Fluoride up- and down-regulates guest encapsulation for ZnII6L4 and ZnII4L4 cages

The development of artificial molecular systems capable of allosteric regulation has the potential to unlock new functions related to the purification, sensing, and transformation of bound guests. Here, we employ the binding of fluoride to boron centers within the walls of metal-organic cages to modulate cage conformations and allosterically tune their host-guest binding. Tetrahedral ZnII4L4 and octahedral ZnII6L4 cages that contain the same boron-centered moiety responded differently to fluoride binding, inhibiting or enhancing the binding of a second guest, respectively. Upon binding the allosteric effector F−, the apertures of the octahedral cage expanded, facilitating guest binding. The apertures of the tetrahedral cage also expanded following F− addition, but this expansion led to a decrease in internal cavity volume, thus leading to an expulsion of guest molecules. Synergetic allosteric regulation between the tetrahedral and octahedral cages was also possible, whereby a guest transferred between the two cages upon binding of fluoride to both.