Gold Bulletin最新文献

In this study, we report on the influence of support and gas atmosphere on the thermal stability of Au nanoparticles on oxidic supports. All samples were prepared with a modified impregnation method and have initial Au particle sizes in the range of 3–4?nm. We observed that in air, Au nanoparticles on SiO₂ and Al₂O₃ are thermally much more stable than Au nanoparticles on TiO₂. For instance, upon treatment up to 700?°C, on SiO₂, Au particles grew from 4 to 6?nm while on TiO₂ from 3 to 13?nm. For Au nanoparticles on TiO₂, growth is accelerated by oxidizing atmospheres and the presence of water and/or chloride. On non-reducible supports and in non-oxidizing atmosphere, the supported Au nanoparticles were remarkably stable. The insight into the growth of oxide-supported Au nanoparticles in reactive atmosphere offers an additional tool for a rational choice of a support for high-temperature gas-phase reactions involving gold nanocatalysts.

Gold nanostructures (AuNP) are important as strong platforms for targeted therapeutic and diagnostic applications. Tireless effort has been devoted nowadays to explore the multifunctionality of AuNP in multicomponent biostructures. Herein, we report the fabrication of horseradish peroxidase enzyme (HRP)-AuNP/ZnAlLDH heterostructure by the facile synthesis of AuNP on the biocompatible matrices of layered double hydroxides (LDH) followed by the immobilization of the enzyme on AuNP/LDH assemblies. During this process, ZnAlLDH have a dual function of exploring its structural “memory effect” for the synthesis of nanogold and acting as a support for the enzyme immobilization. X-ray diffraction (XRD), UV-Vis spectrometry, transmission electronic microscopy (TEM), energy-dispersive X-ray spectroscopy (EDX), and infrared (FTIR) spectroscopy have been used to characterize the structural, chemical composition, optical, and morphology of the novel materials. We present here the release of AuNP from HRP-AuNP/ZnAlLDH by using as controlled variables HRP:LDHs ratio and the pH of the solution. Results show that AuNP established close interactions with HRP and formed an HRP-AuNP bioconjugate. Results reveal that HRP suffers a significant loss of the activity in the presence of nanoparticles of gold, such that, AuNP act to inhibit the activity of the enzyme. AuNP behavior in enzyme-bio-heterostructures should be inspiring for future applications of AuNP in nanomedicine.

Metallic gold is not completely inert towards biological tissues and cells. Cytotoxicity and immunotoxicity are concerns in various gold applications. This study shows that treating the surface of gold with OH^? radicals renders the gold surface non-cytotoxic, as well as prevents any biocorrosion of gold implants by an immune reaction. The detoxification is discussed as resulting from the selective dissolution of active gold atoms from the surface.

Synthesis of gold nanoparticles (Au-NPs) was performed using method of an inorganic chemical reduction. The synthesized Au-NPs showed an intensive surface plasmon resonance band at 525?nm that is typical for corresponding Au-NPs reported in literature. The structural and morphology characterizations of the obtained Au-NPs were carried out using SEM, AFM, TEM, and X-ray spectral analysis. The possibility of usage of Au-NPs as a carrier for covalent immobilization of commercial laccase and the combination of the obtained bio-Au-NPs with ureasil polymers as host matrixes for formation of bio-nanocomposite films was studied. The prospect of using the obtained bio-nanocomposite films in biosensor technologies in order to improve the bioanalytical characteristics of sensory elements has been proved.

In order to recover gold and silver from anode slimes containing Cu, Ni, Sn, and Zn, an integrated hydrometallurgical process consisting of leaching, solvent extraction, and cementation was developed. All the metals together with 10% of Ag(I) were dissolved by the mixture of HCl and H₂O₂ at the optimum conditions. Separation of Au (III) together with Sn (II) was performed by Cyanex 272 from the leaching solution with two-stage counter current extraction. Stripping of Au (III) and Sn (II) from the loaded organic phase was sequentially carried out by NH₄Cl and NaOH. Cu (II) in the raffinate after Au (III) extraction was separated by LIX 63 with three-stage counter current extraction. Pure Cu (II) solution was recovered from the loaded LIX 63 by stripping with dilute HCl solution. Ag powders with extra high purity were obtained by cementation with copper sheet from the raffinate after Cu (II) separation. Au (III) (99.3%) and 96.8% of Sn (II) were recovered by extraction, and purity of Au (III) and Sn (II) stripping solutions was found to be 99.99%. Au powders with extra high purity were directly synthesized by adding ascorbic acid solution into the NH₄Cl stripping solution.

