Intermediate motions and dipolar couplings as studied by Lee–Goldburg cross-polarization NMR: Hartmann–Hahn matching profiles

Abstract

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.