The association of anionic surfactants with beta-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 inclusio n complexes, the results agreed well with a 1:1 association model. Apparent values for the association constants, and changes in the standard molar Gi bbs energies, enthalpies, and entropies were derived for the association pr ocess. The results indicated that the association of surfactants with beta- cyclodextrin is characterized by both favourable enthalpy and favourable en tropy changes. The results also demonstrated that the longer the alkyl chai n of the anionic surfactant, the greater the association constant with beta -cyclodextrin. (C) 1999 Academic Press.