Association of α-helix peptides that have γ-cyclodextrin and pyrene units in their side chain, and induction of dissociation of the association dimer by external stimulant molecules

alpha-Helix peptides bearing one unit of gamma-cyclodextrin (gamma-CD) and one or two units of pyrene in their side chain have been designed and synthesized as a novel system of peptide dimerization. The dimer was formed based on inclusion of two pyrene units in the gamma-cyclodextrin cavity, and the dissociation of the peptide dimer was induced by external stimulant molecules (guests). Circular dichroism studies showed that the cyclodextrin-peptide hybrids (CD-peptides) maintain relatively rich alpha-helix content (61 to 81%), which was not affected by the guest inclusion into the cyclodextrin cavity. Fluorescence studies revealed that these CD-peptides form stable association dimers, which exhibit excimer emission. The intensity of the pyrene excimer emission decreased upon addition of the guest molecules, indicating dissociation of the CD-peptide dimers to the monomer CD-peptides. These CD-peptide hybrids bind structurally similar steroidal compounds with remarkable discrimination. These results demonstrate that this molecule-assembly system, based on host-guest chemistry, could be applicable to the development of molecule-responsive materials or a molecule-sensing system.