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

Amphiphilic heptakis(6-alkylthio-6-deoxy)-beta-cyclodextrin (CD) derivative s were synthesized and their monolayer behavior on a water surface was stud ied on the basis of surface pressure-molecular area (pi-A) isotherms. The m odification involved substitution at the C-6 position in the CD molecules w ith S-hexyl, S-decyl, S-tetradecyl, and S-octadecyl chains. The pi-A isothe rms for these derivatives were recorded under various conditions, varying t he compression rate, the relaxation time before and after compression. The introduction of allyl chains changed the water-soluble character of CD mole cules to amphiphilic. As amphiphilic characters of the CD derivatives diffe r depending on the alkyl chain length, the stability of CD derivatives on t he 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 d erivatives into the water subphase. This phenomenon was conspicuous when th e chain length was shorter. In contrast, the monolayer of the octadecylated derivative was stable enough to maintain the surface pressure for a long t ime. (C) 1999 Elsevier Science S.A. All rights reserved.