Au Interactions Research Articles

Gas-phase generation of dinuclear Au(I)-Au(II) complexes by laser desorption ionization mass spectrometry.

Alkali metal chloroaurates(III) were analysed by laser desorption ionization mass spectrometry. Among a number of generated gas-phase ionic clusters, the unusual ions [MAu2Cl5]- (were M stands for Na, K, Rb, Cs) were detected. The spectra of metastable ions and quantum mechanics calculations show the presence of unprecedented Au(I)-Au(II) interactions in the clusters.

Amplification-free Detection of Cytomegalovirus miRNA Using a Modification-free Surface Plasmon Resonance Biosensor.

Cytomegalovirus (CMV) is the most frequent cause of congenital infection worldwide; congenital CMV may lead to significant mortality, morbidity, or long-term sequelae, such as sensorineural hearing loss. The current study presents a newly designed surface plasmon resonance (SPR) biosensor for CMV-specific microRNAs that does not involve extra care for receptor immobilization or treatment to prevent fouling on bare gold surfaces. The modification-free approach, which utilizes a poly-adenine [poly(A)]-Au interaction, exhibited a high affinity that was comparable to that of the gold-sulfur (Au-S) interaction. In addition, magnetic nanoparticles (MNPs) were used to separate the analyte from complex sample matrixes that significantly reduced nonspecific adsorption. Moreover, the MNPs also played an important role in SPR signal amplification due to the binding-induced change in the refractive index. Our SPR biosensing platform was used successfully for the multi-detection of the microRNAs, UL22A-5p, and UL112-3p, which were associated with CMV. Our SPR biosensor offered the detection limits of 108 fM and 24 fM for UL22A-5p and UL112-3p, respectively, with an R2 of 0.9661 and 0.9985, respectively. The precision of this biosensor has an acceptable CV (coefficient of variation) value of <10%. In addition, our sensor is capable of discriminating between serum samples collected from healthy and CMV-infected newborns. Taken together, we believe that our newly developed SPR biosensing platform is a promising alternative for the diagnosis of CMV-specific microRNA in clinical settings, and its application for the detection of other miRNAs may be extended further.

A Cytotoxic Bis(1,2,3-triazol-5-ylidene)carbazolide Gold(III) Complex Targets DNA by Partial Intercalation.

The syntheses of bis(triazolium)carbazole precursors and their corresponding coinage metal (Au, Ag) complexes are reported. For alkylated triazolium salts, di‐ or tetranuclear complexes with bridging ligands were isolated, while the bis(aryl) analogue afforded a bis(carbene) AuI‐CNC pincer complex suitable for oxidation to the redox‐stable [AuIII(CNC)Cl]+ cation. Although the ligand salt and the [AuIII(CNC)Cl]+ complex were both notably cytotoxic toward the breast cancer cell line MDA‐MB‐231, the AuIII complex was somewhat more selective. Electrophoresis, viscometry, UV‐vis, CD and LD spectroscopy suggest the cytotoxic [AuIII(CNC)Cl]+ complex behaves as a partial DNA intercalator. In silico screening indicated that the [AuIII(CNC)Cl]+ complex can target DNA three‐way junctions with good specificity, several other regular B‐DNA forms, and Z‐DNA. Multiple hydrophobic π‐type interactions involving T and A bases appear to be important for B‐form DNA binding, while phosphate O⋅⋅⋅Au interactions evidently underpin Z‐DNA binding. The CNC ligand effectively stabilizes the AuIII ion, preventing reduction in the presence of glutathione. Both the redox stability and DNA affinity of the hit compound might be key factors underpinning its cytotoxicity in vitro.

