Synchronous spectrofluorimetric study of the supramolecular host-guest interaction of β-cyclodextrin with...

The objective of this work is to assess the use of constant-wavelength synchronous fluorescence spectroscopy (SFS) in comparison to conventional fluorescence spectroscopy (CFS) for the investigation of the supramolecular host-guest interaction of β-CD with propranolol (PPL) in aqueous solutions. Scanning for the optimal Δλ at which the SFS can be performed in the presence of β-CD was examined. The results obtained revealed three distinguishable shapes for PPL using SFS that can be represented by three different Δλ values, namely 10, 40, and 100 nm. However, the effect of the β-CD concentration on the fluorescence intensity of PPL was examined using CFS and SFS of PPL at a Δλ of 10 and 100 nm. The change in the fluorescence intensity was used to calculate the equilibrium constant (Keq) for the formation of the β-CD:PPL inclusion complex by applying the Benesi-Hildebrand method. Keq values of 108, 112, and 117 M(-1) were obtained using SFS with a Δλ of 10 and 100 nm, and CFS, respectively. Further, the SFS method was successfully employed to examine the iodide quenching effect on the fluorescence intensity of PPL, where the results obtained revealed a Stern-Volmer quenching constant of 42.8 M(-1), which is in good agreement with results obtained using CFS. All results obtained using the SFS method were compared with the results obtained using the CFS method.