Coupled electronic and morphologic changes in graphene oxide upon electrochemical reduction

Peer reviewedPostprin

Multiscale Fractal Descriptors Applied to Nanoscale Images

This work proposes the application of fractal descriptors to the analysis of nanoscale materials under different experimental conditions. We obtain descriptors for images from the sample applying a multiscale transform to the calculation of fractal dimension of a surface map of such image. Particularly, we have used the}Bouligand-Minkowski fractal dimension. We applied these descriptors to discriminate between two titanium oxide films prepared under different experimental conditions. Results demonstrate the discrimination power of proposed descriptors in such kind of application

Characterization of nanostructured material images using fractal descriptors

This work presents a methodology to the morphology analysis and characterization of nanostructured material images acquired from FEG-SEM (Field Emission Gun-Scanning Electron Microscopy) technique. The metrics were extracted from the image texture (mathematical surface) by the volumetric fractal descriptors, a methodology based on the Bouligand-Minkowski fractal dimension, which considers the properties of the Minkowski dilation of the surface points. An experiment with galvanostatic anodic titanium oxide samples prepared in oxalyc acid solution using different conditions of applied current, oxalyc acid concentration and solution temperature was performed. The results demonstrate that the approach is capable of characterizing complex morphology characteristics such as those present in the anodic titanium oxide.Comment: 8 pages, 5 figures, accepted for publication Physica

Oxygen doping-induced photogeneration loss in P3HT:PCBM solar cells

This work investigates the loss in performance induced by molecular oxygen in bulk heterojunction solar cells. We observe that upon exposure to molecular oxygen both formation of P3HT+:O2− complex and metal oxidation at the interface between the active layer and metallic contact occur. These two different effects were separately investigated using NOBF4 as an oxidant. Our procedure has allowed studying p-doping of the active layer independently from contact degradation. A loss in photocurrent is associated with formation of P3HT+:O2− complex, which reduces the concentration of neutral P3HT present in the film in accordance with absorption and external quantum efficiency spectra. This complex is regarded as a source of a pathway of reversible degradation. Capacitance–voltage measurements allow for an accurate extraction of p-doping levels of the active layer produced by the presence of charged O2− species. In addition, one of the irreversible degradation pathways is identified to be oxidation of the metallic contact to form CaO. This oxide forms a thin dipole layer producing a voltage drop across the active layer/Ca interface, which has a direct impact on the open circuit voltage and fill factor

Mapping the electronic structure of polypyrrole with image-based electrochemical scanning tunneling spectroscopy

ACKNOWLEDGMENTS The support of this research by FAPESP (grants: 2013/07296-2, 2014/50249-8, 2015/12851-0, 2017/11986-5), Shell, CsF-PVE (99999.007708/2015-07), Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - Brasil (CAPES) - Finance Code 001 and CNPq is gratefully acknowledged.Peer reviewedPublisher PD

In situ microwave-enhanced electrochemical reactions at stainless steel:Nano-iron for aqueous pollutant degradation

Iron nanoparticle deposition and stripping are observed from aqueous Fe2+ solution at pH 3 on stainless electrodes in the presence of focused microwave activation. The effects of Fe2+ concentration and microwave power are evaluated. It is shown that the resulting iron nanoparticle deposit (i) gives well-defined anodic stripping responses, (ii) is readily released into the solution phase, and (iii) is highly reactive towards chlorinated hydrocarbons such as trichloroacetate. The combined effects of increased mass transport and localized microwave heating improve pollutant degradation treatments. Keywords: Iron nanoparticles, Steel electrode, Microwave, Pollutant degradatio

Microwave-Assisted Synthesis of Pt-Au Nanoparticles with Enhanced Electrocatalytic Activity for the Oxidation of Formic Acid

