A fluorescent calixarene-based dimeric capsule constructed via a MII–terpyridine interaction: cage structure, inclusion properties and drug release

Abstract

Two analogues of capsule-like fluorescent cages have been constructed by dimerization of terpyridine-containing calixarene derivatives utilizing a M^II–terpyridine (M = Zn and Cd) interaction. ¹H NMR spectral studies show that the self-assembled molecular capsules Zn₄L1₂ and Cd₄L1₂ have a highly symmetrical D_4h-structure. The encapsulation of the anticancer drug mercaptopurine in their cavities has been documented by NMR, ESI-TOF-MS, fluorescence switching, and molecular simulation, indicating that strong S–π and π–π interactions between drug and cage are of importance for the host–guest binding. The nanoscale cages exhibit excellent behaviors to control the release of mercaptopurine in phosphate buffered saline solution (pH = 7.4). These results further highlight the potential of self-assembled Zn₄L1₂ cages for drug-carrier applications.