Redox-active Element Research Articles

Thermodynamic properties of tooeleite, Fe63+(As3+O3)4(SO4)(OH)4·4H2O

Tooeleite, nominally Fe63+(As3+O3)4(SO4)(OH)4·4H2O, is a relatively uncommon mineral of some acid-mine drainage systems. Yet, if it does occur, it does so in large quantities, indicating that some specific conditions favor the formation of this mineral in the system Fe-As-S-O-H. In this contribution, we report the thermodynamic properties of synthetic tooeleite. The sample was characterized by powder X-ray diffraction, scanning electron microscopy, extended X-ray absorption fine-structure spectroscopy, and Mössbauer spectroscopy. These methods confirmed that the sample is pure, devoid of amorphous impurities of iron oxides, and that the oxidation state of arsenic is 3+. Using acid-solution calorimetry, the enthalpy of formation of this mineral from the elements at the standard conditions was determined as −6196.6±8.6kJmol−1. The entropy of tooeleite, calculated from low-temperature heat capacity data measured by relaxation calorimetry, is 899.0±10.8Jmol−1K−1. The calculated standard Gibbs free energy of formation is −5396.3±9.3kJmol−1. The log Ksp value, calculated for the reaction Fe6(AsO3)4(SO4)(OH)4·4H2O+16H+=6Fe3++4H3AsO3+SO42−+8H2O, is −17.25±1.80. Tooeleite has stability field only at very high activities of aqueous sulfate and arsenate. As such, it does not appear to be a good candidate for arsenic immobilization at polluted sites. An inspection of speciation diagrams shows that the predominance field of Fe3+ and As3+ overlap only at strongly basic conditions. The formation of tooeleite, therefore, requires strictly selective oxidation of Fe2+ to Fe3+ and, at the same time, firm conservation of the trivalent oxidation state of arsenic. Such conditions can be realized only by biological systems (microorganisms) which can selectively oxidize one redox-active element but leave the other ones untouched. Hence, tooeleite is the first example of an “obligatory” biomineral under the conditions prevailing at or near the Earth's surface because its formation under these conditions necessitates the action of microorganisms.

Characterizing Aging Behavior in Li-Ion Batteries Using Micro-XRF

Aging in Li-ion batteries is accompanied by structural and compositional changes of the active and passive material of the electrodes. Visualization of spatial correlation between morphological properties and chemical phase can help to find origins of aging and failure mechanisms and to understand the ongoing processes. Micro X-ray fluorescence (XRF) analysis allows for chemical imaging of elemental distributions of multiple 3d elements simultaneously, or distribution of the state of charge even at low concentrations or under operando conditions. Utilizing focused synchrotron radiation, representative volumes of the electrodes can be studied with sub-micrometer resolution on acceptable time scales. Cutting edge instrumentation in this field is the Maia fluorescence detector. It allows for ultra-fast mapping of areas of multiple mm² with high spatial resolution within minutes. This allows e.g. examination of large electrode areas. The backscattering geometry of the detector enables easy mounting of flat samples such as electrodes or pouch-cells. By variation of the energy in the vicinity of an absorption edge, conclusions on local variations of the state of charge can be drawn, probing the oxidation state of the redox-active element. Furthermore, confocal XRF enables spatially resolved measurements of the deposition of transition metals on the graphitic anode without destruction. This will help to understand the impact on capacity fade and degradation. For the present study, samples of LiNi0.5Mn1.5O4 electrodes cycled vs. Li or graphite were investigated at beamline P06 at DESY, Hamburg Germany.1 The experiment revealed significant inhomogeneities in the local Ni/Mn ratio upon cycling which is correlated to thinning of the electrode. Higher cycling rates showed an increased impact and higher material losses. Inhomogeneities in the phase transformation were also found during the charge and discharge process. The graphitic anodes showed significant amounts of deposited transition metals, few wt%, both Ni and Mn, deeply penetrating into the pores of the electrode. On the other hand, a study on commercial LiFePO4 cathodes with outstanding rate capabilities showed an extremely high degree of homogeneity throughout the investigated areas. These methods are by no means limited to the investigated materials, but are easily transferred to other transition metal containing electrode materials. 1. U. Boesenberg et al., Chem.Mater., 27, 2525–2531 (2015)

