Sequence order controls silver(I) coordination in aqueous His–Met–Pro tripeptide–nitrate mixtures: an ab initio molecular dynamics study

Silver–peptide interactions underpin peptide-directed synthesis of silver nanomaterials and the silver-resistance machinery of bacteria, yet the molecular-level speciation of Ag(I) in the presence of short peptides and nitrate remains poorly resolved. Here we report 100-ps ab initio molecular dynamics simulations of three sequence isomers of the tripeptide His–Met–Pro (HMP, HPM and PHM; 220 atoms each) in water, with four Ag(I) ions, four nitrate anions and 32 water molecules at 298 K, using the PBE–PAW description (VASP 6.1.0, 500 eV plane-wave cutoff, Γ-point sampling). In all three systems silver remains mononuclear, with average coordination numbers of 2.6–2.9 and only transient Ag–Ag contacts (present in 2–9% of frames at a 3.2 Å cutoff). The composition of the coordination shell is strongly sequence-dependent: His–Met–Pro is dominated by the His imidazole nitrogen (0.48 contacts per Ag) and nitrate oxygen (0.57), whereas His–Pro–Met is dominated by the Met thioether sulfur (0.73) with nitrate largely excluded (0.16); Pro–His–Met shows an intermediate, mixed N/S/nitrate shell and the largest peptide conformational rearrangement (heavy-atom RMSD 6.1 Å, radius of gyration 5.8 Å). Nitrate and water exchange on ∼0.2–1 ps timescales, while peptide N/S donors remain bound for several to tens of picoseconds. These results demonstrate that, at fixed composition, sequence order controls which donors are presented to Ag(I) and therefore the speciation from which silver nanomaterials nucleate.