Degradation of the antibiotic amoxicillin by photo-Fenton process - Chemical and toxicological assessment

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

Carbon monoxide oxidation over platinum: Stable, oscillatory and quasi-chaotic regimes

We model the heterogeneously catalyzed oxidation of CO over a Pt surface. A phase diagram analysis is used to probe the several steady state regimes and their stability. We incorporate an experimentally observed 'slow' sub-oxide kinetic step, thereby generalizing a previously presented model. In agreement with experimental data, stable, oscillatory and quasi-chaotic regimes are obtained. Furthermore, the inclusion of the sub-oxide step yields a relaxation oscillation regime. © 1998 Elsevier Science B.V. All rights reserved.

Spectrophotometric determination of manganese in steels by on-line electrochemical oxidation

The aim of this work is to propose a flow spectrophotometric procedure for manganese determination in steel based on electrochemical oxidation of Mn(II) to Mn(VII) at a Pt electrode surface by means of the catalytic effect of Ag(I). The on-line oxidation step was obtained by injecting sample and electrolyte solution directly into an electrolytic cell. After electrolysis, the injectate was homogenized by bubbling air. The permanganate ions produced were passed through the spectrophotometer where absorbance was monitored at 545 nm. Effects of direct current, silver concentration, timing, flow rates, concentration and composition of support electrolyte were investigated. Direct current and silver content manifested themselves as the most relevant parameters. For determination of manganese in the 5.00 - 150 mg L -1 range (r=0,9998) and 60 s electrolysis time, the sample throughput was 20 h -1. Accuracy was assessed by analyzing ten steel standard reference materials. Results are precise (R.S.D. <3%) and in agreement with certified values of reference materials and with standard methods at 95% confidence level.

Comparison between different conditions of the chemical polymerization of polyaniline on top of PET films

Composites produced during the in situ chemical polymerization of aniline on top of a poly(ethylene terephthalate) (PET) film, in different conditions, were studied by open-circuit potential (Voc), ultraviolet-visible, and infrared spectroscopy, electrical conductivity measurements, scanning electron microscopy, and atomic force microscopy. The polymerization monitoring by Voc showed a maximum associated with the intermediate pernigraniline oxidation state and a final formation of polyaniline (PANI) in the doped emeraldine salt (ES) form. Furthermore, high electrical conductivity values were obtained for the PANI-ES coating prepared under selected conditions. A globular formation was observed for the doped PANI-ES coating with globules of sizes of the same order and same shape of the PET, demonstrating the influence of the substrate on the coating morphology.

Horseradish peroxidase-catalyzed oxidation of rifampicin: Reaction rate enhancement by co-oxidation with anti-inflammatory drugs

The tuberculostatic drug rifampicin has been described as a scavenger of reactive species. Additionally, the recent demonstration that oral therapy with a complex of rifampicin and horseradish peroxidase (HRP) was more effective than rifampicin alone, in an animal model of experimental leprosy, suggested the importance of redox reactions involving rifampicin and their relevance to the mechanism of action. Hence, we studied the oxidation of rifampicin catalyzed by HRP, since this enzyme may represent the prototype of peroxidation-mediated reactions. We found that the antibiotic is efficiently oxidized and that rifampicin-quinone is the product, in a reaction dependent on both HRP and hydrogen peroxide. The steady-state kinetic constants Km app (101±23 mmol/l), Vmax app (0.78±0.09 μmol/l·s-1) and kcat (5.1±0.6 s-1) were measured (n=4). The reaction rate was increased by the addition of co-substrates such as tetramethylbenzidine, salicylic acid, 5-aminosalicylic acid and paracetamol. This effect was explained by invoking an electron-transfer mechanism by which these drugs acted as mediators of rifampicin oxidation. We suggested that this drug interaction might be important at the inflammatory site. © 2005 Pharmaceutical Society of Japan.

Photo-oxidation of polyphenylenevinylene chains in Langmuir-Blodgett and cast films

Poly(p-phenylene vinylene) (PPV) derivatives are well known for their applications in polymer light emitting diodes (PLEDs). These derivatives are highly susceptible to photooxidation though, which is mainly caused by the scission of the vinyl double bond on the polymer backbone. In this work, we show that Langmuir-Blodgett (LB) films are less degraded than cast films of a PPV derivative (OC1OC6-PPV). Both films had similar thickness (∼50 nm) to allow for a more realistic comparison. Photodegradation experiments were carried out by illuminating the films with white light from a halogen lamp (50W, 12 V), placed at a fixed dstance from the sample. The decay was monitored by UV-Vis and FTIR spectroscopies. The results showed that cast films are completely degraded in ca. 300 min, while LB took longer times, ca. 1000 min, i.e. 3 times the values for the cast films. The degradation process occurs in at least two stages, the rates of which were calculated assuming that the reaction follows a first order kinetics. The characteristic times for the first stage were 3.6×10-2 and 1.3×10-3 min-1 for cast and LB films, respectively. For the second stage the characteristic times were 5.6×10-2 and 5.0×10 -3 min-1. The differences can be attributed to the more compact morphology in the LB than in the cast films. With a compact morphology the diffusion of oxygen in the LB film is hampered and this causes a delay in the degradation process.

