Showing papers in "Gold Bulletin in 2007"
TL;DR: The Lycurgus Cup as mentioned in this paper is a late Roman cut glass vessel which is extraordinary in several respects, firstly in the method of fabrication and the exceptional workmanship involved and secondly in terms of the unusual optical effects displayed by the glass.
Abstract: The Lycurgus Cup (fig 1) represents one of the outstanding achievements of the ancient glass industry. This late Roman cut glass vessel is extraordinary in several respects, firstly in the method of fabrication and the exceptional workmanship involved and secondly in terms of the unusual optical effects displayed by the glass. The Lycurgus Cup is one of a class of Roman vessels known as cage cups or diatreta, where the decoration is in openwork which stands proud from the body of the vessel, to which it is linked by shanks or bridges Typically these openwork “cages” comprise a lattice of linked circles, but a small number have figurative designs, although none of these is as elaborate or as well preserved as the Lycurgus Cup. Cage cups are generally dated to the fourth century A.D. and have been found across the Roman Empire, but the number recovered is small, and probably only in the region of 50-100 examples are known [1, 2]. They are among the most technically sophisticated glass objects produced before the modern era. The openwork decoration of the Lycurgus Cup comprises a mythological frieze depicting the legend of King Lycurgus from the sixth book of Homer’s Iliad. The figures, carved in deep relief, show the triumph of Dionysus over Lycurgus. However it is not only the cut-work design of the Cup that shows the high levels of skill involved in its production. The glass of the cup is dichroic; in direct light it resembles jade with an opaque greenish-yellow tone, but when light shines through the glass (transmitted light) it turns to a translucent ruby colour (Fig 1a and b). The cup was acquired by the British Museum from Lord Rothschild in 1958 (with the aid of a contribution from the National Art Collection Fund) [3]. The mythological scenes on the cup depict the death of Lycurgus, King of the Edoni in Thrace at the hands of Dionysus and his followers. A man of violent temper, Lycurgus attacked Dionysus and one of his
478 citations
TL;DR: In this paper, the suitability of various gold plating systems for device fabrication is examined and the properties of gold cyanide and sulfite baths and their limitations are considered first.
Abstract: The electrodeposition of gold is a key technology in the fabrication of many microelectronic, optoelectronic and microsystem devices. In this review, we examine some recent applications, and consider the suitability of various gold plating systems for device fabrication. The properties of gold cyanide and sulfite baths and their limitations are considered first. This is followed by an analysis of the latest generation of non-cyanide baths, including the thiosulfate, sulfite-thiosulfate and ammonium gold systems. Plating baths containing mercaptoalkylsulfonic acid and hydantoin ligands are also briefly discussed. Finally an analysis of the stability of gold plating baths is presented.
146 citations
TL;DR: The mechanisms of action of cytotoxic gold(III) complexes seem to be innovative and substantially different from that of cisplatin, and relevant antimitochondrial effects were demonstrated in some cases, eventually leading to cell apoptosis.
Abstract: Gold(III) complexes constitute a new class of metallodrugs, of potential interest for cancer treatment. During the past decade different kinds of gold(III) complexes have been reported to be appreciably stable under physiological-like conditions and to manifest relevant antiproliferative properties against selected human tumor cell lines. Some relevant examples are presented. Recent investigations point out that the interactions of cytotoxic gold(III) complexes with DNA are significantly different and weaker than those of platinum analogues; important interactions with model proteins and target proteins have been reported as well. Accordingly, the mechanisms of action of cytotoxic gold(III) complexes seem to be innovative and substantially different from that of cisplatin. Relevant antimitochondrial effects were demonstrated in some cases, eventually leading to cell apoptosis.
130 citations
TL;DR: Nanosized gold particles (27 +/- 3 nm) have been proven to be effective in ameliorating the symptoms of mycobacterial-, collagen- and pristane-induced arthritis in rat models, contrasting with the drug sodium aurothiomalate that was only effective against myc Cobacterial-inducedthritis but not to the same extent as Au0.
