Di-(2-ethylhexyl) dithiophosphoric acid surface protected gold nanoparticles: micellar synthesis, stabilization, isolation, and properties

Gold nanoparticles (AuNPs) were synthesized in the organic solution by means of the reduction of HAuCl₄ by hydrazine in reverse micelles of oxyethylated surfactant Triton N-42, with decane as the dispersion medium. To isolate the powder of particles, the micelles were destroyed with chloroform in the presence of di-(2-ethylhexyl) dithiophosphoric acid as a surface protecting agent. According to the results of several experiments, the yield is within the limits of 90–98%, calculated for gold. The obtained preparations are dark blue hydrophobic powders containing aggregated but not agglomerated gold nanoparticles, as well as microcrystals (∼0.08–0.2 μm) of NaCl. The powders get re-dispersed in weakly polar organic solvents with the formation of colloidal solutions. The shape of the nanoparticles is spherical. Their nuclei are gold single crystals with a narrow size distribution; their diameter (d _Au) is about two times as large as the diameter of the aqueous nucleus (d _c) of initial micelles: d _Au = 7.7 ± 1.4 nm (d _c = 3.6 nm) and 8.8 ± 1.5 nm (4.6 nm). The preparations were studied by means of dynamic light scattering, atomic force microscopy, transmission electron microscopy, UV–vis spectroscopy, IR spectroscopy, X-ray powder diffraction, and thermogravimetric and elemental analyses. In the case of the particles with d _Au = 8.8 nm, the product is a mixture of AuNPs and the salt with the molar ratio Au/NaCl ≈ 1:4.54, while the gross composition of AuNPs per one gold atom is estimated as Au(C₁₆H₃₄O₂PS₂Na∙2N₂H₄)_0.16 with the number of gold atoms in one particle ∼21,000.     

Impacts of gold nanoparticle exposure on two freshwater species: a phytoplanktonic alga (Scenedesmus subspicatus) and a benthic bivalve (Corbicula fluminea)

For years, nanotechnologies have developed the use of common materials, such as iron or silica, at an extremely small scale because of their new properties (reactivity, conductivity, optical sensitivity). More precisely, gold nanoparticles are used in numerous technologies such as electronics, new paints or research on cancer. But, despite their promising future and expansive utilization, only a few studies deal with their behaviors or impacts on the environment. Thus, we decided to explore the impacts of amine-coated 10nm gold nanoparticle (AuNp) contaminations on two freshwater aquatic models. The green algaScenedesmus subspicatus was submitted to 24 h-direct exposures at four AuNp concentrations (1.6×10², 1.6×10³, 1.6×10⁴ and 1.6×10⁵ AuNp/cell) along with a control condition. The process used for the freshwater bivalvesCorbicula fluminea was a trophic exposure during 7 days to three AuNp concentrations (1.6×10³, 1.6×10⁴ and 1.6×10⁵ AuNp/cell). These conditions were tested in triplicate with controls. For these experiments, OD measurements (γ= 520nm) were performed to verify AuNp concentrations in the water (stability). Cell numerations of algae were used to determine the growth/mortality effects on this species. Cellular impacts and AuNp distributions in the two species were revealed by transmission electron microscopy (TEM). The bioaccumulation rates were assessed by gold dosagesvia MS-ICP procedures. Molecular impacts were analyzed by quantifications of metallothionein concentrations (metal detoxification protein) and genetic expressions via real-time RT-PCR. Our study focused on the expression of six genes encoding proteins involved in: metal detoxification (metallothionein), the response to oxidative stress (catalase and superoxide-dismutase), the mitochondrial respiratory chain (subunit 1 of the cytochrome-C-oxidase), the concentration of mitochondria (RNA12s) and the response to xenobiotics (glutathione S transferase); using the β-actin as reference of the basal rates of gene expressions.     

