Radionuclide, Metal and Non-metal Levels in Percolated Water from Soils Fertilized with Phosphogypsum

Phosphogypsum (PG) is a by-product of the phosphate fertilizer industry, which is produced by precipitation during the wet process of phosphate rocks. While commercial uses, in agriculture and in manufacturing gypsum board and Portland cement, consume less than a few percent of this by-product, the vast majority is disposed of on land in gypsum. In Brazil, three main industries are responsible for the production and storage of about 5.5 × 10⁶ tons per year. PG may contain trace metals, non-metals, fluorides and natural radionuclides. Since, in Brazil, PG has been used for many years as soil amendment, it is important to know its availability, mainly in aquatic environments used for human consumption. In this case, more restrictive limits must be adopted. This work aimed to evaluate the mobility of metals in sand and clayey soils and, consequently, the contamination of drainage water through greenhouse-scale leaching and transport of toxic elements and radionuclides from soils fertilized with PG to crops. In general, it was observed that elemental concentrations were below the actual detection limit of the equipment for all conditions of interest, indicating a low mobility of the analyzed elements in the soil.     

Optimization of solid-phase microextraction procedures for the determination of tricyclic antidepressants and anticonvulsants in plasma samples by liquid chromatography

Simple, sensitive, and reproducible off-line solid-phase microextraction and liquid chromatography (SPME/LC) methods are described for the determination of seven anticonvulsants and tricyclic antidepressants in human plasma. Factorial design and simplex methodology were applied in the optimization of the SPME procedure for tricyclic antidepressants analyses. Important factors in the SPME efficiency are discussed, such as the fiber coatings (both lab-made and commercial), extraction time, pH, ionic strength, influence of plasma proteins, and desorption conditions. The development of the lab-made fiber coatings, namely, octadecylsilane, aminosilane, and polyurethane, are further described and applied to anticonvulsants analyses. The investigated plasmatic range for the evaluated anticonvulsants, using CW-TPR fiber, were the following: phenylethylmalonamide (3.00–40.0 μg mL⁻¹), phenobarbital (5.00–40.0 μg mL⁻¹), primidone (3.00–40.0 μg mL⁻¹), carbamazepine and carbamazepine-epoxide (2.00–24.0 μg mL⁻¹), phenytoin (2.00–40.0 μg mL⁻¹), and lamotrigine (0.50–12.0 μg mL⁻¹). The antidepressants’ linear plasmatic concentration ranged from 75.0 to 500 ng mL⁻¹ for imipramine, amitriptyline, and desipramine, and from 50.0 to 500 ng mL⁻¹ for nortriptyline, being in all cases, the limit of quantification represented by the lowest value. The precision (interassays) for all investigated drugs in plasma sample spiked with different concentrations of each analyte and submitted to the described procedures were lower than 15%. The off-line SPME/LC methodologies developed allow anticonvulsants and antidepressants analyses from therapeutic to toxic levels for therapeutic drug monitoring.     

CsCl effect on the optical properties of the 80GeS2–20Ga2S3 base glass

Optical properties of chalcogenide glasses belonging to the series (80GeS₂–20Ga₂S₃)_100−x (CsCl) _x with x=0;5;10;15;20 were investigated. The linear refractive indices (n ₀) were determined by prism measurements at four wavelengths: 633 nm, 825 nm, 1311 nm, and 1511 nm. Z-scan experiments were performed at 800 nm to measure the non-linear indices (n ₂) and the absorption coefficients (β). CsCl additions in the base glass (80GeS₂–20Ga₂S₃) are characterized by a white shift of the transmission in the visible range and a strong decrease of both n ₀ and n ₂. As the same time, β is also decreasing and this results in a figure of merit FOM=2βλ/n ₂ that remains relatively low at 800 nm, meaning that this series of highly non-linear glasses should be very suitable for optical switching applications at telecommunication wavelengths.     

Gibbs free energy of transfer of a methylene group on {UCON + (sodium or potassium) phosphate salts} aqueous two-phase systems: Hydrophobicity effects

The Gibbs free energy of transfer of a suitable hydrophobic probe can be regarded as a measure of the relative hydrophobicity of the different phases. The methylene group (CH₂) can be considered hydrophobic, and thus be a suitable probe for hydrophobicity. In this work, the partition coefficients of a series of five dinitrophenylated-amino acids were experimentally determined, at 23 °C, in three different tie-lines of the biphasic systems: (UCON + K₂HPO₄), (UCON + potassium phosphate buffer, pH 7), (UCON + KH₂PO₄), (UCON + Na₂HPO₄), (UCON + sodium phosphate buffer, pH 7), and (UCON + NaH₂PO₄). The Gibbs free energy of transfer of CH₂ units were calculated from the partition coefficients and used to compare the relative hydrophobicity of the equilibrium phases. The largest relative hydrophobicity was found for the ATPS formed by dihydrogen phosphate salts.     

Predicting hydration Gibbs energies of alkyl-aromatics using molecular simulation: a comparison of current force fields and the development of a new parameter set for accurate solvation data

The Gibbs energy of hydration is an important quantity to understand the molecular behavior in aqueous systems at constant temperature and pressure. In this work we review the performance of some popular force fields, namely TraPPE, OPLS-AA and Gromos, in reproducing the experimental Gibbs energies of hydration of several alkyl-aromatic compounds--benzene, mono-, di- and tri-substituted alkylbenzenes--using molecular simulation techniques. In the second part of the paper, we report a new model that is able to improve such hydration energy predictions, based on Lennard Jones parameters from the recent TraPPE-EH force field and atomic partial charges obtained from natural population analysis of density functional theory calculations. We apply a scaling factor determined by fitting the experimental hydration energy of only two solutes, and then present a simple rule to generate atomic partial charges for different substituted alkyl-aromatics. This rule has the added advantages of eliminating the unnecessary assumption of fixed charge on every substituted carbon atom and providing a simple guideline for extrapolating the charge assignment to any multi-substituted alkyl-aromatic molecule. The point charges derived here yield excellent predictions of experimental Gibbs energies of hydration, with an overall absolute average deviation of less than 0.6 kJ mol(-1). This new parameter set can also give good predictive performance for other thermodynamic properties and liquid structural information.     

On the [2,3]-sigmatropic rearrangements of sulfenate esters derived from alkenynols: synthesis of vinylallene and vinylacetylene sulfoxides.

The reactions of various alkenynols with phenylsulfenyl chloride result in the formation of either vinylallene sulfoxides or vnylacetylene sulfoxides, depending on the substitution pattern of the starting material.