M. F. Cobo, K. Maliňákowá, D. Reichert, K. Saalwächter,
E. R. deAzevedo.
Intermediate motions and dipolar couplings as studied by
Lee–Goldburg cross-polarization NMR: Hartmann–Hahn matching profiles.
Phys. Chem. Chem. Phys. 11, 7036-7047 (2009). DOI 10.1039/b907674c.
In this article, we evaluate the use of simple Lee–Goldburg cross-polarization
(LG-CP) NMR experiments for obtaining quantitative information of molecular
motion in the intermediate regime. In particular, we introduce the measurement
of Hartmann–Hahn matching profiles for the assessment of heteronuclear dipolar
couplings as well as dynamics as a reliable and robust alternative to the more
common analysis of build-up curves. We have carried out dynamic spin dynamics
simulations in order to test the method’s sensitivity to intermediate motion and
address its limitations concerning possible experimental imperfections. We
further demonstrate the successful use of simple theoretical concepts, most
prominently Anderson–Weiss (AW) theory, to analyze the data. We further propose
an alternative way to estimate activation energies of molecular motions, based
upon the acquisition of only two LG-CP spectra per temperature at different
temperatures. As experimental tests, molecular jumps in imidazole methyl
sulfonate, trimethylsulfoxonium iodide, and bisphenol A polycarbonate were
investigated with the new method.