Structural and optical properties of ZnS/MgNb2O6 heterostructures

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Experimental and theoretical study on the structure, optical properties, and growth of metallic silver nanostructures in Ag3PO4

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Modificação da superfície de óxidos de ferro por dextrana derivatizada para aplicações em liberação de fármaco

Pós-graduação em Química - IQ

Modificação da superfície de óxidos de ferro por dextrana derivatizada para aplicações em liberação de fármaco

Pós-graduação em Química - IQ

Magnetic Ionic Liquids Produced by the Dispersion of Magnetic Nanoparticles in 1-n-Butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide (BMI.NTf2)

This paper reports on the advancement of magnetic ionic liquids (MILs) as stable dispersions of surface-modified gamma-Fe2O3, Fe3O4, and CoFe2O4 magnetic nanoparticles (MNPs) in a hydrophobic ionic liquid, 1-n-butyl 3-methylimidazolium bis(trifluoromethanesulfonyl)imide (BMI.NTf2). The MNPs were obtained via coprecipitation and were characterized using powder X-ray diffraction, transmission electron microscopy, Raman spectroscopy and Fourier transform near-infrared (FT-NIR) spectroscopy, and magnetic measurements. The surface-modified MNPs (SM-MNPs) were obtained via the silanization of the MNPs with the aid of 1-butyl-3[3-(trimethoxysilyl)propyl]imidazolium chloride (BMSPI.Cl). The SM-MNPs were characterized by Raman spectroscopy and Fourier trail: form infrared attenuated total reflectance (FTIR-ATR) spectroscopy and by magnetic measurements. The FTIR-ATR spectra of the SM-MNPs exhibited characteristic absorptions of the imidazolium and those of the Fe-O-Si-C moieties, confirming the presence of BMSPI.Cl on the MNP surface. Thermogravimetric analysis (TGA) showed that the SM-MNPs were modified by at least one BMSPI.Cl monolayer. The MILs were characterized using Raman spectroscopy, differential scanning calorimetry (DSC), and magnetic measurements. The Raman and DSC results indicated an interaction between the SM-MNPs and the IL. This interaction promotes the formation of a supramolecular structure close to the MNP surface that mimics the IL structure and is responsible for the stability of the MIL. Magnetic measurements of the MILs indicated no hysteresis. Superparamagnetic behavior and a saturation magnetization of similar to 22 emu/g could be inferred from the magnetic measurements of a sample containing 50% w/w gamma-Fe2O3 SM-MNP/BMI-NTf2.

The processing of polyelectrolyte-covered magnetite nanoparticles in the form of nanostructured thin films

Magnetic nanoparticles are promising for a variety of applications, such as biomedical devices, spin electronics, magnetic data storage media, to name a few. However, these goals may only be reached if stable and organized structures are fabricated. In this article, we report on a single-step synthetic route with the coprecipitation method, in which iron oxide magnetic nanoparticles (Fe3O4 NPs) were stabilized in aqueous media using the poly(diallyldimethylammonium chloride) (PDAC) polyelectrolyte. The Fe3O4 NPs had a diameter of ca. 5 nm, according to transmission electron microscopy (TEM) images, being arranged in an inverse spinel structure typical of magnetite. An investigation with infrared spectroscopy indicated that the mechanisms of stabilization in the polymer matrix were based on the interaction between quaternary amide groups from PDAC and the nanoparticle surface. The Fe3O4-PDAC NPs exhibited considerable magnetic susceptibility, with a monotonic increase in the magnetization with decreasing temperature. These Fe3O4-PDAC NPs were immobilized in layer-by-layer (LbL) films, being alternated with layers of poly(vinylsulfonic acid) (PVS). The LbL films were much rougher than typical films made with polyelectrolytes, and Fe3O4-PDAC NPs have been responsible for the high electrocatalytic activity toward H2O2 reduction, with an overpotential shift of 0.69 V. Overall, the stability, magnetic properties and film-forming ability indicate that the Fe3O4-PDAC NPs may be used for nanoelectronics and bioelectrochemical devices requiring reversible and magnetic redox materials.

