(Self) assembled news: recent highlights from the supramolecular chemistry literature (Quarter 2, 2023)

Allostery – the control of macromolecule conformation and function by the remote binding to an effector molecule – allows numerous biological machines to carry out their roles in the body. Writing in Chem, Cheng-Yong Su and colleagues have described a metallo-amine cage (MOC-68, Figure 1) that exhibits intricate, proton-driven allostery underpinned by water binding and release [1], with implications in controlled guest binding, transport and release. MOC-68 (Figure 1) comprises flexible, amine corners and face-capping metalloligands containing imidazole linkers; thus, numerous acid/base sites are accessible. When protonated, these sites bind water molecules which rigidify the cage; when deprotonated, water is released and the conformational flexibility of the cage increases. The initial state can only bind guests on the exterior of the cage (exo-binding); however, pH-driven allosteric switching provides a larger cavity, allowing endobinding. Interestingly, the corners of the cage can be capped with CB[10], yielding a rare ‘ring-on-cage’ system. This locks the conformation of the cage, can trigger the release of endo-bound guests, and prevents allosteric switching and endo-guest binding. Another consequence of the changes in protonation state is that the charge of the cage can be drastically altered by changing the pH. This affects the polarity of the system and means that the cage can reversibly phase transfer from polar to non-polar solvent mixtures.