Mutational analyses of human eIF5A-1-identification of amino acid residues critical for eIF5A activity and hypusine modification

The eukaryotic translation initiation factor 5A (eIF5A) is the only protein that contains hypusine [N-epsilon-(4-amino-2-hydroxybutyl)lysine], which is required for its activity. Hypusine is formed by post-translational modification of one specific lysine (Lys50 for human eIF5A) by deoxyhypusine synthase and deoxyhypusine hydroxylase. To investigate the features of eIF5A required for its activity, we generated 49 mutations in human eIF5A-1, with a single amino acid substitution at the highly conserved residues or with N-terminal or C-terminal truncations, and tested mutant proteins in complementing the growth of a Saccharomyces cerevisiae eIF5A null strain. Growth-supporting activity was abolished in only a few mutant eIF5As (K47D, G49A, K50A, K50D, K50I, K50R, G52A and K55A), with substitutions at or near the hypusine modification site or with truncation of 21 amino acids from either the N-terminus or C-terminus. The inactivity of the Lys50 substitution proteins is obviously due to lack of deoxyhypusine modification. In contrast, K47D and G49A were effective substrates for deoxyhypusine synthase, yet failed to support growth, suggesting critical roles of Lys47 and Gly49 in eIF5A activity, possibly in its interaction with effector(s). By use of a UBHY-R strain harboring genetically engineered unstable eIF5A, we present evidence for the primary function of eIF5A in protein synthesis. When selected eIF5A mutant proteins were tested for their activity in protein synthesis, a close correlation was observed between their ability to enhance protein synthesis and growth, lending further support for a central role of eIF5A in translation.

Thermo-reversible sol-gel transition of TiO2 nanoparticles with surface modified by p-toluene sulfonic acid

In this paper an unprecedent thermo-reversible sol-gel transition for titania nanoparticles dispersed in a solution of p-toluene sulfonic acid (PTSH) in isopropanol is reported. The sol formed by the thermo-hydrolysis at 60 degrees C of titanium tetraisopropoxide (Ti((OPr)-Pr-i)(4)) reversibly changes into a turbid gel upon cooling to room temperature. Turbidimetric measurements performed for samples containing different nominal acidity ratios (A = [PTSH]/[Ti]) have evidenced that the gel transformation temperature increases from 20 to 35 degrees C as the [PTSH]/[Ti] ratio increases from 0.2 to 2.0. SAXS results indicate that the thermo-reversible gelation is associated to a reversible aggregation of a monodisperse set of titania nanoparticles with average gyration radius of approximate to 2 nm. From the different PTSH species evidenced by Raman spectroscopy and TG/DTA of dried gels we proposed that the then-no-reversible gelation in this systems is induced by the formation of a supramolecular network, in which the protonated surface of nanoparticles is interconnected through cooperative hydrogen bonds between -SO3 groups of p-toluene sulfonic acid. (C) 2009 Elsevier Ltd. All rights reserved.

Structural and properties of nanocrystalline WO3/TiO2-based humidity sensors elements prepared by high energy activation

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

DFT Study with Inclusion of the Grimme Potential on Anatase TiO2: Structure, Electronic, and Vibrational Analyses

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Influence of TiO2 and AI(2)O(3) on the electrical and microstructural properties of SnO2 ceramics obtained by the Pechini method

Tin oxide has wakened up great scientific and technological interest for its potential use in varistors production and as gas sensor. In order to improve the microstructural and electrical properties in SnO2 varistor ceramics, the influence of differents dopants used, like TiO2 and Al2O3, is under research. The effect of TiO2 and Al2O3 on the properties of Sn-Co-Nb varistor systems obtained by the Pechini method has been investigated in this work. Characterization of synthesized raw material was performed by X-Ray Diffraction (XRD) and Scanning Electronic Microscopy (SEM). The microstructural and electrical characterization of sintered samples show that the TiO2 favors the grain growth and the Al2O3 contributes to the decrease it, effect that is manifested in the Sn-Co-Nb varistor systems. Breakdown field increase up to 6300V/cm with increasing Al2O3 content and non-linear coefficients with alpha=22 were obtained.

