Quick repetition for 1H NMR at ultrafast MAS

All the ¹H nuclei tend to show uniform T₁ relaxation time in the same molecule at moderate MAS rate (<20 kHz), because of rapid ¹H spin diffusion. However, this common belief breaks when the sample is spun at ultrafast MAS rate (>60 kHz). Each ¹H nucleus may show individual T₁ relaxation time. In such a case, the repetition time should be determined by the longest ¹H T₁ relaxation time, even if the other ¹H nuclei have much shorter ¹H T₁ relaxation time. To solve this uncomfortable and inefficient situation, we mix the magnetization during repetition delay by RFDR. The RFDR sequence brings magnetization from quickly polarized ¹Hs to slow ¹Hs and reduces the optimal repetition time, leading to sensitivity enhancement.

Reference

Y.-Q. Ye, M. Malon, C. Martineau, F. Taulelle, Y. Nishiyama, J. Magn. Reson. 239 (2014) 75-80.