Moving from surfactant-stabilized aqueous rhodium (0) colloidal suspension to heterogeneous magnetite-supported rhodium nanocatalysts: Synthesis, characterization and catalytic performance in hydrogenation reactions

Wet impregnation of pre-synthesized surfactant-stabilized aqueous rhodium (0) colloidal suspension on silica was employed in order to prepare supported Rh-0 nanoparticles of well-defined composition, morphology and size. A magnetic core-shell support of silica (Fe(3)O4@SiO2) was used to increase the handling properties of the obtained nanoheterogeneous catalyst. The nanocomposite catalyst Fe3O4@SiO2-Rh-0 NPs was highly active in the solventless hydrogenation of model olefins and aromatic substrates under mild conditions with turnover frequencies up to 143,000 h(-1). The catalyst was characterized by various transmission electron microscopy techniques showing well-dispersed rhodium nanoparticles (similar to 3 nm) mainly located at the periphery of the silica coating. The heterogeneous magnetite-supported nanocatalyst was investigated in the hydrogenation of cyclohexene and compared to the previous surfactant-stabilized aqueous Rh-0 colloidal suspension and various silica-supported Rh-0 nanoparticles. Finally, the composite catalyst could be reused in several runs after magnetic separation. (C) 2011 Elsevier B. V. All rights reserved.

Tailoring the structure, composition, optical properties and catalytic activity of Ag-Au nanoparticles by the galvanic replacement reaction

This Letter reports on the synthesis of Ag-Au nanoparticles (NPs) with controlled structures and compositions via a galvanic replacement reaction between Ag NPs and AuCl4(aq)- followed by the investigation of their optical and catalytic properties. Our results showed the formation of porous walls, hollow interiors and increased Au content in the Ag-Au NPs as the volume of AuCl4(aq)- employed in the reaction was increased. These variations led to a red shift and broadening of the SPR peaks and an increase of up to 10.9-folds in the catalytic activity towards the reduction of 4-nitrophenol relative to Ag NPs. (C) 2012 Elsevier B.V. All rights reserved.

Preparation, structural characterization and catalytic properties of Co/CeO2 catalysts for the steam reforming of ethanol and hydrogen production

In this paper, Co/CeO2 catalysts, with different cobalt contents were prepared by the polymeric precursor method and were evaluated for the steam reforming of ethanol. The catalysts were characterized by N-2 physisorption (BET method), X-ray diffraction (XRD), UV-visible diffuse reflectance, temperature programmed reduction analysis (TPR) and field emission scanning electron microscopy (FEG-SEM). It was observed that the catalytic behavior could be influenced by the experimental conditions and the nature of the catalyst employed. Physical-chemical characterizations revealed that the cobalt content of the catalyst influences the metal-support interaction which results in distinct catalyst performances. The catalyst with the highest cobalt content showed the best performance among the catalysts tested, exhibiting complete ethanol conversion, hydrogen selectivity close to 66% and good stability at a reaction temperature of 600 degrees C. (c) 2012 Elsevier B.V. All rights reserved.

Spectroscopic and Catalytic Characterization of a Functional (FeFeII)-Fe-III Biomimetic for the Active Site of Uteroferrin and Protein Cleavage

