A comparative study on inclusion complexation of substituted anilinonaphthalene sulfonic acids with 1,6,20,25-tetraaza[6.1.6.1]-paracyclophane and β-cyclodextrin

The inclusion complexations of paracyclophane (CP44) and β-cyclodextrin (β-CD) with several anilinonaphthalene sulfonic acids (ANSs) have been characterized via the enhancement of fluorescence spectra upon inclusion. β-CD and CP44 formed 1:1 inclusion complexes with ANSs, and the high stability of inclusion complexes of the latter was demonstrated. The thermodynamic parameters observed from the temperature dependence of the inclusion constants (van’t Hoff analysis) showed that CP44 inclusion complexations with ANSs are enthalpy-driven. Furthermore, the structure of the inclusion complexes was discussed based on ¹H- and 2D ROESY-NMR measurements. It was found that CP44 encapsulates the naphthalene moiety of ANSs. On the other hand, differences in the structures of the β-CD inclusion complexes were observed for the 4-OH-substituted ANS. The molecular recognition for the inclusion of β-CD was found to be sensitive compared with that of CP44. In addition, the local polarity inside the CP44 and β-CD cavities was evaluated using ANSs as the fluorescence probe. Based on these results, we have suggested that the local polarity of ANSs in the hydrophobic cavities of CP44 and β-CD plays an important role in quantum yield enhancement upon inclusion.