Small Gold Nanoparticles Research Articles

Versatility of Supported Gold Nanoparticles on Hydrotalcites used for Oxidation and Reduction Reactions

Regardless of their size, supported gold nanoparticles are largely used for liquid-phase oxidation reactions. Small gold nanoparticles exhibit good performance during the reduction of organic compounds. The direct reduction of carboxylic acid to aldehyde is a famous and familiar reaction in the field of organic chemistry and is considered as one of the fundamental chemical transformations. Herein, we present Au/hydrotalcite, Au/MgO, and Au/Al2O3 systems as heterogeneous versatile catalysts to realize the oxidation of furfural (FF) to furoic acid (FA) and realize the reduction of FA to FF. Experiments showed that in standard aqueous conditions under air, FF can be easily oxidized to FA. When DMSO was used as a solvent to conduct the experiments under an atmosphere of CO2, FA was reduced to FF. The Au/HT series of catalysts was found to be active in both transformations, pointing out the versatility of the gold-based catalysts. The activity significantly depends on the acid-base properties of the catalyst.

Thiol-Responsive Gold Nanodot Swarm with Glycol Chitosan for Photothermal Cancer Therapy.

Photothermal therapy (PTT) is one of the most promising cancer treatment methods because hyperthermal effects and immunogenic cell death via PTT are destructive to cancer. However, PTT requires photoabsorbers that absorb near-infrared (NIR) light with deeper penetration depth in the body and effectively convert light into heat. Gold nanoparticles have various unique properties which are suitable for photoabsorbers, e.g., controllable optical properties and easy surface modification. We developed gold nanodot swarms (AuNSw) by creating small gold nanoparticles (sGNPs) in the presence of hydrophobically-modified glycol chitosan. The sGNPs assembled with each other through their interaction with amine groups of glycol chitosan. AuNSw absorbed 808-nm laser and increased temperature to 55 °C. In contrast, AuNSw lost its particle structure upon exposure to thiolated molecules and did not convert NIR light into heat. In vitro studies demonstrated the photothermal effect and immunogenic cell death after PTT with AuNSW. After intratumoral injection of AuNSw with laser irradiation, tumor growth of xenograft mouse models was depressed. We found hyperthermal damage and immunogenic cell death in tumor tissues through histological and biochemical analyses. Thiol-responsive AuNSw showed feasibility for PTT, with advanced functionality in the tumor microenvironment.

Dibenzyldithiocarbamate-Functionalized Small Gold Nanoparticles as Selective Catalysts for the Electrochemical Reduction of CO2 to CO

Dibenzyldithiocarbamate-functionalized gold nanoparticles (DBDTC-Au NPs) were synthesized in the laboratory, and the effects of the DBDTC ligand on the Au electrocatalytic activity for CO2 reduction reaction to CO were investigated in CO2-saturated KHCO3 electrolyte. Our synthesis route produced sub-2.0 nm Au particles, with the number of gold atoms in the range of 67–120, and with strongly bonded and stable DBDTC ligands on the surface. Online differential electrochemical mass spectrometry (DEMS) experiments on the DBDTC-Au nanoparticles showed higher faradic current and higher CO/H2 ratio of their ionic signals compared to those for citrate-capped Au NPs. Quantitative analyses via gas chromatography (GC) showed that our DBDTC-Au catalyst converts CO2 into CO with a faradic efficiency of approximately 100 ± 1% at −0.8 V and 93 ± 0.5% at −1.0 V vs RHE. The higher activity of the synthesized DBDTC-Au electrocatalyst was attributed to the following important functionalities of the DBDTC ligand: (i) the strong bonding to the surface stabilizes the Au NPs, inhibiting the formation of large agglomerates, and (ii) the hydrophobic character of the dibenzyl moieties allows the permeation of CO2, but repels water from the Au surface, minimizing the electrochemical reduction of water and, therefore, enhancing the faradic efficiency for CO formation.

