The size distribution of sulfur,
vanadium, and nickel was determined
for four crude oils and their distillation cuts using gel permeation
chromatography (GPC) coupled to inductively coupled plasma high-resolution
mass spectrometry (ICP HR MS). The results show a trimodal distribution
of vanadium and nickel compounds in the crude oils, the atmospheric
residues, and the vacuum residues and, for sulfur compounds, either
a mono- or bimodal distribution depending upon the distillation cut
considered. A correlation exists between the sulfur fraction retention
times and the temperature cuts of the distillation for a temperature
below 560 °C and also between the viscosity of the crude oils
and the proportion of trapped sulfur compounds in a higher boiling
temperature fraction. The thermic treatment applied for the distillation
increases the aggregation of low- and medium-molecular-weight compounds
of vanadium and nickel into higher molecular weight aggregates between
the crude oil on the one hand and the atmospheric residue and vacuum
residue on the other hand, especially when the crude oil has a high
total sulfur content.
A Se-targeted bottom-up proteomics approach was developed for the identification of Se-containing proteins in rice grown naturally on seleniferous soils. The proteins were separated by 2D gel electrophoresis. The position of Se-containing spots was tentatively identified by the correlation between the 1D isoelectrofocusing (IEF) and 1D SDS electropherograms of a sample aliquot and confirmed by (78)Se imaging in the 2D gel. The method was complemented by the ICP-MS assisted shotgun proteomics approach. The proteins were identified by capHPLC with the dual ICP MS and electrospray Orbitrap MS detection. The first ever comprehensive study of rice selenoproteome revealed the presence of selenium, as both selenomethionine (SeMet) and selenocysteine (SeCys) residues, in a dozen proteins including a 19 kDa globulin, granule-bound starch synthase, and the family of glutelin-type seed storage proteins.
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