Propriedades analíticas de materiais a base de sílica e óxido de titânio modificados

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

A cubic silsesquioxane modified with purpald (r) : preparation, characterization and a voltammetric application for determination of sulfite

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

A novel hybrid composite formed by reaction of 4,5-diphenyl-2-imidazolethiol with hexacyanoferrate (iii) and subsequent reaction with copper (ii): preparation, characterization and a voltammetric application for determination of l-glutatione

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

A Silsesquioxane Organically Modified with 4-Amino-5-(4-pyridyl)-4H-1,2,4-triazole-3-thiol: Thermal Behavior and Its Electrochemical Detection of Sulfhydryl Compounds

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

Voltammetric behaviour of a modified electrode with azide copper octa(3-aminopropyl)octasilsesquioxane composite in the oxidation of ascorbic acid

A novel nanostructured composite, azide copper octa (3-aminopropyl)octasilsesquioxane (ASCA) was incorporated into a graphite paste electrode and the electrochemical studies were conducted with cyclic voltammetry. The cyclic voltammogram of the modified graphite paste electrode with ASCA (GPE-ASCA), showed one redox couple with formal potential (E  ) = 0.30 V and an irreversible process at 1.1 V (vs Ag/AgCl; NaCl 1.0 mol L-1 ; v = 20 mV s-1 ). The redox couple with (E  ) = 0.30V presents an electrocatalytic response for determination of ascorbic acid. The modified electrode gives a linear range from 1.010-4 – 1.010-3 mol L-1 (r = 0.998) for the determination of ascorbic acid with detection limit of 6.910-5 mol L-1 and standard deviation of 2.3% for n = 3 . The amperometric sensitivity was 122.1 mA/mol L-1 for ascorbic acid. The application this electrode was tested and ascorbic acid in three commercial pharmaceutical product (Cebion, Cewin and Redoxon) have been determined.

Direct preparation and characterization of copper pentacyanonitrosylferrate nanoparticles

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

Voltammetric Behavior of a Chemically Modified Silsesquioxane with 4-Amino-5-Phenyl-4h-[1,2,4]-Triazole-3-Thiol and its Application for Detection of L-Dopamine

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

Electrochemical behaviour of (N-R-4-cyanopyridinium)pentaammineruthenium(II) derivatives in acidic medium. Hydrolysis of coordinated nitriles

The electrochemical behaviour of N-R-4-cyanopyridinium (4-rcp) (R = methyl, decyl, dodecyl, or benzyl) coordinated to pentaammineruthenium(II) in CF3COOH-CF3COONa (μ = 0.1 M, pH 3) aqueous medium was studied by means of cyclic voltammetry and constant potential electrolysis. The electrochemical oxidation of the metallic centre (Ep ca 0.51 V/SCE) can be described as a reversible monoelectronic charge-transfer followed by an irreversible chemical reaction, which is the hydrolysis of N-R-4-cyanopyridiniumpentaammineruthenium(III) (A) to N-R-4-carboxamidepyridiniumruthenium (III) (B) with the kf1 values depending on the type of alkyl group. The E 1 2 values are not significantly influenced by the nature of the alkyl group. At more negative potential (ca -0.5 V/SCE), B undergoes an electrochemical reduction followed by an aquation reaction to produce aquopentaammineruthenium(II) and free N-R-4-carboxamidepyridinium. The amide was identified by comparison of its cyclic voltammogram and UV-vis spectrum with that of a sample prepared by chemical reaction. The results were also discussed by comparison with other systems, and show that nitrile-amide conversion catalysed by pentaammineruthenium(II) complexes is possible. © 1994.

Open circuit interaction of borohydride with oxidized platinum surfaces

An interesting method to investigate the effect of fuel crossover in low temperature fuel cells consists of studying the open circuit interaction between the reducing fuel and an oxide-covered catalyst. Herein we report the experimental study of the open circuit interaction between borohydride and oxidized platinum surfaces in alkaline media. When compared to the case of hydrogen and other small organic molecules, two remarkable new features were observed. Firstly, the interaction with borohydride resulted in a very-fast reduction process with transient times about two to three orders of magnitude smaller. The second peculiarity was that the decrease of the open circuit potential was found to occur in two-stages and this, previously unseen, feature was correlated with the two-hump profile found in the backward sweep in the cyclic voltammogram The consequences of our findings are discussed in connection with fundamental and applied aspects. (C) 2011 Elsevier B.V All rights reserved.

