Conformational changes in monolayers of a cationic amphiphilic porphyrin on saline subphases

Abstract

Langmuir monolayer films of the tetracationic porphyrin tetrakis(octadecyl-4-pyridinium)porphyrinatozinc(II) bromide on various salt containing subphases were analyzed using surface pressure-area isotherms and X-ray reflectivity. The use of these complementary techniques showed that the porphyrin molecules undergo changes in conformation upon compression. Two main phases were identified, one in which the porphyrin moiety is parallel to the subphase and one in which the porphyrin moiety is tilted out of the plane. The addition of different salts into the subphase brought about changes in film behaviour, which are explained in terms of a lyotropic series.