CEM Discover Research Articles

One-pot multi-step synthesis of gamma-valerolactone from furfuryl alcohol: Microwave vs continuous flow reaction studies

Mesoporous materials Al-SBA-15 have been synthesized and functionalized with different Al/Zr molar ratio and 0.5% Au and Ru, respectively, by a mechanochemical approach. Textural and structural properties of synthesized materials have been analysed by TEM (Transmission Electron Microscopy), SEM (Scanning Electron Microscopy), XPS (X-ray photoelectron spectroscopy), XRD (X-ray Diffraction) and N2 adsorption/desorption technique, among others. The catalytic activity of synthesized materials has been evaluated in the one-pot conversion of furfuryl alcohol (FAL) employing 2-propanol as H-donor solvent to obtain γ-valerolactone (GVL), both under microwave-assisted irradiation (CEM Discover® 2.0) and continuous flow conditions (Phoenix Flow ReactorTM, ThalesNano). All materials displayed conversions up to 99%, with a GVL selectivity of ca. 20–41% after one-hour reaction time. The study of the reusability of the materials showed a good GVL production during 3 reaction cycles employing both microwave-assisted and flow reaction conditions.

Newly emerging mesoporous strontium hydroxyapatite nanorods: microwave synthesis and relevance as doxorubicin nanocarrier

A new synthesis method is developed for preparation of mesoporous strontium hydroxyapatite (SrHAp) nanorods using CEM Discover microwave synthesizer. Nanorods preparation with surfactants SrHAp(+) and without surfactants SrHAp(−) were successfully achieved at 160 °C temperature and 15 min of hold time. Particle sizes with standard deviation were found to be 67 ± 18 and 69 ± 24 nm respectively. Mesoporous nanorods were thoroughly characterized using different methods, such as Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), field-emission gun transmission electron microscopy (FEG-TEM), scanning electron microscopy (SEM), Brunauer–Emmett–Teller (BET) surface area and porosity measurement. It was observed that use of trisodium citrate and CTAB resulted in quite agglomerated particles, whereas nanorods synthesized without citrate and CTAB were well dispersed. Cell toxicity of both these materials synthesized was tested in MCF-7 and Zr-75 cell lines using MTT assay. SrHAp nanorods concentration up to 0.25 mg/ml was non-toxic at 48 hours (h) time point in both the cell lines. As SrHAp(−) were found to serve better in terms of cytotoxicity, they were chosen for doxorubicin (Dox) loading, pH depended release and cell uptake study. The successful loading of Dox was ascertained by UV-Visible and FTIR spectroscopy. Entrapment efficiency of Dox in SrHAp nanoparticles was found to be 83.71%, and loading capacity was 0.017 μg Dox per μg SrHAp nanoparticles. Rapid release was observed in the initial hours followed by slow release. Even until 31 days, only 27 and 32% drug was released at pH 7.4 and pH 4.5 respectively, which shows controlled release behavior. Further, cellular uptake of Dox-loaded nanoparticles at different time points was studied in the two breast cancer cell lines by fluorescence imaging. These nanoparticles were found to internalize within both these cells after 3 h of incubation and continued further until 24 h. Overall, high Dox loading efficacy, sustained release behavior, and cell uptake potential render SrHAp nanoparticles to give promising results when applied in vivo and emerge as a robust drug carrier towards solving purpose of slow and prolonged drug release.

