Bimetallic Gold Research Articles

Front Cover: Synthesis and Structural Characterization of Mono‐ and Bimetallic Rhodium(I), Iridium(I) and Gold(I) Methanide and Methandiide Complexes from 2‐Quinolyl‐Linked (Thiophosphoranyl)methane (Eur. J. Inorg. Chem. 24/2016)

Front Cover: Synthesis and Structural Characterization of Mono‐ and Bimetallic Rhodium(I), Iridium(I) and Gold(I) Methanide and Methandiide Complexes from 2‐Quinolyl‐Linked (Thiophosphoranyl)methane (Eur. J. Inorg. Chem. 24/2016)

Potent antimicrobial and antibiofilm activities of bacteriogenically synthesized gold-silver nanoparticles against pathogenic bacteria and their physiochemical characterizations.

The objective of this study was to develop a bimetallic nanoparticle with enhanced antibacterial activity that would improve the therapeutic efficacy against bacterial biofilms. Bimetallic gold-silver nanoparticles were bacteriogenically synthesized using γ-proteobacterium, Shewanella oneidensis MR-1. The antibacterial activities of gold-silver nanoparticles were assessed on the planktonic and biofilm phases of individual and mixed multi-cultures of pathogenic Gram negative (Escherichia coli and Pseudomonas aeruginosa) and Gram positive bacteria (Enterococcus faecalis and Staphylococcus aureus), respectively. The minimum inhibitory concentration of gold-silver nanoparticles was 30-50 µM than that of other nanoparticles (>100 µM) for the tested bacteria. Interestingly, gold-silver nanoparticles were more effective in inhibiting bacterial biofilm formation at 10 µM concentration. Both scanning and transmission electron microscopy results further accounted the impact of gold-silver nanoparticles on biocompatibility and bactericidal effect that the small size and bio-organic materials covering on gold-silver nanoparticles improves the internalization and thus caused bacterial inactivation. Thus, bacteriogenically synthesized gold-silver nanoparticles appear to be a promising nanoantibiotic for overcoming the bacterial resistance in the established bacterial biofilms.

α-Alkylation of ketones with primary alcohols driven by visible light and bimetallic gold and palladium nanoparticles supported on transition metal oxide

The direct α-alkylation of ketones with primary alcohols to obtain the corresponding saturated coupled ketones was achieved with bimetallic gold(Au)-palladium(Pd) nanoparticles(NPs) supported on a transition metal oxide (such as CeO2). This system demonstrated a higher catalytic property than Au/CeO2 and Pd/CeO2 under visible light irradiation at 40±3°C in an Ar atmosphere. Such phenomenon was caused by the synergistic effect between Au and Pd. Isopropyl alcohol was used as the solvent and CH3ONa as the base. The effect of the bimetallic Au-Pd mass ratio and the two different transition metal oxide supports (such as CeO2 or ZrO2) during the reaction process was studied. The highest catalytic activity of those examined happened with the 1.5wt% Au-1.5wt% Pd (Au and Pd mass ratio 1:1)/CeO2 photo-catalyst. The intensity and wavelength of the visible light had a strong influence on the system. The catalyst can be reused for four times. A reaction mechanism was proposed for the α-alkylation of ketones with primary alcohols.

Synthesis and Structural Characterization of Mono‐ and Bimetallic Rhodium(I), Iridium(I) and Gold(I) Methanide and Methandiide Complexes from 2‐Quinolyl‐Linked (Thiophosphoranyl)methane

