Supramolecular assemblies of cucurbit[ n ]urils and 4-aminopyridine controlled by cucurbit[ n ]uril size ( n=5, 6, 7 and 8)

The binding interactions between 4-aminopyridine (4-AP) and a series of cucurbit[ n ]urils (Q[5], Q[6], TMeQ[6], Q[7], Q[8]) have been studied using 1 H NMR spectroscopy, UV-vis absorption spectroscopy, isothermal titration calorimetry (ITC) and X-ray crystallography. The data indicates that the Q[5]@4-AP complex exhibits exo binding, which is not observed in the other four host-guest complexes. Furthermore, X-ray crystallography clearly reveals how the Q[ n ]s bind with 4-AP to form complexes, for example Q[5] forms an outer-surface complex, whilst Q[6], TMeQ[6] and Q[7] formed 1:1 host and guest type complexes, and Q[8] formed a stable 1:2 ternary complex due to its large cavity, which can accommodate two 4-AP molecules. (c) 2023 Published by Elsevier B.V. on behalf of Chinese Chemical Society and Institute of Materia Medica, Chinese Academy of Medical Sciences.