Spectrophotometric Study Of The Selective Binding Behavior Of Aliphatic Oligopeptides By Bridged Bis(Beta-Cyclodextrin) Linked By A 4,4 '-Diaminodiphenyl Disulfide Tether

The conformation and binding behavior of 4,4'-diaminodiphenyl disulfide bridged bis(beta-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 H-1 and 2D NMR spectroscopy at 25 degrees 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(beta-cyclodextrin) 1 gives high binding constants of up to 10(3)-10(4) (mol/L)(-1) for oligopeptides. The bis(beta-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.