Miscibility in binary monolayers of phospholipids and linker lipid

We studied the miscibility in binary lipid matrixes made by the Langmuir-Bl odgett (LB) technique. The components in the lipid matrix were N-(epsilon-m aleimidocaproyl)-dipalmitoyl phosphatidylethanolamine (DPPE-EMC; biofunctio nalized linker lipid) and a phospholipid. Three different matrix phospholip ids were used: 1,2-dipalmitoyl-sn-glycero-3-phosphatidylethanolamine (DPPE) . 1,2-dimyristoyl-sn-glycero-3-phosphatidylethanolamine (DMPE), and 1,2-dip almitoyl-sn-glycero-3-phosphatidylcholine (DPPC). The phase-transition temp erature of the linker lipid as determined by Fourier transform infrared spe ctroscopy 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 phospho lipids. Clear evidence of the miscibility could not be obtained from the su rface pressure - area isotherms. On the contrary, Brewster angle microscopy (BAM) enabled a visual investigation of the miscibility and domain morphol ogy. 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 m icroscopy on solid supported LB films showed domains similar to the BAM ima ges of Langmuir monolayers.