Novel nucleic acid aptamer gold (Au)-nanoparticles (AuNPs-AptHLA-G5-1 and AuNPs-AptHLA-G5-2) to detect the soluble human leukocyte antigen G5 subtype (HLA-G5) in liquid samples.

BackgroundThe human leukocyte antigen G5 subtype (HLA-G5) is a major histocompatibility complex (MHC) molecule that is selectively expressed at the maternal-foetal tissue interface and is required for the successful implantation of the in vitro fertilized embryo. It is critical to detect HLA-G5, especially HLA-G5 expression in embryo fluid, during in vitro embryo incubation and culture. However, the specificity and sensitivity of traditional ELISA methods to detect sHLA-G5 are insufficient. This work aimed to explore novel nucleic acid aptamer gold (Au)-nanoparticles to detect soluble HLA-G5 in liquid samples.MethodsSoluble HLA-G5 was obtained using a prokaryotic expression system, and two novel aptamers (HLA-G5-Apt1 and HLA-G5-Apt2) detecting HLA-G5 were screened by the Systematic Evolution of Ligands by Exponential Enrichment (SELEX) method. Small (10 nm) gold nanoparticles (AuNPs) were incubated with AptHLAs to form two novel nucleic acid aptamers: Au-nanoparticles (AuNPs-AptHLA-G5-1 and AuNPs-AptHLA-G5-2).ResultsThe results showed that AptHLA-G5-1 and AptHLA-G5-2 have a high affinity for HLA-G5 and can detect its presence in liquid samples. Using the colorimetric sensing method, AuNPs-AptHLA-G1 had a detection limit as low as 20 ng/mL (recovery range between 98.7% to 102.0%), while AuNPs-AptHLA-G2 had a detection limit as low as 20 ng/mL (recovery range between 98.9% to 103.6%).ConclusionsOur work demonstrates that novel AuNPs are efficient detectors for HLA-G5 and are useful for diagnosis and treatment in the field of obstetrics-gynaecology.

Radiosensitization Effect of Gold Nanoparticles in Proton Therapy

The number of proton therapy facilities and the clinical usage of high energy proton beams for cancer treatment has substantially increased over the last decade. This is mainly due to the superior dose distribution of proton beams resulting in a reduction of side effects and a lower integral dose compared to conventional X-ray radiotherapy. More recently, the usage of metallic nanoparticles as radiosensitizers to enhance radiotherapy is receiving growing attention. While this strategy was originally intended for X-ray radiotherapy, there is currently a small number of experimental studies indicating promising results for proton therapy. However, most of these studies used low proton energies, which are less applicable to clinical practice; and very small gold nanoparticles (AuNPs). Therefore, this proof of principle study evaluates the radiosensitization effect of larger AuNPs in combination with a 200 MeV proton beam. CHO-K1 cells were exposed to a concentration of 10 μg/ml of 50 nm AuNPs for 4 hours before irradiation with a clinical proton beam at NRF iThemba LABS. AuNP internalization was confirmed by inductively coupled mass spectrometry and transmission electron microscopy, showing a random distribution of AuNPs throughout the cytoplasm of the cells and even some close localization to the nuclear membrane. The combined exposure to AuNPs and protons resulted in an increase in cell killing, which was 27.1% at 2 Gy and 43.8% at 6 Gy, compared to proton irradiation alone, illustrating the radiosensitizing potential of AuNPs. Additionally, cells were irradiated at different positions along the proton depth-dose curve to investigate the LET-dependence of AuNP radiosensitization. An increase in cytogenetic damage was observed at all depths for the combined treatment compared to protons alone, but no incremental increase with LET could be determined. In conclusion, this study confirms the potential of 50 nm AuNPs to increase the therapeutic efficacy of proton therapy.