Microwave Synthesized TiP2O7/Carbon Composites for Use in Aqueous Lithium-Ion Batteries

Nowadays, Lithium ion batteries (LIBs) can be found in every corner of our daily life. However, safety and cost of lithium ion batteries are the two major issues. Aqueous rechargeable lithium ion batteries are believed to be the promising candidates for LIBs due to nonflammable，low cost higher ionic conductivity of aqueous electrolyte [1]. To reduce the cost of aqueous lithium-ion cells, researchers focus on developing methods to synthesize electrode material in an energy efficient way. It has been reported that TiP2O7 has a low intercalation /de-intercalation potential (2.6 V versus Li/Li+) [2], which makes it a promising anode material for aqueous lithium-ion batteries [3,4]. One report demonstrated a solid-state synthesis method annealing at 300◦C for 2 hours, annealing at 800◦C for 3 hours and cooling to room temperature for 4 hours [5]. The solid-state synthesis route is very common in industrial applications due to its simplicity. However, the long calcining duration and high temperature requirement increases the processing cost for the electrode materials. One report applied microwave to synthesize C-NaTi2(PO4)2, the negative electrode for aqueous sodium ion batteries [6]. Functional electrode materials can be synthesized in less than 20 minutes. In this work, a very fast microwave synthesis method was developed to produce C-TiP2O7 (Carbon and TiP2O7 Composite material). The precursor consists of (NH4)2HPO4 and anatase TiO2 in a molar ratio of 2:1, with 10wt%, 15wt% and 20wt%(the weight percent is relative to the precursor mixture) graphite added. After being ball milled together for 1 hour, the mixture was heated in a microwave oven (CEM Discover Proteomics System) for 10 minutes at 150W. The SEM figure shows the surface of Graphite-TiP2O7 composite, and the particle size of Graphite-TiP2O7 composite is around 40nm (Figure 1a). In XRD test (Figure 1b), the pattern of product matches with the reference pattern (JCPDS #38-1468) at major peaks (511), (600), (630), (721), (660), (933). The products we get from this method are tested in cyclic voltammetry tests, which shows promising electrochemical performance (Figure 2a); after ten cycles, the specific capacity of 10% Graphite-TiP2O7 composite maintains 107.4 mAh/g. (Figure 2b). Figure 1 a) SEM of Graphite-TiP2O7 composite. B) XRD patterns of Graphite-TiP2O7 composite and reference peaks. Figure 2 a) Second cycles of cyclic voltammetry curves of 10% Graphite-TiP2O7 composite, 15% Graphite-TiP2O7 composite and 20% Graphite-TiP2O7 composite in 1 M Li2SO4 at scan rate 0.5 mV/s in range of −0.5 V and −1.6 V versus MSE. b) Discharge cycling performance of Graphite-TiP2O7 composite. The total synthesis time is only 10 minutes for heating and 30 minutes for cooling, which is much less than for traditional solid state synthetic methods. Reference: Kim H, Hong J, Park K Y, et al. Aqueous Rechargeable Li and Na Ion Batteries[J]. Chemical Reviews, 2014, 114(23):11788.Aravindan V, Reddy M V, Madhavi S, et al. Hybrid supercapacitor with nano-TiP2O7, as intercalation electrode[J]. Journal of Power Sources, 2011, 196(20):8850-8854.Wang H, Huang K, Zeng Y, et al. Electrochemical properties of TiP2O7, and LiTi2(PO4)3, as anode material for lithium ion battery with aqueous solution electrolyte[J]. Electrochemical Acta, 2007, 52(9):3280-3285.Rai A K, Gim J, Song J, et al. Electrochemical and safety characteristics of TiP2O7 –graphene nanocomposite anode for rechargeable lithium-ion batteries[J]. Electrochemical Acta, 2012, 75(4):247-253.Wu W, Shanbhag S, Wise A, et al. High Performance TiP2O7 Based Intercalation Negative Electrode for Aqueous Lithium-Ion Batteries via a Facile Synthetic Route[J]. Journal of the Electrochemical Society, 2015, 162(9): A1921-A1926.Wu W, Mohamed A, Whitacre J F. Microwave Synthesized NaTi2(PO4)3 as an Aqueous Sodium-Ion Negative Electrode[J]. Journal of the Electrochemical Society, 2013, 160(3): A497-A504. Figure 1

Ureidopyrazine Derivatives: Synthesis and Biological Evaluation as Anti-Infectives and Abiotic Elicitors.

