Monometallic Gold Research Articles

Synthesis of chlorotoxin functionalized metallic nanoparticles and their in vitro evaluation of cytotoxic effects in nervous system cancer cell lines

The treatment of glioblastoma (GB) and neuroblastoma (NB) remains a challenge, as current chemotherapies are plagued with systemic toxicity, drug resistance, and inadequate blood–brain barrier (BBB) penetration. Therefore, novel therapeutic strategies with high specificity and the capacity to bypass the BBB are required. Chlorotoxin (CTX) selectively targets gliomas and neuroectodermal tumors, hence the use of CTX-targeted nanoparticles (NPs) represents a promising therapeutic approach for nervous system (NS) cancers. Bimetallic NPs composed of two metals such as gold-platinum NPs (AuPtNPs) exhibit enhanced anticancer properties compared to single-metal NPs, however their application in studying NS tumors has been relatively limited. CTX-functionalized monometallic gold NPs (CTX-AuNPs) and bimetallic gold-platinum NPs (CTX-AuPtNPs) were synthesized in this study. The NPs were characterized by Ultraviolet-Visible Spectroscopy (UV–vis), Dynamic Light Scattering (DLS), Transmission Electron Microscopy (TEM) and Fourier Transform Infra-Red Spectroscopy (FTIR). Cytotoxicity of NPs was investigated in cancer (U87 and SH-SY5Y) and non-cancer (KMST-6) cells using the water-soluble tetrazolium (WST)-1 assay. The CTX-AuNPs and CTX-AuPtNPs had a core size of ∼5 nm. The CTX-AuPtNPs showed significant anticancer activity in U87 cells possibly due to the synergistic effects of combined metals. Findings obtained from this study demonstrated that CTX can be used to target NS cancers and that bimetallic NPs could be effective in their treatment. More studies are required to investigate the mechanisms of NPs toxicity, and further explore the hyperthermia treatment of NS cancer using the CTX-AuPtNPs.

Catalysis using gold containing materials

This perspective article is based on a plenary lecture delivered by the author at Europacat 2023 in Prague on 29th August in recognition of the Boudart Award of EFCATS in 2021. The article charts the journey taken by the author in the discovery and application of gold catalysts over the preceding 40 years of research. Five topics are discussed. The first three parts describe three facets of monometallic gold catalysts. (1) CO oxidation and the hierarchy of activity of gold species supported on a reducible oxide Fe2O3; (2) acetylene hydrochlorination for the manufacture of vinyl chloride monomer using highly dispersed gold cations supported on carbon; (3) methane oxidation using molecular oxygen with gold nanoparticles dispersed on the zeolite H-ZSM-5. These first three parts emphasise that the active species of a gold catalyst is dependent on the reaction being catalysed and it is not a one size fits all for this catalysis. The final two parts concern gold palladium bimetallic catalysts. (4) alcohol oxidation and the new Cooperative Redox Enhancement effect (CORE); and (5) the use of in situ generation of hydrogen peroxide to enable new oxidative cascade processes. These examples demonstrate the rich tapestry that catalysis by gold can provide to the catalysis community globally, both from an academic and an industrial perspective as well as the societal impact that has been achieved by the commercialisation of gold catalysts.

Label-Free Surface-Enhanced Raman Scattering Detection of Fire Blight Pathogen Using a Pathogen-Specific Bacteriophage.

Fire blight is one of the most devastating plant diseases, causing severe social and economic problems. Herein, we report a novel method based on label-free surface-enhanced Raman scattering (SERS) combined with an Erwinia amylovora-specific bacteriophage that allows detecting efficiently fire blight bacteria E. amylovora for the first time. To achieve the highest SERS signals for E. amylovora, we synthesized and compared plasmonic nanoparticles (PNPs) with different sizes, i.e., bimetallic gold core-silver shell nanoparticles (Au@AgNPs) and monometallic gold nanoparticles (AuNPs) and utilized the coffee-ring effect for the self-assembly of PNPs and enrichment of fire blight bacteria. Furthermore, we investigated the changes in the SERS spectra of E. amylovora after incubation with an E. amylovora-specific bacteriophage, and we found considerable differences in the SERS signals as a function of the bacteriophage incubation time. The results indicate that our bacteriophage-based label-free SERS analysis can specifically detect E. amylovora without the need for peak assignment on the SERS spectra but simply by monitoring the changes in the SERS signals over time. Therefore, our facile method holds great potential for the label-free detection of pathogenic bacteria and the investigation of viral-bacterial interactions.

