C-13/N-14 heteronuclear multiple-quantum correlation with rotary resonance and REDOR dipolar recoupling

A two-dimensional C-13/N-14 heteronuclear multiple quantum correlation (HMQC) experiment using dipolar recoupling under magic-angle spinning (MAS) is described. The experiment is an extension of the recent indirect C-13 detection scheme for measuring N-14 quadrupolar coupling under MAS. The recoupling allows the direct use of the much larger dipolar interaction instead of the small J and residual dipolar couplings for establishing C-13/N-14 correlations. Two recoupling methods are incorporated into the HMQC sequence, both applying rf only to the observed C-13 spin. The first one uses the REDOR sequence with two pi-pulses per rotor cycle. The second one uses a cw rf field matching the spinning frequency, known as rotary resonance. The effects of CSA, T'(2) signal loss, MAS frequency and stability and t(1)-noise are compared and discussed. (c) 2006 Elsevier Inc. All rights reserved.