Gold Palladium Research Articles

Topical Steroids and CO2 Laser in the Treatment of Refractory Oral Lichenoid Drug Reaction and Lichenoid Contact Lesion: a Case Report.

A 54-year-old female presented with severe pain on the gingiva and buccal mucosa. Oral findings revealed generalized fiery red gingiva, ulcerative with white striae covered by pseudo-membranes on both buccal mucosae. She had hypertension, dyslipidemia, subclinical hypothyroidism and arthritis. She was treated with atorvastatin, hydrochlorothiazide, valsartan, levothyroxine and non-steroidal anti-inflammatory drug (NSAIDs). Her oral lesions were a slight improvement from a previous treatment with pimecrolimus cream, triamcinolone acetonide 0.1% orabase and injection. After diclofenac was replaced with tenoxicam and oral lesions were treated with various topical steroids, the lesions showed marked improvement. The biopsy from the buccal mucosa revealed oral lichen planus. Patch test showed positivity to mercury, gold sodium thiosulfate and palladium. One year later the left buccal mucosa showed red, round papillomatous-like lesions. The histopathological report showed a non-specific ulcer with chronic inflammation. The lesions flared up after replacing amalgam with crowns. After CO2 laser treatment, the lesions showed some improvement. Direct and indirect immunofluorescence of the lesions proved to be negative. This first case report showed that the palliative treatment of refractory oral lichenoid lesions with potent topical steroids for 7 years had no side-effects. CO2 laser can be an alternative treatment of refractory lesion in this case.

Oxidation of Benzyl Alcohol using in Situ Generated Hydrogen Peroxide

Catalysts containing bimetallic gold–palladium nanoparticles are extremely active and selective for the oxidation of alcohols to aldehydes and the direct synthesis of hydrogen peroxide from molecular hydrogen and oxygen. We show that the oxidation of benzyl alcohol can be carried out at 50 °C and below by generating hydrogen peroxide in situ. The oxidation of benzyl alcohol to benzaldehyde has been achieved with high selectivity (>85%) at temperatures where no reaction is observed with only molecular oxygen in an autoclave. The effect of temperature, catalyst support, and solvent are studied in an autoclave system and reactions were carried out in a fixed bed reactor at a range of gas flow rates where the catalysts demonstrated stable conversion and selectivity.

Threading different metal nanomaterials on natural PhiX174 DNA to assemble a necklace

Multiple nanomaterials were assembled on a circular DNA to form a necklace. AuNPs were first attached to natural PhiX174 ss-DNA, and then a single-circle PCR was adopted to immobilize the attachments. The structures of the assemblies were confirmed by TEM imaging and UV-vis spectrometry. In this way, various types and shapes of nanomaterials were assembled on the DNA, such as palladium nanocubes and gold nanorods.

Oxygen Electroreduction on Electrodeposited PdAu Nanoalloys

The electrocatalytic activity of electrodeposited palladium–gold (PdAu) alloys towards the oxygen reduction reaction (ORR) was studied in 0.05 M H2SO4 and 0.1 M KOH solutions using the rotating disc electrode (RDE) method. The electrochemical deposition was carried out at a constant potential and the ratio of concentrations of the precursors in the deposition bath was varied. The surface morphology of the deposits was studied using scanning electron microscopy (SEM), and the average particle size for PdAu alloys was determined to be about 6 nm. The X-ray photoelectron spectroscopy (XPS) and cyclic voltammetry (CV) studies suggest that the resulting PdAu coatings are alloyed. The ORR activities of the electrodes were compared by calculating the specific activities on the basis of the real electroactive surface area of Pd. The specific activity did not depend on the composition of the alloy in sulphuric acid solution, but in alkaline medium it increased with decreasing Pd content.

Aminosulfonylation of Arenes, Sulfur Dioxide, and Hydrazines Cocatalyzed by Gold(III) Chloride and Palladium Acetate

AbstractN‐Amino‐sulfonamides can be prepared via a gold(III) and palladium(II) cocatalyzed reaction of arenes, sulfur dioxide, and hydrazines. In the course of the reaction, CH functionalization and aminosulfonylation processes are involved.magnified image

Plasmon Resonance Hybridization of Gold Nanospheres and Palladium Nanoshells Combined in a Rattle Structure.

