Soluble Mn Research Articles

Manganese oxide coated river sand for Mn(II) removal from groundwater

BACKGROUND High levels of soluble Mn(II) are often detected in groundwater in many countries, including the northeast region of China. It is necessary to remove excess amounts of Mn(II) from groundwater, especially in country sites, outside big cities. Coating manganese oxides onto a stable, cheap granular media provides an attractive alternative for Mn(II) removal from water. RESULTS Manganese oxide coated sand (MOCS) was prepared by base activation of sand with 9% NaOH for 24 h, soaking base activated sand with 7% KMnO4 for 24 h and finally calcination at 250 °C for 4 h. The MOCS had a significantly rougher surface and its surface was apparently coated with newly formed clusters of crystalline manganese oxide with a mixed manganese oxidation state of (Mn(III) and Mn(IV)). The manganese oxide effectively oxidized Mn(II) in the water to Mn(III) and Mn(IV). MOCS exhibited good Mn(II) removal performance in the filter bed experiment. The results suggested that a new catalytic flocculent manganese oxide layer was generated on the MOCS surface after filtration. CONCLUSION The new prepared MOCS in this study has potential as a catalytic adsorbent for Mn(II) removal in small waterworks in country sites. © 2014 Society of Chemical Industry

Biochar characteristics and application rates affecting corn growth and properties of soils contrasting in texture and mineralogy

Benefits of biochar as a soil amendment may vary with its properties, time after its application, and in relation to soil texture and mineralogy. Effects of pyrolysis conditions on biochar properties which, in turn, influence soil fertility and plant growth in two different soils were investigated. A pot experiment employing two types of eucalyptus wood derived biochar, i.e. low (350°C) and high (800°C) pyrolysis temperatures, was applied at four rates, i.e., 0, 1, 2, and 4% w/w, once at the beginning of the experiment to a loamy-sand Ultisol and a silty-clay-loam Oxisol. Two consecutive corn crops were grown to investigate biochar temporal effect. Low temperature biochar had lower ash (2.4%) content than its high temperature counterpart (3.9%). Biomass of the first corn crop was significantly depressed under the highest rate of the high temperature biochar compared to control treatment in the sandy Ultisol, but not in the clayey Oxisol. Biomass depression was accompanied by a significant increase in soil pH (5.88) compared to control (4.74), as well as significant increases in tissue K concentrations (43 vs 10.8gkg−1), and decreases in tissue Ca (2.8 vs 3.8gkg−1) and Mg (1.3 vs 2.6gkg−1). Biomass of the second crop increased in most biochar treatments compared to the controls, due to the reduction in phytotoxicity of Al in the Ultisol and Mn in the Oxisol. Both biochars significantly increased soluble Mn concentrations relative to the control (1.39–4.61 vs 1.12mgl−1), while they decreased tissue Mn concentrations compared to the control (0.08–0.17 vs 0.41gkg−1) in the Oxisol. Possible mechanisms underlying biochar mediated increases in soil Mn solubility and decreases in corn Mn uptake were discussed. These results showed clearly that lower temperature biochar gave higher benefits to both contrasting textured soils than the higher temperature counterpart in both first (32days after biochar application, DAA) and second (82 DAA) cropping cycles. The 1–2% w/w rate of the low temperature biochar was appropriate for these soils, the higher rate being more suited to the finer textured soil.

Heterologous expression and characterization of the manganese-oxidizing protein from Erythrobacter sp. strain SD21.

