Studying the effect of microwave heating on the digestion process and identification of proteins

The impact of microwave irradiation on the in‐solution digestion processes and the detection limit of proteins are systematically studied. Kinetic processes of many peptides produced through the trypsin digestion of various proteins under microwave heating at 50°C were investigated with MALDI‐MS. This study also examines the detection limits and digestion completeness of individual proteins under microwave heating at 50°C and at different time intervals (1, 5 and 30 min) using LC‐MS. We conclude that if the peptides without missed cleavage dictate the detection limit, conventional digestion will lead to a better detection limit. The detection limit may not differ between the microwave and conventional heating if the peptides with missed cleavage sites and strong intensity are formed at the very early stage (i.e., less than 1 min) and are not further digested throughout the entire digestion process. The digestion of Escherichia coli lysate was compared under conventional and short time (microwave) conditions. The number of proteins identified under conventional heating exceeded that obtained from microwave heating over heating periods less than 5 min. The overall results show that the microwave‐assisted digestion is not complete. Although the sequence coverage might be better, the detection limit might be worse than that under conventional heating.     

Stille reaction over cis-halocyclohexadienediol derivatives

Stille reaction was performed with several halo cis-diol derivatives by reaction with allyltributyltin in the presence of a palladium catalyst forming allyl cis-dihydrodiol derivatives. These couplings were conducted with conventional heating as well as with microwave irradiation. Allylbenzene cis-dihydrodiol was obtained with excellent yield using mild conventional heating. However, if the diol moiety is protected with the isopropylidene group, the expected product is obtained only under microwave irradiation. The unusual reactivity observed for the polyoxygenated derivatives suggests assistance of the free hydroxyls in the catalytic cycle.     

Microwave-assisted SNAr reaction of 2,4,6-trichloro-1,3,5-triazine for the rapid synthesis of C3-symmetrical polycarboxylate ligands

The microwave-assisted S_NAr reaction of 2,4,6-trichloro-1,3,5-triazine with various unprotected amino acids was developed for the synthesis of C₃-symmetrical polycarboxylate ligands which can be used as structural directing units in metal-organic frameworks. The reactions were performed in water using a domestic microwave oven as the heating device. In comparison to the reactions performed under conventional heating, the reactions under microwave irradiation proceeded much more rapidly within 20 min to afford the desired ligands in comparative yields to those obtained by conventional heating.     

ZnO: a versatile agent for benzylic oxidations

Zinc oxide catalyzed oxidation of various alkylbenzenes, naphthalene and 1,2,3,4-tetrahydronaphthalene in air using microwave irradiation or conventional heating in the presence of N,N-dimethylformamide is described.     

Conventional and Microwave-Assisted Facile One-Pot Synthesis of N-Substituted Pyrrole-2,3,4,5-tetracarboxylates Under Neat Conditions

Highly substituted pyrroles 3a,f were prepared conveniently in a reaction of (dimethyl- and diethyl-)acethylenedicarboxylates 1a–b with N-(methyl- and aryl-) hydroxylamines 2a–d in the presence of NaHCO₃ using both conventional heating and microwave irradiation. Excelent yields of the very pure products were isolated under solvent-free conditions both at classical as well as microwave heating.     

An efficient and rapid synthesis of β-carboxamide derivatives using 2,2-dimethyl-2H,4H-1,3-dioxin-4-ones by microwave irradiation

A general, efficient and rapid method for the synthesis of various β-carboxamide derivatives using microwave irradiation is described. Excellent isolated yields were obtained in very short reaction times when conventional heating was replaced by microwave irradiation.     

A new practical synthesis of 3-amino-substituted 5-aminopyrazoles and their tautomerism

It was found that 3-amino-substituted 5-aminopyrazoles could be effectively prepared via hydrolytic decarboxylation of the corresponding 3,5-diaminopyrazole-4-carboxylates under microwave irradiation. The reactions required short time (4?min) and were successfully reproduced in a larger scale and under conventional heating mimicking the microwave heating pattern. X-ray crystallography identified two different types of tautomers in crystals of related 5-aminopyrazoles with p-toluidyl and p-anisidyl moieties at the position 3, respectively.     

Synthesis of gem-difluorides from aldehydes using DFMBA

Synthesis of gem-difluorides from aldehydes was effectively achieved using DFMBA and Et₃N-3HF under microwave irradiation or conventional thermal heating. Both aromatic and aliphatic aldehydes could be converted to the corresponding gem-difluorides in good yields.     