Plasmon Triggered, Enhanced Light–Matter Interactions in Au–MoS2 Coupled System with Superior Photosensitivity

Enhanced light–matter interactions by integrating plasmonic Au nanostructures as a light harvester on two-dimensional (2D) MoS2 carrier sink layers are reported, leading to broadband optical absorption and significantly enhanced Raman scattering intensity. The calculations of electronic band structure using density functional theory analysis and optical simulations elucidate the metal induced doping in MoS2 and the enhancement of electromagnetic field through localized surface plasmon resonance at the Au/MoS2 interface by forming a number of hot spots, corroborating the spectroscopic results. The ultrafast time-domain results reveal a 200-fold enhancement in the carriers’ lifetime for nanohybrids, as compared to the control sample, which is attributed to the efficient transfer of hot electrons from Au to MoS2. Fabricated metal–semiconductor–metal photodetectors using hybrid nanostructures exhibit a 20-fold enhancement of photoresponsivity (∼1.5 A/W at 640 nm) as compared to pristine MoS2 and a remarkably high peak detectivity (∼4.75 × 1013 Jones at 3 V), which are promising for broadband and multicolor photodetection, making them attractive for large area 2D materials-based nanophotonic devices.

Markedly improved performance of oxide-supported catalysts in hot basic water by three facile ways in synergy

Use oxide-supported catalyst in green solvent, hot water : Au is anchored on oxide via Au┄O-M interaction (M = Fe, Ti, etc). Basic aqueous catalytic system may destruct a part of O M bonds into oxygen vacancies and weaken Au/support interaction, causing leaching and aggregation of Au. Three simple methods synergistically improve reusability of catalyst. • Three facile ways synergistically improve catalyst reusability in green solvent, water. • They raise support stability and Au/support interaction to reduce leaching and aggregation of Au. • Nano supports interact with Au more strongly, and are more stable in hot basic water. • Nano TiO 2 is more stable due to the stronger surface Ti O bond, in line with BOLS theory. Obtaining reusable catalysts and using water as a green solvent still remain huge challenges. Various oxides are frequently used as the support, however, the aqueous catalytic systems, particularly in hot basic water, may decrease their stability and thus cause leaching or aggregation of the supported metal nanoparticles (NPs). In this work, three very simple methods in catalyst preparation are demonstrated to greatly improve the reusability of oxide-supported catalysts in 100 °C basic water, by systematically studying a series of oxides as well as carbons as support of gold (Au) NPs and employing Suzuki-Miyaura cross-coupling (SMCC) reaction as a probe. These methods are prerequisites for obtaining both excellent activity and recyclability. Absence of any of them will badly improve leaching or aggregation of Au NPs. The reasons for the synergistically improved reusability are also elucidated in details. Though it’s extremely hard to thoroughly overcome leaching in hot water, this work achieves the application of Au/oxide to SMCC reaction in water with higher utilization efficiency of Au than some reported work in organic solvent or with other supports. The present work can serve as supplementary strategies to assist in designing high-performance oxide-supported catalysts for varieties of similar aqueous systems.

Reconstituting C-Centered Hexagold(I) Clusters with N-Heterocyclic Carbene Ligands

Abstract Ubiquitous intramolecular aurophilic interactions in gold clusters have usually been assigned as the main determinants of their molecular geometry and various properties. By utilizing N-heterocyclic carbene (NHC) ligands instead of phosphine ligands which have been exclusively used, we have developed ligand-specific photophysical properties of C-centered hexagold(I) (C@Au6) clusters. This account describes the recent development of carbene-protected C@Au6 clusters. First of all, a strong intramolecular C–H⋯Au interaction was found as a key structural feature of these clusters. These are also present in the newly emerged NHC-gold nanoclusters, but are negligible in the phosphine counterparts. Interestingly, the use of NHC ligands also produces clusters with a nearly identical metal kernel, but their luminescence changes significantly. In addition, a simple extension of the π-conjugated system of NHCs from imidazolylidene to benzimidazolylidene is expected to produce significant changes in both absorption coefficient and emission wavelength. These results show the promising potential of carbene ligands in character modulation of metal clusters, and may help in the rational design of carbene ligands for constructing functional metal clusters.

Self-Assembled Chiral Phosphorescent Microflowers from Au Nanoclusters with Dual-Mode pH Sensing and Information Encryption.

