Effects of Cadmium and mercury on the upper part of skeletal muscle glycolysis in mice.

The effects of pre-incubation with mercury (Hg2+) and cadmium (Cd2+) on the activities of individual glycolytic enzymes, on the flux and on internal metabolite concentrations of the upper part of glycolysis were investigated in mouse muscle extracts. In the range of metal concentrations analysed we found that only hexokinase and phosphofructokinase, the enzymes that shared the control of the flux, were inhibited by Hg2+ and Cd2+. The concentrations of the internal metabolites glucose-6-phosphate and fructose-6-phosphate did not change significantly when Hg2+ and Cd2+ were added. A mathematical model was constructed to explore the mechanisms of inhibition of Hg2+ and Cd2+ on hexokinase and phosphofructokinase. Equations derived from detailed mechanistic models for each inhibition were fitted to the experimental data. In a concentration-dependent manner these equations describe the observed inhibition of enzyme activity. Under the conditions analysed, the integral model showed that the simultaneous inhibition of hexokinase and phosphofructokinase explains the observation that the concentrations of glucose-6-phosphate and fructose-6-phosphate did not change as the heavy metals decreased the glycolytic flux.

Estudio cinético de la descomposición catalizada de peróxido de hidrógeno sobre carbón activado

The kinetic study of decomposition of hydrogen peroxide catalyzed by activated carbon was carried out. The effect of concentrations of reactants and temperature were experimentally studied. Kinetic data were evaluated using differential method of initial rates of reaction. When a typical kinetic law for reactions in homogeneous phase is used, first order of reaction is obtained for hydrogen peroxide and activated carbon, and activation energy of 27 kJ mol-1 for the reaction was estimated. Experimentally was observed that surface of activated carbon is chemically modified during decomposition of hydrogen peroxide, based on this result a scheme of reaction was proposed and evaluated. Experimental data fits very well to a Langmuir- Hinshelwood kinetic model and activation energy of 40 kJ mol-1 was estimated for reaction in heterogeneous phase.

Aplicação de um corante tiazolilazo como indicador ácido-base e determinação das suas constantes de ionização ácida

The pKa values of the 6-[2´-(6´-methyl-benzothiazolylazo)]-1,2-dihydroxy-3,5-benzenedisulfonic acid (Me-BDBD) have been determined at 25 °C, in 0.10 mol L-1 NaCl medium by spectrophotometric method. The SQUAD computer program was used to process experimental data in pH range 1.78 - 11.54 and 290 - 720 nm. The pKa values obtained were 4.60 ± 0.04 and 9.48 ± 0.02. The Me-BDBD reagent was applied as indicator in titration of acid-base. The results were compared with phenolphthalein and bromocresol green indicators. Statistical t and F tests indicated that there were no statistically significant differences between the results for indicators with good agreement.

A fórmula barométrica como instrumento de ensino em Química

The barometric equation is revisited. Restrictions imposed for its derivation are investigated. Results are discussed and related to simple themes of ordinary life. The theoretical models fit to experimental data. Correction for temperature effect improves the fitting in comparison to the barometric formula. The scope for application of the model is discussed.

Remoção de Pb2+ e Cr3+ em solução por zeólitas naturais associadas a rochas eruptivas da formação serra geral, bacia sedimentar do Paraná

The capacity of natural zeolites and its host rock (dacite) to remove Pb2+ and Cr3+ from aqueous solutions has been investigated. Results showed that both samples prefer to remove Pb2+ instead of Cr3+. Almost 100% of Pb2+ was removed from solutions with concentration until 50 mg L-1 and 100 mg L-1 of this metal, respectively by dacite and zeolite. The equilibrium of metals adsorption process was reached during the first 30 min by both materials. Na+ can be used to recover Pb2+, but not to remove Cr3+ from the treated samples. The Sips model showed a good fit for experimental data of this study.

Remoção de chumbo(II) em sistemas contínuos por carvão ativado com vapor

Fixed-bed column studies were undertaken to evaluate the performance of a commercial Brazilian activated carbon in removing Pb(II) from aqueous environment. Breakthrough points were found out for the metal adsorption by varying different operating parameters like feed concentrations (10 and 20 mg L-1) and bed heights (0.5, 1.5 and 2.8 cm). A good agreement was observed between the experimental data and the values predicted by the bed depth service time (BDST) model. Regeneration of the exhausted columns was possible with HCl, and the adsorption capacity was maintained after three adsorption-desorption cycles.

Termocromismo em soluções de alcóxidos de Vanádio(IV): uma abordagem pela modelagem molecular

The thermochromic behavior exhibited by vanadium(IV) alkoxides, [V2(μ-OPr i)2(OPr i) 6] and [V2(μ-ONep)2(ONep)6 ], OPr i = isopropoxide and ONep = neopentoxide, was studied by molecular modeling using DFT, TDDFT and INDO/S methods. The vibrational and electronic spectra calculated for [V2(μ-OPr i)2(OPr i) 6] were very similar to the experimental data registered for crystalline samples of the complex and for its solutions at low temperature (< 210 K), while spectra recorded at high temperature (> 315 K) were compatible with those calculated for the monomeric form, [V(OPr i)4]. These results consistently point to a monomer/dimer equilibrium as an explanation for the solution thermochromism of {V(OPr i)4}n. In spite of the structural similarity between [V2(μ-ONep)2(ONep)6 ] and [V2(μ-OPr i)2(OPr i) 6] in the solid state, the thermochromic behavior of the former could not be explained by the same model, and the possibility of tetranuclear aggregation at low temperatures was also investigated.

