Solid Mn Research Articles

Spatially Variable Bioturbation and Physical Mixing Drive the Sedimentary Biogeochemical Seascape in the Louisiana Continental Shelf Hypoxic Zone.

Seasonal hypoxia on the Louisiana continental shelf (LCS) has grown to over 22,000 km2 with limited information available on how low oxygen effects the benthos. Benthic macrofaunal colonization and sediment biogeochemical parameters were characterized at twelve stations in waters 10 - 50 m deep along four transects spanning 320 km across the LCS hypoxic zone in the early fall of 2010 when bottom waters typically return to oxic conditions. Chemical data and sediment profile imaging (SPI) support three primary mechanistic pathways of organic matter degradation on the LCS: (i) metal oxide cycling in depositional muds, (ii) infauna-driven bioturbation delivering oxygen below the sediment-water interface, and (iii) sulfate reduction in sediments where iron oxide availability is limited. The transect nearest the Mississippi River delta had the highest concentrations of porewater and solid phase Mn and Fe with SPI images of recently deposited reddish, mixed muddy sediments suggestive of metal cycling. The deepest stations had high oxidized iron concentrations and rust colored sediments with faunal colonization that suggests sediments are oxidized via bioturbation. Many nearshore and central LCS stations had more black sediments, more disturbed clay layers, lower amounts of oxidized iron, and higher sulfate reduction rates than the deepest stations. Sediment mixing coefficients, DB , determined from chlorophyll-a concentration profiles varied between 33 and 183 cm-2 y-1. DB values were highest at the deepest stations where sediments were colonized. DB were not determined at two nearshore stations where chlorophyll-a concentrations were highly variable in surficial sediments, and on the eastern shelf where sedimentation is high. This study provides a regional view of benthic faunal colonization and sediment biogeochemistry on the LCS, describes regions with potentially different pathways of organic matter degradation, and demonstrates the importance of both bioturbation and physical mixing in processing the large amounts of organic matter in river-dominated continental shelf systems.

Spectrophotometric determination of manganese in acidified matrices from (pore)waters and from sequential leaching of sediments

Manganese (Mn) is a major redox reactive element in marine sediments and it plays an important role in the biogeochemical cycles of carbon, nitrogen, phosphorus, or trace metals. Mn cycle in marine sediments is characterized by an alternation of oxidation and reduction processes depending on physicochemical and biological conditions: assessing the quantification and the speciation of Mn is thus an essential issue to understand redox reaction-transport processes in sedimentary deposits. Solid Mn phases can be determined through chemical extractions techniques that permits selective leaching of operationally defined Mn fractions. Mn oxides and oxyhydroxides are extracted with an ascorbate leaching solution, while the whole Mn (oxyhydr-)oxides and Mn associated to carbonates is extracted with HCl.An existing spectrophotometric method allows to quantify Mn dissolved in (sea) water. We present here a modified version, which permits to measure Mn in acidified matrices, including ascorbate and HCl solutions. A metallic substitution occurs between a Cd-TCPP complex and Mn at pH 7.5–8.0, with imidazole as catalyst. We propose here to use a NaHCO3 solution to dilute the samples in order to be in the necessary pH range to perform the metal substitution. Using this method, Mn(II,III) concentrations were determined in standard solutions with a precision of 3% within a concentration range of 0.5–80 μM. The procedure was successfully applied to determine Mn in acidified pore waters and in ascorbate and HCl sequential extractions from muddy sediments of the Bay of Biscay. Spectrophotometric results agreed closely with results from atomic absorption spectrometry, validating the proposed method.

