Densification and coarsening of SnO2-based materials containing manganese oxide

The present work presents results on natural sintering of tin dioxide ceramics, prepared by a chemical route or by conventional mixing and containing manganese (X-Mn = Mn/(Mn + Sn)(atomic) with 0 less than or equal to X(Mn)less than or equal to 0.15). This cation, which is practically insoluble in SnO2 network, stays at the grain surface. During thermal treatment (500 degrees C less than or equal to T-s less than or equal to 1400 degrees C), as long as the manganese surface concentration is lower than a critical value, equal to 5.10(-6) mol m(-2), no densification takes place. As soon as this value is reached, densification and grain growth occur simultaneously. The shrinkage kinetics is fast and high rho/rho(t) values can be obtained (for example. rho/rho(t)=0.95 for T-s=1300 degrees C and X-Mn=0.004). The dependence between manganese content, manganese distribution, grain size and sintering behaviour is also discussed. (C) 1998 Published by Elsevier B.V. Limited.

8-benzylberbine and N-oxide alkaloids from Aristolochia gigantea

From the ethanol extract of Aristolochia gigantea Mart an 8-benzylberbine-type alkaloid and an N-oxide were isolated together with pinitol and sequoyitol. Structural assignments were based on analysis of spectral data, mainly by 2D NMR spectroscopic techniques. (C) 1997 Elsevier B.V. Ltd.

Layer-by-layer hybrid films of polyaniline and vanadium oxide

Supramolecular structures of polyaniline (PANI) and vanadium oxide (V2O5) have been assembled via the electrostatic layer-by-layer (LBL) technique. The films were characterized by vibrational analyses which indicated that the interactions between the two components lead to different properties in the films when compared to sol-gel films. of the neat compounds. In particular, using surface enhanced Raman scattering we were able to probe LBL film properties that depend on which material comprises the topmost layer.

Study of structural surface modified tin oxide membrane prepared by sol-gel route sintered at 400 degrees C

This work describes the chemical modification by Tiron(R) molecules of the surface of SnO2 nanoparticles used to prepare nanoporous membranes. Samples prepared with Tiron(R) content between 1 and 20 wt% and fired at 400 C were characterised by X-Ray Powder Diffraction (XRPD), Extended X-ray Absorption Fine Structure (EXAFS), N-2 adsorption isotherms analysis and permeation experiments. XRPD and EXAFS results show a continuous reduction of crystallite size by increasing the Tiron(R) contents until 7.5 wt%. The control exercised by Tiron(R) modifying agent in crystallite growth allows the fine tuning of the average pore size that can be screened from 0.4 to 4 nm as the amount of grafted molecules decreases from 10 to 0 wt%. In consequence, the membrane cut-off can be screened from 1500 to 3500 g.mol(-1).

Study of synthesis variables in the nanocrystal growth behavior of tin oxide processed by controlled hydrolysis

Tin dioxide nanoparticle suspensions were synthesized at room temperature by the hydrolysis reaction of tin chloride (II) dissolved in ethanol. The effect of the initial tin (II) ion concentration, in the ethanolic solution, on the mean particle size of the nanoparticles was studied. The Sn2+ concentration was varied from 0.0025 to 0.1 M, and all other synthesis parameters were kept fixed. Moreover, an investigation of the effect of agglomeration on the nanoparticle characteristics (i.e., size and morphology) was also done by modifying the pH of the SnO2 suspensions. The different samples were characterized by transmission electron microscopy, optical absorption spectroscopy in the ultraviolet range, and photoluminescence measurements. The results show that higher initial ion concentrations and agglomeration lead to larger nanoparticles. The concentration effect is explained by enhanced growth due to a higher supersaturation of the liquid medium. However, it was observed that the agglomeration of the nanoparticles in suspension induce coarsening by the oriented-attachment mechanism.

Protective effect of prior physical conditioning on relaxing response of corpus cavernosum from rats made hypertensive by nitric oxide inhibition

