MIXED MONOLAYERS OF AMPHIPHILIC CYCLODEXTRINS AND PHOSPHOLIPIDS .1. MISCIBILITY UNDER DYNAMIC CONDITIONS OF COMPRESSION

The miscibility of per-(6-amino-2,3-di-O-hexyl) beta-CD hydrochloride salt abbreviated NH3-(beta)-CD-OC6 with 1,2 dipalmitoyl, 3-sn-phosphat idyl choline (DPPC) and 1,2 dipalmitoyl, 3-sn-phosphatidic acid (DPPA) and of per-(6-dodecanoylamino-6-deoxy) beta-CD abbreviated C11CONH-be ta-CD with DPPC has been assessed by surface pressure-area experiments under dynamic conditions. The determination of their mixing behavior has been approached by thermodynamic characterization derived from a c omparison of the composition dependence of collapse pressure, for vari ous contents of two components in monolayers, with that predicted from a model of ideal mixing. Component miscibility has additionally been addressed by the use of the Smaby-Brockman state equation for liquid-e xpanded monolayers which characterizes interaction between monolayer c omponents using the water activity coefficient, While for both NH3-bet a-CD-OC6-DPPC and NH3-beta CD-OC6-DPPA systems the average surface are as followed the additivity rule, for the latter system surface pressur es at collapse significantly deviated from ideality, The occurrence of an interaction at the level of oppositely charged polar groups of NH3 -beta-CDOC6 and DPPA was also demonstrated by the nonideal composition dependence of the water activity coefficient (f(1)) characterizing th e interfacial water. The mixing energies and interaction parameters at collapse pressures were calculated using the Joos approach. Positive values of these factors indicated that NH3-beta-CD-OC6 and DPPA mixed films were thermodynamically less stable than the films in which ideal mixing of components occurred. The mixing of NH3-beta-CD-OC6 with DPP C appeared to be almost ideal, In the case of the C11CONH-beta-CD-DPPC system, analysis according to both the Joos and Goodrich approaches s howed the occurrence of an important interaction which resulted in neg ative mixing energies characteristic of thermodynamically stable mixed films. (C) 1996 Academic Press, Inc.