Cluster Coordination and Photoluminescence Properties of alpha-Ag2WO4 Microcrystals

In this paper, we report our initial research to obtain hexagonal rod-like elongated silver tungstate (alpha-Ag2WO4) microcrystals by different methods [sonochemistry (SC), coprecipitation (CP), and conventional hydrothermal (CH)] and to study their cluster coordination and optical properties. These microcrystals were structurally characterized by X-ray diffraction (XRD), Rietveld refinements, Fourier transform infrared (FT-IR), X-ray absorption near-edge structure (XANES), and extended X-ray absorption fine structure (EXAFS) spectroscopies. The shape and average size of these alpha-Ag2WO4 microcrystals were observed by field-emission scanning electron microscopy (FE-SEM). The optical properties of these microcrystals were investigated by ultraviolet-visible (UV-vis) spectroscopy and photoluminescence (PL) measurements. XRD patterns and Rietveld refinement data confirmed that alpha-Ag2WO4 microcrystals have an orthorhombic structure. FT-IR spectra exhibited four IR-active modes in a range from 250 to 1000 cm(-1). XANES spectra at the W L-3-edge showed distorted octahedral [WO6] clusters in the lattice, while EXAFS analyses confirmed that W atoms are coordinated by six O atoms. FE-SEM images suggest that the alpha-Ag2WO4 microcrystals grow by aggregation and the Ostwald ripening process. PL properties of alpha-Ag2WO4 microcrystals decrease with an increase in the optical band-gap values (3.19-3.23 eV). Finally, we observed that large hexagonal rod-like alpha-Ag2WO4 microcrystals prepared by the SC method exhibited a major PL emission intensity relative to alpha-Ag2WO4 microcrystals prepared by the CP and CH methods.

Sorption of aspartic and glutamic aminoacids on calcined hydrotalcite

Sorption of aspartic and glutamic aminoacids by regeneration of calcined hydrotalcite is reported. Hydrotalcite was synthesized by coprecipitation and calcined at 773 K. Sorption experiments were performed at 298 K and 310 K, and the results reveal that at low aminoacids equilibrium concentrations, intercalation of hydroxyl anions takes place while at high equilibrium concentrations, the sorption process occur by means re-hydration and aminoacids intercalation of hydrotalcite. The results also suggested that Asp and Glu sorption is a temperature dependent process. The amount of sorbed amino acid decreases as the temperature increase. The effect is more pronounced for Glu sorption probably due to its higher hydrophobic character, which makes the sorption more difficult in comparison with sorption of Asp at higher temperature.

Synthesis and characterisation of hydrotalcite-like compounds for transesterification reaction

A series of templated [Mg(1-x)Alx(OH)2]x+(CO3)x/n2- with different structural properties have been synthesised using an alkali-free coprecipitation route. The macroporous materials were been obtained using two different kind of templating agents, polymeric materials, in order to cover a bigger size range (750-70 nm). All the materials have been characterized by different techniques: porosimetry, SEM-EDX, TEM-EDX, MP-AES, XRD, CO2 titration before and after the calcinations process. All the materials have been tested for transesterification reaction of C4-C8 triglycerides with methanol for biodiesel production.

Lichtsammler hinter Glas : Stabilisierung und Funktionalisierung des pflanzlichen Hauptlichtsammelkomplexes (LHCII) durch biomineralische Einbettung in Nanopartikel

