Effect of sodium perchlorate on the binding of 2-(4′-aminophenyl)- and 2-(4′-(N,N′-dimethylamino)phenyl)benzothiazole with β-cyclodextrin in aqueous solution

The host-guest complexation of 2-(4'-aminophenyl)- and 2-(4'-(N,N-dimethylamino)phenyl)benzothiazole (APE and DAPB, respectively) with beta-cyclodextrin (beta-CDx) were studied in aqueous solution by use of fluorescence spectroscopy. The induced circular dichroic (ICD) spectra of the inclusion complexes were also measured to confirm complexation and to estimate the orientation of the guest molecule in the cyclodextrin cavity. The association constants for binding of the molecules with beta-CDx were estimated in phosphate buffer containing varying concentrations of NaClO4. The association constant for binding of DAPB is almost 4 times as high as that of APE. In the case of DAPB, the association constant was found to decrease with an increase in salt concentration. However, the association constant of APE initially increases and then decreases with an increase in salt concentration. The optical rotation data of beta-CDx in the absence and presence of NaClO4 suggest complexation of ClO4- with beta-cyclodextrin.