The effect of temperature and ligand structure on the solubility of gold nanoparticles

Abstract

In order to investigate the effect of ligands structure, and temperature on the solubility of the smallest crystallographic gold nanoparticle, Au18S14, quantum mechanical calculations, and molecular dynamics simulations have been performed. Ligands including 2-dimethyl amino Ethan thiol, 4-mercapto benzoic acid, and 3-mercapto-propionic acid have been used to study the effect of ligand type and temperature, and 4-mercapto butyric acid and 5-sulfanyl pentanoic acid ligands have been used in comparison to the 3-mercapto-propionic acid ligand to study the effect of carbon-chain length differences. Furthermore, three different temperatures: 290, 300, and 310 kelvin have been used to study the effect of temperature. The optimized structures of nanoparticles, electronic band-gap, light absorption, dipole moment values, and hardness were obtained using quantum mechanical methods. Further, hydrogen bond number, root mean squared displacement, the moment of inertia, radial distribution functions, mean square displacement, and solvent accessible surface area parameters were studied by molecular dynamic simulation methods. All quantum mechanics analyses indicated that functionalization improves the nanoparticle’s electronic features, solubility, and stability. The studies which have performed with the molecular dynamics simulations indicated that increasing the temperature leads to form more hydrogen bonds between gold nanoparticles and water, making them more soluble. Also, the structures with a longer carbon chain of ligands have stronger interactions with solvent but their mobility in the water can be decreased. From all data of this work, it can be concluded that the 4-mercapto benzoic acid is the ligand that makes more solubility and stability for the mentioned gold nanoparticle.