In this work, we have developed 11-mercaptoundecanoic acid (MUA)-polypeptide "bilayer" systems by adsorbing poly(diethylene glycol-L-lysine)-poly(L-lysine) (PEGLL-PLL) diblock copolypeptide molecules of various architectures onto MUA-functionalized gold substrates. An objective of our present work is to use the PEGLL-PLL/MUA bilayer as a model system for studying the interfacial phenomena that occur when PEGLL-PLL molecules interact with carboxylic acid (COOH) moieties of nanoparticle ligands. Specifically, we have elucidated the nature of the interactions between the PEGLL-PLL and COOH moieties as well as the resulting polypeptide conformation and organization, using a combination of surface techniques-grazing-incidence IR spectroscopy, ellipsometry, and contact angle. We have also thoroughly characterized other film properties such as the packing and graft density of the polypeptide molecules as a function of the PEGLL-PLL architecture. From the IR data, the adsorption process occurs primarily by means of electrostatic interaction between the protonated PLL residues (pK(a) approximate to 10.6) and carboxylate moieties of the MUA self-assembled monolayer (SAM) (pK(a) approximate to 6) that is enhanced by H- bonding. The PLL block is thought to adopt a random-coil (extended) conformation, while the PEGLL. block that is not interacting with the MUA molecules is found to adopt in alpha-helical conformation with an average tilt angle of similar to 60 degrees. The PEGLL-PLL molecules have also been deduced to form a heterogeneous film and adopt liquidlike/disordered packing on the surface. The average contact angle of the MUA-polypeptide bilayer systems is similar to 40 degrees, which implies that the diethylene glycol (EG(2)) side chains of the PEGLL residues may be oriented somewhat toward the surface normal. From ellipsometry measurements, it is found that PEGLL(x)-PLLy molecules with a longer alpha-helical block are associated with a lower graft density on the MUA surface compared to those with a shorter alpha-helical block. This observation may be attributed to the greater repulsion-steric and H-bonding effects-that is imposed by the EG(2) side chains found on and projected area occupied by the longer PEGLL block. The bilayer systems have been found to be extremely stable over a 2-week period with no changes in the contact angle, thickness, polypeptide tilt angle, or conformation. Beyond that, there is a gradual decrease in the thickness and increase in the contact angle of the bilayer that could be attributed to the oxidation of the MUA SAM molecules.