All-Soluble All-Iron Aqueous Redox-Flow Battery

The rapid growth of intermittent renewable energy (e.g., wind and solar) demands low-cost and large-scale energy storage systems for smooth and reliable power output, where redox-flow batteries (RFBs) could find their niche. In this work, we introduce the first all-soluble all-iron RFB based on iron as the same redox-active element but with different coordination chemistries in alkaline aqueous system. The adoption of the same redox-active element largely alleviates the challenging problem of cross-contamination of metal ions in RFBs that use two redox-active elements. An all-soluble all-iron RFB is constructed by combining an iron–triethanolamine redox pair (i.e., [Fe(TEOA)OH]−/[Fe(TEOA)(OH)]2–) and an iron–cyanide redox pair (i.e., Fe(CN)63–/Fe(CN)64–), creating 1.34 V of formal cell voltage. Good performance and stability have been demonstrated, after addressing some challenges, including the crossover of the ligand agent. As exemplified by the all-soluble all-iron flow battery, combining redox pairs o...

Doping cobalt hydroxide nanowires for better supercapacitor performance

Cobalt hydroxide nanowires were synthesized on Ni foam by a one-pot hydrothermal process. The specific capacitance of pure cobalt hydroxide nanowires can reach ∼1600Fg−1 at a current density of 1Ag−1. By suitably doping the redox-active element Mn into cobalt hydroxide nanowires, the specific capacitance is improved to ∼2800Fg−1 at 1Ag−1. Doping with the redox-inactive elements La and Sr gives specific capacitances per cobalt mass of ∼245, ∼2200 and ∼3200Fg−1 at 1Ag−1 for La-doped, Sr-doped and La–Sr-doped cobalt hydroxides, respectively. The effect of doping is clarified in terms of the modifications caused to the morphology, oxidation state of cobalt, electronic conductivity and additional redox reactions of cobalt hydroxide. Our work shows that chemical doping is an effective and simple route to improve the supercapacitor performance of transition metal hydroxides.

Redox Nanocomposite Cathode Materials for Lithium Rechargeable Batteries

Only a small number of Li-containing cathode materials groups are considered for practical use in Li-ion battery systems. The possible candidates of cathode material were limited to the crystals that contain both redox-active element and lithium ion in the open framework. This concept has been conventionally considered as a standard for searching the cathode materials. But, it could be constraints to restrict the choices of materials for cathode in Li-ion battery systems. To expand the sight for seeking new positive electrode material, we suggested a novel strategy to use various kinds of Li-free transition metal ionic compounds (MX, M = transition metal, X = anion or polyanion group) as a positive electrode material by blending with a Li ionic compound (LiY, Y = anion or polyanion group) in nanoscale.[1] MX and LiY provided a redox couple and lithium ion supply for an electrochemical reaction. This concept is unconventional with general system of electrode material (Li ions and transition metal ions are in the same crystal system). In this case, transition metal ion and Li ion in the nanocomposite do not exist in the same crystal system and spatially separated as a mixture of MX and LiY. In this paper, we will introduce and discuss about the transition metal oxide system as a redox couple among the infinite possible combinations of lithium ionic compounds and metal ionic compounds. Transition metal oxides such as FeO, MnO were considered as promising anode materials due to the earth abundance and large capacity from conversion reaction.[2] Although they have redox potential below 1 V as anode material,[3][4] we will show that this transition metal oxides can be applied to the cathode materials (3 V-class) by making nanocomposite with lithium ionic compound. To better understand the mechanisms during electrochemical cycling we have performed XPS, XANES/EXAFS analysis, allowing us to study the local environment change of Fe or Mn during the charge and discharge reaction. FeO and MnO showed different aspects during the electrochemical reaction in terms of electrochemical activity and local environment change. We will discuss about the reaction mechanism in detail.[1] S.-W. Kim, K-Y. Nam, D.-H. Seo, J. Hong, H. Kim, H. Gwon, and K. Kang, Nano Today, 7, 168 (2012)[2] P. Poizot, S. Laruelle, S. Grugeon, L. Dupont, and J.-M. Tarascon, Nature, 407, 496 (2000)[3] M. Gao, P. Zhou, P. Wang, J. Wang, C. Liang, J. Zhang, and Y. Liu, J. Alloy. Compd., 565, 97 (2013)[4] X. Li, D. Li, L. Qiao, X. Wang, X. Sun, P. Wang, and D. He, J. Mater. Chem., 22, 9189 (2012)

Fe(II) uptake on natural montmorillonites. I. Macroscopic and spectroscopic characterization.