Two heptacoordinated manganese(II) complexes of giant pentadentate s -triazine bis -Schiff base ligand: Synthesis, crystal structure, biological and DFT studies

Abstract A new s-triazine bis-Schiff base chelating ligand (L) and two of its heptacoordinated Mn(II) complexes were synthesized and characterized. Reaction of solid Mn(NO3)2·4H2O with methanolic solution of the ligand (L; 5) afford [MnL(MeOH)NO3]NO3.MeOH; (6). While, repeating the reaction in water/methanol solution, the complex [MnL(H2O)2](NO3)2; (7) was formed. In both complexes, the Mn(II) is coordinated with L as a pentadentate ligand via its N-atoms augmented with two axial Mn O bonds leading to a distorted pentagonal bipyramidal configuration around the Mn(II) ion. The two-pyridine moieties at the end of the ligand arms are twisted from one another due to the short contact distance between the two hydrogen atoms at the 6 position of the pyridine moieties. As a result, the strength of the Mn N bonds decrease ongoing from the triazine moiety towards the outside of the ligand arms. The atoms in molecules topological parameters correlated well with the Mn N distances. The Mn N and Mn O bonds were analyzed using natural bond orbital calculations. Both complexes showed higher thermal stability than the free ligand. Antimicrobial studies showed that 7 and L are the best candidates as antifungal and antibacterial agents, respectively. The mechanism of biological activity depends on the interactions between the compound and cell wall.

Nature of the Color of Borates with "Anti-Zeolite" Structure.

Crystals of the Mn xBa12(BO3)8-2 xF8 x phase were grown from a high-temperature solution. This new fluoride borate is built of positively charged [Ba12(BO3)6]6+ blocks, the so-called "anti-zeolite" pattern. Using X-ray single-crystal diffraction, the bulk atomic arrangement in the centrosymmetric tetragonal unit cell in I4/ mcm could be elucidated. Crystals of the (MnF6)4- group-containing solid solution Mn xBa12(BO3)8-2 xF8 x are dark brown in color in contrast to the differently colored crystals of (LiF4)3- group-containing "anti-zeolite" LiBa12(BO3)7F4 ( P42 bc). According to the electron spin resonance and optical spectroscopic investigation, the absorption spectrum of LiBa12(BO3)7F4 crystals results from the absorption of light by both exciton and free charge carriers and can be tuned by varying the initial composition of the high-temperature solution.

X-ray studies of doped bismuth titanates

X-ray diffraction and NEXAS- and XPS-spectroscopy have been investigated thermostable solid solutions Mn, Cu-doped bismuth titanate with a pyrochlore-type structure. It was shown that manganese and copper in said solid solution of bismuth titanate is present mainly in the oxidation state +2, and titanium - in +4.

Kinetics of α-MnOOH Nanoparticle Formation through Enzymatically Catalyzed Biomineralization inside Apoferritin

While biomineralization in apoferritin has effectively synthesized highly monodispersed nanoparticles of various metal oxides and hydroxides, the detailed kinetics and mechanisms of Mn(III) (hydr)oxide formation inside apoferritin cavities have not been reported. To address this knowledge gap, we first identified the phase of solid Mn(III) formed inside apoferritin cavities as α-MnOOH. To analyze the oxidation and nucleation mechanism of α-MnOOH inside apoferritin by quantifying oxidized Mn, we used a colorimetric method with leucoberbelin blue (LBB) solution. In this method, LBB disassembled apoferritin by inducing an acidic pH environment, and reduced α-MnOOH nanoparticles. The LBB-enabled kinetic analyses of α-MnOOH nanoparticle formation suggested that the orders of reaction with respect to Mn2+ and OH– are 2 and 4, respectively, and α-MnOOH formation follows two-step pathways: First, soluble Mn2+ undergoes apoferritin-catalyzed oxidation at the ferroxidase dinuclear center, forming a Mn(III)-protein ...

Interfacial reaction mechanism between multi-component oxides and solid alloys deoxidised by Mn and Si during heat treatment

To clarify the interfacial reaction mechanism between multi-component oxides and solid Mn- and Si-deoxidised alloys during heat treatment, five diffusion couples with different compositions of Fe–Mn–Si alloy and CaO–SiO2–Al2O3–MgO–MnO oxide were produced using a confocal scanning laser microscope. The changes in the chemical compositions of the oxide and alloy by heat treatment at 1273 and 1473 K were investigated. The mechanisms of the ‘solid–solid’ and ‘solid–liquid’ interfacial reactions and the diffusion of elements between the alloy and oxide were revealed thermodynamically and are discussed. The results show that counter-diffusion occurring between Mn and Si in the alloy and oxide was the main reaction in the diffusion couples. The MnO content of the oxide and the Si content of the alloy are the driving forces of the interfacial reactions.

