X-ray Raman scattering study of aligned polyfluorene

We present a non-resonant inelastic x-ray scattering study at the carbon K-edge on aligned poly[9,9-bis(2-ethylhexyl)-fluorene-2,7-diyl] and show that the x-ray Raman scattering technique can be used as a practical alternative to x-ray absorption measurements. We demonstrate that this novel method can be applied to studies on aligned $\pi$-conjugated polymers complementing diffraction and optical studies. Combining the experimental data and a very recently proposed theoretical scheme we demonstrate a unique property of x-ray Raman scattering by performing the symmetry decomposition on the density of unoccupied electronic states into $s$- and $p$-type symmetry contributions.Comment: 19 pages, 8 figure

Guidelines for diagnosis and management of the cobalamin-related remethylation disorders cblC, cblD, cblE, cblF, cblG, cblJ and MTHFR deficiency

BACKGROUND: Remethylation defects are rare inherited disorders in which impaired remethylation of homocysteine to methionine leads to accumulation of homocysteine and perturbation of numerous methylation reactions. OBJECTIVE: To summarise clinical and biochemical characteristics of these severe disorders and to provide guidelines on diagnosis and management. DATA SOURCES: Review, evaluation and discussion of the medical literature (Medline, Cochrane databases) by a panel of experts on these rare diseases following the GRADE approach. KEY RECOMMENDATIONS: We strongly recommend measuring plasma total homocysteine in any patient presenting with the combination of neurological and/or visual and/or haematological symptoms, subacute spinal cord degeneration, atypical haemolytic uraemic syndrome or unexplained vascular thrombosis. We strongly recommend to initiate treatment with parenteral hydroxocobalamin without delay in any suspected remethylation disorder; it significantly improves survival and incidence of severe complications. We strongly recommend betaine treatment in individuals with MTHFR deficiency; it improves the outcome and prevents disease when given early

The structure of a super-saturated solution : a neutron scattering study of aqueous urea

In this study a combination of neutron diffraction measurements and empirical potential structure refinement (EPSR) was used to investigate the time-averaged structure of a 0.30 mol fraction solution of urea in water at both 25 and 35 °C. These two temperatures were chosen in order to compare the structure of an undersaturated solution at 35 °C with that of a supersaturated solution at 25 °C. The results indicate that in moving into the supersaturated state the solutions show a significant and unexpected change in the self-aggregation of urea molecules. Urea-urea interactions present in the undersaturated solution become suppressed in the supersaturated region, in favor of interactions between urea and water so that overall the urea becomes more hydrated. Such a change may be viewed as a response of the system to the imposed supersaturation and a factor playing an important role in the observed metastability of the solutions

EXAFS and x-ray structural studies of (Tb2O3)0.26(P2O5)0.74 Metaphosphate Glass

Although the metaphosphate glasses R(PO3)3 containing high concentrations of rare-earth R3+ ions have potentially important applications in optical communications and laser technologies, there is little previous information about their structures. To establish the essential features of the structure of such a glass, the complementary techniques of x-ray diffraction and extended x-ray-absorption fine structure (EXAFS) have been used upon the terbium metaphosphate glass, having a composition found by electron probe microanalysis to be (Tb2O3)0.26(P2O5)0.74. The combination of the two techniques allows for a more comprehensive interpretation of the structural data, since each method suffers from differing analytical problems, notably the composite radial distribution function obtained from diffraction, and the present lack of a good calibrant for the EXAFS experiment. The diffraction results prove to be consistent with a network model dominated by a phosphate glass skeleton constructed from PO4 tetrahedra bonded to adjacent tetrahedra via bridging oxygen atoms. This previously unestablished structural model has been used formerly to interpret a wide range of thermal, ultrasonic, and optical properties. The EXAFS, being an atom-type specific probe, have provided the more direct information on the local structure at the rare-earth ion site in vitreous (Tb2O3)0.26(P2O5)0.74: notably a strong correlation in 2.25 Å, associated with an average coordination number of 7±1 for oxygen atoms surrounding a Tb3+ ion

Anion bridges drive salting out of a simple amphiphile from aqueous solution

Neutron diffraction with isotope substitution has been used to determine the structural changes that occur on the addition of a simple salting-out agent to a dilute aqueous alcohol solution. The striking results obtained demonstrate a relatively simple process occurs in which interamphiphile anionic salt bridges are formed between the polar groups of the alcohol molecules. These ion bridges drive an increase in the exposure of the alcohol molecule nonpolar surface to the solvent water and hence point the way to their eventual salting out by the hydrophobic effect