Der Haupt-Lichtsammelkomplex des Fotosystems II (LHCII) setzt sich aus einem Proteinanteil und nicht-kovalent gebundenen Pigmenten – 8 Chlorophyll a, 6 Chlorophyll b und 4 Carotinoide - zusammen. Er assembliert in vivo zu einem Trimer, in dem die Monomereinheiten ebenfalls nicht-kovalent miteinander wechselwirken. Die ausgesprochen hohe Farbstoffdichte und die Tatsache, dass der Komplex rekombinant hergestellt werden kann, machen den LHCII zu einem interessanten Kandidaten für technische Anwendungen wie einer Farbstoffsolarzelle. Allerdings muss hierzu seine thermische Stabilität drastisch erhöht werden.rnDer Einschluss von Proteinen/Enzymen in Silikat erhöht deren Stabilität gegenüber Hitze signifikant. LHCII sollte als erster rekombinanter Membranproteinkomplex mittels kovalent verbundener, polykationischen Sequenzen in Silikat eingeschlossen werden. Hierzu wurde der Komplex auf zwei Weisen polykationisch modifiziert: Auf Genebene wurde die Sequenz des R5-Peptids in den N-terminalen Bereich des LHCP-Gens eingeführt und ein Protokoll zur Überexpression, Rekonstitution und Trimerisierung etabliert. Außerdem wurde eine kovalente Modifikation des trimeren LHCII mit dem Arginin-reichen Protamin über heterobifunktionelle Crosslinker entwickelt. Beide resultierenden LHCII-Derivate waren in der Lage, Silikat autogen zu fällen. Die Stabilisierung der so in Silikat präzipitierten Komplexe war jedoch deutlich geringer als bei nicht-modifizierten Komplexen, die durch eine Spermin-induzierte Copräzipitation eingeschlossenen wurden. Dabei zeigte sich, dass für den Anteil der eingebauten Komplexe und das Ausmaß an Stabilisierung die Größe und klare partikuläre Struktur des Silikats entscheidend ist. Kleine Partikel mit einem Durchmesser von etwa 20 nm führten zu einem Einbau von rund 75 % der Komplexe, und mehr als 80 % des Energietransfers innerhalb des Komplexes blieben erhalten, wenn für 24 Stunden bei 50°C inkubiert wurde. Nicht in Silikat eingeschlossene Komplexe verloren bei 50°C ihren Komplex-internen Energietransfer binnen weniger Minuten. Es war dabei unerheblich, ob die Partikelgröße durch die Wahl des Puffers und des entsprechenden pH-Wertes, oder aber durch Variation des Spermin-zu-Kieselsäure-Verhältnisses erreicht wurde. Wurden die polykationisch veränderten Komplexe in solchen Copräzipitationen verwendet, so erhöhte sich der Anteil an eingebauten Komplexen auf über 90 %, jedoch wurde nur bei der R5-modifizierten Variante vergleichbare Ausmaße an Stabilisierung erreicht. Ein noch höherer Anteil an Komplexen wurde in das Silikatpellet eingebaut, wenn LHCII kovalent mit Silanolgruppen modifiziert wurde (95 %); jedoch war das Ausmaß der Stabilisierung wiederum geringer als bei einer Copräzipitation. Die analysierten Fällungssysteme waren außerdem in der Lage, Titandioxid zu fällen, wobei der Komplex in dieses eingebaut wurde. Allerdings muss das Stabilisierungspotential hier noch untersucht werden. Innerhalb eines Silikatpräzipitats aggregierten die Komplexe nicht, zeigten aber einen inter-trimeren Energietransfer, der sehr wahrscheinlich auf einem Förster Resonanz Mechanismus basiert. rnDies und das hohe Maß an Stabilisierung eröffnen neue Möglichkeiten, rekombinanten LHCII in technischen Applikationen als Lichtsammelkomponente zu verwenden.rn

Long-term cell-mediated protein release from calcium phosphate ceramics

Efficient delivery of growth factors from carrier biomaterials depends critically on the release kinetics of the proteins that constitute the carrier. Immobilizing growth factors to calcium phosphate ceramics has been attempted by direct adsorption and usually resulted in a rapid and passive release of the superficially adherent proteins. The insufficient retention of growth factors limited their bioavailability and their efficacy in the treatment of bone regeneration. In this study, a coprecipitation technique of proteins and calcium phosphate was employed to modify the delivery of proteins from biphasic calcium phosphate (BCP) ceramics. To this end, tritium-labeled bovine serum albumin ([(3)H]BSA) was utilized as a model protein to analyze the coprecipitation efficacy and the release kinetics of the protein from the carrier material. Conventional adsorption of [(3)H]BSA resulted in a rapid and passive release of the protein from BCP ceramics, whereas the coprecipitation technique effectively prevented the burst release of [(3)H]BSA. Further analysis of the in vitro kinetics demonstrated a sustained, cell-mediated release of coprecipitated [(3)H]BSA from BCP ceramics induced by resorbing osteoclasts. The coprecipitation technique described herein, achieved a physiologic-like protein release, by incorporating [(3)H]BSA into its respective carriers, rendering it a promising tool in growth factor delivery for bone healing.

