EPR analysis of the interacting properties and the degradation over time and irradiation of mastic resin used for painting protection

Mastic resin used as a covering film for painting protection was analyzed by electron paramagnetic resonance (EPR) spectroscopy, both as received and upon aging in sun-light. The effect of prolonged exposure to sun-light was mimicked by UV and, more so, by xenon lamp irradiation. Solid mastic presented EPR signals due to radicals trapped by PBN in solution. Data in the literature indicated the formation of acyl radicals (RCO·). These radicals preferentially dissolved in medium polarity solvents. The radical concentration in the solid mastic increased over time more than 50 times upon UV irradiation for 96 h and, even more, by xenon irradiation for 800 h. Also the PBN-trapped radicals in solution increased in concentration by irradiation. Small nitroxide radicals (TEMPO) interacted with a polar fraction of mastic dissolved in methanol, but mainly interacted with low polar mastic molecules in hydrophobic solvents. It was suggested, on the basis of both the PBN-spin trapping data and the TEMPO mobility variation in the solvents at different polarities, that terpenoid molecules partially polymerize by a radical mechanism to form low molecular weight products. A polyaromatic-radical (pyrene-TEMPO) and a biomolecule-radical (doxylcholestane) both interact weakly with mastic molecules in cyclohexane solutions. A positively charged surfactant radical (dimethylammonium-TEMPO bromide) was easily adsorbed onto the solid mastic surface suggesting that detergents are responsible for mastic degradation. In conclusion, this study provided information on the degradation mechanism of mastic resin and on its interacting ability towards external molecules and pollutants.     

A simple approach for coupling liquid chromatography and electron ionization mass spectrometry

A miniaturized, aerosol based interface for directly coupling a liquid chromatograph with a mass spectrometer is presented. The interface is entirely within the electron ionization (EI) source of the mass spectrometer and no additional, external devices are needed. This simple and effective approach exploits micro-flow nebulization technology providing a new interface suitable for a variety of applications of environmental and biological interest. The new interface provides necessary linearity, ruggedness, sensitivity, and reproducibility of response for trace level analysis, and readily interpretable mass spectra for unambiguous identification of unknown compounds of small to medium molecular weight.     

Thermal decomposition of n-alkyl[bis(triphenylphosphine)](carbonyl)iridium(I) complex

The decomposition of L₂Ir(CO)R, R = n-alkyl) prepared in situ by the reacton of n-alkyllithium or -magnesium reagents with L₂Ir(CO)Cl(2) produces a mixture of n-alkane and isomerized alkene, the ratio of which is strongly dependent on the concentration [L] of triphenylphosphine as well as certain other additives. When [L] = 0, positional isomerism and isotope scrabling are extensive as is the isomerism of added olefin, suggesting that β-hydride elimination is rapid and reversible and that any olefins participating in an iridium hydride addition-elimination sequence are also capable of exchange with free olefin in solution. When [Ph₃P]/[2] >/ 1, the principal product (>90%) is the 1-alkene. No positional isomerism or isotope scrambling is observed only a minor amount of alkane is produced. A mechanistic scheme consistent these observations is proposed.     

Identification of levoglucosan and related steroisomers in fog water as a biomass combustion tracer by ESI-MS/MS

A conspicuous fraction of the water soluble organic compounds (WSOC) in fog and fine aerosol samples is composed by monosaccharide anhydrides, such as levoglucosan and its stereoisomers, galactosan and mannosan. Levoglucosan is produced exclusively during wood combustion processes, making it a very useful tracer for plant combustion emissions in the atmosphere. This paper describes a new experimental approach, based on electrospray-tandem mass spectrometry (ESI-MS/MS), for the identification of levoglucosan in fog water samples. The analytical method proposed allows to identify the specific sugar anhydrides directly in the liquid phase without the need of any derivatization process.     

An efficient route to tetrahydronaphthols via addition of ortho-lithiated stilbene oxides to alpha,beta-unsaturated fischer carbene Complexes

[reaction: see text] A stereoselective/stereospecific synthesis of polysubstituted tetrahydronaphthols based on the Michael addition of ortho-lithiated stilbene oxides to alpha,beta-unsaturated Fischer carbene complexes followed by an unusual cyclization of the corresponding intermediate in a 6-endo-tet mode is described.     

Bile enterogastric reflux sensor using plastic optical fibers

Abstract

A portable optical-fiber sensor for ambulatory assessment of the enterogastric reflux, based on the optical properties of the bile, was developed. It makes use of two light-emitting diodes and of an appropriate electronic circuit that processes the signals and provides the readout on a display. A suitable probe for in vivo measurements was designed. Plastic fiber bundles are used in order to obtain probe flexibility and low price. In vivo measurements performed on different patients show the superiority of this technique over existing methods.     

Sopra un teorema di R. Sturm

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