Recent Advances in the Development of Magnetically Recoverable Metal Nanoparticle Catalysts

The aim of this Account is to provide an overview of our current research activities on the design and modification of superparamagnetic nanomaterials for application in the field of magnetic separation and catalysis. First, an introduction of magnetism and magnetic separation is done. Then, the synthetic strategies that have been developed for generating superparamagnetic nanoparticles spherically coated by silica and other oxides, with a focus on well characterized systems prepared by methods that generate samples of high quality and easy to scale- up, are discussed. A set of magnetically recoverable catalysts prepared in our research group by the unique combination of superparamagnetic supports and metal nanoparticles is highlighted. This Account is concluded with personal remarks and perspectives on this research field.

Electrooxidation of Ethanol on Pt and PtRu Surfaces Investigated by ATR Surface-Enhanced Infrared Absorption Spectroscopy

Herein, it was investigated for the first time the electro-oxidation of ethanol on Pt and PtRu electrodeposits in acidic media by using in situ surface enhanced infrared absorption spectroscopy with attenuated total reflection (ATR-SEIRAS). The experimental setup circumvents the weak absorbance signals related to adsorbed species, usually observed for rough, electrodeposited surfaces, and allows a full description of the CO coverage with the potential for both catalysts. The dynamics of adsorption-oxidation of CO was accessed by ATR-SEIRAS experiments (involving four ethanol concentrations) and correlated with expressions derived from a simple kinetic model. Kinetic analysis suggests that the growing of the CO adsorbed layer is nor influenced by the presence of Ru neither by the concentration of ethanol. The results suggest that the C-C scission is not related to the presence of Ru and probably happens at Pt sites.

Exploiting the enzymatic machinery of Arthrobacter atrocyaneus for oxidative kinetic resolution of secondary alcohols

We evaluated Arthrobacter atrocyaneus (R1AF57) as producer of oxidoreductases for oxidative kinetic resolution of racemic secondary alcohols via oxidation reaction. This bacterium was isolated from Amazon soil samples using medium enriched with (RS)-1-(4-methylphenyl)ethanol as a carbon source. The kinetic resolution of several secondary alcohols through enantioselective oxidation mediated by resting cells and growing cells of A. atrocyaneus was efficiently achieved for the most alcohols. In general, it was possible to obtain only the (S)-enantiomer from (RS)-1-arylethanols.

Open circuit interaction of borohydride with oxidized platinum surfaces

An interesting method to investigate the effect of fuel crossover in low temperature fuel cells consists of studying the open circuit interaction between the reducing fuel and an oxide-covered catalyst. Herein we report the experimental study of the open circuit interaction between borohydride and oxidized platinum surfaces in alkaline media. When compared to the case of hydrogen and other small organic molecules, two remarkable new features were observed. Firstly, the interaction with borohydride resulted in a very-fast reduction process with transient times about two to three orders of magnitude smaller. The second peculiarity was that the decrease of the open circuit potential was found to occur in two-stages and this, previously unseen, feature was correlated with the two-hump profile found in the backward sweep in the cyclic voltammogram The consequences of our findings are discussed in connection with fundamental and applied aspects. (C) 2011 Elsevier B.V All rights reserved.

Immobilization of a recombinant endo-1,5-arabinanase secreted by Aspergillus nidulans strain A773

An endo-1,5-arabinanase (abnA) encoding gene from Aspergillus niveus was identified, cloned and successfully expressed in Aspergillus nidulans strain A773. Based on amino acid sequence comparison, the 34-kDa enzyme could be assigned to CAZy GH family 43. Characterization of purified recombinant endo-1,5-arabinanase (AbnA) revealed that it is active at a wide pH range (pH 4.0-7.0) and an optimum temperature at 70 degrees C. The immobilization of the AbnA was performed via covalent binding onto agarose-modified supports: glyoxyl iminodiacetic acid-Ni2+, glyoxyl amine, glyoxyl (4% and 10%) and cyanogen bromide activated sepharose. The yield of immobilization was similar on glyoxyl amine and glyoxyl (96%), and higher than glyoxyl iminodiacetic acid-Ni2+ (43%) support. The thermal inactivation of these immobilized preparations showed that the stability of the AbnA immobilized on glyoxyl 4 and 10% was improved by 4.0 and 10.3-fold factor at 70 degrees C. The half-life of glyoxyl 4% derivative at 60 degrees C was >48 h (pH 5), 9 h (pH 7) and 88 min (pH 9). The major hydrolysis product of debranched arabinan or arabinopentaose by glyoxyl agarose-immobilized AbnA was arabinobiose. (C) 2012 Elsevier B.V. All rights reserved.

