154 research outputs found
Stability and Electronic Properties of TiO2 Nanostructures With and Without B and N Doping
We address one of the main challenges to TiO2-photocatalysis, namely band gap
narrowing, by combining nanostructural changes with doping. With this aim we
compare TiO2's electronic properties for small 0D clusters, 1D nanorods and
nanotubes, 2D layers, and 3D surface and bulk phases using different
approximations within density functional theory and GW calculations. In
particular, we propose very small (R < 0.5 nm) but surprisingly stable
nanotubes with promising properties. The nanotubes are initially formed from
TiO2 layers with the PtO2 structure, with the smallest (2,2) nanotube relaxing
to a rutile nanorod structure. We find that quantum confinement effects - as
expected - generally lead to a widening of the energy gap. However,
substitutional doping with boron or nitrogen is found to give rise to
(meta-)stable structures and the introduction of dopant and mid-gap states
which effectively reduce the band gap. Boron is seen to always give rise to
n-type doping while depending on the local bonding geometry, nitrogen may give
rise to n-type or p-type doping. For under coordinated TiO2 surface structures
found in clusters, nanorods, nanotubes, layers and surfaces nitrogen gives rise
to acceptor states while for larger clusters and bulk structures donor states
are introduced
Trends in Metal Oxide Stability for Nanorods, Nanotubes, and Surfaces
The formation energies of nanostructures play an important role in
determining their properties, including the catalytic activity. For the case of
15 different rutile and 8 different perovskite metal oxides, we find that the
density functional theory (DFT) calculated formation energies of (2,2)
nanorods, (3,3) nanotubes, and the (110) and (100) surfaces may be described
semi-quantitatively by the fraction of metal--oxygen bonds broken and the
bonding band centers in the bulk metal oxide
Elucidation of Phosphatidylcholine Composition in Krill Oil Extracted from Euphausia superba
High performance liquid chromatography-electrospray tandem mass spectrometry was used to elucidate the phospholipids in krill oil extracted from Euphausia superba, an emerging source for human nutritional supplements. The study was carried out in order to map the species of the choline-containing phospholipid classes: phosphatidylcholine and lyso-phosphatidylcholine. In addition, the prevalent phosphatidylcholine class was quantified and the results compared with prior analysis. The qualification was performed with separation on a reverse phase chromatography column, while the quantification was obtained with class separation on a normal phase chromatography column. An Orbitrap system was used for the detection, and pulsed-Q dissociation fragmentation was utilized for the identification of the species. An asymmetrical exclusion list was applied for detection of phospholipid species of lower concentration, significantly improving the number of species observed. A total of 69 choline-containing phospholipids were detected, whereof 60 phosphatidylcholine substances, among others seven with probable omega-3 fatty acids in both sn-1 and sn-2. The phosphatidylcholine concentration was estimated to be 34 ± 5 g/100 g oil (n = 5). These results confirm the complexity of the phospholipid composition of krill oil, and the presence of long chained, heavily unsaturated fatty acids
Association of Lipidome Remodeling in the Adipocyte Membrane with Acquired Obesity in Humans
The authors describe a new approach to studying cellular lipid profiles and
propose a compensatory mechanism that may help maintain the normal membrane
function of adipocytes in the context of obesity
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