Efficient one-pot, two-step, microwave-assisted procedure for the synthesis of polysubstituted 2-aminoimidazoles

A microwave-assisted, one-pot, two-step protocol was developed for the construction of polysubstituted 2-aminoimidazoles. This process involves the sequential formation of imidazo[1,2-a]pyrimidinium salts from readily available 2-aminopyrimidines and alpha-bromocarbonyl compounds, followed by opening of the pyrimidine ring with hydrazine. [reaction: see text]     

A fast radiochemical procedure for separating iodine from fission products

The iodine isotopes produced by thermal neutron fission of²³⁵U were separated by a fast chemical procedure, with a separation yield of 95%. The gamma-ray energies and relative intensities in the decay of¹³¹I,¹³²I,¹³³I,¹³⁴I and¹³⁵I were determined using a Ge(Li) detector.     

A microwave-assisted, green procedure for the synthesis of N-aryl sulfonyl and N-aryl pyrroles

A simplified approach to the uncatalyzed Paal-Knorr condensation using microwave irradiation in water is described.     

A fast, convenient and rugged procedure for characterizing the selectivity of alkyl-silica columns

Previous work has shown that the selectivity of reversed-phase columns for HPLC can be described by means of five column parameters: H (hydrophobicity), S* (steric resistance), A (hydrogen-bond acidity), B (hydrogen-bond basicity) and C (cation-exchange capacity). Values of H, S*, etc. can be determined by carrying out retention measurements for 18 test solutes under standardized conditions. The reproducibility of the latter procedure has been evaluated by comparison testing in four different laboratories and found acceptable. An alternative 10-solute test procedure which is more reproducible and convenient (but somewhat less accurate), requires only 2-3 h per column.     

Multichannel autosampler for Curie-point pyrolysis capillary gas chromatography

A multichannel autosampler which can automatically analyze up to 20 samples in sequence has been developed for on-line Curie-point pyrolysis – capillary GC. The results obtained from the system show that the analysis of thermally labile samples could be performed without either thermal degradation or reaction during the waiting time before the final pyrolysis. The reproducibilities of the relative peak areas and retention times of the characteristic pyrolysates of a tricomponent copolymer were significantly better than those obtained by manual sample manipulation.     

A fast derivatization procedure for gas chromatographic analysis of perfluorinated organic acids

A rapid and simple derivatization procedure has been developed for gas chromatographic determination of perfluorinated organic acids (PFCAs, C₆–C₁₂), using isobutyl chloroformate (IBCF) to convert the acids into the more volatile isobutyl esters, under catalysis by pyridine. The procedure was optimized in an acetonitrile medium and applied to GC techniques with electron-capture detection (GC-ECD) and mass spectrometry with electron-impact ionization (GC-EI-MS); for the sake of comparison, HPLC with electrospray-ionization MS (HPLC-ESI(−)-MS) was also tested. The LOD and LOQ values obtained for these three techniques were compared, and the lowest LODs were obtained with GC-ECD (0.06–1.80 μg mL⁻¹). The procedure was further optimized in an aqueous medium, obtaining the best results in a phosphate buffer (pH 2.5, 50 mmol L⁻¹), in which the LOD and LOQ values were measured for GC-ECD a GC-EI-MS. The lowest LODs were found for GC-EI-MS (0.030–0.314 μg mL⁻¹). The practical applicability was tested on Vltava river water samples.     

A validated and fast procedure for FTIR determination of Cypermethrin and Chlorpyrifos

A FTIR methodology has been developed for the simultaneous determination of Cypermethrin and Chlorpyrifos in pesticide commercially available formulations. The method involves the extraction of both active principles with CHCl₃ and direct measurement of the peak area values between 1747 and 1737 cm⁻¹ corrected with a baseline defined at 2000 cm⁻¹ for Cypermethrin and peak height values established at 1549 cm⁻¹ corrected using a baseline situated at 1650 cm⁻¹ for Chlorpyrifos.The limits of detection achieved were of the order of 0.7 and 0.4% (w/w), and the relative standard deviation 0.4 and 0.2% for Cypermethrin and Chlorpyrifos, respectively. The developed procedure provided statistically comparable results with those obtained by HPLC, for a series of commercial samples, which validated the FTIR method. The procedure developed reduces organic solvent consumption, per sample preparation, from 51 ml CH₃CN required for HPLC to 2.5 ml CHCl₃, and reduces waste generation also increasing the sample measurement frequency, from 3 to 30 samples/h, as compared with the HPLC-UV reference method.     

A microcapillary system for simultaneous, parallel microwave-assisted synthesis

A continuous flow, microwave-assisted, parallel-capillary microreactor has been developed. Libraries of drug candidates were prepared on the milligram scale with this reactor by injecting plugs of reagents from separate syringes into common reaction capillaries, thereby producing discrete compounds in excellent yield and purity. Microwave irradiation provides the necessary energy that existing room-temperature microreactor technology lacks for higher activation barrier transformations, producing the required amounts of desired compounds in minutes or less.     

A microwave-assisted microassay for lipases

A quick and efficient two-step assay for monitoring and screening lipase activity that uses a microtitre plate is described.     