Abstract: Nanosized gold particles (27 +/- 3 nm) have been proven to be effective in ameliorating the symptoms of mycobacterial-, collagen- and pristane-induced arthritis in rat models. This contrasts with the drug sodium aurothiomalate that was only effective against mycobacterial-induced arthritis but not to the same extent as Au0. Gold in the traditional Indian Ayurvedic medicine, Swarna bhasma (gold ash), has been characterized as globular particles of gold with an average size of 56-57 nm.
88 citations
TL;DR: Faraday's 1857 lecture as mentioned in this paper focused on the interaction of light with metal particles, but much of this paper focused on various aspects of the formation, nature and properties of ruby gold, and these systematic studies and perceptive interpretations did in fact mark the birth of modern colloidal chemistry.
Abstract: From the paper in Philosophical Transactions entitled ‘Experimental relations of gold (and other metals) to light’ (1), based on his Bakerian lecture to the Royal Society in London on 5 February 1857, it is clear that Michael Faraday was fascinated by the ruby colour of colloidal gold. The objective of his investigations was to examine the interaction of light with metal particles, but much of this paper focused on various aspects of the formation, nature and properties of ruby gold, and these systematic studies and perceptive interpretations did in fact mark the birth of modern colloidal chemistry. This has now led to the strong emergence of the nanoscience of gold and nanotechnology (2), even although ruby glass was known to Faraday and had been used for centuries for stained glass windows, and ‘Purple of Cassius’, made from gold in the presence of tin, had been used for colouring glass and enamels since the seventeenth century (3). The work described in Faraday’s lecture fitted into his investigations into the relations between matter and electrical, magnetic, and optical phenomena (2). He was asking the question “to what extent experimental trials might be devised which, with their results and consequences, might contradict, confirm, enlarge, or modify... that wonderful production of the human mind, the undulatory theory of light...”. The action of light on particles which are small compared with the wavelength of light should produce interesting results, and gold sprang to mind because “known phenomena appeared to indicate that a mere variation in the size of its particles gave rise to a variety of resultant colours.” Although Faraday described work with a number of metals, the ruby colour produced in ‘solution’ by fine particles of gold which are “very minute in their dimensions”, and prepared via various practical approaches, was the main topic of his lecture. A typical preparation used an aqueous solution of a gold compound, e.g. NaAuCl 4 , and treated this with a reducing solution such as phosphorus in carbon disulfide in a two phase system. The yellow colour of sodium chloroaurate (NaAuCl 4 ) changes within minutes to the deep ruby colour of colloidal gold. Faraday concluded that the ruby fluid was gold dispersed in the liquid in a very finely divided metallic form not visible in any of the microscopes available in his day. Nearly 100 years later Turkevich et al (2, 4) used electron microscopic investigations to reveal that the ruby-coloured colloids made by Faraday’s preparative routes produce particles of gold with average sizes in the 6 ± 2 nm range. Faraday’s original gold colloids were very stable and at least one example survived until the second World War, when it was accidentally destroyed by enemy action, and an example is pictured in Figure 1. Gold Bulletin has monitored the development of uses for ruby gold via papers published by W.D. Mogerman (5), Leslie B. Hunt (3) and John Turkevich (4). Mogerman points out that the title for Faraday’s 1857 paper does not do full justice to its contents, but as usual, Faraday had very broad objectives in mind and he was clearly fascinated with the ruby gold ’suspensions’ and the various methods of obtaining them (the word ‘colloid’ was first coined only later by T.H.Graham in 1861 (2, 6). Yet the content of the lecture started from very small beginnings: in a strange statement written in a letter from Michael Faraday to his friend Prof C. F. Schönbein of Basle he wrote “I have been occupying myself with gold this summer; I did not feel headstrong enough for stronger things. This work has been of the Mountain and Mouse fashion; and if I ever publish it and it comes to your sight I dare say you will think so” (5). Hunt in his article entitled ‘The true story of the Purple of Cassius’, published in 1976 says “For the past 300 years the literature on gold, on glass and on ceramics has ascribed to Andrew Cassius the credit for discovering the purple preparation of colloidal gold and stannous hydroxide that bears his name
77 citations
TL;DR: Gold catalysts were prepared on TiO2 supports of different phase structures (i.e., anatase, rutile and biphasic), including surface and textural properties as discussed by the authors.
