Sonochemical synthesis of graphene oxide supported Pt–Pd alloy nanocrystals as efficient electrocatalysts for methanol oxidation

Pt–Pd bimetallic nanoparticles supported on graphene oxide (GO) nanosheets were prepared by a sonochemical reduction method in the presence of polyethylene glycol as a stabilizing agent. The synthetic method allowed for a fine tuning of the particle composition without significant changes in their size and degree of aggregation. Detailed characterization of GO-supported Pt–Pd catalysts was carried out by transmission electron microscopy (TEM), AFM, XPS, and electrochemical techniques. Uniform deposition of Pt–Pd nanoparticles with an average diameter of 3 nm was achieved on graphene nanosheets using a novel dual-frequency sonication approach. GO-supported bimetallic catalyst showed significant electrocatalytic activity for methanol oxidation. The influence of different molar compositions of Pt and Pd (1:1, 2:1, and 3:1) on the methanol oxidation efficiency was also evaluated. Among the different Pt/Pd ratios, the 1:1 ratio material showed the lowest onset potential and generated the highest peak current density. The effect of catalyst loading on carbon paper (working electrode) was also studied. Increasing the catalyst loading beyond a certain amount lowered the catalytic activity due to the aggregation of metal particle-loaded GO nanosheets.

CeO2-promoted Ni/activated carbon catalysts for the water–gas shift (WGS) reaction

The low temperature water–gas shift (WGS) reaction has been studied over carbon-supported nickel catalysts promoted by ceria. To this end, cerium oxide has been dispersed (at different loadings: 10, 20, 30 and 40 wt.%) on the activated carbon surface with the aim of obtaining small ceria particles and a highly available surface area. Furthermore, carbon- and ceria-supported nickel catalysts have also been studied as references. A combination of N2 adsorption analysis, powder X-ray diffraction, temperature-programmed reduction with H2, X-ray photoelectron spectroscopy and TEM analysis were used to characterize the Ni–CeO2 interactions and the CeO2 dispersion over the activated carbon support. Catalysts were tested in the low temperature WGS reaction with two different feed gas mixtures: the idealized one (with only CO and H2O) and a slightly harder one (with CO, CO2, H2, and H2O). The obtained results show that there is a clear effect of the ceria loading on the catalytic activity. In both cases, catalysts with 20 and 10 wt.% CeO2 were the most active materials at low temperature. On the other hand, Ni/C shows a lower activity, this assessing the determinant role of ceria in this reaction. Methane, a product of side reactions, was observed in very low amounts, when CO2 and H2 were included in the WGS feed. Nevertheless, our data indicate that the methanation process is mainly due to CO2, and no CO consumption via methanation takes place at the relevant WGS temperatures. Finally, a stability test was carried out, obtaining CO conversions greater than 40% after 150 h of reaction.

Study of zinc protein ligands in a halophilic enzyme

Glucose dehydrogenase (EC 1.1.1.47) from the halophilic Archaeon Haloferax mediterranei belongs to the medium-chain alcohol dehydrogenase superfamily and requires a zinc ion for catalysis. The zinc ion is coordinated by a histidine, a water molecule and two other ligands from the protein or the substrate, which vary during the catalytic cycle of the enzyme. In many enzymes of this superfamily one of the zinc ligands is commonly cysteine, which is replaced by an aspartate residue at position 38 in the halophilic enzyme. This change has been only observed in glucose dehydrogenases from extremely halophilic microorganisms belonging to the Archaea Domain. This paper describes biochemical studies and structural comparisons to analyze the role of sequence differences between thermophilic and halophilic glucose dehydrogenases which contain a zinc ion within the protein surrounded by three ligands. Whilst the catalytic activity of the D38C GlcDH mutant is reduced, its thermal stability is enhanced, consistent with the greater structural similarity between this mutant and the homologous thermophilic enzyme from Thermoplasma acidophilum.

