Chemoselective cross-coupling Suzuki-Miyaura reaction of (Z)-(2-chlorovinyl)tellurides and potassium aryltrifluoroborate salts

An ultrasound-assisted synthesis of functionalized vinylic chlorides is described by palladium-catalyzed cross-coupling reaction of potassium aryltrifluoroborate salts and (Z)-2-chloro vinylic tellurides. This procedure offers easy access to vinylic chlorides architecture that contains sterically demanding groups in good yields. (C) 2008 Elsevier Ltd. All rights reserved.

Carbon-dispersed Pt-Rh nanoparticles for ethanol electro-oxidation. Effect of the crystallite size and of temperature

This work presents results of studies of carbon-dispersed Pt-Rh (1:1) nanoparticles as electrocatalysts for the ethanol electro-oxidation. The influences of the crystallite size and the cell temperature on the yields of CO2, acetaldehyde and acetic acid are investigated. Metal nanoparticles were prepared by two different routes: (1) impregnation on carbon powder followed by thermal reduction on hydrogen atmosphere and (2) chemical reduction of the precursor salts. The surface active area and the electrochemical activity of the electrocatalysts were estimated by CO stripping and cyclic voltammetry in the absence and in the presence of ethanol, respectively. Reaction intermediates and products were analyzed by in situ Fourier Transform Infra-Red Spectroscopy (FTIR) and Differential Electrochemical Mass Spectrometry (DEMS). The electrochemical stripping of CO and the electrochemical ethanol oxidation were slightly faster on the Pt-Rh electrocatalysts compared to Pt/C. Also, in situ FTIR spectra and DEMS measurements evidenced that the CO2/acetaldehyde and the CO2/acetic acid ratios are higher for the Pt-Rh/C materials in relation to Pt/C. This was ascribed to the activation of the C-C bond breaking by Rh, this being more prominent for the materials with smaller crystallite sizes. (C) 2008 Elsevier B.V. All rights reserved.

Electrocatalysis of ethanol oxidation on Pt monolayers deposited on carbon-supported Ru and Rh nanoparticles

Pt monolayers deposited on carbon- supported Ru and Rh nanoparticles were investigated as electrocatalysts for ethanol oxidation. Electronic features of the Pt monolayers were studied by in situ XANES (X-ray absorption near-edge structure). The electrochemical activity was investigated by cyclic voltammetry and cronoamperometric experiments. Spectroscopic and electrochemical results were compared to those obtained on carbon-supported Pt-Ru and Pt-Rh alloys, and Pt E-TEK. XAS results indicate a modification of the Pt 5d band due to geometric and electronic interactions with the Ru ant Rh substrates, but the effect of withdrawing electrons from Pt is less pronounced in relation to that for the corresponding alloys. Electrochemical stripping of adsorbed CO, which is one of the intermediates, and the currents for the oxidation of ethanol show faster kinetics on the Pt monolayer deposited on Ru nanoparticles, and an activity that exceeds that of conventional catalysts with much larger amounts of platinum. (c) 2007 Elsevier B.V. All rights reserved.

Ethanol electro-oxidation on carbon-supported Pt-Ru, Pt-Rh and Pt-Ru-Rh nanoparticles

This work investigates the effects of carbon-supported Pt, Pt-Ru, Pt-Rh and Pt-Ru-Rh alloy electrocatalysts oil the yields of CO2 and acetic acid as electro-oxidation products of ethanol. Electronic and structural features of these metal alloys were studied by in situ X-ray absorption spectroscopy (XAS). The electrochemical activity was investigated by polarization experiments and the reaction intermediates and products were analyzed by in situ Fourier Transform Infra-Red Spectroscopy (FTIR). Electrochemical stripping of CO. which is one of the adsorbed intermediates, presented a faster oxidation kinetics on the Pt-Ru electrocatalyst, and similar rates of reaction on Pt-Rh and Pt. The electrochemical current of ethanol oxidation showed a higher value and the onset potential was less positive oil Pt-Ru. However, in situ FTIR spectra evidenced that the CO2/acetic acid ratio is higher for the materials with Rh, mainly at lower potentials. These results indicate that the Ru atoms act mainly by providing oxygenated species for the oxidation of ethanol intermediates, and point out ail important role of Rh on the C-C bond dissociation. (C) 2007 Elsevier Ltd. All rights reserved.

