The Diffusion Problem of Toxic Gases in a Tunnel. The Pump Absorption Model

In this work we study the diffusion of a toxic gas in a tunnel due to an explosion in order to realize a control system—via a wireless network of active sensors—for identification and immediate containment procedures. To this end an aspiration pump is turned on instantaneously at a distance of b meters from the explosion to mitigate the effects of the terroristic act. We exactly find the diffusion concentration in order to provide a solution useful for comparison to other models: numerical ones or models with many aspiration pumps. The model is described by the diffusion partial differential equation (PDE) with a non-homogeneous term which models the aspiration pump. A model with more suction pumps is outlined.     

Validated Method to Determine Quetiapine and Norquetiapine in Microsomal Matrix by LC MS–MS: Implication in Quetiapine Metabolism

A sensitive and selective LC–MS/MS method for the quantification of the atypical antipsychotic agent quetiapine and its metabolite norquetiapine (N-desalkyl quetiapine) was developed and validated. Following the protein precipitation technique, the analytes were separated using a reversed phase column with gradient elution. The compounds were ionized in the electrospray positive ionization (ESI+) ion source tandem MS detection in multiple reaction monitoring (MRM) mode. Calibration curves were generated by plotting the peak area ratio of quetiapine and norquetiapine to the IS clozapine for each calibration concentration. The method provides a linear response from a quantitation range of 2.3–452.9 nM (0.9–173.7 ng/mL) and 2.7–543.0 nM (1.0–200.0 ng/mL) for quetiapine and norquetiapine, respectively. Regression analysis showed a correlation coefficient greater than 0.999 and 0.991 for quetiapine and norquetiapine, respectively. To evaluate the metabolism of quetiapine by the cytochrome P450 in microsomes, the method has been subsequently employed. LC–MS/MS procedure has been carried out to determine increasing concentrations of both drugs in microsomal matrix obtained by a pool of mammalian liver microsomes BD UltraPool^TM Human Liver Microsomes (HLM 150).     

d- and l-amino acids in Antarctic lakes: assessment of a very sensitive HPLC-MS method

Amino acids represent a fraction of organic matter in marine and freshwater ecosystems, and a source of carbon, nitrogen and energy. l-Amino acids are the most common enantiomers in nature because these chiral forms are used during the biosynthesis of proteins and peptide. To the contrary, the occurrence of d-amino acids is usually linked to the presence of bacteria. We investigated the distribution of l- and d-amino acids in the lacustrine environment of Terra Nova Bay, Antarctica, in order to define their natural composition in this area and to individuate a possible relationship with primary production. A simultaneous chromatographic separation of 40 l- and d-amino acids was performed using a chiral stationary phase based on teicoplainin aglycone (chirobiotic tag). The chromatographic separation was coupled to two different mass spectrometers—an LTQ-Orbitrap XL (Thermo Fisher Scientific) and an API 4000 (ABSciex)—in order to investigate their quantitative performance. High-performance liquid chromatography coupled with mass spectrometry methods were evaluated through the estimation of their linear ranges, repeatability, accuracy and detection and quantification limits. The high-resolution mass spectrometer LTQ-Orbitrap XL presented detection limits between 0.4 and 7 μg?l ^?1, while the triple quadrupole mass spectrometer API 4000 achieved the best detection limits reported in the literature for the quantification of amino acids (between 4 and 200 ng?l ^?1). The most sensitive method, HPLC-API 4000, was applied to lake water samples. Figure

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Intra- and intermolecular NMR studies on the activation of arylcyclometallated hafnium pyridyl-amido olefin polymerization precatalysts