Radiolysis-Assisted Direct Growth of Gold-Based Electrocatalysts for Glycerol Oxidation.

The electrocatalytic oxidation of glycerol by metal electrocatalysts is an effective method of low-energy-input hydrogen production in membrane reactors in alkaline conditions. The aim of the present study is to examine the proof of concept for the gamma-radiolysis-assisted direct growth of monometallic gold and bimetallic gold-silver nanostructured particles. We revised the gamma radiolysis procedure to generate free-standing Au and Au-Ag nano- and micro-structured particles onto a gas diffusion electrode by the immersion of the substrate in the reaction mixture. The metal particles were synthesized by radiolysis on a flat carbon paper in the presence of capping agents. We have integrated different methods (SEM, EDX, XPS, XRD, ICP-OES, CV, and EIS) to examine in detail the as-synthesized materials and interrogate their electrocatalytic efficiency for glycerol oxidation under baseline conditions to establish a structure-performance relationship. The developed strategy can be easily extended to the synthesis by radiolysis of other types of ready-to-use metal electrocatalysts as advanced electrode materials for heterogeneous catalysis.

SERS Reveals the Presence of Au–O–O–H and Enhanced Catalytic Activity of Electrochemically Dealloyed AgAu Nanoparticles

Due to their high surface-to-volume ratio and large proportion of low coordinated surface atoms, dealloyed nanoparticles have gained increasing attention as porous catalysts for the electrochemical oxygen evolution reaction (OER). Here, we characterize and rationalize the physical and chemical properties of operando gold-enriched porous nanoparticles fabricated by electrochemical dealloying of citrate-capped silver gold alloy nanoparticles in 250 mM KNO3. We combine surface-enhanced Raman spectroscopy (SERS) with electrochemistry for catalyst tracking. With SERS, we observe at 1.05 V (vs platinum quasi-reference electrode) the formation of Au–O–O–H species, a known intermediate of OER, while this is not observed for monometallic gold nanoparticles or bare electrodes. In agreement, qualitative measurements of the catalytic activity prove that appreciable OER currents are detected at lower potentials for gold-enriched porous nanoparticles compared to gold nanoparticles of the same size. Our results pave the way for the application of dealloying-derived nanoparticles as promising catalyst materials.

Rapid Biotransformation of Luminescent Bimetallic Nanoparticles in Hepatic Sinusoids.

Liver sequestration, mainly resulting from the phagocytosis of mononuclear phagocyte system (MPS) cells, is a long-standing barrier in nanoparticle delivery, which severely decreases the disease-targeting ability, leads to nanotoxicity, and inhibits clinical translation. To avoid long-term liver sequestration, we elaborately designed luminescent gold-silver bimetallic nanoparticles that could be rapidly transformed by the hepatic sinusoidal microenvironment rich in glutathione and oxygen, significantly different from monometallic gold nanoparticles that were rapidly sequestrated by Kupffer cells due to the much slower biotransformation. We found that the rapid sinusoidal biotransformation induced by the synergistic reactions of glutathione and oxygen with the reactive silver atoms could help bimetallic nanoparticles to avoid MPS phagocytosis, promote fast release from the liver, prolong blood circulation, enhance renal clearance, and increase disease targeting. With the fast biotransformation in sinusoids, liver sequestration could be turned into a beneficial storage mechanism for nanomedicines to maximize targeting.

Highly Active Large Au Clusters and Even More Active Ag Nanoparticles Supported on Ceria-Zirconia: Impact of Particle Size and Potassium Ion Loading on Activity in Catalytic Transfer Hydrogenation

Although heterogeneous monometallic gold catalysts are commonly more active when the gold particles are smaller, this study shows that the reverse is true in the case of liquid phase catalytic transfer hydrogenation of acetophenone with 2-pentanol. Higher catalytic activity of larger gold particles, i.e., over 30 nm in diameter, than of smaller particles of average 4 nm in size was observed. Moreover, this effect was contradictory to that observed for supported monometallic silver catalysts in which the interaction with the support and hence particle size was shown to cause drastic changes in the activity in this reaction, with the large particles being completely inactive and tiny ones being the most active system studied. In this reaction, the ceria-zirconia solid solutions were used as the supports for the catalysts and both zirconium doped ceria, as well as cerium doped zirconia carriers were tested. The supports themselves exhibited little activity in this reaction. It was shown that the activity of the supports and catalysts depends on the Ce/Zr ratio and potassium content. Both types of catalysts showed excellent selectivity to 1-phenylethanol and conversion of acetophenone, although it was noted that a high loading of potassium carbonate in the gold catalysts propelled undesired reactions, thereby reducing the selectivity to 1-phenylethanol.

