Bonding properties of thiolate-protected gold nanoclusters and structural analogs from X-ray absorption spectroscopy

Abstract

Abstract:Subnanometer, atomically precise thiolateprotected gold nanoclusters represent an important advancement in our understanding of thiolate-protected gold nanoparticles and thiolate-gold chemistry. Aside from being a link between larger gold nanoparticles and small gold complexes, gold nanoclusters exhibit extraordinary molecule-like optical, electronic, and physicochemical properties that are promising for next-generation imaging agents, sensing devices, or catalysts. The success in elucidating a number of unique thiolate-gold surface and gold core structures has greatly improved our understanding of thiolate-gold nanoclusters. Nevertheless, monitoring the structural and electronic behavior of thiolate-protected gold nanoclusters in a variety of media or environments is crucial for the next step in advancing this class of nanomaterials. Not to mention, there are a number of thiolateprotected gold nanoclusters with unknown structures or compositions that could reveal important insights on application-based properties such as luminescence or catalytic activity. This review summarizes some of the recent contributions from X-ray absorption spectroscopy (XAS) studies on the intriguing bonding properties of thiolate-protected gold nanoclusters and some structural analogs. Advantages from XAS include a local structural, site-and elementspecific analysis, suitable for ultra-small particle sizes (1-2 nm), along with versatile experimental conditions.

A Segregated, Partially Oxidized, and Compact Ag10 Cluster within an Encapsulating DNA Host

“…The intensity of this transition inversely varies with the occupancy of the valence states and was analyzed in relation to bulk silver metal (Ag 0 ) and the ionic salt silver acetate (Ag + ) references. 36 The area under the white-line transition was integrated from ±3 eV of the absorption edge and compared with the two reference materials. Linearly interpolating the integrated area from the spectrum of the cluster gave ~35% Ag 0 and ~65% Ag + .…”

“…Two, X-ray absorption spectroscopy studies revealed the cluster oxidation state and fundamental bonding interactions in the cluster/DNA complexes in the native aqueous environment. 36 The Ag L 3 -edge X-ray absorption near-edge spectra gauged the cluster charge via the occupancy of the valence electronic states of silver. The extended X-ray absorption fine-structure region of the Ag K-edge spectra revealed three scattering paths, and these were ascribed to silver-nucleobase and two types of silver–silver interactions.…”

NIR‐Emitting Gold Nanoclusters–Modified Gelatin Nanoparticles as a Bioimaging Agent in Tissue

“…By virtue to the electron‐donating groups in gelatin, Au (I) as an intermediate reduced state of gold has been produced, with a further reduction to Au (0). The aggregation of Au (0) results in the formation of a metal core with Au (I) on the surface as the nanoclusters' shell as a typical structure described in literature . After 24 h of reaction, all Au (III) has been totally reduced to Au (I) and Au (0) (Figure a).…”

“…From the knowledge gained throughout the characterization of the different AuNCs' optical properties and XPS studies introduced in this research work, accompanied with knowledge from literature about the general structure of gold nanoclusters, simplified models for the nanoclusters have been proposed, as shown in Figure c. Aug, where nanoclusters are produced only using gelatin, is considered the parent formulation that is further modified to other formulations with different properties.…”

“…They are composed of several up to tens of gold atoms, giving rise to ultrasmall sized structures of less than 2 nm . Due to their small size, they demonstrate molecule‐like properties having discrete valence electronic states approaching the molecular orbitals . They do not exhibit plasmon resonance as in case of larger gold nanoparticles but rather show fluorescence in the visible or the near‐infrared (NIR) region .…”