Transferência de elétron inversa na quimiexcitação da reação peróxi-oxalato usando ativadores facilmente redutíveis

Chemiluminescence properties of the peroxyoxalate reaction in the presence of activators bearing electron withdrawing substituents were studied, to evaluate the possible occurrence of an inverse electron transfer, from the peroxide intermediate to the activator, in its chemiexcitation step. Relative catalytic rate constants and singlet quantum yields were obtained for the peroxyoxalate reaction, using 9-chloro, 9,10-dichloro, 9-cyano and 9,10-dicyanoanthracenes as activators. The linear free-energy correlation of the relative rate constants with the activators' reduction potentials and the dependence of the quantum yields on the released energy confirm, for the first time, the occurrence of this inverse electron transfer.

Luz: um raro produto de reação

The production of visible light by chemical reactions constitutes interesting and fascinating phenomena and several reaction mechanisms are discussed to rationalize excited state formation. Most efficient chemiluminescence reactions are thought to involve one or more electron transfer steps and chemiexcitation is believed to occur by radical annihilation. A brief introduction to the general principles of light production and the main known chemiexcitation mechanisms will be given here. Subsequently, recent results on the mechanistic elucidation of efficient chemiluminescence systems, as the peroxyoxalate reaction, the induced decomposition of phenoxy-substituted 1,2-dioxetanes and the catalyzed decomposition of new a-peroxylactones will be discussed.

Hydration and N-acetylcysteine in acute renal failure caused by iodinated contrast medium: an experiment with rats

Background: The involvement of nephrotoxic agents in acute renal failure (ARF) has increased over the last few decades. Among the drugs associated with nephrotoxic ARF are the radiologic contrast media whose nephrotoxic effects have grown, following the increasing diagnostic use of these agents. Methods: We evaluated the effect of iodinated contrast (IC) medium, administered in combination, or not, with hyperhydration or N-acetylcysteine (NAC), on creatinine clearance, production of urinary peroxides and renal histology of rats. Adult Wistar rats treated for 5 days were divided into the following groups: control (saline, 3 ml/kg/day, intraperitoneally [i.p.]), IC (sodium iothalamate meglumine, 3 ml/kg/day i.p.), IC + water (12 mL water, orally + IC, 3 ml/kg/day i.p. after 1 hour), IC + NAC (NAC, 150 mg/kg/day, orally + IC, 3 ml/kg/day i.p. after 1 hour) and IC + water + NAC. Results: IC medium reduced renal function, with maintenance of urinary flow. Hyperhydration did not reduce the nephrotoxic effect of the IC agent, which was observed in the group IC + NAC. The combination of hyperhydration and NAC had no superior protective effect compared with NAC alone. An increase in urinary peroxides was observed in the IC group, with NAC or water or the combination of both reducing this parameter. Histopathologic analysis revealed no significant alterations. Conclusions: In summary, given 5 days previously, NAC was found to be more effective than hyperhydration alone in the prevention of contrast-induced acute renal failure.

Effect of the Partial Substitution of Soy Proteins by Highly Methyl-esterified Pectin on Chemical and Sensory Characteristics of Sausages

Pectin can be used as a natural emulsifier in food formulations. In this study, textured soybean protein (TSP), used as an emulsifier in commercial sausages, was partially replaced by a mixture containing pectin and isolated soybean proteins, which were either extruded (EXT) or not extruded (MIX), and the chemical and sensory characteristics of samples were evaluated after 60 days of storage at 4 degrees C. Responses such as oxidation measured by PV and TBARS, hardness, color, pH and sensory characteristics were compared with those of a commercial sausage (CON). The mixture containing highly methyl-esterified pectin, textured soybean proteins and isolated soybean proteins, as emulsifier agent, reduced the hardness (EXT: 21.69 +/- 0.98 and MIX: 20.17 +/- 2.76 N) and the pH (EXT: 5.46 +/- 0.03 and MIX: 5.29 +/- 0.01) of the samples and increased the concentration of peroxides (EXT: 0.10 +/- 0.01 and MIX: 0.15 +/- 0.01 meq/kg) when compared with samples formulated only with TSP (28.57 +/- 2.54 N, pH of 6.92 +/- 0.04 and PV = 0.07 +/- 0.01 meq/kg). These effects were likely caused by the anionic character of the emulsifier. However, no sensory difference was observed between the sausages containing highly methyl-esterified pectin, textured soybean proteins and isolated soybean proteins submitted to the extrusion process (EXT) and the control sausages, suggesting that the formulation proposed in this study can be a potential alternative for the further development of sausages that have functional properties or are free of artificial additives.

