Role In Redox Reactions Research Articles

Removal of Cr(VI) from aqueous solutions by low-temperature biochars from crop residues: role of redox reactions

Removal of Cr(VI) from aqueous solutions by low-temperature biochars from crop residues: role of redox reactions

Remarks on Recent Developments in the Chemical Oxido-reduction Reaction used in Treat the Wastewater

Abstract The first role of these reactions can be emphasized in the biological oxidation of the compounds that appear in water from the rotting process, but it also requires the presence of microorganisms. A second important role of redox reactions for waste water treatment is to convert pollutants into compounds that are less toxic or even harmless. Oxidation of inorganic substances such as: hexavalent chromium, cyanide can be possible by resorting to the energized oxidizing agents such as sodium metabisulfite or sodium hypochlorite. We experimentally tried to treat waste water from electroplating plants that have a high content of hexavalent chromium by using IC 14D system. First of all, the hexavalent chromium was reduced to trivalent chromium by using the sodium metabisulphite as oxidizing agent. Secondly, the trivalent chromium was removed by passing it into a precipitated Cr(OH)3 in an alkaline medium. After sedimentation, the slurry was removed, water thus treated may be discharged in any effluent.

NAD and ADP‐ribose metabolism in mitochondria

Mitochondrial metabolism is intimately connected to the universal coenzyme NAD. In addition to its role in redox reactions of energy transduction, NAD serves as substrate in regulatory reactions that lead to its degradation. Importantly, all types of the known NAD-consuming signalling reactions have been reported to take place in mitochondria. These reactions include the generation of second messengers, as well as post-translational protein modifications such as ADP-ribosylation and protein deacetylation. Therefore, the availability and redox state of NAD emerged as important factors in the regulation of mitochondrial metabolism. Molecular mechanisms and targets of mitochondrial NAD-dependent protein deacetylation and mono-ADP-ribosylation have been established, whereas poly-ADP-ribosylation and NAD-derived messenger generation in the organelles await in-depth characterization. In this review, we highlight the major NAD-dependent reactions occurring within mitochondria and describe their metabolic and regulatory functions. We also discuss the metabolic fates of the NAD-degradation products, nicotinamide and ADP-ribose, and how the mitochondrial NAD pool is restored.

Oxidation Reactions Mediated by Single-Walled Carbon Nanotubes in Aqueous Solution

How single-walled carbon nanotubes (SWCNT) function in redox reactions may be related to their behaviors in the induction of oxidative stress. Herein, oxidation of several biologically relevant reducing agents in the presence of SWCNT was studied in aqueous solutions. The selected reductants included a common indicator for intracellular reactive oxygen species (ROS) (2,7-dichlorodihydrofluorescein), small antioxidants (vitamin C, Trolox, and cysteine), and a high-molecular-weight ROS scavenger (bovine serum albumin). The unmodified or carboxylated SWCNT acted as both the oxidants and the catalysts in reactions. Moreover, they accelerated the oxidation reactions mediated by horseradish peroxidase, a representative member of the enzyme family actively involved in balancing oxidative stress. These diverse roles in redox reactions may serve the chemistry basis for SWCNT to induce oxidative stress in biological systems as potential environmental pollutants.

Astroelectrochemistry: the role of redox reactions in cosmic dust chemistry

We propose that redox reactions on the surface of interstellar dust grains contribute to the synthesis of some polyatomic species that have been identified by spectroscopic signatures. Most of the dust is found in clouds along with a rich abundance of molecular and atomic species, creating a thermodynamically distinct region in the interstellar medium (ISM) where chemistry can be supported. Using knowledge of redox process at the solid/liquid interface, a hypothesis is presented for processing mechanisms involving electron transfer between surface adsorbed species and the solid dust grains found in the ISM. The hypothesis is based on the interaction of dust grains with electromagnetic radiation and plumes of ionised gas, which electrostatically charge dust grains leading to an adjustment of the Fermi energy of electrons on the surface of individual grains. This process is equivalent to applying an external electrochemical potential to an electrode, to drive redox chemistry on an electrode surface in electrolysis or dynamic electrochemistry. Here the individual grains act as 'single electrode' electrochemical reactors in the gas phase. In this paper we highlight a gap in understanding of redox reactions at the solid/gas interface, which is potentially a very fruitful and interesting area of research.

