Sensitivity enhancement in (HCA)CONH experiments

A novel sensitivity-enhancement technique is proposed for experiments which correlate protein backbone resonances and start with magnetization from ¹³C-¹H groups. The technique is based on replenishing magnetization lost by dipole-CSA cross-correlated relaxation of the ¹³C spin with ¹³C steady state magnetization. The principle is demonstrated for the (HCA)CONH experiment, resulting in 1.6-fold sensitivity enhancement compared to the HN(CA)CO experiment. Furthermore, other versions of the (HCA)CONH experiment were evaluated, including a novel experiment with spin-locking of transverse ¹³C-¹H two-spin coherence, and a cross-correlation compensated (CA)CONH experiment which starts from ¹³C rather than ¹H magnetization.