A rapid and simple microwave-assisted digestion procedure for spectrophotometric determination of titanium dioxide photocatalyst on activated carbon

Deposition of titanium dioxide (TiO₂) on activated carbon (AC) surface has been widely utilized for the production of TiO₂/AC photocatalyst, which can be used in photo-degradation of pollutants. In this work, a fast and simple digestion procedure has been developed for the spectrophotometric quantitative analysis of TiO₂ in TiO₂/AC photocatalyst. Microwave-assisted digestion was used in the procedure. The microwave-digestion procedure was optimized using the single-variable method. Variables optimized included time of ashing, effective digestion time, volume and concentration of sulfuric acid, effect of adding a digestion catalyst, effect of sample pulverizing and on–off time cycle of the microwave. The analysis was completed spectrophotometrically after addition of hydrogen peroxide to the digested solution. Procedure precision and accuracy was tested by application to photocatalyst samples containing known amounts of TiO₂, and compared with previously published spectrophotometric procedures. The proposed microwave procedure was capable of recovering 98.4–101.1% of TiO₂ in the catalyst in less than 10 min, without the need for sample ashing. Analytical precision is 1.42–2.39% relative standard deviation (R.S.D.). In terms of accuracy and precision, the proposed microwave procedure was comparable with other procedures, but the proposed microwave procedure was superior in terms of shorter procedure duration.     

A fast procedure for the preparation of vicinal azidoalcohols using polymer supported reagents

Several vicinal azidoalcohols were prepared in good to high yield and purity, starting from aryl α-haloketones, using reagents supported on a macroporous ion exchange resin. This is a fast and new approach to aryl azidoalcohols.     

A fast and parallel route to cyclic isothioureas and guanidines with use of microwave-assisted chemistry

A fast and simple approach to novel cyclic isothioureas and related guanidine derivatives is presented in this study. The construction of the central basic scaffolds is achieved solely by the application of microwave-assisted chemistry, without any need of activating agents or protecting group manipulations. The product formation of various substituted guanidines from the corresponding isothiouronium salts was controlled by the nucleophilicity of the counterion and influenced by the reaction temperature. Further, a new fast-track access to tetrahydropyrimidin-2-ylamines was developed.     

A fast and reliable chromatographic procedure for the purification of virginiamycin M1 factor

Summary The goal of this study was to develop a simple, fast and reliable procedure for the preparation of highly purified virginiamycin M₁ factor using readily available and low cost laboratory equipment. This was achieved by purifying M₁ by reversed-phase flash chromatography after clean-up of the bulk sample by filtration on a silica gel cake. The purity of the final product determined by RP-HPLC was 99% and its identity was confirmed by IR spectroscopy and ESI mass spectrometry.     

A simple and fast procedure for efficient synthesis of β- and γ-azidoarylketones

A simple and efficient method for preparing β- and γ-azido substituted arylketones has been achieved by short microwave irradiation of the corresponding halo arylketones and sodium azide in DMSO.     

Optimization of a microwave-assisted derivatization-extraction procedure for the determination of chlorophenols in ash samples

A procedure for the determination of 17 chlorophenolic compounds in ash samples obtained from the incineration of waste materials is described. Analytes were simultaneously derivatized with acetic anhydride in presence of triethylamine (TEA), and extracted from the sample in a mixture of n-hexane acetone using a microwave system equipped with closed extraction vessels. Influence of five experimental parameters (volume of TEA and acetic anhydride, extraction time and temperature, as well as the volume of n-hexane acetone) on the yield of the derivatization-extraction procedure was systematically studied using a uniform experimental design at four levels, followed by a conventional factorial design at two levels. Under optimal extraction conditions, recoveries from 72 to 94% were obtained for a spiked ash sample with a carbon content of 8.7%. Quantification limits of the proposed procedure ranged from 2 to 5 ng/g using GC-MS as detection technique. The proposed method was applied to the determination of chlorophenols in three ash samples obtained from different incineration plants. Total chlorophenol contents of 423 and 135 ng/g were found in two of these samples.     

A fast procedure to immobilize polyethylene glycols in glass capillary columns

Polyethylene glycols can be immobilized in glass capillary columns by a new procedure involving covering the glass walls with a layer of graphitized carbon black and by flowing a mixture of the stationary phase and dicumyl peroxide. After curing and conditioning the column is ready for use. Excellent performance is reported for Carbowax 20 M and high molecular weight glycols. For other glycols the immobilized layer is less stable and can be washed out.     

A facile, microwave-assisted, palladium-catalyzed arylation of acetone

We report an expedient method for the heteroarylation of acetone under tin-free conditions. The coupling is performed using the commercially available enol silane of acetone (2-trimethylsilyloxypropene) and a corresponding aryl bromide, chloride or triflate under microwave-assisted conditions, with tris(dibenzylideneacetone)dipalladium (Pd₂(dba)₃) or palladium acetate (Pd(OAc)₂) and 2-(2′,6′-dimethoxybiphenyl)dicyclohexylphosphine (S-Phos) as the catalyst system.     

A new procedure for fast soft staining of BN‐PAGEs on photosynthetic complexes

We report a fast and sensitive procedure for blue native PAGE staining, in which the conventional staining step with CBB is avoided. After running, a short exposure to a mix of polar protic solvents (ethanol and acetic acid) leads to a fast and selective removal of the dye from the migration front and a specific binding to the protein bands, while the rest undergo a selective and complete background removal, leading to an intense contrast. This single‐step staining–destaining technique is useful in protein samples that bind colored cofactors such as photosystems, which can be selectively discerned by their characteristic green color. After the staining of such samples, the green color persists, while the other unpigmented protein complexes and the molecular standard remain CBB stained, creating a useful reference system for the assignment of the bands. The advantages and chemical basis of this staining procedure are discussed.