Cleaner water using bimetallic nanoparticle catalysts

Groundwater contaminated by hazardous chlorinated compounds, especially chlorinated ethenes, continues to be a significant environmental problem in industrialized nations. The conventional treatment methods of activated carbon adsorption and air‐stripping successfully remove these compounds by way of transferring them from the water phase into the solid or gas phase. Catalysis is a promising approach to remove chlorinated compounds completely from the environment, by converting them into safer, non‐chlorinated compounds. Palladium‐based materials have been shown to be very effective as hydrodechlorination catalysts for the removal of chlorinated ethenes and other related compounds. However, relatively low catalytic activity and a propensity for deactivation are significant issues that prevent their widespread use in groundwater remediation. Palladium‐on‐gold bimetallic nanoparticles, in contrast, were recently discovered to exhibit superior catalyst activity and improved deactivation resistance. This new type of material is a significant next‐step in the development of a viable hydrodechlorination catalysis technology. Copyright © 2008 Society of Chemical Industry     

Adsorptive removal of hexavalent chromium using sawdust: Enhancement of biosorption and bioreduction

Simultaneous biosorption and bioreduction experienced by Cr(VI) species were initially validated by mixing 500 µM of Cr(VI) with 0.20 g of sawdust biosorbent. Accordingly, a complete disappearance of Cr(VI) species with emergence of 25% of Cr(III) ions was recorded; evidencing that both processes transpired simultaneously. An increase in the initial Cr(VI) concentration to 1500 µM could further induce more reduced Cr(VI) concentration. The enhancement of Cr(VI) biosorption and bioreduction was found to occur upon increasing the sawdust dosage to 4 g L^?1 and decreasing the solution pH to 2. However, the presence of a Zn(II) co-pollutant at 2500 µM had deteriorated the removal of Cr(VI) species.     

Gold nanoparticle ensembles as heaters and actuators: melting and collective plasmon resonances

We describe the peculiar conditions under which optically driven gold nanoparticles (NPs) can significantly increase temperature or even melt a surrounding matrix. The heating and melting processes occur under light illumination and involve the plasmon resonance. For the matrix, we consider water, ice, and polymer. Melting and heating the matrix becomes possible if a nanoparticle size is large enough. Significant enhancement of the heating effect can appear in ensembles of NPs due to an increase of a volume of metal and electric-field amplification.     

Dense CIGS films obtained by blending submicron-sized particles with nanoparticle suspensions using a non-vacuum process

The difficulty in densification easily occur in CIGS thin film absorber fabrication using the non-vacuum process. A novel process is developed in this study to achieve dense, crack-free and large-grained CIGS films by blending submicron-sized particles with nanoparticle suspensions. The addition of slow-sintering submicron-sized particles to the nanoparticle suspensions effectively inhibits crack generation and small grain development in the film microstructure. The submicron-sized particles addition to nanoparticle suspension effect on the microstructure and electrical properties are investigated using scanning electron microscopy, X-ray diffraction, UV-Vis-NIR, Raman spectroscopy and Hall-effect analyzer. A homogeneous dense microstructure with a large grain size and good electric properties can be obtained as the submicron-sized particles ratio to nanoparticles approaches 3:7.     

Clay-chitosan-gold nanoparticle nanohybrid: Preparation and application for assembly and direct electrochemistry of myoglobin

A biocompatible nanohybrid material (clay/AuCS) based on clay, chitosan and gold nanoparticles was explored. The material could provide a favorable microenvironment for proteins to realize the direct electron transfer on glassy carbon electrodes (GCE). Myoglobin (Mb), as a model protein to investigate the nanohybrid, was immobilized between the clay/AuCS film and another clay layer. Mb in the system exhibited a pair of well-defined and quasi-reversible redox peaks at −0.160 V (vs. saturated Ag/AgCl electrode) in 0.1 M PBS (pH 7.0), corresponding to its heme Fe^III/Fe^II redox couples. UV-vis spectrum suggested that Mb retained its native conformation in the system. Basal plane spacing of clay obtained by X-ray diffraction (XRD) indicated that there was an intercalation-exfoliation-restacking process among Mb, AuCS and clay during the modified film drying. Excellent biocatalytic activity of Mb in the modified system was exemplified by the reduction of hydrogen peroxide and nitrite. The linear range of H₂O₂ determination was from 3.9 × 10⁻⁵ to 3.0 × 10⁻³ M with a detection limit of 7.5 μM based on the signal to noise ratio of 3. The kinetic parameters such as α (charge transfer coefficient), k_s (electron transfer rate constant) and K_m (Michaelis-Menten constant) were evaluated to be 0.55, 2.66 ± 0.15 s⁻¹ and 5.10 mM, respectively.     

