Evidence for the rare decay B-->K*l+l- and measurement of the B-->Kl+l- branching fraction

We present evidence for the flavor-changing neutral current decay B-->K*l+l- and a measurement of the branching fraction for the related process B-->K l+l-, where l+l- is either an epsilon+epsilon- or a mu+mu- pair. These decays are highly suppressed in the standard model, and they are sensitive to contributions from new particles in the intermediate state. The data sample comprises 123 x 10(6) Upsilon(4S)-->B(-)B decays collected with the BABAR detector at the SLAC PEP-II epsilon+epsilon- storage ring. Averaging over K(*) isospin and lepton flavor, we obtain the branching fractions B(B-->Kl+l-)=(0.65(+0.14)(-0.13)+/-0.04)x10(-6) and B(B-->K*l+l-)=(0.88(+0.33)(-0.29)+/-0.10)x10(-6), where the uncertainties are statistical and systematic, respectively. The significance of the B-->Kl+l- signal is over 8sigma, while for B-->K*l+l- it is 3.3sigma.     

Development of a stir bar sorptive extraction method coupled to solidification of floating droplets dispersive liquid–liquid microextraction based on deep eutectic solvents for the extraction of acidic pesticides from tomato samples

A stir bar sorptive extraction method coupled with deep eutectic solvent based solidification of floating organic droplets–dispersive liquid–liquid microextraction has been used for the simultaneous derivatization and extraction of some acidic pesticides in tomato samples. In this method, initially the analytes are adsorbed on a coated stir bar from tomato juice filled in a narrow tube. After extraction, the stir bar is removed and a water–miscible deep eutectic solvent is used to elute the analytes. Afterward, a derivatization agent and a water–immiscible deep eutectic solvent (as an extraction solvent) with melting point near to room temperature are added to the obtained eluant at µL–levels and the obtained mixture is rapidly injected into deionized water. Under the optimum conditions, the introduced method indicated high enhancement (1543–3353) and enrichment (2530–2999) factors, low limits of detection (7–14 ng/L) and quantification (23–47 ng/L), good linearity (r² ≥ 0.9982), and satisfactory repeatabilities (relative standard deviation ≤12% for intra– and inter–day precisions at a concentration of 100 ng/L of each analyte). Finally, the proposed method was applied in analysis of the analytes in tomato samples.     

The surface catalytic mechanism: a comparative study with square-wave and staircase cyclic voltammetry

A pseudo-first-order catalytic mechanism in which both reactant and product of a redox reaction are strongly immobilized on an electrode surface is theoretically analysed under conditions of square-wave (SWV) and staircase cyclic voltammetry (SCV). A mathematical procedure is developed under diffusionless conditions. The relationships between the properties of the voltammetric response and both the kinetic parameters of the redox reaction and the parameters of the excitation signal are studied. The phenomenon of the quasi-reversible maximum is discussed. A comparative study between SWV and SCV is presented and the limitations and advantages of both techniques, from analytical and kinetic points of view, are discussed. The theoretical predictions are experimentally confirmed by the redox reaction of azobenzene in the presence of hydrogen peroxide as an oxidizing agent. Electronic Publication     

SYNTHESES A L'AIDE D'HETEROCUMULENES. 6. CYCLOADDITION DIPOLAIRE-1,3 ENTRE LA DIPHENYLNITRILIMINE ET LES ISOCYANATES D'AROXYSULFONYLE ET DE TRICHLORO-2,2,2-ETHOXYSULFONYLE

Abstract

In accordance with a [2 + 3] cycloaddition, aroxy and 2,2,2-tri-chloroethoxysulfonyl isocyanates react with diphenylnitrilimine, to furnish, in high yield, the corresponding 1,3,4-oxadiazolines and 1,2,4-triazolines. The latter are formed too by a direct addition of α-chlorobenzylidene-phenylhydrazine to these heterocumulenes, followed by a dehydrohalogenation of the intermediates.

La cycloaddition [2 + 3] des isocyanates d'aroxy et de trichloro-2,2,2-éthoxysulfonyle sur la diphénylnitrilimine, fournit les oxadiazolines-1,3,4 et les triazolines-1,2,4 correspondants avec de hauts rendements. Ces měmes hétérocycles sont obtenus par une voie différente: addition directe de l'α-chlorobenzylidène-phénylhydrazine sur ces hétérocumulènes, suivie d'une déhydrohalogénation des intermédiaires ainsi formés dans la première étape de la réaction.     

