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Collective water dynamics in the first solvation shell drive the NMR relaxation of aqueous quadrupolar cations

Carof, A; Salanne, M; Charpentier, T; Rotenberg, B; (2016) Collective water dynamics in the first solvation shell drive the NMR relaxation of aqueous quadrupolar cations. Journal of Chemical Physics , 145 (12) , Article 124508. 10.1063/1.4963682. Green open access

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Abstract

Using molecular simulations, we analyze the microscopic processes driving the Nuclear Magnetic Resonance (NMR) relaxation of quadrupolar cations in water. The fluctuations of the Electric Field Gradient (EFG) experienced by alkaline and magnesium cations, which determine the NMR relaxation time, are mainly due to the dynamics of water molecules in their solvation shell. The dynamics of the ion plays a less important role, with the exception of the short-time dynamics in the lighter Li+ case, for which rattling in the solvent cage results in oscillations of the EFG autocorrelation function (ACF). Several microscopic mechanisms that may a priori contribute to the decay of the EFG-ACF occur in fact over too long time scales: entrance/exit of individual water molecules into/from the solvation shell, rotation of a molecule around the ion, or reorientation of the molecule. In contrast, the fluctuations of the ion-water distance are clearly correlated to that of the EFG. Nevertheless, it is not sufficient to consider a single molecule due to the cancellations arising from the symmetry of the solvation shell. The decay of the EFG-ACF, hence NMR relaxation, is in fact governed by the collective symmetry-breaking fluctuations of water in the first solvation shell.

Type: Article
Title: Collective water dynamics in the first solvation shell drive the NMR relaxation of aqueous quadrupolar cations
Open access status: An open access version is available from UCL Discovery
DOI: 10.1063/1.4963682
Publisher version: https://doi.org/10.1063/1.4963682
Language: English
Additional information: This is the published version of record. For information on re-use, please refer to the publisher’s terms and conditions.
UCL classification: UCL
UCL > Provost and Vice Provost Offices > UCL BEAMS
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences
URI: https://discovery.ucl.ac.uk/id/eprint/10038165
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