Propriedades redox da matéria orgânica isolada de material ultrafiltrado das águas do rio Paraíba do Sul

Previous studies indicated that free radicals control organic matter redox activities. In the present study, organic matter of an ultra-filtrated material collected from seven samples taken seasonally from the Paraiba do Sul River for two years were titrated with an oxidizer (I2) in an inert atmosphere. Standard formal potential values for the electrode MO Ox, MO Red ranged from 0.754 to 0.786 V at a 25 ºC temperature. Organic matter oxidation capacity (COx) per carbon mass varied according to pH values, and changes in COx were related to rainfall and river flow intensities.

Descoloração redutiva de corantes azo e o efeito de mediadores redox na presença do aceptor de elétrons sulfato

We investigated the impact of sulphate and the redox mediator Anthraquinone-2,6-disulfonate (AQDS) on the decolorization of the azo dyes Congo Red (CR) and Reactive Black 5 (RB5). In anaerobic reactors free of extra sulphate dosage, the color removal efficiency decreased drastically when the external electron donor ethanol was removed. In presence of an extra dosage of sulphate, CR decolourisations were 47.8% (free of AQDS) and 96.5% (supplemented with AQDS). The decolourisations achieved in both reactors with RB5 were lower than the ones found with CR. Finally, the biogenic sulphide contribution on azo dye reduction was negligiable.

Effect of dye structure and redox mediators on anaerobic azo and anthraquinone dye reduction

We investigated the biological decolourisation of dyes with different molecular structures. The kinetic constant values (k1) achieved with azo dye Reactive Red 120 were 7.6 and 10.1 times higher in the presence of RM (redox mediators) AQDS and riboflavin, respectively, than the assays lacking RM. The kinetic constant achieved with the azo dye Congo Red was 42 times higher than that obtained with the anthraquinone dye Reactive Blue 4. The effect of RM on dye reduction was more evident for azo dyes resistant to reductive processes, and ineffective for anthraquinone dyes because of the structural stability of the latter.

Development of an optical redox chemical sensor for nitrite determination

An optical chemical sensor for the determination of nitrite based on incorporating methyltrioctylammonium chloride as an anionic exchanger on the triacetylcellulose polymer has been reported. The response of the sensor is based on the redox reaction between nitrite in aqueous solution and iodide adsorbed on sensing membrane using anion exchange phenomena. The sensing membrane reversibly responses to nitrite ion over the range of 6.52×10-6 - 8.70×10-5 mol L-1 with a detection limit of 6.05×10-7 mol L-1 (0.03 µg mL-1) and response time of 6 min. The relative standard deviation for eight replicate measurements of 8.70×10-6 and 4.34×10-5 mol L-1 of nitrite was 4.4 and 2.5 %, respectively. The sensor was successfully applied for determination of nitrite in food, saliva and water samples.

Absorção de bário por plantas de arroz (Oryza sativa L.) e mobilidade em solo tratado com baritina sob diferentes condições de potencial redox

Two parallel tests were carried out to evaluate barium solubility in soils treated with barite under reducing conditions: one in leaching columns and another with potted plants cultivated with rice. Soils were treated with three doses of barite and kept at two humidity levels. The reduction (-200 mV) condition promoted an increase in barium in the geochemical fraction of higher liability, higher concentrations of barium in the leached extracts, and higher absorption by rice plants. As a result of increased uptake and accumulation of barium, the plants showed stunted growth

Frações da matéria orgânica e propriedades redox de substâncias húmicas em sedimentos de oceanos profundos

Previous studies have verified that free radicals such as quinone moieties in organic matter participate in the redox reactions in natural systems. These functional groups were positively correlated with the increase in aromaticity and hydrophobicity of the humic substances. As an alternative to relatively complex and expensive spectroscopic methods, the redox properties of the humic substances, determined by potentiometric titrations, have been used to evaluate organic carbon stability in soil and sediments. The present study aimed to perform organic matter fractionation and isolation of humic substances from deep oceans in different isobaths (750; 1,050; 1,350; 1,650; 1,950 m) to determine their redox properties by iodimetric titrations under an inert atmosphere and specified conditions of pH and ionic strength. Sediment samples were collected to the North and South of platforms of petroleum exploration located in the North of Rio de Janeiro State, Brazil. Fractions of organic carbon and redox properties of humic substances varied with origin and depth of the samples and with position North and South of the petroleum exploration area.