Controlled preparation and application of glutathione capped gold and platinum alloy nanoclusters with high peroxidase-like activity

• The Au-PtNCs have been controlled prepared through a hydrothermal method. • The Au-PtNCs show optimal catalytic activity for TMB oxidation. • Doping with platinum is the most efficient way to improve the catalytic properties. • The Au-PtNCs are applied to colorimetric determine H 2 O 2 with high sensitivity. In the present study, we have prepared glutathione capped gold and platinum alloy nanoclusters (Au-PtNCs) in a controlled way by employing the hydrothermal method and optimized through adjusting the ratio of raw materials, reaction temperature, and time. Compared with the corresponding monometallic gold and platinum nanoclusters, the alloy nanoclusters' catalytic activity is improved dramatically in the oxidation of 3,3′,5,5′-tetramethylbenzidine (TMB) in the presence of H 2 O 2 . And the maximum velocity is calculated to be 106 × 10 −8 M · s −1 for TMB as substrate, being much better than that of other reported metallic nanoclusters and nanoparticles. Further study shows that the high catalytic activity mainly attributes to the synergistic effect of gold and platinum. Besides, they have been applied to determine H 2 O 2 in the presence of TMB, which shows high sensitivity with a limit of detection (LOD) at 100 nM. The proposed method has been used to determine H 2 O 2 in milk and contact lens solutions, which shows very good recovery and exhibits high practical application potential. Therefore, the present study provides a new type of alloy nanoclusters with high peroxidase-like activity, which will inspire more research interests on doping and alloying with Pt to improve the catalytic activity of metal nanoclusters.

Investigating the Performance of Near‐Infrared Light Responsive Monometallic Gold and Bimetallic Gold‐Palladium Nanorattles towards Plasmonic Photothermal Therapy

AbstractThe effect of different sizes and shapes of nanomaterials on its extinction spectrum is well studied and accordingly researchers have designed various nanostructures having absorbance in the near infrared (NIR) region for plasmonic photothermal therapy (PPTT) applications. However, the comparative study between the NIR active nanomaterials having different elemental composition for PPTT applications is not well explored. Herein, we investigate the photothermal activity of two different NIR active nanorattles viz. gold nanorattle (Au NRT) and bimetallic gold‐palladium nanorattle (Au−Pd NRT) having identical morphology but different elemental composition. The prepared nanorattles were PEGylated to render biocompatibility and identical surface functionalities. The aqueous solution of both the NRTs displayed a significant rise in temperature upon NIR irradiation which was not compromised on repeated exposure to light. The PPTT applicability of both the nanorattles were evaluated which suggested that the bimetallic Au−Pd NRT have better photothermal conversion efficiency of 35.4 % and better photothermal killing ability towards breast cancer cell line (SK‐BR‐3) compared to that of monometallic Au NRT having photothermal conversion efficiency of only 19.8 %. Thus, the present study indicates that NIR active nanostructures based on palladium acts as a better phototransducing agent than that of gold with similar morphology.

Au-Pd separation enhances bimetallic catalysis of alcohol oxidation.

In oxidation reactions catalysed by supported metal nanoparticles with oxygen as the terminal oxidant, the rate of the oxygen reduction can be a limiting factor. This is exemplified by the oxidative dehydrogenation of alcohols, an important class of reactions with modern commercial applications1-3. Supported gold nanoparticles are highly active for the dehydrogenation of the alcohol to an aldehyde4 but are less effective for oxygen reduction5,6. By contrast, supported palladium nanoparticles offer high efficacy for oxygen reduction5,6. This imbalance can be overcome by alloying gold with palladium, which gives enhanced activity to both reactions7,8,9; however, the electrochemical potential of the alloy is a compromise between that of the two metals, meaning that although the oxygen reduction can be improved in the alloy, the dehydrogenation activity isoften limited. Here we show that by separating the gold and palladium components in bimetallic carbon-supported catalysts, we can almost double the reaction rate compared with that achieved with the corresponding alloy catalyst. We demonstrate this using physical mixtures of carbon-supported monometallic gold and palladiumcatalysts and a bimetallic catalyst comprising separated gold and palladium regions. Furthermore, we demonstrate electrochemically that this enhancement is attributable to the coupling of separate redox processes occurring at isolated gold and palladium sites. The discovery of this catalytic effect-a cooperative redox enhancement-offers an approach to the design of multicomponent heterogeneous catalysts.

