Redução de mercúrio iônico por substâncias húmicas aquáticas

Pós-graduação em Química - IQ

Effect of acid etching time on the degradation of resin-dentin bonds in primary teeth

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

A structural conformation study of aquatic humic acid

In the present work, aquatic humic substances (HS) were extracted by use of adsorbent XAD 8 and the acid humic fraction (AH) was separated throught acidification. After being purified by Hyphan resin and dialyze, the aquatic AH was characterized using Fourier-transform infrared spectroscopy and elemental analysis. The influence of the aquatic HA and electrolyte concentrations, pH and aquatic AH-metal complexation time on the conformation was investigated using UV/Vis spectroscopic studies, employing the equation suggested by Doty and Steiner. The results indicated that the acid humic flexible macromolecule assumes a condensed form at acid and alkaline pH. Other factors favoring condensed conformations are longer metal complexation time (ageing) and higher aquatic AH and electrolyte concentrations. Thus considering the strong influence of the investigated parameters in the structural conformation of the humic macromolecule, we conclude that studies using UV/Vis spectroscopy to estimate the concentration, aromaticity, humification degree of the aquatic AH and so on, require rigorous control over the experimental conditions employed to provide a correct interpretation of the analytical results. ©2006 Sociedade Brasileira de Química.

Resin microtensile bond strength to feldspathic ceramic: Hydrofluoric acid etching vs tribochemical silica coating

This study aimed to compare the microtensile bond strength of resin cement to alumina-reinforced feldspathic ceramic submitted to acid etching or chairside tribochemical silica coating. Ten blocks of Vitadur-α were randomly divided into 2 groups according to conditioning method: (1) etching with 9.6% hydrofluoric acid or (2) chairside tribochemical silica coating. Each ceramic block was luted to the corresponding resin composite block with the resin cement (Panavia F). Next, bar specimens were produced for microtensile testing. No significant difference was observed between the 2 experimental groups (Student t test, P> .05). Both surface treatments showed similar microtensile bond strength values.

Length of resin tags in pit-and-fissure sealants: all-in-one self-etching adhesive vs phosphoric acid etching.

PURPOSE: To investigate the penetration (tags) of adhesive materials into enamel etched with phosphoric acid or treated with a self-etching adhesive, before application of a pit-and-fissure sealant. MATERIALS AND METHODS: The sample comprised six study groups with six specimens each. Before pit-and-fissure sealing with the materials Clinpro SealantTM (Groups I and II), Vitro Seal ALPHA (Groups III and IV) and Fuji II LC (Groups V and VI), the teeth in Groups I, III, and V were etched with 35% phosphoric acid for 30 seconds. Teeth in Groups II, IV, and VI received application of the self-etching adhesive Adper Prompt L-Pop. The treated teeth were sectioned buccolingually, ground to 100-microm thickness, decalcified, and analyzed by conventional light microscopy at 400x magnification. RESULTS: The teeth etched with phosphoric acid exhibited significantly greater penetration than specimens treated with self-etching adhesive. CLINICAL SIGNIFICANCE: When compared with enamel treated with a self-etching adhesive, the penetration (tags) of adhesive materials into enamel was greater when applied on enamel etched with phosphoric acid.

Can Heat Treatment Procedures of Pre-hydrolyzed Silane Replace Hydrofluoric Acid in the Adhesion of Resin Cement to Feldspathic Ceramic?

Purpose: To evaluate the influence of heat treatment (HT) procedures of a pre-hydrolyzed silane on bond strength of resin cement to a feldspathic ceramic.Materials and Methods: Ceramic and composite blocks (N = 30) were divided into six groups (n = 5) and subjected to the following conditioning procedures: G1: 9.6% hydrofluoric acid (HF) for 20 s + silane (RelyX Ceramic Primer, 3M ESPE) + resin cement (Panavia F2.0, Kuraray) (control); G2: HF (20 s) + silane + heat treatment in furnace (HTF) (100 degrees C, 2 min) + resin cement; G3: silane + HTF + resin cement; G4-HF (20 s) + silane + heat treatment with hot air (HTA) (50 +/- 5 degrees C for 1 min) + resin cement; G5: silane + HTA + resin cement; G6: silane + resin cement. The microtensile bond strength (MTBS) test was performed using a universal testing machine (1 mm/min). After debonding, the substrate and adherent surfaces were analyzed using a stereomicroscope and SEM to categorize the failure types. The data were statistically evaluated using one-way ANOVA and Tukey's test (5%).Results: The control group (G1) showed no pre-test failures and presented significantly higher mean MTBS (16.01 +/- 1.12 MPa) than did other groups (2.63 +/- 1.05 to 12.55 +/- 1.52 MPa) (p = 0.0001). In the groups where HF was not used, HTF (G3: 12.55 +/- 1.52 MPa) showed significantly higher MTBS than did HTA (G5: 2.63 +/- 1.05 MPa) (p < 0.05). All failure types were mixed, ie, adhesive between the resin cement and ceramic accompanied by cohesive failure in the cement.Conclusion: Heat treatment procedures for the pre-hydrolyzed silane either in a furnace or with the application of hot air cannot replace the use of HF gel for the adhesion of resin cement to feldspathic ceramic. Yet when mean bond strengths and incidence of pre-test failures are considered, furnace heat treatment delivered the second best results after the control group, being considerably better than hot air application.