Interaction of the receptor FGFRL1 with the negative regulator Spred1

FGFRL1 is a member of the fibroblast growth factor receptor family. It plays an essential role during branching morphogenesis of the metanephric kidneys, as mice with a targeted deletion of the Fgfrl1 gene show severe kidney dysplasia. Here we used the yeast two-hybrid system to demonstrate that FGFRL1 binds with its C-terminal, histidine-rich domain to Spred1 and to other proteins of the Sprouty/Spred family. Members of this family are known to act as negative regulators of the Ras/Raf/Erk signaling pathway. Truncation experiments further showed that FGFRL1 interacts with the SPR domain of Spred1, a domain that is shared by all members of the Sprouty/Spred family. The interaction could be verified by coprecipitation of the interaction partners from solution and by codistribution at the cell membrane of COS1 and HEK293 cells. Interestingly, Spred1 increased the retention time of FGFRL1 at the plasma membrane where the receptor might interact with ligands. FGFRL1 and members of the Sprouty/Spred family belong to the FGF synexpression group, which also includes FGF3, FGF8, Sef and Isthmin. It is conceivable that FGFRL1, Sef and some Sprouty/Spred proteins work in concert to control growth factor signaling during branching morphogenesis of the kidneys and other organs.

Aberrant regulation of the Src -FAK signaling pathway in the human colon adenocarcinoma cell line HT-29

c-Src, a protein tyrosine kinase (PTK) the specific activity of which is increased $>$20-fold in $\sim$80% of colon tumors and colon tumor cell lines, plays a role in both growth regulation and tumorigenicity of colon tumor cells. To examine the effect of increased c-Src specific activity on colon tumor cells, coumarin-derived tyrosine analog PTK inhibitors were assessed in a standard colon tumor cell line, HT-29. Of the nine compounds tested for inhibiting c-Src activity in a standard immune complex kinase assay from c-Src precipitated from HT-29 cells, the 7,8-dihydroxy-containing compounds daphnetin and fraxetin were most effective, with IC$\sb{50}$s of 0.6 $\pm$ 0.2 mM and 0.6 $\pm$ 0.3 mM, respectively. Treatment of HT-29 cells with daphnetin resulted in inhibition of cell growth in a dose-dependent manner. In contrast, scopoletin, a relatively poor Src inhibitor in vitro, did not inhibit HT-29 cell growth in the concentration range tested. In daphnetin treated cells, a dose-dependent decrease of c-Src activity paralleling cell growth inhibition was also observed; the IC$\sb{50}$ was 0.3 $\pm$ 0.1 mM for c-Src autophosphorylation. In contrast, the IC$\sb{50}$ for c-Src protein level was $>$ 0.6 mM, indicating that the effects of daphnetin were primarily an enzymatic activity of c-Src, rather than protein level in HT-29 cells. These results are the first to demonstrate that c-Src specific activity regulates colon tumor cell growth.^ To elucidate the signaling pathways activated by c-Src in colon tumor cells, the Src family substrate FAK, which has been shown to play a role in both extracellular matrix-dependent cell growth and survival, was examined. Coprecipitation assays showed Src-FAK association in detergent insoluble fractions of both attached and detached HT-29 cells, indicating that Src-FAK association in HT-29 cells is stable and, unlike untransformed cells, not dependent on cell-substratum contact. FAK also coprecipitated with Grb2, an adaptor protein also playing a role in cell proliferation and survival, in both attached and detached HT-29 cells, suggesting that a Src-FAK-Grb2-mediated signaling pathway(s) in HT-29 cells is/are constitutively activated.^ FAK was also analyzed in c-src antisense HT-29 clones AS15 and AS33 in which c-Src is specifically reduced by transfection of an antisense expression vector. FAK protein level is unexpectedly decreased in both AS15 and AS33 cells by 5-fold and 1.5-fold compared to HT-29, respectively, corresponding with the decreased expression of c-Src observed in these cells. FAK protein level was not decreased compared to parental in the c-src "sense" clone S8. Northern blot analyses showed decreased FAK mRNA levels compared to parental in AS15 and AS33, correlating with decreased FAK protein level, indicating that FAK activity in the antisense cells is regulated, at least in part, by altering FAK expression, and that this regulation is Src dependent. Because FAK has been implicated in anoikis, the ability of c-src antisense cells to survive in the absence of cell-substratum contact was examined. Decreased cell survival is seen in both AS15 and AS33, correlating with the decreases in c-Src and FAK levels and tumorigenicity in these cells. These results suggest that at least one mechanism by which activation of c-Src contributes to tumorigenic phenotype of colon tumor cells is by aberrantly promoting a survival signal through unregulated Src-FAK-Grb2 complexes. (Abstract shortened by UMI.) ^

