Maximizing Relayed ¹H Hyperpolarization Transfer by Slow-Fast MAS NMR Spectroscopy

¹H-detected dynamic nuclear polarization (DNP)-enhanced fast magic angle spinning (MAS) NMR experiments provide unprecedented sensitivity to study the structure and dynamics in advanced materials and biomolecules. However, in relayed DNP experiments, DNP enhancements decrease with faster MAS rates, which is detrimental for sensitivity. The decrease is because ¹H-¹H spin diffusion rates are significantly reduced at fast MAS frequencies. To improve sensitivity at these fast MAS rates, here, we propose to combine fast polarization build-up by relay at slow MAS rate with high-resolution ¹H NMR at fast MAS for acquisition. We perform experiments on l-histidine·HCl·H₂O with MAS rates of up to 65 kHz using a 0.7 mm DNP probe at 18.8 T and 100 K. We obtain a 35% improvement in sensitivity in experiments where the sample is polarized at 20 kHz MAS and where the signal is acquired at 60 kHz MAS.