Spectroscopic study on the interaction of cyclodextrins with naphthyl groups attached to poly(acrylamide) backbone

The interaction of beta-cyclodextrin (beta-CD) with (1-naphthyl)methyl (1Np) and (2-naphthyl)methyl (2Np) groups attached to the poly(acrylamide) backbone was investigated by several techniques, including steady-state fluorescence and circular dichroism (cd) spectroscopies. When beta-CD was added to polymer aqueous Solutions. the fluorescence intensity increased remarkably, indicative of the formation of inclusion complexes of beta-CD with polymer-carrying Np groups. Comparison of these fluorescence data with those for the guest model Compounds, (1-naphthyl)methanol and (2-naphthyl)methanol (2NpMeOH), indicated that, upon complex formation. the polymer main chain effectively protects Np groups of the singlet excited state from the contact of water molecules. Using steady-state fluorescence data at varying concentrations of beta-CD, association constants (K) were determined to be (1.1 +/- 0.3) x 10(2) and (2.0 +/- 0.4) x 10(2) M-1 for the complex formation of beta-CD with polymer-carrying 1Np and 2Np groups, respectively. The structures of inclusion complexes of beta-CD with Np groups were investigated by cd spectroscopy for the polymers and the model compounds in the presence of beta-CD and by X-ray crystallographic analysis for the inclusion complex of beta-CD with 2NpMeOH. These data indicated that beta-CD included polymer-carrying 1Np groups shallowly but it included polymer-carrying 2Np groups deeply to form inclusion complexes, in which the longer axis of the 2Np group is rather parallel to the rotation axis of beta-CD. On the basis of these data, plausible structures of the inclusion complex of beta-CD with polymer-carrying 2Np groups were proposed. (c) 2005 Elsevier B.V. All rights reserved.