Because the light is better here: correlation-time analysis by NMR
Relaxation data in NMR is often used for dynamics analysis, by modeling motion in the sample with a correlation function consisting of one or more decaying exponential terms, each described by an order parameter, and correlation time. This method has its origins in the Lipari-Szabo model-free approach, which originally considered overall tumbling plus one internal motion and was later expanded to several internal motions. We consider several of these cases in the solid state, and find that if the real motion is more complex than the assumed model, then model fitting is biased towards correlation times where the relaxation data is most sensitive. This leads to unexpected distortions in the resulting dynamics description. We propose using dynamics detectors, which each characterize a range of correlation times, and can be used to give an analysis of protein motion without assuming a specific model of the correlation function.
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