Interaction between organic molecules and a gold nanoparticle: a quantum chemical topological analysis

Abstract

The ligands at the surface of a gold nanoparticle (GNP) have a significant influence on the optical and physical properties, that may render different functionalities to the GNP. Therefore, there is a need in understanding the nature of the interaction at atomic resolution in order to allow rational design of GNPs with desired physico-chemical properties. The interaction between Au$_{79}$ and a series of small organic molecules has been systematically studied at the quantum mechanical level : methane, methanol, formic acid, hydrogen sulfide, benzene, and ammonia. The reactivity of Au$_{79}$ has been first analyzed by performing the condensed Fukui analysis to emphasize that the surface of Au$_{79}$ is dominated by electrophilic sites, with higher reactivity at the corner and edge atoms. The net charge transfer flowing from the organic molecules toward Au$_{79}$ comes from the electrophilic behavior of the GNP. Furthermore, the shape of the frontier molecular orbitals of Au$_{79}$ and of the incoming organic molecules has been found to dictate the preferred orientation of the adsorption. Several quantum chemical topological analyses of the electron density have been performed to further classify the interactions to weak dispersive or van der Waals interactions in methane and stronger non-covalent interactions in ammonia, benzene, hydrogen sulfide, methanol, and formic acid. The analysis of the electron localization function (ELF), on the other hand, provides more insight about the charge transfer, as the population of the basins of the organic molecules has decreased after interacting with Au$_{79}$.