Determination of fenthion and oxidation products in personal protection equipment by gas chromatography

A method for the co-extraction and simultaneous chromatographic determination of fenthion and its five oxidation products (or metabolites) fenoxon, fenoxon-sulfoxide, fenoxon-sulfone, fenthion-sulfoxide, and fenthion-sulfone in personal protection equipment (PPE) of pesticide applicators was developed and validated. Capillary gas chromatography-nitrogen-phosphorus detection was used for the analytical determination of all the aforementioned compounds over the concentration range of 0.1-0.5 microg/mL. All necessary validation criteria of the method were met. The method was found to be highly selective, accurate, and precise, gave satisfactory recovery (>70%) and RSD values (<20%) for fenthion and its metabolites in all tested specimens of personal protection equipment and in air samplers. The limit of quantification (LOQ) and linearity were determined for the most relevant PPE (i.e. inner coverall) for the parent compound and for the metabolites. The LOQ values ranged from 0.05 to 0.1 ppb while the linearity in the tested range of 0.1-0.5 ppm had r(2)>0.994 for all analytes.     

Light-activated functional mesostructured silica

Mesostructured silica thin films and particles provide highly versatile supports or frameworks for functional materials where a desired function (such as energy transfer, electron transfer, or molecular machines) is induced by molecules deliberately placed in specific regions of the structure. The relatively gentle templated sol–gel synthesis methods allow a wide variety of molecules to be used, and the optical transparency of the framework is very suitable for studies of light-induced functionality. In this paper, three types of functionality are used to obtain fundamental understanding of the materials themselves and to develop active materials that can trap and release molecules from the pores upon command. Photo-induced energy transfer is used to verify that molecules can be placed in specific spatially separated regions of the framework; fluorescence resonance energy transfer is used as a molecular ruler to measure quantitatively the distance between pairs of molecules. Secondly, photo-induced electron transfer is used to obtain fundamental information about the electrical insulating properties of the framework. Finally, two types of molecular machines, a light-driven impeller and a light activated nanovalve, are described. Both machines contain moving parts attached to solid supports and do useful work. The valves trap and release molecules from the mesopores, and the impellers expel molecules from the pores. Applications of the materials to drug delivery and the release of drug molecules inside living cells is described.     

Synthesis,Structural and Physicochemical Characterization of a Titanium(IV) Compound with the Hydroxamate Ligand N,2-Dihydroxybenzamide

The siderophore organic ligand N,2-dihydroxybenzamide (H₂dihybe) incorporates the hydroxamate group, in addition to the phenoxy group in the ortho-position and reveals a very rich coordination chemistry with potential applications in medicine, materials, and physical sciences. The reaction of H₂dihybe with TiCl₄ in methyl alcohol and KOH yielded the tetranuclear titanium oxo-cluster (TOC) [Ti^IV₄(μ-O)₂(HOCH₃)₄(μ-Hdihybe)₄(Hdihybe)₄]Cl₄∙10H₂O∙12CH₃OH (1). The titanium compound was characterized by single-crystal X-ray structure analysis, ESI-MS, ¹³C, and ¹H NMR spectroscopy, solid-state and solution UV–Vis, IR vibrational, and luminescence spectroscopies and molecular orbital calculations. The inorganic core Ti₄(μ-O)₂ of 1 constitutes a rare structural motif for discrete Ti^IV₄ oxo-clusters. High-resolution ESI-MS studies of 1 in methyl alcohol revealed the presence of isotopic distribution patterns which can be attributed to the tetranuclear clusters containing the inorganic core {Ti₄(μ-O)₂}. Solid-state IR spectroscopy of 1 showed the presence of an intense band at ~800 cm⁻¹ which is absent in the spectrum of the H₂dihybe and was attributed to the high-energy ν(Ti₂–μ-O) stretching mode. The ν(C=O) in 1 is red-shifted by ~10 cm⁻¹, while the ν(N-O) is blue-shifted by ~20 cm⁻¹ in comparison to H₂dihybe. Density Functional Theory (DFT) calculations reveal that in the experimental and theoretically predicted IR absorbance spectra of the ligand and Ti-complex, the main bands observed in the experimental spectra are also present in the calculated spectra supporting the proposed structural model. ¹H and ¹³C NMR solution (CD₃OD) studies of 1 reveal that it retains its integrity in CD₃OD. The observed NMR changes upon addition of base to a CD₃OD solution of 1, are due to an acid–base equilibrium and not a change in the Ti^IV coordination environment while the decrease in the complex’s lability is due to the improved electron-donating properties which arise from the ligand deprotonation. Luminescence spectroscopic studies of 1 in solution reveal a dual narrow luminescence at different excitation wavelengths. The TOC 1 exhibits a band-gap of 1.98 eV which renders it a promising candidate for photocatalytic investigations.     