Mitochondrial Ferritin in the Substantia Nigra in Restless Legs Syndrome

Restless legs syndrome (RLS) is a neurological disorder that is thought to involve decreased iron availability in the brain. Iron is required for oxidative metabolism and plays a critical role in redox reactions in mitochondria. The recent discovery of mitochondrial ferritin (FtMt) provided the opportunity to identify a potential correlation between iron and mitochondrial function in RLS. Human substantia nigra (SN) and putamen autopsy samples from 8 RLS cases and 8 controls were analyzed. Mitochondrial ferritin levels in RLS SN tissue homogenate samples assessed by immunoblots had more FtMt than control samples (p < 0.01), whereas there were no significant differences in FtMt in the putamen samples. By immunohistochemistry, neuromelanin-containing neurons in the SN were the predominant cell type expressing FtMt. Staining in neurons in RLS samples was consistently greater than that in controls. Cytochrome c oxidase staining, which reflects numbers of mitochondria, showed a similar staining pattern to that of FtMt, whereas there was less immunostaining in the RLS cases for cytosolic H-ferritin. These results suggest that increased numbers of mitochondria in neurons in RLS and increased FtMt might contribute to insufficient cytosolic iron levels in RLS SN neurons; they are consistent with the hypothesis that energy insufficiency in these neurons may be involved in the pathogenesis of RLS.

A new correction model for 14C ages in aquifers with complex geochemistry – Application to the Neogene Aquifer, Belgium

The objective of this paper is to build a general correction model that takes into account all the different radiocarbon-dilution reactions and resolving the processes that are geochemically “aging” the groundwater in the Neogene Aquifer. For this, δ 13 C and radiocarbon in groundwater are investigated with their relationship to other chemical components in groundwater. The δ 13 C values in the Neogene Aquifer are influenced by various geochemical reactions like calcite dissolution, oxidation of organic matter and methanogenesis. Calcite dissolution and CH 4 production increase δ 13 C while the oxidation of organic matter decreases δ 13 C in the groundwater. The reactions that modify δ 13 C also influence the 14 C activity. Due to the complex geochemical environment, existing correction models are not applicable to this situation. A correction model for initial 14 C activity is formulated in which the different C sources that influence 14 C activity are taken into account. It is observed that recent dissolved organic matter plays an important role in redox reactions. The corrected 14 C ages lie between −0.792 and 6.425 ka representing the maximum age. If a part of the organic matter that oxidises is fossil, the determined age will represent an overestimated age.

Role of Redox Reactions in the Vascular Phenotype of Hyperhomocysteinemic Animals

Hyperhomocysteinemia is a risk factor for cardiovascular disease, stroke, and thrombosis. Several animal models of hyperhomocysteinemia have been developed by using both dietary and genetic approaches. These animal models have provided considerable insight into the mechanisms underlying the adverse vascular effects of hyperhomocysteinemia. Accumulating evidence suggests a significant role of altered cellular redox reactions in the vascular phenotype of hyperhomocysteinemia. Redox effects of hyperhomocysteinemia are particularly important in mediating the adverse effects of hyperhomocysteinemia on the endothelium, leading to loss of endothelium-derived nitric oxide and vasomotor dysfunction. Redox reactions also may be key factors in the development of vascular hypertrophy, thrombosis, and atherosclerosis in hyperhomocysteinemic animals. In this review, we summarize the metabolic relations between homocysteine and the cellular redox state, the vascular phenotypes that have been observed in hyperhomocysteinemic animals, the evidence for altered redox reactions in vascular tissue, and the specific redox reactions that may mediate the vascular effects of hyperhomocysteinemia.

Reorganization Energy of the CuA Center in Purple Azurin: Impact of the Mixed Valence-to-Trapped Valence State Transition

Mixed valence (MV) coordination compounds play important roles in redox reactions in chemistry and biology. Details of the contribution of a mixed valence state to protein electron transfer (ET) reactivity such as reorganization energy, however, have not been experimentally defined. Herein we report measurements of reorganization energies of a binuclear CuA center engineered into Pseudomonas aeruginosa azurin that exhibits a reversible transition between a totally delocalized MV state at pH 8.0 and a trapped valence (TV) state at pH 4.0. The reorganization energy of a His120Ala variant of CuA azurin that displays a TV state at both the above pH values has also been determined. We found that the MV-to-TV state transition increases the reorganization energy by 0.18 eV, providing evidence that the MV state of the CuA center has lower reorganization energy than its TV counterpart. We have also shown that lowering the pH from 8.0 to 4.0 results in a similar (approximately 0.4 eV) decrease in reorganization energy for both blue (type 1) and purple (CuA) azurins, even though the reorganization energies of the two different copper centers are different at a given pH. These results suggest that the MV state plays only a secondary role in modulation of the ET reactivity via the reorganization energy, as compared to that of the driving force.

