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Perugia, Italy

Marques J.M.C.,University of Coimbra | Llanio-Trujillo J.L.,University of Coimbra | Alberti M.,University of Barcelona | Aguilar A.,University of Barcelona | Pirani F.,Universitai Of Perugia
Journal of Physical Chemistry A | Year: 2013

We employ a recently developed methodology to study structural and energetic properties of the first solvation shells of the potassium ion in nonpolar environments due to aromatic rings, which is important to understand the selectivity of several biochemical phenomena. Our evolutionary algorithm is used in the global optimization study of clusters formed of K+ solvated with hexafluorobenzene (HFBz) molecules. The global intermolecular interaction for these clusters has been decomposed in HFBz-HFBz and in K +-HFBz contributions, using a potential model based on different decompositions of the molecular polarizability of hexafluorobenzene. Putative global minimum structures of microsolvation clusters up to 21 hexafluorobenzene molecules were obtained and compared with the analogous K+-benzene clusters reported in our previous work (J. Phys. Chem. A 2012, 116, 4947-4956). We have found that both K+-(Bz)n and K+-(HFBz) n clusters show a strong magic number around the closure of the first solvation shell. Nonetheless, all K+-benzene clusters have essentially the same first solvation shell geometry with four solvent molecules around the ion, whereas the corresponding one for K+-(HFBz) n is completed with nine HFBz species, and its structural motif varies as n increases. This is attributed to the ion-solvent interaction that has a larger magnitude for K+-Bz than in the case of K +-HFBz. In addition, the ability of having more HFBz than Bz molecules around K+ in the first solvation shell is intimately related to the inversion in the sign of the quadrupole moment of the two solvent species, which leads to a distinct ion-solvent geometry of approach. © 2013 American Chemical Society.

Verdicchio M.,CNRS Laboratory for Quantum Chemistry and Physics | Verdicchio M.,Universitai Of Perugia | Bendazzoli G.L.,Pam Universitai Of Bologna | Evangelisti S.,CNRS Laboratory for Quantum Chemistry and Physics | Leininger T.,CNRS Laboratory for Quantum Chemistry and Physics
Journal of Physical Chemistry A | Year: 2013

The electronic structure of the beryllium hydride anion, BeH-, was investigated at valence full-configuration-interaction (FCI) level, using large cc-pV6Z basis sets. It appears that there is a deep change of the wave function nature as a function of the internuclear distance: the ion structure goes from a weakly bonded Be···H- complex, at long distance, to a rather strongly bonded system (more than 2 eV) at short distance, having a (:Be-H)- Lewis structure. In this case, it is the beryllium atom that formally bears the negative charge, a surprising result in view of the fact that it is the hydrogen atom that has a larger electronegativity. Even more surprisingly, at very short distances the average position of the total electronic charge is close to the beryllium atom but on the opposite side with respect to the hydrogen position. © 2012 American Chemical Society.

Comez L.,Universitai Of Perugia | Comez L.,CNR Institute of Materials | Lupi L.,Universitai Of Perugia | Morresi A.,Universitai Of Perugia | And 3 more authors.
Journal of Physical Chemistry Letters | Year: 2013

Biological interfaces characterized by a complex mixture of hydrophobic, hydrophilic, or charged moieties interfere with the cooperative rearrangement of the hydrogen-bond network of water. In the present study, this solute-induced dynamical perturbation is investigated by extended frequency range depolarized light scattering experiments on an aqueous solution of a variety of systems of different nature and complexity such as small hydrophobic and hydrophilic molecules, amino acids, dipeptides, and proteins. Our results suggest that a reductionist approach is not adequate to describe the rearrangement of hydration water because a significant increase of the dynamical retardation and extension of the perturbation occurs when increasing the chemical complexity of the solute. © 2013 American Chemical Society.

Alberti M.,University of Barcelona | Pirani F.,Universitai Of Perugia | Laganai A.,Universitai Of Perugia
Journal of Physical Chemistry A | Year: 2013

The ability of a single sodium dodecyl sulfate (SDS) molecule to promote the formation of CO2 clathrate hydrates in water (as it does for methane) has been investigated at the microscopic level. For this purpose, the components of the related force field were carefully formulated and assembled following the procedure previously adopted for methane. The properties of the whole system (as well as those of its components) were analyzed by carrying out extended molecular dynamics calculations. Contrary to what happens for methane, the calculations singled out the propensity of CO2 (pure) water clusters to form clathrate hydrate-like structures and the disappearance of such propensity when a single SDS molecule is added to the clusters. This feature was found to be due to the strong interaction of carbon dioxide with the additive that makes the SDS molecule lose its shape together with its ability to drive water molecules to form a suitable cage. © 2013 American Chemical Society.

Zanatta M.,Universitai Of Perugia | Fontana A.,University of Trento | Fontana A.,CNR Institute for Chemical and Physical Processes | Orecchini A.,Universitai Of Perugia | And 6 more authors.
Journal of Physical Chemistry Letters | Year: 2013

A detailed investigation of the THz dynamics in glassy SiSe2 by means of neutron inelastic scattering is presented. To carefully map the translational dynamics and the region of the boson peak, we carried out two different experiments with sharp and broad resolutions coupled with a narrow and a wide kinematic range, respectively. Data show a complex pattern of excitations made up of three components. The most intense one is the prolongation of the longitudinal acoustic mode while two other modes appear in the boson peak region below 3 meV. We propose an interaction model that allows for a consistent identification of the nature of these modes. © 2013 American Chemical Society.

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