Catalytic ethanolysis of soybean oil with immobilized lipase from Candida antarctica and (1)H NMR and GC quantification of the ethyl esters (biodiesel) produced

The catalytic ethanolysis of soybean oil with commercial immobilized lipase type B from Candida antarctica to yield ethyl esters (biodiesel) has been investigated. Transesterification was monitored with respect to the following parameters: quantity of biocatalyst, reaction time, amount of water added and turnover of lipase. The highest yields of biodiesel (87% by (1)H NMR; 82.9% by GC) were obtained after a reaction time of 24 h at 32 degrees C in the presence of lipase equivalent to 5.0% (w/w) of the amount of soybean oil present. The production of ethyl esters by enzymatic ethanolysis was not influenced by the addition of water up to 4.0% (v/v) of the alcohol indicating that it is possible to use hydrated ethanol in the production of biodiesel catalyzed by lipase. The immobilized enzyme showed high stability under moderate reaction conditions and retained its activity after five production cycles. The (1)H NMR methodology elaborated for the quantification of biodiesel in unpurified reaction mixtures showed good correlations between the signal areas of peaks associated with the alpha-methylene groups of the ethyl esters and those of the triacyl-glycerides in residual soybean oil. Monoacylglycerides, diacylglycerides and triglycerides could also be detected and quantified in the crude biodiesel using (1)H NMR spectroscopic and GC-FID chromatographic methods. The biodiesel production by enzymatic catalysis was promising. In this case, was produced a low concentration of glycerol (0.74%) and easily removed by water extraction. (C) 2010 Elsevier B.V. All rights reserved.

Carbon dioxide reforming of ethanol over Ni/Y(2)O(3)-ZrO(2) catalysts

Supported nickel catalysts of composition Ni/Y(2)O(3)-ZrO(2) were synthesized in one step by the polymerization method and compared with a nickel catalyst prepared by wet impregnation. Stronger interactions were observed in the formed catalysts between NiO species and the oxygen vacancies of the Y(2)O(3)-ZrO(2) in the catalysts made by polymerization, and these were attributed to less agglomeration of the NiO during the synthesis of the catalysts in one step. The dry reforming of ethanol was catalyzed with a maximum CO(2) conversion of 61% on the 5NiYZ catalyst at 800 degrees C, representing a better response than for the catalyst of the same composition prepared by wet impregnation. (C) 2009 Published by Elsevier B.V.

Structural studies of prephenate dehydratase from Mycobacterium tuberculosis H37Rv by SAXS, ultracentrifugation, and computational analysis

Tuberculosis (TB) is one of the most common infectious diseases known to man and responsible for millions of human deaths in the world. The increasing incidence of TB in developing countries, the proliferation of multidrug resistant strains, and the absence of resources for treatment have highlighted the need of developing new drugs against TB. The shikimate pathway leads to the biosynthesis of chorismate, a precursor of aromatic amino acids. This pathway is absent from mammals and shown to be essential for the survival of Mycobacterium tuberculosis, the causative agent of TB. Accordingly, enzymes of aromatic amino acid biosynthesis pathway represent promising targets for structure-based drug design. The first reaction in phenylalanine biosynthesis involves the conversion of chorismate to prephenate, catalyzed by chorismate mutase. The second reaction is catalyzed by prephenate dehydratase (PDT) and involves decarboxylation and dehydratation of prephenate to form phenylpyruvate, the precursor of phenylalanine. Here, we describe utilization of different techniques to infer the structure of M. tuberculosis PDT (MtbPDT) in solution. Small angle X-ray scattering and ultracentrifugation analysis showed that the protein oligomeric state is a tetramer and MtbPDT is a flat disk protein. Bioinformatics tools were used to infer the structure of MtbPDT A molecular model for MtbPDT is presented and molecular dynamics simulations indicate that MtbPDT i.s stable. Experimental and molecular modeling results were in agreement and provide evidence for a tetrameric state of MtbPDT in solution.