The manganese (Mn)-oxidizing protein (MopA) from Erythrobacter sp. strain SD21 is part of a unique enzymatic family that is capable of oxidizing soluble Mn(II). This enzyme contains two domains, an animal heme peroxidase domain, which contains the catalytic site, followed by a C-terminal calcium binding domain. Different from the bacterial Mn-oxidizing multicopper oxidase enzymes, little is known about MopA. To gain a better understanding of MopA and its role in Mn(II) oxidation, the 238-kDa full-length protein and a 105-kDa truncated protein containing only the animal heme peroxidase domain were cloned and heterologously expressed in Escherichia coli. Despite having sequence similarity to a peroxidase, hydrogen peroxide did not stimulate activity, nor was activity significantly decreased in the presence of catalase. Both pyrroloquinoline quinone (PQQ) and hemin increased Mn-oxidizing activity, and calcium was required. The Km for Mn(II) of the full-length protein in cell extract was similar to that of the natively expressed protein, but the Km value for the truncated protein in cell extract was approximately 6-fold higher than that of the full-length protein, suggesting that the calcium binding domain may aid in binding Mn(II). Characterization of the heterologously expressed MopA has provided additional insight into the mechanism of bacterial Mn(II) oxidation, which will aid in understanding the role of MopA and Mn oxidation in bioremediation and biogeochemical cycling.

Spectroscopic (XANES/XRF) characterization of contaminant manganese cycling in a temperate watershed

Many soils around the globe are contaminated with metals due to inputs from anthropogenic activities; however, the long-term processes that retain these metals in soils or flush them into river systems remain unclear. Soils at the Susquehanna/Shale Hills Critical Zone Observatory, a headwater catchment in central Pennsylvania, USA, are enriched in manganese due to past atmospheric deposition from industrial sources. To investigate how Mn is retained in the catchment, we evaluated the spatial distribution and speciation of Mn in the soil–plant system using X-ray fluorescence and X-ray Absorption Near Edge Structure spectroscopies. Weathered soils near the land surface were enriched in both amorphous and crystalline Mn(III/IV)-oxides, presumably derived from biogenic precipitation and atmospheric deposition, respectively. In contrast, mineral soils near the soil–bedrock interface contained Mn(II) in clays and crystalline Mn(III/IV)-oxides that formed as Mn(II) was leached from the parent shale and oxidized. Roots, stems, and foliar tissue were dominated by organic-bound and aqueous Mn(II); however, a small portion of foliar Mn was concentrated as organic-bound Mn(III) in dark spots that denote Mn toxicity. During decomposition of leaves and roots, soluble Mn(II) stored in vegetation was rapidly oxidized and immobilized as mixed-valence Mn-oxides. We propose that considerable uptake of Mn by certain plant species combined with rapid oxidation of Mn during organic matter decomposition contributes to long-term retention in soils and may slow removal of Mn contamination from watersheds.

Accumulation of Mn in Leaves of Rosmarinus officinalis Cultivated in Substrates of Pine Bark

Rosmarinus officinalis is an important aromatic shrub cultivated for medicinal, culinary, and ornamental uses. To assess growth, the contents of trace metals cadmium (Cd), copper (Cu), iron (Fe), manganese (Mn), lead (Pb), and zinc (Zn) and macronutrients calcium (Ca), magnesium (Mg), potassium (K), nitrogen (N), and phosphorus (P) were measured in these plants cultivated on two substrates: pine bark (PB, pH 4.0, 80.5% organic matter) and pruning wastes–biosolids (BS, pH 6.9, 47.5% organic matter). These plants, initially of 3.5 ± 0.5 g dry weight and 31.1 ± 6.9 cm, were maintained under greenhouse conditions for 7 months. Nutrient solution samples were taken from each substrate in situ by rhizon probes, indicating that the concentrations of soluble Mn and Zn in PB were significantly greater than in the nutritive solution BS. At the end of the assay, the dry weight of leaves and height was significantly greater in plants cultivated in BS (40.0 ± 2.2 g and 75.9 ± 14.3 cm) than in PB (27.5 ± 4.0 g and 62.4 ± 10.2 cm). Plants cultivated in PB showed slight chlorosis, attributed to the high concentration of Mn in leaves (106.6 ± 7.8 mg kg−1), which was much greater than in plants cultivated in BS (8.2 ± 0.9 mg kg−1). The concentration of toxic metals Cd and Pb in plants cultivated on both substrates did not exceed the recommended levels for consumption of the leaves as condiment. If R. officinalis is cultivated on the substrate of pine bark to acid pH for food or medicinal use, the accumulation of Mn must be considered.

