Molecular recognition studies on supramolecular systems. 25. Inclusion complexation by organoselenium-bridged bis(β-cyclodextrin)s and their platinum(IV) complexes

A series of novel bis(β-cyclodextrin)s connected by organoselenium linkers, i.e., 6,6'-trimethylene-diseleno-bridged bis(β-cyclodextrin) (2), 2,2'-trimethylenediseleno-bridged bis(β-cyclodextrin) (3), 6,6'-o- phenylenediseleno-bridged bis(β-cyclodextrin) (4), and the corresponding platinum(IV) complexes (5-7) were synthesized from β-cyclodextrin (1). The inclusion complexation behavior of 1-7 with some fluorescent dyes, i.e., ammonium 8-anilino-1-naphthalenesulfonate, sodium 2-(p- toluidinyl)naphthalenesulfonate, Methyl Orange, and Mordant Orange 1, was investigated in aqueous phosphate buffer solution (pH 7.20) at 25 °C by fluorescence and circular dichroism spectrometry, as well as fluorescence lifetime measurements. The spectrofluorometric and spectropolarimetric titrations gave the complex stability constant (K(s)) and Gibbs free energy change (ΔG°) for the stoichiometric 1:1 inclusion complexation of 1-7 with the fluorescent dyes. The bis(β-cyclodextrin)s 2-4 showed higher affinities toward these guests than native β-cyclodextrin, and the binding abilities of 5-7 were further enhanced by incorporating Pt(IV). The cooperative binding abilities of these bis(β-cyclodextrin)s are discussed from the viewpoints of the size/shape-fit concept, the induced-fit interaction, and the multiple recognition mechanism.