Selective binding behavior of nonaromatic oligopeptides by aromatic diamino-bridged bis(β-cyclodextrin)

Binding behavior of 4,4'-ethylenedianiline-bridged bis(6-amino-6-deoxy-beta-cyclodextrin) with seven nonaromatic oligopeptides, i.e., Leu-Gly, Gly-Leu, Glu-Glu, Met-Met, Gly-Gly, Gly-Gly-Gly, and Gly-Pro, was investigated at 25 degrees C in phosphate buffer (pH 7.20) by fluorescence and 2D NMR spectroscopy. The result obtained from the ROESY spectrum shows that the phenyl moieties in the linker of the bis(beta-cyclodextrin) 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, the bis(beta-cyclodextrin) exhibits relatively high sequence selectivity up to 5.3 for the Gly-Leu/Leu-Gly pair and length-selectivity up to 4.6 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.