Miscibility in binary monolayers of phospholipids and linker lipid

We studied the miscibility in binary lipid matrixes made by the Langmuir-Blodgett (LB) technique. The components in the lipid matrix were N-(epsilon-maleimidocaproyl)-dipalmitoyl phosphatidylethanolamine (DPPE-EMC; biofunctionalized linker lipid) and a phospholipid. Three different matrix phospholipids were used: 1,2-dipalmitoyl-sn-glycero-3-phosphatidylethanolamine (DPPE). 1,2-dimyristoyl-sn-glycero-3-phosphatidylethanolamine (DMPE), and 1,2-dipalmitoyl-sn-glycero-3-phosphatidylcholine (DPPC). The phase-transition temperature of the linker lipid as determined by Fourier transform infrared spectroscopy was 45 degrees C. The surface potential of the linker lipid, 290 mV at pH 6.8, was clearly smaller than the values observed for pure phospholipids. Clear evidence of the miscibility could not be obtained from the surface pressure - area isotherms. On the contrary, Brewster angle microscopy (BAM) enabled a visual investigation of the miscibility and domain morphology. The best miscibility was obtained for DPPC/DPPE-EMC matrixes but only to some extent for DPPE/DPPE-EMC and DMPE/DPPE-EMC matrixes. Atomic force microscopy on solid supported LB films showed domains similar to the BAM images of Langmuir monolayers.