Pressure-area isotherms: the behaviour of cyclosporin/pyrene-labelled phospholipid systems

Systems consisting of cyclosporin A (CsA), a cyclic peptide which is an effective immunosuppressive agent for transplanted organs, and dipalmitoylphosphatidylcholine (DPPC), a liposomal phospholipid, obey the molecular area additivity rule when spread as mixed monolayers at the air/water interface. This behaviour is ascribed to the immiscibility of the system components, which orientate themselves differently on the surface. The insertion of a pyrene residue in the DPPC molecule, whether in the non-polar chain to obtain 1-hexa-decanoyl-2-(1-pyrenedecanoyl)-sn-glycero-3-phosphocholine (H-361) or in the polar group to form N-(1-pyrenesulfonyl)-l,2-phospho-ethanolamine triethylammonium (P-58), has no effect on the surface behaviour of the cyclosporin-phos-pholipid system, which remains additive in its molecular areas and hence immiscible at the interface.