Performance of Compton suppression system (CSS) and applicability in food matrices

As a non-destructive and multi-element technique, with high-level metrological properties, instrumental neutron activation analysis (INAA) has an important role to determine chemical elements in food. However, its use may be limited when looking for mass fractions near the detection limits. The Compton scattering of higher energy gamma-rays raised the spectrum baseline thus impairing the determination of several elements. Therefore, the gamma-ray spectrometry with Compton suppression becomes an alternative for improving the performance of INAA, since it can reduce the uncertainty of measurements and the detection limits by increasing the proportion between photopeak area and baseline. Here the performance of a Compton suppression system set by Ortec, with 50% relative efficiency and 2.04?keV resolution (FWHM) for the 1,332?keV photopeak, was evaluated for food analysis. Samples of beans, chickpeas, lentils, peas, and rice were irradiated with neutrons and measured in the suppression system. Detection limits calculated from suppressed and unsuppressed spectra were compared. The suppression factor achieved by the system for ¹³⁷Cs was 5.88?±?0.11 (n?=?20) in the plateau region (358 to 382?keV), which was stable along a 20?week period and similar to the data provided in literature for other systems. Amongst fifteen elements determined, the detection limits for Br, Co, La, Na, Sc, and Se were not improved by the use of Compton suppression. On the other hand, the variable improvement obtained for As, Ca, Cd, Cr, Fe, Hg, K, Rb, and Zn corroborated the idea that the performance of the Compton suppressor must be individually assessed for each type of sample.     

Synthesis and Characterization of Terminal [Re(XCO)(CO)2(triphos)] (X=N,P): Isocyanate versus Phosphaethynolate Complexes

The terminal rhenium(I) phosphaethynolate complex [Re(PCO)(CO)₂(triphos)] has been prepared in a salt metathesis reaction from Na(OCP) and [Re(OTf)(CO)₂(triphos)]. The analogous isocyanato complex [Re(NCO)(CO)₂(triphos)] has been likewise prepared for comparison. The structure of both complexes was elucidated by X‐ray diffraction studies. While the isocyanato complex is linear, the phosphaethynolate complex is strongly bent around the pnictogen center. Computations including natural bond orbital (NBO) theory, natural resonance theory (NRT), and natural population analysis (NPA) indicate that the isocyanato complex can be viewed as a classic Werner‐type complex, that is, with an electrostatic interaction between the Re^I and the NCO group. The phosphaethynolate complex [Re(P?C?O)(CO)₂(triphos)] is best described as a metallaphosphaketene with a Re^I–phosphorus bond of highly covalent character.     

Mass spectrometry of rhenium complexes: a comparative study by using LDI‐MS,MALDI‐MS,PESI‐MS and ESI‐MS

A group of rhenium (I) complexes including in their structure ligands such as CF₃SO₃‐, CH₃CO₂‐, CO, 2,2′‐bipyridine, dipyridil[3,2‐a:2′3′‐c]phenazine, naphthalene‐2‐carboxylate, anthracene‐9‐carboxylate, pyrene‐1‐carboxylate and 1,10‐phenanthroline have been studied for the first time by mass spectrometry. The probe electrospray ionization (PESI) is a technique based on electrospray ionization (ESI) that generates electrospray from the tip of a solid metal needle. In this work, mass spectra for organometallic complexes obtained by PESI were compared with those obtained by classical ESI and high flow rate electrospray ionization assisted by corona discharge (HF‐ESI‐CD), an ideal method to avoid decomposition of the complexes and to induce their oxidation to yield intact molecular cation radicals in gas state [M]^+. and to produce their reduction yielding the gas species [M]^–.. It was found that both techniques showed in general the intact molecular ions of the organometallics studied and provided additional structure characteristic diagnostic fragments. As the rhenium complexes studied in the present work showed strong absorption in the UV–visible region, particularly at 355 nm, laser desorption ionization (LDI) mass spectrometry experiments could be conducted. Although intact molecular ions could be detected in a few cases, LDI mass spectra showed diagnostic fragments for characterization of the complexes structure. Furthermore, matrix‐assisted laser desorption ionization (MALDI) mass spectra were obtained. Nor‐harmane, a compound with basic character, was used as matrix, and the intact molecular ions were detected in two examples, in negative ion mode as the [M]^–. species. Results obtained with 2‐[(2E)‐3‐(4‐tert‐buthylphenyl)‐2‐methylprop‐2‐enylidene] malononitrile (DCTB) as matrix are also described. LDI experiments provided more information about the rhenium complex structures than did the MALDI ones. Copyright © 2012 John Wiley & Sons, Ltd.     