A feasible point adaptation of the Blankenship and Falk algorithm for semi-infinite programming

Discretization methods for semi-infinite programming do not provide a feasible point in a finite number of iterations. We propose a method that computes a feasible point with an objective value better than or equal to a target value f ₀ or proves that such a point does not exist. Then a binary search on the space of objective values can be performed to obtain a feasible, e{\epsilon}-optimal solution. The algorithm is based on the algorithm proposed in (Blankenship JW, Falk JE in J Optim Theory Appl 19(2):261–281, 1976). Under mild assumptions it terminates in a finite number of iterations.     

Bounds and limit theorems for a layered queueing model in electric vehicle charging

Queueing Systems - In this paper, we provide convergence analysis for a class of Brownian queues in tandem by establishing an exponential drift condition. A consequence is uniform exponential...     

A temperature dependence Raman study of the 0.1Nb2O5-0.9TeO2 glass-forming system

Raman spectra of the 0.1Nb₂O₅-0.9TeO₂ binary glass-forming oxide system were measured over a temperature range including the glassy, supercooled and crystalline state to reveal the structural changes caused by temperature variation. The analysis of the reduced Raman spectra made it possible to quantitatively follow the transformation of the TeO₄ trigonal bipyramids—that dominate in the low temperature glass—into TeO₃ trigonal pyramids with temperature rise. Based on the predictions of existing structural models, we estimated with the aid of the Raman data the number of terminal oxygen atoms that inevitably accompany this structural change. The various crystal phases of the system studied in this work and the routes for converting one crystal phase into another were also examined. Finally, the low-energy excitations of the non-crystalline states of 0.1Nb₂O₅-0.9TeO₂ were studied by following the temperature dependence of the Boson peak.     

Encapsulation and Polymerization of White Phosphorus Inside Single-Wall Carbon Nanotubes

Elemental phosphorus displays an impressive number of allotropes with highly diverse chemical and physical properties. White phosphorus has now been filled into single-wall carbon nanotubes (SWCNTs) from the liquid and thereby stabilized against the highly exothermic reaction with atmospheric oxygen. The encapsulated tetraphosphorus molecules were visualized with transmission electron microscopy, but found to convert readily into chain structures inside the SWCNT “nanoreactors”. The energies of the possible chain structures were determined computationally, highlighting a delicate balance between the extent of polymerization and the SWCNT diameter. Experimentally, a single-stranded zig-zag chain of phosphorus atoms was observed, which is the lowest energy structure at small confinement diameters. These one-dimensional chains provide a glimpse into the very first steps of the transformation from white to red phosphorus.     

Stereochemistry of photosolvolysis of a chiral, 18O-labeled 1-arylethyl acetate

The stereochemistry of photosolvolysis of ($\text{R}$)-(+)-1-(3,5-dimethoxyphenyl)ethyl acetate-$\text{ether-}{}^{18}\text{O}$ in methanol-water and 2,2,2-trifluoroethanol has been determined. An ion pair intermediate was detected in the latter solvent.