Abstract: Gold catalysts were prepared on TiO2 supports of different phase structures (i.e., anatase, rutile and biphasic), TiO2 crystal size (i.e., 9–23 nm), surface and textural properties (i.e., hydration and surface area). The CO oxidation on the gold catalysts was carried out in an operando-DRIFTS set-up equipped with DRIFTS reactor cell connected on-line to CO gas analyser and gas chromatograph enabling real time monitoring of surface reaction and simultaneous reaction rate measurements. Gold catalysts supported on pure anatase TiO2 were more resistant to sintering compared to catalysts supported on rutile and bi-phasic TiO2. Besides catalyst sintering, deposition of surface carbonates is an important cause of catalyst deactivation. The best gold catalyst was prepared on 13 nm anatase TiO2. It displays both increased activity and stability for CO oxidation reaction at room temperature. Surface and textural properties of TiO2 also play a role on the performance of the Au/TiO2 catalyst.
76 citations
TL;DR: The mesoporous NH2-MCM-41 adsorbent prepared by grafting aminopropyls on MCM41 is selective towards gold and palladium adsorptions and can separate these precious metals from complex solutions containing other metal ions such as cobalt, nickel, copper and zinc.
Abstract: The mesoporous NH2-MCM-41 adsorbent prepared by grafting aminopropyls on MCM-41 is selective towards gold and palladium adsorptions and can separate these precious metals from complex solutions containing other metal ions such as cobalt, nickel, copper and zinc. Adsorption is rapid and the adsorbent’s capacity for gold is better or comparable to most carbonaceous adsorbents including activated carbons. Furthermore, NH2-MCM-41 can separate palladium from gold solution at pH1.0 with excellent selectivity and capacity. Thus, it is possible to design a two steps separation process for the separation of palladium and then gold from the complex solution. A simple acid wash was sufficient to recover the adsorbed palladium and gold as concentrated, high purity (i.e., > 95%) metal salt solutions and the regenerated adsorbent was reused without lost of performance.
67 citations
TL;DR: In this article, a relationship between metal particle size and the particle's reactivity towards carbon monoxide (CO) was found for gold particles below 5-6 nm, while the contribution of the d-band hybridization energy to the total CO chemisorption energy is unfavourable for bulk gold.
Abstract: Gold nanoparticles used in most experiments (1–10 nm) in gold catalysis show varying degrees of reactivity, with particles below 5 nm generally being more reactive. The origin of this activity is a subject of a number of model experiments and theoretical studies on either clusters of a few atoms in size or extended surfaces (smooth or stepped). In the work described here, a classical theory for the variation of the metal workfunction with cluster size, Extended Huckel Theory (EHT) calculations combined with DFT calculations, as well as a carbon monoxide (CO) chemisorption model are combined to develop a relationship between metal particle size and the particle's reactivity towards CO. For gold, it is shown that while the contribution of the d-band hybridization energy to the total CO chemisorption energy is unfavourable for bulk gold, this is not true for gold particles below 5–6 nm. That is, the d-band hybridization energy is negative for small gold particles. This is believed to be explanation of the onset of high reactivity for small gold particles.
60 citations
TL;DR: The photocatalytic activity of Au modified titanium dioxide was evaluated in the photodegradation of the azo dye acid red 1 (AR1) under 254 nm irradiation as discussed by the authors.
Abstract: The photocatalytic activity of Au modified titanium dioxide was evaluated in the photodegradation of the azo dye Acid Red 1 (AR1) under 254 nm irradiation. Noble metal nanoparticles were deposited on TiO2 either through depositionprecipitation (DP), or by immobilisation of preformed metallic sols (polyvinylalcohol (PVA)/NaBH4 or tetrakis(hydroxymethyl)phosphonium chloride (THPC)/NaOH systems). Gold nanoparticles on the photocatalyst surface had dimensions of around 3–4 nm in diameter, as determined by HRTEM analysis, and exhibited visible light plasmon absorption. THPC Au/TiO2 appears to be the most photoactive amongst the photocatalysts with a 1 wt.% Au loading, while among THPC samples with different Au loadings (0.5–20.0 wt.%) the maximum photoactivity was attained with 5 wt.% Au/TiO2. The higher AR1 photodegradation rate observed on Au/TiO2 at basic pH can be related to the higher concentration of hydroxyl anions at the interface: these are able to effectively scavenge photoproduced valence band holes, possibly in competition with Au0 oxidation to Au+.
