Computational spectroscopy of helium-solvated molecules: effective inertia, from small He clusters toward the nanodroplet regime

Accurate computer simulations of the rotational dynamics of linear molecules solvated in He clusters indicate that the large-size (nanodroplet) regime is attained quickly for light rotors (HCN) and slowly for heavy ones (OCS, N2O, and CO2), thus challenging previously reported results. Those results spurred the view that the different behavior of light rotors with respect to heavy ones-including a smaller reduction of inertia upon solvation of the former-would result from the lack of adiabatic following of the He density upon molecular rotation. We have performed computer experiments in which the rotational dynamics of OCS and HCN molecules was simulated using a fictitious inertia appropriate to the other molecule. These experiments indicate that the approach to the nanodroplet regime, as well as the reduction of the molecular inertia upon solvation, is determined by the anistropy of the potential, more than by the molecular weight. Our findings are in agreement with recent infrared and/or microwave experimental data which, however, are not yet totally conclusive by themselves.     

Hydrozirconation of stannylacetylenes. Synthesis and reactions of ketene Stannyl(Telluro) acetals

Stannylacetylenes 7a-e react with Cp(2)Zr(H)Cl in THF at room temperature to give the alpha-zirconated vinylstannane intermediates 8a-e, which subsequently react with butyltellurenyl bromide (2.0 equiv) to give exclusively ketene stannyl(telluro) acetals 6a-e of E configuration. Similar reactions were performed using phenylselenenyl bromide (2.0 equiv) as the electrophile, but a mixture of products was formed including the expected ketene stannyl(seleno) acetals 12. Otherwise, the use of 1.4 equiv of Cp(2)Zr(H)Cl and 1.0 equiv of PhSeBr results in the exclusive formation of 12, in good yields. Treatment of ketene stannyl(telluro) acetals with iodine or NBS followed by reductive dehalogenation results in the formation of 1-iodo-1-telluroalkenes 4a-e and 1-bromo-1-telluroalkenes 5a-e, respectively, with total retention of the configuration.     

Collective Effects in Ionic Liquid [emim][Tf2N] and Ionic Paramagnetic Nitrate Solutions without Long-Range Structuring

Mesoscopic shear elasticity has been revealed in ordinary liquids both experimentally by reinforcing the liquid/surface interfacial energy and theoretically by nonextensive models. The elastic effects are here examined in the frame of small molecules with strong electrostatic interactions such as room temperature ionic liquids [emim][Tf2N] and nitrate solutions exhibiting paramagnetic properties. We first show that these charged fluids also exhibit a nonzero low-frequency shear elasticity at the submillimeter scale, highlighting their resistance to shear stress. A neutron scattering study completes the dynamic mechanical analysis of the paramagnetic nitrate solution, evidencing that the magnetic properties do not induce the formation of a structure in the solution. We conclude that the elastic correlations contained in liquids usually considered as viscous away from any phase transition contribute in an effective way to collective effects under external stress whether mechanical or magnetic fields.     

Buchbesprechungen

Ohne Zusammenfassung     

Trace elements in sediments and bioaccumulation in European silver eels (Anguilla anguilla L.) from a Mediterranean lagoon (SE Italy)

Samples of surface sediments and tissues (liver and muscle) of commercially available European silver eels (Anguilla anguilla L.) collected from Varano lagoon (Italy) were analysed to determine trace element contents. Univariate and multivariate analyses were performed to highlight both the differences between sampling sites and the influence of channel discharges. Atomic ratios indices for sediment data and biological enrichment factors (BEF) for eel tissues were calculated in order to evaluate the enrichment factor due to human activities. The highest levels of As (11.9?µg?g^?1) and Zn (14.1?µg?g^?1) were observed in the south-eastern zone of the lagoon, which is influenced by urban and agricultural discharges. The low levels of Hg observed in this study (0.04?µg?g^?1) led us to exclude both natural and human local sources of this element. Trace element concentrations of all elements were lower in muscle than in liver tissue. Significant enrichment of Cu and Zn was found in livers.