Electron transport and protein secretion pathways involved in Mn(III) reduction by Shewanella oneidensis.

Soluble Mn(III) represents an important yet overlooked oxidant in marine and freshwater systems. The molecular mechanism of microbial Mn(III) reduction, however, has yet to be elucidated. Extracellular reduction of insoluble Mn(IV) and Fe(III) oxides by the metal-reducing γ-proteobacterium Shewanella oneidensis involves inner (CymA) and outer (OmcA) membrane-associated c-type cytochromes, the extracellular electron conduit MtrCAB, and GspD, the secretin of type II protein secretion. CymA, MtrCAB and GspD mutants were unable to reduce Mn(III) and Mn(IV) with lactate, H2, or formate as electron donor. The OmcA mutant reduced Mn(III) and Mn(IV) at near wild-type rates with lactate and formate as electron donor. With H2 as electron donor, however, the OmcA mutant was unable to reduce Mn(III) but reduced Mn(IV) at wild-type rates. Analogous Fe(III) reduction rate analyses indicated that other electron carriers compensated for the absence of OmcA, CymA, MtrCAB and GspD during Fe(III) reduction in an electron donor-dependent fashion. Results of the present study demonstrate that the S. oneidensis electron transport and protein secretion components involved in extracellular electron transfer to external Mn(IV) and Fe(III) oxides are also required for electron transfer to Mn(III) and that OmcA may function as a dedicated component of an H2 oxidation-linked Mn(III) reduction system.

Intelligent data mining of vertical profiler readings to predict manganese concentrations in water reservoirs

Continuously monitoring and managing manganese (Mn) concentrations in drinking water supply reservoirs are paramount for water suppliers since high soluble Mn loads lead to discoloration of potable water. Despite the Mn level currently being manually sampled throughout the year, in subtropical monomictic lakes such as Hinze Dam, critical Mn concentrations in the epilimnion, where the water is drawn, are typically recorded only during winter lake circulation. A vertical profiling system (VPS) installed can continuously collect physical parameters that determine the transport process of Mn in the lake. Therefore, a long-term historical database gives opportunities for the development of a Mn prediction model. In the present study, VPS and sampling data were collected and analysed, and prediction models applying nonlinear regression techniques and data-driven equations were developed and assessed. They were able to accurately forecast future Mn concentrations from 1 to 7 days ahead and in particular the critical peak concentrations in the epilimnion during the lake destratification. The model also displays the probabilities of the Mn to exceed certain key-thresholds, thus assisting operators in Mn treatment decision-making. Such a tool is very beneficial for the water supplier, since costly and time-consuming water samplings for monitoring Mn concentrations can be avoided, thus relying only on the real time VPS-based model outputs.

Expression of Vitreoscilla hemoglobin in Bacillus thuringiensis BMB171 can promote manganese(II) oxidation under oxygen-restricted conditions

Manganese (Mn) is one of the most abundant elements on the Earth’s crust. Nowadays, soluble Mn(II) contamination in groundwater and surface water as well as industrial wastewater is a critical environmental issue in some regions of the world. The application of Mn(II)-oxidizing microorganisms to treat Mn(II)-contaminated water is one of the most useful approaches to solve this problem. However, dissolved oxygen is a primary limitation factor for both microbial growth and Mn(II) oxidation in bioreactor systems utilizing microbial biofilms. In the study reported here we demonstrated that heterologous expression of Vitreoscilla hemoglobin (VHb) in Bacillus thuringiensis BMB171 not only enhanced the bacterial cell density but also improved the total Mn(II) oxidation activity of the recombinant strain BMB-VHb+ under oxygen-restricted conditions. Previous experiments have verified that VHb, an oxygen carrier, can facilitate the transport of oxygen into bacterial cells. Importantly, we revealed for the first time that the expression of VHb promoted the Mn(II) oxidation rate of each recombinant bacterial cell. There are two possible explanations: (1) VHb improves the concentration of substrate intracellular oxygen, and (2) VHb itself may have oxidase activity. Based on these results, we suggest that this strategy has potential applications for the treatment of the Mn(II)-contaminated water.

