Tópicos em teoria das perturbações cosmológicas

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Geochemical signatures of metasedimentary rocks of high-pressure granulite facies and their relation with partial melting: Carvalhos Klippe, Southern Brasilia Belt, Brazil

High-grade metasedimentary rocks can preserve geochemical signatures of their sedimentary protolith if significant melt extraction did not occur. Retrograde reaction textures provide the main evidence for trapped melt in the rock fabrics. Carvalhos Klippe rocks in Southern Brasilia Orogen, Brazil, present a typical high-pressure granulite assemblage with evidence of mica breakdown partial melting (Ky + Grt + Kfs +/- Bt +/- Rt). The metamorphic peak temperatures obtained by Zr-in-Rt and ternary feldspar geothermometers are between 850 degrees C and 900 degrees C. The GASP bane peak pressure obtained using grossular rich garnet core is 16 kbar. Retrograde reaction textures in which the garnet crystals are partially to totally replaced by Bt + Qtz +/- Fsp intergrowths are very common in the Carvalhos Klippe rocks. These reactions are interpreted as a result of interactions between residual phases and trapped melt during the retrograde path. In the present study the geochemical signatures of three groups of Carvalhos Klippe metasedimentary rocks are analysed. Despite the high metamorphic grade these three groups show well-defined geochemical features and their REE patterns are similar to average compositions of post-Archean sedimentary rocks (PAAS, NASC). The high-pressure granulite facies Grt-Bt-Pl gneisses with immature arenite (wacke, arkose or lithic-arenite) geochemical signatures present in the Carvalhos Klippe are compared to similar rocks in amphibolite facies from the same tectonic framework (Andrelandia Nappe System). The similar geochemical signatures between Grt-Bt-Pl gneisses metamorphosed in high-pressure granulite facies and Grt-Bt-Pl-Qtz schists from the Andrelandia and Liberdade Nappes, with minimal to absent melting conditions, are suggestive of low rates of melt extraction in these high-grade rocks. The rocks with pelitic compositions most likely had higher melt extraction and even under such circumstances nevertheless tend to show REE patterns similar to average compositions of post-Archean sedimentary rocks (PAAS, NASC). (C) 2012 Elsevier Ltd. All rights reserved.

Development of paper based electrodes: From air-breathing to paintable enzymatic cathodes

This work presents the results from the development of bio-cathodes for the application on paper-based biofuel cells. Our main goal here is to demonstrate the possibility of using different designs of air-breathing bio-cathodes and ink-based bio-cathodes for this new type of paper based electrochemical cell. The electrochemical performance for the bio-electrocatalytic oxygen reduction reaction was studied by using open circuit voltage and amperometry measurements, as well as polarization curves to probe the four-electron reduction reaction of ambient oxygen catalyzed by bilirubin oxidase (BOx). The electrochemical measurements showed that all procedures allowed the direct electron transfer from the active site of the bilirubin oxidase to the electrode surface with a limiting current density of almost 500 mu A cm(-2) for an air-breathing BOx cathode and 150 mu A cm(-2) for an ink based BOx cathode. Under a load of 300 mV a stable current density was obtained for 12 h of continuous operation. (C) 2012 Elsevier Ltd. All rights reserved.

Innovative Homogeneous and Heterogeneous Systems for Electrochemically Generated Luminescence Investigations: Towards One-Dimensional ECL

