Interfacial complexation of phospholipid Langmuir monolayers with water-soluble porphyrins and phthalocyanines: An X-ray reflectivity study

The use of Coulombic forces to isolate charged, water-soluble macrocycles at the air-water interface (through their interactions with the oppositely charged headgroups of a phospholipid Langmuir monolayer) is currently being exploited in this laboratory as a means to create two-dimensional arrays of pigments. Significant differences have been observed in the surface pressure-molecular area (pi-A) isotherms of dihexadecyl phosphate on subphases containing either copper (II) tetra-(methylaza)-phthalocyanine or tetra-(methylpyridyl)-porphyrin, both of which are cationic. In-situ X-ray specular reflectivity has been employed to determine interfacial organization in these systems and to elucidate the origin of their different phase behavior at the air-water interface.