Self-Assembling Molecular Capsules Based on α,γ-Cyclic Peptides.

A new capsule based on a β-sheet self-assembling cyclic peptide with the ability to recognize and release several guests is described. The host structure is composed of two self-complementary α,γ-cyclic peptides bearing a Zn porphyrin cap that is used for the selective recognition of the guest. The two components are linked through two dynamic covalent bonds. The combination of binding forces, including hydrogen bonding, metal coordination, and dynamic hydrazone bonds, allows the reversible recognition of long bipyridine guests. The affinity for these ligands showed a strong dependence on the guest length. Delivery of the encapsulated ligand can be achieved by hydrolysis of hydrazones to disrupt the sandwich complex structure.