THE THYMIDINE KINASE-1(TK-1) AS A POTENTIAL TUMOR MARKER: SERUM LEVELS IN SERUM OF PATIENTS WITH SOLID AND SYSTEM MALIGNANCE NEOPLASMS

The review summarizes the results of studies of levels and/or activity in the blood serum of a metabolic marker thymidine kinase-1 (TK-1) of proliferating cells in patients with lymphoproliferative diseases (LPD) and malignant neopasms (NM). Comparison of the data in the literature in some cases have been difficult due to the fundamentally different methods of detection the activity or concentration of TK-1, used by authors, even despite the presence of relatively high (but not absolute) correlation between these parameters (maximum 0.8). Many clinical and laboratory studies have shown levels of correlation and/or TK-1 activity with clinical stages and different types of LPD and solid MN and can serve as a prognostic factor for overall and recurrence-free survival of patients. When solid MN shown that the activity of TK-1 accurately reflects the proliferative status of tumor. A comparison of the dynamics of TC-1 in the process of chemotherapy and its clinical efficacy, different authors have received fundamentally different results: in some cases the marker reduction was associated with treatment efficacy, and in part of publications they show that the clinically relevant effects of the treatment observed increase in the marker after the first chemotherapy. The entire set of received data demonstrates the relevance of the further development of the algorithm use of TK-1 in oncology practice.

Characterization of toluene and ethylbenzene biodegradation under nitrate-, iron(III)- and manganese(IV)-reducing conditions by compound-specific isotope analysis

Ethylbenzene and toluene degradation under nitrate-, Mn(IV)-, or Fe(III)-reducing conditions was investigated by compound specific stable isotope analysis (CSIA) using three model cultures (Aromatoleum aromaticum EbN1, Georgfuchsia toluolica G5G6, and a Azoarcus-dominated mixed culture). Systematically lower isotope enrichment factors for carbon and hydrogen were observed for particulate Mn(IV). The increasing diffusion distances of toluene or ethylbenzene to the solid Mn(IV) most likely caused limited bioavailability and hence resulted in the observed masking effect. The data suggests further ethylbenzene hydroxylation by ethylbenzene dehydrogenase (EBDH) and toluene activation by benzylsuccinate synthase (BSS) as initial activation steps. Notably, significantly different values in dual isotope analysis were detected for toluene degradation by G. toluolica under the three studied redox conditions, suggesting variations in the enzymatic transition state depending on the available TEA. The results indicate that two-dimensional CSIA has significant potential to assess anaerobic biodegradation of ethylbenzene and toluene at contaminated sites.

3003アルミニウム合金の再結晶挙動に及ぼすSi濃度の影響

The effects of Si content on recrystallization of 3003 aluminum alloys were investigated to obtain fundamental knowledge to control the mechanical properties of heat exchanger materials. The 3003 aluminum alloys containing various amounts of Si were cast, hot-rolled, cold-rolled and annealed at various temperatures. The recrystallization temperature became higher, and the decrease in the solid solute Mn content became larger with the decrease in the Si contents. When the annealing temperature was lower than the recrystallization temperature, minute dispersoids with the size of around 10 nm were observed in the alloy without Si addition, whereas they were not observed in the Si-added alloys. These results suggested that the recrystallization was strongly inhibited by the precipitation which was enhanced by nucleation around the dislocations during the annealing, if the Si content of the 3003 alloy was extremely low. The precipitation during the annealing was considered to be caused by the large amount of the solid solute Mn. Since the solid solute Mn was considered to be drastically decreased by the precipitation of Al–Mn–Si compounds during the hot-rolling process, the inhibition of recrystallization by the precipitation during the annealing did not occur under the high Si content.

