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Coronado M.A.,Sao Paulo State University | Coronado M.A.,University of Hamburg | Gabdulkhakov A.,Russian Academy of Sciences | Georgieva D.,University of Hamburg | And 4 more authors.
Acta Crystallographica Section D: Biological Crystallography | Year: 2013

The crystal structure of the myotoxic, cell-penetrating, basic polypeptide crotamine isolated from the venom of Crotalus durissus terrificus has been determined by single-wavelength anomalous dispersion techniques and refined at 1.714;Å resolution. The structure reveals distinct cationic and hydrophobic surface regions that are located on opposite sides of the molecule. This surface-charge distribution indicates its possible mode of interaction with negatively charged phospholipids and other molecular targets to account for its diverse pharmacological activities. Although the sequence identity between crotamine and human β-defensins is low, the three-dimensional structures of these functionally related peptides are similar. Since crotamine is a leading member of a large family of myotoxic peptides, its structure will provide a basis for the design of novel cell-penetrating molecules. © 2013 International Union of Crystallography Printed in Singapore - all rights reserved. © 2013. Source

Almeida B.M.,University of Campinas | Melo Jr M.A.,University of Campinas | Bettini J.,National Center for Energy and Materials Research | Benedetti J.E.,University of Campinas | Nogueira A.F.,University of Campinas
Applied Surface Science | Year: 2015

A novel nanocomposite composed of TiO2 and Cu2O nanoparticles combined with reduced graphene oxide (RGO) was synthesized and characterized. X-ray diffraction (XRD), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), UV-vis diffuse reflectance spectroscopy (UV-vis DRS), X-ray photoelectron spectroscopy (XPS), thermogravimetry (TG) and elemental analysis were employed to investigate the structure, morphology, optical properties and composition of the nanocomposite and the intermediate materials. The photocatalytic activity of TiO2/Cu2O/RGO and the individual materials were studied through the photodegradation of methylene blue under solar radiation. A considerable increase in the photodegradation activity using the nanocomposite was obtained after 5 h (∼95% of MB degradation). Photoelectrochemical studies were carried out and confirmed the superiority of the novel nanocomposite in the photocurrent generation. The highest activity resulted from the synergy of this carbonaceous structure with TiO2 and Cu2O, which could absorb a wider portion of the solar spectrum, adsorb higher quantities of methylene blue on the surface and improve the effective separation of the generated electron-hole pairs. © 2014 Elsevier B.V. All rights reserved. Source

Benedetti J.E.,University of Campinas | Bernardo D.R.,University of Campinas | Morais A.,University of Campinas | Bettini J.,National Center for Energy and Materials Research | Nogueira A.F.,University of Campinas
RSC Advances | Year: 2015

'Together we are stronger' In this work, the preparation of the quaternary nanocomposite TiO2/CdS/rGO/Pt is reported along with its application, for the first time, as a catalyst for the photocatalytic reduction of carbon dioxide (CO2) to methane (CH4). TiO2/CdS nanoparticles and Pt nanoparticle-decorated reduced graphene oxide sheets (rGO/Pt) were synthesized separately and characterized through X-ray diffraction (XRD), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HR-TEM), Raman spectroscopy, UV-vis spectroscopy and photoelectrochemical experiments. Hydrocarbon samples were collected and analysed using gas chromatography (GC). After 5 hours of illumination under visible light, 0.11 μmol of CH4 was produced at an average production rate of 0.0867 μmol h-1, which is higher than the production of CH4 measured from the TiO2/CdS and the TiO2/CdS/Pt control samples. The photoelectrochemical experiments confirmed that the presence of rGO sheets in the nanocomposite enhanced the electrochemical and photocatalytic properties of the nanocomposite as a result of rapid electron transport and the inhibition of charge recombination. © The Royal Society of Chemistry 2015. Source

Da Silva L.L.,University of Campinas | Galembeck F.,University of Campinas | Galembeck F.,National Center for Energy and Materials Research
Journal of Materials Chemistry A | Year: 2015

Freeze-casting liquid dispersions of solid particles is a useful alternative for synthesizing porous solids, thus creating lightweight and mechanically resistant materials for various applications. This work describes and discusses different morphologies obtained by freeze-casting poly(styrene-acrylic) latex aqueous dispersions, either pristine or foamed, and compares them with those prepared by the addition of nanoclay. The surface area and dye sorption capacity of freeze-cast latex-clay nanocomposite monoliths are much higher than those of the freeze-cast latex only and the pore morphology is also different in these solids. The freeze-cast polymer displays an interesting morphology including a fishbone shape unprecedented in non-crystalline solids cast from aqueous media. Quite differently, the latex-clay nanocomposite exhibits only lamellar pores with irregular features on their walls. These differences are assigned to the stiffening role of the clay lamellae in the rubbery polymer, reducing the extent of particle aggregation and coalescence and thus preserving voids. Dispersion foaming prior to freeze-casting produces additional features in the solids but without making a positive contribution to the surface area and dye sorption capacity. These results are understood considering pore templating by ice crystal growth and the templating effect of clay particles on fine ice morphology. © The Royal Society of Chemistry 2015. Source

Burgo T.A.L.,University of Campinas | Silva C.A.,University of Campinas | Balestrin L.B.S.,University of Campinas | Galembeck F.,University of Campinas | Galembeck F.,National Center for Energy and Materials Research
Scientific Reports | Year: 2013

Friction between dielectric surfaces produces patterns of fixed, stable electric charges that in turn contribute electrostatic components to surface interactions between the contacting solids. The literature presents a wealth of information on the electronic contributions to friction in metals and semiconductors but the effect of triboelectricity on friction coefficients of dielectrics is as yet poorly defined and understood. In this work, friction coefficients were measured on tribocharged polytetrafluoroethylene (PTFE), using three different techniques. As a result, friction coefficients at the macro-and nanoscales increase many-fold when PTFE surfaces are tribocharged, but this effect is eliminated by silanization of glass spheres rolling on PTFE. In conclusion, tribocharging may supersede all other contributions to macro-and nanoscale friction coefficients in PTFE and probably in other insulating polymers. Source

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