Clusters Of Gold Atoms Research Articles

Gold Chemistry Guided by the Isolobality Concept†

The general isolobality concept presented by Hoffmann, Stone, and Mingos in the early 1980s has had—tacitly or explicitly—a great impact on the development of many areas of inorganic, organometallic, and coordination chemistry. Pertinent considerations were fruitful especially in gold chemistry, because isolobal relations between gold(I) cations [Au]+ and their complexes [LAu]+ on the one hand and protons [H]+, various carbocations [R]+, and other simple species on the other are particularly obvious. Work guided by these relationships has included almost all fields of gold chemistry, from simple high-energy species in the gas phase to homoatomic clusters of gold atoms or heteroatomic aggregates with main-group and transition elements. Recent work has also concentrated on the specific mechanisms of reactions catalyzed either by protons or by the above gold cations with a variety of new ligands L in separate or tandem reaction sequences. The present review summarizes classical and current lines of research that have followed the original concept up to its present frontier version of “autogenic isolobality”.

Structural evolution study of 1−2 nm gold clusters

We have explored lowest energy minima structures of gold atom clusters both, charged and neutral (Au\hbox{$_{n}^{\nu}$}νn with n = 20, 28, 34, 38, 55, 75, 101, 146, 147, 192, 212 atoms and ν = 0, ±1). The structures have been obtained from first principles generalized gradient approximation, density functional theory (DFT) calculations based on norm-conserving pseudopotentials and numerical atomic basis sets. We have found two new disordered or defective isomers lower in energy than their ordered counterparts for n = 101, 147. The purpose of this work is to systematically study the difference between the electronic properties of the two lowest ordered and disordered isomers for each size. Our results agree with previous first principle calculations and with some recent experimental results (Au20 and Au101). For each case we report total energies, binding energies, ionization potentials, electron affinities, density of states, highest occupied molecular orbital-lowest unoccupied molecular orbital (HOMO-LUMO) gaps, Housdorff chirality measure index and their simulated image in a high resolution transmission electron microscopy (HRTEM). The calculated properties of the two low lying (ordered and disordered) isomers show clear differences as to be singled out in a suitable experimental setting. An extensive discussion on the evolution with size of the cohesive energy, the ionization potentials, the electron affinities, the HOMO-LUMO gaps and their index of chirality to determine the crossover between them is given.

Component-based approach for programming and running scientific applications on grids and clouds

This paper presents an approach to programming and running scientific applications on grid and cloud infrastructures based on two principles: the first one is to follow a component-based programming model, the second is to apply a flexible technology which allows for virtualization of the underlying infrastructure. The solutions described in this paper include high-level composition and deployment consisting of a scripting-based environment and a manager system based on an architecture description language (ADL), a dynamically managed pool of component containers, and interoperability with other component models such as Grid Component Model (GCM). We demonstrate how the proposed methodology can be implemented by combining the unique features of the Common Component Architecture (CCA) model together with the H2O resource sharing platform, resulting in the MOCCA component framework. Applications and tests include data mining using the Weka library, Monte Carlo simulation of the formation of clusters of gold atoms, as well as a set of synthetic benchmarks. The conclusion is that the component approach to scientific applications can be successfully applied to both grid and cloud infrastructures.

A first principles density functional investigation of ligand-protected eight atom gold nanoclusters

Based on first principles density functional calculations we have studied the effect of ligand attachment on eight atom gold clusters of two-dimensional (2D) and three-dimensional (3D) geometries. Recent experimental synthesis of this magic numbered cluster using glutathione [Muhammed et al., Nano Res. 1, 333 (2008)] has instigated this investigation. We have chosen ethyl mercaptan (CH3-CH2SH) as the ligand which is the simplified form of glutathione (HO2CCH2NHCOCH(NH2)-CH2CH2CONHCH(CO2H)-CH2SH). We have analyzed the energetics, sd-hybridization, density of states and charge density distributions of the bare and ligand-capped clusters. Our findings indicate that attachment of ethyl mercaptan ligands on eight atom gold clusters enhances the stability of planar 2D geometries over 3D like structure.

