Monomolecular layer formation of amphiphilic cyclodextrin derivatives at the air water interface

Amphiphilic heptakis(6-alkylthio-6-deoxy)-beta-cyclodextrin (CD) derivatives were synthesized and their monolayer behavior on a water surface was studied on the basis of surface pressure-molecular area (pi-A) isotherms. The modification involved substitution at the C-6 position in the CD molecules with S-hexyl, S-decyl, S-tetradecyl, and S-octadecyl chains. The pi-A isotherms for these derivatives were recorded under various conditions, varying the compression rate, the relaxation time before and after compression. The introduction of allyl chains changed the water-soluble character of CD molecules to amphiphilic. As amphiphilic characters of the CD derivatives differ depending on the alkyl chain length, the stability of CD derivatives on the water surface was influenced by the experimental conditions such as the compression rate and the relaxation time, Therefore, the pi-A isotherms for CD derivatives, with the exception of those which were octadecylated, were not very reproducible. This may be associated with dissolution of the CD derivatives into the water subphase. This phenomenon was conspicuous when the chain length was shorter. In contrast, the monolayer of the octadecylated derivative was stable enough to maintain the surface pressure for a long time. (C) 1999 Elsevier Science S.A. All rights reserved.