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Rania Harrabi

Design and evaluation of polarizing agents for DNP enhanced solid-state Nuclear Magnetic Resonance

Published on 24 March 2022
Thesis presented March 24, 2022

Dynamic Nuclear Polarization (DNP) is a versatile hyperpolarization method, used to enhance the intrinsically limited sensitivity of Magic Angle Spinning (MAS) solid-state Nuclear Magnetic Resonance (ssNMR), by several orders of magnitude. Employing paramagnetic centers as Polarizing Agents (PAs), DNP relies on polarization transfer between the electrons and the nuclear spins, taking advantage of the intrinsically larger polarization of electrons. The recent growth of interest in developing the MAS-DNP method generates a strong motivation to develop robust PAs for improved sensitivity. Participating to these efforts, this thesis focuses of the development and the study of newly designed PAs of different family. The main idea is to rely on the chemical structure, relaxations and Electron Paramagnetic Resonance (EPR) properties of the radicals to develop a highly performing PAs, compared to ubiquitous standards, not to only reveal a higher DNP efficiency at frozen solutions and moderate regimes but also to be able to efficiently polarize challenging systems at challenging regimes.
Overall, we show that the proposed new PAs for MAS-DNP stands out compared to ubiquitous standards PAs, as they first yield improved DNP-NMR sensitivity, seconds their efficiency were demonstrated on challenging application systems and challenging regimes of high field and fast MAS. Their evaluation were completely assessed based on different parameters including depolarization effect, build up time constants and overall sensitivity as well as deep understanding of their properties rationalized by Molecular Dynamics (MD) and Density functional Theory (DFT) simulations along with high field electron Paramagnetic Resonance (EPR). The obtained results illustrate the contribution of this thesis on the development of PAs and consequently on the development of MAS-DNP method.

Nuclear Magnetic Resonance, Dynamic Nuclear Polarization, Polarazing agents