Polyaniline/Au Electrodes for Direct Methanol Fuel Cells

In this paper we demonstrate the use of polyaniline/gold modified electrodes that are to be used as the anode for direct methanol fuel cells (DMFC). The objective of this work was to enhance the performance and viability of DMFCs by developing a more efficient catalyst for the oxidation of methanol. Polyaniline films with angstrom scale atomic gold clusters were used as an electroactive catalyst. These gold clusters are significantly different than what is traditionally used as they are composed of only a handful of atoms (1–10 atoms) and have unique physical and chemical properties. The PANI/Au modified electrodes are a new and promising catalyst for direct methanol fuel cells and can replace existing commercial catalysts. In this study, we illustrate how atomic clusters of gold incorporated in the conducting polymer polyaniline enhanced the oxidation signal of methanol exhibited by cyclic voltammetry.

Gold Cluster Diffusion Kinetics on Stoichiometric and Reduced Surfaces of Rutile TiO2(110)

Gold clusters on rutile TiO2 are known to serve as efficient oxidation catalysts for pollutants and environmental contaminants. However, the mechanism by which highly mobile small clusters migrate and aggregate into larger species relevant to gold’s catalytic activity remains unresolved. We report herein on ab initio simulations of the diffusion of atomic gold clusters up to the trimer on rutile TiO2(110) surfaces. We show that, on the stoichiometric surface, both the dimer and the trimer can exhibit relatively low surface mobility due to high energetic barriers for diffusion out of their energetic minima coupled with low barriers for the reverse motion. On the reduced surface, these clusters can diffuse relatively quickly between energetic minima within the oxygen vacancy site due to the large degree of vibrational entropy in their transition states. Our computed diffusion times provide a point of comparison for future experiments and will aid in development of models of gold cluster island sintering.

Hybrid gold atomic cluster–cobalt oxide scaffolds for dual tandem electrocatalytic sensing of cysteine

Innovations in nanoelectrochemistry have opened a plethora of techniques for the preparation of nanometer sized electrochemical probes with tunable properties. Atomic clusters emerged at the crossroad of physics and chemistry has immense potential as novel “electron antennaes” in electrocatalysis. Herein, we report the electrochemical synthesis and the synergistic electrocatalytic effect of metal oxide supported gold atomic clusters for subnanomolar level sensing of cysteine. The developed gold atomic clusters and the hybrid materials were characterized by spectral, morphological and electrochemical methods. Comparative evaluation of the critical role of surfactants in stabilizing the hybrid material and the mechanistic aspects of support scaffolds has been discussed. Different complexing agents were sequentially screened in order to get the optimum electrolyte composition for developing a uniform, reproducible sensing film. The developed modified electrode exhibits highly reproducible wider calibration range of 10 −10 to 10 −6 M with lower detection limits of 1.6 × 10 −11 M for cysteine. To gain a greater understanding of such advantageous behavior achieved with this electrode, studies on electrode kinetics of charge-transfer processes were also done.

Collisions between a single gold atom and 13 atom gold clusters: an ab initio approach

Collision processes between a single gold atom and a gold cluster are investigated by means of ab initio techniques. The targets we consider are minimum energy 13 gold atom clusters. The kinetic energy of the projectile and its impact parameter are chosen within a range such that the three regimes we are mainly interested in studying (fusion, scattering and fragmentation) are realized. The results of the collision processes are treated using density functional theory molecular dynamics (DFT-MD), analyzed in detail, and compared with previous work, which was carried out using phenomenological potentials and classical molecular dynamics. The differences between classical MD and DFT-MD are quite significant.