My research PhD work is focused on the Electrochemically Generated Luminescence (ECL) investigation of several different homogeneous and heterogeneous systems. ECL is a redox induced emission, a process whereby species, generated at electrodes, undergo a high-energy electron transfer reaction to form excited states that emit light. Since its first application, the ECL technique has become a very powerful analytical tool and has widely been used in biosensor transduction. ECL presents an intrinsically low noise and high sensitivity; moreover, the electrochemical generation of the excited state prevents scattering of the light source: for all these characteristics, it is an elective technique for ultrasensitive immunoassay detection. The majority of ECL systems involve species in solution where the emission occurs in the diffusion layer near to the electrode surface. However, over the past few years, an intense research has been focused on the ECL generated from species constrained on the electrode surface. The aim of my work is to study the behavior of ECL-generating molecular systems upon the progressive increase of their spatial constraints, that is, passing from isolated species in solution, to fluorophores embedded within a polymeric film and, finally, to patterned surfaces bearing “one-dimensional” emitting spots. In order to describe these trends, I use different “dimensions” to indicate the different classes of compounds. My thesis was mostly developed in the electrochemistry group of Bologna with the supervision of Prof Francesco Paolucci and Dr Massimo Marcaccio. With their help and also thanks to their long experience in the molecular and supramolecular ECL fields and in the surface investigations using scanning probe microscopy techniques, I was able to obtain the results herein described. Moreover, during my research work, I have established a new collaboration with the group of Nanobiotechnology of Prof. Robert Forster (Dublin City University) where I spent a research period. Prof. Forster has a broad experience in the biomedical field, especially he focuses his research on film surfaces biosensor based on the ECL transduction. This thesis can be divided into three sections described as follows: (i) in the fist section, homogeneous molecular and supramolecular ECL-active systems, either organic or inorganic species (i.e., corannulene, dendrimers and iridium metal complex), are described. Driving force for this kind of studies includes the search for new luminophores that display on one hand higher ECL efficiencies and on the other simple mechanisms for modulating intensity and energy of their emission in view of their effective use in bioconjugation applications. (ii) in the second section, the investigation of some heterogeneous ECL systems is reported. Redox polymers comprising inorganic luminophores were described. In such a context, a new conducting platform, based on carbon nanotubes, was developed aimed to accomplish both the binding of a biological molecule and its electronic wiring to the electrode. This is an essential step for the ECL application in the field of biosensors. (iii) in the third section, different patterns were produced on the electrode surface using a Scanning Electrochemical Microscopy. I developed a new methods for locally functionalizing an inert surface and reacting this surface with a luminescent probe. In this way, I successfully obtained a locally ECL active platform for multi-array application.

Study of electromagnetic reactions on light nuclei with the Lorentz Integral Transform method

In dieser Arbeit aus dem Bereich der Wenig-Nukleonen-Physik wird die neu entwickelte Methode der Lorentz Integral Transformation (LIT) auf die Untersuchung von Kernphotoabsorption und Elektronenstreuung an leichten Kernen angewendet. Die LIT-Methode ermoeglicht exakte Rechnungen durchzufuehren, ohne explizite Bestimmung der Endzustaende im Kontinuum. Das Problem wird auf die Loesung einer bindungzustandsaehnlichen Gleichung reduziert, bei der die Endzustandswechselwirkung vollstaendig beruecksichtigt wird. Die Loesung der LIT-Gleichung wird mit Hilfe einer Entwicklung nach hypersphaerischen harmonischen Funktionen durchgefuehrt, deren Konvergenz durch Anwendung einer effektiven Wechselwirkung im Rahmem des hypersphaerischen Formalismus (EIHH) beschleunigt wird. In dieser Arbeit wird die erste mikroskopische Berechnung des totalen Wirkungsquerschnittes fuer Photoabsorption unterhalb der Pionproduktionsschwelle an 6Li, 6He und 7Li vorgestellt. Die Rechnungen werden mit zentralen semirealistischen NN-Wechselwirkungen durchgefuehrt, die die Tensor Kraft teilweise simulieren, da die Bindungsenergien von Deuteron und von Drei-Teilchen-Kernen richtig reproduziert werden. Der Wirkungsquerschnitt fur Photoabsorption an 6Li zeigt nur eine Dipol-Riesenresonanz, waehrend 6He zwei unterschiedliche Piks aufweist, die dem Aufbruch vom Halo und vom Alpha-Core entsprechen. Der Vergleich mit experimentellen Daten zeigt, dass die Addition einer P-Wellen-Wechselwirkung die Uebereinstimmung wesentlich verbessert. Bei 7Li wird nur eine Dipol-Riesenresonanz gefunden, die gut mit den verfuegbaren experimentellen Daten uebereinstimmt. Bezueglich der Elektronenstreuung wird die Berechnung der longitudinalen und transversalen Antwortfunktionen von 4He im quasi-elastischen Bereich fuer mittlere Werte des Impulsuebertrages dargestellt. Fuer die Ladungs- und Stromoperatoren wird ein nichtrelativistisches Modell verwendet. Die Rechnungen sind mit semirealistischen Wechselwirkungen durchgefuert und ein eichinvarianter Strom wird durch die Einfuehrung eines Mesonaustauschstroms gewonnen. Die Wirkung des Zweiteilchenstroms auf die transversalen Antwortfunktionen wird untersucht. Vorlaeufige Ergebnisse werden gezeigt und mit den verfuegbaren experimentellen Daten verglichen.

