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

A series of novel bis(beta -cyclodextrin)s tethered with organoselenium linkers, i.e.,6,6'-(o-phenylene-dis eleno)-bridged bis(beta -cyclodextrin) (2), 6,6'-[2,2'-diselenobis(benzoyloxy)]-bridged bis(beta -cyclodextrin) (3, and 6,6'-[2,2'-diselenobis[2-(benzoylamino)ethylemino]]-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 degreesC by UV-vis, fluorescence, and circular dichroism spectrometry, as well as fluorescence lifetime measurements. The complex stability constants (Ks) and Gibbs free energy changes (DeltaG degrees) 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 P-cyclodextrin 1 with fairly good molecular selectivities. The cooperative binding abilities of these bis(beta -cyclodextrin) are discussed from the viewpoints of size/shape-fit interaction, induced-fit concept, and multiple recognition mechanism.