Furin Enzyme and pH Synergistically Triggered Aggregation of Gold Nanoparticles for Activated Photoacoustic Imaging and Photothermal Therapy of Tumors

Specific and effective accumulation of nanoparticles within tumors is highly crucial for precise cancer diagnosis and treatment. Therefore, spatiotemporally manipulating the aggregation of small gold nanoparticles (AuNPs) in a tumor microenvironment is of great significance for enhancing the diagnostic and therapeutic efficacy of tumors. Herein, we reported a novel furin enzyme/acidic pH synergistically triggered small AuNP aggregation strategy for activating the photoacoustic (PA) imaging and photothermal (PTT) functions of AuNPs in vivo. Smart gold nanoparticles decorated with furin-cleavable RVRR (Arg-Val-Arg-Arg) peptides (Au-RRVR) were rationally designed and fabricated. Both in vitro and in vivo experiments demonstrated that such Au-RRVR nanoparticles could be simultaneously induced by furin and acidic pH to form large aggregates within tumorous tissue resulting in improved tumor accumulation and retention, which can further activate the PA and PTT effect of AuNPs for sensitive imaging and efficient therapy of tumors. Thus, we believe that this dual-stimuli-responsive aggregation system may offer a universal platform for effective cancer diagnosis and treatment.

Gold nanoparticle synthesis in contact lenses for drug-less ocular cystinosis treatment

PurposeTo develop gold nanoparticles-loaded contact lens (“GoldinLens”) to bind a significant mass of cystine on the surface of the gold nanoparticles (GNPs) for cystinosis treatment due to the reaction between cystine and gold. MethodsThe GoldinLens was manufactured by synthesizing GNPs inside the preformed contact lens matrix by first loading the lenses (Moist and TrueEye) with gold precursor followed by reduction (with sodium borohydride or trisodium citrate) to gold atoms, which nucleated to GNPs inside the polymeric matrix. The lenses were characterized by SEM, XRD, UV–Vis spectroscopy and mass of GNPs loaded in the lens was determined by direct measurement of mass. Manufactured lenses were soaked in cystine solution for cystine uptake in vitro. ResultsResults show that gold loading in the contact lens increases linearly with gold precursor concentration and number of repetitions of the manufacturing process. The stronger reducing agent sodium borohydride resulted in higher gold loading, with the loading being higher in the Moist lenses due to higher diffusivity of the reducing agent into the lens. However, GNPs were smaller in size and relatively monodispersed in TruEye GoldinLens, resulting in higher cystine uptake of 47 μg/lens over 24 h (vs. 33 μg/lens for Moist GoldinLens). However, the rate of this uptake was higher for Moist GoldiLens (8.25 vs. 2.35 μg/h), with the maximum uptake occurring in one hour (vs. five hours). ConclusionA method for manufacturing GoldinLens, wherein small gold nanoparticles are trapped in contact lenses, has been developed for drugless cystinosis treatment. The lenses withdraw cystine molecules from the surrounding milieu, with the TrueEye GoldinLens being superior for the extent of, while Moist GoldinLens is superior for rate of cystine removal. GoldinLenses of this study can be used for drugless cystine removal cystinosis treatment with one- or five-hour wear at a time.