An electroanalytical application of 2-aminothiazole-modified silica gel after adsorption and separation of Hg(II) from heavy metals in aqueous solution

2-Aminothiazole covalently attached to a silica gel surface was prepared in order to obtain an adsorbent for Hg(II) ions having the following characteristics: good sorption capacity, chemical stability under conditions of use, and, especially, high selectivity. The accumulation voltammetry of mercury(II) was investigated at a carbon paste electrode chemically modified with silica gel functionalized with 2-aminothiazole (SIAMT-CPE). The repetitive cyclic voltammogram of mercury(II) solution in the potential range -0.2 to + 0.6 V versus Ag/AgCl (0.02 mol L-1 KNO3; V = 20 mV s(-1)) show two peaks one at about 0.1 V and other at 0.205 V. The anodic wave peak at 0.205 V is well defined and does not change during the cycles and it was therefore further investigated for analytical purposes using differential pulse anodic stripping voltammetry in differents supporting electrolytes. The mercury response was evaluated with respect to pH, electrode composition, preconcentration time, mercury concentration, cleaning solution, possible interferences and other variables. The precision for six determinations (n = 6) of 0.02 and 0.20 mg L-1 Hg(II) was 4.1 and 3.5% (relative standard deviation), respectively. The detection limit was estimated as 0.10 mu g L-1 mercury(II) by means of 3:1 current-to-noise ratio in connection with the optimization of the various parameters involved and using the highest-possible analyser sensitivity. (c) 2006 Elsevier Ltd. All rights reserved.

Effect of cyclic load on vertical misfit of prefabricated and cast implant single abutment

OBJECTIVES: The purpose of this in vitro study was to evaluate misfit alterations at the implant/abutment interface of external and internal connection implant systems when subjected to cyclic loading. MATERIAL AND METHODS: Standard metal crowns were fabricated for 5 groups (n=10) of implant/abutment assemblies: Group 1, external hexagon implant and UCLA cast-on premachined abutment; Group 2, internal hexagon implant and premachined abutment; Group 3, internal octagon implant and prefabricated abutment; Group 4, external hexagon implant and UCLA cast-on premachined abutment; and Group 5, external hexagon implant and Ceraone abutment. For groups 1, 2, 3 and 5, the crowns were cemented on the abutments and in group 4 crowns were screwed directly on the implant. The specimens were subjected to 500,000 cycles at 19.1 Hz of frequency and non-axial load of 133 N in a MTS 810 machine. The vertical misfit (μm) at the implant/abutment interface was evaluated before (B) and after (A) application of the cyclic loading. Data were analyzed statistically by using two-away ANOVA and Tukey's post-hoc test (p<0.05). RESULTS: Before loading values showed no difference among groups 2 (4.33±3.13), 3 (4.79±3.43) and 5 (3.86±4.60); between groups 1 (12.88±6.43) and 4 (9.67±3.08), and among groups 2, 3 and 4. However, groups 1 and 4 were significantly different from groups 2, 3 and 5. After loading values of groups 1 (17.28±8.77) and 4 (17.78±10.99) were significantly different from those of groups 2 (4.83±4.50), 3 (8.07±4.31) and 5 (3.81±4.84). There was a significant increase in misfit values of groups 1, 3 and 4 after cyclic loading, but not for groups 2 and 5. CONCLUSIONS: The cyclic loading and type of implant/abutment connection may develop a role on the vertical misfit at the implant/abutment interface.

Cyclic nitroxides inhibit the toxicity of nitric oxide-derived oxidants: mechanisms and implications

The substantial therapeutic potential of tempol (4-hydroxy-2,2,6,6-tetramethyl-1-piperidinyloxy) and related cyclic nitroxides as antioxidants has stimulated innumerous studies of their reactions with reactive oxygen species. In comparison, reactions of nitroxides with nitric oxide-derived oxidants have been less frequently investigated. Nevertheless, this is relevant because tempol has also been shown to protect animals from injuries associated with inflammatory conditions, which are characterized by the increased production of nitric oxide and its derived oxidants. Here, we review recent studies addressing the mechanisms by which cyclic nitroxides attenuate the toxicity of nitric oxidederived oxidants. As an example, we present data showing that tempol protects mice from acetaminophen-induced hepatotoxicity and discuss the possible protection mechanism. In view of the summarized studies, it is proposed that nitroxides attenuate tissue injury under inflammatory conditions mainly because of their ability to react rapidly with nitrogen dioxide and carbonate radical. In the process the nitroxides are oxidized to the corresponding oxammonium cation, which, in turn, can be recycled back to the nitroxides by reacting with upstream species, such as peroxynitrite and hydrogen peroxide, or with cellular reductants. An auxiliary protection mechanism may be down-regulation of inducible nitric oxide synthase expression. The possible therapeutic implications of these mechanisms are addressed.

