1-4 linked glycopyranose units and are known respectively The miscibility of per-(6-amino-2,3-di-O-hexyl) b-CD hydroas alpha, beta, and gamma cyclodextrins (a-CD, b-CD, and chloride salt abbreviated NH 3 -b-CD-OC6 with 1,2 dipalmitoyl, 3g-CD). Stabilized by hydrogen bonds between the secondsn-phosphatidyl choline (DPPC) and 1,2 dipalmitoyl, 3-sn-phosary hydroxyls of successive glucose units around the macphatidic acid (DPPA) and of per-(6-dodecanoylamino-6-deoxy) rocycle, the cyclodextrins present a rigid molecule with a b-CD abbreviated C 11 CONH-b-CD with DPPC has been assessed preformed hydrophobic cavity. The presence of this hyby surface pressure-area experiments under dynamic conditions.
drophobic cavity within CD molecules makes the accommo-
The determination of their mixing behavior has been approached dation of guest molecules possible to form water-soluble by thermodynamic characterization derived from a comparison of the composition dependence of collapse pressure, for various inclusion complexes (1-6) and leads consequently to their contents of two components in monolayers, with that predicted wide use in nutrition (7), pharmaceutical (8), and separation from a model of ideal mixing. Component miscibility has additionapplications (9).
ally been addressed by the use of the Smaby-Brockman state
The pseudo ''face to face'' symmetry of cyclodextrins equation for liquid-expanded monolayers which characterizes inarising from the presence of two hydrophilic faces surteraction between monolayer components using the water activity rounding a hydrophobic cavity may be modified by lipophilic coefficient. While for both NH 3 -b-CD-OC6-DPPC and NH 3 -bsubstitution at only one face; this leads to the formation of CD-OC6-DPPA systems the average surface areas followed the amphiphilic molecules possessing a rigid two-dimensional additivity rule, for the latter system surface pressures at collapse polar adhesion surface. A wide range of such molecules are significantly deviated from ideality. The occurrence of an interacnow available (10-15). These amphiphilic cyclodextrins tion at the level of oppositely charged polar groups of NH 3 -b-CD-
OC6 and DPPA was also demonstrated by the nonideal composi-may undergo self-assembly to give micelles, vesicles, and tion dependence of the water activity coefficient ( f 1 ) characterizing monomolecular layers (11,16,17) and there is also evidence the interfacial water. The mixing energies and interaction parameof their multimolecular organization within supramolecular ters at collapse pressures were calculated using the Joos approach. systems (18).
Positive values of these factors indicated that NH 3 -b-CD-OC6 and
The systematic study of cyclodextrin monolayers will DPPA mixed films were thermodynamically less stable than the provide important information on their organization at films in which ideal mixing of components occurred. The mixing the water / air interface and their ability to generate local of NH 3 -b-CD-OC6 with DPPC appeared to be almost ideal. In dipole moments which are in a direct relation with axial the case of the C 11 CONH-b-CD-DPPC system, analysis according molecular symmetries of a, b, and g amphiphilic cycloto both the Joos and Goodrich approaches showed the occurrence dextrins ( 19 ) .
of an important interaction which resulted in negative mixing energies characteristic of thermodynamically stable mixed films.