Measurement of proton chemical shift anisotropy in solid-state NMR spectroscopy.

Proton chemical shift anisotropy (CSA) is significantly important as it provides the information of the dynamics and local environmental structure of the proton. The measurement of proton CSA keeps drawing the attention of NMR researchers, and great efforts have been expended. In the early years, measuring proton CSA in solid-state NMR, especially with the strong 1 H-1 H dipolar network, was hampered by ineffective decoupling or selectively recoupling techniques, and the applications were only limited to those with sparse proton sites or single crystals. Till the latest decades, the dramatic progress on NMR methodology and magic-angle spinning (MAS) technology enable accurate detection of proton CSA in complicated powder samples even proteins. In this review, following a brief description of the measurement of proton CSA in solution and LCs NMR, a retrospect of the experimental development of proton CSA measurement in solid state NMR is presented, from the continuous wave (CW) and multiple pulse sequences for static solid samples, to combined rotation and multiple pulse spectroscopy (CRAMPS), then to the latest methods including rotary resonance, CSA amplification and R-symmetry pulse sequences under MAS conditions.