Probing the reaction pathways of DL-proline on TiO2(001) single crystal surfaces

G J Fleming, Hicham Idriss

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Abstract

The reaction of DL-Proline on O-2-annealed (stoichiometric) and O-defected (sub-stoichiometric) TiO2 (001) single-crystal surfaces has been investigated. This is of significance in trying to understand the concept of how biomolecules interact with the surfaces of biomedical implants (molecular recognition). On an O-2-annealed TiO2 surface, proline is found to largely adsorb then desorb intact at approximate to350 K. DFT (B3LYP) calculations of proline bound to a Ti(OH)(4) Cluster suggest a binding through the carboxylate functional group rather than through the NH group of the ring. In contrast, proline reaction was considerably different on the O-defected surface. First, proline was further stabilized, evidenced by a shift of its desorption temperature (during temperature-programmed desorption) to approximate to530 K. Along with proline desorption, two distinctive sets of reaction processes occurred at 530 and 630 K, respectively. The first pathway (alpha) at 530 K shows desorption of large amounts of m/e 55 (attributed to 1-azetine) and m/e 42 (attributed to ketene). At still higher temperature, 630 K, a pathway (beta) dominated by the appearance of low masses, mainly m/e 28, 27, and 26, is seen. These masses are tentatively attributed to desorption of HCN, ethylene, and/or acetylene as they represent the logical further decomposition of the different fragments of proline.

Original languageEnglish
Pages (from-to)7540-7546
Number of pages7
JournalLangmuir
Volume20
Issue number18
DOIs
Publication statusPublished - 31 Aug 2004

Keywords

  • gas-phase
  • amino acids
  • infrared-spectroscopy
  • metal ions
  • adsorption
  • glycine
  • interface
  • 1-azetine
  • oxide
  • 2-azabutadiene

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