Oxidation of amino acids by chlorpromazine cation radical and co-catalysis by chlorpromazine

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

Protocatechuic Acid Alkyl Esters: Hydrophobicity As a Determinant Factor for Inhibition of NADPH Oxidase

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

Evaluation of the kinetics of xylose formation from dilute sulfuric acid hydrolysis of forest residues of Eucalyptus grandis

Dilute acid hydrolysis studies were performed on forest residues of Eucalyptus grandis, in a cylindrical reactor of stainless steel. The kinetics of this hydrolysis reaction was investigated employing 0.65% sulfuric acid, a residue/acid solution ratio of 1/9 (w/w), temperatures of 130, 140, 150, and 160 degrees C, and reaction times in the range 20-100 min. The results showed that, under the optimized conditions of acid hydrolysis employed in this study, the variables temperature and reaction time had a strong influence on hemicellulose removal and a small influence on the degree of lignin and cellulose removal. The highest xylose extraction yield was 87.6% attained at 160 degrees C, after 70 min reaction time, simultaneously with the formation of decomposition products, namely 2.8% acetic acid, 0.6% furfural, and 0.06% 5-hydroxymethylfurfural. A similar xylose extraction yield (82.8%) was observed at 150 degrees C after 100 min, with the formation of 3.2% acetic acid, 1.0% furfural, and 0.07% 5-hydroxymethylfurfural. The kinetic parameters determined at 130, 140, 150, and 160 degrees C for degradation of xylan present in the hemicellulose of the eucalyptus forest residue during the formation of xylose were the first-order reaction rate constants (k) for each temperature, 1.22 x 10(-4), 2.12 x 10(-4), 5.43 x 10(-4), and 9.05 x 10(-4) s(-1), respectively, and an activation energy (E-a) of 101.3 kJ mol(-1).

High plasma uric acid concentration: causes and consequences

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Effects of chronic acetazolamide administration on gas exchange and acid-base control in pulmonary circulation in exercising horses

P>Reasons for performing study:Carbonic anhydrase (CA) catalyses the hydration/dehydration reaction of CO(2) and increases the rate of Cl- and HCO(3)- exchange between the erythrocytes and plasma. Therefore, chronic inhibition of CA has a potential to attenuate CO(2) output and induce greater metabolic and respiratory acidosis in exercising horses.Objectives:To determine the effects of Carbonic anhydrase inhibition on CO(2) output and ionic exchange between erythrocytes and plasma and their influence on acid-base balance in the pulmonary circulation (across the lung) in exercising horses with and without CA inhibition.Methods:Six horses were exercised to exhaustion on a treadmill without (Con) and with CA inhibition (AczTr). CA inhibition was achieved with administration of acetazolamide (10 mg/kg bwt t.i.d. for 3 days and 30 mg/kg bwt before exercise). Arterial, mixed venous blood and CO(2) output were sampled at rest and during exercise. An integrated physicochemical systems approach was used to describe acid base changes.Results:AczTr decreased the duration of exercise by 45% (P < 0.0001). During the transition from rest to exercise CO(2) output was lower in AczTr (P < 0.0001). Arterial PCO(2) (P < 0.0001; mean +/- s.e. 71 +/- 2 mmHg AczTr, 46 +/- 2 mmHg Con) was higher, whereas hydrogen ion (P = 0.01; 12.8 +/- 0.6 nEq/l AczTr, 15.5 +/- 0.6 nEq/l Con) and bicarbonate (P = 0.007; 5.5 +/- 0.7 mEq/l AczTr, 10.1 +/- 1.3 mEq/l Con) differences across the lung were lower in AczTr compared to Con. No difference was observed in weak electrolytes across the lung. Strong ion difference across the lung was lower in AczTr (P = 0.0003; 4.9 +/- 0.8 mEq AczTr, 7.5 +/- 1.2 mEq Con), which was affected by strong ion changes across the lung with exception of lactate.Conclusions:CO(2) and chloride changes in erythrocytes across the lung seem to be the major contributors to acid-base and ions balance in pulmonary circulation in exercising horses.

