Reaction of [Cp12W2O5] with mercaptocarboxylic acids: Addition rather than reduction. Isolation and characterization of Cp1WO2(SCH2CH2COOH)

The reaction of Cp¹₂W₂O₅ with HS(CH₂)_nCOOH (n = 1, 2) in MeOH or in CH₂Cl₂ solutions at room temperature proceeds in slightly different ways depending on the value of n. For n = 2, it selectively yields compound Cp¹WO₂(SCH₂CH₂CO₂H), which has been isolated and characterized by elemental analysis, NMR and single crystal X-ray diffraction. The reaction is equilibrated, being shifted to the product by absorption of water by anhydrous Na₂SO₄ in CH₂Cl₂, and to the reactants by addition of water. Contrary to the Mo analogue, no products resulting from metal reduction are obtained. The corresponding reaction for n = 1 occurs similarly at low substrate/W ratios (<0.5), but proceeds further to several uncharacterized products for greater substrate amounts. The primary product could not be isolated, but its ¹H NMR spectrum suggests a different, asymmetric structure.     

Quantitative analysis of 15N-labeled positional isomers of glutamine and citrulline via electrospray ionization tandem mass spectrometry of their dansyl derivatives

The enteral metabolisms of glutamine and citrulline are intertwined because, while glutamine is one of the main fuel sources for the enterocyte, citrulline is one of its products. It has been shown that the administration of ¹⁵N‐labeled glutamine results in the incorporation of the ¹⁵N label into citrulline, but it is not clear which of the three nitrogen groups of citrulline is actually labeled. To determine the ¹⁵N‐enrichment of the positional isomers of glutamine and citrulline, a rapid liquid chromatography/tandem mass spectrometry (LC/MS/MS) method was developed. The amino acids were analyzed as their dansyl derivatives. The product ion resulting from the loss of NH₃ from the omega carbon allows for the determination of the enrichment of the ureido (citrulline) or amido groups (glutamine). The protonated pyrrolidine (citrulline) or 5‐oxopyrrolidine (glutamine) product ion contains the 2‐N (amino group) and is used to determine its enrichment. The method described showed no ion suppression and a wide dynamic range ranging from 1.3 picomoles to 2 nanomoles for citrulline. Background samples and standards resulted in enrichments not different from those theoretically expected. The enrichment curves for the different glutamine and citrulline isotopomers were linear (R² > 0.998) over the range of enrichments studied. The method developed provides an additional insight into the metabolism of glutamine and citrulline tracing the precursor‐product relationship between these two amino acids. Copyright © 2011 John Wiley & Sons, Ltd.     

Models to estimate overall analytical measurements uncertainty: assumptions, comparisons and applications

Evaluation of analytical results reliability is of core importance as crucial decisions are taken with them. From the various methodologies to evaluate the fitness of purpose of analytical methods, overall measurement uncertainty estimation is more and more applied. Overall measurement uncertainty allows to combine simultaneously the remaining systematic influences to the random sources of uncertainty and allows assessing the reliability of results generated by analytical methods. However there are various interpretations on how to estimate overall measurement uncertainty, and thus various models for estimating it. Each model together with its assumptions has great impacts on the risks to abusively declare that analytical methods are suitable for their intended purpose. This review paper aims at (i) summarizing the various models used to estimate overall measurement uncertainty, (ii) provide their pros and cons, (iii) review the main areas of application and (iv) as a conclusion provide some recommendations when evaluating overall measurement uncertainty.     

L<Superscript>1</Superscript> Stability of Spatially Periodic Solutions in Relativistic Gas Dynamics

This paper proves the well posedness of spatially periodic solutions of the relativistic isentropic gas dynamics equations. The pressure is given by a γ-law with initial data of large amplitude, provided γ − 1 is sufficiently small. As a byproduct of our techniques, we obtain the same results for the classical case. At the limit c → + ∞, the solutions of the relativistic system converge to the solutions of the classical one, the convergence rate being 1/c ². We also construct the semigroup of solutions of the Cauchy problem for initial data with bounded total variation, which can be large, as long as γ − 1 is small.     

Miniaturized bending-free solitons by restoring symmetry in periodically biased photorefractives

We consider optical propagation through a centrosymmetric photorefractive crystal with the externally applied bias voltage modulated along the optical propagation direction. We analytically prove that, if the modulation scale is smaller than the optical diffraction length, the resulting effective nonlinearity has an even parity in the transverse plane for an even-symmetric intensity profile and supports bending-free solitons down to few-micrometer beam widths. Numerical integration of the full photorefractive model for light-matter interaction allows us to confirm the feasibility of these miniaturized solitons and, for longer modulation periods, to investigate the excitation of self-trapped wiggling optical beams.     

Detection and Quantification of Alprazolam Added to Long Drinks by Near Infrared Spectroscopy and Chemometrics

In the present work, a fast, relatively cheap, and green analytical strategy to identify and quantify the fraudulent (or voluntary) addition of a drug (alprazolam, the API of Xanax^®) to an alcoholic drink of large consumption, namely gin and tonic, was developed using coupling near-infrared spectroscopy (NIR) and chemometrics. The approach used was both qualitative and quantitative as models were built that would allow for highlighting the presence of alprazolam with high accuracy, and to quantify its concentration with, in many cases, an acceptable error. Classification models built using partial least squares discriminant analysis (PLS-DA) allowed for identifying whether a drink was spiked or not with the drug, with a prediction accuracy in the validation phase often higher than 90%. On the other hand, calibration models established through the use of partial least squares (PLS) regression allowed for quantifying the drug added with errors of the order of 2–5 mg/L.     

Polarized and Unpolarized Emission from a Single Emitter in a Bullseye Resonator

Polarized , and unpolarized emission from a single emitter embedded in a single, cylindrically symmetric device design is presented. The polarization stems from a position offset of the single emitter with respect to the cavity center, which breaks the cylindrical symmetry, and a position-dependent coupling to the frequency degenerate eigenmodes of the resonator structure is shown. The experimental results are interpreted by using numerical simulations and by experimental mapping of the polarization-resolved far-field emission patterns. The findings can be generalized to any nanophotonic structure where two orthogonal eigenmodes are not fully spatially overlapping.