PRESTO polarization transfer to quadrupolar nuclei: implications for dynamic nuclear polarization

Abstract

We show both experimentally and numerically on a series of model systems that in experiments involving transfer of magnetization from ¹H to the quadrupolar nuclei under magic-angle-spinning (MAS), the PRESTO technique consistently outperforms traditionally used cross polarization (CP), affording more quantitative intensities, improved lineshapes, better overall sensitivity, and straightforward optimization. This advantage derives from the fact that PRESTO circumvents the convoluted and uncooperative spin dynamics during the CP transfer under MAS, by replacing the spin-locking of quadrupolar nuclei with a single central transition selective 90° pulse and using a symmetry-based recoupling sequence in the ¹H channel. This is of particular importance in the context of dynamic nuclear polarization (DNP) NMR of quadrupolar nuclei, where the efficient transfer of enhanced ¹H polarization is desired to obtain the highest sensitivity.