Spreading and polymerization behavior of diacetylenic phospholipids at the gas-water interface

A variety of polymerizable lipids derived from hexacosa-10,12-diynoic acid and hexacosa-10,12-diyne-1-ol have been synthesized and spread at the gas/water interface. The measured surface pressure/area isotherms indicate that head group charge and bulkiness have strong influences on the area occupied per molecule. In the case of zwitterionic phospholipids additional area changes are brought about by alkaline and acidic subphases, which is probably due to an alteration of head group conformation. Condensed state diacetylenic lipid monolayers in a nitrogen atmosphere are polymerizable by UV irradiation. The polymerization reaction was monitored at the gas/water interface by the area change at constant surface pressure and the change of optical density in the visible region. As already observed for vesicle polymerization, single chain amphiphiles exhibit a different absorption behavior than asymmetric double chain amphiphiles of the phosphoglycerol type. The polymerized monolayers were more densely packed and more stable than their monomeric counterparts as indicated by the smaller areas and higher pressures reached before the collapse points.