Acilação de Friedel-Crafts do 2-metoxinaftaleno usando o ácido dodecafosfotúngstico suportado em sílica (HPW/SiO2) como catalisador e acetonitrila como solvente

The synthesis of fine chemicals intermediates using Friedel-Crafts acylation is one of the most important methods in chemical technology. In this work, the acylation of 2-methoxynaphthalene with acetic anhydride using a silica-supported dodecatungstophosphoric acid catalyst (HPW/SiO2) and acetonitrila as solvent was studied, showing that this reaction is a feasible alternative to produce intermediaries to replace the current methods of production. The reactions using acetonitrile solvent showed yields greater than or equal to the reactions using traditional solvents such as nitrobenzene and dichloroethane. Finally, the modified Eley-Rideal mechanism was proposed to elucidate the experimental data obtained.

Comparação entre métodos compostos no cálculo de afinidades por próton e elétron em sistemas moleculares

The CBS-4M, CBS-QB3, G2, G2(MP2), G3 and G3(MP2) model chemistry methods have been used to calculate proton and electron affinities for a set of molecular and atomic systems. Agreement with the experimental value for these electronic properties is quite good considering the uncertainty in the experimental data. A comparison among the six theories using statistical analysis (average value, standard deviation and root-mean-square) showed a better performance of CBS-QB3 to obtain these properties.

Propriedades eletrônicas, estruturais e constantes elásticas do ZnO

The electronic, structural properties and elastic constants of the wurtzite phase of zinc oxide, ZnO, was investigated using computer simulation at Density Functional Theory level, with B3LYP hybrid functional and Hartree-Fock methodology. The electronic properties as well the band energy was investigated through the analysis of the band structures and density of states (DOS), and the mechanical properties was studied through the calculus of the elastic constants C11, C33, C44, C12 e C13. The results are in good agreement with experimental data found in the literature and in accordance with results obtained by another theoretical methodology.

Efeitos da adição de átomos de Mn na rede do GaN via métodos de estrutura eletrônica

A computational method to simulate the changes in the electronic structure of Ga1-xMn xN was performed in order to improve the understanding of the indirect contribution of Mn atoms. This periodic quantum-mechanical method is based on density functional theory at B3LYP level. The electronic structures are compared with experimental data of the absorption edge of the GaMnN. It was observed that the indirect influence of Mn through the structural parameters can account for the main part of the band gap variation for materials in the diluted regime (x<0.08), and is still significant for higher compositions (x~0.18).

Propriedades reológicas e efeito da adição de sal na viscosidade de exopolissacarídeos produzidos por bactérias do gênero Rhizobium

Viscosity of some polysaccharide solutions supports that these molecules can be applied in food sectors. Four exopolysaccharides (R1, R2, R3, R4) produced by different Rhizobium strains were selected. Sugar composition and differences in the uronic acid contents suggests that chemical structure of these molecules can vary when different culture conditions and strains are analyzed. The Power Law was the rheological model used to represent the experimental data of shear stress versus shear rate. All exopolysaccharides showed non-Newtonian behavior, with pseudoplastic characteristics. R1, R2 and R4 showed a slight increase in viscosity in the presence of 0,2 M NaCl.

Investigação do mecanismo de catálise ROMP do norborneno utilizando métodos de funcional de densidade

This work presents a density functional theory study of the norbornene ROMP metathesis reactions. The energies have been calculated in a Grubbs catalyst model Cl2(PH3)2Ru=CH2. The geometries and energy profile are similar to the Grubbs metilydene (Cl2(PCy3)2Ru=CH2 real model. It was found that the metathesis reaction proceeds via associative mechanism (catalyst-norbonene) followed by dissociative substitution of a phosphine ligand with norbonene, giving a monophosphine complex. The results are in reasonable agreement with the available experimental data. The dissociation energy of the phosphines is predicted to be 23.2 kcal mol-1.

Cloreto de n-(2-hidroxil) propil-3-trimetil amônio quitosana como adsorvente de corantes reativos em solução aquosa

The quaternary chitosan was synthesized by reaction of chitosan with glycidyl trimethylammonium chloride. it was characterized by infrared spectra and conductometric titration. Adsorption of reactive blue 4 (RB4) and reactive red 120 (RR120) by quaternary chitosan was studied from aqueous medium. Two kinetic adsorption models were tested: pseudo first-order and pseudo second-order. The experimental data best fitted the pseudo second-order model. The Langmuir isotherm model provided the best fit to the equilibrium data in the concentration range investigated and the maximum adsorption capacity determined was 415 mg (RR120) and 637 mg (RB4) of reactive dye per gram of adsorbent.

Ácidos orgânicos em aguardentes produzidas em alambique e em coluna

The concentration of 14 organic acids of 50 sugarcane spirits samples was determined by gas chromatography using flame ionization detection. The organic acids analytical quantitative profile in stills and column distilled spirits from wines obtained from the same must were compared. The comparison was also carried in "head", "heart" and "tail fractions of stills distilled spirits. The experimental data were analyzed by Principal Components Analysis (PCA) and pointed out that the distillation process (stills and column) strongly influences the lead spirits' organic acid composition and that producers' operational "cuts off" to produce "tail", "heart" and "head", fractions should be optimized.