Methane dry reforming over Ni supported on pine sawdust activated carbon: Effects of support surface properties and metal loading

The influence of metal loading and support surface functional groups (SFG) on methane dry reforming (MDR) over Ni catalysts supported on pine-sawdust derived activated carbon were studied. Using pine sawdust as the catalyst support precursor, the smallest variety and lowest concentration of SFG led to best Ni dispersion and highest catalytic activity, which increased with Ni loading up to 3 Ni atoms nm-2. At higher Ni loading, the formation of large metal aggregates was observed, consistent with a lower "apparen" surface area and a decrease in catalytic activity. The H2/CO ratio rose with increasing reaction temperature, indicating that increasingly important side reactions were taking place in addition to MDR.

Palladium and Bimetallic Palladium–Nickel Nanoparticles Supported on Multiwalled Carbon Nanotubes: Application to Carbon–Carbon Bond-Forming Reactions in Water

Palladium and bimetallic Pd–Ni nanoparticles (NPs) protected by polyvinylpyrrolidone were prepared by the reduction-by-solvent method and deposited on multiwalled carbon nanotubes (MWCNTs). The catalytic activity of these NPs to carbon–carbon bond-forming reactions was studied by using 0.1 mol % Pd loading, at 120 °C for 1 h and water as a solvent under ligand-free conditions. The Suzuki–Miyaura reaction took place quantitatively for the cross-coupling of 4-bromoanisole with phenylboronic acid, better than those obtained with potassium phenyltrifluoroborate, with Pd50Ni50/MWCNTs as a catalyst and K2CO3 as a base and TBAB as an additive, with good recyclability during 4 cycles with some Ni leaching. The Hiyama reaction of 4-iodoanisole with trimethoxyphenylsilane, under fluoride-free conditions using 50 % aqueous NaOH solution, was performed with Pd/MWCNTs as a catalyst in 83 % yield with low recyclability. For the Mizoroki-Heck reaction 4-iodoanisole and styrene gave the corresponding 4-methoxystilbene quantitatively with Pd50Ni50/MWCNTs using K2CO3 as a base and TBAB as an additive although the recycle failed. In the case of the Sonogashira-Hagihara reaction, Pd/MWCNTs had to be used as a catalyst and pyrrolidine as a base for the coupling of 4-iodoanisole with phenylacetylene under copper-free conditions. The corresponding 4-methoxytolane was quantitatively obtained allowing the recycling of the catalyst during 3 cycles.

Promoter effect of sodium in graphene-supported Ni and Ni–CeO2 catalyst for the low-temperature WGS reaction

The low temperature water–gas shift (WGS) reaction has been studied over Ni–CeO2/Graphene and Ni/Graphene. The catalysts were prepared with 5 wt.% Ni and 20 wt.% CeO2 loadings, by deposition-precipitation employing sodium hydroxide and urea as precipitating agents. The materials were characterized by TEM, powder X-ray diffraction, Raman spectroscopy, H2-temperature-programmed reduction and X-ray photoelectron spectroscopy (XPS). The characterization and the reaction results indicated that the interaction between the active species and the support is higher than with activated carbon, and this hinders the reducibility of ceria and thus the catalytic performance. On the other hand, the presence of residual sodium in samples prepared by precipitation with NaOH facilitated the reduction of ceria. The catalytic activity was highly improved in the presence of sodium, what can be explained on the basis of an associative reaction mechanism which is favored over Ni-O-Na entities.

Mesoporous Metal Complex–Silica Aerogels for Environmentally Friendly Amination of Allylic Alcohols

Two series of mesoporous hybrid iron(III) complex–silica aerogels were prepared in one-pot synthesis by using the sol–gel coordination chemistry approach. The use of the ligands 3-(2-aminoethylamino)propyltrimethoxysilane and 2-(diphenylphosphino)ethyltriethoxysilane, both with terminal triethoxysilyl groups, were used to incorporate metal complexes in situ into the framework of silica, through their co-condensation with a silicon alkoxide during the aerogel formation. This methodology yielded optically translucent hybrid mesoporous gels with homogeneous metal incorporation and excellent textural properties. The catalytic performance of these materials was tested in the direct amination of allylic alcohols in water as a target reaction, with activities comparable or even higher than those corresponding to the homogeneous iron(III) complex. Furthermore, these catalysts were stable and maintained their catalytic activity after six reaction cycles.