58 citations
TL;DR: This work describes how to prepare the conjugated particles, demonstrate that they will selectively attach ‘in vitro’ to their target macrophage cell but not to a non-target cell type and show that their presence renders the target cell susceptible to destruction by a low power laser.
Abstract: Gold nanoparticles can be conjugated with antibodies or other proteins, and the resulting composite particles will selectively attach to various kinds of biological material Although exploitation of this for staining microscopy specimens is well known, there has recently been interest in attaching gold nanoparticles tolive cells for therapeutic reasons One motivation is that gold nanoparticles display a strong plasmon resonance with light, which can be exploited in principle for an ‘in vivo’ photothermal therapy The treatment of cancer by this technique has recently received attention by others, but here we show how gold nanoparticlebased therapies can be developed to target live macrophage cells We have employed ‘active targeting’, a scheme in which gold nanoparticles are functionalised with an antibody specific to the target macrophage cell We describe how to prepare the conjugated particles, demonstrate that they will selectively attach ‘in vitro’ to their target macrophage cell but not to a non-target cell type and show that their presence renders the target cell susceptible to destruction by a low power laser
55 citations
TL;DR: The role of residual silver for catalytic activity towards CO oxidation in the temperature range from −20 to 50°C has been investigated by comparison with Au and Au/Ag zeolite catalysts as mentioned in this paper.
Abstract: Gold with a nanoporous sponge-like morphology, generated by leaching of AuAg alloys is presented as a new unsupported material system for catalytic applications. The role of residual silver for catalytic activity towards CO oxidation in the temperature range from −20 to 50°C has been investigated by comparison with Au and Au/Ag zeolite catalysts. As revealed by a systematic variation of the silver content in the zeolite catalysts, bimetallic systems exhibit a significantly higher activity than pure gold, probably due to activation/dissociation of molecular oxygen by silver. By STEM tomography we can unambiguously prove that at least some of the particles form inside the zeolite lattice.
TL;DR: In this article, the performance of gold nanosensors based on Localized Surface Plasmon Resonance (LSPR) designed by Electron Beam Lithography (EBL) in the context of biological and chemical sensing is discussed.
Abstract: In this paper, we discuss the performances of gold nanosensors based on Localized Surface Plasmon Resonance (LSPR) designed by Electron Beam Lithography (EBL) in the context of biological and chemical sensing. We demonstrate the sensitivity of our gold nanosensors by studying the influence of the concentration of 11-mercaptoundecanoic acid (MUA) on the shift of LSPR wavelength. Additionally, to study the selectivity of our nanosensors, the system Biotin/Streptavidin was used to detect very weak concentration of biomolecules. These results represent new steps for applications in chemical research and medical diagnostics.
TL;DR: In this paper, hybrid density functional calculations have been carried out for Au10, Au10-H2O, AU10-O2, and Au10 O2 model clusters, showing that the presence of H2O enhances the activation of O2 on the surface of an Au cluster.
Abstract: Hybrid Density functional calculations have been carried out for Au10, Au10-H2O, Au10-O2, and Au10-H2 O-O2 model clusters. The results show that all the Au10 clusters examined have a weak interaction with H2O and neutral and negatively charged Au10 clusters have a weak interaction with O2. Moreover, it is also found that the negative charge densities of O2 were greatly increased in the case of the coadsorption of O2 and H2O on the surface of the negatively charged Au10. These findings suggest that the presence of H2O enhances the activation of O2 on the surface of an Au cluster.
TL;DR: Investigations evidence the binding of aleurone protein to gold nanoparticles by electrostatic forces between the negatively charged citrate capped gold particles and the positively charged groups of the protein.
