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摘要
Binding behavior of 4,4'-diaminodiphenyl ether-briged-bis (6-aimino-6-deoxy-beta-cyclodextrin) 2 with four representative bile salts, i.e., cholate (CA), deoxycholate (DCA), glycocholate (GCA) and taurocholate (TCA), has been investigated at 25 degrees C in phosphate buffer (pH 7.20) by fluorescence, circular dichroism and 2D NMR spectroscopy. The result indicated that the bis(beta-cyclodextrin) 2 acts as fluorescent sensor and displays remarkable fluorescence enhancement upon addition of optically inert bile salts. Form the induced circular dichroism (ICD) and ROESY spectra, it is deduced that the phenyl moiety in the linker of bis(beta-cyclodextrin) 2 is partially self-included in the CD cavity, and is not expelled out of the CD cavity upon complexation with bile guests. Owing to the cooperative host-tether-guest binding mode in which the linker and guest are co-included in the two CD cavities, bis(beta-cyclodextrin) 2 significantly enhanced binding ability and molecular selectivity as compared with the native beta-cyclodextrin 1 through the simultaneous contributions of hydrophobic, hydrogen bond, and electrostatic interactions. The complex stability constants are discussed comparatively and globally from the viewpoints of multiple recognition between host and guest.
