Simulation of the interface between titanium oxide and amino acids in solution by first principles MD

The adsorption of glycine, methionine, serine, and cysteine on partially hydroxylated rutile (1 0 0) and (1 1 0) surfaces was simulated by first principles molecular dynamics. Perfect surfaces and well known defects such as oxygen vacancies and facets were modelled. In most runs the simulation cell was filled with H2O molecules up to standard density. Binding of the carboxyl groups to the surface through hydrogen bonds and Ti-O interaction is weak in all cases. The adsorbate-substrate interactions do not seem to be significantly stronger than adsorbate-adsorbate hydrogen bonds. The NH3+ -group of the zwitterion showed only weak interaction with the surface oxygen atoms and rotated around its figure axis. More stable configurations are attained by ester condensation of the carboxyl group and a basic surface hydroxyl group and by the formation of a bond between a deprotonated hydroxyl or thiol group of serine or cysteine, respectively, and a surface Ti. Calculations suggest that these groups bind to the perfect surface rather than inserting into oxygen vacancies. (C) 2003 Elsevier Science B.V. All rights reserved.