Observation of vinylidene emission in mixed phosphine/diimine complexes of Ru(II) at room temperature in solution

The mixed ruthenium(II) complexes trans-[RuCl(2)(PPh(3))(2)(bipy)] (1), trans-[RuCl(2)(PPh(3))(2)(Me(2)bipy)](2), cis-[RuCl(2)(dcype)(bipy)](3), cis-[RuCl(2)(dcype)(Me(2)bipy)](4) (PPh(3) = triphenylphosphine, dcype = 1,2-bis(dicyclohexylphosphino)ethane, bipy = 2,2'-bipyridine, Me(2)bipy = 4,4'-dimethyl-2,2'-bipyridine) were used as precursors to synthesize the associated vinylidene complexes. The complexes [RuCl(=C=CHPh)(PPh(3))(2)(bipy)]PF(6) (5), [RuCl(=C=CHPh)(PPh(3))(2)(Me(2)bipy)]PF(6) (6), [RuCl(=C=CHPh)(dcype)(bipy)]PF(6) (7), [RuCl(=C=CHPh)(dcype)(bipy)]PF(6) (8) were characterized and their spectral, electrochemical, photochemical and photophysical properties were examined. The emission assigned to the pi-pi* excited state from the vinylidene ligand is irradiation wavelength (340, 400, 430 nm) and solvent (CH(2)Cl(2), CH(3)CN, EtOH/MeOH) dependent. The cyclic voltammograms of (6) and (7) show a reversible metal oxidation peak and two successive ligand reductions in the +1.5-(-0.64) V range. The reduction of the vinylidene leads to the formation of the acetylide complex, but due the hydrogen abstraction the process is irreversible. The studies described here suggest that for practical applications such as functional materials, nonlinear optics, building blocks and supramolecular photochemistry. (C) 2011 Elsevier B.V. All rights reserved.

Continuous enzymatic interesterification of lard and soybean oil blend: Effects of different flow rates on physical properties and acyl migration

Continuous enzymatic interesterification is an alternative to chemical interesterification for lipid modification technology which is economically viable for large scale use. A blend of 70% lard and 30% soybean oil was submitted to continuous enzymatic interesterification in a glass tubular bioreactor at flow rate ranging from 0.5 to 4.5 mL/min. The original mixture and the reaction products obtained were examined to determine melting and crystallization behavior by DSC, and analyzed for regiospecific fatty acid distribution. Continuous enzymatic interesterification changed the mixture, forming a new triacylglycerol composition, verified by DSC curves and variation in enthalpy of melting values. The regiospecific distribution of fatty acids was changed by flow variations in the reactor. In the continuous enzymatic interesterification reaction the flow rate of 4.5 mL/min, was more advantageous than slower flow rates, reducing acyl migration and increasing process productivity. (C) 2011 Elsevier B.V. All rights reserved.

Kinetics and product distribution of p-nitrophenyl phosphate dianion solvolysis in ternary DMSO/alcohol/water mixtures are compatible with metaphosphate formation

The rate of solvolysis of p-nitrophenyl phosphate (PNPP) dianion in DMSO/water strongly decreases by increasing water concentration. Addition of linear alcohols (methanol, propanol, butanol, pentanol, and hexanol) at constant DMSO/water molar ratio produced an even sharper rate decrease. Alkyl phosphate formation, resulting from PNPP solvolysis in ternary DMSO/water/alcohol mixtures, increased with alcohol concentration and was essentially temperature independent. Methanol and hexanol were the poorest nucleophiles under all conditions. Activation energies and enthalpies for solvolysis in ternary mixtures were similar and entropies varied with alcohol concentration. Taken together these results can be best interpreted in terms of a dissociative mechanism with the intervention of metaphosphate. Copyright (C) 2011 John Wiley & Sons, Ltd.

