Role of hydrophobic interactions in the adsorption of poly(ethylene glycol) chains on phospholipid membranes investigated with a quartz crystal microbalance.

We have investigated the adsorption of poly(ethylene glycol) (PEG) with different end groups onto phospholipid membranes at the liquid/solid interface by use of a quartz crystal microbalance with dissipation in real time. On a SiO(2)-coated surface, the adsorption of lipid vesicles results in a solid-supported lipid bilayer. Our experiments demonstrate that PEG chains with enough hydrophobic end groups (PEG-C(18)H(37)) can insert in the bilayer and form aggregates on the membrane surface. On the other hand, the adsorbed vesicles are intact on a gold surface. When the end group of PEG chain is not hydrophobic enough, PEG chains do not interact with the vesicles so that they have slight effect on the vesicle stability. However, PEG-C(18)H(37) chains with enough hydrophobic end groups lead to a vesicle-to-bilayer transition because of the insertion of the chains and their aggregation on the membrane surface. In addition, the studies on effect of polymer concentration show that PEG-C(18)H(37) can readily induce the rupture of vesicles at a concentration above the critical micelle concentration.