CryoMAS4DNP

Up to now, the main strategy to circumvent the sensitivity problem in NMR (Nuclear Magnetic Resonance) has consisted in progressively going to higher magnetic fields (up to 23 Tesla nowadays). Nevertheless, this is not a sufficient solution for a large number of studies including large bio-molecules, and systems of interest for nanosciences, catalysis, etc. Complementary approaches based on nuclear hyper-polarization techniques which are able to provide orders of magnitude sensitivity increase (2 to 5) are thus required to broaden the scope of magnetic resonance studies. Concerning solid-state NMR, microwave-induced DNP (Dynamic Nuclear Polarization) performed with high power microwave sources (gyrotrons) and combined with low temperature has recently emerged as an appropriate answer to the sensitivity limitation even at high magnetic fields. Prof. Griffin’s group at MIT was the first to successfully implement DNP at 5 Tesla in the 1990’s and has spearheaded its extension to 10 Tesla and above over the last fifteen years. This work, along with the introduction by Bruker Biospin of a commercial DNP system at 10 Tesla operating down to liquid nitrogen temperature (~105 K), has triggered a strong interest in the NMR community. The primary goal of the project is to go beyond the current state of the art by developing a pioneering experiment able to perform high resolution (magic angle spinning) solid-state Dynamic Nuclear Polarization at cryogenic temperatures (10 – 100 K) and high magnetic field (10 Tesla). This has never been done before and should enable orders of magnitude of additional sensitivity gain and corresponding time savings. The relevance of this approach will be tested on several systems of significant interest for the fields of nano-electronics, catalysis, and structural biology (i.e. functionalized nano-particles, porous materials, bio-molecular systems). The project will require the development of highly challenging pieces of instrumentation (i.e. a cryogenic power supply and a Cryo-MAS DNP probe) and of an adequate methodology (pulse sequences, data interpretation, polarizing agents, DNP sample preparation, etc.). As a consequence, the project notably involves recording high-field EPR spectra of polarizing agents and analyzing in great detail their relaxation mechanisms using the same magnetic fields as the DNP experiment: i.e. ~10 Tesla. A Combination of EPR and DNP measurements at high magnetic field (10 Tesla) is essential to improve our understanding of existing DNP mechanisms and possibly to unravel new interesting phenomena leading to other polarizing agents in the 10-100 K temperature range. Overall, we aim to demonstrate that with several orders of magnitude of additional sensitivity gain, solid-state Magic Angle Spinning Dynamic Nuclear Polarization performed at very low temperature (10-100 K) has the potential to address significant problems for systems where other atomic resolution spectroscopies cannot be applied. Moreover the ability to extend the MAS-DNP experiment to lower temperatures (10-100 K range) will be essential for the further success of this new technology (notably at magnetic fields higher than 10 Tesla), and to truly push the limits of sensitivity in MAS solid-state NMR measurements.