Separation of isomeric disaccharides by traveling wave ion mobility mass spectrometry using CO2 as drift gas

The use of CO₂ as a massive and polarizable drift gas is shown to greatly improve peak‐to‐peak resolution (R_p‐p), as compared with N₂, for the separation of disaccharides in a Synapt G2 traveling wave ion mobility cell. Near or baseline R_p‐p was achieved for three pairs of sodiated molecules of disaccharide isomers, that is, cellobiose and sucrose (R_p‐p = 0.76), maltose and sucrose (R_p‐p = 1.04), and maltose and lactose (R_p‐p = 0.74). Ion mobility mass spectrometry using CO₂ as the drift gas offers therefore an attractive alternative for fast and efficient separation of isomeric disaccharides. Copyright © 2012 John Wiley & Sons, Ltd.     

Losartan potassium,a non‐peptide agent for the treatment of arterial hypertension

In the title compound, potassium 2‐butyl‐4‐chloro‐1‐{[2′‐(5‐tetrazolido)­bi­phenyl‐4‐yl]­methyl}‐1H‐imidazol‐5‐yl­methanol, K⁺·C₂₂H₂₂ClN₆O^?, the imidazole and tetrazole rings are at angles of 85.0 (2) and 51.8 (1)°, respectively, to the phenyl rings to which they are attached, while the dihedral angle between the latter two rings is 46.7 (1)°. The coordination sphere of the metal cation consists of six tetrazoyl N atoms, the methanol O atom and the π cloud of one of the phenyl rings. These interactions determine the formation of columns of molecular anions that lie parallel to the b axis, while hydrogen bonding contributes to intercolumnar cohesion. Far from the centre of the columns, the hydro­carbon chain is immersed in a hydro­phobic environment.     

Tuning Aqueous Supramolecular Polymerization by an Acid-Responsive Conformational Switch

Besides their widespread use in coordination chemistry, 2,2’-bipyridines are known for their ability to undergo cis–trans conformational changes in response to metal ions and acids, which has been primarily investigated at the molecular level. However, the exploitation of such conformational switching in self-assembly has remained unexplored. In this work, the use of 2,2’-bipyridines as acid-responsive conformational switches to tune supramolecular polymerization processes has been demonstrated. To achieve this goal, we have designed a bipyridine-based linear bolaamphiphile, 1 , that forms ordered supramolecular polymers in aqueous media through cooperative aromatic and hydrophobic interactions. Interestingly, addition of acid (TFA) induces the monoprotonation of the 2,2’-bipyridine moiety, leading to a switch in the molecular conformation from a linear (trans) to a V-shaped (cis) state. This increase in molecular distortion along with electrostatic repulsions of the positively charged bipyridine-H⁺ units attenuate the aggregation tendency and induce a transformation from long fibers to shorter thinner fibers. Our findings may contribute to opening up new directions in molecular switches and stimuli-responsive supramolecular materials.     

Comparative bioavailability of two zolpidem hemitartrate formulations in healthy human Brazilian volunteers using high-performance liquid chromatography coupled to tandem mass spectrometry

To assess the bioequivalence of two zolpidem hemitartrate formulations in 30 healthy volunteers. Plasma samples were obtained over a 24 h period. Plasma concentrations of zolpidem were analyzed by liquid chromatography coupled to tandem mass spectrometry with positive ion electrospray ionization using multiple reaction monitoring. Values of peak concentration (C_max), area under curve (AUC), half-life, elimination constant, volume of distribution and clearance showed statistically significant differences when comparing women (604.34 ng h/ml, 127.36 ng/ml, 4.4 h, 0.18 1/h, 50.56 L and 8.55 L/h, respectively) and men (276.1 ng h/ml, 70.9 ng/ml, 3.3 h, 0.26 1/h, 91.42 L and 24.34 L/h, respectively), receiving the same dose (5 mg), respectively. The geometric means with corresponding 90% confidence interval for Test/Reference percentage ratios were 99.73% (CI 93.69–106.16) for C_max, 97.44% (90% CI = 91.85–103.37%) for area under curve of plasma concentration until the last concentration observed (AUC_last) and 98.30% (90% CI = 92.48–104.49) for the area under curve between the first sample (pre-dosage) and infinity (AUC_0–inf). Since the 90% CI for AUC_last, AUC_0–inf and C_max ratios were within the 80–125% interval proposed by the US Food and Drug Administration, it was concluded that zolpidem hemitartrate formulation (5 mg orodispersible tablet) is bioequivalent to the zolpidem hemitartrate formulation (Patz SL 5 mg sublingual tablet) with regard to both the rate and the extent of absorption. A new formulation of zolpidem 2.5 mg may be useful in women for the same clinical benefits as the 5 mg formulation in men.     