Dielectric properties of soft chemical method derived CaCu3Ti4O12 thin films onto Pt/TiO2/Si(100) substrates

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Micellar modification of drug stability: analysis of the effect of hexadecyltrimethylammonium halides on the rate of degradation of cephaclor

The intra- and intermolecular rates of degradation of cephaclor were determined with and without hexadecyltrimethylammonium bromide (CTABr). Micellar-derived spectral shifts were used to measure the association of the ionic forms as well as to determine the effect of CTABr on the apparent acid dissociation constant of the antibiotic. The rate of degradation of cephaclor increased with detergent and was salt sensitive. Micellar effects were analyzed quantitatively within the frame-work of the speudophase ion exchange model. All experimental data were fitted to this model which was used to predict the combined effects of pH and detergent concentration. Micelles increased the rate of OH- attack on cephaclor; most of the effect was due to the concentration of reagents in the micellar pseudophase. The intramolecular degradation was catalyzed 25-fold by micelles, and a working hypothesis to rationalize this effect is proposed. The results demonstrate that quantitative analysis can be utilized to assess and predict effects of detergents on drug stability.

A surface modification for hydrogen storage intermetallic particles by sol-gel method

A new process for the surface modification of hydrogen storage intermetallic particles used as anode material in secondary batteries is proposed in this article. The copper oxide particles coverage obtained by the sol-gel method is proposed to produce, under operational conditions of a Ni-MH battery, a metallic framework that tolerates the volume changes in charge/discharge cycles and does not inhibit the hydrogen absorption. Furthermore it was noticed an enhancement on the discharge capacity of the electrode material that can be related to a new hydrogen storage phase or to an inhibition of the surface oxidation promoted by the film coverage.

Evaluation of the combined solar TiO2/photo-Fenton process using multivariate analysis

The effect of combining the photocatalytic processes using TiO 2 and the photo-Fenton reaction with Fe3+ or ferrioxalate as a source of Fe2+ was investigated in the degradation of 4-chlorophenol (4CP) and dichloroacetic acid (DCA) using solar irradiation. Multivariate analysis was used to evaluate the role of three variables: iron, H2O2 and TiO2 concentrations. The results show that TiO2 plays a minor role when compared to iron and H2O2 in the solar degradation of 4CP and DCA in the studied conditions. However, its presence can improve TOC removal when H2O2 is totally consumed. Iron and peroxide play major roles, especially when Fe(NO3)3 used in the degradation of 4CP. No significant synergistic effect was observed by the addition of TiO 2 in this process. On the other hand, synergistic effects were observed between FeOx and TiO2 and between H 2O2 and TiO2 in the degradation of DCA. © IWA Publishing 2004.

Anelastic spectroscopy in TiO2

Titanium dioxide (rutile) has a lot of interesting and useful features and hence is widely utilized for application. It has been used as white pigment, photocatalyst, biocompatible material and semiconductor material used in solar battery. In semiconducting TiO2 oxygen vacancies are said to play an important role in the electrical conduction. Measurements of the elastic energy loss and modulus (anelastic spectroscopy) as a function of temperature can distinguish among the different atomic jumps, which occur in the various phases or at different local ordering. In this paper, it is reported anelastic relaxation measurements in TiO2 samples using a torsion pendulum operating in frequencies around 40Hz, in the temperature range between -173°C to 330°C with heating rate of 1°C/min. The results shown a reduction in the elasticity modulus with the increase in the corn starch content used for this consolidation.

Inactivation of vesicular stomatitis virus through inhibition of membrane fusion by chemical modification of the viral glycoprotein

Membrane fusion is an essential step in the entry of enveloped viruses into their host cells triggered by conformational changes in viral glycoproteins. We have demonstrated previously that modification of vesicular stomatitis virus (VSV) with diethylpyrocarbonate (DEPC) abolished conformational changes on VSV glycoprotein and the fusion reaction catalyzed by the virus. In the present study, we evaluated whether treatment with DEPC was able to inactivate the virus. Infectivity and viral replication were abolished by viral treatment with 0.5 mM DEPC. Mortality profile and inflammatory response in the central nervous system indicated that G protein modification with DEPC eliminates the ability of the virus to cause disease. In addition, DEPC treatment did not alter the conformational integrity of surface proteins of inactivated VSV as demonstrated by transmission electron microscopy and competitive ELISA. Taken together, our results suggest a potential use of histidine (His) modification to the development of a new process of viral inactivation based on fusion inhibition. © 2006 Elsevier B.V. All rights reserved.

Respuesta eléctrica de películas gruesas del sistema SnO2-TiO2, conformadas con polvos cerámicos obtenidos a través del método pechini

Tin oxide is the compound more used in the gas sensor production, mainly to reduce gases like CO and H2. Their electrical properties are strongly dependent of its surface. For this is of great importance to synthesize nanoscale tin oxide particles to use they later in the films conformation. The synthesis of SnO2-TiO2 nanoparticles by polymeric precursor method is reported in this work. The particles were characterized by DTA/TG, FT-IR, XRD and SEM. Also, the electrical response of thick films measured under oxygen and carbon monoxide atmospheres is was analyzed.