Fig. 5. Schematic representation of the r.f. pulse sequence for the 2Q correlation experiment. The POST-C7 (1) sequence was used to recouple the homonuclear dipolar interactions. Here, seven C_n elements were used for both excitation (2Q_exc) and reconversion (2Q_rec). High-power proton decoupling using CW (during recoupling periods) or TPPM (during evolution and acquisition times) was implemented. The phase cycle is given by: φ₁ = {90°}*4 {270°}*4, φ₂ = {0°}*8, φ₃ = {0°}*8, φ₄ = {270°}*8, φ₅ = {0°}*8, φ₆ = {0° 90° 180° 270°}*2, φ₇ = {90° 180° 270° 0°}*2, φ_rec = {0° 270° 180° 90° 180° 90° 0° 270°}. Additionally, all phases were incremented by 90° every eight scans. For TPPI, φ_3,4,5 were increased by 45° for each subsequent t₁ increment and φ₆ was adjusted as in ref. 2 to ensure rotor synchronization of the recoupling sequence during excitation and reconversion.

1. Hohwy, M., Jakobsen, H. J., Eden, M., Levitt, M. H. & Nielsen, N. C. (1998) J. Chem. Phys. 108, 2686–2694.

2. Brinkmann, A., Eden, M. & Levitt, M. H. (2000) J. Chem. Phys. 112, 8539–8554.