Tuberculosis (TB) caused by Mycobacterium tuberculosis (Mtb) has become a frequently deadly infection due to increasing antimicrobial resistance. This serious issue has driven efforts worldwide to discover new drugs effective against Mtb. One research area is the synthesis and evaluation of pyrazinamide derivatives as potential anti-TB drugs. In this paper we report the synthesis and biological evaluations of a series of ureidopyrazines. Compounds were synthesized by reacting alkyl/aryl isocyanates with aminopyrazine or with propyl 5-aminopyrazine-2-carboxylate. Reactions were performed in pressurized vials using a CEM Discover microwave reactor with a focused field. Purity and chemical structures of products were assessed, and the final compounds were tested in vitro for their antimycobacterial, antibacterial, and antifungal activities. Propyl 5-(3-phenylureido)pyrazine-2-carboxylate (compound 4, MICMtb = 1.56 μg/mL, 5.19 μM) and propyl 5-(3-(4-methoxyphenyl)ureido)pyrazine-2-carboxylate (compound 6, MICMtb = 6.25 μg/mL, 18.91 μM) had high antimycobacterial activity against Mtb H37Rv with no in vitro cytotoxicity on HepG2 cell line. Therefore 4 and 6 are suitable for further structural modifications that might improve their biological activity and physicochemical properties. Based on the structural similarity to 1-(2-chloropyridin-4-yl)-3-phenylurea, a known plant growth regulator, two selected compounds were evaluated for similar activity as abiotic elicitors.

One Pot, Solvent-Free Synthesis of Substituted 3,4-Dihydropyrimidin-2(1H)-Ones/Thiones under Microwave Irradiation (CEM) Using Reusable Nickel Nanoparticles

A library of 3,4-dihydropyrimidin-2(1H)-ones/thiones derivatives were synthesized via Biginelli condensation reaction of β-keto esters, aryl aldehydes and urea/thiourea under solvent-free conditions utilizing nickel nanoparticles under microwave irradiation (CEM Discover). The structures of the all compounds were elucidated with the aid of elemental analysis, IR, 1H-NMR and Mass spectral data. Nickel nanoparticles can be recovered and reused five times without loss of their efficiency. Short reaction time, high yield of products and simple workup procedure, solvent-free conditions and reusability of the catalyst are the superior features of this protocol.

One Pot, Solvent-Free Synthesis of Substituted 3,4-Dihydropyrimidin-2(1H)-Ones/Thiones under Microwave Irradiation (CEM) Using Reusable Nickel Nanoparticles

A library of 3,4-dihydropyrimidin-2(1H)-ones/thiones derivatives were synthesized via Biginelli condensation reaction of β-keto esters, aryl aldehydes and urea/thiourea under solvent-free conditions utilizing nickel nanoparticles under microwave irradiation (CEM Discover). The structures of the all compounds were elucidated with the aid of elemental analysis, IR, 1H-NMR and Mass spectral data. Nickel nanoparticles can be recovered and reused five times without loss of their efficiency. Short reaction time, high yield of products and simple workup procedure, solvent-free conditions and reusability of the catalyst are the superior features of this protocol.

Development of microwave-assisted acid hydrolysis of proteins using a commercial microwave reactor and its combination with LC–MS for protein full-sequence analysis

