Maximizing nuclear hyperpolarization in pulse cooling under MAS

Snædís Björgvinsdóttir; Brennan J Walder; Nicolas Matthey; Lyndon Emsley

doi:10.1016/j.jmr.2019.01.011

Maximizing nuclear hyperpolarization in pulse cooling under MAS

J Magn Reson. 2019 Mar:300:142-148. doi: 10.1016/j.jmr.2019.01.011. Epub 2019 Jan 25.

Authors

Snædís Björgvinsdóttir¹, Brennan J Walder¹, Nicolas Matthey¹, Lyndon Emsley¹

Affiliation

¹ Institut des Sciences et Ingénierie Chimiques, Ecole Polytechnique Fédérale de Lausanne (EPFL), CH-1015 Lausanne, Switzerland.

PMID: 30772753
DOI: 10.1016/j.jmr.2019.01.011

Abstract

It has recently been shown how dynamic nuclear polarization can be used to hyperpolarize the bulk of proton-free solids. This is achieved by generating the polarization in a wetting phase, transferring it to nuclei near the surface and relaying it towards the bulk through homonuclear spin diffusion between weakly magnetic nuclei. Pulse cooling is a strategy to achieve this that uses a multiple contact cross-polarization sequence for bulk hyperpolarization. Here, we show how to maximize sensitivity using the pulse cooling method by experimentally optimizing pulse parameters and delays on a sample of powdered SnO₂. To maximize sensitivity we introduce an approach where the magic angle spinning rate is modulated during the experiment: the CP contacts are carried out at a slow spin rate to benefit from faster spin diffusion, and the spin rate is then accelerated before detection to improve line narrowing. This method can improve the sensitivity of pulse cooling for ¹¹⁹Sn spectra of SnO₂ by an additional factor of 3.5.

Keywords: Cross-polarization; Dynamic nuclear polarization; Solid-state NMR; Spin diffusion.