Binding of dibenzofuran and its derivatives to water-soluble β-cyclodextrin polymers

The binding capacity of β-cyclodextrin polymers (β-CDP), cross-linked with epichlorohydrin, has been compared with that of unimeric β-cyclodextrin for the inclusion of dibenzofuran (DBF) and two of its derivatives: 2-hydroxydibenzofuran (DBFOH) and dibenzofuran 2-carboxylate (DBFC). Gel permeation chromatography, 1H and 13C NMR, and dynamic light scattering, together with membrane ultrafiltration, were used to characterize and fractionate the polymeric samples. Their interactions with the dibenzofuran derivatives have been analyzed by absorption and fluorescence spectroscopies. Fluorescence anisotropy titrations were used to obtain the apparent binding constants. The affinity of the neutral dibenzofurans for the polymers is significantly higher than those of the unimeric β-CD, irrespective of the molecular weight or the microstructure of the polymer, whereas the charge in the anionic dibenzofuran derivative hinders the formation of the complex. The most hydrophobic DBF shows a higher affinity for the polymer with a higher content in β-CD, whereas the opposite behavior is displayed for DBFOH. The results are explained in terms of the synergic effect produced by the glyceryl cross-linking bridges, the relative hydrophobicity of the guest-host system and the density of the polymer network.