Abstract: Gold nanoparticles (size from 10 to 50 nm) were synthesized by three different methods and were characterized by UV-Vis spectroscopy and transmission electron microscopy (TEM). The shape and size distribution of gold nanoparticles were determined. The interaction of major storage protein extracted and purified from aleurone cells of barley with the gold colloids has been examined using absorption UV-Vis spectroscopy and TEM observations. These investigations evidence the binding of aleurone protein to gold nanoparticles. This binding might occur by electrostatic forces between the negatively charged citrate capped gold particles and the positively charged groups of the protein (e.g., arginine and lysine residues).
TL;DR: In this article, two optical effects are demonstrated for the detection of strain applied to elastomeric films, i.e., absorption from the gold nanoparticles and diffraction from the ordered structure, for early detection of structural damage in critical infrastructures.
Abstract: The application of two different optical effects is demonstrated for the detection of strain applied to elastomeric films. On one hand, dense coatings made of silica-coated gold nanoparticles (Au@SiO2 NPs), which are built up onto poly(dimethylsiloxane) (PDMS) elastomeric films, using the layer-by-layer (LbL) method, provide intense surface plasmon resonance (SPR) absorption. On the other hand, polystyrene spheres can be deposited as ordered monolayers to create patterned PDMS films with well-defined light diffraction. Both effects were used to monitor the structural damage of such PDMS films upon stretching, remaining both physical phenomena (absorption from the gold film and diffraction from the ordered structure) active for optical sensing applications in the early detection of structural damage in critical infrastructures.
TL;DR: In this paper, a new class of luminescent materials formed by the combination of pyridine ligands and gold are shown, which can act as emitters themselves or as donor or acceptors of electronic density depending on the electronic character of the substituents of the rings and the metal centers bonded to them.
Abstract: Pyridine-type ligands are considered one of the most versatile ligands in photochemistry since they can act as emitters themselves or as donor or acceptors of electronic density depending on the electronic character of the substituents of the rings and the metal centers bonded to them. Gold is a well known metal with an impressive tendency to form metal aggregates through metal-metal interactions and, therefore, gold complexes bearing these ligands are tailored derivatives with potential as emitting materials. The new possibilities of experimental and theoretical studies that appear with the easy synthesis of a new class of luminescent materials formed by the combination of pyridine ligands and gold are shown here.
TL;DR: In this paper, the changes of the surface plasmon resonance band of the assemblies of gold nanoparticles mediated by several different types of molecular mediators, including multidendate methylthiosilane thioether, homocysteine, 1-(4-methyl)-piperazinyl fullerene, and indolenine cyanine dye, are compared.
Abstract: The understanding of the interparticle interactions and reactivities is essential to the exploitation of the unique optical, electronic, and chemical or biological properties of gold nanoparticles in many areas of nanotechnology. This paper describes findings of a comparison of optical properties of molecularlymediated assemblies of gold nanoparticles where the interparticle interactions and spatial properties are defined by molecular mediators and templates. The changes of the surface plasmon resonance band of the assemblies of gold nanoparticles mediated by several different types of molecular mediators, including multidendate methylthiosilane thioether, homocysteine, 1-(4-methyl)-piperazinyl fullerene, and indolenine cyanine dye, are compared. In the assembly process, the size of individual Au nanoparticles and the volume fraction of gold nanoparticles in the solution should remain largely constant, whereas the interparticle distance changes, which leads to changes in the interparticle dielectric medium constant or refractive index. The changes in the SP band in relation to the change in effective refractive index are discussed, along with their implications to assembly sizes, interparticle interactions, and potential applications in designing electrical and optical sensors.
TL;DR: In this article, the authors used 1% gold on cerium and zirconium oxides (CeO2, Ce0.5Zr 0.5O2 and ZrO2) for the oxidation of volatile organic compounds (VOCs).