Iron is an important redox-active element that is ubiquitous in both engineered and natural environments. In this study, the retention mechanism of Fe(II) on clay minerals was investigated using macroscopic sorption experiments combined with Mössbauer and extended X-ray absorption fine structure (EXAFS) spectroscopy. Sorption edges and isotherms were measured under anoxic conditions on natural Fe-bearing montmorillonites (STx, SWy, and SWa) having different structural Fe contents ranging from 0.5 to 15.4 wt % and different initial Fe redox states. Batch experiments indicated that, in the case of low Fe-bearing (STx) and dithionite-reduced clays, the Fe(II) uptake follows the sorption behavior of other divalent transition metals, whereas Fe(II) sorption increased by up to 2 orders of magnitude on the unreduced, Fe(III)-rich montmorillonites (SWy and SWa). Mössbauer spectroscopy analysis revealed that nearly all the sorbed Fe(II) was oxidized to surface-bound Fe(III) and secondary Fe(III) precipitates were formed on the Fe(III)-rich montmorillonite, while sorbed Fe is predominantly present as Fe(II) on Fe-low and dithionite-reduced clays. The results provide compelling evidence that Fe(II) uptake characteristics on clay minerals are strongly correlated to the redox properties of the structural Fe(III). The improved understanding of the interfacial redox interactions between sorbed Fe(II) and clay minerals gained in this study is essential for future studies developing Fe(II) sorption models on natural montmorillonites.

Invited Presentation: Progress in Redox Composite Cathode for Lithium Rechargeable Batteries

Only a small number of Li-containing cathode material groups have been considered for practical use in Li-ion battery systems. The constraints for cathode material design such as open anion framework and Li-containing conditions restrict the choices of materials for this use. Thus, until now, candidates of positive electrode were limited to crystals that contain both redox-active element (usually transition-metal) and lithium ion in the open framework with few exceptions. To expand the sight for seeking new positive electrode material, we recently suggested a novel strategy to use Li-free transition metal ionic compounds (MX, M = transition metal, X = anion or polyanion group) as a positive electrode material by blending with a simple Li ionic compound (LiY, Y = anion or polyanion group) in nanoscale for Li-ion batteries [1]. In this nanocomposite electrode, MX provided a redox couple for an electrochemical reaction, while Li ions were supplied from LiY.In this talk, we present our recent progress in this concept of new electrode design.Reference[1] Energy Storage in Composites of a Redox Couple Host and a Lithium Ion Host, Kim et. al, Nano Today, Vol 7, pp. 168-173 (2012)

Changes induced by zinc toxicity in the 2-DE protein profile of sugar beet roots

Changes induced by three levels of Zn toxicity in the root proteome from Beta vulgaris were studied by two dimensional gel electrophoresis. 320 spots were consistently detected and 5, 5 and 11% of them showed significant changes in relative abundance as a result of the 50, 100 and 300μM Zn treatments, respectively, when compared to controls (1.2μM Zn). Forty-four spots had consistent changes between all treatments, and 93% were identified. At low and mild Zn excess, the complex I of the mitochondrial transport chain and the oxidative phosphorylation were mildly impaired, and an effort to compensate this effect by increasing glycolysis was observed. At high Zn excess, a general metabolism shutdown occurred, as denoted by decreases in the aerobic respiration and by an impairment of the defense systems against oxidative stress. Accordingly, lipid peroxidation increased as Zn supply increased. This study suggests that metabolic changes at high Zn supply reflect cell death, while changes at low and mild Zn supplies may rather explain the metabolic reprogramming occurring upon Zn toxicity. Results also suggest that Zn competition with divalent ions including Fe may contribute to many of the Zn toxicity symptoms, especially at low and moderate Zn supplies. Results in this work provide a comprehensive overview of the effects of Zn toxicity in roots of sugar beet plants. Effects at low and mild Zn excess are similar and reflect changes in the metabolism aimed to overcome this heavy metal stress, whereas effects at high Zn supply indicate a general shutdown of the metabolism and cell death. Our results indicate that Zn toxicity elicits major impairments in the oxidative stress defense systems, possibly due to Zn competition with divalent cations including Fe, in spite that Zn is not a redox active element by itself.

