A simple and green analytical method for determination of glyphosate in commercial formulations and water by diffuse reflectance spectroscopy

This article describes a simple, inexpensive, and environmentally friendly method for the monitoring of glyphosate using diffuse reflectance spectroscopy. The proposed method is based on reflectance measurements of the colored compound produced from the spot test reaction between glyphosate and p-dimethylaminocinnamaldehyde (p-DAC) in acid medium, using a filter paper as solid support. Experimental designs were used to optimize the analytical conditions. All reflectance measurements were carried out at 495 nm. Under optimal conditions, the glyphosate calibration graphs obtained by plotting the optical density of the reflectance signal (AR) against the concentration were linear in the range 50-500 μg mL(-1), with a correlation coefficient of 0.9987. The limit of detection (LOD) for glyphosate was 7.28 μg mL(-1). The technique was successfully applied to the direct determination of glyphosate in commercial formulations, as well as in water samples (river water, pure water and mineral drinking water) after a previous clean-up or pre-concentration step. Recoveries were in the ranges 93.2-102.6% and 91.3-102.9% for the commercial formulations and water samples, respectively.     

Calorimetric aspects of adsorption of pesticides 2,4-<Emphasis Type="SmallCaps">d</Emphasis>, diuron and atrazine on a magadiite surface

H-magadiite was applied to remove the pesticides 2,4-d, diuron, and atrazine from water. The H-magadiite containing herbicides adsorbed were investigated by FTIR, DRX, N₂ adsorption and desorption isotherms, and surface area. Calorimetric studies were carried out to determine the heat of interaction between pesticides and magadiite. It was possible to ride the cycle of interaction of magadiite–pesticide for a better understanding of the process involved. From the results of the thermal effect of the interaction of magadiite–pesticide, the thermochemical parameters can be determined by using the relationship between the data obtained from adsorption and calorimetry results. The interaction of pesticide–magadiite follows the sequence of adsorption: diuron > atrazine > 2,4-d. The ΔH values for the interactions were determined to be −20.62 ± 1.08, −24.04 ± 0.86–26.34 ± 0.93 kJ mol⁻¹ for 2,4-d, diuron and atrazine, respectively. All the interactions were spontaneous, enthalpically and entropically favored demonstrating the effectiveness and efficiency of the method.     

Molecular dynamics simulation study on the interaction of KRN 7000 and three analogues with human CD1d

Many analogues of KRN 7000, a synthetic glycolipid (α-galactosylceramide) exhibiting immuno-stimulatory activity and antitumor properties, were previously synthesized and tested in order to understand the reasons for the resulting biological activity and Th1/Th2 cytokine profile. Principles have been established for the interaction of such glycolipids with the human CD1d molecule but the exact mechanism by which different ligands with the same polar head elicit distinct biological responses remains unclear. Based on these experiments and on the available crystal structures, protein-ligand interactions are explored using molecular dynamics simulations. Hydrogen bond interactions are examined with regard to the polar group orientation. The influence of modulations on the dynamic behavior of the CD1d-glycolipid complex is addressed. Overall, our data support the mechanism by which the shortening of the α-GalCer sphingosine chain causes a significant twist of the CD1d α1 helix structure from residue Phe84 that affects the position of CD1d residues involved in the TCR recognition.     

Copper(I) and silver(I) complexes of 2-amino-1,3,4-thiadiazole and 2-ethylamino-1,3,4-thiadiazole

The following copper(I) and silver(I) complexes of 2-amino-1,3,4-thiadiazole (atz) and 2-ethylamino-1,3,4-thiadiazole (eatz) have been prepared and studied by conductometric, IR and Raman methods: CuXL(X = Cl, Br, I; L = atz, eatz), CuXL₃(X = ClO₄, NO₃; L = atz, eatz), AgClO₄·1.5atz·1/3 EtOH, AgNO₃·2.5atz, AgClO₄·3eatz, AgNO₃·eatz. The ligands are bonded through the amine nitrogen atoms with ν(MN) bands in the 520–410 cm^?1 region. The CuXL complexes have a trigonal (N, 2X_b) coordination with a probable weaker axial interaction. The CuXL₃ and AgCIO₄·3eatz complexes probably have a trigonal pyramidal (3N,O) coordination. In the atz complexes of silver perchlorate and nitrate some ligand molecules are bridging. The AgNO₃·2.5atz complex is likely to have a dimeric structure with tetrahedral coordination of the silver ion.     

Study of silica-supported heteropoly acids by microcalorimetry

Silica-supported heteropoly acids have been studied by microcalorimetry. The results are greatly dependent on both the activation temperature and the heteropoly acid, in agreement with the n-hexane cracking experiments. It is shown that very strong acid sites are formed on H₄SiW₁₂O₄₀/SiO₂ activated at 623 K and on H₃PW₁₂O₄₀/SiO₂ activated at 423 K.     

Synthesis and excited state properties of a [60]fullerene derivative bearing a star-shaped multi-photon absorption chromophore

The synthesis and excited state properties of a compound assembling C60 with a new multi-photon absorption chromophore are reported.     

A bound on the treewidth of planar even-hole-free graphs

The class of planar graphs has unbounded treewidth, since the k×k grid, ∀k∈N, is planar and has treewidth k. So, it is of interest to determine subclasses of planar graphs which have bounded treewidth. In this paper, we show that if G is an even-hole-free planar graph, then it does not contain a 9×9 grid minor. As a result, we have that even-hole-free planar graphs have treewidth at most 49.     

Efficient Bayesian Inference for Multivariate Probit Models With Sparse Inverse Correlation Matrices

We propose a Bayesian approach for inference in the multivariate probit model, taking into account the association structure between binary observations. We model the association through the correlation matrix of the latent Gaussian variables. Conditional independence is imposed by setting some off-diagonal elements of the inverse correlation matrix to zero and this sparsity structure is modeled using a decomposable graphical model. We propose an efficient Markov chain Monte Carlo algorithm relying on a parameter expansion scheme to sample from the resulting posterior distribution. This algorithm updates the correlation matrix within a simple Gibbs sampling framework and allows us to infer the correlation structure from the data, generalizing methods used for inference in decomposable Gaussian graphical models to multivariate binary observations. We demonstrate the performance of this model and of the Markov chain Monte Carlo algorithm on simulated and real datasets. This article has online supplementary materials.