Abstract
Atomically precise metal nanoclusters, stabilized and functionalized by organic ligands, are emerging nanomaterials with potential applications in plasmonics, nano-electronics, bio-imaging, nanocatalysis, and as therapeutic agents or drug carriers in nanomedicine. The ligand layer has an important role in modifying the physico-chemical properties of the clusters and in defining the interactions between the clusters and the environment. While this role is well recognized from a great deal of experimental studies, there is very little theoretical information on dynamical processes within the layer itself. Here, we have performed extensive molecular dynamics simulations, with forces calculated from the density functional theory, to investigate thermal stability and dynamics of the ligand layer of the meta-mercaptobenzoic acid (m-MBA) protected Au68 and Au144 nanoclusters, which are the first two gold nanoclusters structurally solved to atomic precision by electron microscopy [Azubel et al., Science, 2014, 345, 909 and ACS Nano, 2017, 11, 11866]. We visualize and analyze dynamics of three distinct non-covalent interactions, viz., ligand-ligand hydrogen bonding, metal-ligand O[double bond, length as m-dash]C-OHAu interaction, and metal-ligand Ph(π)Au interaction. We discuss their relevance for defining, at the same time, the dynamic stability and reactivity of the cluster. These interactions promote the possibility of ligand addition reactions for bio-functionalization or allow the protected cluster to act as a catalyst where active sites are dynamically accessible inside the ligand layer.
Highlights
Precise metal nanoclusters, stabilized and functionalized by organic ligands, are emerging nanomaterials with potential applications in plasmonics, nano-electronics, bio-imaging, nanocatalysis, and as therapeutic agents or drug carriers in nanomedicine
It is well-recognized that the ligand layer plays a very important role in the synthesis, forming the protective layer stopping the growth of the nucleating metal core, and modifying the physico-chemical properties of the gold core and the whole Monolayer protected clusters (MPCs).[3]
The PhCOOH moieties were added to the structure after the S positions were determined satisfactorily. In this density functional theory (DFT) study, we consider the two cluster systems with true ligands (m-MBA) and with all atoms free to move in order to optimize the structure
Summary
Precise metal nanoclusters, stabilized and functionalized by organic ligands, are emerging nanomaterials with potential applications in plasmonics, nano-electronics, bio-imaging, nanocatalysis, and as therapeutic agents or drug carriers in nanomedicine. We visualize and analyze dynamics of three distinct non-covalent interactions, viz., ligand–ligand hydrogen bonding, metal–ligand OvC–OH⋯Au interaction, and metal–ligand Ph(π)⋯Au interaction We discuss their relevance for defining, at the same time, the dynamic stability and reactivity of the cluster. Monolayer protected clusters (MPCs) are atomically precise metal nanoparticles with well-defined mass and chemical composition They have a hybrid structure consisting of a tightly packed core of diameter roughly 1–3 nm (from ten to few hundred metal atoms) that is stabilized by a covalently bound molecular layer consisting of ligand molecules. It is clear that understanding of the interactions within the ligand layer becomes crucial for controlling the MPCs’ properties for various applications
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