Theoretical study of the hydrated Gd3+ ion: Structure, dynamics, and charge transfer

The dynamical processes taking place in the first coordination shells of the gadolinium (III) ion are important for improving the contrast agent efficiency in magnetic-resonance imaging. An extensive study of the gadolinium (III) ion solvated by a water cluster is reported, based on molecular dynamics simulations. The AMOEBA force field [P. Y. Ren and J. W. Ponder, J. Phys. Chem. B 107, 5933 (2003)] that includes many-body polarization effects is used to describe the interactions among water molecules, and is extended here to treat the interactions between them and the gadolinium ion. In this purpose accurate ab initio calculations have been performed on Gd3+-H2O for extracting the relevant parameters. Structural data of the first two coordination shells and some dynamical properties such as the water exchange rate between the first and second coordination shells are compared to available experimental results. We also investigate the charge transfer processes between the ion and its solvent, using a fluctuating charges model fitted to reproduce electronic structure calculations on [Gd(H2O)n]3+ complexes, with n ranging from 1 to 8. Charge transfer is seen to be significant (about one electron) and correlated with the instantaneous coordination of the ion

Collision-Induced Dissociation by Helium : A Piecewise Construction of the Cross Section

International audienceMolecular dynamics calculations were performed to simulate the collisions between a helium atom and either a water dimer or various geometries of the Na(H2O)3+ cluster. The trajectory calculations were interrogated to document the partial conversion of the collision energy into internal excitation of the cluster. Owing to the small size of helium, the collision energy, which is transferred as an impulse to the cluster, is deposited initially on one of the atoms of the cluster. The amount of transferred energy in the atom that is collided depends of its mass, and more interestingly if it is involved in a H-bond like bonding with a water molecule. The general rules that have been drawn to describe the energy transfer allowed us for a picewise construction of collision-induced-dissociation cross sections, each piece being the energy tranferred toward a specific atom of the cluster. This offers a framework for extracting quantitative information on binding energies from collision-induced-dissociation experiments by helium in M(H2O)n+ systems (M is a metal atom). Importantly, the fit to the experimental data that is allowed by the present model is not restricted to the threshold energy region of the CID cross section. An application is given for the He + Au(H2O)1,2+ collision

Livres annoncés sommairement

Dognon Paul, Pélissier Léon-Gabriel, Dutil Léon, Calmette Joseph, Poupardin René, Bellanger L., Leroux Alfred, Courteault Paul, Anglade J. Livres annoncés sommairement. In: Annales du Midi : revue archéologique, historique et philologique de la France méridionale, Tome 24, N°94, 1912. pp. 305-318

Livres annoncés sommairement

Dognon Paul, Pélissier Léon-Gabriel, Dutil Léon, Calmette Joseph, Poupardin René, Bellanger L., Leroux Alfred, Courteault Paul, Anglade J. Livres annoncés sommairement. In: Annales du Midi : revue archéologique, historique et philologique de la France méridionale, Tome 24, N°94, 1912. pp. 305-318