title: L-tyrosine on Ag(111): universality of the amino acid 2D zwitterionic bonding scheme?
abstract: We present a combined study of the adsorption and ordering of the l-tyrosine amino acid on the close-packed Ag(111) noble-metal surface in ultrahigh vacuum by means of low-temperature scanning tunneling microscopy (STM), X-ray photoelectron spectroscopy (XPS) and near-edge X-ray absorption fine structure (NEXAFS) spectroscopy. On this substrate the biomolecules self-assemble at temperatures exceeding 320 K into linear structures primarily following specific crystallographic directions and evolve with larger molecular coverage into two-dimensional nanoribbons which are commensurate with the underlying atomic lattice. Our high resolution topographical STM data reveal noncovalent molecular dimerization within the highly ordered one-dimensional nanostructures, which recalls the geometrical pattern already seen in the l-methionine/Ag(111) system and supports a universal bonding scheme for amino acids on smooth and unreactive metal surfaces. The molecules desorb for temperatures above 350 K, indicating a relatively weak interaction between the molecules and the substrate. XPS measurements reveal a zwitterionic adsorption, whereas NEXAFS experiments show a tilted adsorption configuration of the phenol moiety. This enables the interdigitation between aromatic side chains of adjacent molecules via parallel-displaced pi-pi interactions which, together with the hydrogen-bonding capability of the hydroxyl functionality, presumably mediates the emergence of the self-assembled supramolecular nanoribbons.
authors.affiliation: Department of Chemistry, The University of British Columbia, Vancouver, British Columbia V6T 1Z4, Canada.
authors.forename: Joachim
authors.initials: J
authors.lastname: Reichert
authors.forename: Agustin
authors.initials: A
authors.lastname: Schiffrin
authors.forename: Willi
authors.initials: W
authors.lastname: Auwärter
authors.forename: Alexander
authors.initials: A
authors.lastname: Weber-Bargioni
authors.forename: Matthias
authors.initials: M
authors.lastname: Marschall
authors.forename: Martina
authors.initials: M
authors.lastname: Dell'angela
authors.forename: Dean
authors.initials: D
authors.lastname: Cvetko
authors.forename: Gregor
authors.initials: G
authors.lastname: Bavdek
authors.forename: Albano
authors.initials: A
authors.lastname: Cossaro
authors.forename: Alberto
authors.initials: A
authors.lastname: Morgante
authors.forename: Johannes V
authors.initials: JV
authors.lastname: Barth
mesh_terms: D000327:Adsorption; D016252:Microscopy, Scanning Tunneling; D008958:Models, Molecular; D008968:Molecular Conformation; D056951:Photoelectron Spectroscopy; D011868:Radioisotopes; D012834:Silver / Q000737:chemistry*; D013696:Temperature; D014443:Tyrosine / Q000737:chemistry*; D056928:X-Ray Absorption Spectroscopy
chemical_list: D011868:Radioisotopes; D012834:Silver; D014443:Tyrosine