Boosting high-resolution NMR and MRI of high- and low-gamma nuclei in porous media with dynamic nuclear polarization and innovative methods: from MOFs to biological membranes

Equipment, 2019-2

Team: Laboratory of Biomolecules, Structure et dynamique des biomolécules

Project leader: Daniel Abergel


Nuclear magnetic resonance (NMR) spectroscopy provides a unique ensemble of techniques to investigate the structure and dynamics of chemical and biological systems, either in liquids or in the solid state. We propose to optimally exploit the benefits of modern NMR approaches: dynamic nuclear polarization (DNP) coupled to magic angle spinning, parallel acquisition, fast magic-angle spinning, and dissolution DNP coupled to magnetic resonance imaging to investigate the structural and dynamic features of a broad range of porous media, from metal-organic frameworks (MOFs) to trans-membrane channels.

The relatively recent implementation of dynamic nuclear polarization (DNP) techniques in high-field NMR reveals extremely promising. DNP uses low-concentration paramagnetic impurities, introduced in the sample as highly polarized stable radicals. Microwave irradiation leads to a transfer of polarization from the electron spins of the radicals to the nuclear spins to achieve unprecedented enhancements of nuclear polarization and NMR signal. DNP combined with « magic-angle spinning » (MAS-DNP) in solid-state NMR represents a major a methodological breakthrough where sensitivity gains as high as ~200 have been obtained. Lower enhancements are generally observed at higher magnetic fields but ~40–fold enhancement leads to a reduction of the experimental time by a factor 1600, making accessible in one day what would in theory take four years. Nevertheless, MAS-DNP is particularly attractive at 800 MHz, rather than at lower fields, in the investigation of low- quadrupolar nuclei by significantly reducing the effects of second order quadrupolar interactions.

Recent improvements of NMR spectrometer electronics permit to take full advantage of the instrumentation in use in the lab. Thus, increased sensitivity at low receiver gains through an enhanced dynamic range, permit faster, therefore more accurate, phase and RF pulse profile controls, and facilitate multiple detection NMR experiments.

This project includes the studies of microporous solids (MOFs, zeolites, etc) whose exceptional properties are often related to phenomena that occur at the surface or in the pores of these solids. Thus the determination of structural parameters and surface properties of MOF will be undertaken through high-field MAS-DNP. Other applications, such as the use of hyperpolarized 129Xe, or the study of complex biomaterials, as well as ion transport (K+, Li+) trhough transmembrane channels will benefit from higher dynamics and better electronics.