Association of anionic surfactants with β-cyclodextrin. Fluorescence-probed studies on the 1:1 and 1:2 complexation

Abstract

Formation of inclusion complexes between anionic surfactants, alkanesulfonates (n = 5-8, 10, 12) and alkyl sulfates (n = 8, 10, 12, 14, 16, 18), and β-cyclodextrin was studied by a fluorometric method using 1-anilinonaphthalene-8-sulfonate (1,8-ANS) and 2-anilinonaphthalene-7-sulfonate (2,7-ANS) as probes. The association constants for 1:1 complexes of 1,8-ANS and 2,7-ANS with β-CD were determined as 85 and 1500 M -1, respectively, at 25°C. The first and second association constants of the surfactants with β-CD were calculated from competitive binding data of the surfactants and the ANS's with β-CD. The 2:1 β-CD-surfactant complexes were formed with alkanesulfonates of n ≥ 10 and alkyl sulfates of n ≥ 8. The surfactant-β-CD association was accompanied by a large increase in entropy, and hydrophobic binding appeared to contribute to a great extent to the association. Self-association of 1:1 complexes of surfactants of long hydrocarbon chains was also suggested. © 1989 American Chemical Society.