Sulfamic acid: a novel and efficient catalyst for the synthesis of aryl-14H-dibenzo[a.j]xanthenes under conventional heating and microwave irradiation

A simple and convenient procedure for the synthesis of aryl-14H-dibenzo[a.j]xanthenes is described through a one-pot condensation of β-naphthol with aryl aldehydes in the presence of sulfamic acid as the catalyst in a solvent-free media using both conventional heating and microwave irradiation.     

Microwave-assisted, tin-mediated, regioselective 3-O-alkylation of galactosides

A rapid, efficient and versatile microwave-assisted dibutylstannylene-mediated 3-O-alkylation method for galactosides was established. The alkylation reaction was significantly enhanced by microwave irradiation and allowed the use of an alkylating agent too unstable for incorporation using conventional heating.     

Use of ionic liquid and microwave irradiation as a convenient, rapid and eco-friendly method for synthesis of novel optically active and thermally stable aromatic polyamides containing N-phthaloyl-l-alanine pendent group

An efficient, fast and easy method for synthesis of new optically active and thermally stable aromatic polyamides (PAs) containing pendent phthalimide group and l-alanine flexible side spacer using room temperature ionic liquid (RTIL) by microwave irradiation has been investigated. The results found that RTIL efficiently absorb microwave energy, thus leading to a very high heating rate. All the PAs showed excellent solubility and readily dissolved in various organic solvents. Thermogravimetric analysis (TGA) exhibited that polymers were stable, with 10% weight loss recorded above 373 and 418 °C in the nitrogen atmosphere. In order to see the efficiency of microwave irradiation, this method was compared with polycondensation of the same monomers in RTILs using conventional heating.     

Multicomponent synthesis of imidazo[1,2-a]pyridines using catalytic zinc chloride

The novel use of zinc chloride to catalyze the one-pot, three component synthesis of imidazo[1,2-a]pyridines from a range of substrates using either conventional heating or microwave irradiation is described. This methodology affords a number of imidazo[1,2-a]pyridines in reasonable yields and short reaction times without any significant optimization of the reaction conditions.     

Microwave-Assisted Synthesis of Poly(ε-caprolactone)-block-poly(ethylene glycol) and Poly(lactide)-block-poly(ethylene glycol)

Summary: This study reported the preparation and characterization of PCL-b-mPEG (poly(ε-caprolactone)-block-poly(ethylene glycol)) and PLL-b-mPEG (poly(L-lactide)-block-poly(ethylene glycol)) diblock copolymers by microwave heating and comparison of resulted products the ones with prepared by conventional heating. Diblock copolymers were synthesized successfully by the microwave-assisted ROP in the presence of stannous octoate (SnOct₂) as catalyst under nitrogen atmosphere in different monomer ratios. Structural and functional characterization of copolymers were performed by FTIR, ¹H-NMR and DSC. Molecular weight values were determined by GPC and also calculated from ¹H-NMR. According to the results, microwave irradiation allowed to obtain polymers with very narrow size distribution in very short reaction time. Similar polymers prepared by conventional heating were also synthesized for comparison. Molecular weight and conversion of polymers were increased by irradiation time. This change was continued until a certain time point after which no more increase was observed. It was concluded that microwave irradiation is a succesful method to obtain these diblock copolymers in very short reaction time and with a similar conversion obtained by conventional method.     

Simultaneous crosslinking and cationization of cotton cellulose by using dialdehyde and choline chloride: comparison between the pad-dry-cure and microwave irradiation process

Simultaneous crosslinking and cationization of cotton cellulose were carried out by using two dialdehydes, glyoxal (GO) and glutaraldehyde (GA), along with choline chloride (ChCl). Two heating methods, conventional pad-dry-cure (PDC) and microwave irradiation, were investigated and compared. The results revealed that two aldehyde molecules reacted very differently in the presence of ChCl under two different heating methods. GO reacted predominantly with the cellulose molecule, stimulating the crosslinking reaction and consequently resulting in high wrinkle recovery angle (WRA) values regardless of the heating process. Contrarily, GA favored the reaction with ChCl, allowing high K/S values with acid dye under microwave irradiation. The crosslinked and cationized cotton cellulose was only obtained by treatment with GA and ChCl under the PDC process, resulting in high WRA and K/S values. Characteristics of the treated fabrics were also evaluated by Fourier transform infrared analysis, thermogravimetric analysis, scanning electron microscopy, water of imbibition, and tensile strength test. Additionally, the treatments with GA and ChCl also provided high antimicrobial properties of the cotton celluloses; thereby most bacteria reductions of the specimens were close or equal to 99.9 %. Therefore, economically viable yet ecofriendly crosslinking and cationization of cotton cellulose could be made by treatment with GA and ChCl.     

