Nucleophilic debenzoylation of p‐nitrophenyl benzoate in cationic micellar media

Pseudo‐first‐order rate constants for the nucleophilic debenzoylation reaction of p‐nitrophenyl benzoate with various hydroxamate ions [RC = ONHO^?] were investigated in aqueous cationic micellar media at pH 7.8 and 27°C. The kinetic rate data of the reaction revealed that the nucleophilic reactivity sequence of these hydroxamate ions is generally benzohydroxamic acid > salicylhydroxamic acid > acetohydroxamic acid. The k_obs value increases upon addition of cationic surfactants to the reaction medium involving interfacial ion exchange between bulk aqueous media and micellar pseudophase. The effect of surfactant head and tail group is discussed. © 2009 Wiley Periodicals, Inc. Int J Chem Kinet 42: 106–112, 2010     

Determination of 77 Multiclass Pesticides and Their Metabolitesin Capsicum and Tomato Using GC-MS/MS and LC-MS/MS

A quick, sensitive, and reproducible analytical method for the determination of 77 multiclass pesticides and their metabolites in Capsicum and tomato by gas and liquid chromatography tandem mass spectrometry was standardized and validated. The limit of detection of 0.19 to 10.91 and limit of quantification of 0.63 to 36.34 µg·kg⁻¹ for Capsicum and 0.10 to 9.55 µg·kg⁻¹ (LOD) and 0.35 to 33.43 µg·kg⁻¹ (LOQ) for tomato. The method involves extraction of sample with acetonitrile, purification by dispersive solid phase extraction using primary secondary amine and graphitized carbon black. The recoveries of all pesticides were in the range of 75 to 110% with a relative standard deviation of less than 20%. Similarly, the method precision was evaluated interms of repeatability (RSDr) and reproducibility (RSD_wR) by spiking of mixed pesticides standards at 100 µg·kg⁻¹ recorded anRSD of less than 20%. The matrix effect was acceptable and no significant variation was observed in both the matrices except for few pesticides. The estimated measurement uncertainty found acceptable for all the pesticides. This method found suitable for analysis of vegetable samples drawn from market and farm gates.     

Silver nanoparticles embedded cation-exchange membrane for remediation of Hg species and application as the dip catalyst in organic transformation

Silver nanoparticles (Ag NPs) embedded in poly(perfluorosulfonic) acid cation-exchange membrane (Nafion-211) were synthesized by in situ reductions of Ag⁺ ions by sodium borohydride at room temperature and formamide at 65 °C. The formamide-reduction formed Ag NPs uniformly distributed in the membrane matrix. Therefore, the formamide-reduced Ag NPs embedded membranes were used for the sorption-preconcentration of Mercury (Hg)²⁺ ions by the galvanic reaction with Ag NPs in the membrane matrix. The replacement of Ag⁰ in NPs with Hg²⁺ ions resulted in the formation of Hg⁰ accumulated as nanodroplets in the membrane matrix as indicated by the field emission scanning electron microscopy studies. The sorption of Hg²⁺ ions via galvanic reaction in the Nafion membrane was found to be maximum (>93%) from pH = 2.5 to pH = 6.5. The Ag NPs embedded membrane was studied for Hg²⁺ ions sorption from the aqueous samples by radiotracer (²⁰³Hg), spectrophotometry, energy dispersive X-ray fluorescence and cold vapor atomic absorption spectrophotometry. This membrane was successfully applied for the determination and quantification of Hg²⁺ ions in the real water samples and safe storage of Hg for the remediation objective. The Hg⁰ embedded membrane was also found to be promising as the dip catalyst in the representative organic transformation of phenylacetylene to acetophenone. The Hg⁰ embedded membrane dip catalyst was reused in four consecutive cycles under similar conditions and found to be successful by giving an almost similar yield (%) of the product. This demonstrated a possibility of safe application of Hg⁰ stored in the matrix of poly(perfluorosulfonate) membrane for catalysis.     

Fundamental studies on the feasibility of deep eutectic solvents for the selective partition of glaucarubinone present in the roots of Simarouba glauca

Several deep eutectic solvents prepared by the complexation of choline chloride as the hydrogen bond acceptor and hydrogen bond donors such as urea, thiourea, ethylene glycol, and glycerol were employed to partition glaucarubinone, an antimalarial compound present in roots of the plant, Simarouba glauca. Among all the solvents, the deep eutectic solvent consisting of the mixture of choline chloride and urea the most suitable to partition the antimalarial compound from the extract selectively. Analytical tools such as high‐performance liquid chromatography and electrospray ionization mass spectrometry were used for characterizations, and glaucarubinone extracted from the roots of the plant by conventional solvent extraction method was used as a reference for comparison. The hydrogen and noncovalent bonds formed between glaucarubinone and the deep eutectic solvents could be responsible for the selective partition of the drug molecule.     

Geometry and differentiability requirements in multibody railroad vehicle dynamic formulations

The dynamic equations of multibody railroad vehicle systems can be formulated using different sets of generalized coordinates; examples of these sets of coordinates are the absolute Cartesian and trajectory coordinates. The absolute coordinate based formulations do not require introducing an intermediate track coordinate system since all the absolute coordinates are defined in the global system. On the other hand, when the trajectory coordinates are used, a track coordinate system that follows the motion of a body in the railroad vehicle system is introduced. This track coordinate system is defined by the track geometry and the distance traveled by the body along the track centerline. The configuration of the body with respect to the track coordinate system is defined using five coordinates; two translations and three Euler angles. In this paper, the formulations based on the absolute and trajectory coordinates are compared. It is shown that these two sets of coordinates require different degrees of differentiability and smoothness. When an elastic contact formulation is used to study the wheel/rail dynamic interaction, there are significant differences in the order of the derivatives required in both formulations. In fact, as demonstrated in this study, in the absence of a contact constraint formulation, higher order derivatives with respect to geometric parameters are still required when the equations are formulated using the trajectory coordinates. The formulation of the constraints used in the analysis of the wheel/rail contact is discussed and it is shown that when the absolute coordinates are used, only third order derivatives need to be evaluated. The relationship between the track frame used in railroad vehicle dynamics and the Frenet frame used in the theory of curves to describe the curve geometry is also discussed in this paper. Based on the analysis presented in this paper, the advantages and drawbacks of a hybrid method which employs both the absolute and trajectory coordinates and planar contact conditions in order to reduce the number of contact constraints and relax the differentiability requirements are discussed. In this method, the absolute coordinates are used to formulate the equations of motion of the railroad vehicle system. The absolute coordinate solution can be used to determine the trajectory coordinates and their time derivatives. Using the trajectory coordinates, the motion of the body in the vehicle with respect to the track coordinate system can be predicted and used in the formulation of the planar contact model.     

Identification of an Allosteric Pocket on Human Hsp70 Reveals a Mode of Inhibition of This Therapeutically Important Protein

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