Ocean acidification reduces the crystallographic control in juvenile mussel shells

Global climate change threatens the oceans as anthropogenic carbon dioxide causes ocean acidification and reduced carbonate saturation. Future projections indicate under saturation of aragonite, and potentially calcite, in the oceans by 2100. Calcifying organisms are those most at risk from such ocean acidification, as carbonate is vital in the biomineralisation of their calcium carbonate protective shells. This study highlights the importance of multi-generational studies to investigate how marine organisms can potentially adapt to future projected global climate change. Mytilus edulis is an economically important marine calcifier vulnerable to decreasing carbonate saturation as their shells comprise two calcium carbonate polymorphs: aragonite and calcite. M. edulis specimens were cultured under current and projected pCO2 (380, 550, 750 and 1000 µatm), following 6 months of experimental culture, adults produced second generation juvenile mussels. Juvenile mussel shells were examined for structural and crystallographic orientation of aragonite and calcite. At 1000 µatm pCO2, juvenile mussels spawned and grown under this high pCO2 do not produce aragonite which is more vulnerable to carbonate under-saturation than calcite. Calcite and aragonite were produced at 380, 550 and 750 µatm pCO2. Electron back scatter diffraction analyses reveal less constraint in crystallographic orientation with increased pCO2. Shell formation is maintained, although the nacre crystals appear corroded and crystals are not so closely layered together. The differences in ultrastructure and crystallography in shells formed by juveniles spawned from adults in high pCO2 conditions may prove instrumental in their ability to survive ocean acidification.

FM1-43 dye ultrastructural localization in and release from frog motor nerve terminals.

Previous work has shown that the fluorescent styryl dye FM1-43 stains nerve terminals in an activity-dependent fashion. This dye appears to label the membranes of recycled synaptic vesicles by being trapped during endocytosis. Stained terminals can subsequently be destained by repeating nerve stimulation in the absence of dye; the destaining evidently reflects escape of dye into the bathing medium from membranes of exocytosing synaptic vesicles. In the present study we tested two key aspects of this interpretation of FM1-43 behavior, namely: (i) that the dye is localized in synaptic vesicles, and (ii) that it is actually released into the bathing medium during destaining. To accomplish this, we first photolyzed the internalized dye in the presence of diaminobenzidine. This created an electron-dense reaction product that could be visualized in the electron microscope. Reaction product was confined to synaptic vesicles, as predicted. Second, using spectrofluorometry, we quantified the release of dye liberated into the medium from tubocurarine-treated nerve-muscle preparations. Nerve stimulation increased the amount of FM1-43 released, and we estimate that normally a stained synaptic vesicle contains a few hundred molecules of the dye. The key to the successful detection of released FM1-43 was to add the micelle-forming detergent 3-[(3-cholamidopropyl)dimethylammonio]-1-propanesulfonate (CHAPS), which increased FM1-43 quantum yield by more than two orders of magnitude.

Reductive electrochemical formation of 6H-dibenzo[b,d]pyran-6-one and 2-benzopyran-1(1H)-one

In the present Letter several carbolactones (oxidative products) are obtained under aprotic cathodic conditions in the preparative scaled electrolysis of 1,2-quinones in a divided electrochemical cell and in the presence of oxygen. When 9,10-phenanthrenequinone is reduced 6H-dibenzo[b,d]pyran-6-one and [1,1′-biphenyl]-2,2′-dicarboxylic acid are obtained as major products. In the reduction of 1,2-naphthoquinone, 2-benzopyran-1(1H)-one, and 2-(2-carboxyethenyl)-benzoic acid were formed as main products. The proposed mechanism to explain the formation of these and other products, that involves an electron-transfer reaction to the oxygen in air, is now discussed.

