Ferrer, Florian, Marie Juramy, Ribal Jabbour, Samuel Cousin, Fabio Ziarelli, Giulia Mollica, Pierre Thureau, and Stéphane Viel. “Polarization Amplification in Dynamic Nuclear Polarization Magic-Angle Spinning Solid-State Nuclear Magnetic Resonance by Solubilizing Traditional Ionic Salts.” The Journal of Physical Chemistry Letters 14, no. 43 (November 2, 2023): 9619–23.
https://doi.org/10.1021/acs.jpclett.3c02455.
Dynamic nuclear polarization can improve the sensitivity of magicangle spinning solid-state NMR experiments by one to two orders of magnitude. In aqueous media, experiments are usually performed using the so-called DNP juice, a glycerol-d8/D2O/H2O mixture (60/30/10, v/v/v) that can form a homogeneous glass at cryogenic temperatures. This acts as a cryoprotectant and prevents phase separation of the paramagnetic polarizing agents (PAs) that are added to the mixture to provide the source of electron spin polarization required for DNP. Here, we show that relatively high 1H DNP enhancements (~60) can also be obtained in water without glycerol (or other glass forming agents) simply by dissolving high concentrations of electrolytes (such as NaCl or LiCl), which perturb the otherwise unavoidable ice crystallization observed upon cooling, hereby reducing PAs phase separation and restoring DNP efficiency.