A Kinetic Spectrophotometric Method to Determine the Insecticide Methyl Parathion in Commercial Formulations and the Aqueous Environment

Abstract

A simple kinetic-spectrophotometric method for the analysis of the organophosphate insecticide methyl parathien is presented. The method is based on the alkaline hydrolysis of the insecticide into its main metabolite p-nitrophenol. The influence of reaction variables (pH and temperature), and the effect of other pesticides, are discussed. The calibration graphs (initial rate, fixed time, fixed absorbance) were linear from 2 to 30μg/ml. The precision was calculated for the different methods applied, the relative standard deviation being 6.25% for 4μg/ml.

The proposed kinetic method can be applied directly to synthetic mixtures, commercial formulations and different aqueous environment, with recoveries close to 100%.     

A New Synthesis of the Pyrido[2,3-d]Pyrimidine Ring System

Pyrido[2,3-d]pyrimidine derivatives are of chemotherapeutic interest since they have been shown¹ to act as inhibitors of dihydrofolate reductase and also because of their reported² anti-tumor activity. In view of the important biological implications of this ring system, we have investigated a new route to these substances. This paper details a simple and efficient route to the previously unknown 7-amino-1,3-dimethylpyrido[2,3-d]pyrimidine-2,4-dione (I).     

Chiralization in mesogenic 1,3-diacylaminobenzenes

The effect of molecular chirality in thermotropic mesomorphic H-bonded polymeric systems has not really been investigated so far. Therefore, five new chiral mesogenic diamides have been prepared and described. Besides more ordered mesophases, the enantiomers exhibit a chiral nematic polymorphism detected by microcalorimetry and probably corresponding to different modes of chiral coiling to give these singular twisted nematic phases.     

Bis‐clickable Mesoporous Silica Nanoparticles: Straightforward Preparation of Light‐Actuated Nanomachines for Controlled Drug Delivery with Active Targeting

Bis(clickable) mesoporous silica nanospheres (ca. 100 nm) were obtained by the co‐condensation of TEOS with variable amounts (2–5 % each) of two clickable organosilanes in the presence of CTAB. Such nanoparticles could be easily functionalized with two independent functions using the copper‐catalyzed alkyne‐azide cycloaddition (CuAAC) reaction to transform them into nanomachines bearing cancer cell targeting ligands with the ability to deliver drugs on‐demand. The active targeting was made possible after anchoring folic acid by CuAAC click reaction, whereas the controlled delivery was performed by clicked azobenzene fragments. Indeed, the azobenzene groups are able to obstruct the pores of the nanoparticles in the dark whereas upon irradiation in the UV or in the blue range, their trans‐to‐cis photoisomerization provokes disorder in the pores, enabling the delivery of the cargo molecules. The on‐command delivery was proven in solution by dye release experiments, and in vitro by doxorubicin delivery. The added value of the folic acid ligand was clearly evidenced by the difference of cell killing induced by doxorubicin‐loaded nanoparticles under blue irradiation, depending on whether the particles featured the clicked folic acid ligand or not.     

Binding Study of the [Ru(NH3)5pz]2+ Complex to Bile Anion Aggregates through Kinetic Measurements

The electron transfer reaction between [Ru(NH₃)₅pz]²⁺ and [Co(C₂O₄)₃]^3? was studied in the presence of monomers and aggregates of bile salts (sodium deoxycholate, sodium taurodeoxycholate, and sodium glycocholate) at 298.2 ± 0.1 K. The results show a decreasing rate constant with the successive addition of bile salts. To rationalize the trends of the reaction rate on the [bile salts], two models were used. One of them takes into account the aggregation feature by considering a stepwise self‐association between monomers, whereas the other assumes the formation of a critical micellar concentration. Binding constants between [Ru(NH₃)₅pz]²⁺ species and deoxycholate or taurodeoxycholate aggregates were higher than that for glycocholate aggregates. These results are consistent with the way in which the monomers are added to form the bile anion aggregates.     

Experimental characterization of dielectric-loaded plasmonic waveguide-racetrack resonators at near-infrared wavelengths

Dielectric-loaded plasmonic waveguide-racetrack resonators (WRTRs) were designed and fabricated for operating at near-infrared wavelengths (750–850 nm) and characterized using leakage radiation microscopy. The transmission spectra of the WRTRs are found experimentally and compared to the calculated analytical expression. The wavelength-dependent parameters of the analytical expression, i.e. the propagation length and effective-index dispersion, were also estimated experimentally by leakage radiation imaging of direct and Fourier space, respectively. The fabricated structures exhibited high extinction ratio (～20 dB) and good agreement between calculated and measured transmission values.     

Validation of new methodology for the definition of tolerance limits of critical properties in fuels handled in terminals and pipelines—giveaway: compliance with the specification

Accreditation and Quality Assurance - In any commercial transaction, the presence of tolerances from specification limits is essential to ensure that the true value of the property of interest is...