Lysimeter trials to assess the impact of different flood–dry-cycles on the dynamics of pore water concentrations of As, Cr, Mo and V in a contaminated floodplain soil

We hypothesize that the dynamics of water soluble arsenic (As), chromium (Cr), molybdenum (Mo), and vanadium (V) in soils might be controlled by the period of flooding due to changes of redox potential (EH), pH, and carriers of metals such as dissolved organic carbon (DOC), iron (Fe), manganese (Mn) and sulfate (SO42−). Therefore, we aimed to assess the impact of different flood–dry-cycles on the temporal dynamics of pore water concentrations of As, Cr, Mo and V as affected by changes of soil EH/pH and dynamics of DOC, Fe, Mn and SO42− in a contaminated floodplain soil collected at the Elbe River (Germany). For this purpose a specific groundwater lysimeter technique with two separate lysimeters which served as replicates was used. The groundwater level inside the lysimeters was controlled to simulate different flood–dry-cycles sequentially as follows: the long term (LT) includes 94days of flooding followed by similar drying term. The short term (ST) comprises 21days flooding followed by a similar drying term and was repeated six times. The entire experimental period (LT_ST) was about 450days. The presented data are mean values of both lysimeters.Flooding of the soil caused a significant decrease of EH and pH. Concentrations of soluble As, Cr, Fe, Mn, Mo, and DOC were higher under reducing conditions than under oxidizing conditions in LT. However, As and Cr tended to be mobilized under oxidizing conditions during ST, which might be due to slow kinetics of the redox reaction of As and Cr. Dynamics of Mo were more affected by changes of EH/pH as compared to As, Cr, and V and governed mainly by Fe–Mn chemistry. Concentrations of V in ST were higher than in LT and were controlled particularly by pH and chemistry of Fe. The interactions between the elements and carriers studied were stronger during long flood–dry-cycles than during short cycles, which confirmed our hypothesis. We conclude that the dynamics of As, Cr, Mo, and V are determined by the length of time soils are exposed to flooding, because drivers of element mobility need a certain time to provoke reactions in soils under changing conditions.

Quantitative Relation between Mn and S for Mechanical Properties of Flake Graphite Cast Iron

We investigated the effects of Mn and S on the mechanical properties of flake graphite cast iron in detail, specifically, hardness, tensile strength, elongation, impact value, deflection, and transverse load. We also investigated the cause. With increasing Mn amount for a constant S content, a transition point appears for each mechanical property. That is, hardness, tensile strength and transverse load become the smallest, and elongation, impact value and deflection become the largest. The mechanical properties of flake graphite are determined by the intervention of four actions; MnS nucleation action, interfacial energy action of soluble S, action of soluble S and soluble Mn to eutectic solidification temperature and pearlitization action of soluble S and soluble Mn. These four actions are thought to be negated by the formation MnS, resulting in the presence of the transition points. In addition, Mn and S amount showing the transition point demonstrate the best type A graphite shape. With increasing Mn amount for various S content, many transition points appear. When these points are connected, a new transition point appears near S0.03% and Mn0.32%. Excellent mechanical properties are seen at this new transition point. That is, hardness and tensile strength become the highest, and elongation and impact value which conflict with these properties also become the highest. At this new transition point (0.03%S, 0.32%Mn), MnS just starts to form ([S] © [Mn] = 0.01), and soluble S is the highest. Here, [S] means soluble S and [Mn] soluble Mn. Consequently, in flake graphite cast iron, the best excellent properties are obtained at S0.03% and Mn0.32%, which is just before MnS formation. [doi:10.2320/matertrans.F-M2014831]