A new insight into redox mechanisms of cysteamine‐induced duodenal ulcers

Cysteamine (C) (HS-CH2-CH2-NH2) is a reducing aminothiol which may react with transition metals to generate H2O2. C specifically induces ulcers in rat proximal duodenum where most dietary iron absorption takes place. We hypothesized that iron may play a role in redox reactions involved in the pathogenesis of C-induced duodenal ulcers (DU). In rats, using oxygen and redox electrodes we detected a decrease in both oxygen concentration and redox potential in the proximal duodenum at 2 and 12 hr after administration of C (25 mg/100 g, p.o.). A detectable level of C was found by HPLC assay in duodenal mucosa (0.018 ug/mg wet weight) and 4 fold less in gastric mucosa but not in jejunum, colon or liver 2 hr after C administration. Rats fed an iron-deficient diet for 6 weeks had a 34% decrease in iron concentration in the duodenal mucosa, accompanied by a 6.6 fold decrease in C-induced DU size. Pretreatment of rats with Fe3+or Fe2+aggravated DU, whereas iron depletion by deferoxamine decreased DU by 38%. [C14]C uptake by isolated duodenal, gastric, jejunal and colonic enterocytes, and by IEC-6 and Caco-2 cells increased linearly with time (up to 15 min). [C14]C uptake was pH dependent, with higher uptake in more alkaline buffer. Unlabeled C (1 mM) markedly inhibited [C14]C uptake by all cells. Overloading IEC-6 with iron (100 uM for 1 hr) accelerated uptake of [C14]C by 40%, but incubation of cells with deferoxamine (100 or 200 uM for 24 hr) inhibited C uptake by 30% and 61%, respectively. These findings suggest a role for iron-catalyzed redox reactions in the pathogenesis of C-induced organ-specific tissue injury.

Homocysteine

The authors of the much publicized though not yet published Norwegian Vitamin Study (NORVIT)1 of vitamin therapy in coronary artery disease, are widely quoted as saying that vitamin therapy for lowering plasma total homocysteine (tHcy) was harmful, and that “homocysteine is dead.” However, the slides of their presentation1 do not show the B12 status of the participants, nor do they indicate whether B12 injections were given to participants with low levels of B12. Commentators2 have called NORVIT “the largest trial to date to test the hypothesis that folate supplementation reduces risk of cardiovascular disease,” but because there were 4 treatment arms in NORVIT, each with 900 participants, the number of patients randomized to folate/B12 or folate/B12/B6 was essentially the same as that in the Vitamin Intervention for Stroke Prevention (VISP) trial3 (≈1800). They used a much higher dose of B6 than other studies and cannot exclude the possibility that their results were driven by that choice. As did VISP, they also used a dose of B12 that, as has recently become apparent, was too low for adequate absorption of B12 in elderly subjects (discussed below). In this issue of Stroke , a substudy of the Vitamins to Prevent Stroke (VITATOPS) trial4 reports that in Singapore, treatment with 2.5 mg folic acid, 0.5 mg vitamin B12, and 25 mg B6 reduced levels of tHcy by 3.8 μmol/L compared with placebo.5 The authors also studied 2 polymorphism …

Mechanism of radiation purification of polluted water and wastewater.

The paper summarizes the results of the studies on radiation purification of polluted water and wastewater conducted in the author's laboratory in cooperation with other institutions. The removal of heavy metals (cadmium, lead, chromium and mercury) from water and wastewater, the purification of wastewater from surfactant and petroleum products, molasses distillery slops, municipal wastewater in the aerosol flow, river water from colored natural organic pollutants, wastewater of dyeing complex and paper mill, the decomposition of some dyes, hydrogen peroxide, chlorine-containing organic compounds, formic acid, etc. were investigated in detail. As a rule, electron-beam treatment in combination with ordinary methods (biological, coagulation, adsorption, flotation, etc.) was used. The main attention is paid to the mechanism of purification of the studied systems. The role of redox reactions of primary products of water radiolysis and secondary short-lived species formed from pollutants, formation of precipitates capturing the pollutants etc. is discussed.

Redox modulation of reductase and phosphatase activities in human erythrocytes

We have previously reported that ferricyanide reductase activity in human erythrocytes depended on glycolysis and could be modulated by several compounds including oxidants and hormones like insulin. Insulin could activate glycolysis, probably as a consequence of tyrosine phosphorylation of protein band 3, implicating phosphorylation reactions as an important signal for activation of the reductase by insulin. Reversible phosphorylation of cellular proteins is also believed to play a key role in the action of insulin. Cytosolic acid phosphatase activity has been found in human erythrocytes. To further extend initial reports, we studied the effect of modulators on the cytosolic erythrocyte acid phosphatase. Mild oxidants like ferricyanide (1 mM), vanadate (1 mM), Mn2+ (0.5 and 1 mM), and phenylarsine oxide (10 and 100 μM) inhibited the phosphatase activity. Similarly, insulin at concentrations that stimulate ferricyanide reduction (500, 1000 μIU/ml) inhibited the activity of the phosphatase enzyme. The overall results indicated that oxidants are able to inhibit the acid phosphatase and stimulate the redox enzyme. In addition, a significant negative correlation (r = −0.400; P = 0.006) was observed between phosphatase and reductase activities. The observations discussed here, together with previous ones, emphasize that a close association between reductase and phosphatase enzymes may exist and also suggest a role for redox reactions in tyrosine phosphorylation/dephosphorylation-mediated signal transduction pathways.

