L-tyrosine on Ag(111): universality of the amino acid 2D zwitterionic bonding scheme?
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.
Reichert
Joachim
J
Department of Chemistry, The University of British Columbia, Vancouver, British Columbia V6T 1Z4, Canada.
Schiffrin
Agustin
A
Auwärter
Willi
W
Weber-Bargioni
Alexander
A
Marschall
Matthias
M
Dell'angela
Martina
M
Cvetko
Dean
D
Bavdek
Gregor
G
Cossaro
Albano
A
Morgante
Alberto
A
Barth
Johannes V
JV
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
D011868:Radioisotopes; D012834:Silver; D014443:Tyrosine