Kinetic study of the plastoquinone pool availability correlated with H2O2 release in seawater and antioxidant responses in the red alga Kappaphycus alvarezii exposed to single or combined high light, chilling and chemical stresses

Under biotic/abiotic stresses, the red alga Kappaphycus alvarezii reportedly releases massive amounts of H2O2 into the surrounding seawater. As an essential redox signal, the role of chloroplast-originated H2O2 in the orchestration of overall antioxidant responses in algal species has thus been questioned. This work purported to study the kinetic decay profiles of the redox-sensitive plastoquinone pool correlated to H2O2 release in seawater, parameters of oxidative lesions and antioxidant enzyme activities in the red alga Kappaphycus alvarezii under the single or combined effects of high light, low temperature, and sub-lethal doses of 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU) and 2,5-dibromo-3-methyl-6-isopropyl-p-benzoquinone (DBMIB), which are inhibitors of the thylakoid electron transport system. Within 24 h, high light and chilling stresses distinctly affected the availability of the PQ pool for photosynthesis, following Gaussian and exponential kinetic profiles, respectively, whereas combined stimuli were mostly reflected in exponential decays. No significant correlation was found in a comparison of the PQ pool levels after 24 h with either catalase (CAT) or ascorbate peroxidase (APX) activities, although the H2O2 concentration in seawater (R = 0.673), total superoxide dismutase activity (R = 0.689), and particularly indexes of protein (R = 0.869) and lipid oxidation (R = 0.864), were moderately correlated. These data suggest that the release of H2O2 from plastids into seawater possibly impaired efficient and immediate responses of pivotal H2O2-scavenging activities of CAT and APX in the red alga K. alvarezii, culminating in short-term exacerbated levels of protein and lipid oxidation. These facts provided a molecular basis for the recognized limited resistance of the red alga K. alvarezii under unfavorable conditions, especially under chilling stress. © 2006 Elsevier B.V. All rights reserved.

The effect of pH on horseradish peroxidase-catalyzed oxidation of melatonin: Production of N1-acetyl-N2-formyl-5- methoxykynuramine versus radical-mediated degradation

There is a growing body of evidence that melatonin and its oxidation product, N1-acetyl-N2-formyl-5-methoxykynuramine (AFMK), have anti-inflammatory properties. From a nutritional point of view, the discovery of melatonin in plant tissues emphasizes the importance of its relationship with plant peroxidases. Here we found that the pH of the reaction mixture has a profound influence in the reaction rate and products distribution when melatonin is oxidized by the plant enzyme horseradish peroxidase. At pH 5.5, 1 mm of melatonin was almost completely oxidized within 2 min, whereas only about 3% was consumed at pH 7.4. However, the relative yield of AFMK was higher in physiological pH. Radical-mediated oxidation products, including 2-hydroxymelatonin, a dimer of 2-hydroxymelatonin and O-demethylated dimer of melatonin account for the fast consumption of melatonin at pH 5.5. The higher production of AFMK at pH 7.4 was explained by the involvement of compound III of peroxidases as evidenced by spectral studies. On the other hand, the fast oxidative degradation at pH 5.5 was explained by the classic peroxidase cycle. © 2007 The Authors.

Methanol oxidation on PtRu/C electrocatalysts prepared by a microemulsion method

PtRu/C nanocatalysts were prepared by a microemulsion method using different values of water/surfactant molar ratio in order to get different particle sizes. Crystallite sizes and structural properties were determined by X-ray diffraction. Particle size and distribution were characterized by transmission electron microscopy and average composition was determined by energy dispersive X-ray analysis. Differential scanning calorimetry measurements indicated the presence of oxides in the as-prepared catalysts. The general electrochemical behavior was evaluated by cyclic voltammetry in 0.5 M sulfuric acid and the electrocatalytic activity towards the oxidation of methanol was studied in 0.5 M methanol acid solutions by potential sweeps and chronoamperometry. copyright The Electrochemical Society.

Effects of heat treatments on the electrocatalytic activity of Pt-Ru/C for methanol oxidation

The Pt-Ru/C materials of this study were prepared by a microemulsion method with fixed water to surfactant molar ratio and heat treated at low temperatures, to avoid changes in the average particle size, in different atmospheres. All samples were characterized by X-ray diffraction (XRD) and the mean crystallite size was estimated by using Scherrer's equation. Catalysts morphology was characterized by transmission electron microscopy (TEM). Average composition was obtained by energydispersive X-ray analysis (EDX). The general electrochemical behavior was evaluated by cyclic voltammetry in 0.5 M sulfuric acid and the electrocatalytic activity towards the oxidation of methanol was studied in 0.5 M methanol acid solutions by potential sweeps and chronoamperometry. Oxidation of adsorbed CO was used to estimate the electrochemical active area and to infer the surface properties. ©The Electrochemical Society.

