Protein-like proton exchange in a synthetic host cavity

The mechanism of proton exchange in ametal–ligand enzyme active site mimic (compound 1) is described through amide hydrogen–deuterium exchange kinetics. The type and ratio of cationic guest to host in solution affect the rate of isotope exchange, suggestingthat the rate of exchange is driven by a host whose cavity is occupied by water. Rate constants for acid-, base-, and watermediated proton exchange vary by orders of magnitude depending on the guest, and differ by up to 200 million-fold relative to an alanine polypeptide. These results suggest that the unusual microenvironmentof the cavity of 1 can dramatically alter the reactivity of associated water by magnitudes comparable to that of enzymes.