The association of anionic surfactants with β-cyclodextrin.: An isothermal titration calorimeter study

The association of a series of anionic surfactants (CnH2n+1SO4Na, n = 6, 8, 10, 12, 14) with beta-cyclodextrin was studied by means of the isothermal titration calorimeter (i.t.c.) at T = 298.15 K. For these types of inclusion complexes, the results agreed well with a 1:1 association model. Apparent values for the association constants, and changes in the standard molar Gibbs energies, enthalpies, and entropies were derived for the association process. The results indicated that the association of surfactants with beta-cyclodextrin is characterized by both favourable enthalpy and favourable entropy changes. The results also demonstrated that the longer the alkyl chain of the anionic surfactant, the greater the association constant with beta-cyclodextrin. (C) 1999 Academic Press.