Molecular dynamics simulations of the melting of 1,3,3-trinitroazetidine

Physical properties of condensed-phase 1,3,3-trinitroazetidine (TNAZ) have been computed with molecular dynamics (MD) and a nonreactive, fully flexible force field formulated by combining the intramolecular interactions obtained from the Generalized AMBER Force Field and the rigid-molecule force field developed by Sorescu-Rice-Thompson [J. Phys. Chem. B 1997, 101, 798] (AMBER-SRT). The results are compared with MD calculations, using the AMBER force field. The predicted densities of crystalline TNAZ from both force fields are about 10% lower than the experimental value. The calculated thermodynamic melting point at 1 atm from the AMBER-SRT force field is 390 K, in good agreement with the measured value of 374 K, while the AMBER force field predicts a thermodynamic melting point of 462 K. The lattice parameters and the molecular and crystal structures calculated with the AMBER-SRT force field are in excellent agreement with experiment. Simulations with the AMBER-SRT force field were also used to generate the isotherm of TNAZ up to 4 GPa and the bulk modulus and its pressure derivative.     

Layered hybrid organic-inorganic Co(II) alkylphosphonates. Synthesis, crystal structure and magnetism of the first two members of the series: Co[(CH3PO3)(H2O)] and Co[(C2H5PO3)(H2O)]

Co[(CH₃PO₃)(H₂O)] (1) and Co[(C₂H₅PO₃)(H₂O)] (2) were prepared by the hydrothermal method and isolated as blue-violet platelet crystals. They were characterized by X-ray diffraction, FT-IR, TGA-DSC techniques and their magnetic properties studied by a dc-SQUID magnetometer. Compound (1) shows an hybrid layered structure, made of alternating inorganic and organic layers along the a-direction of the unit cell. The inorganic layers contain Co(II) ions six-coordinated by five phosphonate oxygen atoms and one from the water molecule. These layers are separated by bi-layers of methyl groups and van der Waals contacts are established between them. In compound (2), the layered hybrid structure is rather similar to that described for compound (1), but the alternation of the inorganic and organic layers is along the b-direction of the unit cell. The magnetic behavior of (1) and (2) as function of temperature and magnetic field was studied. The compounds obey the Curie-Weiss law at temperatures above 100 K, the Curie C, and Weiss θ constants for the methyl derivative being and and for the ethyl derivative and , respectively. The observed magnetic moments for Co atom at room temperature (i.e. μ_eff=5.18 and 5.38 BM, respectively) are higher than those expected for a spin-only value for high spin Co(II) (S=3/2), revealing a substantial orbital contribution to the magnetic moment. The negative values of θ are an indication of the presence of antiferromagnetic exchange couplings between the near-neighbors Co(II) ions, within the layers. [Co(C_nH_2n+1PO₃)(H₂O)] (n=1,2) are 2D Ising antiferromagnets at low temperatures.     

HPLC determination of 2-furaldehyde and 5-hydroxymethyl-2-furaldehyde in alcoholic beverages

A method for the determination of 2-furaldehyde (F) and 5-hydroxymethyl-2-furaldehyde (HMF) in alcoholic beverages by high performance liquid chromatography (HPLC) is described. A C-18 column and an acetonitrile-water mobile phase with isocratic elution were used. UV detection at 280 nm was carried out. The method was validated according to the EURACHEM guidelines. The procedure offers a high specificity and detection limits of the order of 0.005 μg mL^− 1. Recoveries of 94-103% were obtained from spiked samples at different levels with both analytes. Intermediate precision calculated for a period of 2 months was + 0.8% for HMF and + 0.4% for F. The method was applied to the analysis of alcoholic beverages like bourbon, rum, brandy, liquors and aperitif wines.