Synthesis and antimicrobial activities of gold(I) sulfanylcarboxylates

Reaction of NaAuCl₄·H₂O and thiodiglycol (1:3 molar ratio) with 3-(aryl)-2-sulfanylpropenoic acids, H₂ xspa = [x:p = 3-phenyl-, f = 3-(2-furyl)-, t = 3-(2-thienyl)-, o-py = 3-(2-pyridyl)-, Clp = 3-(2-chlorophenyl)-, -o-mp = 3-(2-methoxyphenyl)-, -p-mp = 3-(4-methoxyphenyl)-, -o-hp = 3-(2-hydroxyphenyl)-, -p-hp = 3-(4-hydroxyphenyl)-, diBr-o-hp = 3-(3,5-dibromo-2-hydroxyphenyl)] and 2-cyclopentylidene-2-sulfanylacetic acid (H₂cpa) in a 1:1 metal/ligand molar ratio gave compounds of the type [Au(Hxspa)] or [Au(Hcpa)]. These compounds were reacted with diisopropylamine to afford [HQ][Au(xspa)] or [HQ][Au(cpa)] (HQ = diisopropylammonium) and with NaOH to afford Na[Au(xspa)]·H₂O and Na[Au(cpa)]·H₂O. All of the new compounds were isolated and characterised by IR and ¹H and ¹³C NMR spectroscopy. The antimicrobial activities of the complexes against Escherichia coli, Staphylococcus aureus, Bacillus subtilis, Candida albicans, Pseudomonas aeruginosa and carbapenem-resistant P. aeruginosa were evaluated and compared to those of the equivalent silver(I) complexes. The comparison shows that the gold compounds generally show better activity than the silver analogues against S. aureus and B. subtilis, but low sensitivity against E. coli, P. aeruginosa and C. albicans, suggesting a different mode of antimicrobial action for equivalent silver and gold compounds.     

A spectroscopic and electrochemical investigation of the oxidation pathway of glycyl-d,l-methionine and its N-acetyl derivative induced by gold(III)

The ¹H nuclear magnetic resonance spectroscopy was applied to study the reaction of the dipeptide glycyl-d,l-methionine (H-Gly-d,l-Met-OH) and its N-acetylated derivative (Ac-Gly-d,l-Met-OH) with hydrogen tetrachloridoaurate(III) (H[AuCl₄]). The corresponding peptide and [AuCl₄]^– were reacted in 1:1, 2:1, and 3:1 molar ratios, and all reactions were performed at pD 2.45 in 0.01 M DCl as solvent and at 25°C. It was found that the first step of these reactions is coordination of Au(III) to the thioether sulfur atom with formation of the gold(III)-peptide complex [AuCl₃(R-Gly-Met-OH-S)] (R=H or Ac). This intermediate gold(III) complex further reacts with an additional methionine residue to generate the R-Gly-Met-OH chlorosulfonium cation as the second intermediate product, which readily undergoes hydrolysis to give the corresponding sulfoxide. The oxidation of the methionine residue in the reaction between H-Gly-d,l-Met-OH and [AuCl₄]^– was five times faster (k ₂ = 0.363 ± 0.074 M^-1s^-1) in comparison to the same process with N-acetylated derivative of this peptide (k ₂ = 0.074 ± 0.007 M^-1s^-1). The difference in the oxidation rates between these two peptides can be attributed to the free terminal amino group of H-Gly-d,l-Met-OH dipeptide. The mechanism of this redox process is discussed and, for its clarification, the reaction of the H-Gly-d,l-Met-OH dipeptide with [AuCl₄]^– was additionally investigated by UV-Vis and cyclic voltammetry techniques. From these measurements, it was shown that the [AuCl₂]^– complex under these experimental conditions has a strong tendency to disproportionate, forming [AuCl₄]^– and metallic gold. This study contributes to a better understanding of the mechanism of the Au(III)-induced oxidation of methionine and methionine-containing peptides in relation to the severe toxicity of anti-arthritic and anticancer gold-based drugs.     

