Improved detection of long-range residual dipolar couplings in weakly aligned samples by Lee-Goldburg decoupling of homonuclear dipolar truncation

Homonuclear H-1 residual dipolar couplings (RDCs) truncate the evolution of transverse H-1 magnetization of weakly aligned molecules in high-resolution NMR experiments. This leads to losses in sensitivity or resolution in experiments that require extended H-1 evolution times. Lee-Goldburg decoupling schemes have been shown to remove the effects of homonuclear dipolar couplings, while preserving chemical shift evolution in a number of solid-state NMR applications. Here, it is shown that the Lee-Goldburg sequence can be effectively incorporated into INEPT- or HMQC-type transfer schemes in liquid state weak alignment experiments in order to increase the efficiency of the magnetization transfer. The method is applied to the sensitive detection of (HN)-H-1-C-13 long-range RDCs in a three-dimensional HCN experiment. As compared to a conventional HCN experiment, an average sensitivity increase by a factor of 2.4 is obtained for a sample of weakly aligned protein G. This makes it possible to detect 170 long-range (HN-13C)-H-1 RDCs for distances up to 4.9 Angstrom.