Probing the reaction pathways of DL-proline on TiO2 (001) single crystal surfaces.
The reaction of DL-Proline on O2-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 O2-annealed TiO2 surface, proline is found to largely adsorb then desorb intact at approximately 350 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 approximately 530 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.
Department of Chemistry, University of Auckland, Private Bag 92019, Auckland, New Zealand.
Gary J
GJ
Fleming
Hicham
H
Idriss
D000114:Acetylene / Q000737:chemistry; D000327:Adsorption; D001385:Azetines / Q000737:chemistry; D001672:Biocompatible Materials / Q000737:chemistry*; D003460:Crystallization; D005030:Ethylenes / Q000737:chemistry; D006856:Hydrogen Cyanide / Q000737:chemistry; D007659:Ketones / Q000737:chemistry; D015394:Molecular Structure; D011392:Proline / Q000737:chemistry*; D013499:Surface Properties; D013816:Thermodynamics; D014025:Titanium / Q000737:chemistry*
D001385:Azetines; D001672:Biocompatible Materials; D005030:Ethylenes; D007659:Ketones; C009495:titanium dioxide; D006856:Hydrogen Cyanide; C036216:ethylene; D011392:Proline; D014025:Titanium; C008223:ketene; D000114:Acetylene; C046804:titanium hydroxide