Cooperative inclusion of sodium 1-pyrenesulfonate by γ-cyclodextrin

Summary

The interaction of γ-cyclodextrin(γ-CD) with sodium 1-pyrenesulfonate(PS) was studied spectrophotometrically. γ-CD was found to cause much larger decrease in the absorption maxima of PS than β-CD. The fluorescence spectra of PS in the presence of γ-CD showed excimer emission, while those of PS with β-CD showed only monomer emission, indicating that γ-CD forms 1∶2 (γ-CD∶PS) complexes in which two PS molecules are included in the γ-CD cavity in a face-to-face fashion. The binding isotherm showed a sigmoidal curve. The association constants were estimated by computer simulation of the binding curve. The 1∶2 (CD∶PS) complex was found to be much more stable (K=10⁶ M⁻¹) than the 1∶1 complex (K=1 M⁻¹). At high concentration of γ-CD another γ-CD cooperates in binding two PS molecules, resulting in the formation of a 2∶2 complex.