Gold Bulletin最新文献

Gold oxides with thicknesses of less than 1?nm that were prepared by an oxygen-dc glow discharge over various periods (0.5–10?min) from gold films at room temperature were characterized by X-ray photoelectron spectroscopy (XPS), and a preservation method was developed for these oxides. The O 1s spectra show three oxygen species comprising components I, II, and III in the gold oxides. Components I and II are both stable and assigned to hydroxyl groups. The angular dependence of the XPS spectra of the gold oxides indicates that the oxygen species of components I and II are present in this order from the top surface of the gold oxide (component III). The gold oxides decompose after 36?h at room temperature and decompose immediately at temperatures exceeding 121?°C in a dark atmosphere. These gold oxides also decompose under ultraviolet (UV) light irradiation (254, 302, and 365?nm) at room temperature and decompose more rapidly in water vapor at the shorter wavelengths. These findings indicate that the gold oxide decomposition is accelerated via a reaction with excited water molecules produced by UV light absorption. The gold oxide decomposes after 6?h in water but decomposes more slowly in hydrocarbons (hexane, octane, and dodecane) at room temperature in a dark atmosphere. The gold oxide can be preserved in the oxidized state for 84?days in anhydrous dodecane. This simple preservation method of a gold oxide immersed in a hydrocarbon with low water content will be helpful for practical use in future applications.

Ligand exchange was triggered at toluene/water emulsion interface between homogeneous gold nanoparticles (Au NPs) with triphenylphosphine (PPh₃) and D-penicillamine (D-PA), resulted in amphiphilic Janus Au NPs with both phosphine and thiolate ligands. TEM and XRD analyses indicate that the product is composed of Au nanocrystals in an average diameter of about 3.7?nm. XPS, FTIR, Raman, and ¹H NMR analyses demonstrate that the Au NPs are protected with hydrophilic D-PA molecules and lipophilic PPh₃ ligands in a molecular ratio of ca. 1.8. The NOESY analysis and contact angle measurement further suggest that the D-PA and PPh₃ molecules are spontaneously separated to form compartmentalized hydrophilic and lipophilic regions on the individual Au NPs, which exhibit good catalytic performance and recyclability on the reduction of 4-nitrophenol. The results demonstrate that amphiphilic Janus Au NPs can be synthesized by partly exchange of PPh₃ with D-PA at toluene/water emulsion interface and are potentially applicable for other phosphine/thiolate pairs to modify Au NPs.

This study reports a new detection process for sensing ultra-low concentrations of tetracycline (TC), using a hot spot surface-enhanced Raman scattering (SERS) sensor. A gold nanoparticles/ macroporous silicon (Au NPs/macroPSi) hot spot SERS sensor was fabricated using a very simple and low cost method. The SERS signal was investigated using Au NPs/macroPSi hot spot SERS sensor for efficient detection of TC antibiotics at lower concentrations of (10^?3–10^?9) mol/L. The sensor showed an excellent performance for TC detection with an enhancement factor (EF) of 2?×?10⁸, ultra-low detection limit of 10^?9?mol/L, and very high reproducibility with a relative standard deviation of 2%. The effect of the pH value on the behavior of the SERS spectra for TC antibiotic was evaluated, and it was found that pH values of 5 and 6 were the best for the detection process of TC antibiotic.

In this paper, the 24 karat (99.99?wt.% pure) and 22 karat gold (Au-5.8wt.%Cu-2.5wt.%Ag) were grain refined with Au-6wt.%Ti master alloy and the mechanism of grain refinement was studied. The Au-6wt.%Ti master alloy containing Au₂Ti and Au₄Ti intermetallic particles was added into 24 karat and 22 karat gold at various addition levels of Ti (0.1, 0.2 and 0.3?wt.%) for grain refinement. The intermetallic particles undergo peritectic reaction with liquid Au in sequence to nucleate α-Au solid. It is observed that both the 24 karat gold and 22 karat gold showed efficient grain refinement at the lowest addition level of Ti (0.1?wt.%). However, 22 karat showed better grain-refining efficiency than 24 karat at all addition level of Ti studied. The mechanism of grain refinement of gold in this study matches with the “Peritectic theory” and “Solute paradigm” proposed for the grain refinement of aluminium. It is also observed that increasing the master alloy addition level to 0.2 and 0.3?wt.% Ti coarsening in the grain size in both 24 karat and 22 karat, but significant in the case of 24 karat gold due to recalescence effect. The grain-refined 24 karat and 22 karat gold at 0.1?wt.% Ti showed improvement in the hardness in comparison to the un-grain refined one.

Au nanorods were prepared through seed growth method. Their lengths and diameters were controlled by adjusting Ag⁺ content in the growth solution. Ethyl orthosilicate were hydrolyzed in alkali solutions to obtain SiO₂-coated Au nanostructures. Au nanorods with ideal morphologies and sizes could only be obtained under the presence of a certain Ag⁺ concentration in the growth solution. Without Ag⁺, only some irregular nanoparticles were generated without nanorods. Longitudinal plasma absorption of Au nanorods shifts first to red shift and then to blue with the increase of Ag⁺ in the growth solution, while transverse plasma absorption hardly changes. However, longitudinal plasma absorption of silica-coated Au nanorods has a blue shift with the increase of the thickness of silica, while the transverse plasma has a slight red shift. Therefore, by coating Au nanorods with silica and by adjusting their aspect ratio by using different Ag⁺ concentration in the growth solution, Au nanoparticles can be synthesized for applications requiring absorption in specific UV regions.

