Gold Atoms Research Articles

Engineering Single‐Atom Catalysts on Conjugated Porphyrin Polymer Photocatalysts via E‐Waste for Sustainable Photocatalysis

AbstractThis study presents a surface engineering strategy utilizing electronic waste (e‐waste) to incorporate single‐atom catalysts on conjugated polymers. Employing a conjugated porphyrin polymeric photocatalyst, gold single‐atom‐site catalysts are successfully introduced using the acidic metal leachates from e‐waste, where metal speciation and composition are regulated during the metal loading processes. The resulting photocatalyst with gold single atoms demonstrates a remarkable hydrogen peroxide (H2O2) selectivity of up to 97.56%, yielding a pure H2O2 solution at 73.3 µm h−1 under white LED illumination. The produced H2O2 is activated to •OH radicals on the same polymer with mixed gold and iron atoms, enabling a photo‐Fenton reaction and the complete degradation of toxic microcystin‐LR within 10 min under visible light. This study highlights the universal applicability of the metal mining strategy in various photoreactions. It is believed that this discovery pioneers sustainable photocatalysis, allowing the tuning of reactivity and selectivity on photocatalytic surfaces using metal waste.

Development of a sensitive ds-DNA/Au NPs/ PGE biosensor for determination of Buprenorphine using electrochemical and molecular dynamic simulation investigation

A sensitive electrochemical DNA biosensor has been developed for the detection of Buprenorphine (Bu), a narcotic pain reliever. To achieve this, double-stranded DNA (ds-DNA) was immobilized on a pencil graphite electrode that was modified with gold nanoparticles (Au NPs/PGE). The gold nanoparticles enhanced the performance of the DNA biosensor. The constructed ds-DNA/Au NPs/ PGE exhibited a linear detection range spanning from 0.05 to 100 μM with an impressive detection limit of 20 nM for Bu detection. Additionally, the DNA biosensor demonstrated good response in real samples evaluations. Finally, the interaction between carbon and gold atoms with DNA was confirmed through molecular dynamics simulation, while the interaction between DNA and the Bu drug was confirmed through molecular docking method. In conclusion, the electrochemical DNA biosensor presented in this study demonstrates exceptional sensitivity and reliability in the detection of buprenorphine. The incorporation of gold nanoparticles, as well as the use of molecular dynamics simulations and docking methods, contributes to a comprehensive understanding of the interactions involved in this detection process.

Gold in Chalcogenide Square Planar Complexes is Electron Richer than is Commonly Considered: Other Cases of Inverted Ligand Field

Electron distribution and bonding in extended structures based on square planar gold complexes, traditionally classified as gold (III), have been addressed through solid‐state DFT calculations. The band structure analysis, taken as a diagnostic tool, highlighted that, when the metal is associated with chalcogen atoms, the gold centers are more electron rich than the classic accepted description. This is in agreement with the Inverted Ligand Field (ILF) theory that predicts a metal center d10 configuration with two electrons vacancy on the orbital combinations of the ligands for sulfur, selenium and tellurium cases. A covalent bond is featured in oxygen compounds, a borderline situation between the ILF and the classical Ligand Field description. In conclusion, the gold atom in chalcogenide square planar complexes should be considered electron richer than commonly thought applying the traditional rules for calculating the oxidation state.

Single active Au1O5 clusters for metabolism-inspired sepsis management through immune regulation

Artificial enzymes with reprogrammed and augmented catalytic activities hold significant potential in biomedicine. However, common issues with biocatalysts are the presence of numerous inactive site atoms, leading to inefficiencies in their catalytic processes. To leverage the full potential of active catalytic sites, we aim to minimize the biocatalyst structure, transitioning from nanoparticles or polymetallic atomic clusters down to singular-active-unit molecules. In this context, we have developed a unique single active-site cluster molecule, Au1-O5-Na9-(OH)4 (AuO) clusters, comprising a single gold atom, five oxygen atoms, and a protective layer, where Au-O acts as a singular-active site displaying elevated catalytic activities without inefficiencies associated with biocatalytic reactions. AuO clusters demonstrate activities reminiscent of nicotinamide adenine dinucleotide oxidase (NOX), glutathione peroxidase (GPx), and urease, among other oxidoreductase functions, through optimal utilization of atoms. Clusters are instrumental in enhancing the redox balance, mitigating inflammation, and averting inflammation-induced cellular apoptosis, thereby preserving immune balance in sepsis. These mechanisms are crucial in sepsis pathogenesis. Demonstrating GPx-like and NOX-like capabilities, the AuO clusters have shown remarkable effectiveness against lipopolysaccharide-induced and cecum ligation puncture-induced multiorgan damage, underscoring their substantial promise for sepsis management.

