L-tyrosine on Ag(111): universality of the amino acid 2D zwitterionic bonding scheme?

ACS Nano. 2010 Feb 23;4(2):1218-26. doi: 10.1021/nn901669p.

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.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adsorption
  • Microscopy, Scanning Tunneling
  • Models, Molecular
  • Molecular Conformation
  • Photoelectron Spectroscopy
  • Radioisotopes
  • Silver / chemistry*
  • Temperature
  • Tyrosine / chemistry*
  • X-Ray Absorption Spectroscopy

Substances

  • Radioisotopes
  • Silver
  • Tyrosine