Isothermal diagrams of the Li2O–MnO–MnO2 system

The isothermal diagrams of the Li2O–MnO–MnO2 system at an oxygen pressure up to 100 kPa were constructed, which allow to consistently represent phase transformations involving stable ternary phases: low-temperature spinel, cubic spinel c-LiMn2O4, tetragonal phase t-LiMn2O4, orthorhombic phase LiMnO2, monoclinic solid solution LixMnO2 (0.33 ≤ x < 0.5), spinel-structure solid solution LixMn3–xO4, and solid solution Mn(Li)O.

Characterization of pH dependent Mn(II) oxidation strategies and formation of a bixbyite-like phase by Mesorhizobium australicum T-G1.

Despite the ubiquity of Mn oxides in natural environments, there are only a few observations of biological Mn(II) oxidation at pH < 6. The lack of low pH Mn-oxidizing bacteria (MOB) isolates limits our understanding of how pH influences biological Mn(II) oxidation in extreme environments. Here, we report that a novel MOB isolate, Mesorhizobium australicum strain T-G1, isolated from an acidic and metalliferous uranium mining area, can oxidize Mn(II) at both acidic and neutral pH using different enzymatic pathways. X-ray diffraction, Raman spectroscopy, and scanning electron microscopy with energy dispersive X-ray spectroscopy revealed that T-G1 initiated bixbyite-like Mn oxide formation at pH 5.5 which coincided with multi-copper oxidase expression from early exponential phase to late stationary phase. In contrast, reactive oxygen species (ROS), particularly superoxide, appeared to be more important for T-G1 mediated Mn(II) oxidation at neutral pH. ROS was produced in parallel with the occurrence of Mn(II) oxidation at pH 7.2 from early stationary phase. Solid phase Mn oxides did not precipitate, which is consistent with the presence of a high amount of H2O2 and lower activity of catalase in the liquid culture at pH 7.2. Our results show that M. australicum T-G1, an acid tolerant MOB, can initiate Mn(II) oxidation by varying its oxidation mechanisms depending on the pH and may play an important role in low pH manganese biogeochemical cycling.

Sedimentation Pulse in the NE Gulf of Mexico following the 2010 DWH Blowout.

The objective of this study was to investigate the impacts of the Deepwater Horizon (DWH) oil discharge at the seafloor as recorded in bottom sediments of the DeSoto Canyon region in the northeastern Gulf of Mexico. Through a close coupling of sedimentological, geochemical, and biological approaches, multiple independent lines of evidence from 11 sites sampled in November/December 2010 revealed that the upper ~1 cm depth interval is distinct from underlying sediments and results indicate that particles originated at the sea surface. Consistent dissimilarities in grain size over the surficial ~1 cm of sediments correspond to excess 234Th depths, which indicates a lack of vertical mixing (bioturbation), suggesting the entire layer was deposited within a 4–5 month period. Further, a time series from four deep-sea sites sampled up to three additional times over the following two years revealed that excess 234Th depths, accumulation rates, and 234Th inventories decreased rapidly, within a few to several months after initial coring. The interpretation of a rapid sedimentation pulse is corroborated by stratification in solid phase Mn, which is linked to diagenesis and redox change, and the dramatic decrease in benthic formanifera density that was recorded in surficial sediments. Results are consistent with a brief depositional pulse that was also reported in previous studies of sediments, and marine snow formation in surface waters closer to the wellhead during the summer and fall of 2010. Although sediment input from the Mississippi River and advective transport may influence sedimentation on the seafloor in the DeSoto Canyon region, we conclude based on multidisciplinary evidence that the sedimentation pulse in late 2010 is the product of marine snow formation and is likely linked to the DWH discharge.