Environmental manganese compounds accumulate as Mn(ii) within the Golgi apparatus of dopamine cells: relationship between speciation, subcellular distribution, and cytotoxicity

Manganese is a neurotoxic element that leads to severe neurological disorders when excessive exposure occurs, mainly in occupational settings, but that can also lead to more subtle neurological deficits, especially to the dopaminergic system, under lower exposure conditions. Mn exists in a variety of chemical species in the environment but the influence of Mn speciation on its neurotoxicity has not been fully evaluated yet. In this study we compared the cytotoxicity towards dopamine producing cells of environmental Mn compounds with a diversity of physico-chemical forms: inorganic compounds having distinct oxidation states and solubility (MnCl2, MnSO4, and Mn2O3) and organic compounds such as MMT, a gasoline additive, and maneb, a Mn-dithiocarbamate fungicide. We observed that maneb exhibited the highest toxicity, followed by MnCl2, MnSO4 and MMT which resulted in a similar intermediate toxicity, the less toxic compound being the insoluble compound Mn2O3. We combined micro-SXRF (Synchrotron X-Ray Fluorescence) for imaging and micro-XANES (X-ray Absorption Near Edge Structure) to determine the Mn oxidation state at the single cell level. Mn2O3 readily entered the cell but remained in its initial state as Mn(III) particles within the cytoplasm. The lack of toxicity of Mn2O3 can be explained by its insolubility. For all the other compounds, Mn(II) was observed and was located mainly in the Golgi apparatus, probably for detoxification purposes via exocytosis. Organic compounds MMT and maneb were degraded releasing Mn and behaved similar to the soluble Mn(II) inorganic compounds. Maneb cytotoxicity was higher probably because of the combined toxicity due to both Mn and dithiocarbamate residues. Overall these results raise the concern about environmental exposure to Mn since either inhalation of Mn combustion products or ingestion of contaminated food and drinking water will end up in neurotoxic soluble and bioavailable Mn species.

Impact of flue gas desulfurization gypsum application on water quality in a coastal plain soil.

There are growing concerns regarding the fate of nutrients, especially phosphorus (P), from land application of animal waste. One approach being studied to reduce runoff losses of P is to treat manure or the soil receiving manure with chemical amendments such as gypsum. This study used rainfall simulations to examine the impact of flue gas desulfurization (FGD) gypsum application on runoff nutrient losses on a Coastal Plains soil (Luverne sandy loam; fine, mixed, semiactive, thermic Typic Hapludults). Four rates of FGD gypsum (0, 2.2, 4.4, and 8.9 Mg ha) were applied to plots of Coastal Bermudagrass ( L.) that had received application of 13.4 Mg ha poultry litter. Plots with 8.9 Mg ha FGD gypsum but no poultry litter and plots with neither poultry litter nor FGD gypsum were also used. Rainfall simulation was used to generate water runoff for 60 min, and samples were analyzed for soluble reactive P (SRP) and soluble Al, B, Ca, Cu, Fe, K, Mg, Mn, Na, and Zn. Total concentration of Ca, Mg, K, Na, Fe, Mn, and Zn and concentration of heavy metals Ar, Hg, Al, Sb, Ba, Be, Cd, Cr, Co, Cu, Pb, Ni, Si, V, Se, Tl, and hexavalent chromium were also analyzed. Results indicated a maximum of 61% reduction in SRP concentration in runoff with the application of 8.9 Mg ha FGD gypsum. This translated to a 51% reduction in total SRP load during the 60-min runoff event. Concentrations of heavy metals in runoff were all found to be below detection limits. The results indicated that use of 4.4 Mg ha FGD gypsum on Coastal Plains pastures receiving poultry litter could be an effective method of reducing SRP losses to the environment.

