Molecular recognition studies on supramolecular systems. 32. Molecular recognition of dyes by organoselenium-bridged bis(beta-cyclodextrin)s.

A series of novel bis(beta-cyclodextrin)s tethered with organoselenium linkers, i.e., 6,6'-(o-phenylene-diseleno)-bridged bis(beta-cyclodextrin) (2), 6,6'-[2,2'-diselenobis(benzoyloxy)]-bridged bis(beta-cyclodextrin) (3), and 6,6'-[2,2'-diselenobis[2-(benzoylamino)ethylamino]]-bridged bis(beta-cyclodextrin) (4), were synthesized from beta-cyclodextrin (1). The inclusion complexation behavior of 1-4 with some dyes, such as 8-anilinonaphthalenesulfonate (ANS), Brilliant Green, Crystal Violet, Tropaeolin OO, Auramine O, and Methyl Orange, was investigated in aqueous phosphate buffer solution (pH 7.20) at 25 degrees C by UV-vis, fluorescence, and circular dichroism spectrometry, as well as fluorescence lifetime measurements. The complex stability constants (Ks) and Gibbs free energy changes (delta Go) for the stoichiometric 1:1 inclusion complexation of 1-4 with the dyes were obtained by the spectrophotometric or spectropolarimetric titrations. The bis(beta-cyclodextrin)s 2-4 showed much higher affinities toward these guest dyes than native beta-cyclodextrin 1 with fairly good molecular selectivities. The cooperative binding abilities of these bis(beta-cyclodextrin)s are discussed from the viewpoints of size/shape-fit interaction, induced-fit concept, and multiple recognition mechanism.