The aim of this work was to evaluate the influence of run training on the responsiveness of corpus cavernosum (CC) from rats made hypertensive by treatment with nitric oxide (NO) synthesis inhibitor. Wistar rats were divided into sedentary control (C-SD), exercise training (C-TR), N(omega)-nitro-L-arginine methyl ester (L-NAME) sedentary (LN-SD) and L-NAME trained (LN-TR) groups. The run training program consisted in 8 weeks in a treadmill, 5 days/week, each session lasted 60 min. L-NAME treatment (2 and 10mg/rat/day) started after 4 weeks of prior physical conditioning and lasted 4 weeks. Concentration-response curves were obtained for acetylcholine (ACh), sodium nitroprusside (SNP), sildenafil and BAY 41-2272. The effect of electrical field stimulation (EFS) on the relaxations responses of CC was evaluated. Run training prevented the arterial hypertension induced by L-NAME treatment (LN-SD: 135+/-2 and 141+/-2 mm Hg for both doses of L-NAME) compared to LN-SD groups (154+/-1 and 175+/-2 mm Hg, for 2 and 10 mg of L-NAME, respectively). Run training produced an increase in the maximal responses (E(max)) of CC for ACh (C-SD: 47+/-3; C-TR: 5271; and LN-TR: 53+/-3%) and SNP (C-SD: 8971; C-TR: 9871; and LN-TR: 95+/-1%). Both potency and E(max) for ACh were reduced in a dose of 10 mg of L-NAME, and run training restored the reduction of E(max) for ACh. No changes were found for BAY 41-2271 and sildenafil. Relaxing responses to EFS was reduced by L-NAME treatment that was restored by prior physical conditioning. In conclusion, our study shows a beneficial effect of prior physical conditioning on the impaired CC relaxing responses in rats made hypertensive by chronic NO blockade.

Femtosecond nonlinear optical properties of lead-germanium oxide amorphous films

The nonlinear (NL) response of lead-germanium oxide amorphous films was investigated using a Ti:saphire laser delivering pulses of approximate to 150 fs at 800 nm. The Kerr shutter technique was employed to reveal the time response of the nonlinearity that is smaller than 150 fs. The sign and magnitude of the nonlinearity were obtained using a novel technique called thermally managed eclipse Z scan which allows the simultaneous characterization of cumulative and noncumulative NL effects. The NL refractive index of electronic origin, n(2)approximate to 2x10(-17) m(2)/W, and the NL absorption coefficient, alpha(2)approximate to 3x10(3) cm/GW, were determined. (c) 2007 American Institute of Physics.

Indium tin oxide films prepared via wet chemical route

In this work, indium tin oxide (ITO) films were prepared using a wet chemical route, the Pechini method. This consists of a polyesterification reaction between an alpha-hydroxicarboxylate complex (indium citrate and tin citrate) with a polyalcohol (ethylene glycol) followed by a post annealing at 500 degrees C. A 10 at.% of doping of Sn4+ ions into an In2O3 matrix was successfully achieved through this method. In order to characterize the structure, the morphology as well as the optical and electrical properties of the produced ITO films, they were analyzed using different experimental techniques. The obtained films are highly transparent, exhibiting transmittance of about 85% at 550 nm. They are crystalline with a preferred orientation of [222]. Microscopy discloses that the films are composed of grains of 30 nm average size and 0.63 nm RMS roughness. The films' measured resistivity, mobility and charge carrier concentration were 5.8 x 10(-3) Omega cm, 2.9 cm(2)/V s and -3.5 x 10(20)/cm(3), respectively. While the low mobility value can be related to the small grain size, the charge carrier concentration value can be explained in terms of the high oxygen concentration level resulting from the thermal treatment process performed in air. The experimental conditions are being refined to improve the electrical characteristics of the films while good optical, chemical, structural and morphological qualities already achieved are maintained. (C) 2007 Elsevier B.V. All rights reserved.

Inhibition of hydrogen peroxide, nitric oxide and TNF-alpha production in peritoneal macrophages by ethyl acetate fraction from Alchornea glandulosa

The effects of Alchornea glandulosa ethyl acetate fraction (AGF) on hydrogen peroxide (H2O2), nitric oxide (NO) and tumor necrosis factor-alpha (TNF-alpha) production in peritoneal macrophages activated with lipopolysaccharide (LPS) or phorbol myristate acetate (PMA) were investigated. Analysis by thin layer chromatography (TLC) of AGF showed several constituents, including flavonoids, which may have anti-inflammatory activity. Inhibitory effects of the fraction in H2O2 and NO production ranged from 8.59 +/- 7.84% to 70.56 +/- 4.16% and from 16.06 +/- 3.65% to 38.73 +/- 3.90%, respectively. The TNF-alpha production was only partially inhibited in the tested concentrations (12.21 +/- 6.23%-15.16 +/- 0.96%). According to these results, it is suggested that AGF has anti-inflammatory activity. This medicinal plant may have therapeutic potential in the control of inflammatory disorders.

Small angle X-ray scattering study of surface modified tin oxide nanoparticles prepared by sol-gel route

The surface properties of SnO2 nanoparticles were modified by grafting ionic (Tiron (R). (OH)(2)C6H2(SO3Na)(2)(H2O)-H-.) or non-ionic (Catechol (R). C6H4-1,2-(OH)(2)) capping Molecules during aqueous sol-gel processing to improve the redispersibility of powdered xerogel. The effect of the amount of grafted organic molecules on the redispersibility of powders in aqueous solution at several basic pH values was Studied. The nanostructural features of the colloidal suspensions were analyzed by small angle X-ray scattering (SAXS) measurements. Irrespective of the nature and amount of grafted molecules, complete redispersion was obtained in aqueous solution at pH = 13. The redispersion at pH = 11 results in a mixture of dispersed primary particles and aggregates. The proportion of well dispersed nanoparticles and aggregates (and their average size) can be tuned by the quantity of grafted ionic molecules.