Electron microscopy studies of the thermal stability of gold nanoparticle arrays

A series of monolayer protected gold nanoparticle colloidal solutions have been prepared with average sizes in the 2–15nm range. If a drop of such a colloidal suspension is deposited onto a Si₃N₄ substrate and the solvent allowed to evaporate, the particles have a tendency to self-assemble into monolayer rafts with varying degrees of structural order depending on the initial mono-dispersity of the particles. The thermal stability of these selfassembled gold nanoparticle rafts as a function of particle size, heating method, heating rate and ligand identity have been assessed in this study. In-situ TEM studies show that sub-8nm Au nanoparticles on Si₃N₄ have a tendency to coarsen upon slow heating, whereas those comprised of larger particles exhibit densification. Increasing the heating rate for the smaller particles promoted densification, forcing them to form highly interconnected string-like structures. Finally, rafts of sub-4nm alkanethiol protected Au nanoparticles are shown to sinter spontaneously under ambient conditions at room temperature on the timescale of several months. This unexpected effect may have important implications for the long term structural stability of any device constructed from sub-4nm gold nanoparticles.     

The combination effects of trivalent gold ions and gold nanoparticles with different antibiotics against resistant Pseudomonas aeruginosa

Despite much success in drug design and development, Pseudomonas aeruginosa is still considered as one of the most problematic bacteria due to its ability to develop mutational resistance against a variety of antibiotics. In search for new strategies to enhance antibacterial activity of antibiotics, in this work, the combination effect of gold materials including trivalent gold ions (Au³⁺) and gold nanoparticles (Au NPs) with 14 different antibiotics was investigated against the clinical isolates of P. aeruginosa, Staphylococcus aureus and Escherichia coli. Disk diffusion assay was carried out, and test strains were treated with the sub-inhibitory contents of gold nanomaterial. Results showed that Au NPs did not increase the antibacterial effect of antibiotics at tested concentration (40 μg/disc). However, the susceptibility of resistant P. aeruginosa increased in the presence of Au³⁺ and methicillin, erythromycin, vancomycin, penicillin G, clindamycin and nalidixic acid, up to 147 %. As an individual experiment, the same group of antibiotics was tested for their activity against clinical isolates of S. aureus, E. coli and a different resistant strain of P. aeruginosa in the presence of sub-inhibitory contents of Au³⁺, where Au³⁺ increased the susceptibility of test strains to methicillin, erythromycin, vancomycin, penicillin G, clindamycin and nalidixic acid. Our finding suggested that using the combination of sub-inhibitory concentrations of Au³⁺ and methicillin, erythromycin, nalidixic acid or vancomycin may be a promising new strategy for the treatment of highly resistant P. aeruginosa infections.     

Novel cycloaurated gold(III) complexes and their effects on styrene polymerization

Novel cycloaurated gold(III) complexes were prepared by using Schiff bases with different substituents. Effects of the synthesized gold(III) complexes and substituent groups on styrene polymerization were investigated. As a result of these investigations, it was observed that gold(III) complexes could not catalyze polymerization reaction without addition of a co-catalyst like NaBAr′₄ (Ar′ = 3,5-bis(trifluoromethyl)phenyl). All ligands and complexes were characterized by using ¹H nuclear magnetic resonance (NMR), ¹³C-NMR, LC-MS, elemental analysis and FT-IR techniques. The architecture of the polymer was determined as an atactic or sydiotactic polymer by using ¹³C-NMR and DSC techniques. Molecular weights of the polymers were analyzed by using gel permeation chromatogram (GPC).     

Printing gold nanoparticles with an electrohydrodynamic direct-write device

A dispersion containing 15nm gold particles in ethanol was subjected to electrohydrodynamic atomization, producing droplets with an average size of ≈26μm as measured by laser diffraction. An electrohydrodynamic direct-write device was used to deposit the dispersion onto silicon wafers with the intention of printing gold tracks. Immediately after deposition ethanol evaporated, leaving the gold particles organised in a ≈75μm wide central region surrounded by two regions, each ≈50μm wide, at the edge of which two further gold tracks, each ≈7μm existed.     

