Magic Angle Spinning - beta

The resolution and sensitivity of the solid-state NMR, unlike the solution-state NMR is influenced by several NMR parameters such as the dipolar couplings, the chemical shift anisotropy (CSA) and quadrupolar couplings etc. Since these cannot be averaged out by the restricted molecular motions in the solid-state samples the spectra will suffer from severe line broadening. To circumvent these problems, the MAS (magic-angle spinning) technique is used. The method involves spinning the sample (inside the rotor) at a high frequency at an angle of 54.7° to the static magnetic field. This causes an averaging out of the CSA and dipolar couplings. As the frequency of the spinning sample is increased, the resolution and intensity of the solid-state spectra increases.

Schematic Representation of the MAS technique. The axis of the sample is at an angle of 54.74 degrees (magic angle) wrt to magnetic field.

References:

1. "Andreas et al. discovered that spinning a sample at a substantially higher speed—that is, 100 kHz or more, as opposed to the more usual ~50 kHz—greatly reduces the problem of spectral overlap of fully protonated proteins. This allowed them to resolve the structures (including side chains) of two proteins—the model protein GB1 and a viral coat protein—in a relatively short amount of experimental time and using a very small sample"

Andreas, L.B. et al. Proc. Natl. Acad. Sci. USA 113, 9187–9192 (2016).