Characterization of the adsorption dynamics of trisodium citrate on gold in water solution

Molecular dynamics simulations (MDs) based on a reactive force field (ReaxFF) are carried out to investigate typical adsorption modes of trisodium citrate (CIT) on gold nanoparticles (AuNPs). All possible configurations of CIT on a model AuNP in solution are identified and the stabilizing role played by the adsorbate on the AuNP structure is disclosed by analyzing protonation state, dynamics and interactions of the molecules with the surrounding environment. A realistic scenario is created by sampling extensively the conformational space of citrate and by validating the simulation results against data extracted from the literature. Carboxyl moieties are found in contact with the gold substrate through one or both oxygens and Na+ ions are present in the adsorbed citrate layer. Citrate binding is relatively strong and its action as a chelator stabilizes surface reconstructions. The molecules have the tendency to self-assemble and form a stable cover, which is reinforced by adatoms. All the results are in perfect agreement with experimental observations and theoretical data.