Exploring cucurbit[6]uril–peptide interactions in the solid state: crystal structure of cucurbit[6]uril complexes with glycyl-containing dipeptides

Abstract

Macrocyclic host cucurbit[6]uril forms supramolecular complexes with dipeptides sequenced as Gly-X (X is either an aromatic amino acid residue Phe, Tyr, and Trp or Gly) in the solid state. Despite exclusion complexation, the interaction between guest dipeptide and host cucurbit[6]uril is multipoint. The ammonium and amide nitrogen atoms of dipeptide participate in hydrogen bonding with a host carbonyl rim and water molecules or chloride anions trapped inside the macrocyclic cavity. The structural study reveals the stabilizing role of the aromatic residues in the supramolecular assembly due to their complementarity with the outer surface of cucurbit[6]uril. In the absence of an aromatic side chain, the calcium ions can stabilize and guide the supramolecular assembly between the macrocycle and Gly-Gly dipeptide.