Solidification mechanisms of unmodified and strontium-modified hypereutectic aluminium-silicon alloys

The effects of strontium on the solidi. cation mode of hypereutectic aluminium-silicon alloys have been studied. Samples were prepared from an aluminium-17wt% silicon-based alloy and strontium was added at several different concentrations. The development of the microstructure was investigated by cooling curve analysis, interrupted solidi. cation experiments and optical and scanning electron microscopy. It was found that nucleation of primary silicon is suppressed by additions of strontium. The suppressed nucleation results in supersaturation of the liquid prior to nucleation, and an increased growth rate after nucleation. As a result, the silicon crystals become less faceted and more dendritic with increasing strontium additions. Increasing the strontium concentration slightly refined the eutectic spacing and introduced a small amount of fibrous silicon. Electron back-scatter diffraction measurements were performed to determine the crystallographic relation between the primary and eutectic silicon phases. The eutectic silicon in the unmodified alloy does not have any crystallographic relationship with the primary silicon crystals. In contrast, the eutectic silicon crystals in the strontium-modified alloys often share an identical or twin relationship with nearby primary silicon crystals. The incidence of twinning within primary silicon crystals was relatively low and did not appear to increase with strontium additions.

Microanalysis of quenched and self-extinguished aluminium rods burned in oxygen

Promoted ignition tests and quench tests have been conducted and analysed for 3.2 mm aluminum rods in 99.995% oxygen. Tests have been conducted in oxygen pressures varying from 538 kPa to 773 kPa. Samples that self-extinguished or were quenched were selected for further analysis. The microstructure of the selected samples were analysed by electron microscopy, using energy dispersive spectrometry and electron back-scatter techniques, to identify and visualize, respectively, the species present. The grain structures of these samples were etched, viewed and photographed under polarized light by an optical microscope. From the micrographs produced by the post-test analysis, clearly defined boundaries between the oxide and the melted and resolidified metal have been observed. In both the melted and resolidified metal and the oxide layer, significant numbers of gas bubbles, solid inclusions and several diffuse oxide bubbles have been captured during the cooling process. It is concluded that convective movement is occurring within the molten drop and that analysis of quenched samples provides more useful information on the state of the burning droplet than samples allowed to cool slowly to room temperature. Recommendations are made regarding future investigations into aluminum burning, focusing on the transport of reactants through the liquid oxide layer.

On the reactivity of naphthalene and biphenyl dianions: tying up loose ends concerning an SN2-ET dichotomy in alkylation reactions

Naphthalene and biphenyl dianions are interesting compounds that can be obtained by double reduction of the corresponding arenes in solution with certain alkali metals. These dianions are highly reactive and rather elusive species with very high laying and highly delocalized electrons. They share many aspects of the reactivity of the alkali metal they originated from and consequently behave primarily as strong electron transfer (ET) reagents. We report here kinetic evidence for a different type of reactivity in their alkylation reactions with alkyl fluorides. By using cyclopropylmethyl fluoride (c-C3H5CH2F) as a very fast radical probe, we were able to settle that this alkylation does not involve the classical electron transfer reaction followed by radical coupling between diffusing radicals, but supports the alternative SN2 concerted mechanism, discerning thus this mechanistic SN2-ET dichotomy.

Non-Marcus energy gap dependence of electron transfer rate in contact ion pairs. Novel interplay between relaxation and reaction in solution

Electron transfer reactions between donor-acceptor pairs in solution and in organized media exhibit diverse behaviour. Recent experiments have indicated an interesting breakdown of the Marcus parabolic energy gap dependence in the normal regime for back electron transfer from contact ion pairs. A novel explanation of this breakdown has recently been proposed (M. Tachiya and S. Murata, J. Am. Chem. Sec., 116(1994) 2434) which attributes the breakdown to the interplay between the relaxation in the reactant well and the reaction. A particularly interesting aspect of the model is that it envisages the electron transfer in the normal regime to take place from a completely non-equilibrium condition. In this article a time dependent solution of the model is presented for the first time, after generalizing it to include a realistic initial population distribution. The decay of the contact ion pair population is completely non-exponential. This can be used to check the validity of the Tachiya-Murata model. The dynamics of electron transfer from the solvent separated ion pair, which seem to obey the Marcus relation, is exponential.

