Adsorption modes of cysteine on Au(111): Thiolate, amino-thiolate, disulfide

The adsorption of cysteine on the (111) surface of gold was studied by means of periodic supercell density-functional theory calculations. A number of different adsorption modes were examined, including adsorption through the thiol group in either thiolate or disulfide form and adsorption through both the thiol and amino functional groups. It was found that at intermediate coverage densities the latter mode of adsorption was favored, followed by thiolate adsorption at the bridge site. The N-Au and S-Au bond strengths in the amino-thiolate adsorption were estimated to be of the order of 6 and 47 kcal/mol, respectively.