Design of luminescent sulfur-containing polynuclear gold(I) complexes for advanced nanomaterials and chemosensors

A series of high-nuclearity gold(I) sulfido complexes with bridging diphosphine ligands have been synthesized and isolated, with the general formulae of [Au₁₀(μ-P^P)₄(μ₃-S)₄]X₂ and [Au₁₂(μ-P^P)₄(μ₃-S)₄]X₄ (P^P = diphosphine; X = PF₆ or ClO₄). Intense green and orange emissions were observed upon excitation at λ > 350 nm both in the solid state and in solutions. The green emission has been attributed to originate from excited states derived from the metal-perturbed intraligand (IL) transition while the orange emission arises from the ligand-to-metal-metal bond charge-transfer (LMMCT; S(Au...Au) states. The switching on and off of the LMMCT emission in a series of dinuclear gold(I) thiolate complexes with crown ether pendants induced by ion-binding has been demonstrated, and this provides a new strategy for the design of luminescence signalling and chemosensing devices in optoelectronics and sensor technology.     

The role of nanosized gold particles in adsorption and oxidation of carbon monoxide over Au/Fe2O3 Catalyst

The presence of gold is found to promote the development of weakly bonded (CO)_ad species over the surface of Au/Fe₂O₃ catalyst during interaction with carbon monoxide (CO) or a mixture of carbon monoxide and oxygen. The concentration of these species and the nature of the bonding depend on the gold particle size. No such species are formed for gold particles larger than ∼11 nm or over gold-free iron oxide. The bulk carbonate-like species, formed in the process with the involvement of the hydroxy groups of the support, are merely side products not responsible for the low temperature activity of this catalyst.     

Intrinsic reactivity of gold nanoparticles: Classical, semi-empirical and DFT studies

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 Hückel 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.     

Vapor pressure of SeO2 (s) and optical density of SeO2 (g)

The optical density of the vapor generated by SeO₂ (s) between about 416 and 505 K has been measured between 400 and 200 nm for optical path lengths of 10.14 and 10.15 cm and temperatures of 533, 733, 1133, and 1420 K. A pressure of oxygen of about 0.7 to 0.9 atm was present in the cells and that of Se₂ was below the minimum detectable of about 0.001 atm. For one cell, complete vaporization occurred at 481.5 K and a vapor pressure of 5.02 × 10⁻³ atm was calculated from the weight of SeO₂ (s), the volume profile of the optical cell, and the temperature distribution along the cell. Assuming Beer’s law is obeyed for a number of vibronic peaks, the vapor pressure is obtained as log₁₀ P (atm)=−5705/T+9.5443 in close agreement with two studies with fused silica Bourdon gauges. Beer’s law constants relating the pressure to the optical density at various wavelengths are obtained for the optical path temperatures listed above. Thermodynamic data previously published for solid and liquid SeO₂ need be changed only slightly to be consistent with the present vapor pressure. We obtain a standard enthalpy of sublimation at 298 K of 112.70 kJ/mol and standard entropies at 298 K of 258.72 and 66.693 J · mol⁻¹ · K⁻¹ for, respectively, gaseous and solid SeO₂.     

Oxygen-free precursor for chemical vapor deposition of gold films: thermal properties and decomposition mechanism

Thermal properties of oxygen-, phosphorus-, and halogen-free dimethylgold(III) diethyldithiocarbamate complex (CH₃)₂AuS₂CN(C₂H₅)₂ (gold, dimethyl(diethylcarbamodithioato -S,S′)-) having excellent storage stability and the mechanism of its decomposition to elemental gold were studied. Saturated vapor pressure was found to be ~10⁻³–10⁻¹ Torr at 50–90°C. Decomposition of the vapor on the surface starts at T = 210°C. The temperature dependence of gas phase composition was studied using the original mass spectrometric technique, it was established that the decomposition of the compound on the surface in vacuum follows three main pathways. Two of them result in the formation of elemental gold, saturated C2–C4 alkanes and (1) protonated ligand or (2) methylated ligand. The third one results in elemental gold and gaseous products: C2–C3 alkylmercaptanes and CH₃SCN(C₂H₅)₂. The formation of gold as a sole solid product within the temperature range 210–240°C was confirmed by X-ray photoelectron spectroscopy analysis. It was shown that the compound exhibits the best combination of volatility, thermal, and storage stability among volatile organogold complexes and thus it may be a promising precursor for obtaining gold films by chemical vapor deposition.     