Microwave-assisted acid hydrolysis (MAAH) can be used to degrade a protein non-specifically into many peptides with overlapping sequences which can be identified by mass spectrometry (MS) to produce a sequence map that covers the full sequence of a protein. The success of this method for protein sequence analysis depends on the proper control of the MAAH process, which is currently done using a household microwave oven. However, to meet the regulatory or good laboratory practice (GLP) requirement in a clinical or pharmaceutical laboratory, using a commercial microwave device is often required. In this paper, we report a method of performing MAAH using a CEM Discover single-mode microwave reactor. It is shown that, using an optimized protocol for MAAH, reproducible results comparable to those obtained using a household microwave oven can be generated using the commercial reactor. To illustrate the potential applications of MAAH MS for characterizing clinically relevant proteins, this method was applied, for the first time, to map the amino acid sequences of normal and sickle-cell human hemoglobin as well as bovine hemoglobin. Full sequence coverage was readily achieved from 294 and 266 unique peptides matched to the alpha and beta subunits of normal hemoglobin, respectively, 334 and 265 unique peptides matched to the alpha and beta submit units of sickle-cell hemoglobin, and 377 and 224 unique peptides matched to the alpha and beta subunits of bovine hemoglobin. This method opens the possibility for any laboratory to use a commercial laboratory equipment to perform MAAH MS for protein full-sequence analysis.

Activated Fly Ash Catalyzing the Synthesis of Novel Potent 4-Thiazolidinones of 4-Amino Antipyrine Anils Using CEM Discover Microwave Methodology and Their Virtual Screening

Fly ash, an industrial waste, has been used as an efficient and cost-effective activating catalyst for the synthesis of new potent thiazolidinones (4a–n), starting from imine (3a–n) and thioacetic acid. The reactions were performed under CEM Discover microwave irradiation in solvent-free conditions. This reaction is scalable to a multigram scale and the methodology has resulted in an efficient synthesis. Herein, a benign, environment friendly, efficient, and extremely fast procedure for the synthesis of thiazolidinones have been demonstrated. The produced thiazolidinone molecules were characterized on the basis of elemental analysis, infrared (IR), mass spectral, and 1H NMR spectral data. The synthesized moieties were screened virtually and discussed for their possible biological activity.

Mechanistic Investigation into the Accelerated Synthesis of Methacrylate Oligomers via the Application of Catalytic Chain Transfer Polymerization and Selective Microwave Heating

The synthesis of methyl methacrylate (MMA) oligomers by catalytic chain transfer polymerization (CCTP) is demonstrated to be significantly accelerated by the use of microwave heating. The CCTP reactions, which use a cobalt-based catalyst to very efficiently control the molecular weight of the final polymer, were conducted in both a conventional oil bath and a CEM Discover microwave reactor with a target set point of 80 °C. The required reaction time was shown to be reduced from 300 to 3 min, while also retaining control over the polymerization. Additionally, for the first time the bulk temperature of these catalyzed polymerizations was monitored in both heating methods by the use of internal optical fiber sensors. It was demonstrated that, to monitor the temperature of the reaction correctly, it is essential to use an optical fiber sensor rather than the external IR sensor supplied with the reactor. The acceleration in the synthesis during microwave heating was attributed to selective heating of the radical and oligomeric species within the reaction, which lead to both rapid heating of the reaction bulk to reaction temperature and average reaction temperatures that were higher than the chosen set point. However, comparative reactions carried out under conventional heating (CH) conditions at the true reaction temperature of the microwave experiments (MWH) showed that MWH was able to produce significantly greater yields than the CH experiments after only 3 min, indicating the existence of a real selective heating effect during the reaction. Three methods have been investigated to optimize the acceleration achieved in the MWH experiments while retaining control and yield levels within the MWH experiments. These were varying the; solvent concentration, initiator concentration and chain transfer agent concentration. It was demonstrated that by understanding the influence of the microwave heating that it was possible to retain control over the molecular structure of the product polymer at the accelerated rate.