The self-assembly of chiral metal nanoclusters into supramolecular chiral aggregates is of interest for developing advanced materials. Herein, we manipulated the self-assembly of Au nanoclusters modified by l-/d-cysteine (l-/d-AuNCs) into ordered microstructures featuring enhanced phosphorescence and optical activities. The formation of these aggregates was driven by synergistic effect of coordination and electrostatic interactions assisted by Cd2+/H+. Detailed structural characterization and theoretical studies confirmed that the compact aggregation structures are essential for the emission enhancement and the chirality amplification of l-/d-AuNCs. Interestingly, upon the formation of microflowers, the emission lifetime was prolonged to 3.34 ms with a switch from fluorescence to phosphorescence induced by aurophilic Au(I)···Au(I) interactions and intensive ligand-to-metal charge transfer (LMCT). Moreover, both the CD and photoluminescence (PL) signals of the microflowers exhibited pH-responsiveness. This dual-mode sensitive platform could be developed as a pH sensor with improved accuracy. Additionally, the pH-responsive photoluminescence ON/OFF switch of the microflowers could be employed for reliable information encryption and decryption. This study provides useful ideas for regulating the self-assembly of nanoclusters to generate desired photophysical properties with potential applications.

Regulating Fe2(MoO4)3 by Au Nanoparticles for Efficient N2 Electroreduction under Ambient Conditions

AbstractAmmonia, as an important chemical, has played an indispensable role in the fields of fertilizer precursors, fuel, and energy carriers over time. The electrocatalytic nitrogen reduction reaction (eNRR) has attracted extensive attention due to the potential availability of clean energy under mild conditions, while electrochemical catalysts still need further optimization and exploration restricted by the strong chemical bonds of NN. In this work, it is proposed that a small amount of noble metal (Au) modified Fe2(MoO4)3 can serve as active sites in eNRR. Density functional theory calculations reveal that the interaction of Au with Fe2(MoO4)3 reduces the reaction energy of the rate determining step and inhibits the hydrogen evolution reaction, which increase the eNRR activity and selectivity of Au/Fe2(MoO4)3. As expected, according to the 1H nuclear magnetic resonance measurement as the exclusive quantitative detection approach, the as‐prepared Au/Fe2(MoO4)3 achieves outstanding eNRR performance with 7.61 µg h−1 mg−1cat. NH3 production rate and 18.79% Faradaic efficiency at −0.4 V versus reversible hydrogen electrode in 0.2 m Na2SO4 under ambient conditions.

Rapid annealing of Au thin films by micron chevron-shaped laser beam scanning toward growth of single-grain crystal

A practicable solution to reduce the density of grain boundaries in metal thin films in order to improve their physical properties, and compatibility with nanoscale fabrications still remains a challenge for the thin film industry. We propose an alternative approach to the problem by using micron chevron-shaped laser beam (μCLB) annealing for rapid and selective growth of crystal grains in metal thin films. We investigate the laser annealing of various Au thin films and discuss the mechanisms of grain growth accounting for the microstructure of the Au films and interaction between the Au films and the substrate. The successful growth of single-grain crystal on a 50 nm Au film by μCLB annealing is also demonstrated and further optimization of the process is discussed.

Substituent-Mediated Transformation of Polynuclear Gold(I)-Sulfido Complexes—From Pentanuclear to Octadecanuclear Cluster-to-Cluster Transformation

Substituent-Mediated Transformation of Polynuclear Gold(I)-Sulfido Complexes—From Pentanuclear to Octadecanuclear Cluster-to-Cluster Transformation

A “nucleophilic” iodine in a halogen-bonded iodonium complex manifests an unprecedented I+···Ag+ interaction

Summary When an electron is removed from a halogen atom, it forms a halenium ion X+ (X = I, Br, Cl). In halogen bonding (XB), X+ is considered as a strong XB donor, and when interacting with two XB acceptors (e.g., pyridine), it forms a halonium XB complex with a [N–I–N] three-center-four-electron bond with the two XB acceptors. An unprecedented I+···Ag+ interaction occurs between a [L1–I–L1]+ halogen-bonded complex and a [L2–Ag–L2]+ complex in which the iodonium ion acts like a nucleophile and donates electrons to the silver(I) cation. The X-ray diffraction analysis reveals a short contact [3.4608(3) A] between the I+ and Ag+ cations, and ITC measurements give a ΔG of −6.321 kcal/mol and Ka∼37,000 M−1 for the 1:1 complex. The DFT computational study on the nature of the I+···Ag+ interaction indicates that the I+ is nucleophilic in character, manifesting an unusual and strongly attractive interaction between the I+ and Ag+ cations.

