(643a) Acid-Base Bridging, Hydrophobic, and Bilayer Fusion Interactions of Pegolated Lipid Bilayers At Rough, Smooth, and Functionalized Gold Surfaces

In this work, the surface interactions of a lipid bilayer exposing amine-functionalized short chain PEG polymers with gold surfaces of varying functionalities are directly measured by the Surface Forces Apparatus (SFA) technique. Different self assembled monolayers (SAMs) are prepared on atomically smooth gold surfaces via thiol chemistry, and varying the SAM terminal group allows for precise measurement and control of the interaction forces. The three SAM functionalities, specifically carboxylic, methyl, and hydroxyl, allow for separate direct measurement of specific acid-base (COOH-NH3) hydrogen binding, hydrophobic PEG backbone segment binding, and steric confinement of the PEG chains, respectively. Interestingly, the highly pH dependent acid-base interaction between the amine-terminated PEG and the carboxylic SAM is very strong, about 10 kT per molecule, and long-ranged; significant adhesion is measured at close to the fully extended length of the polymer. We also examine the interactions of the biomimetic PEGolated bilayer with a clean gold surface, both before and after surface roughening. The membrane adhesion increases by about a factor of two for the rough surface as compared to the smooth surface, due to asperity breakthrough into the hydrophobic interior of the bilayer. The cumulative results depict new understanding of the physical and chemical interactions that control the behavior (i.e., adhesion, fusion, stability) as biomembranes interact with target metallic surfaces.