Amino acid nanopatterning on graphite

The present study provides an experimental and computational insight into amino acid adsorption on a graphite substrate. We investigated two aromatic amino acids, histidine and tyrosine, and their behavior on highly-ordered pyrolytic graphite (HOPG). The study was carried out under ambient conditions, in a 1-octanol solution and at room temperature. We found that both amino acids form well-ordered molecular films on graphite, as opposed to dimer rows found for another amino acid (methionine). Scanning Tunneling Microscopy reveals intermolecular spacings and angular orientations of the individual molecules in the well-ordered molecular layer. Both amino acids arrange themselves into a chevron pattern governed by inter-molecular attractive forces. The configuration consists of adjacent rows of parallel molecules, however, individual molecules in neighboring rows are angled with respect to each other. Additional computational chemistry methods using a Molecular Mechanics approach and the AMBER ff03 force field are employed in support of the experimental findings. These calculations provide suggested molecular geometries and estimated adsorption energies and inter-molecular binding energies for molecules on a graphene sheet.