Morphological features and vascularization study of caprine cyclic corpus luteum

Corpus luteum is a temporary endocrine gland that regulates either the estrous cycle and pregnancy. It presents extreme dependency on the adequate blood supply. This work aims to evaluate goat corpus luteum (CL) vascular density (VD) over the estrous cycle. For that purpose, 20 females were submitted to estrus synchronization/ovulation treatment using a medroxyprogesterone intra-vaginal sponge as well as intramuscular (IM) application of cloprostenol and equine chorionic gonadotrophine (eCG). After sponge removal, estrus was identified at about 72hs. Once treatment was over, female goats were then subdivided into 4 groups (n=5 each) and slaughtered on days 2, 12, 16 and 22 after ovulation (p.o). Ovaries were collected, withdrawn and weighted. CL and ovaries had size and area recorded. Blood samples were collected and the plasma progesterone (P4) was measured through RIA commercial kits. The VD was 24.42±6.66, 36.26±5.61, 8.59±2.2 and 3.97±1.12 vessels/mm² for days 2, 12, 16 and 22 p.o, respectively. Progesterone plasma concentrations were 0.49±0.08, 2.63±0.66, 0.61±0.14 and 0.22±0.04ng/ml for days 2, 12, 16 e 22 p.o, respectively. Studied parameters were affected by the estrous cycle phase. Values greater than 12 p.o were observed. In the present work we observed that ovulation occurred predominantly in the right ovary (70% of the animals), which in turn presented bigger measures than the contra lateral one. There is a meaningful relationship between the weight and size of the ovary and these of CL (r=0.87, r=0.70, respectively, p<0.05). It is possible to conclude that morphology of goat's ovaries and plasma progesterone concentration changed according to estrous cycle stages. We propose these parameters can be used as indicators of CL functional activity.

Cyclooligomerisation of azido-alkyne-functionalised sugars: synthesis of 1,6-linked cyclic pseudo-galactooligosaccharides and assessment of their sialylation by Trypanosoma cruzi trans-sialidase

Cyclic pseudo-galactooligosaccharides were synthesized by cyclooligomerisation of isomeric azido-alkyne derivatives of beta-D-galactopyranose under Cu(I)-catalysed azide-alkyne 1,3-dipolar cycloaddition reaction conditions. The principal products isolated were cyclic dimers and trimers, with lower amounts of cyclic tetramer and pentamer also evident in some cases. Molecular mechanics calculations suggest very compact but flexible structures for the cyclic trimers, with secondary OH groups exposed outside the macrocycle and available for enzymatic glycosylation. The cyclic dimers and trimers represent a new type of acceptor substrate for Trypanosoma cruzi trans-sialidase, giving rise to doubly and triply sialylated glycomacrocycles, respectively.

Cyclic variability of the circumstellar disk of the Be star zeta Tauri II. Testing the 2D global disk oscillation model

Context. About 2/3 of the Be stars present the so-called V/R variations, a phenomenon characterized by the quasi-cyclic variation in the ratio between the violet and red emission peaks of the HI emission lines. These variations are generally explained by global oscillations in the circumstellar disk forming a one-armed spiral density pattern that precesses around the star with a period of a few years. Aims. This paper presents self-consistent models of polarimetric, photometric, spectrophotometric, and interferometric observations of the classical Be star zeta Tauri. The primary goal is to conduct a critical quantitative test of the global oscillation scenario. Methods. Detailed three-dimensional, NLTE radiative transfer calculations were carried out using the radiative transfer code HDUST. The most up-to-date research on Be stars was used as input for the code in order to include a physically realistic description for the central star and the circumstellar disk. The model adopts a rotationally deformed, gravity darkened central star, surrounded by a disk whose unperturbed state is given by a steady-state viscous decretion disk model. It is further assumed that this disk is in vertical hydrostatic equilibrium. Results. By adopting a viscous decretion disk model for zeta Tauri and a rigorous solution of the radiative transfer, a very good fit of the time-average properties of the disk was obtained. This provides strong theoretical evidence that the viscous decretion disk model is the mechanism responsible for disk formation. The global oscillation model successfully fitted spatially resolved VLTI/AMBER observations and the temporal V/R variations in the H alpha and Br gamma lines. This result convincingly demonstrates that the oscillation pattern in the disk is a one-armed spiral. Possible model shortcomings, as well as suggestions for future improvements, are also discussed.