Estudio de copolimerización injerto del acrilato de butilo sobre almidón empleando sistema iniciador redox

The mixture of synthetic and natural materials yields a material with improved physical-chemical properties. One way of obtaining this kind of material is through graft copolymerization. Some natural materials have been used in graft copolymerization with synthetic monomers. In this work, graft copolymerization of butyl acrylate (BA) onto starch using a redox initiator system was carried out. The graft yield was evaluated for different reaction conditions. The graft copolymer was characterized by infrared spectroscopy, thermal analysis and scanning electron microscopy (SEM).

Use of multivariate experimental designs for optimizing the reductive degradation of an azo dye in the presence of redox mediators

The optimization of the anaerobic degradation of the azo dye Remazol golden yellow RNL was performed according to multivariate experimental designs: a 2² full-factorial design and a central composite design (CCD). The CCD revealed that the best incubation conditions (90% color removal) for the degradation of the azo dye (50 mg L- 1) were achieved with 350 mg L- 1 of yeast extract and 45 mL of anaerobic supernatant (free cell extract) produced from the incubation of 650 mg L- 1 of anaerobic microorganisms and 250 mg L- 1 of glucose. A first-order kinetics model best fit the experimental data (k = 0.0837 h- 1, R² = 0.9263).

Medição e interpretação de valores do potencial redox (E H) em matrizes ambientais

Direct measurements of Redox Potential (ORP) have been used to infer the degree of electrons availability in waters, wastewaters, sediments and soils. Although the interpretation of the results obtained in direct measurements is not trivial, this parameter is part of a list of compulsory determinations required by many Environmental State Agencies as well as consulting companies. Nonetheless, the vast majority of E H reported values are not corrected to the reference electrode used, what makes most of the data incomparable with the literature, and not suitable for a correct environmental diagnostics.

RECENTES APLICAÇÕES EM SÍNTESE ORGÂNICA DE CATÁLISE FOTO REDOX MEDIADA POR LUZ VISÍVEL

In the past few years, photoredox catalysis has become a powerful tool in the field of organic synthesis. Using this efficient method, it is possible to excite organic compounds from visible light and attain alternative mechanistic pathways for the formation of chemical bonds, a result which is not obtainable by classical methods. The rapid growth of work in the area of photoredox catalysis is due to its low cost, broad chemical utility protocols, and, especially, its relevancy from the green and sustainable chemistry viewpoints. Thus, this study proposes a brief theoretical discussion of and highlights recent advances in visible-light-induced photoredox catalysis through the analysis of catalytic cycles and intermediates.

Sensitive spectrophotometric determination of lansoprazole in pharmaceuticals using ceric ammonium sulphate based on redox and complex formation reactions

Two simple sensitive and cost-effective spectrophotometric methods are described for the determination of lansoprazole (LPZ) in bulk drug and in capsules using ceric ammonium sulphate (CAS), iron (II), orthophenanthroline and thiocyanate as reagents. In both methods, an acidic solution of lansoprazole is treated with a measured excess of CAS followed by the determination of unreacted oxidant by two procedures involving different reaction schemes. The first method involves the reduction of residual oxidant by a known amount of iron(II), and the unreacted iron(II) is complexed with orthophenanthroline at a raised pH, and the absorbance of the resulting complex measured at 510 nm (method A). In the second method, the unreacted CAS is reduced by excess of iron (II), and the resulting iron (III) is complexed with thiocyanate in the acid medium and the absorbance of the complex measured at 470 nm (method B). In both methods, the amount CAS reacted corresponds to the amount of LPZ. In method A, the absorbance is found to increase linearly with the concentration of LPZ where as in method B a linear decrease in absorbance occurs. The systems obey Beer's law for 2.5-30 and 2.5-25 µg mL-1 for method A and method B, respectively, and the corresponding molar absorptivity values are 8.1×10³ and 1.5×10(4) L mol-1cm-1 . The methods were successfully applied to the determination of LPZ in capsules and the results tallied well with the label claim. No interference was observed from the concomitant substances normally added to capsules.

