1H13C cross-polarization using a modified magic echo sequence for 1H spin locking

A modified magic echo (MME) sequence is reported which can be used for 1H spin locking in the 1H13C cross-polarization (CP) experiment. The amplitude of the effective spin-locking field has been evaluated indirectly by measuring the 13C radio-frequency nutation fields corresponding to the Hartmann-Hahn condition and found to be made as weak as 0.01 G under certain conditions. Since the MME sequence can achieve quenching of the 1H1H dipolar interaction and, simultaneously, modulation of the 1H13C dipolar interaction by the virtually inserted 180° pulses, the dynamics of MME CP become analogous to that of usual CP under high-speed magic angle sample spinning.