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. Author manuscript; available in PMC: 2020 Sep 1.
Published in final edited form as: J Magn Reson. 2019 Jul 11;306:180–186. doi: 10.1016/j.jmr.2019.07.025

Fig. 1. Averaging of NMR interactions and NMR approaches to measure dynamics.

Fig. 1

(Top) Schematic representation of a XAH bond undergoing fluctuations of its bond orientation and the isotropic chemical shift(s). (Center) Averaging of isotropic chemical shifts from two states, separated by 60 Hz and populated to equal amounts, as a function of the exchange rate constant is shown on the left. This averaging occurs in solids and liquids alike. The right side illustrates averaging of dipolar couplings under 40 kHz MAS and a recoupling sequence (REDOR), illustrated here for a 3-site exchange (axially symmetric) with a rigid-limit dipolar coupling of 10 kHz. The techniques that allow determining dynamics, based on fluctuations of the isotropic chemical-shift and the anisotropic (dipolar coupling) interaction are shown to the left and right, respectively. Abbreviations: CEST. Chemical-exchange saturation transfer. EXSY. Exchange spectroscopy. CODEX. Centerband-only detection of exchange. NERRD. Near-rotary resonance relaxation dispersion.