Hydrogen peroxide in the marine environment: cycling and methods of analysis

Hydrogen peroxide (H 2O 2) is a key intermediate in many biological and environmental processes and there are a range of analytical methods available for its quantification, e.g. spectrophotometry, fluorimetry, chemiluminescence and electroanalytical techniques. This article focuses on the determination of H 2O 2 in seawater, wherein it is believed to play a significant role in redox reactions and the photochemical oxidation of dissolved organic matter. The cycling of H 2O 2 in seawater and potential approaches to in-situ monitoring are discussed, with particular reference to chemiluminescence techniques.

Primary processes in the photochemistry of rhodamine dyes

Quantum yields for intersystem crossing in rhodamine 6G, N,N′-diethylrhodamine and rhodamine B as well as their triplet—triplet (T—T) absorption spectra were measured in aqueous solutions. The main pathways of rhodamine singlet excited state decay are fluorescence and internal conversion. The main pathways of rhodamine triplet state decay radiationless deactivation, quenching by impurities and by ion radicals, T—T interaction and self-quenching. The process of the electron transfer is considered to be the result of T—T interaction and self-quenching of rhodamine triplets in plain aqueous solutions. Triplet states of rhodamine dyes play a major role in redox reaction that occur in the presence of exogenic electron donors and acceptors. The kinetic decay of half-reduced and half-oxidized rhodamine species was studied. The peculiar properties of rhodamine 6G photoreactions occurring in alcohol solutions are considered. The rate constants of the rhodamine triplet and ion radical decay processes are determined.

Triplet states of cyanine dyes and reactions of electron transfer with their participation

The radiationless decay processes of the excited singlet states of thiacarbocyanines are considered. It was revealed that the quantum yield (Φ ST) of intersystem crossing is low (Φ ST ?? 0.1) for certain unsubstituted (in the meso position) thiacarbocyanines. The triplet level for unsubstituted thiacarbocyanines can be populated efficiently owing to triplet—triplet energy transfer. The values of Φ ST are increased markedly for 9-CH 3O- and 9-NH 2-thiacarbocyanines where T—T absorption is observed on direct flash excitation. Using triplet—triplet energy transfer it was established that cis—trans isomerization for certain unsubstituted thiacarbocyanines occurs via a singlet excited state. For unsubstituted thiacarbocyanines the main pathways of the singlet excited states decay are cis—trans isomerization and internal conversion. The main processes of the triplet state decay are radiationless deactivation, quenching by impurities ( e.g. traces of oxygen), triplet—triplet annihilation and self-quenching. The values of rate constants were determined for certain thiacarbocyanines. Mixed triplet—triplet annihilation was established on sensitized excitation of thiacarbocyanines in the presence of anthracene (sensitizer). Triplet states of thiacarbocyanines play a major role in redox reactions. Experimental evidence favours the extreme participation of triplet states in electron transfer processes. Efficiency of triplet state quenching by certain electron donors (ascorbic acid, β-naphthylamine) and acceptors ( p-benzoquinone, methylviologen) was considered. In some cases quenching is accompanied by the production of ion-radicals. The oxidative and reductive mechanisms of sensitization are considered and the values of rate constants for some elementary steps with thiacarbocyanines triplet states involved are determined.

Glimpses of the international electrical exhibition

Selenium, first discovered by Berzelius and named after the goddess of the moon Selene, is a trace metalloid present in a variety of chemical forms in the environment, both inorganic and organic. Chemists have studied selenium since the nineteenth century, including a seminal study by Alexander Graham Bell in his early reports of the photophone at the turn of the century. Although selenium was studied for its toxicity in the first half of the twentieth century, experiments on animals in the 1950s led to the knowledge that selenium is essential as a micronutrient in animals. In 1973, selenium was found to be present in both a mammalian enzyme (glutathione peroxidase) and two bacterial enzymes (glycine reductase selenoprotein A and formate dehydrogenase) and these findings led to expansion of the study of selenium at the molecular level, primarily in bacterial model systems. We know that selenium plays a critical role in redox reactions in mammals and that selenium-dependent enzymes are critical for ATP synthesis in a small group of anaerobic bacteria. Even so, not all biological organisms require selenium for growth or metabolism, but for those that are capable of specific incorporation of selenium into a catalytic form within proteins and enzymes, selenium is a critical micronutrient. Moreover, specific incorporation of selenium into macromolecules appears widespread in strict anaerobes, suggesting that an oxygenic environment may have altered the evolutionary pressure to maintain or lose this capability. The emergence of the field of genomics has had a great impact on the prediction of the presence of selenoproteins in a large number of organisms, opening new vistas to experimental discovery in the forthcoming decades.