All pure shift spectra shown in the main manuscript and Supporting Information were acquired with the following parameters unless otherwise stated. Sixteen increments of 1024 complex data points each were acquired with a spectral width of 10 kHz (20 ppm) and a recovery delay of 3 s, and the first 200 complex data points of each free induction decay were taken to construct the pure shift interferogram. The PSYCHE ASR element was used, with two saltire pulses of 30 ms duration, 20° flip angle 10 kHz bandwidth, and a simultaneous PFG of 1.5 G cm -1 nominal amplitude. Interferogram construction used the 'pshift' macro ().