Supramolecular chemistry of cyclodextrin-peptide hybrids: Azobenzene-tagged peptides

AC17, which is composed of 17 amino acids and has an azobenzene moiety but has no cyclodextrin (CD) unit in the side chain, exhibits 54% helix content. However, ACα17, which has both trans-azobenzene and α-CD, shows 82% helix content. This result suggests that the helix structure is stabilized by host (CD)-guest (azobenzene) bridge in the side chain of the peptide. The helix content changed by trans-cis photoisomerization as shown by 64% helix content for ACα17 in its cis form. This result suggests that cis-azobenzene unit is excluded from the α-CD cavity, thus resulting in the smaller helix content. The helix contents for ACβ17, which has both azobenzene and β-CD, are 94% in the cis form and 87% in the trans form, suggesting that the cis form is included in the β-CD cavity. Azobenzene-tagged CD-peptide hybrids with histidine unit were also prepared and photoregulation of catalytic activity in ester hydrolysis was examined.