Oxidative UO2 Dissolution Induced by Soluble Mn(III)

The stability of UO2 is critical to the success of reductive bioremediation of uranium. When reducing conditions are no longer maintained, Mn redox cycling may catalytically mediate the oxidation of UO2 and remobilization of uranium. Ligand-stabilized soluble Mn(III) was recently recognized as an important redox-active intermediate in Mn biogeochemical cycling. This study evaluated the kinetics of oxidative UO2 dissolution by soluble Mn(III) stabilized by pyrophosphate (PP) and desferrioxamine B (DFOB). The Mn(III)-PP complex was a potent oxidant that induced rapid UO2 dissolution at a rate higher than that by a comparable concentration of dissolved O2. However, the Mn(III)-DFOB complex was not able to induce oxidative dissolution of UO2. The ability of Mn(III) complexes to oxidize UO2 was probably determined by whether the coordination of Mn(III) with ligands allowed the attachment of the complexes to the UO2 surface to facilitate electron transfer. Systematic investigation into the kinetics of UO2 oxidative dissolution by the Mn(III)-PP complex suggested that Mn(III) could directly oxidize UO2 without involving particulate Mn species (e.g., MnO2). The expected 2:1 reaction stoichiometry between Mn(III) and UO2 was observed. The reactivity of soluble Mn(III) in oxidizing UO2 was higher at lower ratios of pyrophosphate to Mn(III) and lower pH, which is probably related to differences in the ligand-to-metal ratio and/or protonation states of the Mn(III)-pyrophosphate complexes. Disproportionation of Mn(III)-PP occurred at pH 9.0, and the oxidation of UO2 was then driven by both MnO2 and soluble Mn(III). Kinetic models were derived that provided excellent fits of the experimental results.

The leaching behaviour and geochemical fractionation of trace elements in hydraulically disposed weathered coal fly ash

A five-step sequential extraction (SE) procedure was used to investigate the leaching behaviour and geochemical partitioning of the trace elements As, Zn, Pb, Ni, Mo, Cr and Cu in a 20-year-old fly ash (FA) dump. The weathered FA, which was hydraulically co-disposed with salt laden brine in slurry form (FA: brine ratio of 1:5), was analyzed and compared with fresh FA. The weathered FA samples were collected from three cores, drilled at a coal-fired power station in the Republic of South Africa while the fresh FA sample was collected from the hoppers in the ash collection system at the power station. The FA samples were sequentially leached using: ultrapure water; ammonium acetate buffer solution (pH 7); ammonium acetate buffer solution (pH 5); hydroxylamine hydrochloride in nitric acid (pH 2) and finally the residues were digested using a combination of HClO4: HF: HNO3 acids. Digestion of as received (unleached) FA samples was also done using a combination of HClO4: HF: HNO3 acids in order to determine the total metal content. The trace element analysis was done using ICP-OES (Varian 710-ES). The SE procedure revealed that the trace elements present in the fresh FA and the weathered FA samples obtained from the three cores could leach upon exposure to different environmental conditions. The trace elements showed continuous partitioning between five geochemical phases i.e., water soluble fraction, exchangeable fraction, carbonate fraction, Fe and Mn fraction and residual fraction. Although the highest concentration of the trace elements (ranging 65.51%–86.34%) was contained in the residual fraction, a considerable amount of each trace element (ranging 4.42%–27.43%) was released from the labile phases (water soluble, exchangeable and carbonate fractions), indicating that the trace species readily leach from the dumped FA under environmental conditions thus pose a danger to the receiving environment and to groundwater.