(A) Photoregulation of DNA Functions by Cyclic Azobenzene-tethered Oligonucleotides (B) Site-specific Fluorescent Labeling of DNA using Inverse Electron Demand Diels-Alder Reaction between trans-Cyclooctene Derivatives and BODIPY-Tetrazine Adducts

(A) Most azobenzene-based photoswitches require UV light for photoisomerization, which limit their applications in biological systems due to possible photodamage. Cyclic azobenzene derivatives, on the other hand, can undergo cis-trans isomerization when exposed to visible light. A shortened synthetic scheme was developed for the preparation of a building block containing cyclic azobenzene and D-threoninol (cAB-Thr). trans-Cyclic azobenzene was found to thermally isomerize back to the cis-form in a temperature-dependent manner. cAB-Thr was transformed into the corresponding phosphoramidite and subsequently incorporated into oligonucleotides by solid phase synthesis. Melting temperature measurement suggested that incorporation of cis-cAB into oligonucleotides destabilizes DNA duplexes, these findings corroborate with circular dichroism measurement. Finally, Fluorescent Energy Resonance Transfer experiments indicated that trans-cAB can be accommodated in DNA duplexes. (B) Inverse Electron Demand Diels-Alder reactions (IEDDA) between trans-olefins and tetrazines provide a powerful alternative to existing ligation chemistries due to its fast reaction rate, bioorthogonality and mutual orthogonality with other click reactions. In this project, an attempt was pursued to synthesize trans-cyclooctene building blocks for oligonucleotide labeling by reacting with BODIPY-tetrazine. Rel-(1R-4E-pR)-cyclooct-4-enol and rel-(1R,8S,9S,4E)-Bicyclo[6.1.0]non-4-ene-9-ylmethanol were synthesized and then transformed into the corresponding propargyl ether. Subsequent Sonogashira reactions between these propargylated compounds with DMT-protected 5-iododeoxyuridine failed to give the desired products. Finally a methodology was pursued for the synthesis of BODIPY-tetrazine conjugates that will be used in future IEDDA reactions with trans-cyclooctene modified oligonucleotides.

Ozone-induced dissociation of conjugated lipids reveals significant reaction rate enhancements and characteristic odd-electron product ions

Ozone-induced dissociation (OzID) is an alternative ion activation method that relies on the gas phase ion-molecule reaction between a mass-selected target ion and ozone in an ion trap mass spectrometer. Herein, we evaluated the performance of OzID for both the structural elucidation and selective detection of conjugated carbon-carbon double bond motifs within lipids. The relative reactivity trends for \[M + X](+) ions (where X = Li, Na, K) formed via electrospray ionization (ESI) of conjugated versus nonconjugated fatty acid methyl esters (FAMEs) were examined using two different OzID-enabled linear ion-trap mass spectrometers. Compared with nonconjugated analogues, FAMEs derived from conjugated linoleic acids were found to react up to 200 times faster and to yield characteristic radical cations. The significantly enhanced reactivity of conjugated isomers means that OzID product ions can be observed without invoking a reaction delay in the experimental sequence (i.e., trapping of ions in the presence of ozone is not required). This possibility has been exploited to undertake neutral-loss scans on a triple quadrupole mass spectrometer targeting characteristic OzID transitions. Such analyses reveal the presence of conjugated double bonds in lipids extracted from selected foodstuffs. Finally, by benchmarking of the absolute ozone concentration inside the ion trap, second order rate constants for the gas phase reactions between unsaturated organic ions and ozone were obtained. These results demonstrate a significant influence of the adducting metal on reaction rate constants in the fashion Li > Na > K.