Polyionic Nanoclays: Tailorable Hybrid Organic–Inorganic Catalytic Platforms

We unveil the synthesis and initial application of a hybrid inorganic–organic architecture comprising two-dimensional, few nanometer-thick magnesium phyllo(organo)silicate nanosheets displaying an ordered array of covalently linked imidazolium functionalities. Accessible via a simple, one-pot ambient-temperature synthesis using a custom organosiloxane, these so-called polyionic nanoclays (PINCs) represent an emergent class of supported ionic liquid phase and hold a number of attractive features, including: (i) an extremely high ionic density (e.g., 3.8 mmol g–1 for the 1-methyl-3-propylimidazolium chloride PINC, roughly two-thirds the imidazolium cation density observed in the analogous free-flowing ionic liquid); (ii) the exchangeability of the associated counteranions to impart supplementary functionality or modulate solvent dispersibility; and (iii) the facility for tailoring the organic component, for example incorporating different (e.g., pyrrolidinium, pyridinium, phosphonium) or mixed onium moieties by employing the appropriate organosiloxane precursor(s). As a preliminary investigation of PINCs as nanocatalytic supports, we performed anion exchange with [AuCl4]−, followed by in situ reduction to generate small (<5 nm) gold nanoparticles (AuNPs) on the clay lamellae. The resulting nanosized gold-modified PINCs dispersed in water exhibited an astonishing turnover frequency of 25 000 h–1 for 4-nitrophenol reduction at room temperature, making this hybrid material the most active gold nanocatalyst reported for this model reaction. Most remarkably, AuNPs supported on the PINC showed a dramatically enhanced catalytic activity (4000% increase) compared to similar gold nanoparticles suspended in water (600 h–1), suggesting a major synergistic effect arising from the PINC support. Overall, the generality and flexibility of this route to lamellar hybrid nanoclays, coupled with the ability to accommodate a wide range of pendant organic ionic moieties suggests an auspicious future for PINCs in catalysis, ion exchange, energy storage, separations, (bio)sensing, imaging, and the construction of nanoscale assemblies.

Modulation of Nanoparticle Diffusion by Surface Ligand Length and Charge: Analysis with Molecular Dynamics Simulations.

To help better interpret experimental measurement of nanoparticle size, it is important to understand how their diffusion depends on the physical and chemical features of surface ligands. In this study, explicit solvent molecular dynamics simulations are used to probe the effect of ligand charge and flexibility on the diffusion of small gold nanoparticles. The results suggest that despite a high bare charge (+18 e), cationic nanoparticles studied here have reduced diffusion constants compared to a hydrophobic gold nanoparticle by merely a modest amount. Increasing the ligand length by 10 CH2 units also has a limited impact on the diffusion constant. For the three particles studied here, the difference between estimated hydrodynamic radius and radius of gyration is on the order of one solvent layer (3-5 Å), confirming that the significant discrepancies found in the size of similar nanoparticles by recent transmission electron microscopy and dynamic light scattering measurements were due to aggregation under solution conditions. The limited impact of electrostatic friction on the diffusion of highly charged nanoparticles is found to be due to the strong anticorrelation between electrostatic and van der Waals forces between nanoparticle and environment, supporting the generality of recent observation for proteins by Matyushov and co-workers. Including the first shell of solvent molecules as part of the diffusing particle has a minor impact on the total force autocorrelation function but reduces the disparity in relaxation time between the total force and its electrostatic and van der Waals components.

Gold Nanoclusters Display Low Immunogenic Effect in Microglia Cells.

Gold nanoparticles hold a great promise for both clinical and preclinical applications. The major factors impeding such applications are toxicity of new nanomaterials including e.g., pro-apoptotic activities or inflammatory effects, but also their potential to accumulate in the body or inadequate absorption, distribution, metabolism and excretion (ADME) profiles. Since such adverse effects depend on the size, form and coating of nanomaterials, the search for new, less toxic nanomaterials with low tendency to accumulate is highly active domain of research. Here, we describe optical and biological properties of Au18 gold nanoclusters (NCs), small gold nanoparticles composed of 18 atoms of gold and stabilized with glutathione ligands. These nanoclusters may be suitable for in vivo applications owing to their low toxicity and biodistribution profile. Specifically, using lactate dehydrogenase (LDH) test in P19 cell line we found that Au18 NCs display low toxicity in vitro. Importantly, using primary microglial cells we showed that at low concentrations Au18 NCs display anti-inflammatory signaling on evidence of reduced interleukin 1-β (IL1-β) levels and unchanged levels of tumor necrosis factor (TNF-α) or Ym1/2. Such effect was dose dependent as higher concentrations of Au18 NCs induced expression of pro-inflammatory cytokines and suppression of anti-inflammatory cytokine Ym1/2, pointing, thus, to global inflammatory activity. Finally, we also showed that within 3 days Au18 NCs can be completely eliminated from the liver reported as the major target organ for accumulation of gold nanoparticles. These data point to a potential of gold nanoparticles for further biomedical studies.

