Ligand effects on the structure and vibrational properties of the thiolated Au18 cluster

Most of the studies devoted to thiolated gold clusters suppose that their core and Au-S framework do not suffer from distortion independently of the protecting ligands (-SR) and it is assumed as correct to simplify the ligand as SCH3. In this work is delivered a systematic study of the structure and vibrational properties (IR and Raman) of the Au18(SR)14 cluster. The pursued goal is to understand the dependency of the displayed vibrational properties of the thiolated Au18 cluster with the ligands type. A set of six ligands was considered during calculations of the vibrational properties based on density functional theory (DFT) and in its dispersioncorrected approach (DFT-D)

Ligand effects on the optical and chiroptical properties of the thiolated Au18cluster

The effect of chiral and achiral ligands protecting the inner Au9 core of the Au18(SR)14 cluster is studied based on density functional theory (DFT) and its corrected long-range interaction (DFT-D) approach. It was found that the electronic properties (energy levels) depend on the specific ligands, which induce distinct distortions on the Au–S framework. However, the substitution of S-c-C6H11 as SCH3 ligands may be considered to be correct given the obtained resemblance to the displayed bonding, optical and chiroptical properties. A further comparison of the CD and UV spectra displayed by the Au18 cluster protected by chiral and achiral ligands attests that more intense profiles are featured by ligands including phenyl rings and/or oxygen atoms such that the Au18 cluster protected by either achiral metamercaptobenzoic acid (m-MBA) or achiral SPh ligands displays more intense UV and CD signals. These results provide new insight into the effect of ligands on thiolated gold clusters

On the structure of the Au18(SR)14 cluster

First principles calculations are used for a systematic search of the lowest-energy (most-stable) structure of the recently synthesized Au18(SR)14 cluster. A comparison of the calculated optical absorption and electronic circular dichroism spectra, which are highly sensitive to the cluster structure and chirality, with the experimental spectra of the glutathione-protected gold cluster, Au18(SG)14, is used to discriminate between low-energy isomers of the Au18(SR)14 (R = CH3) cluster. From the good agreement between calculated and measured spectra, it is predicted that the structure of the Au18(SR)14 cluster consists of a prolate Au8 core covered with two dimer (SR–Au–SR–Au–SR) and two trimer (SR–Au–SR–Au–SR–Au–SR) motifs. These results provide additional evidence on the existence of longer trimer motifs as protecting units of small thiolated gold clusters.

Following the creation of active gold nanocatalysts from phosphine-stabilized molecular clusters

The phosphine-stabilised gold cluster [Au6(Ph2P-o-tolyl)6](NO3)2 is converted into an active nanocatalyst for the oxidation of benzyl alcohol through low-temperature peroxide-assisted removal of the phosphines, avoiding the high-temperature calcination process. The process was monitored using in-situ X-ray absorption spectroscopy, which revealed that after a certain period of the reaction with tertiary butyl hydrogen peroxide, the phosphine ligands are removed to form nanoparticles of gold which matches with the induction period seen in the catalytic reaction. Density functional theory calculations show that the energies required to remove the ligands from the [Au6Ln]2+ increase significantly with successive removal steps, suggesting that the process does not occur at once but sequentially. The calculations also reveal that ligand removal is accompanied by dramatic re-arrangements in the topology of the cluster core.

Benchmarking Density Functional Based Tight-Binding for Silver and Gold Materials: From Small Clusters to Bulk

International audience

The Gold Coast marine precinct : pre-packaging entrepreneurship

We investigate the evolving quality of entrepreneurship in the Gold Coast Marine Precinct, a purpose-built industrial district in Southeast Queensland, Australia. Our findings are that the environment in the Precinct can be conducive to a better quality of entrepreneurship than may be feasible for firms in other settings; that a successful industrial district can be created artificially, with appropriate social relationships evolving afterwards; and that improvements in information and communications technology have undermined some aspects of traditional behaviour in the Precinct, but the essential nature of internal relationships remains intact.

Exploiting the facile oxidation of evaporated gold films to drive electroless silver deposition for the creation of bimetallic Au/Ag surfaces

Gold is often considered as an inert material but it has been unequivocally demonstrated that it possesses unique electronic, optical, catalytic and electrocatalytic properties when in a nanostructured form.[1] For the latter the electrochemical behaviour of gold in aqueous media has been widely studied on a plethora of gold samples, including bulk polycrystalline and single-crystal electrodes, nanoparticles, evaporated films as well as electrodeposited nanostructures, particles and thin films.[1b, 2] It is now well-established that the electrochemical behaviour of gold is not as simple as an extended double-layer charging region followed by a monolayer oxide-formation/-removal process. In fact the so-called double-layer region of gold is significantly more complicated and has been investigated with a variety of electrochemical and surface science techniques. Burke and others[3] have demonstrated that significant processes due to the oxidation of low lattice stabilised atoms or clusters of atoms occur in this region at thermally and electrochemically treated electrodes which were confirmed later by Bond[4] to be Faradaic in nature via large-amplitude Fourier transformed ac voltammetric experiments. Supporting evidence for the oxidation of gold in the double-layer region was provided by Bard,[5] who used a surface interrogation mode of scanning electrochemical microscopy to quantify the extent of this process that forms incipient oxides on the surface. These were estimated to be as high as 20% of a monolayer. This correlated with contact electrode resistance measurements,[6] capacitance measurements[7] and also electroreflection techniques...