The green synthesis of gold nanoparticles has attracted tremendous interest owing to their unique physicochemical properties and widespread applications which are primarily size-dependent. The stability, less reaction time, and use of biological resources as novel nanofactories as an alternative to conventional synthesis strategies are the main objectives of green synthesis approaches. However, to attain size-controlled synthesis from the biogenic route is still a challenge. Hence, use of nontoxic stabilizers becomes increasingly essential. Herein, we describe an emerging, simple, nonconventional approach to synthesize stable and size-controlled biogenic nanogold using cell lysate supernatant containing nitrate reductase of Bacillus licheniformis in the presence of Tween 20 and dodecanethiol respectively. The face-centered central composite design used for the optimization of gold nanoparticles (AuNPs) biosynthesis. The maximum AuNPs biosynthesis obtained using the optimized media variables, glucose (2.1 g/L), peptone (14.05 g/L), yeast extract (4.14 g/L), and potassium nitrate (3.91 g/L) was 0.769 a.u. Highly stable monodispersed nanogold of 10.4 ± 0.6 nm and 12.5 ± 0.9 nm sizes arranged in ordered self-assembly was obtained. The stability profile and kinetics of bioreduction was evaluated with respect to time, and the involvement of the nitrate reductase enzyme in bioreduction was validated by inhibitor study. The physicochemical properties of biogenic nanoparticles were characterized using multiple spectroscopy and microscopy techniques. The obtained nanogold demonstrated excellent bactericidal property against both gram-negative and gram-positive bacteria in size-dependent manner and thus could find tremendous utility in clinical, biological, and environmental applications as a broad-spectrum antibacterial agent.

Herein, we report a simple one-pot synthesis of water-dispersible gold nanoparticles (AuNPs) by using meso-tetra(methyl) meso-tetra hydrazide-functionalized calix[4]pyrrole (ECPTH) as both reducing and stabilizing template. The characterization of ECPTH-AuNPs has been carried out by UV-Vis spectroscopy, transmission electron microscope, X-ray diffraction (XRD), dynamic light scattering (DLS), and zeta potential techniques. The spherical shaped nanoparticles are highly stable with an average size of 8 ± 2 nm. The mechanistic insights rendered by the computational study have suggested that ECPTH can successfully cap the Au via utilizing the hydrazide arms. The nanoparticles functioned as an effective heterogeneous catalyst for the 4-nitrophenol reduction and ECPTH as capping ligand enhances the catalytic activity via a synergistic effect. This work contributes a new catalytic pathway for the degradation of hazardous and toxic pollutants using highly efficient and cost-effective supramolecular-functionalized nanocatalyst.

The electrochemical corrosion behaviour of 22k gold (Au-5.8wt.%Cu-2.5wt.%Ag) and Ti containing 22k (Ti-22k) gold (Au-5.8wt.%Cu-2.0wt.%Ag-0.5wt.%Ti) was studied. Elemental Ti was added as the quaternary element to 22k gold by replacing Ag, resulting in the formation of secondary phase precipitates during age hardening treatment, thereby improving the hardness of the alloy. Anodic polarization tests were conducted for both 22k and Ti-22k samples in their as-cast annealed, cold-rolled annealed and age-hardened conditions using 0.9% sodium chloride and 1% lactic acid as medium. The as-cast and annealed 22k samples showed better corrosion resistance in both corrosion media whereas the 22k samples in the cold-rolled, annealed condition and Ti-22k samples in the as-cast, annealed condition showed poor corrosion resistance. After age-hardening treatment, cold-rolled Ti-22k samples showed better corrosion resistance due to the formation of passive layer (of TiO₂) on the surface. However, corrosion gets initiated in the age-hardened Ti-22k due to the breaking and decomposition of the passive layer (TiO₂) at a potential > 1.3 V.

This work introduces an innovative new method to transport gold nanoparticles (Au-NPs) toward specific organs using as transporter the M13 filamentous phage. The aim is to improve the radiotherapy efficiency by injecting gold nanoparticles in the tumor tissues in order to increase the effective atomic number and, consequently, to produce higher locally deposited doses. The biocompatible Au-NPs can be bonded to the phage surface for their transport in the biological fluids and tissues. M13 phages can be prepared to arrive in specific tissues and organs depending on their biochemical preparation and functionalization. Evidence about the real attachment of spherical Au-NPs, 10 nm in diameter, to the M13 phages is obtained using different microscopies. Other analyses have been also performed to evaluate the number of gold nanoparticles that can be transported by M13 phages inside the organism. Our results on the study of the spherical Au-NP size distribution, deduced by AFM, EFM, and TEM analyses, have indicated that in average, 2 couples of Au-NPs are attached to each phage. Moreover, the size of the NPs ranges between 10 and 30 nm, demonstrating a little aggregation of the nanoparticles, which remain usefully sized to be vehicled with the blood flux towards specific organs.

A new nanocomposite material based on gold nanorods and polyurethane foam was obtained, and a method for the determination of catecholamines with the use of this nanocomposite modified with silver nitrate was developed. The determination is based on the measuring hypsochromic shift of a short-wave surface plasmon resonance band in a diffuse reflection spectrum of the nanocomposite. This shift is caused by reduction of silver from silver ions on the surface of gold nanorods under the influence of catecholamines. Effects of time, pH, volume of the reaction mixture, concentration of silver ions, and catecholamines on the interaction were examined. The proposed method allows to determine dobutamine, epinephrine, norepinephrine and dopamine with the detection limits of 0.1, 0.07, 0.07, and 0.05 μg mL^?1, respectively. The developed method can be applied to analysis of medicines.