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Effect of rotation in NMR diffusion experiments on micron-sized particles: A generalized theoretical treatment

Posted: 17.11.2022
A theory is developed to describe the effect of particle rotation in PFG NMR experiments. The rotation can produce 1.5-fold or even greater acceleration of apparent diffusion rates. Large macromolecular assemblies always diffuse much more slowly than their constituent monomers.

Ivan S.Podkorytov, Nikolai R.Skrynnikov

https://doi.org/10.1016/j.jmr.2022.107303

 

We have recently developed an analytical framework to interpret the results of pulsed field gradient (PFG) NMR experiments on solution samples of micron-sized amyloid fibrils [Angew. Chem. Int. Ed. 60 (2021) 15445–15451. https://doi.org/10.1002/anie.202102408]. Here we generalize this result by reporting a rigorous theoretical model of such experiments, implemented in a form of efficient computational scheme. In particular, the new treatment fully accounts for the anisotropy of fibrils’ translational diffusion and takes into consideration the finite length of the gradient pulses. The results hold not only for the historic spin-echo sequence, but also for the widely used stimulated echo experiment. We have found that fibrils’ rotation can attenuate the echo by a factor comparable with that of translation. However, contrary to some recent claims, the rotational mechanism cannot lead to an apparent fast-diffusion situation.


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