Molecular recognition of aliphatic oligopeptides by aromatic diamine-bridged bis(β-cyclodextrin)

Binding behavior of 4,4′-diaminodiphenyl ether-bridged-bis (6-amino-6-deoxy-β-cyclodextrin) 1 with the aliphatic oligopeptides, i.e., Leu-Gly, Gly-Leu, Glu-Glu, Met-Met, Gly-Gly, Gly-Gly-Gly, and Gly-Pro was investigated at 25°C in phosphate buffer (pH 7.20) by fluorescence and 2-D NMR spectroscopy. Owing to the cooperative “cyclodextrin-guest-cyclodextrin” sandwich binding mode, bis(β-cyclodextrin) 1 not only afford high binding constants of up to 103–104 M−1 for guest oligopeptides, but can also recognize the size and hydrophobicity of oligopeptides. As a result of multiple recognition mechanisms, bis(β-cyclodextrin) 1 gives high length-selectivity up to 5.8 for the Gly-Gly-Gly/Gly-Gly pair and sequence-selectivity up to 2.8 for the Gly-Leu/Leu-Gly pair, respectively. The molecular binding ability and selectivity are discussed from the viewpoints of induced-fit and multiple recognition between host and guest.