High field dynamic nuclear polarization methods: Microwave sources and mechanisms

In thirty years of active development, dynamic nuclear polarization (DNP) has emerged as a forefront technique for expanding the scope of solid state nuclear magnetic resonance. For the most part, and particularly at high fields, these advances have come with continuous-wave microwave irradiation and the introduction of nitroxide-based biradicals exploiting the cross effect mechanism. In this thesis, I argue that this approach is not necessarily optimal and report progress towards arbitrary-waveform DNP, in the construction of a suitable solid-state microwave source, and the use of narrow-line monoradicals exploiting the Overhauser effect. My colleagues and I have also investigated the Overhauser mechanism through selective deuteration of radicals, leading to a relatively simple modification which yielded a significant increase in Overhauser enhancement. Finally, I detail studies of two unexplored DNP mechanisms in trityl: the three-spin solid effect and resonant mixing. With solid-state microwave sources and Overhauser radicals, DNP is now more accessible as we can achieve reasonable enhancement without the need for a gyrotron. Moreover, as amplifier and resonator technologies continue to develop, it is likely that pulsed DNP will emerge at high fields and overtake continuous-wave DNP in absolute sensitivity enhancement as well.

Name thesis:degree_name

Doctoral

Department dc:contributor.department

Massachusetts Institute of Technology. Department of Chemistry

Grantor dc:publisher

Massachusetts Institute of Technology

Year dc:date.issued

2024

Author dc:creator

• Mardini, Michael

Advisor dc:contributor.advisor

• Griffin, Robert G.

Statement dc:rights

• Attribution-NonCommercial-NoDerivatives 4.0 International (CC BY-NC-ND 4.0)
• Copyright retained by author(s)

Licence dc:rights.uri

• https://creativecommons.org/licenses/by-nc-nd/4.0/

Handle dc:identifier.uri

https://hdl.handle.net/1721.1/157830

OAI identifier oai:identifier

oai:dspace.mit.edu:1721.1/157830