Histometric Analysis of Bone Repair in Bone-Implant Interface Using a Polylactic/Polyglycolic Acid Copolymer Associated With Implants in Rabbit Tibia

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

Hybrid layer thickness and resin tag length of a self-etching adhesive bonded to sound dentin

Objectives: the purpose of this study is to employ optical microscopy to measure the thickness of the hybrid layer and the penetration (tags) of an aggressive self-etching adhesive system into sound dentin.Methods: occtusat cavities were prepared in 40 extracted human posterior teeth. The prepared teeth were randomly assigned to four experimental groups with 10 specimens each. The self-etching adhesive system Adper Prompt L-Pop was applied to the dentin surface as follows: Group 1: cavosurface enamel was etched for 60 s and dentin for 20 s with 35% phosphoric acid get, immediately followed by application of the self -etching adhesive with a brush to the entire cavity for 15 s; Groups 2, 3, and 4: no pre-etching was performed, and the self -etching adhesive was applied to both enamel and dentin for 15, 30 and 45 s, respectively. After curing, the cavities were fitted with composite resin Fittek Z250. Afterwards, the teeth were decalcified and the restorations were carefully removed for later embedding in paraffin. The specimens were serially sectioned at 6 mu m of thickness and sequentially mounted in glass slides. These sections were stained with Brown and Brenn staining for posterior analysis and measurement of the hybrid layer and resin tags on a tight microscope with a micrometric ocular 40/075. The results were submitted to analysis of variance at the 5% level.Results: whenever there was significance, the Tukey test was applied at the 5% level. The specimens receiving application of acid etching before the selfetching. adhesive displayed a larger thickness of the hybrid layer; on the other hand, specimens receiving only application of the self -etching adhesive on dentin for 15, 30 and 45 s exhibited similar thickness of the hybrid layer. As regards the resin tags, no statistically significant differences could be found between the study groups.Conclusions: it could be concluded that the increase in the time of application of the self-etching adhesive Adper Prompt L-Pop did not significantly influence the formation and thickness of hybrid layer, as well as its penetration into the sound dentin surface. (c) 2005 Elsevier Ltd. All rights reserved.

Short-term evaluation of the pulpo-dentin complex response to a resin-modified glass-ionomer cement and a bonding agent applied in deep cavities

Objectives. To evaluate the response of the pulpo-dentin complex following application of a resin-modified glass-ionomer cement or an adhesive system in deep cavities performed in human teeth.Methods. Deep class V cavities were prepared on the buccal surface of 26 premolars. In Group I the cavity walls (dentin) and enamel were conditioned with 32% phosphoric acid and the dentin adhesive system One Step (Bisco, Inc., Itasca, IL, USA) was applied. In Groups 2 and 3, before total etching and application of bonding agent, the cavity floor was lined with the resin-modified glass-ionomer cement-Vitrebond (3M ESPE Dental Products Division, St. Paul, MN, USA) or the calcium hydroxide cement-Dycal (control group, Dentsply, Mildford, DE, USA), respectively. The cavities were restored using light-cured Z-100 composite resin (3M ESPE). The teeth were extracted between 5 and 30 days and prepared for microscopic assessment. Serial sections were stained with H/E, Masson's trichrome, and Brown and Brenn techniques.Results. In Group 1, the inflammatory response was more evident than in Groups 2 and 3. Diffusion of dental material components across dentinal tubules was observed only in Group 1, in which the intensity of the pulp response increased as the remaining dentin thickness decreased. Bacteria were evidenced in the lateral walls of two samples (Group 2) which exhibited no inflammatory response or tissue disorganization.Conclusions. Based on the experimental conditions, it was concluded total acid etching followed by application of One Step bonding agent cannot be recommended as adequate procedures. In this clinical condition the cavity walls should be lined with a biocompatible dental material, such as Vitrebond or Dycal. 2003 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.

Chlorhexidine increases the longevity of in vivo resin-dentin bonds

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)