A simple and efficient synthesis and dynamic NMR studies of some new podands of dithiocarbamates formed from bis(naphthyl) derivatives

The reaction of dithiocarbamate salts ( IV _{a − c} ) with bis(naphthalene chloroacetates) ( II _a,b ) and bis(naphthalene ethoxybromide) ( II _c ) in dimethylformamide (DMF) furnished corresponding podands as V _{a − i} in high to excellent yields. Three reacting ligands, ( II _a,b ) and ( II _c ), were obtained in the reaction of bis(naphthalene) ( I _a,b ) with chloroacetylchloride and 1,2‐dibromoethane. Dynamic NMR spectroscopic data of three series of podands ( V _{a − c} , V _d−f , and V _{g − i} ) are discussed, and their free energy of activation (Δ G_C^≠) at coalescence temperatures are figured out. The Δ G_C^≠ s of these podands were attributed to conformational isomerization in the range of 14.5–18.3 kcal mol⁻¹ due to rotation and resonance effects about thioamide C N bond. © 2011 Wiley Periodicals, Inc. Heteroatom Chem 22:659–668, 2011; View this article online at wileyonlinelibrary.com . DOI 10.1002/hc.20730     

Single facility location and relocation problem with time dependent weights and discrete planning horizon

In this paper a single facility location problem with multiple relocation opportunities is investigated. The weight associated with each demand point is a known function of time. We consider either rectilinear, or squared Euclidean, or Euclidean distances. Relocations can take place at pre-determined times. The objective function is to minimize the total location and relocation costs. An algorithm which finds the optimal locations, relocation times and the total cost, for all three types of distance measurements and various weight functions, is developed. Locations are found using constant weights, and relocations times are the solution to a Dynamic Programming or Binary Integer Programming (BIP) model. The time horizon can be finite or infinite.     

Quicksort algorithm: Application of a fixed point theorem in intuitionistic fuzzy quasi-metric spaces at a domain of words

In this paper, we apply an intuitionistic fuzzy quasi-metric version of a fixed point theorem, to obtain the existence of solution for a recurrence equation associated with the analysis of Quicksort algorithms.     

The clique numbers of regular graphs of matrix algebras are finite

Let F be a field, char(F)≠2, and SGL_n(F), where n is a positive integer. In this paper we show that if for every distinct elements x,yS, x+y is singular, then S is finite. We conjecture that this result is true if one replaces field with a division ring.     

The study of an infinite class of dendrimer nanostars by topological index approaches

A topological index for a molecular graph G is a numeric quantity invariant under automorphisms of G. A dendrimer is an artificially manufactured or synthesized molecule built up from branched units called monomers. In this article an infinite class of dendrimer nanostars is investigated under three topological indices containing PI, Szeged and edge Szeged.     

A nonlinear theory for shells with slowly varying thickness

We study the Γ-limit of 3d nonlinear elasticity for shells of small, variable thickness, around an arbitrary smooth 2d surface. To cite this article: M. Lewicka et al., C. R. Acad. Sci. Paris, Ser. I 347 (2009).     

Amino acid dependent formation of phosphate anhydrides in water mediated by carbonyl sulfide

Carbonyl sulfide (COS), a component of volcanic gas emissions and interstellar gas clouds, is shown to be an efficient condensing agent in the context of phosphate chemistry in aqueous solutions. We report that high-energy aminoacyl-phosphate anhydrides and aminoacyl adenylates are generated in solutions containing amino acids, COS, and the corresponding phosphate molecule. We further show that the mixed anhydrides of amino acids and inorganic phosphate are phosphorylating agents, producing pyrophosphate in better than 30% yield in the presence of Ca2+ precipitates. The amino acid dependent activations of phosphate reported here, which occur in parallel with the production of peptides, suggest that these two reactions may have shared a common intermediate on the prebiotic Earth.     

Monitoring of the insecticide trichlorfon by phosphorus-31 nuclear magnetic resonance (31P NMR) spectroscopy

Trichlorfon is an organophosphorus insecticide, which is extensively being used for protection of fruit crops. Trichlorfon is a thermal labile compound, which cannot be easily determined by gas chromatography (GC) and has no suitable group for sensitive detection by high performance liquid chromatography (HPLC). In this study, a ³¹P nuclear magnetic resonance (³¹P NMR) has been described for monitoring of trichlorfon without any separation step. The quantitative works of ³¹P NMR spectroscopy has been performed in the presence of an internal standard (hexamethylphosphoramide). Limit of detection (LOD) for this method has been found to be 55 mg L⁻¹, without any sample preparation, and the linear working range was 150-5500 mg L⁻¹. Relative standard deviation (R.S.D.%) of the method for three replicates within and between days was obtained ≤9%. The average recovery efficiency was approximately 99-112%. This method was applied for monitoring trichlorfon in a commercial insecticide sample and tomato sample.     

New cold-fiber headspace solid-phase microextraction device for quantitative extraction of polycyclic aromatic hydrocarbons in sediment

A new automated headspace solid-phase microextraction (HS-SPME) sampling device was developed, with the capability of heating the sample matrix and simultaneously cooling the fiber coating. The device was evaluated for the quantitative extraction of polycyclic aromatic hydrocarbons (PAHs) from solid matrices. The proposed device improves the efficiency of the release of analytes from the matrix, facilitates the mass transfer into the headspace and significantly increases the partition coefficients of the analytes, by creating a temperature gap between the cold-fiber (CF) coating and the hot headspace. The reliability and applicability of previously reported cold-fiber devices are significantly enhanced by this improvement. In addition, it can be easily adopted for full automation of extraction, enrichment and introduction of different samples using commercially available autosampling devices. Sand samples spiked with PAHs were used as solid matrices and the effect of different experimental parameters were studied, including the extraction temperature, extraction time, moisture content, and the effect of sonication and modifier under optimal experimental conditions, linear calibration curves were obtained in the range of 0.0009-1000 ng/g, with regression coefficients higher than 0.99 and detection limits that ranged from 0.3 to 3 pg/g. Reproducible, precise and high throughput extraction, monitoring and quantification of PAHs were achieved with the automated cold-fiber headspace solid-phase microextraction (CF-HS-SPME) device coupled to GC-flame ionization detection. Determination of PAHs in certified reference sediments using the proposed approach exhibited acceptable agreement with the standard values.     

Aromatization of 1,4‐dihydropyridines in the presence of methanesulfonic acid/NaNO2/wet SiO2 under both heterogeneous and solvent free conditions

A combination of methanesulfonic acid and sodium nitrite in the presence of wet SiO₂ was used as an effective oxidizing agent for the oxidation of 1,4‐dihydropyridines to the corresponding pyridine derivatives under mild and heterogeneous conditions in excellent yields.