Photocatalytic C-H Thiocyanation of Corroles: Development of Near-Infrared (NIR)-Emissive Dyes.

A new method of activating corrole macrocycles via an in situ generated SCN radical has been developed at very mild conditions at room temperature. This photoredox reaction resulted in the generation of tetrathiocyanatocorroles in good yields. The synthesis of tetrathiocyanatocorroles was never reported earlier. Single-crystal XRD analysis reveals that the insertion of four thiocyanate moieties at the four β-pyrrolic positions has imparted significant distortion to the corrole macrocycle. The generated tetrathiocyanatocorroles are different from the parent corroles in many ways. The photophysical properties of the newly synthesized tetrathiocyanatocorroles are dramatically altered from the parent corroles. The absorption feature of these modified corrole derivatives (both position and intensity) bears a nice similarity with the chlorophyll-a macrocycle. Thus, these newly synthesized molecules can be considered as spectroscopic model systems for chlorophyll-a pigments. The observed absorption and emission spectra of these tetrathiocyanatocorroles certainly point out that these newly developed ligand scaffolds and their various metal complexes will have immense potential as pigments in solar cells and also as NIR-emissive dyes. The observed C-H···Au weak interactions in a representative Au(III)-corrole complex point out that these complexes are capable of activating the unfunctionalized C-H groups and thus will have potential implications in C-H activation reactions.

Au(III), Ta(V), Nb(V), Se(IV) and Te(IV) ions interaction with aurin tricarboxylic acid triammonium salt in methanolic solvent at neutral system: Focusing on the structures, morphology, thermal stability, and biology of the complexes

The present study investigated the structural, morphological, thermal, and pharmacological properties of aurin tricarboxylic acid triammonium salt (AAS) complexed with Au(III), Ta(V), Nb(V), Se(IV), and Te(IV) ions. The formed complexes were characterized by spectroscopic and physicochemical techniques, such as CHN elemental analysis, magnetic moment, conductivity, FTIR, 1H NMR, and UV–visible spectroscopies; XRD; SEM; TEM; and thermogravimetry. The analytical and spectral data suggest that Ta(V), Nb(V), Se(IV), and Te(IV) ions formed octahedral complexes, where Au(III) ion formed square planar complex. The biological activity of the formed complexes was evaluated using two human cancer cell lines and four microbes. The Kirby-Bauer disc diffusion and MTT-based assay methods were used for antibacterial screening and cytotoxicity towards MCF-7 and HepG2 cell lines, respectively. Investigation on cytotoxic activity showed that the complexation with Au(III) ions increased the cytotoxic activity of AAS by 57% towards HepG2 cells and by 45% towards MCF-7cells. Investigation on antibacterial activity showed that the Te(IV) complex had a remarkable profile towards Gram-negative bacteria.

Formation and evolution of the nanoparticle environmental corona: The case of Au and humic acid

Studying the behaviour of nanomaterials after their release into natural water is essential to understand the risk associated to their environmental exposure. In particular, the interaction and adsorption of dissolved organic matter onto nanoparticles strongly influence the behaviour and fate of nanomaterials in natural water systems. We herein study the interaction of Au and Ag nanoparticles and humic acids, the principal component of natural dissolved organic matter. Physicochemical characterization results showed the formation of an organic matter corona, consisting of two layers: a “hard” one, firmly bound to the nanoparticle surface, and a “soft” one, in dynamic equilibrium and, consequently, highly dependent on the media organic matter concentration. The extent of the electro-steric stabilization of the so called environmental corona depends on the size of the supramolecular association of humic acid (which depends on its hydrophilic and lipophilic moieties), the nanoparticle size, the total concentration of organic matter in the media, and the ratio between them. Interestingly, environmental coronas can eventually prevent Ca2+ and Mg2+ induced aggregation at concentrations range present in most of the freshwater bodies. The humic coating formed on top of the Au or control Ag nanoparticles presented a similar profile, but the corrodibility of Ag led to a more natural detachment of the corona. These results were further confirmed by exposing the nanoparticles to a model of natural water and standard mud (LUFA 2.2 dispersion). In the latter case, after several days, nanoparticle sedimentation was observed, which was attributed to interactions with macro organic and inorganic matter (fraction larger than particulate matter).

