Nucleation of platinum clusters on biopolymers: a first principles study of the molecular mechanisms

The heterogeneous nucleation of platinum clusters on DNA and proteins is investigated by means of first principles molecular dynamics simulations. We find that a Pt dimer forms from a Pt(II) complex covalently bound to a biopolymer and a free Pt(II) complex after a single reduction step. A water ligand detaches from one of the Pt complexes immediately after the formation of the Pt-Pt bond, which is significantly strengthened as a result. Remarkably, this reaction step is only possible in the presence of strong donor ligands such as purine DNA bases or histidine amino acids, and appears to be forbidden in the corresponding homogeneous dimer formation reaction, which leads to a weaker Pt-Pt bond. Moreover, due to the presence of delocalized electronic states on the heterocyclic ligands, Pt atoms or dimers bound to biopolymers accept reducing electrons more easily than free complexes or dimers. This can explain why noble metal clusters are observed to grow purely heterogeneously on DNA molecules and selectively on histidine amino acids of protein templates in carefully accomplished metallization experiments.