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) is gratefully acknowledged for financial support under Research Project BJT-2014/400117/2014-2 and for the research support (HV: grant #306151/2010-3). Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) is also acknowledged for financial support (grants #2013/07296-2 and #2013/16930-7), and scholarship (FWH: grant #2014/08030-9). GC gratefully acknowledges R. Camargo for his collaboration in the acquisition of the HR-TEM images and for useful discussion and suggestions.Peer reviewedPostprin

Trypanosoma cruzi Epimastigotes Are Able to Store and Mobilize High Amounts of Cholesterol in Reservosome Lipid Inclusions

Reservosomes are lysosome-related organelles found in Trypanosoma cruzi epimastigotes. They represent the last step in epimastigote endocytic route, accumulating a set of proteins and enzymes related to protein digestion and lipid metabolism. The reservosome matrix contains planar membranes, vesicles and lipid inclusions. Some of the latter may assume rectangular or sword-shaped crystalloid forms surrounded by a phospholipid monolayer, resembling the cholesterol crystals in foam cells.Using Nile Red fluorimetry and fluorescence microscopy, as well as electron microscopy, we have established a direct correlation between serum concentration in culture medium and the presence of crystalloid lipid inclusions. Starting from a reservosome purified fraction, we have developed a fractionation protocol to isolate lipid inclusions. Gas-chromatography mass-spectrometry (GC-MS) analysis revealed that lipid inclusions are composed mainly by cholesterol and cholesterol esters. Moreover, when the parasites with crystalloid lipid-loaded reservosomes were maintained in serum free medium for 48 hours the inclusions disappeared almost completely, including the sword shaped ones.Taken together, our results suggest that epimastigote forms of T. cruzi store high amounts of neutral lipids from extracellular medium, mostly cholesterol or cholesterol esters inside reservosomes. Interestingly, the parasites are able to disassemble the reservosome cholesterol crystalloid inclusions when submitted to serum starvation

Lipidomic Analysis of Extracellular Vesicles from the Pathogenic Phase of Paracoccidioides brasiliensis

Background: Fungal extracellular vesicles are able to cross the cell wall and transport molecules that help in nutrient acquisition, cell defense, and modulation of the host defense machinery.Methodology/Principal Findings: Here we present a detailed lipidomic analysis of extracellular vesicles released by Paracoccidioides brasiliensis at the yeast pathogenic phase. We compared data of two representative isolates, Pb3 and Pb18, which have distinct virulence profiles and phylogenetic background. Vesicle lipids were fractionated into different classes and analyzed by either electrospray ionization- or gas chromatography-mass spectrometry. We found two species of monohexosylceramide and 33 phospholipid species, including phosphatidylcholine, phosphatidylethanolamine, phosphatidic acid, phosphatidylserine, phosphatidylinositol, and phosphatidylglycerol. Among the phospholipid-bound fatty acids in extracellular vesicles, C181 predominated in Pb3, whereas C18:2 prevailed in Pb18. the prevalent sterol in Pb3 and Pb18 vesicles was brassicasterol, followed by ergosterol and lanosterol. Inter-isolate differences in sterol composition were observed, and also between extracellular vesicles and whole cells.Conclusions/Significance: the extensive lipidomic analysis of extracellular vesicles from two P. brasiliensis isolates will help to understand the composition of these fungal components/organelles and will hopefully be useful to study their biogenesis and role in host-pathogen interactions.Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)National Institutes of Health (NIH)Universidade Federal de São Paulo, UNIFESP, Dept Microbiol Imunol & Parasitol, São Paulo, BrazilUniv Texas El Paso, Dept Biol Sci, Border Biomed Res Ctr, El Paso, TX 79968 USAUniversidade Federal de São Paulo, UNIFESP, Dept Microbiol Imunol & Parasitol, São Paulo, BrazilFAPESP: 06/05095-6FAPESP: 07/04757-8FAPESP: 07/59768-4CNPq: 301666/2010-5National Institutes of Health (NIH): 5G12RR008124-16A1National Institutes of Health (NIH): 5G12RR008124-16A1S1National Institutes of Health (NIH): G12MD007592Web of Scienc