Gold Bulletin最新文献

Consisted of closely packed nanoflakes, γ-Al₂O₃ hollow microspheres with ca. 4–6?μm in diameter, and 500–700?nm in shell thickness have been hydrothermally synthesized through utilizing Al(NO₃)₃·9H₂O as precursor, urea as precipitant agent and sulfate K₂SO₄, (NH₄)₂SO₄, or KAl(SO₄)₂·12H₂O as additive, followed by a calcination step. The samples were further characterized by thermogravimetric analysis, scanning electron microscope, x-ray powder diffraction, nitrogen adsorption, and in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) of adsorbed CO etc. The morphology of alumina products was strongly dependent on the presence of SO₄ ^2?. Then via a deposition–precipitation method, 3?wt.% Au nanoparticles supported on γ-Al₂O₃ hollow microspheres exhibit excellent performance with a complete CO conversion at 0?°C (T _100%?=?0?°C) and 50?% conversion at ?25?°C (T _50%?=??25?°C). The good catalytic activity is associated with the special hollow microsphere structures assembled by nanoflakes of γ-Al₂O₃ support. The DRIFTS confirms the presence of Au^δ+ and Au⁰ on the surface of γ-Al₂O₃ hollow microspheres. As a contrast, Au catalyst prepared using alumina support with undefined morphology shows low activity under the same catalytic test conditions (T _100%?=?190?°C, T _50%?=?80?°C).

Nanomaterials have been the object of intense study due to promising applications in a number of different disciplines. In particular, medicine and biology have seen the potential of these novel materials with their nanoscale properties for use in diverse areas such as imaging, sensing and drug vectorisation. Gold nanoparticles (GNPs) are considered a very useful platform to create a valid and efficient drug delivery/carrier system due to their facile and well-studied synthesis, easy surface functionalization and biocompatibility. In the present study, stable antibiotic conjugated GNPs were synthesised by a one-step reaction using a poorly water soluble antibiotic, amoxicillin. Amoxicillin, a member of the penicillin family, reduces the chloroauric acid to form nanoparticles and at the same time coats them to afford the functionalised nanomaterial. A range of techniques including UV–vis spectroscopy, dynamic light scattering (DLS), transmission electron microscopy (TEM) and thermogravimetric analysis (TGA) were used to ascertain the gold/drug molar ratio and the optimum temperature for synthesis of uniform monodisperse particles in the ca. 30–40?nm size range. Amoxicillin-conjugated gold showed an enhancement of antibacterial activity against Escherichia coli compared to the antibiotic alone.

The synthesis of shape and size-controlled free gold nanoparticles (AuNPs) was achieved by wet chemical methods. The UV–vis spectroscopy measurements and transmission electron microscopy characterizations confirmed the fine distribution in size and shape of the AuNPs. The zeta potential measurements permitted the evaluation of the stability of the AuNPs suspension. For the first time, the shape dependence on the electrocatalytic activity of these NPs is thoroughly investigated. The underpotential deposition (UPD) of lead reveals that their crystallographic facets are affected by their shape and growth process. Moreover, the glucose oxidation reaction strongly depends on the shape of AuNPs. Indeed, the gold nanocuboids (GNCs) and the spherical gold nanoparticles (GNSs) are significantly more active than the gold nanorods (GNRs) followed by the polyhedrons (GNPs). The oxidation process occurs at low potential for GNCs whereas the current densities are slightly higher for GNSs electrodes. Most importantly, the control of the shape and structure of nanomaterials is of high technological interest because of the strong correlation between these parameters and their optical, electrical and electrocatalytic properties.

The first colour diagram of the gold-silver-copper system was published over 30 years ago by Josef Leuser. This was based on visual, and therefore subjective, colour assessment. Renewed interest in the colour characteristics of gold alloys, as well as the development of improved instrumentation for their measurement, have stimulated recent research on the subject. This has now progressed to the point where objective, quantitative information on the relationship between alloy colour and composition is available.

The cost of producing electricity from solar energy by means of solar cells is still high and limits the use of such devices to special situations. Gold has important roles not only in older types of cells but also in newer types which are being developed to achieve increased efficiencies.

The dissolution of gold in alkaline solutions containing cyanide ions is of great importance and its application in the MacArthur-Forrest process towards the end of the last century revolutionized the extraction of gold from its ores. Because of this, and its use in many industrial processes involving gold, it has been widely studied. What is known — and still unknown — about this reaction constitutes the main theme of this second instalment of a review of the anodic behaviour of gold.

