoliths using the ionic liquid N-(2-hydroxyethyl)ammonium formate

The environmentally friendly ionic liquid N-(2-hydroxyethyl)ammonium formate works as a reaction medium, reducing and templating agent in the mild microwave synthesis (5 min, 80 degrees C) of a macroporous silver framework from AgNO(3).

Fabrication and morphology control of BaWO 4 thin films by microwave assisted chemical bath deposition

Highly crystallized barium tungstate (BaWO 4) thin films with dumbbell-like, kernel-like, bowknot-like and cauliflower-like microstructure were synthesized from an aqueous solution containing barium nitrate, ethylenediamine tetraacetate acid disodium and sodium tungstate, via mild microwave assisted chemical bath deposition process. The resulting BaWO 4 films with different morphologies were characterized by X-ray diffraction spectrum, scanning electron microscope, Raman and photoluminescence spectra. The results indicate that the morphologies of final products significantly depend on the reaction conditions including the reaction time, the initial concentration of precursor reagent and the physicochemical characteristics of the substrates. Furthermore, the oriented aggregation mechanism is proposed as a possible formation mechanism of the films with specific morphologies.