No abstract

No abstract

No abstract

Several mass spectrometry methods were explored to determine the regiospecificity of deuterium substitutions in hydrocarbon mixtures. The case investigated in this work was that of ethane mixtures obtained by catalytic H™D exchange between either C 2 H 6 and D 2 or C 2 D 6 and H 2 over platinum surfaces. A total of ten isotopologs are possible, and were indeed detected in all cases. Deconvolution of low-resolution mass spectra was found sufficient to determine the composition of the gas mixtures in terms of the total number of deuterium substitutions, but not to identify symmetric versus asymmetric substitutions in the C 2 D 2 H 4 , C 2 D 3 H 3 , and C 2 D 4 H 2 products. High-resolution mass spectrometry allowed the separation of the intensities due to C 2 X 4 ϩ fragments from those from molecular C 2 X 6 ϩ signals (X ϭ H or D), and with that for a more accurate determination of the composition of the mixtures. Relative probabilities were determined for the symmetric versus asymmetric removal of X 2 from C 2 X 6 ϩ ions and for isotope scrambling in the mass spectrometer, and with that information fairly good cracking patterns were then calculated for the C 2 X 4 ϩ fragments produced by each individual pure C 2 X 6 isotopologue. However, total deconvolution of all ten components in the ethane mixtures obtained by H™D exchange catalysis was beyond the experimental accuracy of the measurements. Tandem mass spectrometry/collision-induced decomposition mass spectrometry (MS/CID-MS) proved more useful for this task. In particular, it was possible to determine the proportion of symmetric versus asymmetric double H™D exchange in samples for which the total ethane-d 2 (in the case of C 2 H 6 ϩ D 2 ) or ethane-d 4 (with C 2 D 6 ϩ H 2 ) amounted to only ϳ3% on the ethane mix. A comparison with other analytical methods, NMR in particular, is provided. (J Am Soc Mass Spectrom 2004, 15, 1366 -1373

Gas chromatography (GC) analysis of 159 specimens (144 females and 15 males) of Lutzomyia youngi collected in Shannon traps in a coffee plantation in the Andean region of western Venezuela, where leishmaniasis is endemic, revealed the presence of fructose, sucrose, glucose and maltose in the gut and crop of the wild sandflies. The identification of the sugars was confirmed by comparing retention times with those observed for standard sugars and those obtained from sandflies experimentally fed on known sugar solutions. Although the sandflies in nature may ingest each of the four sugars, the results suggest that it is more probable there is an invertase enzyme (glycosidase?) in the gut or crop of the sandfly which hydrolyses ingested disaccharides (e.g. sucrose) to the constituent monosaccharides (i.e. fructose and glucose). Ecological and altitudinal distributions of sandfly species may be related to the availability of specific sugar sources, with epidemiological implications. Identification of the preferred sugar could make breeding easier and would facilitate further research on Leishmania-vector relationships.