Elemental silver nanoparticles are an effective antibacterial substance and are found as additive in various medical applications. Gold nanoparticles are used due to their optical properties in microscopy and cancer therapy. These advantages might be combined within alloyed nanoparticles of both elements and thereby open new fields of interest in research and medical treatment. In this context, laser ablation of solid alloys in liquid gives access to colloidal silver–gold alloy nanoparticles with a homogeneous ultrastructure. Elemental and alloy silver–gold nanoparticles with increasing molar fractions of silver (50, 80, and 100?%) were produced and stabilized with citrate or albumin (BSA). Particles were embedded in agar at concentrations of 3–100?μg?cm^?3 and tested on clinical relevant Staphylococcus aureus regarding their antibacterial properties. Cytotoxic effects were measured within the same particle concentration range using human gingival fibroblasts (HGFib). As expected, a reduced fraction of silver in the nanoalloys decreased the antibacterial effect on S. aureus according to the evaluated minimal inhibitory concentrations. However, this decrease turned out stronger than expected by its relative mass per particle, due to the electrochemical, disproportionally high effect of gold on the bioresponse to silver within silver–gold nanoalloy particles. BSA was able to stabilize all colloids and maintain antibacterial activity, whereas sodium citrate reduced antibacterial effects and cytotoxicity even at high nanoparticle concentrations. The alloying of silver with gold by laser ablation in liquid produced nanoparticles with both reduced antibacterial and cytotoxic properties in comparison to silver nanoparticles but still retains the application spectrum of both elements combined in one colloid. In particular, alloying with gold may render silver nanoparticles more biocompatible, and allows bioconjugation via established thiol chemistry.

Large-sized gold nanoparticles, promising imaging and therapeutic tools in human cancer, need long-term studies evaluating tissue bio-distribution in blood, organs and tumor. In a preclinical model of mouse xenografted with human renal cancer, we analysed the bio-distribution of a single dose (160?μg/kg) intravenously injected of poly-ethylene glycol (PEG)ylated gold nanoshells (~150?nm), in blood, normal and tumoral tissues. Using inductively coupled plasma mass spectrometry (ICP-MS), dark field and electron microscopy, we performed a sequential study of nanoshell uptake and distribution in the tumor. We also studied microscopically the organs most sensitive to efficient anticancer drugs to detect a possible long-term toxicity. Gold quantities significantly decreased in blood between early and late time points, whereas they significantly increased in liver and spleen. In addition, gold nanoshells did not induce any tissue damage, such as necrosis, inflammatory infiltrate or fibrosis in mouse liver, spleen, kidney or bone marrow after 6?months. In human renal cancer xenografts, ICP-MS showed an early decrease of gold, with 1-week stability before decrease at Day 15. Dark field microscopy showed gold particles within the vessel lumen 5 to 30?min after nanoshell injection, while 24?h later, gold particle distribution was mainly intracellular. Electron microscopy identified nanoshells within blood vessels at 5 and 30?min, within endothelial cells at 3 and 6?h and within cytoplasms of macrophages in the tumoral tissue after 24?h. In conclusion, no toxicity was observed in mice 6?months after administration of PEGylated gold nanoshells and the distribution kinetics progressed from intravascular flow at 30?min to intratumoral cells 24?h later.

A dental Au–Ag–Cu–Pd alloy with a relatively low Au content and a high Cu/Ag content ratio was examined to determine the correlation between the microstructural changes by the spinodal decomposition and age-hardening behaviour using a hardness test, X-ray diffraction study, field emission scanning electron microscopy and energy-dispersive X-ray spectrometry. Separation of the parent α₀ phase occurred by spinodal decomposition during aging at 350?°C after the solution treatment at 750?°C, and not by a nucleation and growth mechanism, resulting in the formation of the stable Ag-rich α₁ and AuCu I phases through a metastable state. Hardening resulted from the coherency lattice strain which occurred along the a-axis between the metastable Ag-rich α₁′ and AuCu I′ phases. In addition, lattice distortion occurred along the c-axis between the stable Ag-rich α₁ and AuCu I phases due to the tetragonality of the AuCu I ordered phase. The transformation of the stable Ag-rich α₁ and AuCu I phases from the metastable state introduced the formation of the fine and uniform cuboidal structures, which compensated for the increased gap in the lattice parameters through the phase transformation. Replacement of the fine cuboidal structures with the coarser lamellar structures occurred without a phase transformation, and resulted in softening by reducing the interfaces between the stable Ag-rich α₁ and AuCu I phases.

A stable colloidal solution of gold nanoparticles (AuNPs) has been prepared in tetrahydrofuran by gas reduction of AuCl(tetrahydrothiophene) and alkylamines (1-octylamine,1-dodecylamine, and 1-hexadecylamine) as stabilizing agents. Carbon monoxide is a better reducing agent than hydrogen. The important parameters for control of the synthesis of AuNPs are the temperature, the molar ratio of ligand/metal, and the structure of the stabilizing agent. A high concentration of long alkyl chains (10?eq.) favours the control of the growth of AuNPs of defined size and shape with a diameter of 4.7?nm and a narrow size distribution. For the first time, liquid-state combined with solid-state NMR spectroscopies were used in order to determine the role of the long chain alkylamines in the synthesis of AuNPs in CO atmosphere. This combination enables the understanding of the complex chemistry of the surface of AuNPs involved in the stabilization of the AuNPs. Indeed, carbamide species were formed during the synthesis. They were strongly coordinated to the surface of AuNPs and exchange phenomena of the alkylamines present in solution occurred, too.