Application of dynamic nuclear polarization techniques of nuclear magnetic resonance for the study of porous media (Compressed air system, NMR probe inserts and radiofrequency filters)

Equipment, AAP 2018

Compressed air system, NMR probe inserts and radiofrequency filters

Team : Laboratory of Biomolecules, Structure and dynamics of biomolecules Team

Project leader : Daniel Abergel

Abstract :

Nuclear magnetic resonance (NMR) spectroscopy provides a unique ensemble of techniques that enable one to investigate the molecular structure, conformation and dynamics, in liquids or in the solid state.

One of the major limitations of NMR is its low sensitivity, which has motivated the development of magnets with higher magnetic fields, and of probes with higher sensitivities. However, sensitivity remains an issue, especially when observing low-g nuclei. In this context, dynamic nuclear polarization (DNP) techniques reveal extremely promising to increase signal in high-field NMR. By making use of the much more highly polarized electron spins of stable radicals, this leads, through complex mechanisms involving microwave irradiation of the electron spin transition, to unprecedented enhancements of the nuclear polarization, therefore of the magnetization and NMR signal.

Application of DNP to solid-state NMR, when combined with the so-called « magic-angle spinning » (MAS), or to liquid-state experiments, appears as a methodological breakthrough. In MAS-DNP experiments, sensitivity gains as high as 200 have been published in the literature. But even in less favorable cases, a sensitivity enhancement of ~40 leads to an experimental time divided by 402. In other words, an experiment performed in 5 hours using DNP would require one year of conventional experimental time.

In this project, MAS-DNP experiments will be performed, in association with the development of new pulse sequences, on various materials, including MOFs. This will give the possibility to access specific spectroscopic and structural information from within pores.

Experiments require an efficient compressed air system, for the operation of the gyrotron (the waveguide of which is connected to the compressed air system), but also as a prerequisite for the conventional use of the spectrometer and the development of new pulse sequences, as well as for a reliable estimate of the improvement provided by the DNP, by comparison with experiments carried out under usual conditions.


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