Extended Hückel Tight-Binding Calculations of Electronic Resonances in Linear Chains of Gold Atoms and Clusters

Electronic excitations in linear chains and icosahedra clusters of gold atoms have been studied using an approximate version of time-dependent density functional theory based on the extended Hückel tight-binding method. The formation and development of two longitudinal collective resonances in the absorption spectra were studied as a function of the chain length. We show that in the case of a gold cluster dimer, the classical description breaks down at intercluster distances below 0.5 nm due to the neglect of important quantum effects. In addition, a blue shifting of the collective resonances at these distances is observed. Analysis of these results yields a general picture of electronic resonances in one-dimensional atomic structures.

One Step Synthesis of the Smallest Photoluminescent and Paramagnetic PVP-Protected Gold Atomic Clusters

Gold atomic clusters of only two and three atoms were prepared by a simple electrochemical technique based on the anodic dissolution of a gold electrode in the presence of PVP, and subsequent electroreduction of the Au-PVP complexes. These clusters show stable photoluminescent and magnetic properties, which make them the smallest and most elemental gold (0) building blocks in nature (after atoms) bringing new possibilities to construct novel nano/microstructures with large potential interest in biomedicine, catalysis, and so forth.

Aqueous-based synthesis of atomic gold clusters: Geometry and optical properties

Gold clusters synthesized by the solution-based growth technique have exhibited ultraviolet (UV) light emission with nearly zero Stokes shift. Atomic arrangement decided optical properties of the Au microclusters have been studied extensively. In addition to the time-of-flight mass spectra, the comparison of experimental and theoretical emission and absorption spectra confirms the presence of Au8 clusters with the planar hexagon+1-shaped geometry. The observed UV emission is attributed to the transition from the highest occupied to the lowest unoccupied molecular orbitals of the hexagon+1 structured Au8 clusters.

Aqueous CTAB‐Assisted Electrodeposition of Gold Atomic Clusters and Their Oxygen Reduction Electrocatalytic Activity in Acid Solutions

Gradual, yet a great leap: electrosynthesized surfactant-stabilized gold atomic clusters (AuACs; Au(n) , 5≤n≤13) electrocatalyze the oxygen reduction reaction (ORR) in acid solution at low overpotentials. Depending on the surfactant concentration, the ORR mechanism gradually transits from a direct four-electron to a two-electron pathway (see picture; SHE=standard hydrogen electrode), which suggests the transformation of atomic clusters into nanoparticles.

Aqueous CTAB‐Assisted Electrodeposition of Gold Atomic Clusters and Their Oxygen Reduction Electrocatalytic Activity in Acid Solutions

Aqueous CTAB‐Assisted Electrodeposition of Gold Atomic Clusters and Their Oxygen Reduction Electrocatalytic Activity in Acid Solutions

Synthesis and characterization of gold atomic clusters by the two-phase method

In this work we present a simple procedure for the production of gold atomic clusters by means of a modification of the Brust’s two-phase method, using tetrahexylammonium bromide as capping agent. The gold atomic clusters obtained have the following formula: Aun, with \(3 \leq \textit{n} \leq 13\), where n is the number of gold atoms per cluster. We report the formation of different species at different stages of the reduction reaction. Au clusters were characterized by TEM, MALDI-TOF mass spectrometry and UV-vis spectroscopy. Gold clusters are stable in solution after several years of preparation.

Cyanide leaching of Au/CeO2: highly active gold clusters for 1,3-butadiene hydrogenation

Ceria-supported gold catalysts before and after leaching by NaCN were investigated by X-ray absorption spectroscopy at the Au L(III) edge. After gold leaching, isolated gold cations remain in close interaction with the support. These ions form an ideal precursor to very small clusters of a few gold atoms upon reduction. The resulting gold clusters exhibit a very high intrinsic activity in the hydrogenation of 1,3-butadiene, which is at least one order of magnitude higher than that of the nanometre-sized gold particles in the non-leached parent catalyst. These findings point to a very strong structure sensitivity of the gold-catalyzed hydrogenation of dienes.