(Bio)funcionalização de superfícies nanoestruturadas para eletrocatálise e desenvolvimento de biossensores eletroquímicos e óticos

Tese de doutoramento, Química (Química Física), Universidade de Lisboa, Faculdade de Ciências, 2016

Rôles de la protéine tyrosine phosphatase DEP-1 dans l'angiogenèse, la perméabilité vasculaire et la progression tumorale

L’angiogenèse et l’augmentation de la perméabilité vasculaire sont des éléments clés pour la croissance et la progression tumorale. Par conséquent, de nombreux efforts sont déployés à comprendre les mécanismes moléculaires impliqués dans la formation et le remodelage des vaisseaux sanguins de manière à identifier de nouvelles cibles thérapeutiques potentielles. De cette optique, les travaux de cette thèse se sont concentrés sur la protéine tyrosine phosphatase DEP-1, initialement identifiée comme un régulateur négatif de la prolifération et de la phosphorylation du VEGFR2 lorsque fortement exprimée dans les cellules endothéliales. Toutefois, en utilisant une approche d’ARNi, il a été démontré que via sa capacité à déphosphoryler la tyrosine inhibitrice de Src (Y529), DEP-1 était également un régulateur positif de l’activation de Src dans les cellules endothéliales stimulées au VEGF. Puisque Src joue un rôle central dans la promotion de l’angiogenèse et la perméabilité vasculaire, nous avons en plus démontré que DEP-1 était un promoteur de ces fonctions in vitro et que la tyrosine phosphorylation de sa queue C-terminale, permettant l’interaction et l’activation de Src, était requise. Les travaux de recherche présentés dans cette thèse démontrent dans un premier temps à partir d’une souris Dep1 KO, dont le développement ne présente aucun phénotype apparent, que la perte de l’expression de DEP-1 se traduit en une inhibition de l’activation de Src et de l’un de ses substrats, la VE-Cadherine, en réponse au VEGF chez la souris adulte. Nos résultats démontrent donc, pour la première fois, le rôle primordial de DEP-1 dans l’induction de la perméabilité vasculaire et de la formation de capillaires in vivo. Conséquemment, la croissance tumorale et la formation de métastases aux poumons sont réduites due à une inhibition de leur vascularisation ce qui se traduit par une diminution de la prolifération et une augmentation de l’apoptose des cellules cancéreuses. De façon intéressante, l’expression élevée de DEP-1 dans les vaisseaux sanguins tumoraux de patientes atteintes du cancer du sein corrèle avec une vascularisation accrue de la tumeur. En plus du rôle de DEP-1 dans la réponse angiogénqiue à l’âge adulte, nos travaux ont également démontré le rôle important de DEP-1 lors de la vascularisation de la rétine, un modèle in vivo d’angiogenèse développementale. Dans ce contexte, DEP-1 inhibe la prolifération des cellules endothéliales et limite leur bourgeonnement et la complexification du réseau vasculaire rétinien en permettant l’expression adéquate du Dll4, un régulateur crucial de l’organisation de la vascularisation développementale. Cette expression du Dll4 découlerait de la stabilisation de la β-caténine par l’inactivation de la GSK3β, un régulateur important de la dégradation de la β-caténine, en réponse au VEGF selon la voie de signalisation VEGFR2-Src-PI3K-Akt-GSK3β. Ainsi, ces travaux identifient DEP-1 comme un régulateur important de l’organisation vasculaire rétinienne. Les rôles positifs de DEP-1 dans les cellules endothéliales découlent principalement de sa capacité à lier et activer la kinase Src. En plus de contribuer à la réponse angiogénique, Src est également un oncogène bien caractérisé notamment pour sa contribution au programme invasif des cellules cancéreuses mammaires. Les travaux de cette thèse illustrent que DEP-1 est préférentiellement exprimée dans les cellules cancéreuses mammaires invasives et qu’il régule l’activation de Src, de voies de signalisation invasives et, par le fait même, de l’invasivité de ces cellules in vitro et in vivo. De façon intéressante, ces observations corrèlent avec des données cliniques où l’expression modérée de DEP-1 est associée à un mauvais pronostic de survie et de rechute. Ces résultats démontrent donc, pour la première fois, le rôle positif de DEP-1 dans l’activation de Src au niveau des cellules endothéliales et des cellules cancéreuses mammaires ce qui permet la régulation du bourgeonnement endothélial, de la perméabilité vasculaire, de l’angiogenèse normale et pathologique en plus de l’invasion tumorale.