On the Ionization Energy of the Atomic Gold Ion Au2+

On the Ionization Energy of the Atomic Gold Ion Au2+

Surface gold atoms determine peroxidase mimic activity in gold alloy nanoparticles.

The development of peroxidase mimic nanocatalysts is relevant for oxidation reactions in biosensing, environmental monitoring and green chemical processes. Several nanomaterials have been proposed as peroxidase mimic, the majority of which consists of noble metals and oxide nanoparticles (NPs). Yet, there is still limited information about how the change in the composition influences their catalytic activity. Here, the peroxidase mimic behaviour of gold NPs is compared to a traditional nanoalloy as Au-Ag and to the Au-Fe and the Au-Co nanoalloys, which were not tested before as oxidation catalysis. Since the alloys of gold with iron and cobalt are thermodynamically unstable, laser ablation in liquid (LAL) is exploited for the synthesis of these NPs. Using LAL, no chemical stabilizers or capping agents are present on the NPs surface, allowing the evaluation of the oxidation behaviour as a function of the alloy composition. The results point to the importance of surface gold atoms in the catalytic process, but also indicate the possibility of obtaining active nanocatalysts with a lower content of Au by alloying it with iron, which is earth-abundant, non-toxic and low cost. Overall, Au nanoalloys are worth consideration as a more sustainable alternative to pure Au nanocatalysts for oxidation reactions.

Atomic-level into the microscopic mechanism of gold capture by FeS during gold collection in matte process

Understanding the microscopic mechanisms involved in gold capture by FeS at the atomic level is crucial for optimizing the matte process and improving the gold recovery from gold concentrate containing arsenic and antimony. Herein, the DFT method was employed to explore the adsorption structure and electronic characteristics of a gold (Au) atom on the FeS surface. Furthermore, the effects of Fe/S vacancy and As/Sb dopant on Au adsorption were also investigated. The results reveal that the FeS(100) with S termination exhibits the smallest surface energy (0.56 J/m2) and possesses the highest stability amongst the low-index surfaces. Furthermore, the Au atom exhibits a preference for adsorption on the Fe-bridge site of FeS(100) through chemisorption due to the formation of a strong Au-Fe metallic bond, large adsorption energy (−5.40 eV), and small adsorption distance. Moreover, the presence of S vacancy enhances the Au capture capability of FeS(100) with an adsorption energy of −6.35 eV, while the Fe vacancy slightly weakens it. Additionally, the doping of As and Sb enhances the adsorption of Au atoms on FeS(100), and the Sb doping showcases a more distinct enhancement in Au capture efficiency. The findings of this work contribute to the advancement of matte processing technology, enabling enhanced gold recovery and potentially opening new avenues for the treatment of refractory gold ores.

Self-assembled oligomeric structures of an asymmetric molecular linker; 4-isocyanophenyl disulfide on Au(111)

Para-substituted benzenes, such as 1,4-benzene dithiol and 1,4-phenyl diisocyanide, have been observed to oligomerize on the Au(111) surface by incorporating gold adatoms extracted from the substrate. This work investigates if oligomerization occurs for an analogous but asymmetric linker, 4-isocyanophenyl disulfide (ICPD) on Au(111). This molecule is comprised of both disulfide and isocyanide terminal groups attached to the phenyl ring. The resulting surface structures formed on Au(111) following exposure to ICPD are studied using scanning tunneling microscopy (STM). 1,4-isocyanophenyl thiolate (ICPT), formed through scission of ICPD’s disulfide bond, was also found to oligomerize on the surface, and potential oligomer structures and binding geometries are proposed with the aid of density functional theory (DFT) calculations, along with simulated STM images of the resulting structures. It is observed in this work that ICPT forms oligomeric structures that cover large sections of the substrate and appear to create etch pits resulting from gold atom extraction. Numerous potential binding geometries are investigated based on the distances between substrate gold atom adsorption sites compared to the monomer length. Selected structural candidates were optimized using DFT and were used to generate simulated STM images using the Tersoff–Hamann method to compare with experiment. It has been shown previously that the isocyanide- and thiol-connected oligomers conduct electrons, suggesting the possibility that the asymmetric oligomers found here might form the basis for fabricating molecular diodes.

