Solvation of gold nanoparticles passivated with functionalized alkylthiols: A molecular dynamics study

Molecular dynamics simulations of gold nanoparticles (NPs) passivated with end-group functionalized alkylthiols, namely CH3, NH2, or COOH in solvents of varying degrees of repulsion-dispersion and electrostatic interactions ranging from strongly polar SPC/E water to modified hybrid water models (H1.56 and H3.00), where the Lennard-Jones contribution to the potential energy is enhanced relative to SPC/E to completely non-polar, decane, are performed. The effects due to solvent reorganization around the NP as a function of the ligand and solvent chemistry are monitored using the NP-solvent pair correlation functions and tetrahedral order parameter. The solvent penetration inside the ligand shell is maximum for decane, indicating better solute–solvent interaction in decane as compared to other solvents. The COOH end-group functionalized NP is observed to break the tetrahedral structure of water molecules more as compared to other NPs used in this study. Radial density profiles and radius of gyration values show significant stretching of the ligands in decane than in the model waters, which is also consistent with the ligand asymmetry parameter. The ligand shell anisotropy for all NPs is maximum in SPC/E water and minimum in decane. The isotropic potential of mean force between two identical end-group functionalized NPs show attractive well depth in vacuum, SPC/E water, and H3.00 modified hybrid water. The implications for self-assembly of passivated gold NPs from aqueous dispersions as well as the dependence of calculated quantities on ligand and solvent chemistry are highlighted.