Mitochondrial energy metabolism and redox responses to hypertriglyceridemia

In this work we review recent findings that explain how mitochondrial bioenergetic functions and redox state respond to a hyperlipidemic in vivo environment and may contribute to the maintenance of a normal metabolic phenotype. The experimental model utilized to evidence these adaptive mechanisms is especially useful for these studies since it exhibits genetic hypertriglyceridemia and avoids complications introduced by high fat diets. Liver from hypertrigliceridemic (HTG) mice have a greater content of glycerolipids together with increased mitochondrial free fatty acid oxidation. HTG liver mitochondria have a higher resting respiration rate but normal oxidative phosphorylation efficiency. This is achieved by higher activity of the mitochondrial potassium channel sensitive to ATP (mitoK(ATP)). The mild uncoupling mediated by mitoK(ATP) accelerates respiration rates and reduces reactive oxygen species generation. Although this response is not sufficient to inhibit lipid induced extra-mitochondrial oxidative stress in whole liver cells it avoids amplification of this redox imbalance. Furthermore, higher mitoK(ATP) activity increases liver, brain and whole body metabolic rates. These mitochondrial adaptations may explain why these HTG mice do not develop insulin resistance and obesity even under a severe hyperlipidemic state. On the contrary, when long term high fat diets are employed, insulin resistance, fatty liver and obesity develop and mitochondrial adaptations are inefficient to counteract energy and redox imbalances.

Sigmosceptrins A-C: New norditerpenes from a southern Australian marine sponge, Sigmosceptrella sp.

A Sigmosceptrella sp. of sponge collected during trawling operations in the Great Australian Eight, Australia, has yielded a series of new norterpenes. These include a new bisnorditerpene, sigmosceptrin-A (5); two new norditerpenes, sigmosceptrin-B (14) and sigmosceptrin-C (15), isolated as their methyl esters (6) and (7) respectively; and an ethylated artefact, sigmosceptrin-B ethyl ester (8). Complete stereostructures were assigned to the sigmosceptrins by spectroscopic analysis, chemical degradation, derivatization, and by a single-crystal X-ray structural analysis. A biosynthetic pathway is proposed that requires a common biosynthetic precursor to both the sigmosceptrins and norterpene cyclic peroxides.

Mycaperoxides F and G and a related norterpene ketone from southern Australian marine sponges, Mycale species

Investigation of two southern Australian marine sponges, Mycale spp., resulted in isolation of the known norsesterterpene mycaperoxide F methyl ester (5) together with a new norsesterterpene mycaperoxide G methyl ester (10) and a new norterpene ketone 11. All structures were secured by spectroscopic analysis and chemical derivatization. The absolute stereochemistry previously assigned to 5 by application of the Horeau procedure has been revised by application of the Mosher procedure.

Marine bioprospecting - Trawling for treasure and pleasure

This Microreview seeks to highlight the molecular diversity present in marine organisms, and illustrate by example some of the challenges encountered in exploring this resource. Marine natural products exhibit an impressive array of structural motifs, many of which are derived from biosynthetic pathways that are uniquely marine, Most importantly some marine metabolites possess noteworthy biological activities, activities that have potential application outside marine ecosystems, such as antibiotics, antiparasitics, anticancer agents etc... The isolation, spectroscopic characterisation and assignment of stereostructures to these unusual metabolites is both challenging and rewarding. Examples featured in this Microreview follow a common theme in that they are all recent accounts of the isolation of natural products from Australian marine sponges, carried out in the laboratories of the author. In addition to presenting brief comments on specific structure elucidation strategies, an effort is made to emphasize techniques for solving stereochemical issues, as well as to speculate on the biosynthetic origins of some of these exotic marine natural products.