Effect of silicon on the phase formation in mechanically activated systems based on Fe(75)C(25): Temperature-induced transformations in mechanosynthesized composites

Transformations realized in mechanosynthesized amorphous-nanocrystalline Fe(75)C(25 − x)Si(x) (0 ≤ x ≤ 10 at %) alloys during heating have been studied using dynamic magnetic susceptibility measurements, X-ray diffraction, and metallography. In contrast to mechanosynthesized alloys consisting of α-Fe, Fe₃C, and amorphous phases, the annealed alloys with x > 5 at % were found to exhibit the formation of an additional phase such as Fe₅SiC. After heating to 700 and 800°C, the powder particles of alloys contain a large amount of uniformly distributed graphite particles of ∼0.5 μm in size. The formation of particles results from the cementite decomposition, which is accelerated at the expense of partial silicon dissolution in cementite and in the presence of α-Fe nanograins as well.     

A review on fulminating gold (Knallgold)

Expensive and explosive! The reaction of ammonia and gold(III) compounds leads to explosive products known as “fulminating gold”. Gold scientists should be aware of the potential hazards involved in the reaction of these starting materials. Herein, a historic and scientific review on this fascinating substance is presented. Fulminating gold has been known since medieval times, but cannot be fully characterized due to its polymeric and heterogeneous character. Magnetic measurements confirm previous EXAFS analyses that the gold atoms have a square planar coordination environment (AuN₄-moieties that are party connected and form a 3-dimensional network). The explosive properties and resulting safety instructions are discussed in detail as well.     

Growing and stability of gold nanoparticles and their functionalization by cysteine

Gold nanoparticles in aqueous dispersion were prepared using the trisodium citrate reduction method to control the size of particles by changing the concentration of HAuCl₄. The average particle size measured by DLS is higher than that obtained by TEM at a zeta potential of -40 mV. When trisodium citrate concentration is kept constant, the particle size increases with gold concentration. The kinetics of growth was studied and apparent kinetic rate constants were determined at various gold/citrate ratios. Gold nanoparticles were attached to silanized glass surfaces; Au rods were grown (ca. 200 nm) by adding more precursors and the rods’ growth rate was monitored by UV-Vis spectroscopy as well as by AFM. Surface functionalization of gold surface was influenced by cysteine. The surface modification by cysteine at pH=6.0 results in aggregation and the red shift of absorption maximum is nearly 200 nm. When glutathione molecules are bound onto the cysteinelinked Au rods on the glass surface, the spectral shift reaches only an amount of 5–10 nm, because the surface attachment hinders the tendency to aggregate.     

Polymer-induced generation and characterization of electrophoretic properties of hollow TiOX nanospheres for electronic paper

Hollow TiO_X nanospheres have been successfully prepared using hollow core–double shell latex particles (poly(styrene-co-methyl methacrylate-co-butyl acrylate-co-methacrylic acid) (abbreviated in poly(St-co-MMA-co-BA-co-MAA)) as template, which involves the deposition of inorganic coating on the surface of hollow core–shell latex particles and subsequent removal of the latex by calcinations in air or ammonia gas. Ti(OBu)₄ was used as precursor for the preparation of hollow TiO_X nanospheres. TEM of white hollow core–double shell polymers particles with an aperture of approximately 225 nm displays the perfect characteristic hollow nanospheres structure of primary core–double shell particles. The formation of TiO_X was confirmed by XRD analysis and hollow structure of the particles was revealed by transmission electron microscopy (TEM). When the calcined temperature was at 800 °C, hollow TiO₂ nanospheres were arranged regularly with the diameter range of 130–170 nm. The electrophoretic properties were characterized by JS94J micro-electrophoresis apparatus. The electrophoretic mobility of white TiO₂ and black TiO hollow spheres in tetrachloroethylene were 1.09 × 10⁻⁵ and 3.12 × 10⁻⁵ cm²/V s, and the zeta potentials were 7.10 and 20.24 mV, respectively. The results show that white TiO₂ particles and black TiO hollow nanoparticles are suitable as electrophoretic particles and possess the application potential in the future electrophoretic display.     

