A computational study of thiol-containing cysteine amino acid binding to Au and Au gold clusters.

Density functional theory (DFT) calculations are employed to examine the adsorption behaviors of cysteine on the gold surface using Au and Au species as model reactants. Computed results show that cysteine molecules prefer to bind with gold clusters via the S-atom of the thiol group in vacuum and thiolate group in water. The gas-phase adsorption energies are around 20.2 kcal/mol for Au and 24.4 kcal/mol for Au. In water environment, such values are slightly reduced for Au (19.6 kcal/mol), but increased a little more for Au (25.6 kcal/mol). As a result, if a visible light with a frequency of ν ≈ 6 × 10 Hz (500 nm) is applied, the time for the recovery of Au and Au from the most stable complexes will be about 0.38 and 9.3 × 10 s, respectively, at 298 K in water. The Au is in addition found to benefit from a larger change of energy gap that could be converted to an electrical signal for detection of cysteine.