Aerobic exercise training improves the role of high-density lipoprotein antioxidant and reduces plasma lipid peroxidation in type 2 diabetes mellitus

In this study, we analyzed the effect of aerobic exercise training (AET) and of a single bout of exercise on plasma oxidative stress and on antioxidant defenses in type 2 diabetes mellitus (DM) and in healthy control subjects (C). DM and C did not differ regarding triglycerides, high-density lipoprotein cholesterol (HDL-c), insulin, and HOMA index at baseline and after AET. To measure the lag time for low-density lipoprotein (LDL) oxidation (LAG) and the maximal rate of conjugated diene formation (MCD), participants` plasma HDL(2) and HDL(3) were incubated with LDL from pooled healthy donors` plasma. In the presence of HDL(3), both LAG and MCD were similar in C and DM, but only in DM did AET improve LAG and reduce MCD. In the presence of HDL(2), the lower baseline LAG in DM equaled C after AET. MCD was unchanged in DM after AET, but was lower than C only after AET. Furthermore, after AET plasma thiobarbituric acid-reactive substances were reduced only in DM subjects. Despite not modifying the total plasma antioxidant status and serum paraoxonase-1 activity in both groups, AET lowered the plasma lipid peroxides, corrected the HDL(2), and improved the HDL(3) antioxidant efficiency in DM independent of the changes in blood glucose, insulin, and plasma HDL concentration and composition.

Sodium nitrite downregulates vascular NADPH oxidase and exerts antihypertensive effects in hypertension

Dietary nitrite and nitrate are important sources of nitric oxide (NO). However, the use of nitrite as an antihypertensive drug may be limited by increased oxidative stress associated with hypertension. We evaluated the antihypertensive effects of sodium nitrite given in drinking water for 4 weeks in two-kidney one-clip (21(1 C) hypertensive rats and the effects induced by nitrite on NO bioavailability and oxidative stress. We found that, even under the increased oxidative stress conditions present in 2K1C hypertension, nitrite reduced systolic blood pressure in a dose-dependent manner. Whereas treatment with nitrite did not significantly change plasma nitrite concentrations in 2K1C rats, it increased plasma nitrate levels significantly. Surprisingly, nitrite treatment exerted antioxidant effects in both hypertensive and sham-normotensive control rats. A series of in vitro experiments was carried out to show that the antioxidant effects induced by nitrite do not involve direct antioxidant effects or xanthine oxidase activity inhibition. Conversely, nitrite decreased vascular NADPH oxidase activity. Taken together, our results show for the first time that nitrite has antihypertensive effects in 2K1C hypertensive rats, which may be due to its antioxidant properties resulting from vascular NADPH oxidase activity inhibition. (C) 2011 Elsevier Inc. All rights reserved.

Efficient cyclohexane oxidation with hydrogen peroxide catalysed by a C-scorpionate iron(II) complex immobilized on desilicated MOR zeolite

The hydrotris(pyrazol-1-yl)methane iron(II) complex [FeCl2{eta(3)-HC(pz)(3)}] (Fe, pz = pyrazol-1-yl) immobilized on commercial (MOR) or desilicated (MOR-D) zeolite, catalyses the oxidation of cyclohexane with hydrogen peroxide to cyclohexanol and cyclohexanone, under mild conditions. MOR-D/Fe (desilicated zeolite supported [FeCl2{eta(3)-HC(pz)(3)}] complex) provides an outstanding catalytic activity (TON up to 2.90 x 10(3)) with the concomitant overall yield of 38%, and can be easy recovered and reused. The MOR or MOR-D supported hydrotris(pyrazol-1-yl)methane iron(II) complex (MOR/Fe and MOR-D/Fe, respectively) was characterized by X-ray powder diffraction, ICP-AES, and TEM studies as well as by IR spectroscopy and N-2 adsorption at -196 degrees C. The catalytic operational conditions (e.g., reaction time, type and amount of oxidant, presence of acid and type of solvent) were optimized. (C) 2013 Elsevier B.V. All rights reserved.