Density of liquid gold measured by a non-contact technique

Electrostatic levitation together with multi-beam laser heating and ultraviolet imaging made possible to handle a sample of liquid gold, without any contamination, and to determine its density over a large temperature range. Over the 1337–1800 K interval, the density of Au was measured as ρ(T)=1.74× 10⁴−1.44 (T−T_m) kg·m⁻³, where Tm, the melting temperature, was 1337 K. These data yield a calculated volume expansion coefficient of 8.3×10⁻⁵ K⁻¹. The values agree well with the literature values.     

Vapor pressure of SeO2 (s) and optical density of SeO2 (g)

The optical density of the vapor generated by SeO₂ (s) between about 416 and 505 K has been measured between 400 and 200 nm for optical path lengths of 10.14 and 10.15 cm and temperatures of 533, 733, 1133, and 1420 K. A pressure of oxygen of about 0.7 to 0.9 atm was present in the cells and that of Se₂ was below the minimum detectable of about 0.001 atm. For one cell, complete vaporization occurred at 481.5 K and a vapor pressure of 5.02 × 10⁻³ atm was calculated from the weight of SeO₂ (s), the volume profile of the optical cell, and the temperature distribution along the cell. Assuming Beer’s law is obeyed for a number of vibronic peaks, the vapor pressure is obtained as log₁₀ P (atm)=−5705/T+9.5443 in close agreement with two studies with fused silica Bourdon gauges. Beer’s law constants relating the pressure to the optical density at various wavelengths are obtained for the optical path temperatures listed above. Thermodynamic data previously published for solid and liquid SeO₂ need be changed only slightly to be consistent with the present vapor pressure. We obtain a standard enthalpy of sublimation at 298 K of 112.70 kJ/mol and standard entropies at 298 K of 258.72 and 66.693 J · mol⁻¹ · K⁻¹ for, respectively, gaseous and solid SeO₂.     

Synthesis, processing and forming gold structures from a 0.1 wt. % concentration solution

A very low concentration (≈0.1 wt. %) of spherical 15nm diameter gold nanoparticles were produced by the sodium citrate reduction method and later transferred to ethanol using poly vinyl pyrrolidone (PVP) as a stabilizing agent. The alcosol was then subjected to electrohydrodynamic atomisation to generate fine droplets with an average droplet diameter of < 30μm and deposited on substrates accordingly. With the assistance of various deposition methods, three different microstructures were produced. Firstly, the droplets produced by atomisation with the help of an electric field were deposited at various times on a substrate to fabricate gold films with a thickness range of ~500nm to 2000nm. Secondly, the droplets were deposited on a moving table which is computer controlled to form an array of inter-connected droplets, thus enabling us to pattern microstructures containing gold nanoparticles of different geometries (electrohydrodynamic atomisation printing). Thirdly, to reduce the track size as well as to form a dense assembly of particles in the microstructures templates were used in conjunction with electrohydrodynamic atomisation (templateassisted patterning). In order to encapsulate gold nanoparticles in a fibre a co-axial needle set-up was used with a polyethylene oxide (PEO) and polyethylene glycol (PEG) mixture as the encapsulating media. Lastly, a gold hydrosol was used to produce near-monodisperse gold microbubbles with the help of a T-junction device having an average diameter of ≈150μm. The ability to generate such a range of structures starting from a very low concentration of gold is a significant achievement.