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

The recoupling of heteronuclear dipolar interactions between 14N and 1H with symmetry-based RN sequences of the R 20 5 9 type applied to protons in samples spinning at the magic angle allows one to excite 14N 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 14N quadrupolar tensors can be determined in peptides, both in rotating 14 N 1 H 3 + groups in protonated amines and in rigid 14N1H pairs in amide groups.