Competing interactions in self-assembled monolayers containing peptide groups: Molecular dynamics studies of long-chain perfluoro mercaptans on Au(111)

The structure of self-assembled monolayers of a long-chain perfluoro mercaptan has been investigated using molecular dynamics simulations. The particular system investigated, namely perfluorooctyl mercaptoethylamide, † has been chosen because it offers the possibility of generating a Teflon-like coating on top of a polar film consisting of hydrogen-bonded peptide groups. We find that the monolayer consists of close-packed perfluoro alkanes standing more or less upright and of hydrogen-bonded chains of peptide groups. The intramolecular flexibility of the molecule enables it to form hydrogen bonds with the peptide oxygen and nitrogen separated by ca. 2.8 Å and to accommodate simultaneously the 5.8 Å spacing of the tails. From our molecular dynamics simulations we have also determined the spectrum of the motion of the polarization associated with the peptide groups.