High current-density anodic electro-dissolution in flow-injection systems for the determination of aluminium, copper and zinc in non-ferroalloys by flame atomic absorption spectrometry

An automatic Procedure with a high current-density anodic electrodissolution unit (HDAE) is proposed for the determination of aluminium, copper and zinc in non-ferroalloys by flame atonic absorption spectrometry, based on the direct solid analysis. It consists of solenoid valve-based commutation in a flow-injection system for on-line sample electro-dissolution and calibration with one multi-element standard, an electrolytic cell equipped with two electrodes (a silver needle acts as cathode, and sample as anode), and an intelligent unit. The latter is assembled in a PC-compatible microcomputer for instrument control, and far data acquisition and processing. General management of the process is achieved by use of software written in Pascal. Electrolyte compositions, flow rates, commutation times, applied current and electrolysis time mere investigated. A 0.5 mol l(-1) HNO3 solution was elected as electrolyte and 300 A/cm(2) as the continuous current pulse. The performance of the proposed system was evaluated by analysing aluminium in Al-allay samples, and copper/zinc in brass and bronze samples, respectively. The system handles about 50 samples per hour. Results are precise (R.S.D < 2%) and in agreement with those obtained by ICP-AES and spectrophotometry at a 95% confidence level.

Dynamical study of ZnO nanocrystal and Zn-HDS layered basic zinc acetate formation from sol-gel route

We have pointed out that zinc based particles obtained from ethanolic solution of a zinc acetate derivative (zinc oxy-acetate, Zn4O(Ac)(6)) are a mixture of nanometer sized ZnO, zinc oxy-acetate, and zinc hydroxide double salt (Zn-HDS). The knowledge of the mechanisms involved in the formation of ZnO and Zn-HDS phases, and the evolution of Zn species in reaction medium was monitored in situ during 14 h by simultaneous measurements of UV-vis absorption and extended X-ray absorption fine structures (EXAFS) spectra. This spectroscopic monitoring was initialized just after the addition of an ethanolic lithium hydroxide solution ([LiOH]/[Zn] = 0. 1) to the reaction medium kept under controlled temperature (40 degrees C). This study points out the first direct evidence of the reaction between ZnO nanoparticles and unreacted zinc oxy-acetate to form a Zn-HDS phase. The dissolution of ZnO and the reprecipitation of Zn-HDS are induced by the gradual release of water mainly produced by ethanol esterification well evidenced by gas chromatography coupled to mass spectroscopy and FT-IR measurements.

Effect of zinc administration on thyrotropin releasing hormone-stimulated prolactinemia in healthy men

Previous in vitro studies have demonstrated zinc (Zn++) inhibition of basal and of potassium (K+) or thyrotropin-releasing hormone (TRH)-stimulated prolactin (PRL) secretion, in a selective, reversible, and dose-dependent manner. Thus, Zn++ may regulate physiologically pituitary PRL secretion. Furthermore, studies with patients with uremia, cirrhosis or prolactinoma, have shown the coexistence of hypozincemia and hyperprolactinemia and zinc supplementation did not correct hyperprolactinemia in these patients. In normal individuals Zn++ administration produced controversial results on PRL secretion. Here, we investigated whether zinc administration affects TRH-stimulated PRL in healthy men. We found that Zn++ administration does not change the TRH-stimulated PRL. Therefore, in normal conditions, Zn++ does not inhibit TRH-stimulated prolactinemia. In addition, we found that acute increases of blood PRL and TRH do not alter blood Zn++ levels.

Prolactin and zinc in dialysis patients

The objectives of the present study were to investigate the frequencies of hyperprolactinemia and hypozincemia in patients undergoing hemodialysis (HD) or continuous ambulatory peritoneal dialysis (CAPD), the associations between blood levels of zinc (Zn2+) and hormones, and dietary zinc intake amount and its relation to zincemia. We studied 28 patients (14 HD and 14 CAPD) who had their blood levels of Zn2+, prolactin (PRL), parathyroid hormone (PTH), and gonadotropins (LH, FSH) evaluated. Thirteen patients had dietary nutrient amounts evaluated from a 3-d nutritional record. Hyperprolactinemia occurred in 29% patients (HD = CAPD), hypozincemia in 62% (20% HD and 42% CAPD), and low dietary Zn2+ intake in 90% of patients. No correlation among blood concentration of Zn2+ and PRL, PTH, LH, and FSH were observed in the two modalities of dialysis or between zincemia and Zn2+ ingestion. We concluded that the occurrence of hyperprolactinemia and hypozincemia were not related to dialysis modality and that zincemia did not reflect the observed low dietary intake of Zn2+.