(Table 1) Concentrations of the main organochlorine pesticides in liver and plasma samples of ringed seals (Phoca hispida)

The present study investigates the concentrations and patterns of organochlorine pesticides (OCPs) and their metabolites in liver and plasma of two ringed seal populations (Phoca hispida): lower contaminated Svalbard population and more contaminated Baltic Sea population. Among OCPs, p,p'-DDE and sum-chlordanes were the highest in concentration. With increasing hepatic contaminant concentrations and activities of xenobiotic-metabolizing enzymes, the concentrations of 3-methylsulfonyl-p,p'-DDE and the concentration ratios of pentachlorophenol/hexachlorobenzene increased, and the toxaphene pattern shifted more towards persistent Parlar-26 and -50 and less towards more biodegradable Parlar-44. Relative concentrations of the chlordane metabolites, oxychlordane and -heptachlorepoxide, to sum-chlordanes were higher in the seals from Svalbard compared to the seals from the Baltic, while the trend was opposite for cis- and trans-nonachlor. The observed differences in the OCP patterns in the seals from the two populations are probably related to the catalytic activity of xenobiotic-metabolizing enzymes, and also to differences in dietary exposure.

Discoloration and mineralization of Reactive Red HE-3B by heterogeneous photo-Fenton reaction

Discoloration and mineralization of Reactive Red HE-3B were studied by using a laponite clay-based Fe nanocomposite (Fe-Lap-RD) as a heterogeneous catalyst in the presence of H2O2 and UV light. Our experimental results clearly indicate that Fe-Lap-RD mainly consists of Fe2O3 (meghemite) and Fe2Si4O10(OH)2 (iron silicate hydroxide) which have tetragonal and monoclinic structures, respectively, and has a high specific surface area (472m(2) / g) as well as a high total pore volume (0.547 cm(3)/g). It was observed that discoloration of HE-3B undergoes a much faster kinetics than mineralization of HE-3B. It was also found that initial HE-3B concentration, H2O2 concentration, UV light wavelength and power, and Fe-Lap-RD catalyst loading are the four main factors that can significantly influence the mineralization of HE-3B. At optimal conditions, complete discoloration of 100 mg/L HE-3B can be achieved in 30 min and the total organic carbon removal ratio can attain 76% in 120 min, illustrating that Fe-Lap-RD has a high photo-catalytic activity in the photo-assisted discoloration and mineralization of HE-3B in the presence of UV light (254nm) and H2O2. (C) 2003 Elsevier Science Ltd. All rights reserved.