Design and Synthesis of Ionic Liquid-Based Matrix Metalloproteinase Inhibitors (MMPIs): A Simple Approach to Increase Hydrophilicity and to Develop MMPI-Coated Gold Nanoparticles

Selective and potent matrix metalloproteinase 12 (MMP-12) inhibitors endowed with improved hydrophilicity are highly sought for potential use in the treatment of lung and cardiovascular diseases. In the present paper, we modified the structure of a nanomolar MMP-12 inhibitor by incorporating an ionic liquid (IL) moiety to improve aqueous solubility. Four biologically active salts were obtained by linking the sulfonamide moiety of the MMP-12 inhibitor to imidazolium-, pyrrolidinium-, piperidinium-, and DABCO-based ILs. The imidazolium-based bioactive salt was tested on human recombinant MMPs and on monocyte-derived dendritic cells, showing activity similar to that of the parent compound, but improved water solubility. The imidazolium-based bioactive salt was then used to prepare electrostatically stabilized MMP inhibitor-coated gold nanoparticles (AuNPs) able to selectively bind MMP-12. These AuNPs were used to study subcellular localization of MMP-12 in monocyte-derived dendritic cells by transmission electron microscopy analysis.     

Three Microbial Musketeers of the Seas: Shewanella baltica,Aliivibrio fischeri and Vibrio harveyi,and Their Adaptation to Different Salinity Probed by a Proteomic Approach

Osmotic changes are common challenges for marine microorganisms. Bacteria have developed numerous ways of dealing with this stress, including reprogramming of global cellular processes. However, specific molecular adaptation mechanisms to osmotic stress have mainly been investigated in terrestrial model bacteria. In this work, we aimed to elucidate the basis of adjustment to prolonged salinity challenges at the proteome level in marine bacteria. The objects of our studies were three representatives of bacteria inhabiting various marine environments, Shewanella baltica, Vibrio harveyi and Aliivibrio fischeri. The proteomic studies were performed with bacteria cultivated in increased and decreased salinity, followed by proteolytic digestion of samples which were then subjected to liquid chromatography with tandem mass spectrometry analysis. We show that bacteria adjust at all levels of their biological processes, from DNA topology through gene expression regulation and proteasome assembly, to transport and cellular metabolism. The finding that many similar adaptation strategies were observed for both low- and high-salinity conditions is particularly striking. The results show that adaptation to salinity challenge involves the accumulation of DNA-binding proteins and increased polyamine uptake. We hypothesize that their function is to coat and protect the nucleoid to counteract adverse changes in DNA topology due to ionic shifts.     

Radiolabeled Gold Nanoseeds Decorated with Substance P Peptides: Synthesis,Characterization and In Vitro Evaluation in Glioblastoma Cellular Models

Despite some progress, the overall survival of patients with glioblastoma (GBM) remains extremely poor. In this context, there is a pressing need to develop innovative therapy strategies for GBM, namely those based on nanomedicine approaches. Towards this goal, we have focused on nanoparticles (AuNP-SP and AuNP-SPTyr8) with a small gold core (ca. 4 nm), carrying DOTA chelators and substance P (SP) peptides. These new SP-containing AuNPs were characterized by a variety of analytical techniques, including TEM and DLS measurements and UV-vis and CD spectroscopy, which proved their high in vitro stability and poor tendency to interact with plasma proteins. Their labeling with diagnostic and therapeutic radionuclides was efficiently performed by DOTA complexation with the trivalent radiometals ⁶⁷Ga and ¹⁷⁷Lu or by electrophilic radioiodination with ¹²⁵I of the tyrosyl residue in AuNP-SPTyr8. Cellular studies of the resulting radiolabeled AuNPs in NKR1-positive GBM cells (U87, T98G and U373) have shown that the presence of the SP peptides has a crucial and positive impact on their internalization by the tumor cells. Consistently, ¹⁷⁷Lu-AuNP-SPTyr8 showed more pronounced radiobiological effects in U373 cells when compared with the non-targeted congener ¹⁷⁷Lu-AuNP-TDOTA, as assessed by cell viability and clonogenic assays and corroborated by Monte Carlo microdosimetry simulations.     