Determination of amino acids by capillary electrophoresis-electrospray ionization-mass spectrometry: An evaluation of different protein hydrolysis procedures

In this work, a CE equipment, online hyphenated to an IT MS analyzer by a linear sheath liquid interface promoting ESI, was used to develop a method for quantitative determination of amino acids. Under appropriate conditions (BGE composition, 0.8% HCOOH, 20% CH(3)OH; sheath liquid composition, 0.8% HCOOH, 60% methanol; V(ESI), +4.50 W), analytical curves of all amino acids from 3 to 80 mg/L were recorded presenting acceptable linearity (r > 0.99). LODs in the range of 16-172 mu mol/L were obtained. BSA, a model protein, was submitted to different hydrolysis procedures (classical acid and basic, and catalyzed by the H(+) form of a cation exchanger resin) and its amino acid profiles determined. In general, the resin-mediated hydrolysis yields were overall similar or better than those obtained by classical acid or basic hydrolysis. The resulting experimental-to-theoretical BSA concentration ratios served as correction factors for the quantitation of amino acids in Brazil nut resin generated hydrolysates.

Synthesis of 2-oxo-16-(3', 4'-methylenedioxyphenyl)-trans-15-hexadecene

This work presents the progress made towards synthesizing 2-oxo-16-(3', 4'methylenedioxyphenyl)-trans-15-hexadecene, an antimycobacterial compound that was originally isolated from the leaves of Piper Sanctum. The hydrocarbon chain of the molecule was synthesized first by opening a 15-pentadecanolactone ring by means of HI, and performing an E2 elimination reaction on the molecule followed by an organolithium reaction with CH3Li. Hexadec-15-en-2-one that was afforded this way was later reacted with 5-bromobenzo[d][1,3]dioxole following the appropriate Heck reaction protocol that allows for the formation of a palladium catalyzed carbon-carbon bond. The modes of action of 2-oxo-16-(3', 4'-methylenedioxyphenyl)-trans-15hexadecene are comparable to the ones of rifampicin, a marketable drug that has been successfully used in the treatment of tuberculosis in the past. Additionally, this compound can serve as an intermediate towards the synthesis of 2-oxo-16-(3', 4' methylenedioxyphenyl)-hexadecane and 2-oxo-14-(3', 4' -methylenedioxyphenyl) tetradecane, both strong inhibitors of the growth of Mycobacterium tuberculosis. Lastly, due to Multi-Drug Resistant tuberculosis, there has been an increasing need to find alternative cures for tuberculosis. Therefore, the work on 2-qxo-16-(3', 4'methylenedioxyphenyl)-trans-15-hexadecene is not only chemically interesting but it is also biologically important.

New metallomolecular wires based on carbon-rich bridging systems: a systematic study

This dissertation presents and discusses the preparation of molecular wires (MW) candidates that would then be probed for electron transfer properties. These wires are bridged by 1,4-diethynylbenzene derivatives with alkoxy side chains with palladium and ruthenium metal complex termini. Characterization of these compounds was performed by usual spectroscopic techniques like 1H, 13C{1H} and 31P{1H} NMR, MS, FTIR and UV-Vis as well as by cyclic voltammetry which allowed classifying the candidates in the Robin–Day system and determination of bridges side chain and length effects on electronic transport. Preparation of the 1,4-diethynylbenzene derivatives was done with synthetic pathways that relied heavily in palladium catalyzed cross-couplings (Sonogashira). A family of single ringed 1,4-diethynylbenzene ligands with different length alkoxy side chains (OCH3, OC2H5, OC7H15) was thus prepared allowing for the influence of these ring decorations to be assessed. The ruthenium binuclear rods showed communication between metal centres only when the shorter ligands were used whereas the longer Ru complexes showed only one redox pair in CV studies which is in agreement to non-communicating metal centres. Cyclic voltammetry studies show irreversible one wave processes for palladium dinuclear complexes, making these rods function as molecular insulators. Fluorescence decay studies performed on the prepared compounds (ligands and complexes) show a pattern of decreasing decay times upon coordination to the metal centres which can due to ligand charge redistribution upon coordination leading to non-radiative relaxation paths. Regarding the X-ray structures, two new ligand related structures were obtained as well as new structure for a palladium rod. The effect of the side chains was observed to be important to the wires’ electronic properties when comparing with the analogues without a side chain. The effect brought by longer chains is nevertheless almost negligible.