Abstract: Catalysts for the oxidation of volatile organic compounds (VOCs) were prepared by supporting 1% gold on cerium and zirconium oxides (CeO2, Ce0.5Zr0.5O2, ZrO2) using a simple impregnation method followed by reduction of gold in the presence or absence of ammonia (N). The catalysts were tested in model reactions, namely the total oxidation of benzene, hexane and chlorobenzene, using a micro flow reactor at atmospheric pressure in the temperature range 100–500°C and their activity was compared to that of Au/TiO2 and Au/Fe2O3 reference catalysts supplied by the World Gold Council (WGC). Benefits on the light-off temperatures were observed by adding gold to cerium-containing oxides: 100% conversion of hexane was obtained with Au/Ce0.5Zr0.5O2 at the lowest temperature (300°C). Full conversion of benzene was reached at only 250°C with Au/CeO2 (N), at 290°C with Au/Fe2O3 (WGC) and at 300°C with Au/Ce0.5Zr0.5O2. In the case of chlorobenzene oxidation, the addition of gold was of even greater relevance because of a drop in the light-off temperature of over 100°C for Au/Ce0.5Zr0.5O2 and Au/CeO2, with respect to the gold-free oxide supports; but in this case rapid deactivation took place.
TL;DR: In this paper, a review of existing nanolithographic techniques for the fabrication of nanoscale precious metal artefacts is presented, and a survey of the existing and potential applications for these structures is given.
Abstract: Gold is the material of first choice for the realisation of a large number of interesting nanoscale devices and structures due to its unique chemical and optical properties. However, conventional photolithographic processes cannot be used to manufacture such tiny structures in gold (or any other material) due to limitations imposed by the diffraction of light. New methods of lithography have been developed to overcome this limitation. In this article we review these new nanolithographic techniques, describe how they have been used to produce nanoscale precious metal artefacts, and briefly survey some of the existing and potential applications for these structures.
TL;DR: A facile and completely green route to synthesize Au nanoparticles by mixing the Au(III) ions-dissolved rice wine and soda at a slightly elevated temperature in the absence of extra protective agents was developed as discussed by the authors.
Abstract: A facile and completely green route to synthesize Au nanoparticles by mixing the Au(III) ions-dissolved rice wine and soda at a slightly elevated temperature in the absence of extra protective agents was developed. Rice wine was used as a solvent and a reducing agent. Also, soda not only functioned as a protective agent but also played a role of base catalyst. No extra protective agents are needed. From the analyses of UV/VIS absorption spectra, TEM, and XRD patterns, the formation of Au nanoparticles was recognized. The appropriate pH and temperature were around 6.5 and 25–55°C, respectively. The resultant solution was quite stable. No precipitation occurred even after several months. In addition, rice wine and soda are often used as the additives of drinks or foods, and are easily obtained in our daily life. So, it becomes possible that people can easily make the Au nanoparticles at home by the route proposed in this work.
TL;DR: In this article, the optical properties of Au2Cl2(μ-dpephos) compounds have been revisited and new results on the use of the complexes as Ag(I) probes are discussed.
Abstract: In the last few years we have analysed the factors that affect the structures and luminescence properties of Au(I) compounds, specifically in relation with the presence of aurophilic contacts and their application as cation probes. EXAFS studies have allowed us to obtain for the first time direct structural data of dissolved Au(I) compounds. An overview of the work reported to date is presented here. The optical properties of complex [Au2Cl2(μ-dpephos)] (dpephos =bis(2-diphenylphosphino) phenylether, 1) have been revisited and new results are now included. New aspects on the use of the complexes as Ag(I) probes are also discussed.
TL;DR: In this article, two different kinds of sensors have been developed by using the same kind of vapochromic complexes: sol-gel and electrostatic self-assembly (ESA).
Abstract: Two different kinds of sensors have been developed by using the same kind of vapochromic complexes. The vapochromic materials [Au2Ag2(C6F5)4L2]n have different colours depending on the ligand L. These materials change, reversibly, their optical properties, colour and fluorescence, in the presence of the vapours of volatile organic compounds (VOCs). For practical applications, two different ways of fixing the vapochromic material to the optical fibre have been used: the sol-gel technique and the electrostatic self-assembly method (ESA). With the first technique the sensors can even be used to detect VOCs in aqueous solutions, and using the second method it has been possible to develop nanosensors.