Highly efficient isocyanate-free microwave-assisted synthesis of [6]-oligourea

A new eco-friendly, isocyanate-free, energy-saving method for the production of [6]-oligourea, utilizing a green carbonylating agent, viz. propylene carbonate, is reported. It comprises an organocatalyzed, microwave-assisted, solvent-free synthesis. Two modes of microwave-assisted synthesis, viz. dynamic and fixed energy modes, were applied. Upon optimization, the dynamic mode gave 79% yields of [6]-oligourea. On the other hand, almost quantitative yields were obtained using the fixed mode, within 20 min, at 10 W and with the same catalyst loading. Combination of both organocatalysis and microwave energy input appears to be a key issue for the efficiency of the reaction, with the fixed energy mode being best suited. It should be noted that all data reported are reproducible (due to the homogeneous microwave technology used by CEM Discover S-Class of microwave reactors). To the best of our knowledge, this is the best eco-friendly synthetic approach for the preparation of the title oligomers. It paves the way for using more of the biorenewable and sustainable chemicals as a feedstock for the production of polyureas. The oligomer produced was analyzed by EA, ATR-FTIR, XRD, 1H and 13CNMR. Furthermore, thermal properties of the resulting [6]-oligourea were analyzed using TGA and DSC.

On the parametric sensitivity of heat generation by resonant microwave fields in process fluids

Although microwave enhanced chemistry has become an established research topic, the actual electromagnetic interactions have received little attention. Following a previous study on the spatial distribution of heat generation, this study addresses the high sensitivity of the overall heating rate to geometrical and medium parametric variations in a highly celebrated microwave heating device (CEM Discover), which serves as a representative example of resonant microwave systems. It is demonstrated, both by experiment and simulation, that this high sensitivity hampers the prediction of total heat generation. Consequently, in order to optimize process performance, precise information regarding all relevant geometrical and medium parameters of the coupled microwave equipment-reactor system should be taken into account.

Thermal effect on the microwave assisted biodiesel synthesis catalyzed by lipases

The esterification reaction mediated by lipases was investigated applying both microwave irradiation and conventional heating in order to evaluate the existence of nonthermal microwave effects on the biodiesel synthesis. All transformations were conducted at 40oC in both Monowave 300 and CEM Discover instruments that allowed accurate internal reaction temperature measurements with use of fiber-optic probes. The conventional heating experiment was performed in an EasyMaxTM reactor (Mettler-Toledo), which also allowed accurate measurement of the internal temperature. The results revealed no difference on the reaction time or yield, differently than indicated by some results in the literature.

Solvent-free Cleavage of tert-Butyl Esters under Microwave Conditions

-butyl esters by combination of silica gel (230-400 mesh, standard grade for flash column chroma-tography) and two different type of microwave irradiation (CEM Discover microwave as a single-mode microwave unit and CEM MARS5 microwave as a multi-mode microwave unit) in solvent-free conditions (Scheme 1).The reactions were carried out by simple mixing

Microwave Synthesis of SAPO‐11 and AlPO‐11: Aspects of Reactor Engineering

AlPO-11 and SAPO-11 are synthesized using microwave heating. The effects of precursor volume, reaction temperature, reactor geometry, stirring, applicator type and frequency on the microwave synthesis of SAPO-11 and AlPO-11 are studied. The nucleation time and crystallization rate are determined from crystallization curves for SAPO-11 (and/or AlPO-11), for the various parameters investigated. Increasing volume of the reacting material decreases the reaction rate of SAPO-11 at 160 degrees C. In particular, the nucleation time increases with increase in the reaction volume. Increasing the reaction temperature increases the crystallization rate and decreases the nucleation time, however it decreases the particle size. Nucleation of SAPO-11 and AlPO-11 under microwave heating is strongly dependant on the reaction temperature. Using wider geometry vessel (33 mm compared to 11 mm diameter) enhances the reaction rate, producing larger crystals in the same reaction time, even though the crystallization rate is decreased. The crystallization rate is enhanced by applicator type in the following order CEM MARS-5 oven>CEM Discover "focused" system>monomode waveguide. Stirring the reacting solution during heating affects primarily the nucleation time. The effect of microwave frequency on the nucleation and growth of SAPO-11 shows a dependence on the applicator type more than the specific frequency, for the frequency range 2.45-10.5 GHz. The difference between the crystallization rate observed at higher frequencies and that at 2.45 GHz maybe due to the multimode nature of the waveguide at frequencies above 2.45 GHz. Sweeping the microwave frequency linearly between 8.7 and 10.5 GHz at rates of 10 min(-1) and 100 min(-1) shows an intermediate crystallization curve to that for fixed frequencies of 2.45 GHz and that for 5.8, 8.7 and 10.5 GHz.

