Spectrofluorometric Study of the Inclusion Complexation of Fluorescent Whitening Agents and <i>&beta;</i>-Cyclodextrins

Abstract

The inclusion complexation behavior of 2,5-Bis(5-tert-butyl-benzoxazol-2yl)-thiophene (UVOB) with native β -cyclodextrin ( β CD) and β CD-monochlorotriazinyl ( β CD-MCT) was evaluated by fluorescence spectroscopy. The association constant (K s ), stoichiometry, , and were evaluated at 25 ℃ ± 0.1 ℃ in phosphate buffer solution (pH = 10.5, 0.1 mo &bull; 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 K s values for UVOB were 4916 ± 137 M – 1 and 655 ± 19 M – 1 (acetone: water 90/10, v/v) with β CD and β CD-MCT, respectively. The value obtained indicates a spontaneous and stable complex formation, but the complex β CD-UVOB showed high K s value as an indicative of a high concentration of complex formed. Additionally, K s and thermodynamic parameters and 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).