Gold and palladium nanoparticles are characterized by their localized surface plasmon resonance (LSPR). In contrast with the sharp LSPR spectrum of gold nanoparticles, palladium nanoparticles had a broad LSPR spectrum. Palladium-gold nanorattles (PdAuNRT) are an ideal system with optical properties that are a hybrid of gold and palladium nanoparticles. The PdAuNRTs consisted of small gold nanospheres (AuNSs) located inside hollow palladium nanospheres (PdHNSs) of larger sizes without touching each other. PdAuNRTs of various sizes were synthesized by systematic variation of the experimental parameters. Interestingly, for the PdAuNRTs, where PdHNSs and AuNSs are separated by a distance, it was found that the broad plasmon resonance band of the PdHNSs hybridizes with the sharp plasmon resonance of the AuNSs located in its center. This was further confirmed experimentally by optical absorption measurements and theoretically using discrete dipole approximation technique. The plasmon resonance hybridization resulted in broadening of the LSPR spectrum of the PdAuNRTs and the appearance of a dip due to a Fano resonance.

Scanning electron microscopy in liver biopsy interpretation in children: a mini atlas

We have extensively studied the ultrastructural picture of the liver by scanning electron microscopy ( SEM) but these studies were not used, up to now, in clinical practice because they were considered to be mainly a means of research in the 3D structure of liver specimens. Our new technique allows us to introduce ourselves to the 3D structure of intracellular organelles, making it possible to study them in normal and pathologic conditions. We used a very small part of the liver biopsies from 5 children aged 3 to 8 years old, who underwent a liver biopsy for diagnostic purposes. The specimens were fixed and processed according to our modification of the OsO 4 maceration method of Tanaka and Mitsushima. Liver biopsies fixed for 20’ in a mixture of glutaraldehyde and paraformaldehyde, postfixed in 1% OsO 4 for 2 h, cut with a tissue sectioner and then macerated in 0.1% OsO 4 for 60 h at room temperature. Specimens were dehydrated in graded acetone, critical point dried and coated with gold palladium. To selectively remove cell components, some specimens were subjected to ultrasound treatment (25 Hz for 1’) prior to dehydration. To demonstrate the hepatic stroma, some aldehyde-fixed specimens were submitted to maceration with NaOH 1N according to Ohtani method. With this method, all cells were removed, allowing the visualization of collagen fibers. Observation was carried out by an Hitachi S4000 Field Emission SEM (Hitachi High-Technologies Co., Tokyo, Japan) operated at 20 kV. We are showing the results of our new technique applied to the liver tissue. These data open, in our opinion, a new field in the research of nuclear pathology, with possible intriguing data on pathological nuclear pore changes in the setting of different liver diseases.

Oxygen fugacity control in piston-cylinder experiments: a re-evaluation

Jakobsson (Contrib Miner Petrol 164(3):397–407, 2012) investigated a double capsule assembly for use in piston-cylinder experiments that would allow hydrous, high-temperature, and high-pressure experiments to be conducted under controlled oxygen fugacity conditions. Using a platinum outer capsule containing a metal oxide oxygen buffer (Ni–NiO or Co–CoO) and H2O, with an inner gold–palladium capsule containing hydrous melt, this study was able to compare the oxygen fugacity imposed by the outer capsule oxygen buffer with an oxygen fugacity estimated by the AuPdFe ternary system calibrated by Barr and Grove (Contrib Miner Petrol 160(5):631–643, 2010). H2O loss or gain, as well as iron loss to the capsule walls and carbon contamination, is often observed in piston-cylinder experiments and often go unexplained. Only a few have attempted to actually quantify various aspects of these changes (Brooker et al. in Am Miner 83(9–10):985–994, 1998; Truckenbrodt and Johannes in Am Miner 84:1333–1335, 1999). It was one of the goals of Jakobsson (Contrib Miner Petrol 164(3):397–407, 2012) to address these issues by using and testing the AuPdFe solution model of Barr and Grove (Contrib Miner Petrol 160(5):631–643, 2010), as well as to constrain the oxygen fugacity of the inner capsule. The oxygen fugacities of the analyzed melts were assumed to be equal to those of the solid Ni–NiO and Co–CoO buffers, which is incorrect since the melts are all undersaturated in H2O and the oxygen fugacities should therefore be lower than that of the buffer by 2 log \(a_{{{\text{H}}_{ 2} {\text{O}}}}\).