Multi-scale analysis of the occurrence of Pb, Cr and Mn in the NIST standards: Urban dust (SRM 1649a) and indoor dust (SRM 2584)

Adverse health effects of ambient particulate matters are closely related to the speciation of the constituting organic matters and toxic metals. To determine multi-parameters of the metal speciation in urban and indoor dusts, we have performed systematic bulk- to nano-scale (“multi-scale”) analysis on the speciation of Pb, Mn, and Cr in two National Institute of Standards and Technology (NIST) standard reference materials (SRMs): urban dust (SRM 1649a) and indoor dust (SRM 2584), utilizing X-ray absorption near-edge structure, powder X-ray diffraction analysis, electron microprobe analysis, scanning electron microscopy, and transmission electron microscopy.Major crystalline phases are quartz, gypsum, kaolinite, and muscovite in SRM 1649a, while quartz, gypsum, calcite, and possibly muscovite (or chabazite) in SRM 2584. A number of Pb sulfate nanoparticles (50–200 nm) occur in SRM 1649a, whereas micron-sized Pb carbonate is present containing various concentrations of Zn and Ti in the complex texture in SRM 2584. Relatively soluble Mn(II) sulfate is the bulk-averaged Mn speciation in SRM 1649a, although discrete Mn sulfate particles are not characterized by individual particle analysis, implying the diluted Mn distribution within other sulfate. In SRM 2584, Mn speciation includes a mixture of oxides and carbonates, and trace Mn in chromite. Chromite (FeCr2O4) is the major Cr speciation in SRM1694a, while unidentified Cr(III) phases with minor chromite and Pb chromate are present in SRM 2584, among which the Pb chromate is composed of Cr(VI). A significant number of the metal-bearing particles are distributed to the submicron-size fraction in the urban dust, SRM 1649a, suggesting that these metal nanoparticles can potentially penetrate into the deep respiratory system. This study demonstrates that multi-scale analysis combining nano and bulk analytical techniques is a powerful approach to investigate the multi-parameters of metal-bearing nanoparticles in heterogeneous PM samples.

Oscillations in the Permanganate Oxidation of Glycine in a Stirred Flow Reactor

Oscillatory behavior is reported in the permanganate oxidation of glycine in the presence of Na2HPO4 in a stirred flow reactor. In near-neutral solutions, long-period sustained oscillations were recorded in the potential of a Pt electrode and in the light absorbance measured at λ = 418 and 545 nm, characteristic wavelengths for following the evolution of the intermediate [Mn(IV)] and reagent [MnO4(-) ] during the course of the reaction. No evidence of bistability was found. The chemical and physical backgrounds of the oscillatory phenomenon are discussed. In the oscillatory cycle, the positive feedback is attributed to the autocatalytic formation of a soluble Mn(IV) species, whereas the negative feedback arises from its removal from the solution in the form of solid MnO2. A simple model is suggested that qualitatively simulates the experimental observations in batch runs and the dynamics that appears in the flow system.

Characterization of indigenous barberry germplasm in Pakistan: variability in morphological characteristics and nutritional composition

Introduction . Barberry (Berberis aristata DC.), a small fruit, is found growing in the wild in the temperate region of northern Pakistan. Materials and methods . Three different locations of Azad Jammu and Kashmir, i.e ., Topa, Banjosa and Neriyan Sharif, were explored; thirty accessions of barberry were identified and characterized on the basis of their growth habit, flowering, fruiting and chemical composition of fruits. Results . The accessions exhibited high diversity in their phenotypical/morphological traits such as growth habit, intensity and time of flowering, fruit setting, ripening time, productivity, and fruit shape and color. The location had a great impact on quantitative parameters. Accessions collected from Neriyan Sharif had significantly greater plant height, higher number of branches per plant, extended flowering duration (days), took more time to maturity (days) and had high fruit setting (%), while those from Topa had large-sized leaves and fruits with greater average fruit weight. The nutritional composition of fruits indicated that the accessions from Topa had higher carbohydrate, ash, total soluble solids and Mn contents, with significantly higher juice pH, and lower acidity; while the accessions from Neriyan Sharif had significantly higher moisture, protein, fat, fiber, K, Ca, Na, Fe, Cu, Pb and Cr contents and were highly acidic. The accessions collected from Banjosa were almost intermediate for the quantitative characteristics studied. Conclusions . The results suggested that not only the genotype but its growing location as well are the main factors that determine the growing habit, productivity and nutritional composition of barberry fruits, and this ultimately provides important information on how to make the best use of them.

