Electrocatalytic oxidation of beta-dicarbonyl compounds using ceric methanesulphonate as mediator

beta-dicarbonyl compounds were oxidized electrocatalytically, with fragmentation and loss of "ch2", using ceric methanesulphonate as a mediator. 2,4-pentanedione yields acetic acid (90%), methyl acetoacetate yields acetic acid (84%) plus methanol and dimethyl malonate yields methanol (64%). For 1,3-diphenyl-1,3-propanedione and 1,3-cyclohexanedione, benzoic acid (61% yield) and glutaric acid (75% yield) were obtained, respectively. Methyl cyanoacetate and malononitrile were inert.

Estudo comparativo da seletividade de um método cinético-catalítico: a determinação de Cr(VI) pela oxidação da o-dianisidina pelo peróxido de hidrogênio

Selectivity studies for the determination of Cr(VI) using the catalytic oxidation of the o-dianisidine by hydrogen peroxide showed two distincts situations. In the first, when interferents were studied by a univariate procedure, Cr(III) and Cu(II) cause serious interferences even at the 2:1 proportion, relative to Cr(VI), while Fe(III) interfered at the 15:1 ratio and EDTA at the 10:1 ratio. On the other hand, when a multivariate investigation was performed, Cr(III) did not present any significant principal effects and its significant interaction effects were negative, in contrast to EDTA, that presented positive interaction effects although, like Cr(III), did not show significant interaction effects. In view of the interferent's action it become necessary to separate Cr(VI) by extraction with methylisobutylketone in a chloridric acid medium before its determination in vegetals and in wastewater from a cellulose industry samples. Using this procedure, the method precision is ±0,5% at the 10 ng/mL Cr(VI) concentration level. The detection and quantification limits, calculated by means of absorbance measurements of ten replicates of blank reagents were 1,1 and 3,2 ng/mL, respectively. The results obtained with real samples showed a relative standard deviation between 1,2% and 3,0% relative to their reference values.

The determination of the stoichiometry of the mixed complex of vanadium with hydrogen peroxide and with 4-(2-Pyridilazo) Resorcinol

The present study reports details of the stoichiometric characterization of the mixed complex system, V(H2O2)PAR, formed when vanadium adequately reacts with hydrogen peroxide and with 4-(2-Pyridilazo)Resorcinol. Also the presence of polynuclear species was investigated in order to elucidate about unambiguous assignment of the molar absorptivity, stability constant and composition of the complex. Two mathematical treatments methods of the experimental results were employed. From the results it can be concluded that this system corresponds to a mononuclear complex with 1:1:1 stoichiometry.

Metallien talteenotto kloridiliuoksesta

Diplomityön tarkoituksena oli tutkia ja kehittää menetelmä arvometallien kuten kuparin, sinkin, koboltin ja nikkelin talteenottoon metallikloridiliuoksesta. Tavoitteena oli valita taloudellisin ja ympäristöystävällisin menetelmä, jolla saadaan nämä arvometallit myyntituotteiksi. Lisäksi puhdistetun prosessiveden tuli täyttää asetetut tavoitteet. Kirjallisuustyön perusteella laskettiin viidelle eri prosessivaihtoehdolle ainetaseet HSC Sim 6.0 ohjelmalla, joka on HSC Chemistry-pohjainen prosessien simulointi- ja mallinnusohjelma. Kaikissa vaihtoehdoissa oli ensimmäisenä prosessiosana kuparin, sinkin, koboltin ja nikkelin sulfidisaostus ja sakan pesu. Sulfidisaostusta seurasi vaihtoehtoisesti joko 1) hapetus hapella ja hydroksidisaostus, 2) hapetus vetyperoksidilla ja hydroksidisaostus, 3) pelkkä hydroksidisaostus, 4) hapetus SO2/O2-kaasuseoksella ja hydroksidisaostus tai 5) karbonaattisaostus. Taselaskennan perusteella valittiin kokeelliseen osaan tutkittavat prosessivaihtoehdot, jotka olivat sulfidisaostus, hydroksidisaostus, SO2/O2- hapetus ja hydroksidisaostus sekä karbonaattisaostus. Kokeissa arvometallit saatiin talteenotettua sulfidisaostuksella selektiivisimmin lämpötilassa 55 °C ja pH:ssa 4. Näissä olosuhteissa reagenssin kulutus verrattaessa muihin tehtyihin sulfidisaostuksiin oli pienin. Sakka laskeutui ja suotautui hyvin. Loppusakan sisältämien metallien (kupari, sinkki ja koboltti) pitoisuudet olivat korkeimmat. Myös nikkelin määrä oli suuri. Mangaani ja rauta saatiin talteenotettua selektiivisimmin karbonaattisaostuksella lämpötilassa 65 °C. Sakka sisälsi eniten mangaania. Sakka laskeutui ja suotautui hyvin. Tällä menetelmällä puhdistetun prosessiveden laatu täytti asetetut tavoitteet.