Characterization of cellular and molecular functions of the p21 -activated kinase, Shk1, in the fission yeast, Schizosaccharomyces pombe

The p21-activated kinase, Shk1, is an essential serine/threonine kinase required for normal cell polarity, proper mating response, and hyperosmotic stress response, in the fission yeast, Schizosaccharomyces pombe. This study has established a novel role for Shk1 as a microtubule regulator in fission yeast and, in addition, characterized a potential biological substrate of Shk1. Cells defective in Shk1 function were found to exhibit malformed interphase and mitotic microtubules, are hypersensitive to the microtubule disrupting drug thiabendazole (TBZ), and are cold sensitive for growth. Microtubule disruption by TBZ results in a significant reduction of Shk1 kinase activity, which is restored after cells are released from the drug, thus providing a correlation between Shk1 kinase activity and active microtubule polymerization. Consistent with a role for Shk1 as a microtubule regulator, GFP-Shk1 fusion proteins localize to interphase microtubules and mitotic microtubule spindles. Furthermore, loss of Tea1, a presumptive microtubule regulator in fission yeast, exacerbates the growth and microtubule defects of cells deficient in Shk1 function, and results in illicit Shk1 localization. Moreover, loss of the Cdc2 inhibitory kinase Wee1, which has been implicated as a mediator of the Shk1 pathway, leads to significant microtubule defects. Intriguingly, Wee1 protein levels are markedly reduced both by partial loss of Shk1 function and by treatment with TBZ. These results suggest that Shk1 is required for proper regulation of microtubule dynamics in fission yeast and may interact with Tea1 and Wee1 in this regulatory process. ^ To further understand Shk1 function in fission yeast, a yeast two-hybrid screen for proteins that interact with the Shk1 catalytic domain was performed. This screen led to the identification of a novel protein, Skb10 (for S&barbelow;hk1 k&barbelow;inase b&barbelow;inding protein 10). Coprecipitation experiments demonstrated that Skb10 associates with Shk1 in S. pombe cells. (Abstract shortened by UMI.) ^

Annotated record and chemical composition of manganese nodules from station VITYAZ 4575, Indian Ocean

Analyses are given for the core and outer colliform shell of a manganese nodule collected at a depth of 5000 m in the Indian Ocean, and for the red clay that encloses the nodules. Trace elements determined include rare earths, Nb, Ta, Th, and V. The cores of the nodules were once composed of basaltic rock, but now are phillipsite and nontronite. The outer shell is composed of manganite, with admixed quartz, phillipsite, and some geothite. The correlations established between the redox potentials and the concentration coefficients for 12 elements indicate that Eh plays a greater role in the formation of the manganiferous shells than coprecipitation properties.