On the microscopic fluctuations driving the NMR relaxation of quadrupolar ions in water - CEA - Commissariat à l’énergie atomique et aux énergies alternatives Accéder directement au contenu
Article Dans Une Revue Journal of Chemical Physics Année : 2015

On the microscopic fluctuations driving the NMR relaxation of quadrupolar ions in water

Résumé

Nuclear Magnetic Resonance (NMR) relaxation is sensitive to the local structure and dynamics around the probed nuclei. The Electric Field Gradient (EFG) is the key microscopic quantity to understand the NMR relaxation of quadrupolar ions, such as 7 Li + , 23 Na + , 25 Mg 2+ , 35 Cl − , 39 K + , or 133 Cs +. Using molecular dynamics simulations, we investigate the statistical and dynamical properties of the EFG experienced by alkaline, alkaline Earth, and chloride ions at infinite dilution in water. Specifically, we analyze the effect of the ionic charge and size on the distribution of the EFG tensor and on the multi-step decay of its auto-correlation function. The main contribution to the NMR relaxation time arises from the slowest mode, with a characteristic time on the picosecond time scale. The first solvation shell of the ion plays a dominant role in the fluctuations of the EFG, all the more that the ion radius is small and its charge is large. We propose an analysis based on a simplified charge distribution around the ion, which demonstrates that the auto-correlation of the EFG, hence the NMR relaxation time, reflects primarily the collective translational motion of water molecules in the first solvation shell of the cations. Our findings provide a microscopic route to the quantitative interpretation of NMR relaxation measurements and open the way to the design of improved analytical theories for NMR relaxation for small ionic solutes, which should focus on water density fluctuations around the ion.

Domaines

Matériaux
Fichier principal
Vignette du fichier
JChemPhys143_194504.pdf (2.88 Mo) Télécharger le fichier
Origine : Fichiers éditeurs autorisés sur une archive ouverte
Loading...

Dates et versions

cea-01230107 , version 1 (17-11-2015)

Identifiants

Citer

Antoine Carof, Mathieu Salanne, Thibault Charpentier, Benjamin Rotenberg. On the microscopic fluctuations driving the NMR relaxation of quadrupolar ions in water. Journal of Chemical Physics, 2015, 143, pp.194504. ⟨10.1063/1.4935496⟩. ⟨cea-01230107⟩
120 Consultations
248 Téléchargements

Altmetric

Partager

Gmail Facebook X LinkedIn More