A mixed-valence complex, [Fe(III)Fe(II)L1(mu-OAc)(2)]BF4 center dot H2O, where the ligand H(2)L1 = 2-{[[3-[((bis-(pyridin-2-ylmethyl)amino)methyl)-2-hydroxy-5-methylbenzyl](pyridin-2-ylmethyl)amino]methyl]phenol}, has been studied with a range of techniques, and, where possible, its properties have been compared to those of the corresponding enzyme system purple acid phosphatase. The (FeFeII)-Fe-III and Fe-2(III) oxidized species were studied spectroelectrochemically. The temperature-dependent population of the S = 3/2 spin states of the heterovalent system, observed using magnetic circular dichroism, confirmed that the dinuclear center is weakly antiferromagnetically coupled (H = -2JS(1).S-2, where J = -5.6 cm(-1)) in a frozen solution. The ligand-to-metal charge-transfer transitions are correlated with density functional theory calculations. The (FeFeII)-Fe-III complex is electron paramagnetic resonance (EPR)-silent, except at very low temperatures (<2 K), because of the broadening caused by the exchange coupling and zero-field-splitting parameters being of comparable magnitude and rapid spin-lattice relaxation. However, a phosphate-bound Fe-2(III) complex showed an EPR spectrum due to population of the S-tot = 3 state (J= -3.5 cm(-1)). The phosphatase activity of the (FeFeII)-Fe-III complex in hydrolysis of bis(2,4-dinitrophenyl)phosphate (k(cat.) = 1.88 x 10(-3) s(-1); K-m = 4.63 x 10(-3) mol L-1) is similar to that of other bimetallic heterovalent complexes with the same ligand. Analysis of the kinetic data supports a mechanism where the initiating nucleophile in the phosphatase reaction is a hydroxide, terminally bound to Fe-III. It is interesting to note that aqueous solutions of [Fe(III)Fe(II)L1(mu-OAc)(2)](+) are also capable of protein cleavage, at mild temperature and pH conditions, thus further expanding the scope of this complex's catalytic promiscuity.

Electrodeposition of catalytic and magnetic gold nanoparticles on dendrimer-carbon nanotube layer-by-layer films

Magnetic and catalytic gold nanoparticles were electrodeposited through potential pulse on dendrimer-carbon nanotube layer-by-layer (LbL) films. A plasmon absorption band at about 550 nm revealed the presence of nanoscale gold in the film. The location of the Au nanoparticles in the film was clearly observed by selecting the magnetic force microscopy mode. To our knowledge, this is the first report on the electrochemical synthesis of magnetic Au nanoparticles. In addition to the magnetic properties, the Au nanoparticles also exhibited high catalytic activity towards ethanol and glycerol oxidation in alkaline medium.

Effect of the relationship between particle size, inter-particle distance, and metal loading of carbon supported fuel cell catalysts on their catalytic activity

The effect of the relationship between particle size (d), inter-particle distance (x(i)), and metal loading (y) of carbon supported fuel cell Pt or PtRu catalysts on their catalytic activity, based on the optimum d (2.5-3 nm) and x(i)/d (>5) values, was evaluated. It was found that for y < 30 wt%, the optimum values of both d and x(i)/d can be always obtained. For y >= 30 wt%, instead, the positive effect of a thinner catalyst layer of the fuel cell electrode than that using catalysts with y < 30 wt% is concomitant to a decrease of the effective catalyst surface area due to an increase of d and/or a decrease of x(i)/d compared to their optimum values, with in turns gives rise to a decrease in the catalytic activity. The effect of the x(i)/d ratio has been successfully verified by experimental results on ethanol oxidation on PtRu/C catalysts with same particle size and same degree of alloying but different metal loading. Tests in direct ethanol fuel cells showed that, compared to 20 wt% PtRu/C, the negative effect of the lower x(i)/d on the catalytic activity of 30 and 40 wt% PtRu/C catalysts was superior to the positive effect of the thinner catalyst layer.

Strontium zirconate heterogeneous catalyst for biodiesel production: Synthesis, characterization and catalytic activity evaluation

Strontium zirconate oxide was synthesized by co-precipitation and the citrate route and was evaluated as a heterogeneous catalyst for biodiesel production. The catalyst samples were characterized by XRD, FTIR, and TG, and catalytic activity was measured based on the ester content of the biodiesel produced that was quantified by GC. The co-precipitate samples were obtained in alkaline pH and had a mixture of the perovskite and pure strontium and zirconium oxide phases. Ester conversion using these samples was approximately 1.6%, indicating no catalytic activity. The citrate route was more efficient in producing perovskite when carried out at pH 7-8; excess SrCO3 was found on the catalyst surface due to CO2 adsorption, thus demonstrating no catalytic activity. The same synthesis carried out at pH 2 resulted in free OH- groups, with a small amount of the carbonate species that produced ester yield values of 98%. Therefore, matrices based on strontium zirconate produced via the citrate route in acidic media are potential heterogeneous catalysts for transesterification. (C) 2012 Elsevier B.V. All rights reserved.