Role of glutamic acid 216 in cytochrome P450 2D6 substrate binding and catalysis

Human cytochrome P450 (P450) 2D6 is an important enzyme involved in the metabolism of drugs, many of which are amines or contain other basic nitrogen atoms. Asp301 has generally been considered to be involved in electrostatic docking with the basic substrates, on the basis of previous modeling studies and site-directed mutagenesis. Substitution of Glu216 with a residue other than Asp strongly attenuated the binding of quinidine, bufuralol, and several other P450 2D6 ligands. Catalytic activity with the substrates bufuralol and 4-methoxyphenethylamine was strongly inhibited by neutral or basic mutations at Glu216 (>95%), to the same extent as the substitution of Asn at Asp301. Unlike the Asp301 mutants, the Gln216 mutant (E216Q) retained 40% enzyme efficiency with the substrate spirosulfonamide, devoid of basic nitrogen, suggesting that the substitutions at Glu216 affect binding of amine substrates more than other catalytic steps. Attempts to induce catalytic specificity toward new substrates by substitutions at Asp301 and Glu216 were unsuccessful. Collectively, the results provide evidence for electrostatic interaction of amine substrates with Glu216, and we propose that both of these acidic residues plus at least another residue(s) is (are) involved in binding the repertoire of P450 2D6 ligands.

Immobilization of aluminum chloride on MCM-41 as a new catalyst system for liquid-phase isopropylation of naphthalene

A great deal of effort has been made at searching for alternative catalysts to replace conventional Lewis acid catalyst aluminum trichloride (AlCl3). In this paper, immobilization of AlCl3 on mesoporous MCM-41 silica with and without modification was carried out. The catalytic properties of the immobilized catalyst systems for liquid-phase isopropylation of naphthalene were studied and compared with those of H/MCM-41 and H/mordenite. The structures of the surface-immobilized aluminum chloride catalysts were studied and identified by using solid-state magic angle spinning nuclear magnetic resonance (MAS NMR), Fourier transform infrared (FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS), nitrogen adsorption, and X-ray diffraction (XRD) techniques. The catalytic activity of the immobilized catalysts was found to be similar to that of acidic mordenite zeolite. A significant enhancement in the selectivity of 2,6-diisopropylnaphthalene (2,6-DIPN) was observed over the immobilized aluminum chloride catalysts. Immobilization of aluminum chloride on mesoporous silica coupled with surface silylation is a promising way of developing alternative catalyst system for liquid-phase Friedel-Crafts alkylation reactions. (C) 2002 Elsevier Science B.V. All rights reserved.

Microstructure and application of mesoporous nanosize zirconia

The mesoporous nanoscale zircoina zeolite was firstly synthesized via solid state - Structure directing method without addition of any stabilizer. The sample bears lamellar or worm pore structures, relatively high surface area compared with that reported. The mesoporous nanosize structure can also resist higher calcination temperature. The introduction of above zirconia to the catalyst of methanol synthesis dedicates the nanosize particle size to the catalyst, which significantly changes the physical structure and electronic effect of the catalyst. The catalyst shows higher catalytic activity and selectivity to methanol. The active sites for methanol synthesis are demonstrated over various catalysts in this paper.

Disulfide-linked dimers of human adrenaline synthesizing enzyme PNMT are catalytically active

The crystal structure of human phenylethanolamine N-methyltransferase (hPNMT) reveals a disulfide- linked dimer, despite the presence of reducing agent in the crystallisation conditions. By removing the reducing agent, hPNMT crystals grow more rapidly and at lower protein concentrations. However, it was unclear whether the disulfide bonds are only present in the crystal form or whether these affect enzyme activity. The solution oligomeric state of hPNMT was investigated using biochemical techniques and activity assays. We found that in the absence of reducing agent, hPNMT forms dimers in solution. Furthermore, the solution dimer of hPNMT incorporates disulfide bonds, since this form is sensitive to reducing agent. The C48A and C139A mutants of hPNMT, which are incapable of forming the disulfide bond observed in the crystal structure, have a decreased propensity to form dimer in solution. Those dimers that do form are also sensitive to reducing agent. Further, the C48A/C139A double mutant shows only monomeric behaviour. Both dimeric and monomeric hPNMT, as well as mutants have wildtype enzyme activity. These results show that a variety of disulfides, including those observed in the crystal structure, can form in solution. In addition, disulfide-linked dimers are as active as the monomeric enzyme indicating that the crystal structure of the protein is a valid target for inhibitor design. Crown Copyright (c) 2005 Published by Elsevier B.V. All rights reserved.