Abstract 5553: Development of novel selenium-NSAIDs as potential cancer therapeutics.

Abstract Several non-steroidal anti-inflammatory drugs (NSAIDs) have been shown to be effective chemopreventive agents in both pre-clinical and clinical studies on various cancer types. Here in, we developed several selenium (Se)-NSAID hybrid molecules and evaluated their efficacy as cancer therapeutics. The rationale for introducing Se into the NSAIDs is that this redox-active trace element is an essential micronutrient and a normal component of diets with chemopreventive and anticancer properties. Our recent studies have also shown that appropriately designed organoselenium compounds exhibited promising anti-tumor properties in various preclinical cancer models. We hypothesized that the rational incorporation of Se into NSAIDs should enhance their anti-cancer properties and therefore, we synthesized 16 novel Se-NSAID hybrid agents designed by incorporating Se moieties into the structures of aspirin, ibuprofen, and naproxen. In the first phase, a selenocyanate moiety was incorporated to these NSAIDs and screened for their cytotoxicity in various cancer cell lines. The cell viability results at 24 and 48 h showed that the introduction of this Se functionality on aspirin scaffold achieved a dramatic increase in the activity as compared to aspirin, as well as other NSAIDs or their Se hybrids. Thus, we continued optimization of aspirin with a variety of Se moieties, such as selenides and selenomethyl functionalities. Most of these compounds reduced cell viability in a dose dependent manner, while aspirin had no significant effect. Based on these studies we identified two Se-aspirin hybrid compounds; ASD-43, having a selenide functionality and ASD-49, with a selenocyanate functionality, as the most potent compounds for further development. The IC50 values after 48 h treatment in HCT116 cells were 2.5μM and 1.0 μM and in MiaPaCa-2 cells were 5.0 μM and 2.5 μM for ASD-43 and ASD-49, respectively. To further establish the cytotoxic potential of these compounds, an esterase staining (live and dead) assay was performed in colon (HCT116) and pancreatic (MiaPaCa-2) cancer cells. Treatment of ASD-43 and ASD-49 reduced cell viabilities dose dependently in both HCT116 and MiaPaCa-2 cells, while aspirin had no significant effects. In addition, both these compounds induced caspase-mediated PARP cleavage as early as 24 h in HCT116 cells. In conclusion, new Se-NSAID hybrid agents have been developed which showed a solid potential to be effective cancer therapeutics in our initial studies. Detailed results of these investigations will be presented. Citation Format: Daniel Plano, Deepkamal Karelia, Manoj Pandey, Shantu Amin, Arun K. Sharma. Development of novel selenium-NSAIDs as potential cancer therapeutics. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 5553. doi:10.1158/1538-7445.AM2013-5553

Factors that Affect the Phase Behavior of Multi-Component Olivine (LiFexMnyCo1-x-yPO4; 0 < x, y< 1) in Lithium Rechargeable Batteries: One-Phase Reaction vs. Two-Phase Reaction

The structural evolution of multi-component olivines upon delithiation and lithiation was investigated by ex-situ X-ray diffraction. We found that one-phase de/lithiation occurs for multi-component olivines for a fairly large compositional range of transition metal species given that two-phase de/lithiation is generally accepted for olivine cathodes. We discuss the driving force that determines the phase behavior (two-phase reaction vs. one-phase reaction) of olivines in terms of enthalpy of mixing presumably dominated from the electrostatic interaction among cations and the elastic strain stored in the crystal due to the volume change of redox active element. We believe that this fundamental study on the phase behavior of olivines will provide insight into the intrinsic electrochemical properties of olivine electrodes for rechargeable lithium batteries.