Influence of a fat overload on lipogenic regulators in metabolic syndrome patients

Several epidemiological studies have related an increase of lipids in the postprandial state to an individual risk for the development of CVD, possibly due to the increased plasma levels of TAG and fatty acids (FA) through enzymes of FA metabolism. The interaction between nutrition and the human genome determines gene expression and metabolic response. The aim of the present study was to evaluate the influence of a fat overload on the gene mRNA levels of lipogenic regulators in peripheral blood mononuclear cells (PBMC) from patients with the metabolic syndrome. The study included twenty-one patients with criteria for the metabolic syndrome who underwent a fat overload. Measurements were made before and after the fat overload of anthropometric and biochemical variables and also the gene mRNA levels of lipogenic factors. The main results were that the fat overload led to an increased mRNA levels of sterol regulatory element binding protein-1 (SREBP1), retinoid X receptor α (RXRα) and liver X receptor α (LXRα) in PBMC, and this increase was associated with the FA synthase (FASN) mRNA levels. We also found that TAG levels correlated with FASN mRNA levels. In addition, there was a positive correlation of SREBP1 with RXRα and of LXRα with the plasma lipoperoxide concentration. The fat overload led to an increase in regulators of lipogenesis in PBMC from patients with the metabolic syndrome.

Efectos del consumo de aceites termo-oxidados sobre la peroxidación lipídica en animales de laboratorio.

INTRODUCTION The quality of fats and oils used for frying is as important as the quality of the final product since during the frying process oxidization by-products are formed and become part of the diet, being potentially harmful for the consumers' health. OBJECTIVE To determine the effects of thermo-oxidised fats and oils on the oxidization of plasma lipoproteins inexperimental rats. METHODS Determination by means of spectrophotometric techniques of those substances reacting with thiobarbituric acid and total cholesterol (enzymatic method) in the sera of 40 Wistar rats that consumed crude thermooxidised oils and fats with different levels of malonil aldehyde(MDA) for 30 days. RESULTS The group of rats receiving a diet with thermooxidised oils and fats experienced significant increases in MDA plasma levels throughout the study period, lipid peroxidation being higher with increasing MDA content (p < 0.05) regardless the type of fat compound consumed. However, those rats receiving crude oils and fats kept plasma levels of lipidic peroxides without significant changes throughout the experimental period (p > 0.05). By contrast, cholesterol levels increased towards the end of the experimental period in both the rats consuming crude fats and those consuming thermo-oxidised fats (p < 0.05). CONCLUSIONS Consumption of oils and fats submitted to repeat thermal heating has an influence on plasma lipidic peroxidation, which becomes higher with increasing number of heating processes applied, so that it would advisable not to abuse of reheating the oils used for frying foods.

Mechanisms of hydrogen peroxide-induced vasoconstriction in the isolated perfused rat kidney.

The vasoconstrictor effect of hydrogen peroxide (H(2)O(2)) on isolated perfused rat kidney was investigated. H(2)O(2) induced vasoconstriction in the isolated rat kidney in a concentration-dependent manner. The vasoconstrictor effects of H(2)O(2) were completely inhibited by 1200 U/ml catalase. Endothelium-removal potentiated the renal response to H(2)O(2). The H(2)O(2) dose-response curve was not significantly modified by administration of the NO inhibitor L-NAME (10(-4) mol/l), whereas it was increased by the non-specific inhibitor of K+-channels, tetraethylammonium (3.10(-3) mol/l). Separately, removal of extracellular Ca(2+), administration of a mixture of calcium desensitizing agents (nitroprusside, papaverine, and diazoxide), and administration of a protein kinase C (PKC) inhibitor (chelerythrine, 10(-5) mol/l) each significantly attenuated the vasoconstrictor response to H(2)O(2), which was virtually suppressed when they were performed together. The pressor response to H(2)O(2) was not affected by: dimethyl sulfoxide (7.10(-5) mol/l) plus mannitol (3.10(-5) mol/l); intracellular Ca(2+) chelation using BAPTA (10(-5) mol/l); calcium store depletion after repeated doses of phenylephrine (10(-5) g/g kidney); or the presence of indomethacin (10(-5) mol/l), ODYA (2.10(-6) mol/l) or genistein (10(-5) mol/l). We conclude that the vasoconstrictor response to H(2)O(2) in the rat renal vasculature comprises the following components: 1) extracellular calcium influx, 2) activation of PKC, and 3) stimulation of pathways leading to sensitization of contractile elements to calcium. Moreover, a reduced pressor responsiveness to H(2)O(2) in female kidneys was observed.