QM study of interaction between arginine amino acid and Au clusters and the effects on arginine acidity

Understanding the various structures of gold clusters and the interaction modes between Au clusters and biomolecules is an important issue in material science such as biosensors and catalysts. The binding of small gold clusters (Aun n = 2–5) with neutral and anionic forms of arginine (Arg) amino acid is investigated in this study using density functional theory (DFT) and B3LYP level. The relative stability among different forms of Au clusters including linear, zigzag, planar, and three-dimensional Au clusters was estimated, initially. The calculated findings show that the zigzag structure for Au3 and the planar structure for Au4 and Au5 are the best form. Furthermore, the different modes of interaction were taken into account from thermodynamic view point between the most stable conformers of Arg and Arg− with gold clusters. Finally, the arginine is considered as a weak organic acid to investigate the impact of Au clusters on the gas phase acidity. The acidity of isolated arginine and the acidity of [Aun/Arg] complexes were also compared. Based on the obtained results, upon the complexation with Au clusters at 298 K, for the interaction of Au, Au2, Au3, Au4, and Au5 clusters with arginine, the gas phase acidity (GPA) of arginine alters from 342.12 to 314.17, 303.04, 299.42, 303.41, and 331.66 kcal/mol respectively. These calculated values predict that when a weak organic acid is complexed with Au clusters, it will be altered to super acid. Furthermore, for isolated and complexed species of Arg, pKa values were evaluated in water solvent.

Covalent immobilization of gold nanoparticles on a plastic substrate and subsequent immobilization of biomolecules.

We propose a novel approach to stably immobilize gold nanoparticles (AuNPs) on a plastic substrate and demonstrate that the modified substrate is also capable of immobilizing biomolecules. To immobilize citrate-capped AuNPs, an acrylic substrate was simply dip-coated in a functional polymer solution to decorate the outermost surface with amino groups. Electrostatic interactions between AuNPs and the amino groups immobilized the AuNPs with a high density. The AuNP-modified acrylic substrate was transparent with a red tint. A heat treatment promoted the formation of amide bonds between carboxy groups on the AuNPs and amino groups on the substrate surface. These covalent bonds stabilized the immobilized AuNPs and the resulting substrate was resistant to washing with acid and thiol-containing solutions. The surface density of AuNPs was controlled by the surface density of amino groups on the substrate surface, which was in turn controlled by the dip-coating in the functional polymer solution. We attempted to immobilize functional biomolecules on the AuNPs-functionalized plastic surface by two different approaches. An enzyme (horseradish peroxidase) was successfully immobilized on the AuNPs through amide formation and 5′-thiolated DNA was also immobilized on the AuNPs through S–Au interactions. These chemistries allow for simultaneous immobilization of two different kinds of biomolecules on a plastic substrate without loss of their functional properties.

Exploring a near-Hartree-Fock-Kohn-Sham approach to study electronic properties of azobenzene in interaction with gold: From clusters to the Au(111) surface.

The electronic properties of azobenzene (AB) in interaction with gold clusters and adsorbed on the Au(111) surface are investigated by adopting a near-Hartree-Fock-Kohn-Sham (HFKS) scheme. This scheme relies on a hybrid Perdew-Burke-Ernzerhof functional, in which the exact non-local HF exchange contribution to the energy is taken as 3/4. Ionization energies and electron affinities for gas phase AB are in very good agreement with experimental data and outer valence Green's function) calculations. The presence of C-H⋯Au interactions in AB-Aun complexes illustrates the role played by weak interactions between molecular systems and Au nanoparticles, which is in line with recent works on Au-H bonding. In AB-Aun complexes, the frontier orbitals are mainly localized on the gold platform when n ≥ 10, which indicates the transition from a molecular to a semiconducting regime. In the latter regime, the electronic density reorganization in AB-Aun clusters is characterized by significant polarization effects on the Au platform. The accuracy of the near-HFKS scheme for predicting adsorption energies of AB on Au(111) and the interest of combining exact non-local HF exchange with a non-local representation of the dispersion energy are discussed. Taking into account the significant computational cost of the exact non-local HF exchange contribution, calculations for the adsorption energies and density of states for AB adsorbed on Au(111) were carried out by using a quantum mechanics/molecular mechanics approach. The results strongly support near-HFKS as a promising methodology for predicting the electronic properties of hybrid organic-metal systems.