Abundant Porewater Mn(III) Is a Major Component of the Sedimentary Redox System

Soluble manganese(III) [Mn(III)] can potentially serve as both oxidant and reductant in one-electron-transfer reactions with other redox species. In near-surface sediment porewater, it is often overlooked as a major component of Mn cycling. Applying a spectrophotometric kinetic method to hemipelagic sediments from the Laurentian Trough (Quebec, Canada), we found that soluble Mn(III), likely stabilized by organic or inorganic ligands, accounts for up to 90% of the total dissolved Mn pool. Vertical profiles of dissolved oxygen and dissolved and solid Mn suggest that soluble Mn(III) is primarily produced via oxidation of Mn(II) diffusing upwards from anoxic sediments with lesser contributions from biotic and abiotic reductive dissolution of MnO2. The conceptual model of the sedimentary redox cycle should therefore explicitly include dissolved Mn(III).

Mn(II,III) oxidation and MnO 2 mineralization by an expressed bacterial multicopper oxidase

Reactive Mn(IV) oxide minerals are ubiquitous in the environment and control the bioavailability and distribution of many toxic and essential elements and organic compounds. Their formation is thought to be dependent on microbial enzymes, because spontaneous Mn(II) to Mn(IV) oxidation is slow. Several species of marine Bacillus spores oxidize Mn(II) on their exosporium, the outermost layer of the spore, encrusting them with Mn(IV) oxides. Molecular studies have identified the mnx (Mn oxidation) genes, including mnxG, encoding a putative multicopper oxidase (MCO), as responsible for this two-electron oxidation, a surprising finding because MCOs only catalyze single-electron transfer reactions. Characterization of the enzymatic mechanism has been hindered by the lack of purified protein. By purifying active protein from the mnxDEFG expression construct, we found that the resulting enzyme is a blue (absorption maximum 590 nm) complex containing MnxE, MnxF, and MnxG proteins. Further, by analyzing the Mn(II)- and (III)-oxidizing activity in the presence of a Mn(III) chelator, pyrophosphate, we found that the complex facilitates both electron transfers from Mn(II) to Mn(III) and from Mn(III) to Mn(IV). X-ray absorption spectroscopy of the Mn mineral product confirmed its similarity to Mn(IV) oxides generated by whole spores. Our results demonstrate that Mn oxidation from soluble Mn(II) to Mn(IV) oxides is a two-step reaction catalyzed by an MCO-containing complex. With the purification of active Mn oxidase, we will be able to uncover its mechanism, broadening our understanding of Mn mineral formation and the bioinorganic capabilities of MCOs.

One-pot synthesis of stable water soluble Mn:ZnSe/ZnS core/shell quantum dots

In this paper, Mn:ZnSe/ZnS core/shell-doped quantum dots (d-dots) with 3-mercaptopropionic acid as the stabilizer are successfully synthesized through a simple one-pot synthesis procedure in aqueous solution. The average diameter of Mn:ZnSe/ZnS core/shell d-dots is about 2.9 nm, which is lager than that of Mn:ZnSe cores (about 1.9 nm). The optical features and structure of the obtained Mn:ZnSe/ZnS core/shell quantum dots have been characterized by UV–Vis and fluorescence spectroscopy, X-ray diffraction, transmission electron microscopy, and X-ray photoelectron spectroscopy. The photostability against UV irradiation and chemical stability against H2O2 etching have been studied, and the results showed that the prepared Mn:ZnSe/ZnS core/shell d-dots are more stable than CdTe quantum dots prepared in aqueous solution. Finally, the resulting core/shell quantum dots are used as fluorescent label in human osteoblast-like HepG2 cell imaging.