RENAL EXCRETION OF ZINC IN NORMAL INDIVIDUALS DURING ZINC TOLERANCE-TEST AND GLUCOSE-TOLERANCE TEST

The urinary excretion, renal clearance, and tubular reabsorption of zinc were investigated in 30 adult healthy subjects under basal conditions and during the zinc and glucose tolerance tests. After a 12h overnight fast, each subject was submitted to renal clearance of zinc. The procedures were performed between 8.00 and 12.00 a.m., after emptying the bladder and ingestion of 4 ml deionized water/kg body weight at 8.00 a.m. The first urine sample was collected at 10.00 a.m., and the second at 12.00 a.m. A dose of 110 mg ZnSO4.7H(2)O was administered orally to each subject, diluted in 20 mi deionized water, at time 0 min. Blood samples were collected from an antecubital vein at times -30, 0, and 30 min and at 30 min intervals up to 240 min. Glucose was administered intravenously (0.5 ml 50%/kg body weight) during the first 3 min of the test, and blood samples were collected from an unconstricted, contralateral, antecubital vein at times -30, 0, 3, 5, 10, 20, 30, 45, 60, and 90 min. The results showed that urinary zinc excretion, and renal zinc clearance were significantly higher during the zinc and glucose tolerance tests than in the control condition. on the other hand, renal zinc clearance was more elevated during the glucose tolerance test than during the zinc tolerance test. Variations in zinc tubular reabsorption and glomerular filtration rate were not detected. The results suggest that urinary excretion and renal clearance of zinc in healthy subjects increase during acute zinc ingestion and glucose infusion. Although zinc ingestion raised urinary zinc excretion, glucose infusion was more effective in increasing renal zinc clearance. These normal parameters are important in the investigation of diabetic patients with serum and urine zinc changes.

Electroluminescence of zinc oxide thin-films prepared via polymeric precursor and via sol-gel methods

Zinc oxide (ZnO) is an electroluminescent (EL) material that can emit light in different regions of electromagnetic spectrum when electrically excited. Since ZnO is chemically stable, inexpensive and environmentally friendly material, its EL property can be useful to construct solid-state lamps for illumination or as UV emitter. We present here two wet chemical methods to prepare ZnO thin-films: the Pechini method and the sol-gel method, with both methods resulting in crystalline and transparent films with transmittance > 85% at 550 nm. These films were used to make thin-film electroluminescent devices (TFELD) using two different insulator layers: lithium fluoride (LiF) or silica (SiO2). All the devices exhibit at least two wide emission bands in the visible range centered at 420 nm and at 380 nm attributed to the electronic defects in the ZnO optical band gap. Besides these two bands, the device using SiO2 and ZnO film obtained via sol-gel exhibits an additional band in the UV range centered at 350 nm which can be attributed to excitonic emission. These emission bands of ZnO can transfer their energy when a proper dopant is present. For the devices produced the voltage-current characteristics were measured in a specific range of applied voltage. (C) 2007 Elsevier B.V. All rights reserved.

Zinc supplementation does not inhibit basal and metoclopramide-stimulated prolactinemia secretion in healthy men

Dopamine (DA) and zinc (Zn++) share common mechanisms in their inhibition of prolactin (PRL) secretion. Both substances are present in the same brain areas, where Zn++ is released together with DA, suggesting a modulatory effect of Zn++ on dopaminergic receptors. The aim of the present study was to evaluate the effect of Zn supplementation on basal and PRL secretion stimulated by metoclopramide (MCP), a dopaminergic antagonist. Seven healthy men were evaluated in controlled study, where MCP (5 mg) was given intravenously, before and after 3 months of oral Zn++ (25 mg) administration. Our results indicate that chronic Zn++ administration does not change basal or MCP-stimulated plasma PRL secretion suggesting that, in humans, Zn++ does not interfere on PRL secretion mediated through dopaminergic receptors.

Neo-clerodane diterpenoid, a new metalloprotease snake venom inhibitor from Baccharis trimera (Asteraceae): anti-proteolytic and anti-hemorrhagic properties

Many plants are used in traditional medicine as active agents against various effects induced by snakebite. Few attempts have been made however to identify the nature of plain natural products with anti-ophidian properties. Baccharis trimera (Less) DC (Asteraceae), known in Brazil as carqueja. has been popularly used to treat liver diseases. rheumatism. diabetes, as well as digestive, hepatic and renal disorders. The active component was identified as 7alpha-hydroxy-3,13-clerodadiene-16,15:18,19-diolide, C20H28O5, (clerodane diterpenoid, Bt-CD). We report now the anti-proteolytic and anti-hemorrhagic propenies against snake venoms of a Bt-CD inhibitor from B. trimera. Bt-CD exhibited full inhibition of hemorrhage and proteolytic activity caused by Bothrops snake venoms. The inhibitor was able to neutralize the hemorrhagic, fibrinogenolytic and caseinolytic activities of class P-I and III metalloproteases isolated from B. neuwiedi and B. jararacussu venoms. No inhibition of the coagulant activity was observed. Bt-CD also partially inhibited the edema induced by other crude venoms, metallopronteases, basic and acidic phospholipases A(2). To further elucidate the inhibitory specificity of Bt-CD against metalloproteases isolated from snake venoms, a deeper understanding of its Structure and function is necessary. Furthermore, the potential use of these inhibitors to complement anti-venom as an alternative treatment of snakebite envenomations needs to be evaluated in future Studies. (C) 2004 Elsevier B.V.. All rights reserved.

Histological evaluation of the response of apical tissues to glass ionomer and zinc oxide eugenol based sealers in dog teeth after root canal treatment

The object of the study was to compare two commercial root canal sealers: Ketac-Endo (a glass ionomer cement) and Fill Canal (a zinc oxide-eugenol cement). A total of 34 root canals from dog premolars with vital pulps were used. After instrumentation, the root canals were sealed with Ketac-Endo and Fill Canal cements using gutta-percha and a lateral condensation technique. After 270 days the animals were sacrificed with an anesthetic overdose and the maxillae and mandibles were removed and fixed in formalin for 48 h. After routine histological processing the sections were stained with hematoxylin-eosin and Mallory trichrome stains. Microscopic analysis revealed that Ketac-Endo cement presented better results than Fill Canal cement.