Molecular selective binding of aliphatic oligopeptides by bridged bis(β-cyclodextrin)s with aromatic diamine linkers

Binding behavior of two aromatic diamine-bridged bis(β-cyclodextrin)s 1–2 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, 1H and 2D NMR spectroscopy. The results obtained from ROESY spectra show that the linker groups of bis(β-cyclodextrin)s 1–2 are partly self-included in the cyclodextrin cavity, and are entirely expelled out of the cyclodextrin cavity upon complexation with guest oligopeptides. Owing to the cooperative “cyclodextrin-guest-cyclodextrin” sandwich binding mode, these bis(β-cyclodextrin)s not only afford high binding constants of up to 103–104 M−1 for guest oligopeptides, but also can recognize the size and hydrophobicity of oligopeptides. As a result of multiple recognition mechanism, bis(β-cyclodextrin) 2 gives exciting residue selectivity up to 41.7 for Gly-Gly-Gly/Glu-Glu pair and high length selectivity up to 3.9 for the Gly-Gly-Gly/Gly-Gly pair. The molecular binding ability and selectivity are discussed from the viewpoints of induced-fit and multiple recognition between host and guest.