MIXED MONOLAYERS OF AMPHIPHILIC CYCLODEXTRINS AND PHOSPHOLIPIDS .2. SURFACE POTENTIAL-AREA BEHAVIOR OF PER-(6-AMINO-2,3-DI-O-HEXYL)BETA-CD HYDROCHLORIDE SALT AND 1,2-DIPALMITOYL, 3-SN-PHOSPHATIDIC ACID MIXED MONOLAYERS

The dielectric properties of mixed monolayers of per-(6-amino-2,3-di-O -hexyl) beta-CD hydrochloride (NH3-beta-CD-OC6) and 1,2 dipalmitoyl, 3 -sn-phosphatidic acid (DPPA) have been assessed using surface potentia l measurements at constant area, From the comparison of these surface potential (Delta V) versus surface density (delta) relationships with those of surface pressure (pi) against surface density (delta) it was apparent that the increase in the NH3-beta-CD-OC6 content in mixed fil ms gave rise to a gradual increase in the saturation value of the surf ace potential (Delta V-max). This potential for pure DPPA was found to be equal to 396 mV and for pure CD 554 mV. The Delta V-max values ref lect the onset of reorientation effects that arrive at molar areas bef ore the collapse of these films, Independently of reorientation effect s, the obtained results strongly indicate that the dipolar term contri buting to the overall Delta V value was for NH3-beta-CD-OC6 due to the hydration of its NH: group, For both DPPA and NH3-beta-CD-OC6 molecul es the contribution of the electric double layer (psi) was calculated and was found for DPPA and NH3-beta-CD-OC6 to be equal to -249 and +25 2 mV, respectively, These calculated psi values made possible the eval uation of dipole moments for NH3-beta-CD-OCB and DPPA monolayers which revealed a marked difference in dipolar properties between these two film forming components, In contrast to DPPA which exhibited a decreas e in the surface dipole moment (mu(perpendicular to)) with the decreas e in A, NH3-beta-CD-OC6 displayed an increase in mu(perpendicular to) with the decrease in A for A values above 580 Angstrom(2). Below this value mu(perpendicular to), decreases with decreasing molecular area a nd this variation arises from a change in the polarity of the electric double layer arising from interactions with the complementary anion, The differences in dielectric properties between the two film forming molecules have been attributed to modification, during compression, in the structure of the interfacial water bound to the cyclodextrin. (C) 1996 Academic Press, Inc.