In situ UV–vis plasmon resonance spectroscopic assessment of oxygen and hydrogen adsorption location on supported gold catalysts

Here we report an in situ UV–vis spectroscopy study of O2 and H2 adsorption on small gold nanoparticles supported on SiO2, Al2O3, ZrO2, ZnO, and TiO2 P-25 at high temperature which provides insights into gold adsorption and active sites. In situ gold surface plasmon resonance peak shifts from alternating and consecutive adsorption of O2 to H2 were correlated to relative charge transfer from/to gold via a Drude-Lorentz model considering contributions from free electrons and interband transitions. A novel methodology matching the relative charge transfer (from O2 and H2 adsorption at 398 K and flowing conditions) with Au surface site statistics derived from a truncated octahedron geometric model was used to provide strong in situ experimental and spectroscopic evidence for adsorption of O2 and H2 at the gold-support perimeter, which agrees with prior hypotheses for active site location from reactivity and theoretical studies. The prepared catalysts were also evaluated for CO oxidation at 398 K. The resulting TOFs normalized per different surface site location indicated that conversion rates were not limited by the density of sites at the gold-support perimeter, but primarily by the total gold surface sites, which were also further differentiated by the reducibility of the catalyst support.

Effect of Gold Nanoparticle Aggregation on the Kinetic Aspect of AuNPs/DNA Interactions

Since successful therapy for curing cancer and others genetic diseases requires the transport of DNA into the cell by delivery vehicles, the understanding of the factors that control the complexation and condensation of the DNA is a key problem. During the last decade, researchers have developed some uses of nanoparticles-DNA systems, the majority of these studies dealing with NPs, which are covalently bound to the DNA. However, the kinetic aspect of AuNPs/DNA system by non-covalent interactions is less explored. Moreover, the role of high salt concentrations in these studies is of great interest due to the majority of nanoparticles have a great tendency to aggregate upon exposure to biological medium, significantly alter the uptake extent, rate, and mechanism of AuNPs/DNA interaction. As a contribution to this field, we have studied kinetics aspects of the binding of small tiopronin gold nanoparticles, AuNPs, to double stranded DNA in at high salt concentration by using the stopped-flow technique. The kinetic curves are biexponential and reveal the presence of two kinetic steps. Moreover, AFM studies reveal AuNPs aggregation in the presence of high salt content, while the same particle are well-dispersed in water. A two-step series mechanism reaction scheme was proposed. According to the reaction scheme, the formation of an intermediate complex formed by aggregated gold nanoparticles and DNA precedes the rate-determining step of the reaction.

Theoretical Study on Tuning Band Gap and Electronic Properties of Atomically Thin Nanostructured MoS2/Metal Cluster Heterostructures.

Nano-heterostructures have attracted immense attention recently due to their remarkable interfacial properties determined by the heterointerface of different nanostructures. Here, using first-principles density functional theory (DFT) calculations, we examine what range the variable electronic properties such as the electronic band gap can be tuned by combining two dissimilar nanostructures consisting of atomically thin nanostructured MoS2 clusters with small silver and gold nanoparticles (Ag/Au NPs). Most interestingly, our calculations show that the electronic band gap of the nanostructured MoS2 cluster can be tuned from 2.48 to 1.58 and 1.61 eV, by the formation of heterostructures with silver and gold metal nanoclusters, respectively. This band gap is ideal for various applications ranging from flexible nanoelectronics to nanophotonics applications. Furthermore, the adsorption of H2 molecules on both nano-heterostructures is investigated, and the computed binding energies are found to be within the desirable range. The reported theoretical results provide inspiration for engineering various optoelectronic applications for nanostructured MoS2-based heterostructures.

The Interplay of Ligand Properties and Core Size Dictates the Hydrophobicity of Monolayer-Protected Gold Nanoparticles.