Unlocking the Power of Human Ferritin: Enhanced Drug Delivery of Aurothiomalate in A2780 Ovarian Cancer Cells

Aurothiomalate (AuTM) is an FDA‐approved antiarthritic gold drug with unique anticancer properties. To enhance its anticancer activity, we prepared a bioconjugate with human apoferritin (HuHf) by attaching some AuTM moieties to surface protein residues. The reaction of apoferritin with excess AuTM yielded a single adduct, that was characterized by ESI MS and ICP‐OES analysis, using three mutant ferritins and trypsinization experiments. The adduct contains ~3 gold atoms per ferritin subunit, arranged in a small cluster bound to Cys90 and Cys102. MD simulations provide a plausible structural model for the cluster. The adduct was evaluated for its pharmacological properties and was found to be significantly more cytotoxic than free AuTM against A2780 cancer cells mainly due to higher gold uptake. NMR‐metabolomics showed that AuTM bound to HuHf and free AuTM induced qualitatively similar changes in treated cancer cells, indicating that the effects on cell metabolism are approximately the same, in agreement with independent biochemical experiments. In conclusion, we have demonstrated here that a molecularly precise bioconjugate formed between AuTM and HuHf exhibits anticancer properties far superior to the free drug, while retaining its key mechanistic features. Evidence is provided that human ferritin can serve as an excellent carrier for this metallodrug.

Nanocomposite hydrogel for skin motion sensing – An antifreezing, nanoreinforced hydrogel with decorated AuNP as a multicrosslinker

In this study, we present a nanocomposite hydrogel designed for skin motion sensing. The hydrogel is based on poly(acrylamide) crosslinked with gold nanoparticles covalently bound to the polymer matrix, yielding a robust, highly elastic and conductive material. The choice of amino acid derivative – N,N’-diacryloylcystine salt (BISS) – as a crosslinker allows for the introduction of gold nanoparticles, due to the presence of sulfide groups in its structure. During the nanoparticle modification process, covalent bonds between gold and sulfur atoms are formed as the disulfide bond is cleaved. In result of this self-assembly process, a multifunctional Au–BISS crosslinker is formed, enhancing the material’s mechanical properties and introducing electrical conductivity. To confer anti-freezing properties and limit water evaporation, a binary mixture of water and glycerol was used. The resultant hydrogel exhibits high elasticity, strain sensitivity across a wide strain range and various types of deformation (elongation, bending, compression) with exceptional response time (120 ms) and recovery time (90 ms). The material’s cold-resistance, resilience, and conductivity make it well-suited for real-time monitoring of joint movements and speech recognition, with potential applications in electronic skin and healthcare monitoring devices.

Synthesis of fluorescent AuNCs with RNA as template

Although nucleic acids have been widely used as templates for the synthesis of nanomaterials, the synthesis of RNA-templated gold nanoclusters (AuNCs) has not been explored. In this work, we developed a simple strategy for synthesis of RNA-templated fluorescent AuNCs. We first evaluated the adsorption of different nucleoside monophosphates (NMP) on gold atoms. Our density function theory simulation and isothermal titration calorimetry measurements demonstrated that adenosine monophosphate (AMP) is a superior gold binder than other NMPs or deoxyadenosine monophosphate. Afterwards, NMP-templated synthesis of AuNCs was conducted in various pH environments, and our results indicated that bright green light-emitting AMP-templated AuNCs can be obtained at pH ∼6.0. In order to study the synthesis mechanism of AuNCs, we investigated the effects of reducing agent type and addition time, and the negative charge carried by template nucleotides on the fluorescence of AuNCs. Finally, we extended the template AMP into RNA hairpin structure, the fluorescence intensity was the highest when the cyclic bases were poly 16 A. This study opens new routes to synthesize fluorescent AuNCs using RNA templates.