Spectrophotometric determination of lansoprazole in pharmaceuticals using bromate-bromide mixture based on redox and complexation reactions

Two sensitive spectrophotometric methods are described for the determination of lansoprazole (LPZ) in bulk drug and in capsule formulation. The methods are based on the oxidation of lansoprazole by insitu generated bromine followed by determination of unreacted bromine by two different reaction schemes. In one procedure (method A), the residual bromine is treated with excess of iron (II), and the resulting iron (III) is complexed with thiocyanate and measured at 470 nm. The second approach (method B) involves treating the unreacted bromine with a measured excess of iron (II) and remaining iron (II) is complexed with orthophenanthroline at a raised pH, and measured at 510 nm. In both methods, the amount of bromine reacted corresponds to the amount of LPZ. The experimental conditions were optimized. In method A, the absorbance is found to decrease linearly with the concentration of LPZ (r = -0.9986) where as in the method B a linear increase in absorbance occurs (r = 0.9986) The systems obey Beer's law for 0.5-4.0 and 0.5-6.0 µg mL-1 for method A and method B, respectively. The calculated molar absorptivity values are 3.97µ10(4) and 3.07µ10(4) L mol-1cm-1 for method A and method B, respectively, and the corresponding Sandell sensitivity values are 0.0039 and 0.0013 µg cm-2. The limit of detection (LOD) and quantification (LOQ) are also reported for both methods. Intra-day and inter-day precision, and accuracy of the methods were established as per the current ICH guidelines. The methods were successfully applied to the determination of LPZ in capsules and the results tallied well with the label claim and the results were statistically compared with those of a reference method by applying the Student's t-test and F-test. No interference was observed from the concomitant substances normally added to capsules. The accuracy and validity of the methods were further ascertained by performing recovery experiments via standard-addition method.

Cerimetric determination of simvastatin in pharmaceuticals based on redox and complex formation reactions

Two sensitive spectrophotometric methods are described for the determination of simvastatin (SMT) in bulk drug and in tablets. The methods are based on the oxidation of SMT by a measured excess of cerium (IV) in acid medium followed by determination of unreacted oxidant by two different reaction schemes. In one procedure (method A), the residual cerium (IV) is reacted with a fixed concentration of ferroin and the increase in absorbance is measured at 510 nm. The second approach (method B) involves the reduction of the unreacted cerium (IV) with a fixed quantity of iron (II), and the resulting iron (III) is complexed with thiocyanate and the absorbance measured at 470 nm. In both methods, the amount of cerium (IV) reacted corresponds to SMT concentration. The experimental conditions for both methods were optimized. In method A, the absorbance is found to increase linearly with SMT concentration (r = 0.9995) whereas in method B, the same decreased (r = -0.9943). The systems obey Beer's law for 0.6-7.5 and 0.5-5.0 µg mL-1 for method A and method B, respectively. The calculated molar absorptivity values are 2.7 X 10(4) and 1.06 X 10(5) Lmol-1 cm-1, respectively; and the corresponding sandel sensitivity values are 0.0153 and 0.0039µg cm-2, respectively. The limit of detection (LOD) and quantification (LOQ) are reported for both methods. Intra-day and inter-day precision, and accuracy of the methods were established as per the current ICH guidelines. The methods were successfully applied to the determination of SMT in tablets and the results were statistically compared with those of the reference method by applying the Student's t-test and F-test. No interference was observed from the common excipients added to tablets. The accuracy and validity of the methods were further ascertained by performing recovery experiments via standard addition procedure.

Influência da espécie vegetal cultivada nas condições redox de sistemas alagados construídos

