Study on the aggregation and electrochemical properties of Rose Bengal in aqueous solution of cyclodextrins

The interactions of Rose Bengal (RB) with α-cyclodextrin (α-CD), hydroxypropyl-β-cyclodextrin (HP-β-CD), hydroxypropyl-γ-cyclodextrin (HP-γ-CD), heptakis(2,3,6-tri-O-methyll)-β-cyclodextrin (TM-β-CD) were studied in aqueous solutions of 0.1 M KClO4 and 0.1 M LiClO4 by vis absorption, fluorescence spectroscopy as well as electrochemical measurements at 298 K. The spectrophometric results indicate that RB is included in all β- and γ-CDs forming complexes with a stoichiometry 1:1 whose stability is slightly higher in KClO4 than in LiClO4 solutions. The complex stability constants determined for salt-containing CD solutions are lower than those for water solutions. The complexation of RB with β- and γ-CD and the differences between the complexes obtained in the presence of the two salts were confirmed by an electrochemical study.