Desenvolvimento de um dispositivo de baixo custo para medidas por quimiluminescência

A simple and low cost device (ca. US$ 150) that comprises two photodiodes fixed in lab-made Perspex flow cell is proposed for chemiluminescence measurements. The characteristics of the device (large observation window and reduced thickness) allow maximizing the amount of the emitted radiation detected. A sensitivity improvement of ca. 50 % was observed by employing two photodiodes for signal measurements. The performance of the device was assessed by the oxidation of luminol by hydrogen peroxide, yielding a linear response within the range of 2.50 to 500 µmol L-1 H2O2. The detection limit was estimated as 0.8 µmol L-1 hydrogen peroxide which is comparable with those obtained by using equipments based on photomultipliers.

Determinação de paracetamol em produtos farmacêuticos usando um biossensor de pasta de carbono modificado com extrato bruto de abobrinha (Cucurbita pepo)

Crude extracts of several vegetables such as peach (Prunus persica), yam (Alocasia macrorhiza), manioc (Manihot utilissima), artichoke (Cynara scolymus L), sweet potato (Ipomoea batatas (L.) Lam.), turnip (Brassica campestre ssp. rapifera), horseradish (Armoracia rusticana) and zucchini (Cucurbita pepo) were investigated as the source of peroxidase (POD: EC 1.11.1.7). Among those, zucchini (Cucurbita pepo) crude extract was found to be the best one. This enzyme in the presence of hydrogen peroxide catalyses the oxidation of paracetamol to N-acetyl-p-benzoquinoneimine which the electrochemical reduction back to paracetamol was obtained at a peak potential of ¾0.10V. A cyclic voltammetric study was performed by scanning the potential from + 0.5 to ¾ 0.5 V. The recovery of paracetamol from two samples ranged from 97.3 to 106% and a rectilinear calibration curve for paracetamol concentration from 1.2x10-4 to 2.5x10-3 mol L-1 (r=0.9965) were obtained. The detection limit was 6.9x10-5 mol L-1 and the relative standard deviation was less than 1.1% for a solution containing 2.5x10-3 mol L-1 paracetamol and 2.0x10-3 mol L-1 hydrogen peroxide (n=12). The results obtained for paracetamol in pharmaceutical products using the proposed biosensor and Pharmacopoeial procedures are in agreement at the 95% confidence level.

Efeitos da beta-polinitração na eficiência catalítica de rutenioporfirinas em reações de oxidação de cicloexano

Rutheniumporphyrins, especially with several nitro groups in b-positions, were used in the cyclohexane oxidation in the presence of iodosylbenzene, hydrogen peroxide and sodium hypochlorite as oxygen donors, under mild conditions. The beta-polynitrated complexes were able to promote the catalytic cyclohexane oxidation. They show an exceptionally high catalytic efficiency and resistance to attack by strong oxidizing agents. The cyclohexane oxidation was monitored by gas chromatography and the results showed that the beta-polynitrated rutheniumporphyrins are better catalysts when compared to other complexes not beta-polynitrated. In all cases, the 2-phenylsubstituted complexes were more efficient than 4-phenylsubstituted complexes. The importance of the ortho effect to oxidation was shown.

Um experimento de análise em fluxo envolvendo reações enzimáticas e quimiluminescência

An experiment is proposed to introduce some fundamentals of flow analysis, chemiluminescence and kinetic monitoring of enzymatic reactions in undergraduate courses. Chemiluminescence detection is performed with a simple spectrophotometer equipped with a lab-made spiral flow cell constructed from a polyethylene tube. The hydrogen peroxide produced by the glucose oxidation in the presence of glucose oxidase is continuously monitored by the reaction with luminol in alkaline media in a flow injection system. The exercise allows also the discussion of important analytical features and the comparison with different optical methods of analysis.

Cu and Co exchanged ZSM-5 zeolites: activity towards no reduction and hydrocarbon oxidation

|Cu x|[Si yAl]-MFI and |Co x|[Si yAl]-MFI catalysts were prepared by ion exchange from |Na|[Si yAl]-MFI zeolites (y = 12, 25 and 45). The activity of the catalysts was evaluated in the reduction of NO to N2 in an oxidative atmosphere using propane or methane as reducing agents. The Cu catalysts were only active with propane and they presented higher activity than the Co-based catalysts, the latter being active with both hydrocarbons. H2-TPR and DRS-UV/Vis data allowed correlation between the activity towards NO reduction and the presence of cationic charge-compensating species in the zeolite. It was also verified that the hydrocarbons are preferentially oxidised by O2, a reaction that occurs simultaneously with their oxidation with NO.