Microwave effects in solvent-free esters aminolysis

Solvent-free ester aminolysis was studied under microwave or conventional heating either in the absence of base or induced by KOtBu with or without a phase transfer agent. The specific microwave effects were shown to be dependent on the conditions and discussed in terms of relative polarities of ground and transition states.     

In situ SAXS/WAXS of zeolite microwave synthesis: NaY, NaA, and beta zeolites.

A custom waveguide apparatus is constructed to study the microwave synthesis of zeolites by in situ small-angle X-ray scattering (SAXS) and wide-angle X-ray scattering (WAXS). The WR-284 waveguide is used to heat precursor solutions using microwaves at a frequency of 2.45 GHz. The reaction vessels are designed to include sections of thin-walled glass, which permit X-rays to pass through the precursor solutions with minimal attenuation. Slots were machined into the waveguide to provide windows for X-ray energy to enter and scatter from solutions during microwave heating. The synthesis of zeolites with conventional heating is also studied using X-ray scattering in the same reactor. SAXS studies show that the crystallization of beta zeolite and NaY zeolite is preceded by a reorganization of nanosized particles in their precursor solutions or gels. The evolution of these particles during the nucleation and crystallization stages of zeolite formation depends on the properties of the precursor solution. The synthesis of NaA and NaX zeolites and sodalite from a single zeolite precursor is studied by microwave and conventional heating. Microwave heating shifts the selectivity of this synthesis in favor of NaA and NaX over sodalite; conventional heating leads to the formation of sodalite for synthesis from the same precursor. The use of microwave heating also led to a more rapid onset of NaA zeolite product crystallization compared to conventional heating. Pulsed and continuous microwave heating are compared for zeolite synthesis. The resulting rates of formation of the zeolite products, and the relative amounts of the products determined from the WAXS spectra, are similar when either pulsed or continuous microwave heating is applied in the reactor while maintaining the same synthesis temperature. The consequences of these results in terms of zeolite synthesis are discussed.     

Sulfuric acid catalyzed addition of β-dicarbonyl compounds to alcohols under conventional heating and microwave-assisted conditions

The highly efficient direct addition of β-dicarbonyl compounds to secondary alcohols has been achieved using one of the cheapest acids, H₂SO₄, as the catalyst. For a series of β-dicarbonyl compounds and various secondary alcohols, the addition reactions all complete in 5 min with high yields both under the conventional heating condition and under the microwave heating condition. The comparison of the results obtained from the microwave heating condition with those obtained from the conventional heating condition shows that no obvious specific or nonthermal microwave effects exist in the microwave-assisted addition reactions.     

Monomode Microwave‐Assisted Atom Transfer Radical Polymerization

Summary: The first monomode microwave‐assisted atom transfer radical polymerization (ATRP) is reported. The ATRP of methyl methacrylate was successfully performed with microwave heating, which was well controlled and provided almost the same results as experiments with conventional heating, demonstrating the absence of any “microwave effect” in ATRP (in contrast to several literature reports). Furthermore, we found that the main advantage of the microwave‐assisted reactions over conventional reactions, i.e., a significant increase of reaction rates, only had its limited application in ATRP, even in very slow ATRP systems with high targeted molecular weights.

Comparison of the kinetic plots of the ATRP of MMA ([MMA]₀/[EBIB]₀/[CuCl]₀/[NHPMI]₀ = 200:1:1:3, MMA/DMF = 1:1 v/v) carried out at 90 °C in DMF with microwave (▴) and conventional heating (•), respectively.     

Rapid and amenable suzuki coupling reaction in water using microwave and conventional heating

It is possible to prepare biaryls in good yield very rapidy (5-10 min) on small (1 mmol) and larger (10-20 mmol) scales from aryl halides and phenylboronic acid using water as a solvent and palladium acetate as catalyst. The reaction can be performed equally well using microwave and conventional heating, showing that using these conditions probably no nonthermal microwave effects are associated with the impressive speed of the reaction.     

Microwave-assisted epoxidation of hindered homoallylic alcohols using VO(acac)2: application to polypropionate synthesis

The VO(acac)₂ catalyzed epoxidation of hindered homoallylic alcohols was conducted under microwave irradiation in an open vessel using toluene as solvent. The reaction time for the epoxidation of a series of cis- and trans-2-methyl-3-alkenols was dramatically reduced from 6 to 10 days to less than 3 h when compared to conventional heating. The cis alkenols exhibited very high diastereoselectivity. The more elaborated polypropionate precursors 12, 14 and 16 were epoxidized in good yield and excellent diastereoselectivities using the microwave-assisted epoxidation technique described here, which is safe and suitable for multi-gram scales.