NMR diffusion measurements under chemical exchange between sites involving a large chemical shift difference

Abstract : This study concerns the thallium-205 cation in aqueous solution in the presence of a calixarene molecule. While the measurement of the self-diffusion coefficient of pure thallium (without calixarene in the aqueous solution) does not pose any particular problem, major difficulties are encountered with the standard method employing gradient strength increment as soon as thallium is partly complexed by calixarene. With static magnetic field gradients, the NMR signal is so weak that it prevents any reliable measurement whereas radio-frequency (rf) field gradients lead to an unrealistic value of the diffusion coefficient. This failure is explained by the fact that thallium is in fast exchange between two sites (complexed and free thallium) thus exhibiting a single NMR signal although, in the course of the experiment, two signals, with an important difference in resonance frequencies (due to the large thallium chemical shift range), are effectively involved. With the objective to understand these quite unexpected observations, the theory underlying NMR diffusion experiments is first reviewed and criteria of fast exchange are discussed for three parameters: chemical shifts, relaxation rates, diffusion coefficients. It turns out that off-resonance effects are responsible for unwanted defocusing due to rf pulses in the static magnetic field gradient method and for time-dependent gradients in the rf field gradient method. Concerning the latter, a remedy is proposed which consists in applying the stronger gradient and incrementing the gradient pulse durations. After correction for relaxation, the expected value of the diffusion coefficient is retrieved.
Type de document :
Article dans une revue
Concepts in Magnetic Resonance Part A: Bridging Education and Research, Wiley, 2010, 36, pp.127 - 137. 〈10.1002/cmr.a.20154〉
Liste complète des métadonnées

Littérature citée [18 références]  Voir  Masquer  Télécharger

https://hal.univ-lorraine.fr/hal-01482078
Contributeur : Sebastien Leclerc <>
Soumis le : vendredi 3 mars 2017 - 11:21:55
Dernière modification le : jeudi 24 mai 2018 - 10:56:05
Document(s) archivé(s) le : mardi 6 juin 2017 - 12:10:30

Fichiers

Diff Tl.pdf
Fichiers produits par l'(les) auteur(s)

Licence


Distributed under a Creative Commons Paternité - Pas d'utilisation commerciale - Partage selon les Conditions Initiales 4.0 International License

Identifiants

Collections

Citation

Sébastien Leclerc, L Guendouz, A Retournard, D Canet. NMR diffusion measurements under chemical exchange between sites involving a large chemical shift difference. Concepts in Magnetic Resonance Part A: Bridging Education and Research, Wiley, 2010, 36, pp.127 - 137. 〈10.1002/cmr.a.20154〉. 〈hal-01482078〉

Partager

Métriques

Consultations de la notice

90

Téléchargements de fichiers

52