Mn Diffusion and Reactive Diffusion in Ge: Spintronic Applications

In this paper, we report investigations concerning the fabrication of a diluted Ge (Mn) solution using solid state Mn diffusion, and Mn/Ge reactive diffusion for spintronic applications. The study of Mn diffusion shows that the quasi-totality of the incorporated Mn atoms occupies Ge substitutional sites and probably exhibits two negative elementary charges. The solubility limit of Mn in Ge is comprised between 0.7 and 0.9 % (T  600 °C). We show that substitutional Mn atoms are not ferromagnetic in Ge and consequently that Ge (Mn) diluted magnetic semiconductor can not be produced. Beside the ferromagnetic signal from Mn5Ge3, ferromagnetic signals detected in the samples could be always attributed to surface or bulk Mn-Ge clusters. Furthermore, we show that the CMOS Salicide process is potentially applicable to Mn5Ge3 nanolayer fabrication on Ge for spintronic applications. During Mn (thin-film)/Ge reaction, Mn5Ge3 is the first phase to form, being thermally stable up to 310 °C and exhibiting ferromagnetic properties up to TC ~ 300 K.

Effect of exopolymers on oxidative dissolution of natural rhodochrosite by Pseudomonas putida strain MnB1: An electrochemical study

Oxidative dissolution of natural rhodochrosite by the Mn(II) oxidizing bacterium Pseudomonas putida strain MnB1 was investigated based on batch and electrochemical experiments using natural rhodochrosite as the working electrode. Tafel curves and batch experiments revealed that bacterial exopolymers (EPS) significantly increased dissolution of natural rhodochrosite. The corrosion current significantly increased with reaction time for EPS treatment. However, the corrosion process was blocked in the presence of cells plus extra EPS due to formation of the passivation layer. Moreover, the scanning electron microscopy and the energy dispersive spectroscopy (SEM–EDS) results showed that the surface of the natural rhodochrosite was notably changed in the presence of EPS alone or/and bacterial cells. This study is helpful for understanding the role of EPS in bacterially oxidation of Mn(II). It also indicates that the Mn(II) oxidizing bacteria may exert their effects on Mn(II) cycle and other biological and biogeochemical processes much beyond their local ambient environment because of the catalytically dissolution of solid Mn(II) by EPS and the possible long distance transport of the detached EPS.

Fabrication of ordered mesoporous carbons anchored with MnO nanoparticles through dual-templating approach for supercapacitors

Ordered mesoporous carbons anchored with MnO nanoparticles (Cs–Mn) for supercapacitor have been produced by a simple double-template strategy. Pluronic F127 and polyurethane (PU) foam are used as the soft and hard template, respectively, and phenolic resol as a carbon source, and the MnO nanoparticles were in-situ anchored by directly dissolved solid Mn(CH3COO)2⋅2H2O in the phenolic resol solution through evaporation induced self-assembly (EISA) of the mesostructure on the struts of the PU foam scaffold, followed by carbonization. The microstructure, morphology and electrochemical performance of Cs–Mn were investigated by small angle X-ray scattering, transmission electron microscopy, Raman spectropy, nitrogen adsorption–desorption and electrochemical measurements. Results show that Cs–Mn have a hexagonally ordered mesostructure. The pore size of Cs–Mn centered at ca. 2.0–4.2nm, high specific surface area (222m2/g) and great pore volume (up to 0.14cm3/g). The electrochemical measurements show that the Cs–Mn as an electrical double-layer capacitor electrode presents high specific capacitance of 100F/g at a current density of 0.125A/g and excellent rate capability using 0.5M Na2SO4 aqueous solution.

Structural elucidation of novel mixed ligand complexes of 2-thiophene carboxylic acid [M(TCA)2(H2O)x(im)2] [x=2 M: Mn(II), Co(II) or Cd(II), x=0 Cu(II)

