Chemical Synthesis,Structure Characterization,and Optical Properties of Hollow PbSx–Solid Au Heterodimer Nanostructures

Heterodimer nanostructures have attracted extensive attention, owing to an increasing degree of complexity, functionality, and then importance. So far, all the reported ones are built from solid nanoparticles. Herein, nearly monodisperse heterodimer nanostructures are constructed by hollow PbS_x and solid Au domains simultaneously through a mild reaction between PbS nanocrystals and the gold species in the presence of dodecylamine. Control experiments clearly reveal the underlying formation mechanism of the hollow PbS_x–solid Au heterodimers. The Au^III species in the solution, lead to the etching of PbS nanocrystals and the Au^I species facilitate the control of the number of gold domains per nanoparticle. Dodecylamine molecules not only work as a stabilizer in the reaction, but also act as a reducing agent that could greatly affect the morphology of the product. The optical properties of the heterodimers are investigated based on UV/Vis absorption spectroscopy and Raman spectroscopy. This novel heterodimer nanostructure pushes the development of complex nanocrystal‐based architectures forward, and also provides many opportunities for potential applications.     

Superoxide Formation on Isolated Cationic Gold Clusters

Gold nanoparticles are known to be highly versatile oxidation catalysts utilizing molecular oxygen as a feedstock, but the mechanism and species responsible for activating oxygen remain unclear. The reaction between unsupported cationic gold clusters and molecular oxygen has been investigated. The resulting complexes were characterized in the gas phase using IR spectroscopy. A strong red‐shift in the observed ν(O‐O) stretching frequency indicates the formation of superoxo (O₂^?) moieties. These moieties are seen to form spontaneously in systems, which upon electron transfer attain a closed shell within the spherical jellium model (Au₁₀⁺ and Au₂₂⁺), whereas an oxygen induced self‐promotion in the activation is observed for other systems (Au₄⁺, Au₁₂⁺, Au₂₁⁺).     

Quantum chemical study of the charged gold atom influence on the mechanism of allylbenzene double bond migration

The DFT calculations of allylbenzene double bond migration were performed in the presence of gold ions Au^? and Au⁺ and the cluster Au₄, which are models of active sites of the gold-containing catalysts. The mechanism of isomerization is determined by the charge of the metal. For the allylbenzene + Au⁺ system, the most appropriate mechanism is the multistage metal-allylic process passing through either the formation of a gold-hydride complex, or no hydride complex is formed in the presence of Au^?. The calculated rate constant of the rate-determining step of the catalytic reaction increases in the order Au₀ < Au^? < Au⁺. The Au^??+ particles are active sites in allylbenzene isomerization. Additional routes of accumulation of the trans-isomer result in the selective formation of trans-??-methylstyrene observed in the catalytic conversion of allylbenzene in the presence of gold nanoparticles. The metal-allylic mechanism is the most preferential in the presence of Au₄ cluster. The high energy of the bond of allylbenzene with the cluster is possibly due to the high reactivity of the latter.     

Synthesis of alginate stabilized gold nanoparticles by γ-irradiation with controllable size using different Au3+ concentration and seed particles enlargement

Gold nanoparticles with pre-selected size in the range 5–40 nm were synthesized by γ-irradiation of Au³⁺ solution containing natural polysaccharide alginate as a stabilizer. The gold nanoparticles with controllable size were prepared by two approaches: (i) varying the concentration of Au³⁺ from 0.25 to 1 mM and alginate from 0.25% to 1% (w/v) and (ii) enlargement of seed particles with double size from 20 to 40 nm at [Au³⁺]/[Au⁰]=6. The obtained gold nanoparticles were characterized by UV–vis spectroscopy and transmission electron microscopy. The results indicated that γ-irradiation method is suitable for production of gold nanoparticles with controllable size and high purity.     

Surface characterization of immunosensor conjugated with gold nanoparticles based on cyclic voltammetry and X-ray photoelectron spectroscopy

This investigation describes the surface characterization of rabbit immunoglobulin G (IgG) conjugated with gold nanoparticles. Goat anti-rabbit immunoglobulin G tagged with 5 nm gold nanoparticles was applied to detect the IgG. Then, the autocatalyzed deposition of Au³⁺ onto the surface of anti-IgGAu increased the surface area per gold nanoparticle. The immobilization chemistries and the atomic concentrations of Au_4f, P_2p, S_2p, C_1s, N_1s and O_1s of the resulting antibody-modified Au electrodes were determined by X-ray photoelectron spectroscopy (XPS). The sulfur that is involved in the cysteamine binding and the enlargement of the gold nanoparticles are identified using cyclic voltammetry. The results reveal that the surface area per gold particle, following the autocatalyzed deposition Au³⁺ on the surface of anti-IgGAu, was approximately seven times higher than that before deposition.     