The synthesis and structural characterization of RhI, IrI and AuI metal complexes derived from 2‐quinolyl‐linked (thiophosphoranyl)methane CH2(iPr2P=S)(C9H6N‐2) (A) are reported. Metathesis reactions of 2‐quinolyl‐thiophosphinoyl potassium complex [K{CH(iPr2P‐S)(C9H6N‐2)}]n (1) with 1 equiv. of [MCl(COD)]2 (M = Rh, Ir; COD = cycloocta‐1,5‐diene) afforded monomeric 2‐quinolyl‐thiophosphinoyl‐rhodium(I) and iridium(I) complex [M(COD){CH(iPr2P=S)(C9H6N‐2)}] {M = Rh (2), Ir (3)}, respectively. Upon treatment of 1 with 2 equiv. of [MCl(COD)]2 (M = Ir, Rh), bimetallic complexes [M(COD){CH(iPr2P=S)(C9H6N‐2)(M(COD)Cl)}] {M = Rh (4), Ir (5)} were obtained. The reaction of 1 with [AuCl(PPh3)] afforded a geminal dinuclear gold(I) methandiide complex [{Au(PPh3)}2{C(iPr2P‐S)(C9H6N‐2)}] (6), featuring an aurophilic interaction. Meanwhile, the metathesis reaction of 1 with 1 equiv. of gold(I) complex [AuCl(IPrNHC)] {IPrNHC = C[N(2,6‐iPr2C6H3)CH]2} afforded a monomeric two‐coordinate monoaurated product, 2‐quinolyl‐thiophosphinoyl‐gold(I) N‐heterocyclic carbene complex [Au(IPrNHC){CH(iPr2P‐S)(C9H6N‐2)}] (7). The structures of 3–7 have been determined by X‐ray crystallography and the UV/Vis absorption properties of 2–6 have also been studied.

Bimetallic Gold(I)/Chiral N,N'-Dioxide Nickel(II) Asymmetric Relay Catalysis: Chemo- and Enantioselective Synthesis of Spiroketals and Spiroaminals.

A highly efficient asymmetric cascade reaction between keto esters and alkynyl alcohols and amides is reported. The success of the reaction was attributed to the combination of chiral Lewis acid N,N'-dioxide nickel(II) catalysis with achiral π-acid gold(I) catalysis working as an asymmetric relay catalytic system. The corresponding spiroketals and spiroaminals were synthesized in up to 99 % yield, 19:1 d.r., and more than 99 % ee under mild reaction conditions. Control experiments suggest that the N,N'-dioxide ligand was essential for the formation of the spiro products.

Bimetallic Gold(I) Complexes with Ethynyl-Helicene and Bis-Phosphole Ligands: Understanding the Role of Aurophilic Interactions in their Chiroptical Properties.

Monometallic gold(I)-alkynyl-helicene complexes (1 a,b) and bimetallic gold(I)-alkynyl-helicene architectures featuring the presence (2 a,b) or absence (3 a,b) of aurophilic intramolecular interactions were prepared by using different types of phosphole ligands (mono-phosphole L1 or bis-phospholes L2,3). The influence of the Au(I) d(10) metal center(s) on the electronic, photophysical, and chiroptical properties of these unprecedented phosphole-gold(I)-alkynyl-helicene complexes was examined. Experimental and theoretical results highlight the importance of ligand-to-ligand-type charge transfers and the strong effect of the presence or absence of Au(I) -Au(I) interactions in 2 a,b.

Insights into the use of Au19Cu and Au19Pd clusters for adsorption of trivalent arsenic

The adsorption of trivalent arsenic [As(OH)3] onto the bimetallic Au19Cu and Au19Pd clusters was computationally studied to get insights about as embedded electrodes with bimetallic gold nanostructures can serve for the adsorption and subsequent sensing of arsenic traces from polluted waters. It was found that the As(OH)3 chemisorption onto Au19Cu and Au19Pd is reached with adsorption energies of up to 1.02 and 1.48 eV, respectively, with even a stable physisorption with energies of up to 0.57 eV. Both arsenic and oxygen atoms were determined to bind with adsorbent Cu and Pd atoms, and all the interactions appear to be stable in an aqueous environment. The stability of the adsorbent–pollutant interactions was explained in terms of metal–pollutant chemical binding, charge transfer, dispersion force interactions and non-conventional OH···Au hydrogen bonds. Moreover, the As(OH)3 adsorption on the metal clusters is also accompanied by changes in the reactivity, electron transfer and decreases of the HOMO–LUMO energy gap with respect to the isolated substrates; the highest changes obtained in the mentioned properties are classified in the order Au19Pd > Au19Cu > Au20.

