Interaction of Triton X-100 with cyclodextrins. A fluorescence study

The interaction of Triton X-100 (TX) with alpha- and beta-cyclodextrins (CD) has been studied, using 2,6-p-toluidinonaphthalene sulfonate (TNS) as a fluorescent probe, by steady-state and time-resolved emission spectroscopy. The critical micellar concentration (c.m.c.) is indicated by the point of abrupt increase of emission intensity and lifetime of TNS. The apparent c.m.c. increases significantly in the presence of beta-CD by as much as 28 +/- 1 times at 10 mM beta-CD but remains more or less unaffected in the presence of alpha-CD at similar concentrations. This is attributed to the very strong binding of TX with the large beta-CD cavity and negligible binding to the small alpha-CD. At concentrations below the c.m.c., on addition of TX to aqueous TNS solution containing beta-CD the emission intensity decreases. This is ascribed to the competitive binding of TNS and TX with beta-CD. This causes displacement of TNS from the CD cavity by the TX surfactant molecules. The binding constant of TX with beta-CD is found to be ca. 9400 +/- 1300 L mol(-1).