Regulation of the Histidine Utilization (Hut) System in Bacteria

The ability to degrade the amino acid histidine to ammonia, glutamate, and a one-carbon compound (formate or formamide) is a property that is widely distributed among bacteria. The four or five enzymatic steps of the pathway are highly conserved, and the chemistry of the reactions displays several unusual features, including the rearrangement of a portion of the histidase polypeptide chain to yield an unusual imidazole structure at the active site and the use of a tightly bound NAD molecule as an electrophile rather than a redox-active element in urocanase. Given the importance of this amino acid, it is not surprising that the degradation of histidine is tightly regulated. The study of that regulation led to three central paradigms in bacterial regulation: catabolite repression by glucose and other carbon sources, nitrogen regulation and two-component regulators in general, and autoregulation of bacterial regulators. This review focuses on three groups of organisms for which studies are most complete: the enteric bacteria, for which the regulation is best understood; the pseudomonads, for which the chemistry is best characterized; and Bacillus subtilis, for which the regulatory mechanisms are very different from those of the Gram-negative bacteria. The Hut pathway is fundamentally a catabolic pathway that allows cells to use histidine as a source of carbon, energy, and nitrogen, but other roles for the pathway are also considered briefly here.

Energy storage in composites of a redox couple host and a lithium ion host

The quest for new positive electrodes for rechargeable lithium-ion batteries has been escalating in recent years. Until now, candidates of positive electrode were limited to crystals that contain both redox-active element (usually transition-metal) and lithium ion in the open framework with few exceptions. Here, we demonstrate lithium-free compounds, a material with little activity by itself, can be activated electrochemically by addition of LiF after the first charging. This general strategy is exemplified in various lithium-free iron compounds. Reversible lithium ion extraction and reinsertion take place for Fe2+F2, Fe2+SO4, and Fe22+P2O7, when blended with LiF in nanoscale, in which a simultaneous valence change of Fe2+/3+ occurs above 3V. FeF2–LiF could deliver 190mAhg−1 (∼3.53V) at 50mAg−1 which is even higher energy density than that crystalline LiFePO4 can offer. Various combinations of blending are possible using this approach, which can bring a new branch of material group for positive electrodes in lithium-ion batteries.

The microbial ferrous wheel: iron cycling in terrestrial, freshwater, and marine environments

The microbial ferrous wheel: iron cycling in terrestrial, freshwater, and marine environments

Amplified electrochemical DNA sensor using peroxidase-like DNAzyme

A novel electrochemical DNA sensor was developed here by using peroxidase-like G-quadruplex-based DNAzyme as a biocatalytic label. A hairpin structure including the G-quadruplex-based DNAzyme in a caged configuration and the target DNA probe were immobilized on Au-electrode surface. Upon hybridization with the target, the hairpin structure was opened, and the G-quadruplex-based DNAzyme was generated on the electrode surface, triggering the electrochemical oxidization of hydroquinone by H 2O 2, which provide a quantitative measure for the detection of the target DNA. The DNA target was analyzed with a detection limit of 0.6 nM. This method is simple and easy to design without direct conjugation of redox-active element.

Arsenic in an alkaline AMD treatment sludge: Characterization and stability under prolonged anoxic conditions

