Neutron diffraction data with hydrogen isotope substitution on aqueous solutions of NaCl and KCl at concentrations ranging from high dilution to near-saturation are analyzed using the Empirical ...Potential Structure Refinement technique. Information on both the ion hydration shells and the microscopic structure of the solvent is extracted. Apart from obvious effects due to the different radii of the three ions investigated, it is found that water molecules in the hydration shell of K+ are orientationally more disordered than those hydrating a Na+ ion and are inclined to orient their dipole moments tangentially to the hydration sphere. Cl- ions form instead hydrogen-bonded bridges with water molecules and are readily accommodated into the H-bond network of water. The results are used to show that concepts such as structure maker/breaker, largely based on thermodynamic data, are not helpful in understanding how these ions interact with water at the molecular level.
We find, by means of a deep inelastic neutron scattering experiment, a significant excess of proton mean kinetic energy E_(k) in supercooled water, compared with that measured in stable liquid and ...solid phases. The measured values of E_(k) at moderate degrees of supercooling do not fit the predicted linear increase with temperature observed for the water stable phases. This anomalous behavior is confirmed by the shape of the measured momentum distribution, thus supporting a likely occurrence of ground-state quantum delocalization of a proton between the O atoms of two neighboring molecules. These results strongly suggest a transition from a single-well to a double-well potential felt by the delocalized proton, with a reduced first neighbor O-O distance, in the supercooled state, as compared to ambient condition.
Solvation of KSCN in Water Botti, A; Pagnotta, S. E; Bruni, F ...
The journal of physical chemistry. B,
07/2009, Letnik:
113, Številka:
29
Journal Article
Recenzirano
The results of a neutron diffraction experiment performed on aqueous solutions of KSCN are analyzed and discussed in comparison with similar data for KCl and KOH solutions. The effect of the ...different ions on the structure of water and the differences and similarities among the ion solvation shells are discussed in detail. In particular it is shown that the effect of KSCN on the structure of water is visible as a shift and a broadening of the second peak of the oxygen−oxygen radial distribution function, which corresponds to a lower number of interstitial water molecules, compared to pure water. The hydration shell of the cation is similar to that found in the case of KCl solutions, and more interestingly the hydration shell of SCN− is asymmetric, with water molecules H-bonded to the N site and weakly correlated to the S site. These results provide a reasonable microscopic description of the mechanism for the high efficiency of thiocyanate in crystallizing basic proteins.
Highlights • ADC map are used to guide dose painting voxel based planning on 5 GBM recurrence. • Dose painting by numbers, by contours and commercially TPS planning are combined. • QF index assure ...the quality of TPS plans versus voxel-based prescribed dose. • γ-index analysis was successfully performed on the Tomotherapy DQA plans.
Highlights • Robustness of bladder absorbed dose relative to daily inter-fraction motion. • Systematic (SE) and random errors (RE) of bladder dose surface maps (DSM), DVH/DSH. • DSH and DVH show ...small population SE (<3.4 cm2 and <8.4 cm3 ) at the highest doses. • DSM show mean SE <1 Gy and population SE and RE (<4 and <3 Gy) at the posterior base. • Larger variations are present in the anterior and more cranial portion of bladder.
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