Novel mixed ligand complexes containing thiophene-2-carboxylic acid (HTCA) and imidazole (im) ligands, [M(TCA)2(H2O)2(im)2] (M: Mn, Co, Cd) and [Cu(TCA)2(im)2] were obtained. The complexes were characterized by X-ray single crystal diffraction. Also, spectroscopic (IR and UV-Vis), magnetic and thermal properties were investigated. The thiophene-2-carboxylate acted in a monoanionic monodentate manner and bonded to the metals via its carboxylate oxygen. The im ligands bonded to the metals via hydrogen free nitrogen atoms. The geometry around the metal centers was octahedral [MO4N2] for Mn(II), Co(II) and Cd(II) complexes and square-planar [CuO2N2] for the Cu(II) complex. Due to intermolecular interactions in the solid state, the Co(II), Mn(II) and Cd(II) complexes showed three-dimensional networks, while the copper complex was a one-dimensional network. In consideration of the anhydrous form of the complexes, the thermal stability of the complexes was of the following order: Co (273°C)>Cu (229°C)>Cd (175°C)>Mn (167°C).

Analysis of Solid Electrolyte Interphase in Mn-Based Cathode/Graphite Li-Ion Battery with Glow Discharge Optical Emission Spectroscopy

Solid electrolyte interphase (SEI) and Mn deposition formed on capacity-degraded graphite electrodes in commercially available Mn-based/Graphite lithium ion batteries were characterized using glow discharge-optical emission spectroscopy (GD-OES). The depth profile of the whole electrode showed a homogeneous distribution of Li and Mn except for the surface region at the initial state. With the progress of degradation, Li and Mn concentrations increased inhomogeneously in the depth-direction of the electrode; the Li and Mn concentrations were high in the outer layer and decreased with depth to the current collector in the degraded electrodes. The SEI layer deposited on the electrode surface was separately analyzed in detail. The GD-OES surface profile was explained by comparing to the XPS analysis results. The amount of Li deposited on the electrode surface was almost constant with the capacity degradation, though the Li concentration in the whole electrode increased along with the capacity degradation. In contrast, the amount of Mn deposition increased with the capacity degradation both in the surface deposition layer and in the whole electrode.

Microstructure and Properties of Alloys with Equal Atomic Principal Components

Four high-entropy alloys are prepared by an arc furnace under argon atmosphere. The microstructure and the properties of the alloys are investigated. The results show that NiCrCuCoFe alloy consists of a single FCC solid solution. When Al presents in the alloys, the microstructures of the alloys change to a BCC+ FCC solid solution. It is indicated that Al element promotes the formation of BCC solid solution, and Si and Mn promote the formation of complicated compounds. The hardness of alloys with BCC structure is higher than that of the alloys with FCC structure. The complicated compounds are formed, the hardness increases further. The highest hardness of the alloys reaches 882 HV due to the strengthening of the second phase precipitation.

Microbial Mn(IV) reduction requires an initial one-electron reductive solubilization step

Mn(IV) and Mn(II) are the most stable and prevalent forms of manganese in natural environments. The occurrence of Mn(III) in minerals and the detection of soluble Mn(III) in natural waters, however, suggest that Mn(III) is an intermediate in both the oxidation of Mn(II) and the reduction of Mn(IV). Mn(III) has recently been proposed as an intermediate during the oxidation of Mn(II) by Mn-oxidizing bacteria but has never been considered as an intermediate during the bio-reduction of Mn(IV). Here we show for the first time that microbial Mn(IV) reduction proceeds step-wise via two successive one-electron transfer reactions with production of soluble Mn(III) as transient intermediate. Incubations with mutant strains demonstrate that the reduction of both solid Mn(IV) and soluble Mn(III) occurs at the outer membrane of the cell. In addition, pseudo-first order rate constants obtained from these incubations indicate that Mn(IV) respiration involves only one of the two potential terminal reductases (c-type cytochrome MtrC and OmcA) involved in Fe(III) respiration. More importantly, only the second electron transfer step is coupled to production of dissolved inorganic carbon, suggesting that the first electron transfer reaction is a reductive solubilization step that increases Mn bioavailability. These findings oppose the long-standing paradigm that microbial Mn(IV) reduction proceeds via a single two-electron transfer reaction coupled to organic carbon oxidation, and suggest that diagenetic models should be revised to correctly account for the impact of manganese reduction in the global carbon cycle.