The fungal metabolite eugenitin as additive for Aspergillus niveus glucoamylase activation

Endophytic microorganisms live inside tissues of host plants apparently do not causing warning to them, and area promising source of bioactive molecules as antimicrobial and antitumoral drugs. In this work, we report the isolation of eugenitin from cultures of the endophyte Mycoleptodiscus indicus and its potential as additive for Aspergillus niveus glucoamylase activation. The glucoamylase hydrolytic activity increased twofold using 5 mM of eugenitin and this activation could be explained by the binding mode of eugenitin with the three-dimensional structure of glucoamylase. The in silica prediction of ligand binding sites revealed at least 9 possible interaction sites able to accommodate eugenitin on glucoamylase from Hypocrea jecorina. Besides, we evaluated the effect of pH and temperature on activity and stability, as well as in the hydrolysis of different substrates and kinetic parameters either in presence or absence of eugenitin. The results displayed by eugenitin as additive to glucoamylase activation are promising and provide novel perspectives for applications of fungal metabolites. (C) 2011 Elsevier B.V. All rights reserved.

Metalloporphyrins as cytochrome P450 models for chlorhexidine metabolite prediction

The catalytic oxidation of chlorhexidine (CHX, a strong microbicidal agent) mediated by ironporphyrins has been investigated by using hydrogen peroxide, mCPBA, tBuOOH, or NaOCl as oxidant. All of these oxygen donors yielded p-chloroaniline (pCA) as the main product. The higher pCA yields amounted to 71% in the following conditions: catalyst/oxidant/substrate molar ratio of 1:150:50, aqueous medium, FeTMPyP as catalyst. The medium pH also had a strong effect on the pCA yields; in physiological pH, formation of this product was specially favored in the presence of the catalysts, with yields 58% higher than those achieved in control reactions. This provided strong evidence that CHX is metabolized to pCA upon ingestion. (c) 2012 Elsevier B.V. All rights reserved.

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.

The local environment of Co2+ ions intercalated in vanadium oxide/hexadecylamine nanotubes

Vanadium oxide nanotubes constitute promising materials for applications in nanoelectronics as cathode materials, in sensor technology and in catalysis. In this work we present a study on hybrid vanadium oxide/hexadecylamine multiwall nanotubes doped with Co ions using state of the art x-ray diffraction and absorption techniques, to address the issue of the dopant location within the nanotubes' structure. The x-ray absorption near-edge structure analysis shows that the Co ions in the nanotubes are in the 2+ oxidation state, while extended x-ray absorption fine structure spectroscopy reveals the local environment of the Co2+ ions. Results indicate that Co atoms are exchanged at the interface between the vanadium oxide's layers and the hexadecylamines, reducing the amount of amine chains and therefore the interlayer distance, but preserving the tubular shape. The findings in this work are important for describing Co2+ interaction with vanadium oxide nanotubes at the molecular level and will help to improve the understanding of their physicochemical behavior, which is desired in view of their promising applications.

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.

Study of CuO/CeO2 catalyst with for preferential CO oxidation reaction in hydrogen-rich feed (PROX-CO)

The CuO/CeO2 system was investigated as a catalyst for preferential CO oxidation reaction in hydrogen-rich feed (PROX-CO). The catalysts were prepared by deposition-precipitation (DEP) and co-precipitation (COP) methods and the catalytic performance reveals that the preparation method influences the properties of solids prepared, where a direct consequence is the difference in behavior of the catalysts in the PROX-CO reaction. A high specific area and a better dispersion of the metallic phase were obtained in the catalyst prepared by co-precipitation. The redox properties during the reaction were reported by measures of temperature programmed reduction (TPR), OSC measurements and X-ray absorption near edge structure (XANES-TPR) in situ showed the relationship between the preparation method, the physicochemical characteristics and redox properties in the PROX-CO reaction. By this means, the good dispersion of CuO and the best oxygen capacity are the response of the high performance of CuO/CeO2-COP catalysts for the PROX-CO reaction. Crown Copyright (c) 2012 Published by Elsevier B.V. All rights reserved.

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.