Dissolution patterns of gold on various structural surfaces in thiosulfate solutions: The effect of interface adsorption on thiosulfate oxidation and gold atom dissociation

Passivation caused by the adsorption and decomposition of thiosulfate on gold surfaces significantly influences the leaching rate of gold. The surface structure often determines the reactivity of an interface. Studying the effects of different surfaces on the decomposition of thiosulfate ions and gold dissolution can provide insights into the passivation formation mechanism. In this study, the oxidation of thiosulfate on different surfaces is investigated using linear voltammetry. The oxidation response of thiosulfate was weaker on granular (1 1 1) and (5 4 1) surfaces than on nanoflakes with (1 1 1) surface. Furthermore, the Tafel test results indicate that the potential for gold dissolution is higher on the granular (1 1 1) and (5 4 1) surfaces, leading to a smaller current value of gold dissolution. Raman spectroscopy indicates that the response signals of the polysulfides and polythionate were stronger on the granular (1 1 1) and (5 4 1) surfaces. The chemical bond changes of thiosulfate adsorbed on different surfaces are studied through molecular simulations based on density functional theory. These results indicate that as the saturation of surface gold atoms decreases, their reaction activity increases, and the bonding effect with thiosulfate ions becomes stronger during adsorption. The changes in the SS bonds in thiosulfate reflect the influence of the different surfaces on their stability. On the (1 1 1) surface, the SS bond changes from the initial 2.102 Å to the adsorbed 2.254 Å, while on the (5 4 1) surface, the SS bond changes to 2.274 Å Although the reaction activity of the granular (1 1 1) and (5 4 1) surfaces is high, the energy barrier for dissociating individual gold atoms from them is higher. The adsorption of sulfur-containing substances on the surface, along with the increased energy barrier for gold dissociation are both factor contributing to the greater difficulty of gold dissolution from granular (1 1 1) and (5 4 1) surfaces.

Crystal structures of four gold(I) complexes [AuL 2]+[AuX 2]- and a by-product (L·LH+)[AuBr2]- (L = substituted pyridine, X = Cl or Br).

Bis(2-methyl-pyridine)-gold(I) di-bromido-aurate(I), [Au(C6H7N)2][AuBr2], (1), crystallizes in space group C2/c with Z = 4. Both gold atoms lie on twofold axes and are connected by an aurophilic contact. A second aurophilic contact leads to infinite chains of alternating cations and anions parallel to the b axis, and the residues are further connected by a short H⋯Au contact and a borderline Br⋯Br contact. Bis(3-methyl-pyridine)-gold(I) di-bromido-aurate(I), [Au(C6H7N)2][AuBr2], (2), crystallizes in space group C2/m with Z = 2. Both gold atoms lie on special positions with symmetry 2/m and are connected by an aurophilic contact; all other atoms except for one methyl hydrogen lie in mirror planes. The extended structure is closely analogous to that of 1, although the structures are formally not isotypic. Bis(3,5-di-methyl-pyridine)-gold(I) di-chlor-ido-aurate(I), [Au(C7H9N)2][AuCl2], (3) crystallizes in space group P with Z = 2. The cation lies on a general position, and there are two independent anions in which the gold atoms lie on inversion centres. The cation and one anion associate via three short H⋯Cl contacts to form a ribbon structure parallel to the b axis; aurophilic contacts link adjacent ribbons. Bis(3,5-di-methyl-pyridine)-gold(I) di-bromido-aurate(I), [Au(C7H9N)2][AuBr2], (4) is isotypic to 3. Attempts to make similar compounds involving 2-bromo-pyridine led instead to 2-bromopyridinium di-bromido-aurate(I)-2-bromo-pyridine (1/1), (C5H5BrN)[AuBr2]·C5H4BrN, (5), which crystallizes in space group P with Z = 2; all atoms lie on general positions. The 2-bromo-pyridinium cation is linked to the 2-bromo-pyridine mol-ecule by an N-H⋯N hydrogen bond. Two formula units aggregate to form inversion-symmetric dimers involving Br⋯Br, Au⋯Br and H⋯Br contacts.