Small-angle x-ray scattering study of the aggregation of gold nanoparticles during formation at the toluene-water interface

We report the results of an in situ small-angle x-ray scattering (SAXS) study of the aggregation of gold nanoparticles formed by an interfacial reaction at the toluene-water interface. The SAXS data provide a direct evidence for aggregate formation of nanoparticles having 1.3 nm gold core and an organic shell that gives a core-core separation of about 2.5 nm. Furthermore, the nanoparticles do not occupy all the cites of 13-member cluster. This occupancy decreases with reaction time and indicate reorganization of the clusters that generates planner disklike structures. A gradual increase in fractal dimension from 1.82 to 2.05 also indicate compactification of cluster aggregation with reaction time, the final exponent being close to 2 expected for disklike aggregates.

The fragmentation of gold nanoparticles induced by small biomolecules

Spherical gold nanoparticles (3-5 nm) undergo a surprising fragmentation without extra energy imput and are converted into ultrasmall particles (less than 1.5 nm), which is a direct result of electron transfer between gold nanoparticles and cysteine.

Green synthesis of 1-2 nm gold nanoparticles stabilized by amine-terminated ionic liquid and their electrocatalytic activity in oxygen reduction

Stable gold nanoparticles with average size 1.7 nm synthesized by an amine-terminated ionic liquid showed enhanced electrocatalytic activity and high stability.

Sensitive detection of cysteine based on fluorescent silver clusters

In this work,we report the application of novel, water-soluble fluorescent Ag clusters in fluorescent sensors for detecting cysteine, an important biological analyte. The fluorescence of poly(methacrylic acid) (PMAA)templated Ag clusters was found to be quenched effectively by cysteine, but not when the other alpha-amino acids were present. By virtue of the specific response, a new, simple, and sensitive fluorescent method for detecting cysteine has been developed based on Ag clusters. The present assay allows for the selective determination of cysteine in the range of 2.5 x 10(-8) to 6.0 x 10(-6) M with a detection limit of 20 nM at a signal-to-noise ratio of 3. Based on the absorption and fluorescence studies, we suggested that cysteine quenched the emission by the thiol-adsorption-accelerated oxidation of the emissive Ag clusters. The present study shows a promising step toward the application of silver clusters, a new class of attractive fluorescence probes.

Spontaneous formation of two-dimensional gold networks at the air-water interface and their application in surface-enhanced Raman scattering (SERS)

Two-dimensional (2-D) gold networks were spontaneously formed at the air-water interface after HAuCl4 reacted with fructose at 90 degrees C in a sealed vessel, in a reaction in which fructose acted as both a reducing and a protecting agent. Through fine-tuning of the molar ratio of HAuCl4 to fructose, the thus-formed 2-D gold networks can be changed from a coalesced pattern to an interconnected pattern. In the coalesced pattern, some well-defined single-crystalline gold plates at the micrometer-scale could be seen, while in the interconnected pattern, many sub-micrometer particles and some irregular gold plates instead of well-defined gold plates appeared. It is also found that the 2-D gold networks in the form of an interconnected pattern can be used as substrates for surface-enhanced Raman scattering (SERS) because of the strong localized electromagnetic field produced by the gaps between the neighboring particles in the 2-D gold networks.

A method to construct polyelectrolyte multilayers film containing gold nanoparticles

Gold nanoparticles in polyelectrolyte multilayers film can be easily prepared by repeating immersion of a substrate in poly(diallyl dimethylammonium) chloride (PDDA)-AuCl4- complexes solution followed by reduction Au3+ through heating. UV-vis spectroscopy, cyclic voltammetry (CV) and tapping-mode atomic force microscopy (AFM) are used to confirm the successful construction of the polyelectrolyte multilayers film and the formation of gold nanoparticles. The multilayers film shows electrocatalytic activity to dioxygen reduction.

One-step synthesis of gold-polyaniline core-shell particles

A one-step method has been developed for synthesizing gold-polyaniline (Au@PANI) core-shell particles by using chlorauric acid (HAuCl4) to oxidize aniline in the presence of acetic acid and Tween 40 at room temperature. SEM images indicated that the resulting core-shell particles were composed of submicrometre-scale Au particles and PANI shells with an average thickness of 25 nm. Furthermore, a possible mechanism concerning the growth of Au@PANI particles was also proposed based on the results of control experiments.

Size-dependent phase transfer of gold nanoparticles from water into toluene by tetraoctylammonium cations: A wholly electrostatic interaction

In this study, it is demonstrated that the tetraoctylammonium cation can be used directly as a phase-transfer reagent of negatively charged water-based gold nanoparticles. The transference is size-dependent and is based on a wholly electrostatic interaction.