Influence of EfOM on the oxidation of micropollutants by Ozone and UV/H2O2 in secondary effluents

The aim of this work was to study the influence of effluent organic matter (EfOM) on micropollutants removal by ozone and UV/H2O2. To perform the experiments, deionized water and municipal secondary effluents (SE) were artificially contaminated with atrazine (ATZ) and treated by the two proposed methods. ATZ concentration, COD and TOC were recorded along the reaction time and used to evaluate EfOM effect on the system efficiency. Results demonstrate that the presence of EfOM can significantly reduce the micropollutant removal rate due to competition of EfOM components to react with radicals and/or molecular ozone. The hydroxyl radical scavenging caused by EfOM was quantified as well as the contribution of molecular ozone and �OH radicals during the ozonation of SE. EfOM components promoted higher inhibition of ATZ oxidation by hydroxyl radicals than by molecular ozone.

Oxidação de proteínas por oxigênio singlete: mecanismos de dano, estratégias para detecção e implicações biológicas

Proteins are potential targets for singlet molecular oxygen (¹O2) oxidation. Damages occur only at tryptophan, tyrosine, histidine, methionine, and cysteine residues at physiological pH, generating oxidized compounds such as hydroperoxides. Therefore, it is important to understand the mechanisms by which ¹O2, hydroperoxides and other oxidized products can trigger further damage. The improvement and development of new tools, such as clean sources of ¹O2 and isotopic labeling approaches in association with HPLC/mass spectrometry detection will allow one to elucidate mechanistic features involving ¹O2-mediated protein oxidation.

Myoglobins: the link between discoloration and lipid oxidation in muscle and meat

Aerobic metabolism changes rapidly to glycolysis post-mortem resulting in a pH-decrease during the transformation of muscle in to meat affecting ligand binding and redox potential of the heme iron in myoglobin, the meat pigment. The "inorganic chemistry" of meat involves (i) redox-cycling between iron(II), iron(III), and iron(IV)/protein radicals; (ii) ligand exchange processes; and (iii) spin-equilibra with a change in coordination number for the heme iron. In addition to the function of myoglobin for oxygen storage, new physiological roles of myoglobin are currently being discovered, which notably find close parallels in the processes in fresh meat and nitrite-cured meat products. Myoglobin may be characterized as a bioreactor for small molecules like O2, NO, CO, CO2, H2O, and HNO with importance in bio-regulation and in protection against oxidative stress in vivo otherwise affecting lipids in membranes. Many of these processes may be recognised as colour changes in fresh meat and cured meat products under different atmospheric conditions, and could also be instructive for teaching purposes.

Cyclin-dependent kinases 4 and 6 control tumor progression and direct glucose oxidation in the pentose cycle

Cyclin-dependent kinases CDK4 and CDK6 are essential for the control of the cell cycle through the G1 phase. Aberrant expression of CDK4 and CDK6 is a hall- mark of cancer, which would suggest that CDK4 and CDK6 are attractive targets for cancer therapy. Herein, we report that calcein AM is a potent specific inhibitor of CDK4 and CDK6 in HCT116 human colon adenocarcinoma cells, inhibiting retinoblastoma protein (pRb) phosphorylation and inducing cell cycle arrest in the G1 phase. The metabolic effects of calcein AM (the calcein acetoxymethyl-ester) on HCT116 cells were also evaluated and the flux between the oxidative and non-oxidative branches of the pentose phos-phate pathway was significantly altered. To elucidate whe-ther these metabolic changes were due to the inhibition of CDK4 and CDK6, we also characterized the metabolic profile of a CDK4, CDK6 and CDK2 triple knockout of mouse embryonic fibroblasts. The results show that the metabolic profile associated with the depletion of CDK4, CDK6 and CDK2 coincides with the metabolic changes induced by calcein AM on HCT116 cells, thus confirming that the inhibition of CDK4 and CDK6 disrupts the balance between the oxidative and non-oxidative branches of the pentose phosphate pathway. Taken together, these results indicate that low doses of calcein can halt cell division and kill tumor cells. Thus, selective inhibition of CDK4 and CDK6 may be of greater pharmacological interest, since inhibitors of these kinases affect both cell cycle progression and the robust metabolic profile of tumors.

Mitochondrial fatty acid oxidation in obesity

Significance: Current lifestyles with high-energy diets and little exercise are triggering an alarming growth in obesity. Excess of adiposity is leading to severe increases in associated pathologies, such as insulin resistance, type 2 diabetes, atherosclerosis, cancer, arthritis, asthma, and hypertension. This, together with the lack of efficient obesity drugs, is the driving force behind much research. Recent Advances: Traditional anti-obesity strategies focused on reducing food intake and increasing physical activity. However, recent results suggest that enhancing cellular energy expenditure may be an attractive alternative therapy. Critical Issues: This review evaluates recent discoveries regarding mitochondrial fatty acid oxidation (FAO) and its potential as a therapy for obesity. We focus on the still controversial beneficial effects of increased FAO in liver and muscle, recent studies on how to potentiate adipose tissue energy expenditure, and the different hypotheses involving FAO and the reactive oxygen species production in the hypothalamic control of food intake. Future Directions: The present review aims to provide an overview of novel anti-obesity strategies that target mitochondrial FAO and that will definitively be of high interest in the future research to fight against obesity-related disorders.