A novel bis(β-cyclodextrin) was synthesized, and its binding behavior with steroids was investigated to demonstrate that the cooperative co-inclusion of guest and tether by two cyclodextrin moieties is operative to afford the highest molecular selectivity of up to 3.6 for deoxycholate over taurocholate.

A series of β-cyclodextrin(β-CD) dimers with 4,4′-diselenobis(benzoyl) linkers, that is, 6,6′-[4,4′-diselenobis-(benzoyloxyl)]-bridged bis(β-CD)(1a), 6,6′-[4,4′-diselenobis(2-(benzoylamino)ethyleneamino)]-bridged bis(β-CD)(2a), and 6,6′-[4,4′-diselenobis(2-(benzoylamino)-3,6-diazaoctylamino)]-bridged bis(β-CD)(3a), were synthesized in moderate yields by the reaction of 4,4′-diselenobis(benzoic acid] with β-CD or oligo(ethylenediamino)-6-deoxy-β-CD. Their binding behaviors with some structure-related substrates, such as acridine red(AR), neutral red(NR), rhodamine B(RhB), ammonium 8-anilino-1-naphthalenesulfonate(ANS), and 6-p-toluidino-2-naphthalenesulfonic acid(tNS), were investigated in aqueous phosphate buffer solution(pH 7.20) at 298.15 K by means of fluorescence, NMR, as well as circular dichroism spectroscopy and compared with those of their 2,2′-diselenobis(benzoyl)-linked analogues, that is, 6,6′-[2,2′-diselenobis-(benzoyloxyl)]-bridged bis(β-CD)(1b), 6,6′-[2,3′-diselenobis(2-(benzoylamino)ethyleneamino)]-bridged bis-(β-CD)(2b), and 6,6′-[2,2′-diselenobis(2-(benzoylamino)-3,6-diazaoctylamino)]-bridged bis(β-CD)(3b). The results showed that bis(β-CD)s 1a-3a, whose Se-Se bonds were located at the para position of the carboxyl group, gave stronger binding abilities toward nonlinear guests(RhB and ANS) than their analogues 1b-3b, whose Se-Se bonds were located at the ortho position relative to the carboxyl group. The molecular binding ability and selectivity of model substrates by these ditopic hosts were sufficiently discussed to reveal not only the cooperative contributions of the linker group and CD cavities upon inclusion complexation with dye guest molecules but also the controlling factors for the molecular selective binding.

An xanthene dye, pyronine Y, was found to exhibit opposite fluorescence behaviors at different pH values in the presence of N,N’-bis(2- aminoethyl)-2,2’-biquinoline-4,4’-dicarboxamide-bridged bis(β-cyclodextrin)(2). That is, pyronine Y showed the quenched fluorescence in an acidic(pH 2.0) or a neutral(pH 7.2) environment, while the enhanced fluorescence in a basic environment(pH 12.0), with the addition of 2. Further studies by fluorescence titrations and 2D NMR indicated that different binding modes of positively charged and neutral PY molecules upon complexation with bis(β-cyclodextrin) 2 should be responsible for opposite fluorescence behaviors. This result may enable the biquinolino-bridged bis(β-cyclodextrin) as an efficient chemical sensor for the protonation and deprotonation of xanthene dyes.

Studies on linear aggregation prepared by inclusion complexation of bridged bis(β-cyclodextrin)s and calix[4]arene derivatives provide a simple method to control linear aggregation compactness by molecular recognition.