ChemInform Abstract: The Direct Synthesis of Hydrogen Peroxide Using Platinum‐Promoted Gold—Palladium Catalysts.

AbstractThe addition of a small amount of Pt to a CeO2‐supported AuPd (weight ratio of 1:1) catalyst significantly enhances the activity in the direct synthesis of H2O2 (autoclave, 5% H2/CO2 and 25% O2/CO2, 4.0 MPa, 2 °C, 30 min) and decreases the non‐desired over‐hydrogenation and decomposition reactions.

SEM imaging of membranes: Importance of sample preparation and imaging parameters

SEM imaging has been used by researchers to characterize the membrane properties. However, limited information is generally reported regarding the sample preparation and imaging parameters used, making it difficult to compare results from different studies. The present study focuses on the influences of sample preparation and imaging parameters on the observed membrane surface properties obtained from SEM images. Polymeric membranes were prepared with different coating metals (gold, gold–palladium and iridium) and coating thicknesses, and imaged with different imaging parameters (magnification, detector, sample orientation). Image analysis was done using a custom Matlab application. The effects were observed both qualitatively and quantitatively (pore size/shape and porosity). All of the sample preparation and imaging parameters affected the observed membrane properties of interest. In general, the membrane properties were less sensitive to the parameters when membranes were coated with iridium than with gold or gold–palladium. Iridium should be used as the coating metal in the studies where coating thickness and/or, one or more imaging parameters need to be varied. The results suggest the need of a standardized SEM procedure for membrane characterization, and clear reporting of the parameters used in any SEM study, to enable appropriate comparison of the results obtained in different studies.

Effects of post core materials on stress distribution in the restoration of mandibular second premolars: A finite element analysis

Previous studies have not resolved the question as to which post and core combination optimizes the stress distribution within the post restoration and tooth. The purpose of this study was to determine which post and core combination provides the most favorable stress distribution upon loading. Three-dimensional models of teeth were created with the Ansys program to simulate different materials used for post and cores (Ti, NiCr, AuPd, zirconia, zirconia post/composite resin core, glass fiber post/composite resin core, and carbon fiber post/composite resin core) and metal ceramic crowns (nickel chromium alloy [Group NiCr] and gold palladium alloy [Group AuPd]). A force of 400 N was applied to the occlusal surface, and von Mises equivalent stress values were calculated. Carbon fiber post/composite resin core/metal ceramic crowns with NiCr alloy core had the highest stress values in the weakened root, tooth/post interface, and post. NiCr post/NiCr core/metal ceramic crowns with NiCr alloy core had the lowest stress values in the weakened root and post. The zirconia post and core had the lowest stress value in the tooth/post interface. A post material with a high elastic modulus led to lower stress in the weakened root (approximately 6%) and tooth/post interface (approximately 12%) and to higher stress in the post (approximately 5 times). A composite resin core led to higher stress in the weakened root (approximately 11% to 17%) and lower deformation in the tooth/post interface (approximately 17.5%) and post materials (approximately 24%). Group AuPd resulted in lower stress in the root and high stress in the post (approximately 4.5% to 7%) and affected the amount of deformation in posts with a composite resin core.

Selective oxidation using supported gold bimetallic and trimetallic nanoparticles