Sintering and crystallite growth of nanocrystalline copper doped tin oxide

The effect of Cu2+ contents and of firing temperature on sintering and crystallite growth of nanocrystalline SnO2 xerogels was analyzed by thermoanalysis (mass loss (TG), linear shrinkage, and differential thermal analysis (DTA)), X-ray powder diffraction (XRPD), and EXAFS (extended X-ray absorption fine structures) measurements. Samples were prepared by two methods: (a) coprecipitation of a colloidal suspension from aqueous solution containing both Sn(IV) and Cu(II) ions and (b) grafting copper(II) species on the surface of tin pride gel. The thermoanalysis has shown that the shrinkage associated with the mass loss decreases by increasing the amount of copper. The EXAFS measurements carried out at the Cu K edge have evidenced the presence of copper in substitutional solid solution for the dried xerogel prepared with 0.7 mol % of copper, while for higher concentration of doping, copper has been observed also at the external surface of crystallites. The solid solution is metastable and copper migrates toward the surface during firing. The XRPD and DTA results have shown a recrystallization process near 320 degrees C, which leads to crystallite growth. The presence of copper segregated near the crystallite surface controls its growth.

Vascular effects of long-term propranolol administration after chronic nitric oxide blockade

Long-term propranolol treatment reduces arterial blood pressure in hypertensive individuals mainly by reducing peripheral vascular resistance, but mechanisms underlying their vasodilatory effect remain poorly investigated. This study aimed to investigate whether long-term propranolol administration ameliorates the impairment of relaxing responses of aorta and mesenteric artery from rats made hypertensive by chronic nitric oxide (NO) deficiency, and underlying mechanisms mediating this phenomenon. Male Wistar rats were treated with N-omega-Nitro-L-arginine methyl ester (L-NAME; 20 mg/rat/day) for four weeks. DL-Propranolol (30 mg/rat/day) was given concomitantly to L-NAME in the drinking water. Treatment with L-NAME markedly increased blood pressure, an effect largely attenuated by DL-propranolol. In phenylephrine-precontracted aortic rings, the reduction of relaxing responses for acetylcholine (0.001-10 mu M) in L-NAME group was not modified by DL-propranolol, whereas in mesenteric rings the impairment of acetylcholine-induced relaxation by L-NAME was significantly attenuated by DL-propranolol. In mesenteric rings precontracted with KCl (80 MM), DL-propranolol failed to attenuate the impairment of acetylcholine-induced relaxation by L-NAME. The contractile responses to extracellular CaCl2 (1-10 mM) were increased in L-NAME group, and co-treatment with DL-propranolol reduced this response in both preparations in most Ca2+ concentrations used. The NO2/NO3 plasma levels and superoxide dismutase (SOD) activity were reduced in L-NAME-treated rats, both of which were significantly prevented by DL-propranolol. In conclusion, propranolol-induced amplification of the relaxation to acetylcholine in mesenteric arteries from L-NAME-treated rats is sensitive to depolarization. Additional mechanisms involving blockade of Ca2+ entry in the vascular smooth muscle and increase in NO bioavailability contributes to beneficial effects of long-term propranolol treatment. (C) 2007 Elsevier B.V. All rights reserved.

Effect of Mouriri pusa extracts on experimentally induced gastric lesions in rodents: Role of endogenous sulfhydryls compounds and nitric oxide in gastroprotection

Several plants are used in folk medicine to treat gastrointestinal disorders. Mouriri pusa Gardn. (Melastomataceae) is a medicinal plant commonly used in the central region of Brazil against gastric ulcer. Two organic extracts methanolic (MeOH) and dichloromethane (DCM) obtained by sequential extraction from the leaves of Mouriri pusa were evaluated for their ability to protect the gastric mucosa against injuries caused by necrotizing agents (0.3 M HCl/60% EtOH, absolute ethanol, non-steroidal anti-inflammatory drug, stress and pylorus ligature) in mice and rats. The best results were obtained after pretreatment with MeOH extract whereas the DCM extract did not show the same significant antiulcerogenic activity. No acute toxicity was observed in animals treated with 5 g/kg, p.o. of MeOH extract. The mechanism involving the antiulcerogenic action of MeOH extract seemed to be related to NO generation and also suggested the effective participation of endogenous sulfhydryl group in the gastroprotective action. Phytochemical investigation of the MeOH extract of Mouriri pusa yielded tannins, flavonoids and (-)-epicatechin. The presence of these phenolic compounds probably would explain the antiulcerogenic effect of the polar extract of Mouriri pusa leaves. (c) 2006 Elsevier B.V.. All rights reserved.