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