Supported gold nanoparticles are highly effective for a range of redox reactions. In these reactions the activity is often enhanced by the addition of a second or indeed a third metallic component. A model reaction that is often investigated is the selective oxidation of benzyl alcohol using molecular oxygen as terminal oxidant. In the presence of a solvent the complexity of this reaction can often be missed. However, in the solvent-free oxidation of benzyl alcohol to benzaldehyde using supported gold palladium nanoparticles as catalysts, there are two pathways to the principal product, benzaldehyde. One is the direct catalytic oxidation of benzyl alcohol to benzaldehyde by O2, while the second is the disproportionation of two molecules of benzyl alcohol to give equal amounts of benzaldehyde and toluene. The formation of toluene is an unwanted side reaction. In this paper the research on this reaction will be reviewed and two strategies described that can be used to switch off the formation of the non desired toluene. The first involves the use of basic supports for the gold palladium nanoparticles, which is highly effective in suppressing the formation of toluene and this may be related to the morphology of the gold palladium nanoparticles and their interaction with the support. The second involves the introduction of platinum to the gold palladium nanoparticles which also switches off toluene formation on supports that permit toluene formation in the absence of platinum. This effect may be related to the relative stability of platinum hydride.

Computational Study of Carbostannylation Implicating Bimetallic Catalysis Involving “AuI–Vinyl–PdII” Species

We have investigated computationally the gold and palladium cocatalyzed reaction of alkynes with vinylstannane. Our work has involved a careful and thorough exploration of different mechanistic possibilities. We find that palladium acting alone as a catalyst leads to a very high reaction barrier, consistent with the experimental observation that there is no reaction in the presence of just palladium. However, the involvement of a gold(I) complex lowers the reaction barrier considerably, and the vinylstannylation reaction can proceed with a modest activation energy of about 10 kcal/mol. Our key finding is that the introduction of the gold complex avoids the formation of high-energy structures involving vinyl species in a trans arrangement on palladium. Our work confirms the role of intermediates containing both palladium and gold as suggested by Blum. For the gold–palladium cocatalyzed reaction, we also investigated an alternative mechanism suggested by Blum. With some modifications, this mechanism has a slightly higher reaction barrier, but if it does occur, then we predict a strong dependency on the counterion, in agreement with related experimental findings.

Disentangling ensemble, electronic and coverage effects on alloy catalysts: Vinyl acetate synthesis on Au/Pd(1 1 1)

The activation energies for the reaction of gas-phase ethylene with adsorbed acetate species on Au/Pd(111) alloys are measured as a function of gold coverage in the alloy to probe the elementary steps in gold–palladium alloy catalyzed vinyl acetate monomer (VAM) synthesis. The activation energy decreases with increasing gold coverage in the alloy up to a gold coverage of ∼0.25ML and then increases. The reaction exhibits a kinetic isotope effect when using C2D4 for gold coverages below ∼0.25ML, and no isotope effect for alloys with larger gold coverages. This is ascribed to a change in rate-limiting step for the reaction, which is postulated to proceed via an initial coupling between ethylene and adsorbed acetate species to form an acetoxyethyl intermediate, which decomposes via a β-hydride elimination reaction to form VAM. For low gold coverages, the second step is rate limiting, while at higher coverage, the coupling step becomes rate limiting. This allows the reaction energies for each of the steps to be obtained as a function of gold coverage, where it is found that both energies decrease with increasing gold coverage, causing an increase in overall reaction rate. The activation energy for β-hydride elimination decreases more rapidly than that for the coupling step. The contributions to the energy change are estimated, and it is found that the effect of coverage on the reaction energies is comparable to the more commonly considered ensemble and electronic effects.

The Direct Synthesis of Hydrogen Peroxide Using Platinum‐Promoted Gold–Palladium Catalysts

AbstractThe direct synthesis of hydrogen peroxide offers a potentially green route to the production of this important commodity chemical. Early studies showed that Pd is a suitable catalyst, but recent work indicated that the addition of Au enhances the activity and selectivity significantly. The addition of a third metal using impregnation as a facile preparation method was thus investigated. The addition of a small amount of Pt to a CeO2‐supported AuPd (weight ratio of 1:1) catalyst significantly enhanced the activity in the direct synthesis of H2O2 and decreased the non‐desired over‐hydrogenation and decomposition reactions. The addition of Pt to the AuPd nanoparticles influenced the surface composition, thus leading to the marked effects that were observed on the catalytic formation of hydrogen peroxide. In addition, an experimental approach that can help to identify the optimal nominal ternary alloy compositions for this reaction is demonstrated.

Solvent-free aerobic oxidation of alcohols using supported gold palladium nanoalloys prepared by a modified impregnation method

The synthesis of stable, supported, bimetallic nanoalloys with controlled size, morphology and composition for selective alcohol oxidation.

