No abstract

No abstract

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.

Geometry optimisation and metal ion affinities (MIAs) of the binding configurations of Be2+, Mg2+ and Ca2+ to L‐proline were calculated using the hybrid Density Functional Theory (DFT‐B3LYP) and second order Møllet−Plesset perturbation theory (MP2) methods. Be2+ was found to bind preferentially in a charge transfer type arrangement through the carbonyl oxygen (CO) and the lone pair of the imino‐group nitrogen atom (NH). On the contrary Mg2+ and Ca2+ were found to prefer binding in a bi‐dentate manner through the carboxylate group of L‐proline (OCO) in a zwitterion form. The main types of interactions found to influence the binding preference of M2+ ions to L‐proline were (i) charge transfer in the case of Be2+ ions and (ii) electrostatic interactions in the case of Mg2+ and Ca2+ ions. Inspection of the IR stretching of the NH and the OH groups of L‐proline with M2+ ions in a chelating configuration (to both O and N atoms) indicated a considerable shift to higher frequency with decreasing MIA. On the other hand, the MIA for the zwitterion L‐proline with M2+ tracks the reciprocal distance of the M2+OCO bond further confirming that the nature of the bond is mainly electrostatic. Comparison with other molecules containing the carboxylic function is also included in order to gain more insight on the types of interaction of this amino acid with metal ions in general. Copyright © 2007 John Wiley & Sons, Ltd.