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‘-trimethylenediseleno-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 (Δ G °) 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.