An in situ infrared spectroscopic study of glutamic acid and of aspartic acid adsorbed on TiO2:: Implications for the biocompatibility of titanium

In situ AIR-IR spectroscopy has been applied to the study of glutamic (Glu) and aspartic (Asp) acid adsorbed on amorphous TiO2 particle films. Unlike Asp, which gives evidence of one major adsorbed species, Glu yields several spectroscopically distinct structures upon adsorption to TiO2. The pH dependence of Glu and Asp adsorption is also different, with Glu adsorbing markedly to TiO2 at pH where electrostatic interactions between the surface and adsorbate are unfavorable. Application of the Langmuir model to adsorption isotherms yields a single binding constant for Asp and two binding constants for Glu, further supporting the evidence for different adsorbed Glu species. This is the first investigation of the molecular structure of Glu and Asp species adsorbed on amorphous TiO2 using in situ ATR-IR spectroscopy. (C) 2000 Academic Press.