Molecular Recognition of Bridged Bis(β-cyclodextrin) s Linked by Phenylenediseleno Tether on the Primary or Secondary Side with Fluorescent Dyes^†

A novel β-cyclodextrin dimer, 2, 2′-o-phenylenediseleno-bridged bis (β-cyclodextrin) (2), has been synthesized by reaction of mono-[2-O-(p-tolylsulfonyl)]-β-cyclodextrin and poly(o-phenylenediselenide). The complexation stability constants (K₂) and Gibbs free energy changes (-ΔG°) of dimer 2 with four fluorescence dyes, that is, ammonium 8-anilino-1-naphthalenesulfonate (ANS), sodium 6-(p-toluidino)-2-naphthalenesulfonate (TNS), Acridine Red (AR) and Rhodamine B (RhB) have been determined in aqueous phosphate buffer solution (pH = 7.2, 0.1 mol-L⁻¹) at 25 °C by means of fluorescence spectroscopy. Using the present results and the previously reported corresponding data of β-cyclodextrin (1) and 6, 6′-o-phenylenediseleno-bridged bis (β-cyclodextrin) (3), binding ability and molecular selectivity are compared, indicating that the bis (β-cyclodextrin)s 2 and 3 possess much higher binding ability toward these dye molecules than parent β-cyclodextrin 1, but the complex stability constant for 2 linked from the primary side is larger than that of 3 linked from the secondary side, which is attributed to the more effective cooperative binding of two hydrophobic cavities of host 3 and the size/shape-fit relationship between host and guest. The binding constant (K₂,) upon inclusion complexation of host 3 and AR is enhanced by factor of 27.3 as compared with that of 1. The 2D ¹H NOESY spectrum of host 2 and RhB is performed to confirm the binding mode and explain the relative weak binding ability of 2.