Ultrasensitive electrochemical immunoassay for surface array protein, a Bacillus anthracis biomarker using Au–Pd nanocrystals loaded on boron-nitride nanosheets as catalytic labels

Bacillus anthracis, the causative agent of anthrax, is a well known bioterrorism agent. The determination of surface array protein (Sap), a unique biomarker for B. anthracis can offer an opportunity for specific detection of B. anthracis in culture broth. In this study, we designed a new catalytic bionanolabel and fabricated a novel electrochemical immunosensor for ultrasensitive detection of B. anthracis Sap antigen. Bimetallic gold–palladium nanoparticles were in-situ grown on poly (diallyldimethylammonium chloride) functionalized boron nitride nanosheets (Au–Pd NPs@BNNSs) and conjugated with the mouse anti-B. anthracis Sap antibodies (Ab2); named Au–Pd NPs@BNNSs/Ab2. The resulting Au–Pd NPs@BNNSs/Ab2 bionanolabel demonstrated high catalytic activity towards reduction of 4-nitrophenol. The sensitivity of the electrochemical immunosensor along with redox cycling of 4-aminophenol to 4-quinoneimine was improved to a great extent. Under optimal conditions, the proposed immunosensor exhibited a wide working range from 5pg/mL to 100ng/mL with a minimum detection limit of 1pg/mL B. anthracis Sap antigen. The practical applicability of the immunosensor was demonstrated by specific detection of Sap secreted by the B. anthracis in culture broth just after 1h of growth. These labels open a new direction for the ultrasensitive detection of different biological warfare agents and their markers in different matrices.

Remarkable in vitro anti-HIV activity of new silver(I)– and gold(I)–N-heterocyclic carbene complexes. Synthesis, DNA binding and biological evaluation

A novel metallomacrocyclic silver complex [Ag(C13H13N5)]2Br21 and a bimetallic bridged gold complex [Au2(C13H13N5)Cl2] 2 derived from 2,6-bis(3-methylimidazolin-2-yliden-1-yl)pyridine dibromide L1 have been synthesized and fully characterized by UV–Vis, elemental analysis, FT-IR, NMR techniques and DFT calculations. The DNA interactions with the compounds were investigated by UV-spectrophotometric studies, viscosity measurements and DNA electrophoresis. Additionally, the lipophilicity values were determined from the water/n-octanol partition coefficient. Experimental data indicated that all the compounds interacted with DNA, through a non-covalent binding mode. L1 and 2 were found to be hydrophilic character while 1 was somewhat lipophilic. The biological activities of L1, 1 and 2 were tested against a panel of cancer cell lines (MCF-7, PC-3, A459, HeLa, HT-29 and the 4T1 murine tumor cell line). In vitro antiviral studies against HIV-1 were performed in infected MT4 leukemia cells. All the compounds exhibited a low activity against the cell lines, associated possibly with low lipophilicity values. However, complexes 1 and 2 showed remarkable viral inhibition at low concentrations. The complexes may inhibit virus infectivity through interaction with the HIV-1 envelope proteins.

Improving Light Harvesting in Dye-Sensitized Solar Cells Using Hybrid Bimetallic Nanostructures

In this work we demonstrate improved light trapping in dye-sensitized solar cells (DSSCs) with hybrid bimetallic gold core/silver shell nanostructures. Silica-coated bimetallic nanostructures (Au/Ag/SiO2 NSs) integrated in the active layer of DSSCs resulted in 7.51% power conversion efficiency relative to 5.97% for reference DSSCs, giving rise to 26% enhancement in device performance. DSSC efficiencies were governed by the particle density of Au/Ag/SiO2 NSs with best performing devices utilizing only 0.44 wt % of nanostructures. We performed transient absorption spectroscopy of DSSCs with variable concentrations of Au/Ag/SiO2 NSs and observed an increase in amplitude and decrease in lifetime with increasing particle density relative to reference. We attributed this trend to plasmon resonant energy transfer and population of the singlet excited states of the sensitizer molecules at the optimum concentration of NSs promoting enhanced exciton generation and rapid charge transfer into TiO2.

ChemInform Abstract: Dimeric TADDOL Phosphoramidites in Asymmetric Catalysis: Domino Deracemization and Cyclopropanation of Sulfonium Ylides.