Bimetallic gold-copper nanoparticles in the catalytic reaction of deuterium-hydrogen exchange: A synergistic effect

Catalyst systems containing bimetallic Au and Cu nanoparticles exhibited higher specific catalytic activity (H2/D2 exchange reaction) than monometallic gold nanoparticles and catalytically inactive copper monoparticles. A synergistic effect was found in the reaction of homomolecular isotope exchange of hydrogen. The activity was observed to depend on the ratio of metals in the nanoparticle. The maximum activity was exhibited by particles for the preparation of which solutions of salts taken in the ratio Au:Cu = 50%:50% were used as precursors. The addition of gold to copper led not only to the appearance of the activity of the Aun-Cum heteroparticles, but also to the stabilization of the surface and catalytic activity, which allowed us to conclude about the promoting effect of gold.The combination of several metals in a catalytic system provides a unique opportunity to create new highly active catalysts in processes involving hydrogen.

Organotrialkoxysilane-Functionalized Noble Metal Monometallic, Bimetallic, and Trimetallic Nanoparticle Mediated Non-Enzymatic Sensing of Glucose by Resonance Rayleigh Scattering.

Organotrialkoxysilanes like 3-aminopropyltrimethoxysilane (3-APTMS)-treated noble metal cations were rapidly converted into their respective nanoparticles in the presence of 3-glycidoxypropylytrimethoxysilane (3-GPTMS). The micellar activity of 3-APTMS also allowed us to replace 3-GPTMS with other suitable organic reagents (e.g., formaldehyde); this approach has significant advantages for preparing bimetallic and trimetallic analogs of noble metal nanoparticles that display efficient activity in many practical applications. The formation of monometallic gold, silver, and palladium nanoparticles, bimetallic Ag-Pd, and Au-Pd nanoparticles at various ratios of noble metal cations, and trimetallic Ag-Au-Pd nanoparticles were studied; their biocatalytic activity in non-enzymatic sensing of glucose based on monitoring synchronous fluorescence spectroscopy (SFS) was assessed. Of these nanoparticles, Au-Pd made with an 80:20 Au:Pd ratio displayed excellent catalytic activity for glucose sensing. These nanoparticles could also be homogenized with Nafion to enhance the resonance Rayleigh scattering (RRS) signal. In this study, the structural characterization of noble metal nanoparticles as well as bi- and tri-metallic nanoparticles in addition to their use in non-enzymatic sensing of glucose are reported.

The Application of Copper-Gold Catalysts in the Selective Oxidation of Glycerol at Acid and Basic Conditions

The crude glycerol is produced during the transesterification of animal fats and vegetable oils, but it is a by-product of this process. Currently, its elimination is a problem in the chemical industry. The main goal of this work was the preparation, characterization and application of mesoporous cerium-zirconium oxide as supports for copper and gold species and the comparison of selected factors on the properties of catalysts in glycerol oxidation in the liquid phase. The samples were characterized using adsorption and desorption of nitrogen, XRD, UV-vis, XPS, TEM, SEM, and STEM-EDXS. The obtained results of glycerol oxidation show that the bimetallic copper-gold catalysts are more active and selective to glyceric acid in this reaction than analogous monometallic gold catalysts. Additionally, bimetallic catalysts are also characterized by the catalytic stability, and their application leads to the increase of selectivity to glyceric acid during their reusing in glycerol oxidation in alkali media. In this work, the influence of selected factors, e.g., oxygen source and its pressure, solution pH, and base content on the catalytic activity of bimetallic catalysts is discussed.

