Cysteine on gold: An ab-initio investigation

We present a first principles analysis of the adsorption of the amino acid cysteine on the Au(110) surface. We carry out density functional theory calculations using the repeated-slab supercell method to investigate the molecule-surface interaction. We investigate the adsorption for four different adsorption geometries: one upright configuration, in which the molecule binds to the surface solely via the deprotonized thiolate head group and three flat configurations, which form an additional bond via the amino side group. We analyze bonding energy, charge redistribution, and changes in the density of states. We find that a flat geometry with the Au-thiolate bond at an off-bridge site and the Au-amino bond close to the Au-top site is energetically favored. The electron redistributions exhibit the combined characteristics of the isolated bonds found in earlier studies, supporting the view of strongly localized interaction between the functional groups and the metal surface. The electrostatic nature of the Au-amino bond and the covalent character of the Au-thiolate bond are still visible in the adsorption of the complete molecule.