Em vista da escassez de informações sobre a influência de diferentes macrófitas nas condições ambientais de Sistemas Alagados Construídos (SACs), monitorou-se o potencial redox (Eh) da água residuária da suinocultura (ARS) em tratamento, em 5 SACs, com dimensões de 24,0 m x 1,1 m x 0,70 m. A ARS, previamente tratada em filtros, foi aplicada numa vazão de 0,8 m³ d-1, com tempo de residência aproximado de 4,8 d. Nos SAC1, SAC2 e SAC3 foram plantados, respectivamente, taboa (Typha latifolia L.), alternanthera (Alternanthera philoxeroides (Mart.) Griseb) e capim tifton-85 (Cynodon dactylon Pers.); no SAC4 foi plantado, no primeiro terço do tanque, alternanthera, no segundo terço, taboa e no terceiro terço, capim tifton-85. No SAC5, nada foi plantado. Coletaram-se amostras do afluente luente dos filtros e nos pontos de coleta posicionados a 4; 8; 12; 16; 20 e 24 m (saída) de cada SAC. Os valores de Eh nos afluentes dos SACs variaram entre -18 e -152 mV, entretanto, houve predomínio de condições anóxicas/aeróbias, geralmente a partir de 4 m nos sistemas. Os efluentes dos SACs apresentaram potencial redox que variou de 53 a 226 mV. Houve tendência de mais rápida oxigenação das águas residuárias no SAC1, cultivado com a taboa e, a partir de 12 m de percurso, a condição redox do meio foi semelhante em todos os SACs.

Ca2+ dependence of gluconeogenesis stimulation by glucagon at different cytosolic NAD+-NADH redox potentials

The influence of Ca2+ on hepatic gluconeogenesis was measured in the isolated perfused rat liver at different cytosolic NAD+-NADH potentials. Lactate and pyruvate were the gluconeogenic substrates and the cytosolic NAD+-NADH potentials were changed by varying the lactate to pyruvate ratios from 0.01 to 100. The following results were obtained: a) gluconeogenesis from lactate plus pyruvate was not affected by Ca2+-free perfusion (no Ca2+ in the perfusion fluid combined with previous depletion of the intracellular pools); gluconeogenesis was also poorly dependent on the lactate to pyruvate ratios in the range of 0.1 to 100; only for a ratio equal to 0.01 was a significantly smaller gluconeogenic activity observed in comparison to the other ratios. b) In the presence of Ca2+, the increase in oxygen uptake caused by the infusion of lactate plus pyruvate at a ratio equal to 10 was the most pronounced one; in Ca2+-free perfusion the increase in oxygen uptake caused by lactate plus pyruvate infusion tended to be higher for all lactate to pyruvate ratios; the most pronounced difference was observed for a lactate/pyruvate ratio equal to 1. c) In the presence of Ca2+ the effects of glucagon on gluconeogenesis showed a positive correlation with the lactate to pyruvate ratios; for a ratio equal to 0.01 no stimulation occurred, but in the 0.1 to 100 range stimulation increased progressively, producing a clear parabolic dependence between the effects of glucagon and the lactate to pyruvate ratio. d) In the absence of Ca2+ the relationship between the changes caused by glucagon in gluconeogenesis and the lactate to pyruvate ratio was substantially changed; the dependence curve was no longer parabolic but sigmoidal in shape with a plateau beginning at a lactate/pyruvate ratio equal to 1; there was inhibition at the lactate to pyruvate ratios of 0.01 and 0.1 and a constant stimulation starting with a ratio equal to 1; for the lactate to pyruvate ratios of 10 and 100, stimulation caused by glucagon was much smaller than that found when Ca2+ was present. e) The effects of glucagon on oxygen uptake in the presence of Ca2+ showed a parabolic relationship with the lactate to pyruvate ratios which was closely similar to that found in the case of gluconeogenesis; the only difference was that inhibition rather than stimulation of oxygen uptake was observed for a lactate to pyruvate ratio equal to 0.01; progressive stimulation was observed in the 0.1 to 100 range. f) In the absence of Ca2+ the effects of glucagon on oxygen uptake were different; the dependence curve was sigmoidal at the onset, with a well-defined maximum at a lactate to pyruvate ratio equal to 1; this maximum was followed by a steady decline at higher ratios; at the ratios of 0.01 and 0.1 inhibition took place; oxygen uptake stimulation caused by glucagon was generally lower in the absence of Ca2+ except when the lactate to pyruvate ratio was equal to 1. The results of the present study demonstrate that stimulation of gluconeogenesis by glucagon depends on Ca2+. However, Ca2+ is only effective in helping gluconeogenesis stimulation by glucagon at highly negative redox potentials of the cytosolic NAD+-NADH system. The triple interdependence of glucagon-Ca2+-NAD+-NADH redox potential reveals highly complex interrelations that can only be partially understood at the present stage of knowledge