Combination of solid-phase extraction-hollow fiber for ultra-preconcentration of some triazole pesticides followed by gas chromatography-flame ionization detection

In this study, an extraction and preconcentration technique using solid-phase extraction (SPE) along with hollow fiber (HF) has been developed as an ultra-preconcentration technique for some triazole pesticides in aqueous samples. Triazole pesticides were employed as model compounds to assess the method and were monitored by gas chromatography-flame ionization detection (GC-FID). Initially, an aqueous solution of target analytes was passed through an RP-8 SPE cartridge and then the adsorbed analytes were eluted with μL amounts of toluene. The collected elute was slowly introduced into an HF that had one end blocked. This allowed precipitation inside the lumen and pores of the HF. Finally, the obtained HF was mounted on a home-made solid-phase microextraction syringe and entered into the GC injection port for thermal desorption-GC analysis. The effect of various experimental parameters including injection port temperature, desorption time, state of HF, washing solvent, elution solvent and its volume, sample volume, etc. were investigated for finding the optimum conditions. The calibration graphs were linear in the ranges of 2-1000 ng/mL (penconazole and hexaconazole), 5-1000 ng/mL (tebuconazole), 15-1000 ng/mL (triticonazole) and the detection limits (LODs) ranged from 0.6 to 4.5 ng/mL. The enhancement factors were in the range of 870-950. The relative standard deviations (RSD%) for five repeated experiments (C=250 ng/mL of each pesticide) varied from 4.5 to 8.7%. The relative recoveries obtained for analytes in grape juice samples, spiked with different levels of each pesticide, were in the range of 87-119%.     

Inside-Needle Extraction Method Based on Molecularly Imprinted Polymer for Solid-Phase Dynamic Extraction and Preconcentration of Triazine Herbicides Followed by GC–FID Determination

An inside-needle extraction method was developed through thermal polymerization of atrazine-molecularly imprinted polymer (MIP) on the internal surface of a stainless steel hollow needle, which was oxidized and silylated. The fabricated coating (MIP layer) for the needle was durable and showed very good chemical and thermal stability. It could be mounted on a glass syringe and be directly coupled with gas chromatographic (GC) systems. The parameters being effective on the coating and extraction processes, namely nature of oxidizing agent, silylation time, nature and amount of porogen, template-to-MIP components ratio, polymerization time and temperature, sample volume, flow rate, pH and ionic strength of the sample were investigated and optimized. The extraction needle showed high selectivity as well as a great extraction capacity for triazines. The extraction of atrazine, simazine, cyanazine, ametryn, prometryn and terbutryn using the fabricated extraction needle and followed by GC analysis resulted in detection limits of 2.6, 21, 24, 32, 38 and 42 ng mL⁻¹, respectively. The fabricated needle proved to be applicable to the analysis of real samples by comparing the results obtained for non-spiked and spiked samples of grape juice, tap water and groundwater.

     

Development of a new dispersive liquid–liquid microextraction method in a narrow-bore tube for preconcentration of triazole pesticides from aqueous samples

In the present work a new, simple, rapid and environmentally friendly dispersive liquid–liquid microextraction (DLLME) method has been developed for extraction/preconcentration of some triazole pesticides in aqueous samples and in grape juice. The extract was analyzed with gas chromatography–flame ionization detection (GC–FID) or gas chromatography–mass spectrometry (GC–MS). The DLLME method was performed in a narrow-bore tube containing aqueous sample. Acetonitrile and a mixture of n-hexanol and n-hexane (75:25, v/v) were used as disperser and extraction solvents, respectively. The effect of several factors that influence performance of the method, including the chemical nature and volume of the disperser and extraction solvents, number of extraction, pH and salt addition, were investigated and optimized. Figures of merit such as linearity (r² > 0.995), enrichment factors (EFs) (263–380), limits of detection (0.3–5 μg L^?1) and quantification (0.9–16.7 μg L^?1), and relative standard deviations (3.2–5%) of the proposed method were satisfactory for determination of the model analytes. The method was successfully applied for determination of target pesticides in grape juice and good recoveries (74–99%) were achieved for spiked samples. As compared with the conventional DLLME, the proposed DLLME method showed higher EFs and less environmental hazards with no need for centrifuging.     

An organocatalytic direct Mannich-cyclization cascade as [3+2] annulation: asymmetric synthesis of 2,3-substituted pyrrolidines

A new method for asymmetric synthesis of 2,3-substituted pyrrolidines from N-PMP aldimines and succinaldehyde via formal [3+2] cycloaddition is reported. This reaction involves proline catalyzed direct Mannich reaction and acid catalyzed reductive cyclization with high yields (up to 78%) and excellent enantioselectivities (up to >99%).     

A Novel Hydrogen Peroxide Sensor Based on the Direct Electron Transfer of Catalase Immobilized on Nano‐Sized NiO/MWCNTs Composite Film

MWCNTs‐nanoNiO composite was used as a glassy carbon electrode modifier for construction of a novel catalase nanobiosensor for hydrogen peroxide. The immobilized catalase exhibited excellent electrocatalytic activity towards the reduction of H₂O₂. The resulting amperometric biosensor exhibited a linear response over a concentration range of 200 µM to 2.53 mM with a low detection limit of 19.0 µM. Electrochemical impedance measurements revealed that the modified electrode can be used for the sensitive detection of H₂O₂. The charge transfer resistance found to decrease significantly after enzymatic reaction of nanobiosensor with H₂O₂. The resulting impedance was highly sensitive to H₂O₂ over a linear range of 19–170 nM with a detection limit of 2.4 nM.     

Molecular tectonics: infinite cationic double stranded helical coordination networks

Upon crystallisation of two bismonodentate tectons based on two pyridine units, interconnected at the meta position by a tetra- or hexa-ethylene glycol fragment and Ag+ cation, double stranded helical infinite coordination networks were formed and structurally characterised. The cationic double helical architectures obtained may be regarded as analogues of DNA in terms of topology.