1,721,239 research outputs found
THE MASS-SPECTROMETRIC BEHAVIOR OF TRANS-[PTHCL(PPH3)2] AND ITS GAS-PHASE, ION MOLECULE REACTION WITH SNCL2
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PIROLISI A PUNTO DI CURIE /GC/MS NELLA CARATTERIZZAZIONE DEI LEGANTI USATI IN CAMPO ARTISTICO.
No full textNeighboring-group participation: a "quasi-SNi" mechanism in the acetolysis and thioacetolysis of 1-(phenylthio)-2-[(p-tolylsulfonyl)oxy]ethane
No full textThe acetolysis and the thioacetolysis of the title compound, selectively deuteriated at one of the two methylenes, was studied. The excess of the unrearranged acetate in the acetolysis at 40°C has been explained in terms of coordination of the acid to the sulfur, followed by a "quasi-SNi" displacement of the leaving group. This pathway is concurrent with the equilibration of the two isomeric tosylates (through the agency of the episulfonium ion 2) and with the acetolysis of 2, resulting in a 1:1 mixture of 4 and 5. The thioacetolysis of 1 and 3 at 40°C gave in turn a 1:1 mixture of the thiolacetates 8 and 9, along with the thionoacetate 6 in the reaction of 1 and the thionoacetate 7 in that of 3. When the acetolysis and the thioacetolysis of 1 were run at the boiling temperature of the solvent, the reactions afforded only a 1:1 mixture of 4 and 5 and 8 and 9, respectively, showing that at higher temperature coordination of the acid is not at work. In the dichloroacetolysis of 1, a 1:1 mixture of the isomeric dichloroacetates 10 and 11 was always obtained. The results show that in the case of 2-(arylthio)ethyl tosylates there are several competing solvolytic pathways, whose relative importance depends upon the acidity and nucleophilicity of the solvent
High performance liquid chromatography electrospray ionisation and atmospheric pressure chemical ionisation mass spectrometry for the analysis of butylated amino resins
No full textEtherified amino resins are used in conjunction with alkyds, polyesters, epoxy or acrylic resins in coating formulation. They are formed from the reaction between formaldehyde and compounds containing NH2 groups, for example, amide, amine or imide groups. Control of this reaction is important in order to obtain the appropriate mixture targeted for the intended use and, as a consequence, the development of analytical procedures able to describe the different species present in the final resin mixtures is necessary. The use of high-performance liquid chromatography, coupled with electrospray ionisation or atmospheric pressure chemical ionisation mass spectrometry, proved to be efficient in the characterisation of n-butylated melamine-formaldehyde resins. The same analytical approach was also applied to describe the first steps in the synthesis of i-butylated urea-formaldehyde resins
Mass spectrometry in the characterization of ambers. II. Free succinic acid in fossil resins of different origin
No full textBaltic amber contains high levels of succinic acid, most of which is part of the polymer framework, and only recently has the presence of microcrystals of free succinic acid been documented by scanning electron microscopy and X-ray diffraction analysis. The determination of succinic acid can be used for an easy identification of Baltic amber among other fossil resins and to distinguish it from imitations, widely diffused on the market, produced with natural or modified recent or sub-fossil resins, such as copals. We report here a simple method, based on negative ion electrospray ionization mass spectrometry, for evaluating the free succinic acid content in water/methanol extracts of ambers from different origin, using a sample of about 20 mg. The limit of quantification is better than 1 ppm and, when applied to a set of amber samples of different origin, it was able to distinguish those of Baltic origin (showing free succinic acid levels in the range 50-400 ppm) from the others (for which succinic acid was undetectable, i.e. at levels lower than 1 ppm)
Importance of measuring products of non-enzymatic glycation of proteins.
No full textNon-enzymatic glycation products are a complex and heterogeneous group of compounds which accumulate in plasma and tissues in diabetes and renal failure. There is emerging evidence that these compounds may play a role in the pathogenesis of chronic complications associated with diabetes and renal failure. So measurement of the products of non-enzymatic glycation has a twofold meaning: on one hand, measurement of early glycation products can estimate the extent of exposure to glucose and the subject's previous metabolic control; on the other hand, measurement of intermediate and late products of the glycation reaction is a precious instrument in verifying the relationship between glycation products and tissue modifications. This review summarizes current knowledge about the diagnostic utility of measuring non-enzymatic glycation products
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