Nanocatalysts for sustainable industrial processses

In Chapter 1, rhodium nanoparticles were supported on multiwalled carbon nanotubes (MWCNTs) and bound to the magnetic core-shell system Fe3O4@TiO2. The composite Fe3O4@TiO2-Rh-MWCNT and the intermediates were characterized by SEM, EDS and TEM. Their catalytic activity was studied using i) the hydrogenation transfer of nitroarenes and cyclohexene in the presence of hydrazine hydrate; ii) the reduction of 2-nitrophenol with NaBH4; and iii) the decoloration of pigments in the presence of hydrogen peroxide. The results were monitored by gas chromatography (i) and UV Visible (ii and iii). In the second chapter, the catalytic activity of six oxidovanadium(V) aroylhydrazone complexes, viz. [VOL1(OEt)][VOL1(OEt)(EtOH)] (1), [VOL2(OEt)] (2), [Et3NH][VO2L1] (3), [VO2(H2L2)]2·EtOH (4), [VOL1(µ -O)VOL1] (5) and [VOL2(µ -O)VOL2] (6) (H2L1 = 3,5-di-tert-butyl-2-hydroxybenzylidene)-2hydroxybenzohydrazide and H2L2 = 3,5-di-tert-butyl-2-hydroxybenzylidene)-2 aminobenzohydrazide), anchored on nanodiamonds with different treatments, was studied towards the microwave-assisted partial oxidation of 1-phenylethanol to acetophenone in the presence of tert-butyl hydroperoxide (TBHP) as oxidant. A high selectivity for acetophenone was achieved for the optimized conditions. The possibility of recycling and reuse the heterogeneous catalysts was also investigated. In chapter 3, the catalytic activity of gold nanoparticles supported at different metal oxides, such as Fe2O3, Al2O3 ZnO or TiO2, was studied for the above reaction. The effect of the support, quantity of the catalyst and temperature was investigated. The recyclability of the gold catalysts was also studied. In the last chapter, a new copper nanocomposite with functionalized mutiwalled carbon nanotubes (Cu-MWCNT) was synthesized using a microwave assisted polyol method. The characterization was performed using XRD and SEM. The catalytic activity of Cu-MWCNT was studied through the degradation of pigments, such as amaranth, brilliant blue, indigo, tartrazine and methylene blue.

Integrated valorization of Anona Cherimola Mill. seeds

Agricultural and agro-industrial residues are often considered both an environmental and an economical problem. Therefore, a paradigm shift is needed, assuming residues as biorefinery feedstocks. In this work cherimoya (Annona cherimola Mill.) seeds, which are lipid-rich (ca. 30%) and have a significant lignocellulosic fraction, were used as an example of a residue without any current valorization. Firstly, the lipid fraction was obtained by solvent extraction. Extraction yield varied from 13% to 28%, according to the extraction method and time, and solvent purity. This oil was converted into biodiesel (by base-catalyzed transesterification), yielding 76 g FAME/100 g oil. The obtained biodiesel is likely to be incorporated in the commercial chain, according to the EN14214 standard. The remaining lignocellulosic fraction was subjected to two alternative fractionation processes for the selective recovery of hemicellulose, aiming different products. Empirical mathematical models were developed for both processes, aiming future scale-up. Autohydrolysis rendered essentially oligosaccharides (10 gL-1) with properties indicating potential food/feed/pharmacological applications. The remaining solid was enzymatically saccharified, reaching a saccharification yield of 83%. The hydrolyzate obtained by dilute acid hydrolysis contained mostly monosaccharides, mainly xylose (26 gL-1), glucose (10 gL-1) and arabinose (3 gL-1), and had low content of microbial growth inhibitors. This hydrolyzate has proven to be appropriate to be used as culture media for exopolisaccharide production, using bacteria or microbial consortia. The maximum conversion of monosaccharides into xanthan gum was 0.87 g/g and kefiran maximum productivity was 0.07 g.(Lh)-1. This work shows the technical feasibility of using cherimoya seeds, and materials as such, as potential feedstocks, opening new perspectives for upgrading them in the biorefinery framework.

