Mononuclear isoheterocyclic rearrangements. Note I. Interconversion of 3-benzoylamino-5-methyl-1,2,4-oxadiazole and 3-acetylamino-5-phenyl-1,2,4-oxadiazole

The first example of mononuclear isoheterocyclic rearrangement is reported. The 3-benzoylamino-5-methyl-1,2,4-oxadiazole ( 5 ) furnishes through a reversible process (slowly at room temperature in methanol, acetone or dioxane, fast in DMSO or in methanol in the presence of strong bases) a mixture of 5 and 3-acethylamino-5-phenyl-1,2,4-oxadiazole ( 6 ). The equilibrium process can be achieved also by heating 5 at 181° and the same reaction mixture can be obtained using 6 as the starting material. 3-Trichloroacetylamino-5-methyl-1,2,4-oxadiazole ( 7 ) was unaffected by similar treatment. The results obtained are discussed.     

New conditions for matrix-assisted laser desorption/ionization mass spectrometry of native bacterial R-type lipopolysaccharides

A new sample preparation method for matrix-assisted laser desorption/ionization (MALDI) analysis of native rough-type lipopolysaccharides (R-type LPSs) is presented. In our MALDI mass spectra, besides the [M--H](-) ions, abundant ions originating from the cleavage between the 3-deoxy-D-manno-oct-2-ulosonic acid (Kdo) unit and the lipid A moiety are always present, giving important pieces of information about the structure of the molecules analyzed. Remarkably, in most cases, the comparison of the MALDI mass spectra of the intact R-type LPS with the O-deacylated one allowed us to obtain the structure of the lipid A moiety.     

Where are embarrassingly parallel problems? The atom-diatom quasiclassical reactivity

Summary The apparently embarrassingly parallel problem of calculating a batch of quasiclassical trajectories to evaluate cross sections or rate constants has been analyzed. The study shows that only an accurate evaluation of the performance parameters and a consequent appropriate restructuring of the computer code allows the achievement of high speedup and efficiency especially when large calculations are implemented on massively parallel systems.     

Food safety: screening tests used to detect and quantify GMO proteins

GMO protein content in maize flours or fresh crops can be easily assessed by the enzyme-linked immunosorbent assays (ELISA) and immunochromatographic (lateral flow) strip tests commercially available. Therefore, ELISA can be seen as a useful tool for screening, for control purposes and for traceability implementation. In order to highlight the importance of monitoring GMO protein presence in food products and to investigate the performance of representative ELISA commercial kits, we evaluated three commercial kits by measuring the amount of Cry1Ab/Cry1Ac in IRMM certified reference materials. Presented at AOAC Europe/Eurachem Symposium March 2005, Brussels, Belgium     

Mesomorphic behaviour of forty benzylidene-aniline-p,p′-dialkoxy derivatives

The transition temperatures of forty mesomorphic homologous benzylidene-aniline-p,p′-dialkoxy derivatives are reported.

The transition diagrams show different paths for heating and cooling for most of the compounds. Moreover, some compounds with higher length-breadth ratios, show very complicated thermal cycles with some monotropic phases. In any case, the clearing temperatures (T_c) alternate within every series.

The experimental data are discussed briefly and some general considerations on the structure and mesomorphic behaviour are suggested.     

Studies in organic mass spectrometry. Part 15 [1]. Electron ionization mass spectra of some 5-nitro-3-thiophenecarboxanilides

The study of the electron ionization mass spectra of 5-nitro-3-thiophenecarboxanilides 1-24 has shown peculiar effects induced by the 5-nitro group on the fragmentation of molecular ions M and the thenoyl cation a (Scheme 1). A comparison of the abundances of the important fragment ions for 5-nitro-3-thiophene-carboxanilides with those of the corresponding 3-thiophenecarboxanilides shows that the extent of C-N amide bond cleavage decreases in the former series as a consequence of the increased bond strength. The produced ion a does not eliminate carbon monoxide as 2- and 3-thenoyl cations usually do. Again this behaviour depends on the electronic effects of the nitro group which strongly destabilizes the 5-nitro-3-thienyl cation and consequently strengthens the carbon-3 carbonyl carbon bond. Recalling the behavior of the previously studied 2- and 3-thiophenecarboxanilides most of the 2′-substituted 5-nitro-3-thiophenecarboxanilides give loss of the ‘ortho’ substituent of the phenyl ring furnishing the cyclic ion g(Scheme 2). In the instance of 2′-alkyl substituted derivatives the formation of abundant ions h' by loss of 5-nitrothenoyl radical from M (Scheme 3) was observed, thus confirming the occurrence of a cryptic ‘ortho’ effect. The results are also discussed in relation to those obtained on some related benzoylanilides.     

Synthesis of 2,6-disubstituted morpholines through regioselective oxiranes ring opening by tosylamide under PTC conditions

Symmetric and non-symmetric 2,6-disubstituted morpholines were synthesized through regioselective nucleophilic ring opening of oxiranes with tosylamide under solid-liquid phase transfer catalysis (SL-PTC) conditions followed by cyclization of the tosylamido diols thus obtained and final deprotection of the corresponding N-tosyl morpholines. The morpholines prepared are interesting building blocks in the synthesis of pharmaceuticals and agrochemicals.     

Interpretation of atmospheric pollution phenomena in relationship with the vertical atmospheric remixing by means of natural radioactivity measurements (radon) of particulate matter

In this paper the results of seasonal monitoring campaign for primary (benzene and carbon monoxide) and secondary (nitrogen dioxide and ozone) pollutants and for the natural radioactivity of the particulate matter in the urban area of Rome, are reported to investigate acute atmospheric pollution episodes. Comparing the daily concentration trends of primary and secondary pollutants with those of the natural radioactivity, considered as index of the vertical diffusion in the low boundary layer, it has been evidenced that the acute pollution episodes in Rome occur in the winter period for the high atmospheric stability (primary pollution) and in the summer period for the strong diurnal atmospheric remixing (secondary pollution).     

Combined non-destructive XRF and SR-XAS study of archaeological artefacts

We report on a non-destructive study of Sicilian ceramic fragments of cultural heritage interest, classified as “proto-majolica” pottery and dating back to the twelfth to thirteen centuries AD. The analytical approach used is based on the employment of two totally non-invasive spectroscopic techniques: X-ray fluorescence (XRF), using a portable energy-dispersive XRF analyser, and X-ray absorption spectroscopy, using synchrotron radiation as a probe (SR-XAS). XRF measurements allowed us to collect elemental and spatially resolved information on major and minor constituents of the decorated coating of archaeological pottery fragments, so providing preliminary results on the main components characterizing the surface. In particular, we assigned to Fe and Mn the role of key elements of the colouring agent. With the aim of obtaining more detailed information, we performed SR-XAS measurements at the Fe and Mn K-edges at the Italian BM08 beamline at the European Synchrotron Radiation Facility (Grenoble, France). The experimental data were analysed by applying principal component analysis and least-squares fitting to the near-edge part of the spectra (X-ray absorption near-edge structure) to determine the samples’ speciation. From the overall results, umber, a class of brownish pigments characterized by a mixture of hydrated iron and manganese oxides, has been ascribed as a pigmenting agent.