Adsorption and disproportionation of carbon monoxide on faceted-gold surfaces and edges

Localized surface plasmons (LSP) on faceted surfaces of gold nanoparticles enable carbon monoxide disproportionation to be driven at room temperature. In order to expand the known surfaces that catalyze this reaction, we explore the adsorption of carbon monoxide at top, long bridge, short bridge, and hole sites on gold (100), (110), (111), (211), and (311) faceted surfaces, as well as the reaction barriers for disproportionation at the lowest energy adsorption site on each surface and edges between two (311) surfaces and (100) and (110) surfaces. Generally, the less atomically dense, higher index facets promote both good adsorption and reactivity, and the edges show lower barriers for disproportionation. For most of the explored surfaces, adsorption directly on top of a gold atom is most favorable. The lowest activation energy for carbon monoxide disproportionation to amorphous carbon and carbon dioxide is predicted for two carbon monoxides adsorbed on top of atoms on the (311)/(311) edge.

Precision engineering of nano-assemblies in superfluid helium by the use of van der Waals forces

The ability to precisely engineer nanostructures underpins a wide range of applications in areas such as electronics, optics, and biomedical sciences. Here we present a novel approach for the growth of nanoparticle assemblies that leverages the unique properties of superfluid helium. Unlike viscous solvents at or near room temperature, superfluid helium provides an unperturbed and cold environment in which weak van der Waals interactions between molecular templates and metal atoms become significant and can define the spatial arrangement of nanoparticles. To demonstrate this concept, diol and porphyrin-based molecules are employed as templates to grow gold nanoparticle assemblies in superfluid helium droplets. After soft-landing on a solid surface to remove the helium, transmission electron microscopy (TEM) imaging shows the growth of gold nanoparticles at specific binding sites within the molecular templates where the interaction between gold atoms and the molecular template is at its strongest.

Enhanced Molecular Interaction of 3D Plasmonic Nanoporous Gold Alloys by Electronic Modulation for Sensitive Molecular Detection.

Three-dimensional gold and its alloyed nanoporous structures possess high surface areas and strong local electric fields, rendering them ideal substrates for plasmonic molecular detection. Despite enhancing plasmonic properties and altering molecular interactions, the effect of alloy composition on molecular detection capability has not yet been explored. Here, we report molecular interactions between nanoporous gold alloys and charged molecules by controlling the alloy composition. We demonstrate enhanced adsorption of negatively charged molecules onto the alloy surface due to positively charged gold atoms and a shifted d-band center through charge transfer between gold and other metals. Despite similar EM field intensities, nanoporous gold with silver (Au/Ag) achieves SERS enhancement factors (EF) up to 6 orders of magnitude higher than those of other alloys for negatively charged molecules. Finally, nanoporous Au/Ag detects amyloid-beta at concentrations as low as approximately 1 fM, with SERS EF up to 10 orders of magnitude higher than that of a monolayer of Au nanoparticles.

Micelle-mediated growth of gold nanocrystals on a surface

Understanding nanocrystal growth is crucial for several reasons, as it plays a significant role in various scientific, technological, and industrial applications. Knowledge of nanocrystal growth allows scientists and engineers to control the size, shape, and composition of nanocrystals. This control is essential for tailoring the properties of nanomaterials for specific applications, such as electronics, catalysis, sensing and medicine. Nanocrystals are used in various biomedical applications, such as drug delivery, imaging, etc. Understanding their growth is essential for designing nanomaterials with specific functionalities for targeted drug delivery and imaging modalities. A molecular dynamics simulation study has been carried out to investigate the growth of nanocrystals in aqueous solutions in the presence of surfactants. In this study, we investigated the structural and thermodynamic properties of a micelle formed by cetyltrimethylammonium bromide (CTAB) in the aqueous solution and used that to quantify its role in the nucleation process when gold nucleates are in close proximity to another gold nanoparticle or surface. The path through which the nucleate gets fused with other entities, such as gold nanoparticles or surfaces, in the presence of a micelle in solution needs an explanation. We have shown the path and quantified energy required for the gold nucleate to get infused into the gold surface. Well-dispersed sets of gold atoms in solution were subjected to a series of steered molecular dynamics simulations, and it revealed that gold atoms, individually, must overcome an energy barrier of 10.52 ± 0.3 kcal/mol to start nucleating on the substrate. Due to this energy barrier, atoms form aggregate or nucleate inside the micelle. To control the release of the engulfed nucleate into the micelle onto the substrate, one needs to understand the mechanism of its release and quantify the energy requirement for the process. Here, we have used an enhanced sampling technique (umbrella sampling) to calculate the free energy required for the process mentioned above. A gold nucleate would require an additional energy of ∼10.36 kcal/mol to break the strong layering of micelle and water on the substrate. The radius of gyration and order parameter calculations show the extent of deformation of the micelle while releasing the engulfed nucleate on the substrate, and it gives us a recipe to alter the shape of the micelle and easier release of the nucleate on the surface. This study summarizes the path of nucleation of nucleates in the micellar solution and the recipe for the easier release of nucleates on the substrate.