Novel cross-coupling reactions between organotellurides and Grignard reagents employing a MnCl2/CuI catalytic system

We present a general protocol for the cross-coupling reaction of Grignard reagents and organic tellurides. Aryl Grignard reagents react stereospecifically with vinyl tellurides in the presence of a catalytic amount of manganese (II) chloride and copper (I) iodide to produce good yields of the corresponding cross-coupling products. (C) 2012 Published by Elsevier Ltd.

Improving the catalytic activity of formate dehydrogenase from Candida boidinii by using magnetic nanoparticles

Formate dehydrogenase from Candida boidinii (FDH) was immobilized on three different magnetic supports: one composed by magnetite nanoparticles directly silanized with ARTS (aminopropyltriethoxysilane), i.e. MagNP-APTS: the second one containing a silica gel coated magnetite core which was further silanized with APTS (MagNP@SiO2-APTS), and the third one consisting of magnetite-APTS coated with Glyoxyl-Agarose (MagNP-Glyoxyl-Agarose). The catalytic activity of the three FDH systems was investigated as a function of pH and temperature. The silica gel coated nanoparticles provided the highest conversion rates; however, in terms of recycling, magnetite without the silica shell led to the most stable system. By using the enzyme tryptophan residues as internal fluorescence probes, the structure-activity behavior was investigated in the presence of the formate and NAD(+) substrates, revealing a rather contrasting behavior in the three cases. Because of its peculiar behavior, a direct interaction of the magnetic nanoparticles with the catalytic sites seems to be implicated in the case of MagNP-APTS. (C) 2012 Elsevier B.V. All rights reserved.

Association of genetic variants in the promoter region of genes encoding p22phox (CYBA) and glutamate cysteine ligase catalytic subunit (GCLC) and renal disease in patients with type 1 diabetes mellitus

Background Oxidative stress is recognized as a major pathogenic factor of cellular damage caused by hyperglycemia. NOX/NADPH oxidases generate reactive oxygen species and NOX1, NOX2 and NOX4 isoforms are expressed in kidney and require association with subunit p22phox (encoded by the CYBA gene). Increased expression of p22phox was described in animal models of diabetic nephropathy. In the opposite direction, glutathione is one of the main endogenous antioxidants whose plasmatic concentrations were reported to be reduced in diabetes patients. The aim of the present investigation was to test whether functional single nucleotide polymorphisms (SNPs) in genes involved in the generation of NADPH-dependent O2•- (-675 T → A in CYBA, unregistered) and in glutathione metabolism (-129 C → T in GCLC [rs17883901] and -65 T → C in GPX3 [rs8177412]) confer susceptibility to renal disease in type 1 diabetes patients. Methods 401 patients were sorted into two groups according to the presence (n = 104) or absence (n = 196) of overt diabetic nephropathy or according to glomerular filtration rate (GFR) estimated by Modification of Diet in Renal Disease (MDRD) equation: ≥ 60 mL (n = 265) or < 60 mL/min/1.73 m2 (n = 136) and were genotyped. Results No differences were found in the frequency of genotypes between diabetic and non-diabetic subjects. The frequency of GFR < 60 mL/min was significantly lower in the group of patients carrying CYBA genotypes T/A+A/A (18.7%) than in the group carrying the T/T genotype (35.3%) (P = 0.0143) and the frequency of GFR < 60 mL/min was significantly higher in the group of patients carrying GCLC genotypes C/T+T/T (47.1%) than in the group carrying the C/C genotype (31.1%) (p = 0.0082). Logistic regression analysis identified the presence of at least one A allele of the CYBA SNP as an independent protection factor against decreased GFR (OR = 0.38, CI95% 0.14-0.88, p = 0.0354) and the presence of at least one T allele of the GCLC rs17883901 SNP as an independent risk factor for decreased GFR (OR = 2.40, CI95% 1.27-4.56, p = 0.0068). Conclusions The functional SNPs CYBA -675 T → A and GCLC rs17883901, probably associated with cellular redox imbalances, modulate the risk for renal disease in the studied population of type 1 diabetes patients and require validation in additional cohorts.