AbstractThe diastereo‐ and enantioselective intramolecular cyclopropanation of allylic esters is achieved in the presence of the novel bimetallic gold catalyst (AUP).

Characterizing the optical properties of single palladium-coated core-shell gold nanorods as multifunctional orientation probes.

Bimetallic core-shell gold nanorods are promising multifunctional orientation probes due to the synergetic effect of two different metals, as examined under an optical microscope. Herein, we performed a single particle study to characterize the optical properties of palladium-coated core-shell gold nanorods (Pd-AuNRs) using scattering-based dark-field (DF) and differential interference contrast (DIC) microscopy, and to examine their use as multifunctional orientation probes in biological and physical studies. The longitudinal surface plasmon resonance (SPR) was strongly damped with the increased SPR linewidth for single Pd-AuNRs due to Pd metals coated on the AuNR surface under single particle scattering spectroscopy. Despite the strong plasmon damping with much reduced scattering intensity, DIC microscopy allowed us to detect single Pd-AuNRs with much higher sensitivity. We found polarization-dependent DIC images and intensities of single Pd-AuNRs, which enabled the determination of their orientation angle under DIC microscopy. Furthermore, we found that DIC polarization anisotropy can be obtained from the orthogonally polarized bright and dark intensities for more accurate and reliable angle measurements of the Pd-AuNR probes. The results support the idea that bimetallic Pd-AuNRs can be used to develop multifunctional orientation probes.

Bimetallic gold–silver nanocluster fluorescent probes for Cr(iii) and Cr(vi)

Bimetallic gold–silver nanocluster fluorescent probes for the detection of Cr(iii) and Cr(vi) and the achievement of chemical speciation.

Structural Analysis of AuPdAu Nanocubes via Aberration-Corrected STEM and Nanobeam Diffraction

Controlling the morphology of bimetallic nanoscale systems at the atomic level is of utmost importance in fields such as nanocatalysis, plasmonics, or optics. In this report we emphasize an experimental observation of superlattice formation in bimetallic gold–palladium nanocubes of the order of 30 nm synthesized by a seed-mediated growth method. By combining our experimental observations based on high-angle annular dark-field scanning transmission electron microscopy and nanobeam diffraction, we have established that a process of galvanic replacement takes place in our third deposition step, triggering the formation of vacancies and atomic diffusion, triggering short-range ordering in our three-layer AuPdAu nanocubes.

In-Situ DRIFT Study of Au–Ir/Ceria Catalysts: Activity and Stability for CO Oxidation

Monometallic gold and iridium, and bimetallic gold–iridium on ceria catalysts were synthesized by deposition–precipitation with urea. The activity of these ceria supported catalysts for CO oxidation was: Au–Ir ≫ Au > Ir. The bimetallic catalyst was highly active and stable during the carbon monoxide oxidation reaction, showing synergism between both metals. The catalysts were thoroughly characterized chemical and structurally. High-resolution electron microscopy coupled with energy dispersive spectroscopy and X-ray photoelectron spectroscopy showed evidences of iridium–gold intimacy. In situ infrared spectroscopy in the diffuse reflectance mode was used to investigate the reactivity of the active sites. Concentration-modulation excitation spectroscopy allowed selective identification of intermediates and ‘spectator’ species. CO chemisorbed onto iridium sites (2096, 2060 and 2012 cm−1) was found inactive, whereas carbon monoxide on metallic gold sites (Au0–CO, 2110 cm−1) exhibited reactivity for CO oxidation. In the bimetallic catalyst, new active sites (Auδ−–CO, 2095 and 2026 cm−1) together with Au0–CO species were observed, most likely produced by the isolation and stabilization of gold atoms by iridium.

Ultrasensitive electrochemical biosensor based on reduced graphene oxide-tetraethylene pentamine-BMIMPF6 hybrids for the detection of α2,6-sialylated glycans in human serum.

