Molecular Recognition of a Novel Bridged Bis(<EM>β</EM>-cyclodextrin) Tethered with Aromatic Diamine for Dyes

Abstract

A novel bridged bis(β-cyclodextrin)with rigid aromatic diamino tethers,3,3'-methylenedianilino-briged-bis(6-aimino-6-deoxy-β-cyclodextrin)(2),was synthesized by the reaction of mono-[6-o-(p-tolysulfonyl)]-β-cyclodextrin with 3,3'-methylenedianiline.The inclusion complexation behaviors of native β-cyclodextrin(1)and the novel briged(β-cyclodextrin)(2)with some organic dyes,i.e.,acridine red(AR),neutral red(NR),sodium 6-toluidino-2-naphthalenes-ulfonate(TNS),ammonium 8-anilino-1-naphthalenesulfonate(ANS),rhodamine B(RhB)and brilliant green(BG)were investigated at 25 ℃ in aqueous phosphate buffer solution(pH=7.20)by means of fluorescence and ultraviolet spectroscopy.The spectral titrations gave the complex stability constants(KS)and Gibbs free energy changes(ΔG0)for the stoichiometry 1∶1 inclusion complexation of hosts examined with dye molecules.The obtained results demonstrated that bis(β-cyclodextrin)2 showed much higher binding ability and molecular selectivity toward these guest dyes than native β-cyclodextrin 1.Typically,dimmer 2 displayed the highest binding ability upon inclusion complexation with BG,affording 22.2 times higher KS value than native β-cyclodextrin.The cooperative binding ability of the bis(β-cyclodextrin)was discussed from the viewpoints of size/shape-fit interaction and multiple recognition mechanism.