Potential chlorinated and brominated interferences on the polybrominated diphenyl ether determinations by gas chromatography-mass spectrometry

The analysis of polybrominated diphenyl ether (PBDE) congeners by GC-MS was studied in terms of potential interferences. Different MS approaches were normally used for the PBDE analyses: negative ion chemical ionization (NICI-MS) and electron ionization (EI-MS). This paper studied the presence of potential interferences in each instrumental technique approach, principally those corresponding to different chlorinated compounds (PCBs, PCNs, etc.) as well as brominated compounds (PBBs, MeO-PBDEs, TBBPA, etc.). The two ionization modes are subjected to different types of interferences. In general, EI-MS is affected by chlorinated interferences, especially PCBs. NICI-MS eliminated chlorinated interferences but presented different brominated interferences, well resolved with the EI-MS approach.     

Efficient Synthesis of Muramic and Glucuronic Acid Glycodendrimers as Dengue Virus Antagonists

Carbohydrates are involved in many important pathological processes, such as bacterial and viral infections, by means of carbohydrate-protein interactions. Glycoconjugates with multiple carbohydrates are involved in multivalent interactions, thus increasing their binding strengths to proteins. In this work, we report the efficient synthesis of novel muramic and glucuronic acid glycodendrimers as potential Dengue virus antagonists. Aromatic scaffolds functionalized with a terminal ethynyl groups were coupled to muramic and glucuronic acid azides by click chemistry through optimized synthetic strategies to afford the desired glycodendrimers with high yields. Surface Plasmon Resonance studies have demonstrated that the compounds reported bind efficiently to the Dengue virus envelope protein. Molecular modelling studies were carried out to simulate and explain the binding observed. These studies confirm that efficient chemical synthesis of glycodendrimers can be brought about easily offering a versatile strategy to find new active compounds against Dengue virus.     

A general thiol assay based on the suppression of fluorescence resonance energy transfer in magnetic-resin core-shell nanospheres coated with gold nanoparticles

A simple, rapid and sensitive fluorescence resonance energy transfer (FRET) method is presented for the determination of thiols. It is based on the thiol-induced enhancement effect of the surfactant sodium dodecyl sulfate (SDS) on the efficiency of fluorescence resonance energy transfer (FRET) in nanospheres consisting of a magnetic (Fe₃O₄) core and a phenol-formaldehyde resin (PFR) shell containing gold nanoparticles (AuNPs). The luminescence of the core-shell nanospheres at excitation/emission wavelengths of 390/445 nm, respectively, is quenched by the AuNPs which act as energy acceptors. The interaction of AuNPs with thiol compounds in the presence of SDS suppresses FRET and gives rise to a fluorescent signal whose intensity is proportional to the thiol concentration. The analytical features of seven thiols (homocysteine, thioglycolic acid, glutathione, dodecanethiol, cysteamine, cysteine and N-acetylcysteine) were studied. Detection limits are in the range from 0.14 to 0.49 μmol L⁻¹. The precision of the method, expressed as the relative standard deviation, ranges from 0.4 to 4.9 %. The method was applied to the determination of total thiols in water samples with recovery values between 88.7 and 104.6 %.

The fluorescence resonance energy transfer in magnetic-resin core-shell nanospheres coated with gold nanoparticles is inhibited by thiol compounds in the presence of sodium dodecyl sulfate. This gives rise to a fluorescent signal whose intensity is proportional to the thiol concentration.

     

Effect of ion nitriding on the crystal structure of 3 mol% Y2O3-doped ZrO2 thin-films prepared by the sol-gel method

We investigated the effect of ion nitriding on the crystal structure of 3 mol% Y₂O₃-doped ZrO₂ (3YSZ) thin-films prepared by the sol-gel method. For this purpose, we used X-ray diffractometry to determine the crystalline phases, the lattice parameters, the crystal sizes, and the lattice microstrains, and glow discharge-optical emission spectroscopy to obtain the depth profiles of the elemental chemical composition. We found that nitrogen atoms substitute oxygen atoms in the 3YSZ crystal, thus leading to the formation of unsaturated-substitutional solid solutions with reduced lattice parameters and Zr_0.94Y_0.06O_1.72N_0.17 stoichiometric formula. We also found that ion nitriding does not affect the grain size, but does generate lattice microstrains due to the increase in point defects in the crystalline lattice.     

Determination of fenthion and fenthion-sulfoxide, in olive oil and in river water, by square-wave adsorptive-stripping voltammetry

Square-wave adsorptive-stripping voltammetry technique has been used to develop a method for the determination of fenthion in olive oil. Due to the fact that fenthion does not give any electrochemical signal at mercury electrode, the method has been based on a previous oxidation of fenthion to its metabolite, fenthion-sulfoxide, by using KMnO₄. The metabolite gives rise to a peak due to an adsorptive-reductive process at −0.786 V. Fenthion is isolated from olive oil by carrying out a solid–liquid extraction procedure using silica cartridge, followed by a liquid–liquid partitioning with acetonitrile. The detection limit in olive oil is 78.8 ng g⁻¹ and recoveries for four levels of fortification are ranged from 85% to 109%. On the other hand, it has been developed a method for the simultaneous determination of fenthion and its metabolite fenthion-sulfoxide, in river water. Pesticides are isolated from water by carrying out a liquid–liquid partitioning with trichloromethane. The detection limits are 0.41 ng g⁻¹ and 0.44 ng g⁻¹, for fenthion and fenthion-sulfoxide, respectively. Recoveries for three levels of fortification are ranged from 96% to 103% for fenthion and 94% to 104% for fenthion-sulfoxide.     

Structure and dynamics of Cu(I) binding in copper chaperones Atox1 and CopZ: a computer simulation study

Copper chaperones deliver reduced copper (i.e., Cu(I)) to metal-binding domains of P-type ATPases in the cytoplasm of a range of organisms. Both chaperones and target domains have a ferredoxin-like fold and metal-binding motifs involving two Cys residues. Here, we investigated the Cu-binding geometry and structural dynamics of two homologous Cu(I) chaperones, Homo sapiens Atox1 and Bacillus subtilis CopZ, using a combination of quantum mechanical-molecular mechanics (QM-MM) and classical molecular dynamics (MD) methods. Our QM-MM optimized geometries for the holo- proteins suggested that Cu(I) in Atox1 favors a linear Cys(S)-Cu-Cys(S) arrangement but that this angle is close to 150 degrees in CopZ. Classical MD simulations suggest that both Atox1 and CopZ apo- forms have an increased conformational flexibility as compared to the respective holo- forms. This difference is most pronounced in CopZ and correlates with a lower in vitro thermal stability. Both average fluctuation (i.e., rmsd) and radius of gyration data demonstrate that the effects of Cu(I) coordination extend throughout the proteins. Distinct deviations between the two homologues were found in protein-solvent interactions, entropy of Cu(I) binding, and apo-protein Cys-Cys distance distributions. Our in silico results provide new insights into copper chaperone behavior with direct implications for copper transport mechanisms in vivo.     

Characterization of scraps produced by the industrial laser cutting of steels

We have studied some properties relevant for technological applications of the debris produced by industrial laser cutting of steels. The investigated material is made up of spheroidal particles, hollow and solid, which get oxidized over the cutting process, and that we have reduced afterwards in a H₂ atmosphere. The samples, before and after the reduction, were characterized by X-ray diffraction, scanning electron microscopy, specific surface area and Mössbauer spectroscopy. We have found that, after the reduction treatment, the shape remains unchanged but that the chemical composition and the physical properties of the external and internal surface structures are modified. In particular, the specific surface area of the material increased by one order of magnitude.