Synthesis and Differential Antibacterial Activity of Bioconjugated Bimetallic Nanoparticles

Core-shell nanoparticles are preferable due to their new and/or improved properties over monometallic nanoparticles. Shell metals are present as a film on the surface of a core metal, which leads to an increase in reactivity of the surface. The synthesis of core-shell nanoparticles using biomolecules is an important strategy to get more activity with less toxicity. The present work was intended to prepare bimetallic nanoparticle preparation by green synthetic method. Aqueous extract of Muntingia calabura flowers was used for the preparation of metal core-shell nanoparticles where flower extract acted as both reducing agent and stabilizing agent. Monometallic gold nanoparticles (AuNPs) and silver nanoparticles (AgNP) were prepared using metal precursors chloroauric acid (HAuCl4) and silver nitrate (AgNO3), respectively. For the preparation of bimetallic core-shell nanoparticles, a shell metal precursor (copper acetate) was added. The obtained nanoparticles were characterized by various instrumental methods including UV–Vis spectrophotometry, TEM and SEM techniques, and EDX spectral analysis. Preliminary antibacterial screening of Au@Cu NP and Ag@Cu NP was performed by disk diffusion assay. TEM and SEM images showed that Au@Cu NPs were spherical whereas Ag@Cu NPs had irregular shapes. The EDX analysis revealed that more Cu was deposited in AuCuNPs than in AgCuNPs. The antibacterial activity assay proved that spherical AuCuNPs were more potent than irregular shaped AgCuNPs.

Study of Ultrasonic Attenuation and Thermal Conduction in Bimetallic Gold/Platinum Nanofluids

Here, we report the frequency dependent ultrasonic attenuation of monometallic gold and bimetallic gold/platinum based aqueous nanofluids (NFs). The as-synthesised bimetallic NFs (BMNFs) revealed less resistance to ultrasonic waves compared to the monometallic NFs. Thermal conductivity of both NFs taken at different concentrations revealed substantial conductivity improvement when compared to the base fluid, although gold/platinum showed lesser improvement compared to gold. Characterisation of the as-synthesised nanoparticles (NPs) and fluids was carried out with X-ray diffraction (XRD), ultraviolet-visible (UV-vis) spectroscopy, transmission electron microscopy (TEM) and energy-dispersive X-ray spectroscopy (EDS). The distinct two-phase bimetallic nature of gold/platinum, its two plasmonic band optical absorption features and the spherical morphology of the particles were shown. The findings were correlated with the observed thermal and ultrasonic behaviour and proper rationalisation is provided. It was revealed that the comparatively lesser thermal conductivity of gold/platinum had direct implication on its attenuation property. The findings could have important repercussions in both industrial applications and in the mechanistic approach towards the field of ultrasonic attenuation in NFs.

Nano and Sub-nano Gold–Cobalt Particles as Effective Catalysts in the Synthesis of Propargylamines via AHA Coupling

Titania supported Au–Co catalysts with nano- and sub-nanoparticles, were prepared with 1% Au and different contents of cobalt by one pot deposition precipitation with urea. Monometallic gold and cobalt catalysts were also prepared by the same method for a comparative purpose. The characterization of bimetallic catalyst evidenced the presence of sub-nanoparticles where 50% of cobalt and 40% of gold particles are smaller than 1 nm and the formation Au–Co particles. The results show a positive effect of cobalt on gold particles size and the catalytic activity. The effectiveness of these catalysts in the synthesis of several propargylamines via amine, CH2Cl2 and alkyne coupling (AHA coupling) was demonstrated. Different propargylamines were synthesized with very good yields (71%–88%). A comparative study of monometallic gold, monometallic cobalt and bimetallic gold–cobalt catalysts was investigated. The most efficient catalyst was reused for up to six reaction cycles without significant activity loss.

Application of Gold and Platinum Bimetallic Nanoparticle to enhance Surface Plasmon Resonance Signal

Sensors based on the surface plasmon resonance (SPR) technique are useful devices to detect and monitor interactions between biomolecules in real-time. SPR is a label-free method that monitors the variation of reflectivity of a biochip composed of a metal-coated glass prism and can be applied in several areas, such as biotechnology, food safety and clinical diagnosis. In the last years, several researchers have proven the efficiency of metallic nanoparticles (NPs) in the enhancement of SPR signal. This feature allowed the detection of biomolecules at very low concentration. Aiming to further enhance SPR signal towards the detection of proteins at low concentration and by a simple procedure, the present work compared the performance of gold and platinum bimetallic NPs (AuPtNPs) with that of monometallic gold NPs (AuNPs) in the enhancement of SPR signal. In order to evaluate the NPs, protein peanut agglutin (PNA) was used as target analyte and anti-PNA antibody was used as sensing molecule. Firstly NPs were functionalized with anti-PNA antibody and incubated with a solution containing PNA. Then, the NPs bound to PNA were injected into the SPR equipment containing a biochip previously modified with anti-PNA antibody. The results demonstrated that the AuPtNPs provided a 91-fold increase compared to the direct detection of free PNA in solution. In comparison with AuNPs, the signal generated by AuPtNPs was about 4 times higher. This encouraging result indicated that the application of bimetallic NPs may be a better strategy to further enhance sensitivity of SPR biosensors and could drive the development of new strategies that are not only simple, but also able to detect proteins at low concentrations, which is of great importance, especially in clinical diagnostics.