The direct synthesis of hydrogen peroxide using platinum promoted gold–palladium catalysts

The direct synthesis of hydrogen peroxide using platinum promoted gold–palladium catalysts.

Visible light enhanced oxidant free dehydrogenation of aromatic alcohols using Au–Pd alloy nanoparticle catalysts

We find that visible light irradiation of gold–palladium alloy nanoparticles supported on photocatalytically inert ZrO2 significantly enhances their catalytic activity for oxidant-free dehydrogenation of aromatic alcohols to the corresponding aldehydes at ambient temperatures. Dehydrogenation is also the dominant process in the selective oxidation of the alcohols to the corresponding aldehydes with molecular oxygen. The alloy nanoparticles strongly absorb light and exhibit superior catalytic and photocatalytic activity when compared to either pure palladium or gold nanoparticles. Analysis with a free electron gas model for the bulk alloy structure reveals that the alloying increases the surface charge heterogeneity on the alloy particle surface, which enhances the interaction between the alcohol molecules and the metal NPs. The increased surface charge heterogeneity of the alloy particles is confirmed with density function theory applied to small alloy clusters. Optimal catalytic activity was observed with a Au : Pd molar ratio of 1 : 186, which is in good agreement with the theoretical analysis. The rate-determining step of the dehydrogenation is hydrogen abstraction. The conduction electrons of the nanoparticles are photo-excited by the incident light giving them the necessary energy to be injected into the adsorbed alcohol molecules, promoting the hydrogen abstraction. The strong chemical adsorption of alcohol molecules facilitates this electron transfer. The results show that the alloy nanoparticles efficiently couple thermal and photonic energy sources to drive the dehydrogenation. These findings provide useful insight into the design of catalysts that utilize light for various organic syntheses at ambient temperatures.

Gold-Based Nanoparticulate Catalysts for the Oxidative Esterification of 1,4-Butanediol to Dimethyl Succinate

The effect of the reaction conditions and catalyst composition on the oxidation of 1,4-butanediol has been investigated. We have shown that gold and gold–palladium nanoparticles supported on titania can be effective catalysts for this oxidation reaction. We have demonstrated that the formation of butyrolactone, methyl-4-hydroxybutyrate and dimethyl succinate follow a sequential reaction pathway. We have also investigated the role of acid/base on the reaction and have shown a beneficial synergistic effect of alloying gold with palladium on both the conversion and selectivity towards dimethyl succinate.

DNAzyme-functionalized gold–palladium hybrid nanostructures for triple signal amplification of impedimetric immunosensor

A highly sensitive and selective impedimetric immunosensor with triple signal amplification was designed for ultrasensitive detection of prostate-specific antigen (PSA) by using anti-PSA antibody and DNAzyme-functionalized gold–palladium hybrid nanotags (Ab2–AuPd–DNA). The signal was amplified based on the Ab2–AuPd–DNA toward the catalytic precipitation of 4-choloro-1-naphthol (4-CN). DNAzyme (as a kind of peroxidase mimic) could catalyze the oxidation of 4-CN, whilst AuPd hybrid nanostructures could not only provide a large surface coverage for immobilization of biomolecules but also promote 4-CN oxidation to some extent. The produced insoluble benzo-4-chlorohexadienone via 4-CN was coated on the electrode surface, and hindered the electron transfer between the solution and the electrode, thereby increasing the Faradaic impedance of the base electrode. Three labeling strategies including Ab2–AuNP, Ab2–AuPd and Ab2–AuPd–DNA were investigated for determination of PSA, and improved analytical features were obtained with the Ab2–AuPd–DNA strategy. Under optimal conditions, the dynamic concentration range of the impedimetric immunosensor spanned from 1.0pgmL−1 to 50ngmL−1 PSA with a detection limit of 0.73pgmL−1. Intra- and inter-assay coefficients of variation were below 8.5% and 9.5%, respectively. Importantly, no significant differences at the 0.05 significance level were encountered in the analysis of 6 clinical serum specimens and 6 diluted standards between the impedimetric immunosensor and the commercialized electrochemiluminescent method for PSA detection.