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

- Experimental demonstration of heteronuclear decoupling interference.
- Efficient 13C13C double quantum filtering without a proton decoupling field.
- New symmetry conditions explored experimentally for SPC-n mixing.
- Strategies for double quantum excitation at MAS rates up to 40 kHz.

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.

148