Imaging mass spectrometry of gold nanoparticles in a tissue section as an immunohistochemical staining mass probe

For analysis of low abundance peptides in a tissue section, immunohistochemical staining through antibody‐antigen interaction is a usual technique. The antibody is conjugated with a probe moiety that aids in highly sensitive detection. Gold nanoparticles, which show excellent chemical stability and variation of surface modifications, are expected to act as a sensitive mass probe to desorb gold ions (Au⁺, Au₂⁺, Au₃⁺) that are distinguishable from fragment ions from organic molecules. Here, green fluorescent proteins (GFP) in a tissue section of a transgenic zebrafish were detected by the gold mass probe conjugated with antibodies. Due to the efficient ionization and desorption of gold ions, imaging mass spectrometry of Au₂⁺ ions indicated the distribution of gold nanoparticles stained in a tissue section, and the mass signal distribution was consistent with the area where the GFP‐expressing cells were distributed. Conventional immunofluorescence techniques showed intense autofluorescence that come from intrinsic fluorophores in the tissue section. In contrast, the gold nanoparticles acted as an immunostaining mass probe that displayed significantly lower background signals.     

Synthesis and study of gold nanoparticles stabilized by bioflavonoids

A new procedure for the preparation of biocompatible gold nanoparticles using bioflavonoids: rutin, quercetin, and luteolin as reducing agents and stabilizers was proposed. On varying the bioflavonoid concentration, nanoparticles of different size are formed. By the combined use of spectroscopy and atomic force microscopy, the nanoparticle size was estimated (40–50 nm). Uniform and highly dispersed gold nanoparticles were obtained at Au: rutin ratios of 1: 1, 2: 1, and 4: 1 and Au: quercetin ratios of 2: 1 and 4: 1. The nanoparticle yield remains almost constant as the Au: rutin ratio varies over a broad range from 1: 1 to 12: 1. It was suggested that complete reduction of Au^III to Au⁰ with a large excess of Au is accompanied by extensive oxidation of bioflavonoid involving an intermediate oxidant formed in the system due to the high oxidative capacity of Au^III. For elucidating the catalytic role of bioflavonoids in the formation of gold nanoparticles, quantum chemical modeling of the process was performed.     

Synthesis of gold nanoparticles by reduction of HAuCl4 under UV irradiation

Gold nanoparticles were prepared in surfactant solutions by reduction of HAuCl₄ under UV irradiation without adding extra reductants or other organic substances. The effect of the structure and the property of surfactant on the size and the optical properties of prepared gold nanoparticles were studied. It was found that the longer the alkyl chain of the surfactant, the larger gold particles are obtained. On the other hand, lengthen the geminis spacer benefits the formation of smaller gold particles. The formation of adduct micelles composed of the charged surface active portion of the surfactant molecule and the (Au^IIICl₄)⁻ ion in cationic surfactant solution serves as the gold source and favors the formation of gold particles with larger sizes. While the repulsion between the (Au^IIICl₄)⁻ ion and the negative charged surface of anionic surfactant micelle is in favor of the formation of gold nanoparticles with smaller sizes. The nonionic surfactants can also assist the formation of dispersed gold nanoparticles.     

Self‐Assembly of a Au16 Ring via Metal–Metal Bonding Interactions

Metal–metal bonding interactions have been employed as an efficient strategy to generate a number of unique gold(I) metallo‐macrocycles with fascinating functions. The self‐assembly, crystal structure and emission property of novel nest‐like tetramer 1₄ , namely, {[Au₄(μ‐dppm)₂(μ‐dctp^2?)](BF₄)₂}₄ ? (CH₃CN)₂ (dppm=bis(diphenylphosphino)methane, dctp^2?=N,N′‐bis(dicarbodithioate)‐2,11‐diaza[3.3]paracyclophane) is reported. The complex has been characterized by single‐crystal X‐ray diffraction analysis, ¹H NMR spectroscopy, ¹³C NMR spectroscopy, and CSI‐MS spectrometry. The aggregate demonstrates the sixteen gold(I) atoms are arranged in a ring with a circumference of 50.011(68) Å generated by Au^I???Au^I attractions. UV/visible and luminescence spectroscopy revealed that this Au^I???Au^I bonded metallo‐macrocycle exhibited yellow phosphorescence.     

