Proton-detected nitrogen-14 NMR by recoupling of heteronuclear dipolar interactions using symmetry-based sequences

The recoupling of heteronuclear dipolar interactions between N-14 and H-1 with symmetry-based RN sequences of the R20(5)(9) type applied to protons in samples spinning at the magic angle allows one to excite N-14 single-quantum (SQ) or double-quantum (DQ) coherences and reconvert them into observable proton coherences. This offers an alternative to the recoupling of heteronuclear dipolar interactions by rotary resonance. The experimental efficiency of the two-way coherence transfer process is on the order of 9 and 4% for SQ and DQ spectroscopy. Spectra were obtained at 400 and 800 MHz for protons. The parameters of the N-14 quadrupolar tensors can be determined in peptides, both in rotating (NH3+)-N-14-H-1 groups in protonated amines and in rigid (NH)-N-14-H-1 pairs in amide groups. (C) 2007 Elsevier B.V. All rights reserved.