Microwave Synthesis of Zeolites. 2. Effect of Vessel Size, Precursor Volume, and Irradiation Method

The enhancement of synthesis reactions under microwave heating is dependent on many complex factors. We investigated the importance of several reaction engineering parameters relevant to microwave synthesis. Of interest to this investigation were the reaction vessel size, volume of precursor reacted, microwave power delivery, and microwave cavity design. The syntheses of NaY zeolite and beta-zeolite were carried out under a number of varying conditions to determine the influence of these parameters on the nucleation rate, the crystallization rate, and the particle size and morphology. The rates of NaY and beta-zeolite nucleation and crystallization were more rapid in the multimode CEM MARS-5 oven compared to the more uniform field CEM Discover. The faster synthesis rate in the MARS-5 may be the result of the multimode microwave electric field distribution. Slower rates of NaY and beta-zeolite formation observed in the Discover and a circular waveguide may be the result of a more uniform microwave electric field distribution. Changes in reaction vessel size and precursor volume during the microwave synthesis of beta- and NaY zeolite were found to influence the rate of zeolite formation. These results indicate that reactor geometry needs to be considered in the design of systems used for microwave synthesis. Comparative synthesis reactions were carried out with conventional heating, and microwave heating was shown to be up to over an order of magnitude faster for most of these syntheses.

Reactivities of Shenfu Chars Toward Gasification with Carbon Dioxide

Abstract Five Shenfu char samples were prepared from Shenfu raw coal at different temperatures (950, 1100, 1200, 1300 and 1400 °C) using a muffle furnace. Demineralization of the char samples was performed by treating them with 10% nitric acid for 10 min in a CEM Discover microwave reactor. The gasification of the chars, and corresponding demineralized chars, in a carbon dioxide (CO 2 ) atmosphere was conducted in a Netzsch STA 409C131F temperature-programmed thermogravimetry apparatus. The effects of charring temperature and demineralization on the gasification reactivity of chars were systematically investigated. The results show that a char formed at a lower temperature is more reactive except for demineralized char formed at 1100 °C, which is less reactive than char formed at 1200 °C. Demineralization decreases the char reactivities toward gasification with CO 2 to a small extent.

Microwave-assisted synthesis of SnO 2–graphite nanocomposites for Li-ion battery applications

SnO 2–graphite nanocomposites are prepared by urea-mediated homogeneous hydrolysis of SnCl 4. Heating in a CEM Discover microwave reactor (Sn–C-1), in a household microwave oven (Sn–C-2), or by a conventional conduction method (Sn–C-3) are used to decompose the urea and release hydroxide ions for SnCl 4 hydrolysis. The nanocomposites are characterized by XRD, ICP, FE-SEM, SEM and TEM/SAED and used as the material for negative electrodes (anodes) in Li-ion batteries. The SnO 2 particles in Sn–C-1 are the smallest and have the narrowest size distribution (1–3 nm, mean: 2.1 nm, standard deviation: 0.3 nm) compared with those in Sn–C-2 (2–5 nm, mean: 3.8 nm, standard deviation: 0.5 nm) and Sn–C-3 (3–9 nm, mean: 6.4 nm, standard deviation: 0.9 nm). The microwave preparation allows smaller SnO 2 particles to be produced and more homogenously dispersed in the graphite. This results in improved electrochemical performance as a lithium storage compound. The specific capacities decrease in the order: Sn–C-1 > Sn–C-2 > Sn–C-3. For the 14.2 wt.% SnO 2–graphite composite (Sn–C-1), the initial specific capacity was 465 mAh g −1 and 80% of the initial specific capacity, or 372 mAh g −1 can still be obtained after 60 charge and discharge cycles.