Structural and bonding characteristics in Au2Ge9ˉ and Au2Ge10ˉ clusters: Insights from photoelectron spectroscopy and theoretical calculations

Germanium-based materials exhibit promising properties for applications in electronics, sensing, and catalysis. Gold-germanium clusters are of particular interest due to their potential for enhanced stability and tailored electronic properties. This study investigates the structures, bonding, and electronic properties of Au2Ge9ˉ and Au2Ge10ˉ clusters using anion photoelectron spectroscopy and theoretical calculations. The clusters were generated using laser vaporization and studied using anion photoelectron spectroscopy. Theoretical calculations employed density functional theory and coupled-cluster methods. Au2Ge9ˉ and Au2Ge10ˉ clusters exhibit weak aurophilic interactions between the two gold atoms. The gold atoms mimic the electronic and structural properties of germanium atoms, acting as surrogates within the cluster framework. Understanding the role of gold in these germanium clusters provides insights for designing novel materials with tailored properties for applications in catalysis, electronics, and other fields.

Modified Halloysite as Catalyst for the Conversion of Hydroxymethylfurfural to Furandicarboxylic Acid: A DFT Investigation

AbstractThe reaction steps involved in the 5‐hydroxymethylfurfural to 2,5‐furandicarboxylic acid conversion by means of H2O2 were investigated employing a dedicated computational protocol based on density functional theory. The catalytic environment of choice was a molecular model representing a portion of the halloysite nanotube outer surface, functionalized by an organosilane, the 3‐aminopropyltriethoxysilane, whose amino group bonds one gold atom. At this stage of the investigation, the process was fully detailed in terms of the interactions between the reaction intermediates and the catalyst, and the reaction standard free energies. In addition, the energy barriers of the elementary steps involving the hydrogen migration from the adsorbed organic species to the gold atom were analyzed. On the basis of the interaction geometries, a certain distinction among the preferred reaction path can be inferred as a function of the net negative charge characterizing the catalyst outer surface. Since the inner surface of halloysite can represent the acid environment needed to obtain 5‐hydroxymethylfurfural through dehydration of fructose, the present study is framed in a wider research field where the possibility to consider functionalized halloysite as one‐pot reactor for the valorization of biomass is explored.

Chiroptical Activity Amplification of Chiral Metal Nanoclusters via Surface/Interface Solidification.

It remains a grand challenge to amplify the chiroptical activity of chiral metal nanoclusters (NCs) although it is desirable for fundamental research and practical application. Herein, we report a strategy of surface/interface solidification (SIS) for enhancing the chiroptical activity of gold NCs. Structural analysis of [Au19(2R,4R/2S,4S-BDPP)6Cl2]3+ (BDPP is 2,4-bis(diphenylphosphino)pentane) clusters reveals that one of the interfacial gold atoms is flexible between two sites and large space is present on the surface, thus hampering chirality transfer from surface chiral ligands to metal core and leading to low chiroptical activity. Following SIS by filling the flexible sites and replacing chlorides with thiolate ligands affords another pair of [Au20(2R,4R/2S,4S-BDPP)6(4-F-C6H4S)2]4+, which shows a more compact and organized structure and thus an almost 40-fold enhancement of chiroptical activity. This work not only provides an efficient approach for amplifying the chiroptical activity of metal nanoclusters but also highlights the significance of achiral components in shaping chiral nanostructures.