One-Pot Myrtenol Amination over Au, Au–Pd and Pd Nanoparticles Supported on Alumina

One-pot bio-based myrtenol amination was studied in the presence of alumina supported Au, Au–Pd and Pd nanoparticles subjected to the thermal treatment under oxidizing or reducing atmosphere. Myrtenol amination with aniline was carried out under nitrogen atmosphere (9 bar) at 453 K using toluene as a solvent. The effect of the active metal along with the influence of redox pre-treatment on the catalytic behavior in the hydrogen borrowing reaction was explored. The catalyst characterization was done by transmission electron microscopy, X-ray photoelectron spectroscopy, inductively coupled plasma optical emission spectroscopy, nitrogen adsorption. The active metal and the catalysts redox pretreatment affected more noticeably selectivity to the reaction products rather than myrtenol conversion. Monometallic Au/Al2O3 catalyst promoted predominantly formation of the target secondary amine and the corresponding imine without a significant impact of the side reaction of C=C bond hydrogenation in myrtenol, whereas monometallic Pd catalyst activated C=C bond resulting in its hydrogenation. At the same time in the presence of Au–Pd simultaneous hydrogenation of both C=C and C=N bond occurred. Au–Pd catalysts activated in oxygen and hydrogen showed different catalytic activity determined by the composition of surface active sites. Monometallic gold catalyst was more effective in the hydrogen transfer in the case of substrates with competitive unsaturated functional groups.

Rapid Synthesis and Antiproliferative Properties of Polyazamacrocycle-Based Bi- and Tetra-Gold(I) Phosphine Dithiocarbamate Complexes.

A family of bi- and tetrametallic gold(I) phosphine dithiocarbamate complexes were synthesized, starting from cyclam and dimethylcyclam polyazamacrocycles, respectively, along with their monometallic gold(I) chloridophosphine precursors. Their antiproliferative properties were evaluated on two cancer cell lines (A549 and NSCLC-N6-L16). Most of the mono- and bimetallic complexes displayed strong activities and, in particular, one bimetallic derivative showed antiproliferative properties in the low micromolar range. Insights into the structure-activity relationships are given, along with determination of the thioredoxin reductase inhibition potential, two-photon imaging of the fluorescent derivatives, and evaluation of gold uptake.

Factors affecting the activity and selectivity of niobia-based gold catalysts in liquid phase glycerol oxidation

Abstract The present study aims at the elucidation of the influence of niobia crystallinity, gold deposition method and the presence of copper dopant on the activity and selectivity of niobia supported gold catalysts in liquid phase oxidation of glycerol. The role of niobium pentoxide crystallinity was estimated with the use of gold catalysts supported on three different niobia supports but prepared by the same gold loading method, while the influence of gold deposition method and the presence of copper promoter were studied using mono- (Au, Cu) and bimetallic (AuCu) catalysts supported on the same niobia support but synthesized using different metal loading methods. The activity of the catalysts in glycerol oxidation was tested under different reaction conditions, i.e. different reaction time and various concentrations of sodium hydroxide as a base. Detailed analysis of relationship between the properties of catalysts and their activity/selectivity in glycerol oxidation considered in this study showed that niobia crystallinity had negligible influence on the activity of gold catalysts containing small metal nanoparticles with the size of ca. 5 nm. Furthermore, it was documented that copper species in the bimetallic AuCu catalyst play double roles. Firstly, copper acts as a structural promoter which enhances the dispersion of the active phase, and thus enables high activity in glycerol oxidation. Secondly, copper itself promotes the C C bond cleavage during glycerol oxidation. It was found that the bimetallic catalyst was much more selective to glycolic and formic acids than the monometallic gold catalyst, despite the fact that both catalysts contained gold particles of similar average size of ca. 5 nm. This observation allowed drawing the conclusion that the changes in selectivity of the bimetallic AuCu sample did not result from different size of gold nanoparticles, but were more likely to be related to the presence of copper dopant which improved the catalyst ability to C C bond cleavage.