Spectrophotometric study on the controlling factor of molecular selective binding of dyes by bridged bis(beta-cyclodextrin)s with diselenobis(benzoyl) linkers

A series of beta-cyclodextrin (beta-CD) dimers with 4,4'-diselenobis(benzoyl) linkers, that is, 6,6'-[4,4'-diselenobis(benzoyloxyl)]-bridged bis(beta-CD) (1a), 6,6'-[4,4'-diselenobis[2-(benzoylamino)ethyleneamino]]-bridged bis(beta-CD) (2a), and 6,6'-[4,4'-diselenobis[2-(benzoylamino)-3,6-diazaoctylamino]]-bridged bis(beta-CD) (3a), were synthesized in moderate yields by the reaction of 4,4'-diselenobis(benzoic acid) with beta-CD or oligo(ethylenediamino)-6-deoxy-beta-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(beta-CD) (1b), 6,6'-[2,3'-diselenobis[2-(benzoylamino)ethyleneamino]]-bridged bis(beta-CD) (2b), and 6,6'-[2,2'-diselenobis[2-(benzoylamino)-3,6-diazaoctylamino]]-bridged bis(beta-CD) (3b). The results showed that bis(beta-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.