Oxygen reduction and diffusion in electroactive nanostructured membranes (ENM) using a layer-by-layer dendrimer-gold nanoparticle approach

The fabrication of an electroactive nanostructured membrane (ENM) for oxygen reduction, made of layer-by-layer (LbL) films comprising Au nanoparticle-containing amine-terminated G4 PAMAM dendrimer alternated with poly(vinylsulfonic acid) (PVS) layers is reported. Electrochemical impedance spectroscopy and cyclic voltammetry show that electrodes with PVS/PAMAM-Au multiple bilayers are efficient for oxygen reduction and diffusion. A linear increase of oxygen reduction current occurs for up to 3 bilayers, with no further significant increase occurring for more than 3 bilayers. The 3-bilayer PVS/PAMAM-Au electrode, as an Au-ENM, is an attractive new system with potential for building diverse electrocatalytic devices with high molecular control.     

Synthesis of in situ functionalized iron oxide nanoparticles presenting alkyne groups via a continuous process using near-critical and supercritical water

The preparation of iron oxide nanoparticle dispersions of varying properties (e.g. color, crystal structure, particle size distribution) in a continuous hydrothermal pilot plant operating under near-critical and supercritical conditions with the aim of producing in situ functionalized nanoparticles suitable for secondary functionalization via click chemistry is reported. The effect of varying the mixing setup, reaction temperature and the starting material (iron salt) in the presence of different carboxylic acids on the resulting nanoparticle dispersions was investigated. The stability of the clickable ligands in the harsh hydrothermal environment was also tested and the clickability of the functionalized particles was demonstrated by means of XPS and fluorescence measurements after model click reactions.     

Physicochemical properties and film formation of the chitin hydrocolloid fabricated by a novel green process

Chitin is a valuable natural material, but its applications are limited because of its insolubility in water. Size reduction of natural materials has been found to offer certain benefits, including enhancing dispersibility. We employed media milling to produce a chitin micro-suspension with water as the sole solvent, and to fabricate the chitin film. The particle size and molecular weight were decreased from 96.86 to 21.95 μm and 173 to 75 kDa (M_n), respectively, post milling; however, the degree of deacetylation slightly increased (from 21.26 to 24.31) with milling time. Moreover, limited water-soluble fractions were generated, the quantity (1.5–2.0% d.b.) and molecular weight (M_n 15–34 kDa) of which were characterized. These fractions enabled the formation of a chitin film through the induction of hydrogen bonds. The particle size affected the morphology and mechanical properties of the film. The fabricated chitin film had tunable thickness (61.3–80.7 μm), tensile strength (38.95–64.61 MPa), elongation (0.93%–2.16%), Young's modulus (2994–4246 MPa), WVP (12.04–17.79 g mm/m² day kPa), swelling ratio and surface smoothness. This novel method for fabricating chitin films through aqueous suspension can improve applications of chitin in packaging and particularly fulfill environmentally friendly requirements.     

Gold nanoparticle‐functionalized thread as a substrate for SERS study of analytes both bound and unbound to gold

The potential of thread for use as a substrate for inexpensive, disposable diagnostics for surface‐enhanced Raman scattering (SERS) spectroscopy has been showed in this study. Gold‐nanoparticle coated thread can be embedded into fabrics to detect chemical or biological analytes in military and medical applications through SERS. Using this inexpensive and widely available material enables reduction in the volumes of nanoparticle solution required compared to alternatives. By testing multiple analytes, it was observed that molecular structure played a significant role in SERS signal amplification, and hence, the technique is limited to the detection of a small number of analytes possessing highly polarizable structures. Although direct chemical bonding between analyte molecules and nanoparticles gives the strongest signal enhancement, it remains possible to easily discern signals generated by analytes not directly bound, provided they possess suitable structure. Amplification of SERS signal by controlling the aggregation state of the gold nanoparticles to increase the number of SERS hotspots was observed. © 2014 American Institute of Chemical Engineers AIChE J, 60: 1598–1605, 2014     

Gold Catalysis: First Applications of Cationic Binuclear Gold(I) Complexes and the First Intermolecular Reaction of an Alkyne with a Furan

Reaction of the cationic binuclear gold(I) complex [(Ph₃PAu)₂Cl]BF₄ with ω‐alkynylfurans furnished phenols as the major product and anellated furans as the side‐products. The analogous trimesitylphosphane complex [(Mes₃PAu)₂Cl]BF₄ selectively afforded only the phenols. The latter catalyst then enabled the first intermolecular gold‐catalyzed phenol synthesis.     

