Probing the interaction of the amino acid alanine with the surface of ZnO(10(1)over-bar0)

Y. K. Gao, F. Traeger, O. Shekhah, Hicham Idriss, C. Woell

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Abstract

The adsorption modes and stability of the amino acid alanine (NH2-CH(CH3)-COOH) have been studied on the nonpolar single crystal surface of zinc oxide, ZnO(10 (1) over bar0), experimentally by X-ray photoelectron spectroscopy (XPS) and computationally using density functional theory (DFT). Deposition at 200 K was found to lead to the formation of multilayers identified by an XPS N1s peak at 401.7 eV assigned to the NH3+ group, a fingerprint of the zwitterionic structure of alanine in the solid state. Heating to 300 K resulted in the removal of most of the multilayers with the remaining surface coverage estimated to 0.4 with respect to Zn cations. At this temperature most of the alanine molecules are found to be deprotonated (dissociated), yielding a carboxylate species (NH2-CH(CH3)-COO-(a)+OH (s); where O is surface oxygen, (a) for adsorbed and (s) for surface species). Further heating of the surface resulted in a gradual decrease of the surface coverage and by 500 K a large fraction of adsorbed alanine molecules have desorbed from the surface. Total energy DFT computations of different adsorbate species identified two stable dissociative adsorption modes: bidentate and monodentate. The bidentate species with adsorption energy of 1.75 eV was found to be more stable than the monodentate species by about 0.7 eV. (C) 2009 Elsevier Inc. All rights reserved.

Original languageEnglish
Pages (from-to)16-21
Number of pages6
JournalJournal of Colloid and Interface Science
Volume338
Issue number1
DOIs
Publication statusPublished - 1 Oct 2009

Keywords

  • alanine
  • ZnO
  • single crystal
  • adsorption
  • XPS
  • DFT
  • monodendate
  • bidentate
  • zwitterion
  • single-crystal surfaces
  • level binding-energies
  • AB-initio calculations
  • reflection-absorption
  • glycine adsorption
  • reaction pathways
  • maleic-anhydride
  • oxide surfaces
  • ZNO surfaces
  • zinc-oxide

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