MOLECULAR FILMS FROM THE POLYMERIZABLE LIPID ETHYL MORPHOLINE PENTACOSADIYNOIC AMIDE

A new polymerizable lipid, ethyl morpholine pentacosadiynoic amide (EM PDA), was synthesized. Monomeric and polymeric films formed from this lipid at the air-water interface were investigated by microfluorescenc e filmbalance techniques. Below 25-degrees-C, monomeric EMPDA exhibite d a pronounced fluid-solid coexistence with a transition enthalpy of a pproximately 100 kJ/mol at room temperature. The coexistence pressure was found to increase with decreasing pH; below pH 4.5 no fluid-solid coexistence was measurable. Microfluorescence revealed that large achi ral single-crystalline domains grow in the coexistence regime. Upon ul traviolet exposure only the lipids in the crystalline domains were fou nd to polymerize, indicating that the polymerization is a topochemical reaction. The polymerized domains exhibited a pronounced intrinsic fl uorescence with a strong excitation anisotropy which is correlated wit h the macroscopic crystal axises. Polymerized films transferred onto w afers with thermally grown silicon oxide were investigated by atomic f orce microscopy. In the polymeric domains, stripelike corrugations wer e found with an orientation parallel to the fluorescence polarization. At high magnifications molecular resolution images were obtained. The lattice constants of the crystalline arrangement of the lipids are a = 0.51 +/- 0.03 nm, b = 0.48 +/- 0.06 nm, alpha = 74 +/- 7-degrees. La teral force images revealed that the friction between tip and sample i s dependent on the orientation of the polymer backbone with respect to the fast scan direction.