The co-catalytic effect of chlorpromazine on peroxidase-mediated oxidation of melatonin: enhanced production of N-1-acetyl-N (2)-formyl-5-methoxykynuramine

Accumulating evidence points to relationships between increased production of reactive oxygen or decreased antioxidant protection in schizophrenic patients. Chlorpromazine (CPZ), which remains a benchmark treatment for people with schizophrenia, has been described as a pro-oxidant compound. Because the antioxidant compound melatonin exerts protective effects against CPZ-induced liver disease in rats, in this investigation, our main objective was to study the effect of CPZ as a co-catalyst of peroxidase-mediated oxidation of melatonin. We found that melatonin was an excellent reductor agent of preformed CPZ cation radical (CPZ(center dot+)). The addition of CPZ during the horseradish peroxidase (HRP)-catalyzed oxidation of melatonin provoked a significant increase in the rate of oxidation and production of N-1-acetyl-N-2-formyl-5-methoxykynuramine (AFMK). Similar results were obtained using myeloperoxidase. The effect of CPZ on melatonin oxidation was rather higher at alkaline pH. At pH 9.0, the efficiency of oxidation of melatonin was 15 times higher and the production of AFMK was 30 times higher as compared with the assays in the absence of CPZ. We suggest that CPZ is able to exacerbate the rate of oxidation of melatonin by an electron transfer mechanism where CPZ(center dot+), generated during the peroxidase-catalyzed oxidation, is able to efficiently oxidize melatonin.

Avaliação do desenvolvimento sustentável na bacia hidrográfica do Rio Seridó em face das políticas públicas e da gestão dos recursos hídricos

The reality of water resources management in semiarid regions, such as the Seridó region, has been shaped by a complex chain involving social-cultural, political, economic and environmental aspects, covering different spheres of activity - from local to federal. Because water is a scarce element, the most rational way pointed out by our recent history has been to move towards an increasing emphasis on the need for a truly rational, integrated, sustainable and participatory water resources management, supported by legislation and by a network of institutions that could materialize it. In this sense, despite all the advances in the formulation of public policies in water resources, which ones have indeed lead to significant changes that have occurred or are underway in semiarid regions such as Seridó? What factors may be preventing the realization of the desires rationality embedded in the framers of water policies intents? How to properly manage water resources if the current actors who promote their management and the political, human, cultural and institutional processes that intervene in this management, show strong traces of unsustainability? The research methodology adopted in this paper led to a breakdown of the traditional approach to water resource management, to integrate it into other areas of knowledge, especially to political science and public administration, catalyzed by the concept of "sustainable development". From a broad, interdisciplinary literature review, an exhaustive characterization of the river basin Seridó, a set of interviews with key people in the public administration acting in the region, a series of diagnoses and a set of propositions were made in order to correct the direction of current public policies for the region. From the point of view of public policies, it is in the deployment phase, not in its formulation, which lies a major problem of the lack of significant progress in water management. The lack of coordination between government programs are well characterized, as well as the lack of efficiency and effectiveness of their actions. The causes of this secular model are also discussed, including political factors and social relations of production, which led to a stalemate difficult, but of possible solution. It can be perceived there is a scenario of progressive deterioration of natural resources of the fragile ecosystem and a network of environmental and social consequences difficult to reverse, the result of a persistent and inertial sociopolitical culture, whose main factors reinforce itself. The work leads towards a characterization of the water resources management also from the perspective of environmental, institutional, political and human sustainability , the latter being identified, particularly as investment in the development of people as autonomous beings - not based in ideological directives of any kind - in the emancipation of the traditional figure of the poor man of the hinterland" to the "catalyst for change" responsible for their own decisions or omissions, based upon an education for free-thinking that brings each one as co-responsible epicenter of (self-) sustainable changes in their midst

Electrochemical modified electrodes based on metal-salen complexes

A general view of the electroanalytical applications of metal-salen complexes is discussed in this review. The family of Schiff bases derived from ethylenediamine and ortho-phenolic aldehydes (N,N'-ethylenebis(salicylideneiminato) - salen) and their complexes of various transition metals, such as Al, Ce, Co, Cu, Cr, Fe, Ga, Hg, Mn, Mo, Ni, and V have been used in many fields of chemical research for a wide range of applications such as catalysts for the oxygenation of organic molecules, epoxidation of alkenes, oxidation of hydrocarbons and many other catalyzed reactions; as electrocatalyst for novel sensors development; and mimicking the catalytic functions of enzymes. A brief history of the synthesis and reactivity of metal-salen complexes will be presented. The potentialities and possibilities of metal-Salen complexes modified electrodes in the development of electrochemical sensors as well as other types of sensors, their construction and methods of fabrication, and the potential application of these modified electrodes will be illustrated and discussed.