Highly pH-sensitive ion pair amphiphile vesicle

Several ion pair amphiphiles (IPA) that are composed of two positive parts (ammonium surfactants) and one negative part (dicarboxlyate surfactant) are prepared to test whether the IPA vesicles can sense the change in pH of surrounding solution and respond by reassembling their aggregation structures. Among IPA candidates, one with asymmetric chain length of positive parts showed high and reliable pH-sensitivity as compared with IPA with symmetric chain length, which can be utilized in switching-on of release of encapsulated fluorescence marker and design of pH-sensitive drug delivery vehicle. Reasons for such high pH-sensitivity are sought from combined physical properties such as turbidity, zeta potential, surface tension, and release rate of marker through the bilayer membrane. (C) 2002 Elsevier Science B.V. All rights reserved.