Pyridyl-amido catalysts have emerged recently with great promise for olefin polymerization. Insights into the activation chemistry are presented in an initial attempt to understand the polymerization mechanisms of these important catalysts. The activation of C1-symmetric arylcyclometallated hafnium pyridyl-amido precatalysts, denoted Me2Hf{N(-),N,C(-)} (1, aryl = naphthyl; 2, aryl = phenyl), with both Lewis (B(C6F5)3 and [CPh3][B(C6F5)4]) and Br?nsted ([HNR3][B(C6F5)4]) acids is investigated. Reactions of 1 with B(C6F5)3 lead to abstraction of a methyl group and formation of a single inner-sphere diastereoisomeric ion pair [MeHf{N(-),N,C(-)}][MeB(C6F5)3] (3). A 1:1 mixture of the two possible outer-sphere diastereoisomeric ion pairs [MeHf{N(-),N,C(-)}][B(C6F5)4] (4) is obtained when [CPh3][B(C6F5)4] is used. [HNR3][B(C6F5)4] selectively protonates the aryl arm of the tridentate ligand in both precatalysts 1 and 2. A remarkably stable [Me2Hf{N(-),N,C2}][B(C6F5)4] (5) outer-sphere ion pair is formed when the naphthyl substituent is present. The stability is attributed to a hafnium/eta(2)-naphthyl interaction and the release of an eclipsing H-H interaction between naphthyl and pyridine moieties, as evidenced through extensive NMR studies, X-ray single crystal investigation and DFT calculations. When the aryl substituent is phenyl, [Me2Hf{N(-),N,C2}][B(C6F5)4] (10) is originally obtained from protonation of 2, but this species rapidly undergoes remetalation, methane evolution, and amine coordination, giving a diastereomeric mixture of [MeHf{N(-),N,C(-)}NR3][B(C6F5)4] (11). This species transforms over time into the trianionic-ligated [Hf{N(-),C(-),N,C(-)}NR3][B(C6F5)4] (12) through activation of a C-H bond of an amido-isopropyl group. In contrast, ion pair 5 does not spontaneously undergo remetalation of the naphthyl moiety; it reacts with NMe2Ph leading to [MeHf{N(-),N}NMe2C6H4][B(C6F5)4] (7) through ortho-metalation of the aniline. Ion pair 7 successively undergoes a complex transformation ultimately leading to [Hf{N(-),C(-),N,C(-)}NMe2Ph][B(C6F5)4] (8), strictly analogous to 12. The reaction of 5 with aliphatic amines leads to the formation of a single diastereomeric ion pair [MeHf{N(-),N,C(-)}NR3][B(C6F5)4] (9). These differences in activation chemistry are manifested in the polymerization characteristics of these different precatalyst/cocatalyst combinations. Relatively long induction times are observed for propene polymerizations with the naphthyl precatalyst 1 activated with [HNMe3Ph][B(C6F5)4]. However, no induction time is present when 1 is activated with Lewis acids. Similarly, precatalyst 2 shows no induction period with either Lewis or Br?nsted acids. Correlation of the solution behavior of these ion pairs and the polymerization characteristics of these various species provides a basis for an initial picture of the polymerization mechanism of these important catalyst systems.     

Synthesis and structural and magnetic characterization of cobalt(II) phosphonate cage compounds

Reaction of cobalt salts with phosphonic acids in the presence of 6-chloro-2-hydroxypyridine as a co-ligand, normally in its deprotonated form, leads to a series of new polymetallic cobalt cages. The most common structural type is a {Co(14)} cage which resembles a fragment of cobalt hydroxide. Variation of the phosphonate present and the cobalt salt leads to {Co(6)}, {Co(8)}, {Co(10)}, {Co(11)}, {Co(12)}, {Co(13)}, and {Co(20)} cages, all of which have been characterized by X-ray crystallography. Magnetic studies of these cages show a general decline in the product chi(m)T with T, but for {Co(6)}, {Co(8)}, and {Co(12)} there are maxima at low temperature, which suggests nondiamagnetic ground states. Investigation of the dynamic behavior of the magnetization of these complexes shows that the octanuclear cage displays slow relaxation of magnetization.     

Formation of new pyridyl substituted enamines. Observation of a diaza-Cope rearrangement

Some 2-arylthiopyridinium imides when reacted with dimethyl acetylene dicarboxylate exhibited ambident behaviour: either a 1,3-dipolar cyclization occurred followed by a ring transformation to yield pyrrolopyridines or 5-pyridyl substituted enamines were formed in a different route. Mechanistic considerations revealed that this latter unusual transformation is initiated by a Michael addition of the imide nitrogen atom of the starting pyridinium compound on the reagent, which is followed by a [3,3]-sigmatropic (‘diaza-Cope’) rearrangement. Ring opening of the pyrrolopyridine compounds by a base also yielded pyridylenamines, which proved to be positional isomers of the sigmatropic rearrangement products. The new pyridyl derivatives seem to be valuable compounds for further transformations. Thus, they can undergo thermal electrocyclization to 7-azaindoles.     

Geographical traceability of Italian white truffle (Tuber magnatum Pico) by the analysis of volatile organic compounds

Results are presented that were obtained on the geographic traceability of the white truffle Tuber magnatum Pico. Solid-phase microextraction coupled to gas chromatography/mass spectrometry (SPME-GC/MS) was employed to characterize the volatile profile of T. magnatum white truffle produced in seven geographical areas of Italy. The main components of the volatile fraction were identified using SPME-GC/MS. Significant differences in the proportion of volatile constituents from truffles of different geographical areas were detected. The results suggest that, besides genetic factors, environmental conditions influence the formation of volatile organic compounds. The mass spectra of the volatile fraction of the samples were used as fingerprints to characterize the geographical origin. Next, stepwise factorial discriminant analysis afforded a limited number of characteristic fragment ions that allowed a geographical classification of the truffles studied.