TL;DR: In this paper, nonionic surfactants such as T-80 not only act as stabilizing or protecting agents, but also can act as reducing agents for a facile "one-pot" synthesis of gold nanoparticles in an aqueous medium with tunable size at ambient conditions.
Abstract: We demonstrated for the first time that nonionic surfactants such as T-80 not only act as stabilizing or protecting agents, but also can act as reducing agents for a facile “one-pot” synthesis of gold nanoparticles in an aqueous medium with tunable size at ambient conditions.
[...]
TL;DR: In this paper, high activation barriers were obtained for the electrophilic substitution in [Au(HCO2)2]- and [AI(acac) 2]- complexes with methane, which excludes the possibility that these reactions might proceed under mild conditions.
Abstract: The reactions of methane with the gold complexes [Au(OH)]−, [Au(OCH3)4]−, [Au(O(CO)2O2]− and [Au(O2CH)2]+, [AuI(acac)], [AuIII(acac)2]+ (acac-acetylacetonato) were studied using the DFT/PBE method with the SBK basis set. High activation barriers were obtained for the electrophilic substitution in [Au(OH)]−, [Au(OCH3)4]−, [Au(O(CO)2O)2]-and [AuIII(acac)2]+ complexes, which excludes the possibility that these reactions might proceed under mild conditions. The reactions of the [Au(HCO2)2]+ and [AuI(acac)] complexes with methane have rather low energy barriers and proceed through the formation of an intermediate complex. The alternative mechanism of methane oxidation with a gold complex in the presence of oxygen is simulated.
TL;DR: In this article, the interaction of the major storage protein extracted and purified from aleurone cells of barley with the gold nanostructured films has been examined using absorption UV-Vis spectroscopy and atomic force microscopy (AFM).
Abstract: Gold auto-assembled films were prepared from gold colloidal aqueous solutions on glass slides silanized with 3-aminopropyl-triethoxysilane at room temperature and with a thermal treatment at 200°C. The interaction of the major storage protein extracted and purified from aleurone cells of barley with the gold nanostructured films has been examined using absorption UV-Vis spectroscopy and atomic force microscopy (AFM). The UV-Vis spectra evidence the binding of major aleurone protein to gold nanostructured films. The AFM allowed the examination of the topography of the protein adsorbed films on gold auto-assembled films at the nanometric scale and confirmed that the protein forms a stable layer, following the morphology of gold nanostructured films decreasing the roughness of the gold surface. In all cases, protein was found to be adsorbed on gold surfaces and to form a stable protein layer.
TL;DR: In this article, two pretreatments are found possible to activate these catalysts for CO oxidation: (i) high-temperature hydrogen reduction and (ii) aqueous base treatment using NH3(aq).
Abstract: In this study, Au/TiO2, Au/γ-Al2O3, and Au/C catalysts were prepared by an incipient-wetness impregnation method. The CO oxidation activity after different pretreatment was analyzed. Two pretreatments are found possible to activate these catalysts for CO oxidation: (i) high-temperature hydrogen reduction and (ii) aqueous base treatment using NH3(aq). The high-temperature hydrogen reduction is effective for Au/TiO2 and Au/C, but not Au/Al2O3. The base treatment is effective for Au/Al2O3 and Au/TiO2, but not Au/C. Small Au particles of ca. 2 nm size were observed in activated Au catalysts from both pretreatments; however, the high-temperature H2 reduction procedure also resulted in large Au particles of ca. 25 nm size which makes it a less efficient pretreatment than the base treatment. The activated Au/TiO2 catalysts show comparable turnover frequency as the Au/TiO2 catalyst prepared by a deposition precipitation method. The effective pretreatments were found to be accompanied by a reduced acidity, which is measured by the pH of aqueous catalyst suspension. Reasons for such activation are discussed.
TL;DR: In this paper, an overview of the precious alloys that could be of interest due to the inherent properties of the thermo-elastic martensitic transformation that they exhibit is presented.
