Efficient dipolar double quantum filtering under magic angle spinning without a ¹H decoupling field

We present a systematic study of dipolar double quantum (DQ) filtering in ¹³C-labeled organic solids over a range of magic-angle spinning rates, using the SPC-n recoupling sequence element with a range of n symmetry values from 3 to 11. We find that efficient recoupling can be achieved for values n ≥ 7, provided that the ¹³C nutation frequency is on the order of 100 kHz or greater. The decoupling-field dependence was investigated and explicit heteronuclear decoupling interference conditions identified. The major determinant of DQ filtering efficiency is the decoupling interference between ¹³C and ¹H fields. For ¹³C nutation frequencies greater than 75 kHz, optimal performance is observed without an applied ¹H field. At spinning rates exceeding 20 kHz, symmetry conditions as low as n = 3 were found to perform adequately.