Functionalization of Titanium Surfaces with Lysine: A Micro Raman Study of the Intermolecular Interactions of Lysine-TiO2

Abstract

Raman scattering (RS) was used as a powerful, efficient, and sensitive technique for studying intermolecular interactions between an organic ligand adsorbate and a metallic substrate. Functionalization of titanium (TiO2[Formula: see text]Ti) surfaces was performed using lysine (Lys) as adsorbate and later developing a hydroxyapatite (HA) layer onto this functionalized surface. The functionalization process was performed at different pH values of the interacting chemical species. Chemisorption onto the TiO2Ti substrates through the Lys carboxylic group was demonstrated spectroscopically. Analysis of vibrational spectra showed that the CH side chain of Lys was relatively distant from the (TiO2[Formula: see text]Ti) surface, preventing direct contact with the surface. Additionally, the signals corresponding to the unbound [Formula: see text]-NH2 group indicate that it is available for additional complexation. In vitro bioactivity of the Lys–TiO2[Formula: see text]Ti surface was achieved by developing an HA layer onto already functionalized TiO2[Formula: see text]Ti surfaces at various pH values. Spectroscopic data using the spectral markers of HA and Lys provided a decisive role in establishing the necessary baseline data for evidencing the intermolecular bonding. The functionalized TiO2[Formula: see text]Ti surface reactivity is linked to the specific intermolecular interactions of –COO− (pH 7.0) with Ca[Formula: see text] ions, as well as the –COOH (pH 2.0 and 12.0) groups of Lys, with the –OH groups of PO[Formula: see text] belonging to HA.