Abstract: In this paper we will consider an overview of the precious alloys that could be of interest due to the inherent properties of the thermoelastic martensitic transformation that they exhibit. For sure one of the main representatives of these materials can be considered the AuAlCu system (and the related well known SpangoldTM). Actually in the literature, since the late '70s, other systems have been indicated of interest but they knew a very limited success. We refer here to some pioneering work from G.B. Brook In more recent time the increasing experience in the science and technology of conventional shape memory alloys like NiTi (which in the meantime successfully reached the application field) brought a new interest for a clear understanding of the potential of these gold alloys. Here we report on results obtained in the three areas: spangold-like alloys, AuCuZn alloys, and a ternary modification of NiTi, i.e. NiTiAu. The samples used for the investigation have been prepared starting from pure metals and thoroughly investigated by means on differential scanning calorimetry, X-ray diffraction at different temperatures and optical microscopy. When possible the samples were submitted to simple recovery test to verify the amount of shape memory and/or pseudoelastic properties.
TL;DR: In this article, the authors describe the microstructuring of gold-ruby glasses with synchrotron radiation and show that plasmonic or luminescent microstructures with a lateral width of minimum 5 μm can be written directly into the glasses by implementing X-ray lithography.
Abstract: We describe the microstructuring of gold-ruby glasses with synchrotron radiation. Plasmonic or luminescent microstructures with a lateral width of minimum 5 μm can be written directly into the glasses by implementing X-ray lithography. The technique involves two steps: First, gold containing glass samples are irradiated with synchrotron X-rays through a microstructured mask. And second, subsequent annealing at minimum 500°C induces the growth of gold nanoparticles. The patterned sites are ruby coloured due to the gold surface plasmon resonance of gold nanoparticles. Furthermore we investigated the photoluminescence of the microstructured glass. After synchrotron irradiation a red photoluminescence is observed under UV light excitation. Subsequent annealing for a few minutes at 300°C induces the quenching of the red luminescence. If the irradiated sample is annealed for 5 minutes at a higher temperature of 500°C a bright green light emission is detected. The green photoluminescence decreases after further annealing and finally vanishes. We assume that the origin of the luminescence are silicate hole centres. The technique of generating gold particles with synchrotron X-ray lithography has potential to produce micro-optical devices like optical storage units, photonic crystals, gratings or sensors.
TL;DR: In this paper, the performance of catalysts for selective catalytic reduction of NO by propene under an oxygen-rich atmosphere was investigated over Au/ CeO2, Au/CeO2/Al2O3 and Au/Al 2O3 catalysts prepared by deposition-precipitation.
Abstract: Selective catalytic reduction of NO by propene under an oxygen-rich atmosphere has been investigated over Au/ CeO2, Au/CeO2/Al2O3 and Au/Al2O3 catalysts prepared by deposition-precipitation. The results demonstrated that Au/16%CeO2/Al2O3 had good low-temperature activity, selectivity towards N2 and stability, which is superior to that of Pt/Al2O3. It was also found that adding 2% water vapour to the feed stream enhanced the NO conversions at low temperatures while the presence of 20 ppm SO2 increased NO conversions at higher temperatures. It is particularly interesting that under the simultaneous presence of 2% water vapour and 20 ppm SO2, the NO conversions to N2 were significantly increased and the temperature window was widened significantly. The catalysts were characterized by Xray diffraction (XRD), high resolution transmission electron microscopy coupled with energy dispersive X-ray spectroscopy (HRTEM-EDX) and temperatureprogrammed reduction (H2-TPR) techniques. Both XRD and HRTEM revealed that CeO2 was highly dispersed on the alumina support, and HRTEM combined with EDX showed that gold particles were preferentially deposited on those highly dispersed CeO2 particles. The gold deposition made CeO2 more reducible and interaction between gold and those highly dispersed CeO2 particles became stronger than that with the bulk CeO2, and this interaction is probably responsible for the superior catalytic performance of the Au/CeO2/Al2O3.
TL;DR: Phenol synthesis using a homogeneous gold catalyst serves as an example of the tremendous progress in homogeneous catalysis by gold, which has been made in the past few years.
Abstract: Phenol synthesis using a homogeneous gold catalyst serves as an example of the tremendous progress in homogeneous catalysis by gold which has been made in the past few years. Various aspects of this reaction, including catalyst selectivity and activity and the simple conditions used are described; and the mechanism is discussed in this context.