Adsorption of Silver and Gold Ions from their Aqueous Solutions using a Magnetic Chelating Resin Derived from a Blend of Bisthiourea/Thiourea/Glutaraldehyde

A magnetic chelating resin was obtained from copolymerization of a blend of bisthiourea/thiourea/glutaraldehyde in the presence of magnetite (Fe₃O₄). The uptake of Ag(I) and Au(III) by the resin using batch and column techniques was studied. The maximum uptake capacity showed 6.2 and 5.78 mmol/g for Ag(I) and Au(III), respectively. Breakthrough curves showed critical bed height values of 0.03 cm and 0.04 cm for Ag(I) and Au(III), respectively, indicating the higher affinity of resin to Ag(I) relative to Au(III). Regeneration of the resins was achieved using acidified thiourea at efficiency of 98% over five cycles with no appreciable change in durability. The investigated resin was found to be able to remove 13 different metal ions from a real wastewater matrix at efficiency of 91%.     

Internal Alkyne Regio‐ and Chemoselectivity using a Zwitterionic N‐Heterocyclic Carbene Gold Catalyst in a Silver‐Free Alkyne Hydration Reaction

An alkyne hydration of terminal and internal alkynes is reported using a zwitterionic N‐heterocyclic carbene gold catalyst [(BNHC)Au(SMe₂)] in the absence of silver and Brønsted acid additives. The hydration demonstrates good regioselectivity in alkyne hydration and chemoselectivity for internal alkynes vs. terminal. In addition, (BNHC)Au(SMe₂) performs a propargyl alcohol hydration to predominantly form α‐hydroxymethyl ketone over the more common Meyer–Schuster rearrangement product. While complex (BNHC)Au(SMe₂) is active without silver additives, addition of silver hexafluoroantimonate (AgSbF₆) increases reaction rate and decreases selectivity for internal alkyne hydration over terminal substrates. To the best of our knowledge, the rate enhancement of (BNHC)Au(SMe₂) by AgSbF₆ is the first such demonstration of a silver effect for a “halide‐free” Au catalyst.

     

Gold nanoparticles obtained by Au(III) reduction with Sn(II): Preparation and electrocatalytic properties in oxidation of reducing agents

Gold colloid solutions were prepared by reduction of Au(III) with Sn(II) in both acidic (HCl) and alkaline (carbonate) media, and characterized by electron microscopy, X-ray diffraction and light absorption spectra. Depending on the colloid preparation conditions, metal particles of 5-30 nm in size were obtained. Light absorption spectra of the Au colloid solutions contain an absorption band at 500-600 nm, typical of small gold particles. According to XRD data, colloid particles contain the metallic Au and SnO₂ phases. The colloid formation rate and colloid solution stability depend on solution pH; the alkaline colloid solutions are formed more slowly and are more stable. The gold nanoparticles adsorbed on the dielectrics surface were found to initiate the electroless copper deposition process. The glassy carbon (GC) electrode modified by Au nanoparticles (200-900 ng cm⁻² Au) was found to be an electrocatalyst for dimethylamine borane, borohydride, hydrazine, and formaldehyde oxidation in alkaline solutions. The activity of the reducers can be arranged as follows: DMAB > NaBH₄ > N₂H₄ > CH₂O.     

Production of Lactobionic Acid from its Sodium Salt Solution by Ion-Exchange on a Commercial Strong Acid Resin: Kinetic Data and Modeling

Lactobionic acid (LBA) is a high value added product obtained from lactose oxidation. Since this reaction should be conducted in alkaline media by adequate addition of a Na-, Ca- or K-base, the final product is a lactobionate salt solution instead of the acid form. In this study, the behavior of a strong cation exchange resin (Amberlite^TM FPC23 H) for the production of a LBA solution from its sodium lactobionate salt (LBNa), was investigated. The sodium exchange efficiency was evaluated at three different temperatures (5, 25, and 35ºC). The resin exhibited a good performance in the removal of sodium from the LBNa solution. In all cases, sodium concentration in LBA solution was reduced below 5 mg/L. A complete sodium removal was achieved after about 30 min at 5ºC, and after circa 10 min at 25 and 35ºC. Various kinetic models were used for the evaluation of experimental ion-exchange kinetic data. The rate constants, transient capacities, and related correlation coefficients for each kinetic model were calculated and discussed. Results showed that the pseudo-second order and the reversible reaction models adequately describe the experimental kinetic data. The activation energies computed using the rate constants obtained with these models were 50.87 and 36.12 kJ/mol, respectively.