Unique Fluorogenic Ratiometric Fluorescent Chemodosimeter for Rapid Sensing of CN− in Water

A new benzimidazole‐spiropyran conjugate chemosensor molecule ( BISP ) has been synthesized and characterized by ¹H NMR spectroscopy, mass spectrometry (ESI‐MS), and elemental analysis. The two isomeric forms ( BISP ? BIMC ) were shown to be highly selective and sensitive to CN^? among the ten anions studied in aqueous HEPES buffer, as shown by fluorescence and absorption spectroscopy and even by visual color changes, with a detection limit of 1.7 μM for BIMC . The reaction of CN^? with BIMC was monitored by ¹H NMR spectroscopy, high‐resolution mass spectrometry (HRMS), UV/Vis measurements, and fluorescence spectroscopy in HEPES buffer of pH 7.4. TDDFT calculations were performed in order to correlate the electronic properties of the chemosensor with its cyanide complex. Further, titration against thiophilic metal ions like Au³⁺, Cu²⁺, Ag⁺, and Hg²⁺ with [ BIMC‐CN ] in situ showed that it acts as a secondary recognition ensemble toward Au³⁺ and Cu²⁺ by switch‐on fluorescence. In addition, a reversible logic‐gate property of BIMC has been demonstrated through a feedback loop in the presence of CN^? and Au³⁺ ions, respectively. Furthermore, the use of BIMC to detect CN^? in live cells by fluorescence imaging has also been demonstrated. Notably, test strips based on BIMC were fabricated, which could serve as convenient and efficient CN^? test kits.     

Polynuclear Gold [AuI]4, [AuI]8, and Bimetallic [AuI4AgI] Complexes: C−H Functionalization of Carbonyl Compounds and Homogeneous Carbonylation of Amines

The synthesis of tetranuclear gold complexes, a structurally unprecedented octanuclear complex with a planar [Au^I₈] core, and pentanuclear [Au^I₄M^I] (M=Cu, Ag) complexes is presented. The linear [Au^I₄] complex undergoes C?H functionalization of carbonyl compounds under mild reaction conditions. In addition, [Au^I₄Ag^I] catalyzes the carbonylation of primary amines to form ureas under homogeneous conditions with efficiencies higher than those achieved by gold nanoparticles.     

On the Non‐Metallicity of 2.2 nm Au246(SR)80 Nanoclusters

The transition from molecular to plasmonic behaviour in metal nanoparticles with increasing size remains a central question in nanoscience. We report that the giant 246‐gold‐atom nanocluster (2.2 nm in gold core diameter) protected by 80 thiolate ligands is surprisingly non‐metallic based on UV/Vis and femtosecond transient absorption spectroscopy as well as electrochemical measurements. Specifically, the Au₂₄₆ nanocluster exhibits multiple excitonic peaks in transient absorption spectra and electron dynamics independent of the pump power, which are in contrast to the behaviour of metallic gold nanoparticles. Moreover, a prominent oscillatory feature with frequency of 0.5 THz can be observed in almost all the probe wavelengths. The phase and amplitude analysis of the oscillation suggests that it arises from the wavepacket motion on the ground state potential energy surface, which also indicates the presence of a small band‐gap and thus non‐metallic or molecular‐like behaviour.     

Facile Synthesis of Gold Icosahedra in an Aqueous Solution by Reacting HAuCl4 with N‐Vinyl Pyrrolidone

Herein we describe a protocol that generates Au icosahedra in high yields by simply mixing aqueous solutions of HAuCl₄ and N‐vinyl pyrrolidone. Our mechanistic study reveals that water plays an important role in this synthesis: as a nucleophile, it attacks the gold–vinyl complex, leading to the production of an alcohol‐based Au^I intermediate. This intermediate then undergoes a redox reaction in which Au^I is reduced to Au⁰, leading to the formation of Au atoms and then Au icosahedra of about 18 nm in size at a yield of 94 %, together with a carboxylic acid in the final product. This new protocol has also been employed to prepare multiply twinned nanoparticles of Ag (15–20 nm in size), spherical aggregates (25–30 nm in size) of Pd nanoparticles, and very small nanoparticles of Pt (2 nm in size). Since no organic solvent, surfactant, or polymer stabilizer is needed for all these syntheses, this protocol may provide a simple, versatile, and environmentally benign route to noble‐metal nanoparticles having various compositions and morphologies.     

Synthesis of Au13(glutathionato)8@β-cyclodextrin nanoclusters and their use as a fluorescent probe for silver ions

Heating and drying of the mixture of glutathione-etched gold nanoparticles (Au-SG) and β-cyclodextrin (β-CD) results in the formation of β-CD-capped and glutathionate-protected Au₁₃ nanoclusters (Au₁₃(SG)₈@β-CD). Their particle size, composition, and number of gold atoms and the capping molecules were characterized by scanning electron microscopy, fluorescence, UV–vis absorption, FT-IR spectroscopy and mass spectrometry. The fluorescence of these nanoclusters is specifically enhanced by the addition of Ag(I) ions to the aqueous solution. This effect was exploited to develop a selective and sensitive method for the fluorometric determination of Ag(I) in water in the concentration range between 0.5 nM and 0.1 μM, with a detection limit at 0.3 nM (at a signal-to-noise ratio of 3). Graphical Abstract

β-CD-capped Au₁₃ nanoclusters has been synthesized by heating and drying the mixture of glutathione-etched gold nanoparticles and β-CD. A simple, sensitive and selective FL sensing method for Ag⁺ in environmental water has developed using the Au nanoclusters.     

