Spectrofluorometric Study of the Inclusion Complexation of Fluorescent Whitening Agents and β-Cyclodextrins

The inclusion complexation behavior of 2,5-Bis(5-tert-butyl-benzoxazol-2yl)-thiophene
(UVOB) with native β-cyclodextrin (βCD) and βCD-monochlorotriazinyl (βCDMCT) was evaluated by fluorescence spectroscopy. The association constant ( ) KS ,
stoichiometry, ∆Gº , ∆H º and ∆Sº were evaluated at 25˚C ± 0.1˚C in phosphate
buffer solution (pH = 10.5, 0.1 mol∙dm−3
) in order to find out the complex formation
ability and stability. Fluorescence enhancement for UVOB and UVBNB with both
CDs has been observed as a result of the complex formation. A stoichiometry 1:1 for
UVOB in both CDs was observed; a stoichiometry 3:1 for UVBNB in both CDs has
been observed. The KS values for UVOB were 4916 ± 137 M−1 and 655 ± 19 M−1
(acetone: water 90/10, v/v) with βCD and βCD-MCT, respectively. The ∆Gº value
obtained indicates a spontaneous and stable complex formation, but the complex
βCD-UVOB showed high KS value as an indicative of a high concentration of
complex formed. Additionally, KS and thermodynamic parameters ∆Gº and
∆H º were evaluated in a commercial product UVBNB (UVOB, 13%, v/v). In
aqueous solution, the values obtained were 2552 ± 115 and 1787 ± 75 M−1 respectively. Complexation of UVOB with CDs is an interesting approach for utilization of
UVOB in aqueous systems without the need of solvents and or surfactants used in
commercial product (UVBNB).