MOLECULAR-CONFORMATION AND SOLVATION OF OLIGO(ETHYLENE GLYCOL)-TERMINATED SELF-ASSEMBLED MONOLAYERS AND THEIR RESISTANCE TO PROTEIN ADSORPTION

We study the interaction of water with oligo(ethylene glycol) (OEG)-te rminated alkane thiolate self-assembled monolayers (SAMs) in the helic al and the planar ''all-trans'' form with ab initio methods to determi ne the stability and density distribution in water clusters as a funct ion of molecular conformation. We find that the amphiphilic behavior o f the OEG moieties depends on their molecular conformation and that th e energetics of water adsorption is dominated by electrostatic interac tions. The SAM surface of helical OEG provides a template for water nu cleation, whereas water is not stable on a surface of planar OEG stran ds. These results suggest that protein resistance of OEG-terminated se lf-assembled monolayers is a consequence of the stability of the inter facial water layer, which prevents direct contact between the surface and the protein.