Gold Bulletin最新文献

The decree of Mining Arc, endorsed in 2016, proposes the exploitation of minerals in an approximate area of 112,000?km² that has generated a very intense controversy which has been very publicized by the media. However, there have been artisanal gold mining for several hundred years, commercial mining for 175?years, and in recent times, forms of industrial mining that have satisfied Venezuelan environmental standards. In the last 20?years, mining has had a very erratic policy; in 2004, a Piar Mission was implemented, aligned with a socialist vision of land use, which promoted the most destructive form of mining—hydraulic monitors and amalgam with mercury. That generated a situation of anarchy that led to the emergence of criminal armed groups that control most of the mines today. At present, there are more than 200,000 people who depend on mining directly or indirectly; therefore, an absolute ban on mining is not viable. The decree of Mining Arc was integrated with the destruction of the environmental control institutionality and the creation of a military mining company, so it must be rejected. All this is an example of how gold mining can go wrong, while in other countries these projects can be successful. Venezuela requires foreign exchange to recover the damaged production infrastructure; a rational way of mining may contribute to this recovery, but that requires restoring to the Ministry of the Environment, formulating and executing a mining policy with a long-term vision according to the economic, social, and environmental realities of the nation.

Nanotechnology has the impending ability to improve the therapeutic potential of drugs and radiation-based treatment approaches for reducing cancerous cell death while curtailing collateral toxicity to non-cancerous cells. Among all metal nanomaterials, gold nanoparticles (AuNPs) are establishing themselves as an excellent radiosensitizer and serve as a multimodal modality due to their unique physicochemical properties. The primordial purpose of the work is to evaluate the synergistic effect and molecular level interaction of gamma (γ) radiation on human cervical cancer cell (HeLa) in the presence of AuNPs. Biocompatible AuNPs in combination with γ-radiation were found to exhibit elated cytotoxic effects on cancer cells as evidenced by cell-based assays. The implication of AuNPs facilitates the minimization of radiation dose employment on cultured cells. As per our experimental evaluation, the modus operandi of dual effectors ascertained that a higher amount of reactive oxygen species (ROS) plays a key role in cellular functionality collapse. In that scenario, it can be concluded that AuNP-mediated radiosensitization proved to be the plausible candidate for preclinical testing in nanoparticle-based radiotherapy.

The construction of porous organic polymer from 5,10,15,20-tetraphenylporphyrin (TPP) was described using one-pot Friedel-Crafts alkylation reaction. Au was simultaneously loaded on the porphyrin-based polymer denoted as Au/KAPs(DCM-TPP). This polymer-supported Au was fully characterized by many physicochemical methods. It was found to possess BET surface area of 796?m²?g^?1, good thermal stability above 250?°C and Au nanoparticles with an average size of 8?nm. It was used as an efficient heterogeneous catalyst for alkyne hydration and alcohol oxidation in water. This Au catalyst exhibited excellent catalytic efficiency and recycling performance without loss of activity at least five times. A new strategy to synthesize polymer-supported Au nanoparticle catalyst was finally provided.

The color of ternary Au-Ag-Cu alloys is investigated; a simple and efficient model relying only on the reflectance of gold, silver, and copper is suggested. The alloy color diagram (a^?,b^?) based on the alloy proportion (u, v) has the shape of a “wizard’s hat” with special properties. Leuser’s classical triangle can be improved upon these results.

Bimetallic Ag–Au alloy nanoparticles with a tunable size and composition were synthesized by laser beam power density. A set of Psi substrates with different morphologies fabricated by laser-assisted etching process with laser power density from 10 to 40?mW/cm² was explored as a substrate for materialization bimetallic Ag–Au alloy nanoparticles by a simple immersion plating process of Psi in a mixture of AgNO3 and HAuCl4 solutions. The materialization of alloy nanoparticles was confirmed by scanning electron microscopy (SEM), X-ray diffraction (XRD), and energy-dispersive X-ray analysis (EDS). The results showed that the sizes and distribution of Ag–Au alloy nanoparticle sizes were easily well-ordered by changing the surface morphologies of Psi layer. Pore-like structures with different pores shapes: ultra-fine pores, irregular (grotto form), circular, and star full pore shape (gambling pores) with different sizes were prepared by changing the irradiation laser power density. Bimetallic Ag–Au alloy nanoparticles, phases, crystalline size, specific surface area, and growth sites of Ag–Au alloy nanoparticles were significantly influenced by pore shape. The lower nanoparticle size with higher S.S.A was obtained when the laser power intensity was about 30?mW/cm².

