Spectrophotometric study of the selective binding behavior of aliphatic oligopeptides by bridged bis(β-cyclodextrin) linked by a 4,4′-diaminodiphenyl disulfide tether

The conformation and binding behavior of 4,4′-diaminodiphenyl disulfide bridged bis(β-cyclodextrin) (1) towards representative aliphatic oligopeptides, i.e., Leu-Gly, Gly-Leu, Glu-Glu, Met-Met, Gly-Gly, Gly-Gly-Gly, and Gly-Pro, were investigated by circular dichroism, fluorescence, and 1H and 2D NMR spectroscopy at 25 °C in phosphate buffer (pH 7.20). The results indicated that 1 acts as an efficient fluorescent sensor and displays remarkable fluorescence enhancement upon addition of optically inert oligopeptides. Owing to the cooperative host–linker–guest binding mode in which the linker and guest are coincluded in the two cyclodextrin cavities, the bis(β-cyclodextrin) 1 gives high binding constants of up to 103–104 (mol/L)–1 for oligopeptides. The bis(β-cyclodextrin) 1 can recognize not only the size and shape of oligopeptides but also the hydrophobicity, giving an exciting residue selectivity of up to 61.3 for the Gly-Leu/Glu-Glu pair. These phenomena are discussed from the viewpoints of multiple recognition and induce-fit interactions between host and guest.