Synthesis, structural characterization, docking simulation and in vitro antiproliferative activity of the new gold(III) complex with 2-pyridineethanol

Gold(III) complex containing 2-pyridineethanol has been synthesized and characterized structurally by single crystal X-ray diffraction, vibrational spectroscopy, 1H NMR spectroscopy, electrochemical study, and DFT calculations. The Au(III) ion is four coordinated with one N–donor ligand (L) and three Cl anions. The Okuniewski's (τ’4=0.018) has been used to estimate the angular distortion from ideal square planar geometry. The vibrational spectroscopy studies, in the solid state and DMSO solution and cyclic voltammetry, have been performed to determine its stability and redox activity, respectively. A complete assignment of the IR and Raman spectra has been made based on the calculated potential energy distribution (PED). The theoretical calculations have been made for two functionals and several basis sets. The compound has been evaluated for its antiproliferative properties in a human lung adenocarcinoma cell line (A549), mouse colon carcinoma (CT26), human breast adenocarcinoma (MCF-7), human prostate carcinoma derived from the metastatic site in the brain (DU-145), and PANC-1 human pancreas/duct carcinoma cell line and non-tumorigenic cell lines: HaCat (human keratinocyte), and HEK293T (human embryonic kidney). Au(III) complex cytotoxicity is significantly against A549 and MCF-7 cells as in the reference drug: cisplatin. Studies of the interactions of Au(III) complex with DNA, HSA (human serum albumin) have been performed. The results from modeling docking simulations indicate that the title complex exerts anticancer effects in vitro based on different mechanisms of action to compare with cisplatin.

Chiral gold(I)-containing polymeric composites: chiroptical sensing and circularly polarized luminescence

Fiber-like gold(I)-containing polymeric composites have been constructed in water by coupling poly(ethylene glycol)-block-poly-(L-glutamic sodium) (PEGn-b-PLGSm) with cationic gold(I) complex. The resulting composites showed a gradual luminescence enhancement with increasing molecular weight of the PLGSm block, due to gradually increasing aurophilic Au(I)···Au(I) interactions in the gold(I) complex. Moreover, the chiral transfer from the chiral block copolymers to the gold(I) complex was achieved for the first time, leading to strong circularly polarized luminescence (CPL). Such chiroptical sensing offers a general approach for constructing CPL active polymer/metal complex composites.

Strong metal-support interaction induced O2 activation over Au/MNb2O6 (M = Zn2+, Ni2+ and Co2+) for efficient photocatalytic benzyl alcohol oxidative esterification

A series of metal niobates (MNb2O6, M = Zn2+, Ni2+ and Co2+) were prepared from H-niobate precursor under hydrothermal conditions, in which amino groups of l-lysine play an important role. Au nanoparticles were then supported on these niobates by NaBH4 reduction method. More importantly, the strong interaction between Au nanoparticles and ZnNb2O6 generates negatively charged Au which can activate molecular oxygen to form the exclusive high-active peroxide (NbOOAu) species on Au/ZnNb2O6 surface under visible light irradiation, observed in situ by diffuse reflectance infrared Fourier transform spectra (DRIFTS). The optimal NbOOAu species produced on the surface of Au/ZnNb2O6 can remove the H atom of the methylene group (−CH2–) of benzyl alcohol, leading to high photocatalytic activity of Au/ZnNb2O6 compared with Au/NiNb2O6 and Au/CoNb2O6. This modulation of interaction of Au and niobates for the activation of molecular oxygen provides a new prospect for highly selective photocatalytic oxidation reactions.