Determination of aflatoxin B1 in cereals by homogeneous liquid-liquid extraction coupled to high performance liquid chromatography-fluorescence detection

A simple and rapid method based on homogeneous liquid-liquid extraction coupled to HPLC with fluorescence detection was developed for the determination of aflatoxin B1 (AFB1) in the rice and grain samples after post-column derivatization. The proposed method eliminated the use of immunoaffinity columns for clean-up in the determination of AFB1. The parameters affecting recovery and preconcentration such as type and volume of organic solvent, volume ratio of water/methanol, concentration of phase separator reagent and extraction time were optimized. Under the optimized conditions, the calibration graph was linear in the concentration range of 0.01-1.0 ng/g with the detection limit of 0.003 ng/g. This method was successfully applied for the analysis of AFB1 in different cereal samples.     

Optical detection of terahertz radiation by using nonlinear parametric upconversion

We describe and demonstrate sensitive room-temperature detection of terahertz (THz) radiation by nonlinearly upconverting terahertz to the near-infrared regime, relying on telecommications components. THz radiation at 700 GHz is mixed with pump light at 1550 nm in a bulk GaAs crystal to generate an idler wave at 1555.6 nm, which is separated and detected by using a commercial p-i-n diode. The THz detector operates at room temperature and has an intrinsic THz-to-optical photon conversion efficiency of 0.001%.     

Heterocycles [h]fused onto 4-oxoquinoline-3-carboxylic acid, part IV. Convenient synthesis of substituted hexahydro [1,4]thiazepino[2,3-h]quinoline-9-carboxylic acid and its tetrahydroquino[7,8-b]benzothiazepine homolog

Substituted [1,4]thiazepino[2,3-h]quinolinecarboxylic acid 3 is prepared by PPA-catalyzed thermal lactamization of the respective 8-amino-7-[(2-carboxyethyl)thio]-1,4-dihydroquinoline-3-carboxylic acid 9. The latter synthon is obtained by reduction of the 8-nitro-1,4-dihydroquinoline precursor 8 which, in turn, is made accessible via interaction of 3-mercaptopropionic acid with 7-chloro-1-cyclopropyl-6-fluoro-8-nitro-1,4-dihydroquinoline-3-carboxylic acid 7 in the presence of triethylamine. A benzo-homolog of 3, namely tetrahydroquino[7,8-b]benzothiazepine-3-carboxylic acid 6, is analogously prepared via the reaction of 2-mercaptobenzoic acid with 7, followed by reduction of the resulting 7-[(2-carboxyphenyl)thio]-8-nitro product 10 into the corresponding 8-amino derivative 11, and subsequent lactamization. The structures assigned to 3, 6 and 8-11 are based on microanalytical and spectral (IR, MS, NMR) data.     

Facile synthesis of some novel pyrido[3',2':4,5]thieno[2,3-b][1,4]thiazine-8-carboxylic acids

Model tetrahydropyrido[3',2':4,5]thieno[2,3-b][1,4]thiazines 9a-c were synthesized via reductive lactamization, using sodium dithionite, of the respective 2-[(carboxyalkyl)thio]-3-nitro-4,7-dihydrothieno[2,3-b]pyridine-5-carboxylic acids 7a-c. The latter derivatives were made via interaction of 2-chloro-7-cyclopropyl-3-nitro-4,7-dihydrothieno[2,3-b]pyridine-5-carboxylic acid (6) with each of alpha-mercaptoacetic, alpha-mercaptopropionic, and alpha-mercaptosuccinic acids and triethylamine in aqueous acetone at room temperature. The structures of 7a-7c and 9a-9c are supported by microanalytical and spectral (IR, MS, NMR) data. Compounds 9a and 9c showed potent inhibitory activity against the IGROV1 (Ovarian Cancer) cell line.     

Rapid microwave assisted esterification method for the analysis of poly-3-hydroxybutyrate in Alcaligenes latus by gas chromatography

In the present study, we used microwave energy instead of conventional heating to transform poly-3-hydroxybutyrate (PHB) into methyl 3-hydroxybutyrate (Me-3HB) in acidified methanol (H2SO4, 10%, v/v) mixture in less than 4 min at 10% microwave power. The microwave assisted method was then applied to analyze PHB produced by Alcaligenes latus. The PHB content in the biomass determined using microwave heating was comparable to the amount found by conventional heating. Moreover, the new esterification method was at least 50 times faster than the conventional method, affording a significant saving of time and energy.     

The effect of emitter geometry on lateral field emission diodes fabricated by AFM-based electrochemical nanolithography

Lateral field emission diodes were successfully fabricated using atomic force microscopy (AFM)-based electrochemical nanolithography and tetramethyl ammonium hydroxide (TMAH) wet etching method. Field emission (FE) current of the silicon emitter cathode was measured as a function of the applied anode voltage under vacuum environment. For narrowed nanogaps from 55 to 35 nm, the turn-on voltage was decreased from 21 to 16 V. The turn-on voltage of the 35 nm gap was reduced from 16 to 8 V by changing the curvature radius of the cathode tip. The sharper emitter had the lowest turn-on voltage, largest field-enhancement factor, and good stability, which were attributed to the small emitter radius at the cathode tip and very slight changes in the local field factor. These results indicate that the diodes fabricated using this technique had the lowest value of turn-on voltage ever reported for lateral silicon FE devices.     

Size and morphology controlling of PLGA microparticles produced by electro hydrodynamic atomization

Among the various methods used to produce microparticles, electrospraying is becoming increasingly popular, and it has the advantage of control over the size, shape and morphology of the produced particles. Particle size and morphology are the main factors used to control the rate of microsphere degradation and drug diffusion. The aim of this study was to use some process and solution parameters of the electrospraying such as flow rate, collecting distance, nozzle diameter and polymer molecular weight to control size, shape and morphology of the produced particles. Tests demonstrated that the size of microparticle can be fine‐tuned by adjusting the variables of flow rate, collecting distance and nozzle diameter. Other relevant factors that can be as tuning parameters were those of solvent vapor pressure and application of a polymer mix with different molecular weights. Results showed that microparticle size increased under an increased flow rate and needle gauge setting and a decreased electrical field. Results of the tests showed that morphology of the produced microsphere could be adjusted by the aforementioned parameters. For example, by lowering solvent vapor pressure by adding solvent with a high boiling point, the morphology was changed from a textured surface to a smooth one. Molecular weight of the polymer had a significant effect on morphology, whereas polymer with a low molecular weight caused defect in the produced microparticle, and a high molecular weight produced cup‐like morphology, but a polymer mix that constituted polymers of high and low Molecular weights improved morphology of the produced particles. Copyright © 2015 John Wiley & Sons, Ltd.     

Highly efficient synthesis of polysubstituted fluorene via iron-catalyzed intramolecular Friedel-Crafts alkylation of biaryl alcohols

An efficient and mild Fe(III)-catalyzed intramolecular Friedel-Crafts alkylation of biaryl methanol derivatives has been developed to achieve the substituted fluorene derivatives. The present reaction provides an excellent alternative to published methods because of its high yields, operational simplicity, mild conditions, and use of inexpensive and sustainable catalyst.