Species of Drosophila (Diptera: Drosophilidae) attracted to dung and carrion baited pitfall traps in the Uruguayan Eastern Serranías

This study investigates the species richness and abundance of Drosophila Fallén, 1823 attracted to dung and carrion baited pitfall traps in natural areas with heterogeneous habitats at the Sierra de Minas, Eastern Serranías, southeastern Uruguay. Collecting was carried out on a monthly basis (May 2002 through April 2003). Drosophilids accounted for 0.84% (n = 131) and 3.61% (n = 158) of the Diptera collected from dung (n = 15,630) and carrion (n = 4,382) pitfall traps, respectively. A total of 12 species were identified, 11 of which belong to the subgenus Drosophila (the richest) and one to the subgenus Sophophora Sturtevant, 1939. Over 90% of the Drosophila specimens collected belong to five species of the subgenus Drosophila, namely D. gaucha Jaeger & Salzano, 1953, D. immigrans Sturtevant, 1921, D. mediovittata Frota-Pessoa, 1954, D. aff. nappae Vilela, Valente & Basso-da-Silva, 2004, and D. ornatifrons Duda, 1927. Drosophila cardini Sturtevant, 1916 is recorded for the first time from Uruguay. Drosophila abundance and species richness in the four habitats sampled in the Uruguayan Eastern Serranías, namely woodlands sierra, riparian forest, pine plantation and grazing grassland, were considered to be a function of habitat conservation. Diversity indices were low in all habitats. Different habitats supported particular coprophilous and necrophilous Drosophila species. The woodland sierra represents the most preserved habitat, and contributed with the highest species richness observed. Drosophila ornatifrons was the dominant species, with a restricted habitat distribution. On the other hand, grazed grassland, an environment modified by livestock management, had the lowest species richness: only a few specimens of D. repleta Wollaston, 1858. Regarding species composition, significant differences were found in some pairwise comparisons of groups of Drosophila species that included D. ornatifrons. Fly attraction to dung can be exploited as an alternative and/or complementary collecting method in ecological studies of Drosophila assemblages in natural areas.

Molecular origin of charge traps in polyfluorene-based semiconductors

The comprehensive control of morphology and structure is of extreme importance in semiconducting polymers when used as active layers in optoelectronic devices. In the work reported here, a systematic investigation of the structural and dynamical properties of poly(9,9-di-n-octyl-fluorene-alt-benzothiadiazole), known as F8BT, and their correlation with electrical properties is presented when the material is used as an active layer in optoelectronic devices. By means of X-ray diffraction, one observes that in thick layer films (thickness of about 4 μm) grown by drop-cast deposition, a solvent induced crystalline phase exists which evolves to a stable phase as the temperature is raised. This was not observed in thin films (thickness of about 250 nm) prepared by spin-coating within the investigated temperature range. By modeling the current-voltages characteristics of both thick and thin film devices, important information on the influence of crystallization on the trapping states could be drawn. Furthermore, the temperature dependence of the charge carrier mobility was found to be closely related to that of the molecular relaxation processes. The understanding of the nature of such molecular relaxations, measured by solid-state nuclear magnetic resonance methods, allows one to understand the importance of molecular relaxations and microstructure changes on the trap states of the system.