Apocynin: Chemical and biophysical properties of a NADPH oxidase inhibitor

Apocynin is the most employed inhibitor of NADPH oxidase (NOX), a multienzymatic complex capable of catalyzing the one-electron reduction of molecular oxygen to the superoxide anion. Despite controversies about its selectivity, apocynin has been used as one of the most promising drugs in experimental models of inflammatory and neurodegenerative diseases. Here, we aimed to study the chemical and biophysical properties of apocynin. The oxidation potential was determined by cyclic voltammetry (Epa = 0.76V), the hydrophobicity index was calculated (logP = 0.83) and the molar absorption coefficient was determined (ε275nm = 1.1 × 104 M-1 cm-1). Apocynin was a weak free radical scavenger (as measured using the DPPH, peroxyl radical and nitric oxide assays) when compared to protocatechuic acid, used here as a reference antioxidant. On the other hand, apocynin was more effective than protocatechuic acid as scavenger of the non-radical species hypochlorous acid. Apocynin reacted promptly with the non-radical reactive species H2O2 only in the presence of peroxidase. This finding is relevant, since it represents a new pathway for depleting H2O2 in cellular experimental models, besides the direct inhibition of NADPH oxidase. This could be relevant for its application as an inhibitor of NOX4, since this isoform produces H 2O2 and not superoxide anion. The binding parameters calculated by fluorescence quenching showed that apocynin binds to human serum albumin (HSA) with a binding affinity of 2.19 × 104 M -1. The association did not alter the secondary and tertiary structure of HSA, as verified by synchronous fluorescence and circular dichroism. The displacement of fluorescent probes suggested that apocynin binds to site I and site II of HSA. Considering the current biomedical applications of this phytochemical, the dissemination of these chemical and biophysical properties can be very helpful for scientists and physicians interested in the use of apocynin.

Electrochemical oxidation of wastewater containing aromatic amines using a flow electrolytic reactor

Aromatic amines are environmental pollutants and represent one of the most important classes of industrial and natural chemicals. Some types of complex effluents containing these chemical species, mainly those originated from chemicals plants are not fully efficiently treated by conventional processes. In this work, the use of electrochemical technology through an electrolytic pilot scale flow reactor is considered for treatment of wastewater of a chemical industry manufacturer of antioxidant and anti-ozonant substances used in rubber. Experimental results showed that was possible to remove between 65% and 95% of apparent colour and chemical oxygen demand removal between 30 and 90% in 60 min of treatment, with energy consumption rate from 26 kWh m-3 to 31 kWh m-3. Absorbance, total organic carbon and toxicity analyses resulted in no formation of toxic by-products. The results suggest that the presented electrochemical process is a suitable method for treating this type of wastewater, mainly when pre-treated by aeration. Copyright © 2013 Inderscience Enterprises Ltd.

Evaluation of mechanical and thermal properties after chemical degradation of PVC and HDPE geomembranes

Chemical compatibility between geomembranes and site-specific waste liquids should be assessed since the waste liquids are highly complex mixtures. This paper presents some considerations about the chemical compatibility of geomembranes and some results of mechanical tests in HDPE and PVC geomembranes that were exposed to leachate and chemical residue (niobium). PVC and HDPE geomembranes of two thicknesses were tested: 1.0, 2.0 mm (PVC) and 0.8, 2.5 mm (HDPE). The results obtained show that after exposure the PVC geomembranes (1.0, 2.0 mm) were more rigid and stiffer than fresh samples. The HDPE geomembranes, on the other hand, when exposed to leachate and niobium residue presented increases in deformation. Melt flow index (MFI) tests were also carried out to verify the oxidation. © 2013 ejge.

Chemical composition and antioxidant activity of dried powder formulations of Agaricus blazei and Lentinus edodes

Several mushroom species have been pointed out as sources of antioxidant compounds, in addition to their important nutritional value. Agaricus blazei and Lentinus edodes are among the most studied species all over the world, but those studies focused on their fruiting bodies instead of other presentations, such as powdered preparations, used as supplements. In the present work the chemical composition (nutrients and bioactive compounds) and antioxidant activity (free radical scavenging activity, reducing power and lipid peroxidation inhibition) of dried powder formulations of the mentioned mushroom species (APF and LPF, respectively) were evaluated. Powder formulations of both species revealed the presence of essential nutrients, such as proteins, carbohydrates and unsaturated fatty acids. Furthermore, they present a low fat content (<2 g/100 g) and can be used in low-calorie diets, just like the mushrooms fruiting bodies. APF showed higher antioxidant activity and higher content of tocopherols and phenolic compounds (124 and 770 μg/100 g, respectively) than LPF (32 and 690 μg/100 g). Both formulations could be used as antioxidant sources to prevent diseases related to oxidative stress. © 2012 Elsevier Ltd. All rights reserved.

Physico-chemical characterization of seed oils extracted from oranges (Citrus sinensis)

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)