Nanoparticle (NP) trophic transfer is reported as an important exposure route for organisms in aquatic ecosystems. This study focused on gold nanoparticle (AuNP, PEG-coated, 10?nm diameter) transfer using an experimental benthic food chain which included two trophic levels: natural river biofilm and grazer fish Hypostomus plecostomus. AuNP biofilm accumulation was assessed via water AuNP concentrations and total biofilm mass. An extended range of six AuNP concentrations in water (0, 0.0048, 0.048, 0.48, 4.8, and 48?mg Au L^?1) was set. A dose-dependent relation between gold concentrations in water and natural river biofilm was observed after a 48-h exposure. This pointed out the high propensity of natural biofilms to accumulate gold. Additionally, total biofilm mass appeared to influence AuNP accumulation at the highest exposure levels. This first step enables the set-up of the transfer experiment in which grazer fish were exposed for 21?days to natural biofilms, previously contaminated by low AuNP concentrations in water (NP0.1: 0.48 and NP1: 4.8?mg Au L^?1). Gold was quantified in eight fish organs, and histology was observed. Gold was transferred from biofilms to fish; bioaccumulation was organ- and exposure level-dependent. Interestingly, the brain showed significant gold accumulation at the highest exposure level (NP1). Histological observations indicated distinct inflammatory responses in fish liver, spleen, and muscle. The overall results suggest the potential hazards of subchronic nanoparticle exposure in aquatic organisms.

One percent gold supported on three different metal oxides (TiO₂, ZnO and Al₂O₃) has been evaluated as a catalyst, to reduce sulphur dioxide with carbon monoxide at different reaction temperatures. During the reaction, no carbonyl sulphide was formed and the only sulphur-containing product that was detected was elemental sulphur which condensed as S₈ at the reactor exit. High-resolution transmission electron microscopy, X-ray photoemission spectroscopy and powder X-ray diffraction have been used to study the interaction between the metal and the support as well as the size of metal particles before and after the reaction. We found that gold nanoparticles supported on TiO₂ had the best performance among all the supported catalysts (86.4% conversion) at a reaction temperature of 300?°C, a feed ratio of CO:SO₂?=?2:1 and a gas hourly space velocity of 3600?mL?g_cat^?1?h^?1. Au/ZnO and AuAl₂O₃ were only slightly active for SO₂ reduction at a range of temperatures from 50 to 300?°C. After 144?h on stream, the conversion of SO₂ over Au/TiO₂ was still the same as it was initially. The high activity of the 1% Au/TiO₂ catalyst resulted from the size of the gold particles and the strong interaction between the metal and the titania.

We report five effective fluorescence resonance energy transfer (FRET) systems based on gold nanoparticles (AuNPs) and organic fluorescent dyes, including ionic [fluorescein sodium (FS) and Eosin B (EB)] and cationic [rhodamine 6G (Rh6G), acridine orange (AO), and safranine T (ST)] fluorescent dyes. The fluorescence intensity of the five FRET systems demonstrates that efficient quenching is possible. The quenching efficiencies of Rh6G and FS by FRET were nearly 100%, 89% for AO, 60% for EB, and 55% for ST. A series of UV absorbance spectra and fluorescence emission spectra were used to explain the mechanism of fluorescence quenching. We found that there were different degrees of overlap between the absorption spectrum of the AuNPs and the emission spectrum of fluorescence dyes. This outcome indicates that highly efficient FRET is the possible mechanism of fluorescence quenching. We applied the FRET system to establish a sensitive and simple strategy for the determination of mercury (Hg²⁺). The maximum excitation was at 523?nm (λex?=?523?nm). The enhanced fluorescence intensity at 551?nm was proportional to the concentration of Hg²⁺ with a range of 0.44–100?nmol?L^?1. The detection limit was 0.13?nM. The linear regression equation was ΔF?=?27.05c (nmol?L^?1) ??79.88, and the regression coefficient was 0.9954. The proposed method has high sensitivity and convenience and does not require complex and expensive instruments.

Uniformly sized and shaped gold nanoparticles (AuNP) were produced by microwave irradiation using Euphorbia tirucalli latex. The AuNPs were characterized by ultraviolet visible spectroscopy (UV–Vis), Fourier transform infrared spectroscopy (FTIR), dynamic light scattering, zeta potential, and transmission electron microscopy (TEM). UV–Vis analysis was employed to detect the characteristic surface plasmon resonance pattern of the AuNPs (550?nm). The carboxylic and polyphenolic groups were associated with the euphol-capped AuNP, which was confirmed using FTIR spectroscopy. The AuNPs studied here show a z-average diameter varying from 35 to 500?±?0.8?nm. TEM reveals that the particles were spherical and polydispersed. The latex itself is very toxic and can be harmful during manipulation, thus highlighting a negative aspect in it use. However, we have demonstrated that the isolation procedure did not impair the reduction action of the dry latex powder. This study provides a robust solution for the synthesis of stable capped gold nanoparticles. Furthermore, the dried powdered E. tirucalli latex seems to be an attractive capping agent for nanoparticles in drug delivery.