Selective confinement of potassium, rubidium, or caesium ions in a non-covalent hydroxyproline octamer cage stabilized by cis -hydroxyl locks.

While numerous studies have focused on the impact of chirality on some magic amino acid clusters, this article investigates the effects of steric isomerization using 4-hydroxyproline octamers as a model system. Through mass spectrometry, infrared photodissociation spectroscopy, and theoretical calculation, it was demonstrated that the -4-hydroxy-L-proline octamer can selectively cage potassium, rubidium, or caesium ions through stable -hydroxyl locks, while the -form cannot. The results highlight the importance of hydroxyl group orientation in designing biocompatible membrane transporters with high ion-selectivity.