Construction and Hierarchical Self-Assembly of Multifunctional Coordination Cages with Triangular Metal-Metal-Bonded Units

Herein, a series of face-capped (Tr2M3)4L4 (Tr = cyclo-heptatrienyl cationic ring; M = metal; L = organosulfur ligand) tetrahedral cages 1-3 functionalized with 12 appended crown ether moieties were designed and synthesized. The reversible binding of ammonium cations with peripheral crown ether moieties to adjust internal guest-binding was realized. Combination of a bisammonium linker and cage 3 led to the formation of a supramolecular gel SPN1 via host-guest interactions between the crown ether moieties and ammonium salts. The obtained supramolecular gel exhibited multiple-stimuli responsiveness, injectability, and excellent self-healing proper-ties and could be further developed to a SPN1-based drug delivery system. In addition, the storage modulus of SPN1 was 20 times higher than that of the model gel without Pd-Pd bonded blocks, and SPN1 had better self-healing properties compared with the latter, demonstrating the importance of such cages in improving mechanical strength without losing the dynamic properties of the material. The cytotoxicity in vitro of the drug-loaded (doxorubicin or methotrexate) SPN1 was significantly improved compared to that of free drugs.

Automated summary

A series of tetrahedral cages functionalized with crown ether moieties were designed and synthesized, which exhibited reversible binding of ammonium cations and could be further developed as a drug delivery system. The combination of a bisammonium linker and one of the cages resulted in the formation of a supramolecular gel with multiple-stimuli responsiveness and excellent self-healing properties. The drug-loaded gel showed significantly improved cytotoxicity compared to free drugs.