Wang, Y. and I.J. Dmochowski, Cucurbit[6]uril is an ultrasensitive (129)Xe NMR contrast agent. Chem Commun (Camb), 2015. 51(43): p. 8982-5.
http://www.ncbi.nlm.nih.gov/pubmed/25929681
A lack of molecular contrast agents has slowed the application of ultrasensitive hyperpolarized (129)Xe NMR methods. Here, we report that commercially available cucurbit[6]uril (CB[6]) undergoes rapid xenon exchange kinetics at 300 K, and is detectable by Hyper-CEST NMR at 1.8 pM in PBS and at 1 muM in human plasma where many molecules, including polyamines, can compete with xenon for CB[6] binding.