Synthesis of Atomic Gold Clusters with Strong Electrocatalytic Activities

Small atomic gold clusters in solution, Au n , stabilized by tetrabutyl ammonium bromide (TBABr), have been synthesized by a simple electrochemical technique, based on the anodic dissolution of a gold electrode in the presence of TBABr salt, and using acetronitrile as solvent. The presence of clusters in the range Au3-Au11 were detected by MALDI-TOF spectroscopy, and further characterized by UV-vis absorption spectroscopy, TEM, AFM, X-ray diffraction, and cyclic voltammetry. Clusters display a semiconductor behavior with a band edge of approximately 2.5 eV. We report here their extraordinarily high electrocatalytic activity toward the O2 reduction reaction in acid solutions, which can explain Zhang's results, showing that a four-electron mechanism seems to occur because of the facile reduction of H2O2 on gold clusters compared to bulk gold or larger gold nanoparticles.

Formation of high- and low-density clusters in a 1D system

The properties of monoatomic chains have been studied theoretically by means of statistical mechanics methods. The applied approach can be used to evaluate the interatomic distances and lifetimes of one-dimensional (1D) and quasi-1D systems. In particular, we show that the 1D clusters of gold atoms can exist in two states with different lattice parameters (∼3.6 and ∼2.8 Å) that can explain the whole variety of experimental observations on monoatomic gold chains without assuming any wire contamination.

Molecular characteristics and surface layer structure of poly(siloxane imides)

The effects of spontaneous ordering of molecular chains of poly(siloxane imide) block copolymers in the surface layers of thin films on glass and gold supports have been studied by the oblique polarized beam and photoelasticity methods. The effective thermodynamic rigidity of molecular chains of the block copolymers (the statistical segment length) has been found to be A = 10.4 × 10−7 cm. The orientational ordering of molecular chains in poly(siloxane imide) surface layers is characterized by small values of the orientational order parameter (S 0 ∼ 0.007). This finding is explained by the microphase separation of the block copolymers. The evaporated gold layer contributes to the effect of surface birefringence owing to formation of the ordered system composed of islets—clusters of gold atoms.

Etching Colloidal Gold Nanocrystals with Hyperbranched and Multivalent Polymers: A New Route to Fluorescent and Water-Soluble Atomic Clusters

We report a novel ligand-induced etching process in which hyperbranched and multivalent coordinating polymers such as polyethylenimine (PEI) react with preformed gold nanocrystals to form atomic gold clusters that are soluble in water and are highly fluorescent upon UV light excitation. These “as-prepared” fluorescent clusters appear to be in an oxidized electronic state, with their excitation and emission maxima located at 421 and 505 nm, respectively. Upon treatment by strong reducing agents such as NaBH4, the cluster's excitation and emission peaks are shifted to 353 and 445 nm. Electrospray ionization (ESI) mass spectrometry data indicate that the light-emitting species are small atomic nanoclusters consisting of only 8 gold atoms (Au8). There is also evidence to suggest that a ligand-to-metal electronic transition in the ultraviolet is superimposed on the cluster absorption spectra, but it is not directly related to the intrinsic fluorescent properties of these atomic clusters. These surprising resul...

Immobilisation of proteins by atomic clusters on surfaces

In this Opinion article, we describe a nanotechnology-based approach to immobilize and orient proteins onto surfaces using atomic clusters prepared by physical methods. This is relevant to future protein biochips where dilute arrays of protein binding sites, each designed to immobilize no more than one protein molecule, would be ideal. In the case of a surface consisting of size-selected atomic gold clusters, proteins containing free cysteine residues can chemisorb directly to the bare cluster surface, thus effecting oriented immobilisation. The selection of atomic gold clusters in the size range 1-100 atoms (<3nm in diameter) is intended to ensure that, typically, only one protein can bind directly to the cluster surface. These nanoclusters of a smaller size scale than that of the protein present minimal contact between the gold and the protein, and hence imply a reduced risk of protein denaturing compared with gold films or extended surfaces.