A method to construct polyelectrolyte multilayers film containing gold nanoparticles

Gold nanoparticles in polyelectrolyte multilayers film can be easily prepared by repeating immersion of a substrate in poly(diallyl dimethylammonium) chloride (PDDA)-AuCl₄⁻ complexes solution followed by reduction Au³⁺ through heating. UV-vis spectroscopy, cyclic voltammetry (CV) and tapping-mode atomic force microscopy (AFM) are used to confirm the successful construction of the polyelectrolyte multilayers film and the formation of gold nanoparticles. The multilayers film shows electrocatalytic activity to dioxygen reduction.     

One-pot synthesis of pH and temperature sensitive gold clusters mediated by a recombinant elastin-like polymer

Here, we described a “one-pot” synthesis of smart hybrid materials based on elastin-like recombinamers (ELRs) and gold nanoparticles. Outstandingly, the reduction of auric acid in the presence of ELR Glu15 gave biohybrid Au-Glu15. TEM analysis carried out for Au-Glu15 exhibited nano-sized gold crystals with diameter ranging from 2 to 11 nm. Furthermore, Au-Glu15 promoted the formation of linear arrangements of gold clusters in areas of low particle density. Remarkable was that analogous architectures were obtained in a control experiment carried out with Glu15 and gold nanoparticles synthesized via a citrate reduction route. Therefore, Glu15 promoted the formation of 2D linear arrangements of gold clusters that exhibited interparticle distances in the range from 10 to 40 nm. Notable were the branched nanostructures exhibited by Au-Glu15B obtained for reduced gold-ELR mixtures that exhibited a lower gold ratio. On the other hand, Au-Glu15 exhibited spectroscopic properties (UV-vis absorption) that could be modulated as function of pH and temperature of the environment as result of reversible aggregation-expansion of gold nanoparticles. Thereby, Au-Glu15 displayed remarkable features suitable for the development of stimuli responsive optical sensors and detectors for biological applications that could operate in aqueous media and under a wide range of pH’s.     

First‐principles calculation of OH−/OH adsorption on gold nanoparticles

The OH^? and OH adsorption structures on Au₅₅ and Au₁₃ nanoparticles surfaces are analyzed using density functional theory. The most stable OH^? adsorption site of Au₅₅ and Au₁₃ nanoparticles is found to be the vertex top site followed by the (111)‐(100) edge bridge site. On the contrary, the stability order of OH adsorption is opposite to that of OH^?. The adsorption of OH^? is calculated to be weaker than that of OH, which shows different charge transfer and interactions with gold surface. Coadsorption on nanoparticles is studied to find that multiple OH^? species prefer the most stable sites of single OH^? adsorption. The hydrogen bonding between adsorbed OH^? on gold surface is a key factor in stabilizing the adsorbates on the Au surface. © 2015 Wiley Periodicals, Inc.     

Spectroscopic characteristics of gold nanoparticles synthesized in an aqueous solution of a micelle-forming surfactant (AOT)

Gold nanoparticles were synthesized in aqueous solutions of AOT using hydrazine as the reducing agent and characterized by spectrophotometry, transmission electron microscopy, and photon-correlation spectroscopy. The effect of gold (C_Au = 10^–4–10^–3 mol/L) and AOT (C_AOT = 5 × 10^–4–2.5 × 10^–2 mol/L) concentrations on the formation of stable gold sols (λ_max = 520 nm) was studied. According to transmission electron microscopy data, the average size of gold nanoparticles in the dispersions was ~10 nm, which was in good agreement with the n-averaged hydrodynamic diameter determined by the photon correlation spectroscopy.     

Controllable Conversion of CO2 on Non‐Metallic Gold Clusters

Gold nanoparticles in metallic or plasmonic state have been widely used to catalyze homogeneous and heterogeneous reactions. However, the catalytic behavior of gold catalysts in non‐metallic or excitonic state remain elusive. Atomically precise Au_n clusters (n=number of gold atoms) bridge the gap between non‐metallic and metallic catalysts and offer new opportunities for unveiling the hidden properties of gold catalysts in the metallic, transition regime, and non‐metallic states. Here, we report the controllable conversion of CO₂ over three non‐metallic Au_n clusters, including Au₉, Au₁₁, and Au₃₆, towards different target products: methane produced on Au₉, ethanol on Au₁₁, and formic acid on Au₃₆. Structural information encoded in the non‐metallic clusters permits a precise correlation of atomic structure with catalytic properties and hence, provides molecular‐level insight into distinct reaction channels of CO₂ hydrogenation over the three non‐metallic Au catalysts.