Afterglow solid-state NMR spectroscopy

Biomolecular solid-state NMR experiments have traditionally been collected through detection of ¹³C or ¹⁵N nuclei. Since these nuclei have relatively low sensitivity stemming from their smaller gyromagnetic ratios relative to ¹H, the time required to collect multi-dimensional datasets serves as a limitation to resonance assignment and structure determination. One improvement in the field has been to employ simultaneous or parallel acquisition techniques with the goal of acquiring more than one dataset at a time and therefore speeding up the overall data collection process. Central to these experiments is the cross-polarization (CP) element, which serves as a way to transfer magnetization between nuclei via magnetic dipolar couplings. In this chapter, we show how residual signal remaining after CP is a polarization source that can be used to acquire additional datasets. The setup of this class of experiments, referred to as Afterglow spectroscopy, is described and demonstrated using a membrane protein transporter involved in multidrug resistance.