In this paper, a simple, ultrasensitive and label-free electrochemical α2,6-sialylated glycans biosensor based on reduced graphene oxide-tetraethylene pentamine-1-butyl-3-methylimidazolium hexafluorophosphate (BMIMPF6) hybrids was developed. Due to the abundance of amino groups from reduced graphene oxide-tetraethylene pentamine (rGO-TEPA) and the electrostatic interaction of BMIMPF6, bimetallic gold platinum alloy nanoparticles (AuPtNPs) were densely adsorbed onto the surface of the nanocomposite, providing a large surface area available for the immobilization of Sambucus nigra agglutinin (SNA). AuPtNPs have excellent conductivity and catalytic activity, which can promote electron transfer between the electrolyte solution and the surface of electrode and can enhance the sensitivity of biosensor. SNA, which specifically binds α2,6-sialylated glycans, was covalently immobilized on AuPtNPs for specific detection of α2,6-sialylated glycans in human serum. Under optimal experimental conditions, amperometric response changes were used to detect α2,6-sialylated glycans with a broad linear range of 10 fg mL(-1) -1 μg mL(-1) and a low detection limit of 3 fg mL(-1) (S/N=3). When applied to spiked serum samples, the recovery of the developed biosensor ranged from 100.8% to 101.4%, suggesting that the electrochemical biosensor would be suitable for the practical detection of α2,6-sialylated glycans.

Self-consistent nonlocal feedback theory for electrocatalytic swimmers with heterogeneous surface chemical kinetics.

We present a self-consistent nonlocal feedback theory for the phoretic propulsion mechanisms of electrocatalytic micromotors or nanomotors. These swimmers, such as bimetallic platinum and gold rods catalyzing decomposition of hydrogen peroxide in aqueous solution, have received considerable theoretical attention. In contrast, the heterogeneous electrochemical processes with nonlocal feedback that are the actual "engines" of such motors are relatively neglected. We present a flexible approach to these processes using bias potential as a control parameter field and a locally-open-circuit reference state, carried through in detail for a spherical motor. While the phenomenological flavor makes meaningful contact with experiment easier, required inputs can also conceivably come from, e.g., Frumkin-Butler-Volmer kinetics. Previously obtained results are recovered in the weak-heterogeneity limit and improved small-basis approximations tailored to structural heterogeneity are presented. Under the assumption of weak inhomogeneity, a scaling form is deduced for motor speed as a function of fuel concentration and swimmer size. We argue that this form should be robust and demonstrate a good fit to experimental data.

ChemInform Abstract: Oxidative Coupling of Alcohols and Amines over Bimetallic Unsupported Nanoporous Gold: Tailored Activity Through Mechanistic Predictability.

ChemInform Abstract: Oxidative Coupling of Alcohols and Amines over Bimetallic Unsupported Nanoporous Gold: Tailored Activity Through Mechanistic Predictability.

One-pot wet-chemical co-reduction synthesis of bimetallic gold–platinum nanochains supported on reduced graphene oxide with enhanced electrocatalytic activity

In this work, a simple, rapid and facile one-pot wet-chemical co-reduction method is developed for synthesis of bimetallic Au–Pt alloyed nanochains supported on reduced graphene oxide (Au–Pt NCs/RGO), in which caffeine is acted as a capping agent and a structure-directing agent, while no any seed, template, surfactant or polymer involved. The as-prepared nanocomposites display enlarged electrochemical active surface area, significantly enhanced catalytic activity and better stability for methanol and ethylene glycol oxidation, compared with commercial Pt–C (Pt 50 wt%), PtRu–C (Pt 30 wt% and Ru 15 wt%) and Pt black.

Liquid phase oxidation of cyclohexane using bimetallic Au–Pd/MgO catalysts

A detailed study of the selective oxidation of cyclohexane has been performed using bimetallic gold–palladium catalysts supported on magnesium oxide. Mono-metallic supported gold or palladium catalysts show limited activity for cyclohexane oxidation. However, a significantly enhanced catalytic performance is observed when supported gold–palladium alloy catalysts are used for this particular reaction. This synergy is observed for alloys spanning a wide range of gold-to-palladium molar ratios. Mechanistic studies reveal a promotion effect that occurs from alloying palladium with gold on the supported catalyst, which significantly improves the homo-cleavage of the O–O bond in cyclohexyl hydroperoxide, an important intermediate species in cyclohexane oxidation.