The hydrophobicity of monolayer-protected gold nanoparticles is a crucial design parameter that influences self-assembly, preferential binding to proteins and membranes, and other nano-bio interactions. Predicting the effects of monolayer components on nanoparticle hydrophobicity is challenging due to the nonadditive, cooperative perturbations to interfacial water structure that dictate hydrophobicity at the nanoscale. In this work, we quantify nanoparticle hydrophobicity by using atomistic molecular dynamics simulations to calculate local hydration free energies at the nanoparticle-water interface. The simulations reveal that the hydrophobicity of large gold nanoparticles is determined primarily by ligand end group chemistry, as expected. However, for small gold nanoparticles, long alkanethiol ligands interact to form anisotropic bundles that lead to substantial spatial variations in hydrophobicity even for homogeneous monolayer compositions. We further show that nanoparticle hydrophobicity is modulated by changing the ligand structure, ligand chemistry, and gold core size, emphasizing that single-ligand properties alone are insufficient to characterize hydrophobicity. Finally, we illustrate that hydration free energy measurements correlate with the preferential binding of propane as a representative hydrophobic probe molecule. Together, these results show that both physical and chemical properties influence the hydrophobicity of small nanoparticles and must be considered together when predicting gold nanoparticle interactions with biomolecules.

Cotreatment of Small Gold Nanoparticles Protects Against the Increase in Cerebral Acetylcholinesterase Activity and Oxidative Stress Induced by Acute Ethanol Exposure in the Zebrafish

Gold nanoparticles (GNP) have emerged as an alternative to biomaterials in biomedical applications. Research has clearly demonstrated the relative safety and low toxicity of these molecules. However, the possible neuroprotective effect of GNP on the central nervous system (CNS) and its relationship with neurological and psychiatric disorders remain unclear. Zebrafish is a reliable model to investigate the impact of ethanol (EtOH) consumption on the CNS, including reward signaling such as the cholinergic neurotransmission system. Here, we investigated whether cotreatment or pretreatment with GNP prevented EtOH-induced changes in acetylcholinesterase activity and oxidative stress in the brain of zebrafish. We exposed adult zebrafish to 2.5 mg·L−1 GNP 1 h prior to EtOH (1% v/v) treatment for 1 h, and cotreated adult zebrafish simultaneously with both substances for 1 h. Pretreatment with GNP did not prevent EtOH-induced increase in the acetylcholinesterase activity, whereas cotreatment with 2.5 mg·L−1 GNP and EtOH protected against this increase. The results also suggested similar protective effect on oxidative stress parameters in the zebrafish pretreated with GNP at 2.5 mg·L−1. GNP significantly decreased the levels of thiobarbituric acid reactive species and dihydrodichlorofluorescein levels when cotreated with EtOH. GNP also prevented EtOH-induced increase in superoxide dismutase and catalase activities, suggesting a modulatory role of GNP in enzymatic antioxidant defenses. Our results showed that GNP was able to modulate the disruption of cholinergic and oxidative homeostasis in the brain of zebrafish. These findings indicate for the first time that zebrafish is an interesting perspective to investigate nanoparticles against disorders related to alcohol abuse.

Binding of chloroaurate to polytyrosine-PEG micelles leads to an anti-Turkevich pattern of reduction.

Here we report formation of gold nanoparticles (GNPs) in micelles of polytyrosine-PEG copolymers that combine the properties of a reducer and a stabilizer. The size and properties of the GNPs were tailored by the excess chloroaurate over the copolymer. The latter quickly formed non-covalent complexes with HAuCl4 and then slowly reduced it to form GNPs. 3 Tyr residues are consumed by reduction of one mole of chloroaurate. The size of the GNPs was controlled by the [Tyr]/[Au(iii)] molar ratio. Small GNPs with D ≅ 8 nm were formed at [Tyr]/[Au(iii)] = 0.5-1.5. 90% of these small GNPs remained bound to the copolymer and could be stored in a lyophilized state. Such polypeptide-gold hybrid materials produced at [Tyr]/[Au(iii)] = 0.5 demonstrated high activity in the catalytic reduction of 4-nitrophenol by sodium borohydride. [Tyr]/[Au(iii)] = 5 led to the formation of large nanoplates (D ≅ 30-60 nm). Thus, in the polymer-based system the GNP size grew in line with the excess of the reducing agent in contrast to Turkevich synthesis of GNPs with citric acid, which also combines the functions of a stabilizer and a reducer. The difference results from the reduction of HAuCl4 in solution according to the Turkevich method and in the micelles of the amphiphilic polymer where the seed growth is limited by the amount of neighboring reducer.

