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PubMed | National Center for Energy and Materials Research and University of Sao Paulo
Type: Journal Article | Journal: The FEBS journal | Year: 2016

In a search for better comprehension of -galactosidase function and specificity, we solved the crystal structures of the GH42 -galactosidase BbgII from Bifidobacterium bifidum S17, a well-adapted probiotic microorganism from the human digestive tract, and its complex with d--galactose. BbgII is a three-domain molecule that forms barrel-shaped trimers in solution. BbgII interactions with d--galactose, a competitive inhibitor, showed a number of residues that are involved in the coordination of ligands. A combination of site-directed mutagenesis of these amino acid residues with enzymatic activity measurements confirmed that Glu161 and Glu320 are fundamental for catalysis and their substitution by alanines led to catalytically inactive mutants. Mutation Asn160Ala resulted in a two orders of magnitude decrease of the enzyme kStructural data are available in the PDB under the accession numbers 4UZS and 4UCF.

Burgo T.A.L.,University of Campinas | Ducati T.R.D.,University of Campinas | Francisco K.R.,University of Campinas | Clinckspoor K.J.,University of Campinas | And 3 more authors.
Langmuir | Year: 2012

Tribocharged polymers display macroscopically patterned positive and negative domains, verifying the fractal geometry of electrostatic mosaics previously detected by electric probe microscopy. Excess charge on contacting polyethylene (PE) and polytetrafluoroethylene (PTFE) follows the triboelectric series but with one caveat: net charge is the arithmetic sum of patterned positive and negative charges, as opposed to the usual assumption of uniform but opposite signal charging on each surface. Extraction with n-hexane preferentially removes positive charges from PTFE, while 1,1-difluoroethane and ethanol largely remove both positive and negative charges. Using suitable analytical techniques (electron energy-loss spectral imaging, infrared microspectrophotometry and carbonization/colorimetry) and theoretical calculations, the positive species were identified as hydrocarbocations and the negative species were identified as fluorocarbanions. A comprehensive model is presented for PTFE tribocharging with PE: mechanochemical chain homolytic rupture is followed by electron transfer from hydrocarbon free radicals to the more electronegative fluorocarbon radicals. Polymer ions self-assemble according to Flory-Huggins theory, thus forming the experimentally observed macroscopic patterns. These results show that tribocharging can only be understood by considering the complex chemical events triggered by mechanical action, coupled to well-established physicochemical concepts. Patterned polymers can be cut and mounted to make macroscopic electrets and multipoles. © 2012 American Chemical Society.

Sanfelici L.,National Center for Energy and Materials Research | De Mattos F.,National Center for Energy and Materials Research
Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment | Year: 2011

The MX2, a wiggler beamline dedicated to macromolecular crystallography, started routinely operating for users in 2007. Late in the commissioning phase, several experiments started to be conducted in order to characterize photon-beam stability. At that time, position movements of typically 150 μm per shift and severe energy drifts reaching 0.8 eV/h were observed at sample position, which would certainly spoil the MAD experiments. The severity of this scenario for a recently delivered beamline led us to install temperature sensors and inclinometers along the optical hutch, besides performing exhaustive tests to clarify the disturbance paths. To elucidate the main instability mechanisms, three control systems for beam stabilization were considered - position stabilization, ground motion canceling and, the most important of all, temperature control for the optical hutch. Results and perspectives are presented hereafter. © 2011 Elsevier B.V. All rights reserved.

Coronado M.A.,São 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.

Gouveia R.F.,University of Campinas | Bernardes J.S.,University of Campinas | Bernardes J.S.,National Center for Energy and Materials Research | Ducati T.R.D.,University of Campinas | And 2 more authors.
Analytical Chemistry | Year: 2012

Electrostatic potential at the surface of acidic or basic solids changes under higher relative humidity (RH), as determined by using Kelvin force microscopy (KFM). The potential on acid surfaces becomes more negative as the water vapor pressure increases, while it becomes more positive on basic solids. These results verify the following hypothesis: OH- or H+ ions associated with atmospheric water ion clusters are selectively adsorbed on solid surfaces, depending on the respective Brønsted acid or base character. Therefore, Kelvin microscopy, under variable humidity, is a rigorous but convenient alternative to determine the acid-base character of solid surfaces, with a great advantage: it uses only one amphoteric and simple reagent to determine both the acid and base sites. Moreover, this technique provides information on the spatial distribution of acid-base sites, which is currently inaccessible to any other method. © 2012 American Chemical Society.

Santos L.P.,University of Campinas | Bernardes J.S.,University of Campinas | Bernardes J.S.,National Center for Energy and Materials Research | Galembeck F.,University of Campinas | Galembeck F.,National Center for Energy and Materials Research
Langmuir | Year: 2013

Top and bottom surfaces of polyethylene (PE) films exposed to corona discharge display large and opposite electrostatic potentials, forming an electric bilayer in agreement with recent and unexpected findings from Zhiqiang et al. Water wetting, chemical composition and roughness of the two surfaces are different. Surprisingly, the bottom surface, opposite to the corona electrode is charged but it is not oxidized, neither is it wetted with water. Moreover, its morphology is unaltered by charging, while the hydrophilic top surface is much rougher with protruding islands that are the result of oxidation followed by phase separation and polymer-polymer dewetting. Common liquids extract the oxidized, hydrophilic material formed at the upper surface, a result that explains the well-known sensitivity of adhesive joints made using corona-treated thermoplastics to liquids, especially water. These results show that poling the surface closer to the corona electrode triggers another but different charge build-up process at the opposite surface. The outcome is another poled PE surface showing high potential but with unchanged chemical composition, morphology and wetting behavior as the pristine surface, thus opening new possibilities for surface engineering. © 2012 American Chemical Society.

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.

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.

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.

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.

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