Lime treatment of acid mine drainage (AMD) generates large volumes of neutralization sludge that are often stored under water covers. The sludge consists mainly of calcite, gypsum and a widespread ferrihydrite-like Fe phase with several associated species of metal(loid) contaminants. The long-term stability of metal(loid)s in this chemically ill-defined material remains unknown. In this study, the stability and speciation of As in AMD sludge subjected to prolonged anoxic conditions is determined. The total As concentration in the sludge is 300 mg kg{sup -1}. In the laboratory, three distinct water cover treatments were imposed on the sludge to induce different redox conditions (100%N{sub 2}, 100%N{sub 2} + glucose, 95%N{sub 2}:5%H{sub 2}). These treatments were compared against a control of oxidized, water-saturated sludge. Electron micro-probe (EMP) analysis and spatially resolved synchrotron X-ray fluorescence (SXRF) results indicate that As is dominantly associated with Fe in the sludge. In all treatments and throughout the experiment, measured concentrations of dissolved As were less than 5 {micro}g L{sup -1}. Dissolved Mn concentration in the N{sub 2} + glucose treatment increased significantly compared to other treatments. Manganese and As K-edge X-ray absorption near edge structure spectroscopy (XANES) analyses showed that Mn was the redox-active element in themore » solid-phase, while As was stable. Arsenic(V) was still the dominant species in all water-covered sludges after 9 months of anoxic treatments. In contrast, Mn(IV) in the original sludge was partially reduced into Mn(II) in all water-covered sludges. The effect was most pronounced in the N{sub 2} + glucose treatment, suggesting microbial reduction. Micro-scale SXRF and XANES analysis of the treated sludge showed that Mn(II) accumulated in areas already enriched in Fe and As. Overall, the study shows that AMD sludges remain stable under prolonged anoxic conditions. External sources of chemical reductants or soluble C were needed to induce lower redox state in the systems, and even under these imposed treatments, only weakly reducing conditions (Mn threshold) developed. The results suggest that As(V) in AMD sludge will remain stable under prolonged anoxic conditions as long as Mn(IV) is present and organic matter accumulation is negligible.« less

Self‐Assembled Monolayers of Mono‐Tetrathiafulvalene Calix[4]pyrroles and Their Electrochemical Sensing of Chloride

Since the first reports more than a half-century ago, interest in self-assembled monolayers (SAMs) on metal surfaces has increased almost exponentially. At present, such supported SAMs are used for numerous applications, ranging from metallurgy—wherein the surface properties, such as conductivity, wettability, corrosion resistance, and etching resistance, are modified—to the preparation of sensors and materials for use in separations. In fact, the use of SAMs is now recognized as offering a convenient, flexible, and simple way to tailor the interfacial properties of metals. This is because the spontaneous organization and absorption of molecules on metal, metal oxide, or semiconducting surfaces often creates highly ordered systems with well-defined dimensions on the nanoscale. During the last decade, increasing attention has been dedicated to the design and elaboration of SAMs that integrate a molecular or ionic receptor unit with a transducer element so as to create sensing devices for environmental or biologic purposes. If a redox-active element is incorporated into the monolayer or the guest, the recognition event can be followed by cyclic voltammetry (CV). In other cases, the monitoring can be completed by using impedance spectroscopic measurements. Although, cation (generally metallic ions) recognition using SAMs is well documented, and several systems that exhibit both excellent selectivity and sensitivity have been described in the literature, much less work on anion recognition by using SAMs has been reported, perhaps reflecting the fact that anions have variable sizes and shapes and exhibit strong solvation in most solvents. The first anion recognition SAM systems were reported by Astruc et al. and involved the use of ferrocene derivatives for dihydrogenophosphate anion detection. More recently, Echegoyen et al. described SAMs for use in acetate anion recognition. Although these systems are very selective, their sensitivity is relatively low and the limits of detection do not reach the sub-millimolar scale. Calix[4]pyrrole and its derivatives have been extensively studied in the search for chemosensors capable of recognizing specific chemical species, with a number of optically active calix[4]pyrrole-based sensors having now been reported. Some of us have recently described the first fully successful examples of electrochemically active sensors based on calix[4]pyrroles; these were prepared by attaching one, two, or four redox-active tetrathiafulvalene (TTF) units directly to the calix[4]pyrrole platform so as to produce receptors with enhanced binding affinities toward anions as compared to the parent meso-octamethyl calix[4]pyrrole. In the case of the mono-TTF calix[4]pyrrole, we observed selectivity between the chloride anion (Ka= 2900m ) and the bromide anion (Ka=96m ) in CH2Cl2 solution. This success has led us to consider that TTF calix[4]pyrroles could be used to create anion-sensing SAMs. These kinds of receptors are attractive in this regard because they incorporate within one molecular framework both pyrrolebased anion recognition and TTF-derived transducer subACHTUNGTRENNUNGunits. We wish to report here that such SAMs may be prepared and that they are effective for chloride anion recognition at the sub-millimolar level, thus providing a sensitivity that differs dramatically from previously reported systems. [a] L. G. Jensen, Dr. K. A. Nielsen, Prof. J. O. Jeppesen Department of Physics and Chemistry University of Southern Denmark Campusvej 55, DK-5230, Odense M (Denmark) Fax: (+45)6615-8780 E-mail : joj@ifk.sdu.dk Homepage: http://www.jojgroup.sdu.dk [b] Dr. T. Breton, Prof. Dr. E. Levillain, Dr. L. Sanguinet Universit d’Angers—CNRS 2 boulevard Lavoisier 49045, Angers Cedex (France) E-mail : eric.levillain@iniv-angers.fr lionel.sanguinet@univ-angers.fr [c] Prof. J. L. Sessler Department of Chemistry and Biochemistry The University of Texas at Austin 1 University Station, A5300, Austin, TX 78712-0165 (USA) Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/chem.200901394.

