A novel one-pot synthesis of 2-alkylthio-1,3,4-oxadiazoles in water

A facile and one-pot protocol for the synthesis of 2-alkylthio-1,3,4-oxadiazoles is reported. This green method relies on the reaction of acid hydrazides with CS₂ and an alkyl halide. The reaction is carried out under mild and environmentally friendly procedure in water with high to excellent yields. Thirteen different valuable alkylthio-1,3,4-oxadiazoles are synthesized from cheap and easily available CS₂ with this method. This is the first report for the synthesis of 1,3,4-oxadiazoles in water.     

Electrochemical synthesis and mechanestic study of quinone imines exploiting the dual character of N,N-dialkyl-p-phenylenediamines

Two one-pot electrochemical approaches for the synthesis of similar quinone imines via either the nucleophilic character of N,N-dialkyl-p-phenylenediamines or electrophilic reactivity of their oxidized forms through Michael-type addition reactions are reported.     

Structure of bottle-brush brushes under good solvent conditions: a molecular dynamics study

We report a simulation study for bottle-brush polymers grafted on a rigid backbone. Using a standard coarse-grained bead-spring model extensive molecular dynamics simulations for such macromolecules under good solvent conditions are performed. We consider a broad range of parameters and present numerical results for the monomer density profile, density of the untethered ends of the grafted flexible backbones and the correlation function describing the range that neighboring grafted bottle-brushes are affected by the presence of the others due to the excluded-volume interactions. The end beads of the flexible backbones of the grafted bottle-brushes do not access the region close to the rigid backbone due to the presence of the side chains of the grafted bottle-brush polymers, which stretch the chains further in the radial directions. Although a number of different correlation lengths exist as a result of the complex structure of these macromolecules, their properties can be tuned with high accuracy in good solvents. Moreover, qualitative differences with 'typical' bottle-brushes are discussed. Our results provide a first approach to characterizing such complex macromolecules with a standard bead-spring model.     

Trace determination of malachite green in water samples using dispersive liquid–liquid microextraction coupled with high-performance liquid chromatography-diode array detection

A simple and reliable method has been developed for the rapid analysis of trace levels of malachite green from water samples using dispersive liquid–liquid microextraction and high-performance liquid chromatography-diode array detection. Factors relevant to the microextraction efficiency, such as the type and volume of extraction solvent, nature and volume of the disperser solvent, the effect of salt, sample solution temperature and the extraction time were investigated and optimised. Under the optimal conditions the linear dynamic range of malachite green was from 0.2 to 100.0?µg?L^?1 with a correlation coefficient of 0.9962. The detection limit and limit of quantification were 0.1?µg?L^?1 and 0.3?µg?L^?1, respectively. The relative standard deviation (RSD) was less than 2.6% (n?=?5) and the recoveries of malachite green (5.0?µg?L^?1) from water samples were in the range of 99.2?±?1.7%. Finally the proposed method was successfully applied for the analysis of malachite green from fish farming water samples.     

Tandem Oxidation Process Using Ceric Ammonium Nitrate: Three-Component Synthesis of Trisubstituted Imidazoles Under Aerobic Oxidation Conditions

By combining a ceric ammonium nitrate (CAN)–catalyzed aerobic oxidation of α-hydroxy ketones with a subsequent three-component condensation reaction using aldehydes and ammonium acetate, highly substituted imidazole derivatives can be assembled. This reaction is an important approach for the synthesis of highly substituted imidazole derivatives and was carried out in good to excellent yields in ethanol as an environmentally benign solvent.     

Ionic liquid promoted one-pot synthesis of 3-aminoimidazo[1,2-a]pyridines

3-Aminoimidazo[1,2-a]pyridines have been synthesized in good to excellent yields in the presence of the ionic liquid 1-butyl-3-methylimidazolium bromide [bmim]Br, the reaction workup is simple and the ionic liquid can be easily separated from the product and reused.     

A sol‐gel based solid phase microextraction fiber for the analysis of aliphatic alcohols in apple juices

A new fiber based on titania‐chitin sol‐gel coated on a silver wire for the headspace solid phase microextraction of aliphatic alcohols from apple juice samples was developed. The influences of fiber coating composition and microextraction conditions (extraction temperature, extraction time, and ionic strength of the sample matrix) on the fiber performance were investigated. Also, the influence of temperature and time on desorption of analytes from fiber were studied. Under the optimized conditions, a porous fiber with a high extraction capacity and good thermal stability (up to 250°C) was obtained. The proposed headspace solid‐phase microextraction‐GC method was successfully used for the analysis of aliphatic alcohols in apple juice and concentrate samples. The recovery values were from 92.8 to 98.6%. The RSD (n=5) for all analytes were below 7.8%.     

Liquid chromatography/tandem mass spectrometric bioanalysis using normal-phase columns with aqueous/organic mobile phases - a novel approach of eliminating evaporation and reconstitution steps in 96-well SPE

Bioanalytical methods using automated 96-well solid-phase extraction (SPE) and liquid chromatography with electrospray tandem mass spectrometry (LC/MS/MS) are widely used in the pharmaceutical industry. SPE methods typically require manual steps of drying of the eluates and reconstituting of the analytes with a suitable injection solvent possessing elution strength weaker than the mobile phase. In this study, we demonstrated a novel approach of eliminating these two steps in 96-well SPE by using normal-phase LC/MS/MS methods with low aqueous/high organic mobile phases, which consisted of 70-95% organic solvent, 5-30% water, and small amount of volatile acid or buffer. While the commonly used SPE elution solvents (i.e. acetonitrile and methanol) have stronger elution strength than a mobile phase on reversed-phase chromatography, they are weaker elution solvents than a mobile phase for normal-phase LC/MS/MS and therefore can be injected directly. Analytical methods for a range of polar pharmaceutical compounds, namely, omeprazole, metoprolol, fexofenadine, pseudoephedrine as well as rifampin and its metabolite 25-desacetyl-rifampin, in biological fluids, were developed and optimized based on the foregoing principles. As a result of the time saving, a batch of 96 samples could be processed in one hour. These bioanalytical LC/MS/MS methods were validated according to "Guidance for Industry - Bioanalytical Method Validation" recommended by the Food and Drug Administration (FDA) of the United States.     

Palladium nanoparticle decorated carbon ionic liquid electrode for highly efficient electrocatalytic oxidation and determination of hydrazine

In this work arrays of palladium nanoparticles were synthesized on carbon ionic liquid electrode (CILE) (Pd/CILE), and the electrocatalytic oxidation of hydrazine was investigated using this electrode. Electrochemical oxidation of hydrazine in phosphate buffer (pH 7) was performed using cyclic voltammetry and square wave voltammetric techniques (SWV). Using the proposed electrode, a highly reproducible and well-defined peak was obtained for hydrazine at a very low potential of −0.02 V versus Ag/AgCl. A linear dynamic range of 5-800 μM with an experimental detection limit of 0.82 μM was obtained. These results show that the proposed electrode displays better electrocatalytic activity compared to the previously reported palladium modified electrodes towards oxidation of hydrazine.