The proton-driven spin diffusion (PDSD) experiment in rotating solids is one of the key techniques in solid-state nuclear magnetic resonance (NMR) spectroscopy for site-specific determination of the hierarchical structures of molecules, especially peptides and proteins. Nevertheless, the long spin diffusion mixing time, typically around seconds under fast MAS conditions, will unavoidably and dramatically increase the experimental time. In this study, we proposed a modified PDSD pulse sequence via the combined use of continuous-wave (CW) decoupling and a flip-back pulse, which can greatly increase the signal sensitivity per unit time. In addition, depending on the proton T1ρ of samples and signal sensitivity, such an experiment can even be performed without a recycle delay, denoted as PDSD-WORD (proton-driven spin diffusion without a recycle delay), leading to a dramatic reduction in the required experimental time and thus holding huge potential even for naturally abundant organic solids. We envisage that such an experiment can be well utilized for the structural elucidation of various molecular systems.
Yang et al. (Mon,) studied this question.