Ceruloplasmin Alters the Tissue Disposition and Neurotoxicity of Manganese, but not its Loading onto Transferrin

Manganese (Mn) is a redox-active element, and whereas its uptake, disposition, and toxicity in mammals may depend in part on its oxidation state, the proteins affecting manganese oxidation state and speciation in vivo are not well known. Studies have suggested that the oxidase protein ceruloplasmin (Cp) mediates iron and manganese oxidation and loading onto plasma transferrin (Tf), as well as cellular iron efflux. We hypothesized that ceruloplasmin may also affect the tissue distribution and eventual neurotoxicity of manganese. To test this, aceruloplasminemic versus wild-type mice were treated with a single i.p. (54)Mn tracer dose, or elevated levels of manganese subchronically (0, 7.5, or 15 mg Mn/kg s.c., three doses per week for 4 weeks), and evaluated for transferrin-bound manganese, blood manganese partitioning, tissue manganese disposition, and levels of brain glutathione, thiobarbituric acid reactive substances (TBARS), and protein carbonyls as measures of oxidative stress, and open arena activity. Results show that ceruloplasmin does not play a role in the loading of manganese onto plasma transferrin in vivo, or in the partitioning of manganese between the plasma and cellular fractions of whole blood. Ceruloplasmin did, however, affect the retention of manganese in blood and its distribution to tissues, most notably kidney and to a lesser extent brain and lung. Results also indicate that ceruloplasmin interacted with chronic elevated manganese exposures to produce greater levels of brain oxidative stress. These results provide evidence that metal oxidase proteins play an important role in altering neurotoxicity arising from elevated manganese exposures.

Targeted alterations in iron homeostasis underlie plant defense responses

Iron (Fe) is a ubiquitous redox-active element essential for most life. The formation of localized cell wall appositions, the oxidative burst and the production of pathogenesis-related proteins are hallmarks of plant defense responses. Here, we report that iron is a central mediator linking these three phenomena. We show that in response to pathogen attack, reactive Fe3+, but not Fe2+, is deposited at cell wall appositions where it accumulates and mediates the oxidative burst. We provide evidence that the bulk secretion of Fe3+ provoked by pathogen attack leads to intracellular iron depletion, and that H2O2 itself induces ATP-dependent intracellular iron efflux. Finally, we demonstrate that this intracellular iron depletion promotes the transcription of pathogenesis-related genes in concert with H2O2. This work identifies iron as an underlying factor associated with the oxidative burst and regulating cereal defenses, and establishes links between disease-related iron homeostasis in plants and animals.

Flavin-linked peroxide reductases: protein-sulfenic acids and the oxidative stress response.

Sequence analyses of the Streptococcus faecalis NADH peroxidase and the flavoprotein component of the Salmonella typhimurium alkyl hydroperoxide reductase indicate clear evolutionary links with members of the flavoprotein disulfide reductase family. However, chemical and spectroscopic evidence demonstrate that the non-flavin redox center in NADH peroxidase is an unusual stabilized cysteine-sulfenic acid (Cys-SOH) derivative, and not a cystine disulfide as found in the disulfide reductases. This redox-active element, when appropriately stabilized by the respective protein environment, appears to play key roles in both the catalytic and regulatory aspects of the bacterial response to oxidative stress.