Optical properties and stability of small hollow gold nanoparticles.

In the current work, small hollow Au nanoparticles (d ≈ 16 nm) with excellent thermal stability and high photo-thermal conversion efficiency, which have great potential for use in photo-thermal cancer therapy, were prepared through galvanic replacement reaction between Ag nano-templates and gold salt. The position of surface plasmon resonance (SPR) bands for these nanoparticles could be tuned by varying the amount of gold salt. The hydrophobic hollow nanostructures were made water-dispersible by being encapsulated with poly(maleic anhydride-alt-1-octadecene) – PMAO. The obtained nanostructures were stable in an aqueous solution of NaCl with concentration up to 280 mM. The hollow gold nanoparticles (HGNPs) were then heated using an 808 nm laser at different power densities, the obtained data showed that they are highly photo-thermal stable under a high power density laser up to 1.6 W cm−2 after three circles of irradiation at 20 min per circle (20 min continuous irradiation for each circle). The facile synthesis of small size HGNPs with a plasmon peak in the near infrared range, colloidal and photo-thermal stability, and high capacity of conversion of photon energy into heat makes them a promising material for photo-thermal and imaging applications.

Deposition of highly dispersed gold nanoparticles onto metal phosphates by deposition–precipitation with aqueous ammonia

Deposition–precipitation with aqueous ammonia enabled small gold nanoparticles to be deposited onto a series of metal phosphates with high dispersity and density.

Generalized non-integer Lennard-Jones potential function vs. generalized Morse potential function for calculating cohesive energy and melting point of nanoparticles

A generalized non-integer Lennard-Jones (L-J) potential function with an additional parameter m is proposed to calculate the cohesive energy and melting point of nanoparticles. The model based on the new generalized non-integer L-J potential function has been successful in predicting experimental values. The calculated cohesive energies show an excellent agreement with the experimental values of the cohesive energies of molybdenum (Mo) and tungsten (W) nanoparticles (Kim et al., 2002). Moreover, the calculated melting points based on the generalized non-integer L-J potential function agree with the experimental values for large gold (Au) nanoparticles including n≥1000 atoms (Buffat and Borel, 1976) and small silica-encapsulated gold (Au) nanoparticles including n≤1500 atoms (Dick et al., 2002). The stability of nanoparticles is due to two conditions: the increase of the range of the attractive force and the high gradient attractive interaction in the potential function when rij≈r0.

Visualization of the Mechanical Wave Effect on Liquid Microphases and Its Application for the Tuning of Dissipative Soft Microreactors.

The development of approaches for creation of adaptive and stimuli-responsive chemical systems is particularly important for chemistry, materials science, and biotechnology. The understanding of response mechanisms for various external forces is highly demanded for the rational design of task-specific systems. Here, we report direct liquid-phase scanning electron microscopy (SEM) observations of the high frequency sound-wave-driven restructuring of liquid media on the microlevel, leading to switching of its chemical behavior. We show that under the action of ultrasound, the microstructured ionic liquid/water mixture undergoes rearrangement resulting in formation of separated phases with specific compositions and reactivities. The observed effect was successfully utilized for creation of dissipative soft microreactors formed in ionic liquid/water media during the sonication-driven water transfer. The performance of the microreactors was demonstrated using the example of controlled synthesis of small and uniform gold and palladium nanoparticles. The microsonication stage, designed and used in the present study, opened unique opportunities for direct sonochemical studies with the use of electron microscopy.