The adsorption of hydrogen on the surface of gold nanoparticles deposited on a graphite support was studied in the presence of an external electric field by means of scanning tunneling microscopy (STM) and spectroscopy (STS). Hydrogen was adsorbed from the gas phase onto the surface of gold nanoparticles synthesized by impregnation-precipitation method. During the adsorption process, the STM tip was removed from the surface of the sample so that the measurable tunneling current could not flow, and potential differences of various polarities were applied to the vacuum gap between the sample and the grounded tip. Thus, the system of the STM tip and sample surface formed an asymmetric capacitor inside which an inhomogeneous electric field existed. No hydrogen adsorption was observed in the case of a positive potential difference, while dissociative adsorption of hydrogen took place in the cases of zero and negative potential differences. The ability to control the adsorption process of hydrogen by means of a weak electric field was demonstrated.

Although antimicrobial photothermal inactivation of naked gold nanostructures using powerful pulsed lasers has been previously studied, there are little reports about their photodynamic antimicrobial properties under the irradiation of low-power density continuous wave lasers. Therefore, this paper attempts to fill this gap. In this paper, we studied the effects of a 40-mW/cm² continuous Nd:Yag laser at 532?nm and naked gold nanoparticles on inactivation of Escherichia coli ATCC25922. According to our results, 60?min illumination using the Nd:Yag laser caused a 0.15log reduction of the bacterial viability. Also, the employed gold nanoparticles with an average size of 15?nm were toxic to E. coli ATCC 25922 in the concentrations above 0.5?μg/ml. In addition, synergistic effects of 0.5?μg/ml gold nanoparticles and the light illumination led to a 2.43log reduction of the viability after a 60-min exposure and did not show any considerable temperature change on the media. The obtained results were justified based on the possible interaction mechanisms of low-power density laser lights and naked gold nanoparticles. The paper is proposed as a prelude for future research about localized inactivation of resistant pathogens with minimum side effects on neighbor tissues.

The Au(CN)₂^? ion and its metal-ligand compounds have recently gained considerable interest in industrial applications such as optical diagnostics systems as well as pharmacology with antirheumatic and antitumor activity. Here, [Ni₂(N-bishydeten)₂][Au(μ-CN)₂]₃[Au(CN)₂]·H₂O (C1), [Cu₂(N-bishydeten)₂][Au(μ-CN)₂]₃[Au(CN)₂]·H₂O (C2), and [Zn₂(μ-N-bishydetenH)(N-bishydeten)(NC)₂Au][Au(CN)₂] (C3) were synthesized by reaction of the metal salts with N,N-bis(2-hydroxyethyl)ethylenediamine (N-bisyhdeten) and K[Au(CN)₂]. The Au(I) compounds were characterized using elemental analysis and FT-IR. ESI-MS and thermal measurement techniques and their pharmacological properties were also tested. The DNA/bovine serum albumin (BSA) interactions of these compounds were demonstrated by spectrophotometric titration, fluorometric ethidium bromide kinetics, and DNA electrophoresis studies, and the stability of these compounds in physiological solution was also determined. The findings indicate that these compounds displayed a DNA/BSA-binding activity similar to that of cisplatin and exhibited a strong aqueous stability. The Au(I) compounds were potent antiproliferative agents with low necrotic activity and exhibited dose-dependent growth inhibition of cancer cells with IC50 value of 0.12–0.73?μM. Accumulation of p53 and decrease in Bcl-2 in cells exposed to Au(I) compounds may be the main causes for apoptotic effects, such as DNA fragmentation and nuclear collapse. Investigations regarding the mode of action of Au(I) compounds on cells revealed that they reduce the cell migration rate and the level of cytoskeletal proteins, namely CK7 and CK20. On the basis of this evidence, we suggest that strong antiproliferative activity, low necrotic effect, and micromolar dose range observed for Au(I) compounds make them suitable candidates for further pharmacological evaluation as chemotherapeutic agents in colon and cervix cancer.