Synthesis of very large cavitand-based bimolecular capsules

Abstract

Very large, ‘three-storey’ tetra(amido)cavitands and their dimeric capsules were designed and synthesized by the combination of a highly efficient, five-step covalent synthetic procedure with noncovalent, spontaneous self-assembly. Semi-empirical calculations suggest that the two halves of these capsular assemblies are held together by four intermolecular hydrogen bonds between the neighboring N–H⋯OC groups installed on the upper rim of each cavitand ‘hemisphere’. Using the modified Stokes-Einstein equation, the hydrodynamic radius of capsule 6₂ was found to be 14.8 Å³, which is in relatively good agreement with the theoretical approximation (13.0 Å³). The semi-empirical calculations also revealed that these bimolecular capsules have an intercavity volume of about 1940 Å³. However, the presence of enlarged lateral portals may pose some limitations on their use as host molecules.