Stoichiometry Of Mn Research Articles

Enhanced localized corrosion resistance of Ni-based alloy 625 processed by directed energy deposition additive manufacturing

We report a significant improvement in localized corrosion resistance of Ni-based alloy 625 processed by directed energy deposition (DED) in 7.6 mol/L LiCl at 50 °C. Disparities observed in polarization behavior between DED and wrought alloy 625 are analyzed through compositional and microstructural differences. The exceptional localized corrosion resistance of the DED alloy likely stems from the refinement of secondary phases resultant from the DED process. The prototypical precipitates larger than ≈1 μm in the wrought material, primarily Nb,Ti-enriched face centered cubic nitrides with the stoichiometry of MN where M = Nb, Ti, Cr, served as pit initiation sites and likely degraded the corrosion resistance.

Hydrothermally synthesized aster flowers of MnCo2O4 for development of high-performance asymmetric coin cell supercapacitor

In this study, manganese cobaltite (MnCo2O4) grown on Ni-foam are deposited by hydrothermal method at different deposition times (2, 4, 6, and 8 h). The MnCo2O4 electrodes were systematically characterized in terms of their structural, morphological, and electrochemical properties. The cubic crystal system of MnCo2O4 with Fd3m space group is revealed by X-ray diffraction. A morphological evolution from nanograins towards aster-flower-like nanostructures can be seen in the field emission scanning electron microscopy images. The stoichiometry of Mn, Co, and O elements and their valance states are studied using Energy Dispersive Spectroscopy. and X-ray Photoelectron Spectroscopy respectively. An aster-flower-like nanostructure of MnCo2O4 (8 h), exhibits areal capacitance of 11.4 Fcm−2, and an energy density of about 0.98 mWhcm−2 was evaluated at 3 mAcm−2 current density within the −0.3 to 0.5 V potential window. An asymmetric coin cell (ASCC) device demonstrated an areal capacitance of 47.4 mFcm−2, energy density of 13.0 μWhcm−2, and power density of about 0.525 mWcm−2 was measured at 0.5 mAcm−2 applied current with exceptional cyclability of 95 % measured up to 9000 cycles.

Thermally Induced Solid-Phase Quasi-Intramolecular Redox Reactions of [Hexakis(urea-O)iron(III)] Permanganate: An Easy Reaction Route to Prepare Potential (Fe,Mn)Ox Catalysts for CO2 Hydrogenation.

Research on new reaction routes and precursors to prepare catalysts for CO2 hydrogenation has enormous importance. Here, we report on the preparation of the permanganate salt of the urea-coordinated iron(III), [hexakis(urea-O)iron(III)]permanganate ([Fe(urea-O)6](MnO4)3) via an affordable synthesis route and preliminarily demonstrate the catalytic activity of its (Fe,Mn)Ox thermal decomposition products in CO2 hydrogenation. [Fe(urea-O)6](MnO4)3 contains O-coordinated urea ligands in octahedral propeller-like arrangement around the Fe3+ cation. There are extended hydrogen bond interactions between the permanganate ions and the hydrogen atoms of the urea ligands. These hydrogen bonds serve as reaction centers and have unique roles in the solid-phase quasi-intramolecular redox reaction of the urea ligand and the permanganate anion below the temperature of ligand loss of the complex cation. The decomposition mechanism of the urea ligand (ammonia elimination with the formation of isocyanuric acid and biuret) has been clarified. In an inert atmosphere, the final thermal decomposition product was manganese-containing wuestite, (Fe,Mn)O, at 800 °C, whereas in ambient air, two types of bixbyite (Fe,Mn)2O3 as well as jacobsite (Fe,Mn)T-4(Fe,Mn)OC-62O4), with overall Fe to Mn stoichiometry of 1:3, were formed. These final products were obtained regardless of the different atmospheres applied during thermal treatments up to 350 °C. Disordered bixbyite formed first with inhomogeneous Fe and Mn distribution and double-size supercell and then transformed gradually into common bixbyite with regular structure (and with 1:3 Fe to Mn ratio) upon increasing the temperature and heating time. The (Fe,Mn)Ox intermediates formed under various conditions showed catalytic effect in the CO2 hydrogenation reaction with <57.6% CO2 conversions and <39.3% hydrocarbon yields. As a mild solid-phase oxidant, hexakis(urea-O)iron(III) permanganate, was found to be selective in the transformation of (un)substituted benzylic alcohols into benzaldehydes and benzonitriles.

Secondary-Phase Formation in Spinel-Type LiMn2O4-Cathode Materials for Lithium-Ion Batteries: Quantifying Trace Amounts of Li2MnO3 by Electron Paramagnetic Resonance Spectroscopy

Spinel-type lithium manganese oxides are considered as promising cathode materials for lithium-ion batteries. Trace amounts of Li2MnO3 usually occur as a secondary phase in lithium-manganese spinels in the common high-temperature, solid-state synthesis, affecting the overall Li–Mn stoichiometry in the spinel phase and thereby the electrochemical performance. However, the formation of Li2MnO3 lower than 1 wt.% can hardly be quantified by the conventional analytical techniques. In this work, we synthesized lithium-manganese spinels with different Li/Mn molar ratios and demonstrate that electron paramagnetic resonance (EPR) enables quantifying trace amounts of Li2MnO3 below 10−2 wt.% in the synthesized products. The results reveal that the formation of Li2MnO3 secondary phase is favored by lithium excess in the synthesis. Based on the quantitative evaluation of the EPR data, precise determining Li–Mn stoichiometry in the spinel phase in Li1+xMn2−xO4 materials can be assessed. Accordingly, it is possible to estimate the amount of lithium on 16d-sites in the Li-rich manganese spinels.

Sodium and Manganese Stoichiometry of P2-Type Na2/3 MnO2.

To realize a reversible solid-state Mn(III/IV) redox couple in layered oxides, co-operative Jahn-Teller distortion (CJTD) of six-coordinate Mn(III) (t2g (3) -eg (1) ) is a key factor in terms of structural and physical properties. We develop a single-phase synthesis route for two polymorphs, namely distorted and undistorted P2-type Na2/3 MnO2 having different Mn stoichiometry, and investigate how the structural and stoichiometric difference influences electrochemical reaction. The distorted Na2/3 MnO2 delivers 216 mAh g(-1) as a 3 V class positive electrode, reaching 590 Wh (kg oxide)(-1) with excellent cycle stability in a non-aqueous Na cell and demonstrates better electrochemical behavior compared to undistorted Na2/3 MnO2 . Furthermore, reversible phase transitions correlated with CJTD are found upon (de)sodiation for distorted Na2/3 MnO2 , providing a new insight into utilization of the Mn(III/IV) redox couple for positive electrodes of Na-ion batteries.

Sodium and Manganese Stoichiometry of P2‐Type Na2/3MnO2

AbstractTo realize a reversible solid‐state MnIII/IV redox couple in layered oxides, co‐operative Jahn–Teller distortion (CJTD) of six‐coordinate MnIII (t2g3–eg1) is a key factor in terms of structural and physical properties. We develop a single‐phase synthesis route for two polymorphs, namely distorted and undistorted P2‐type Na2/3MnO2 having different Mn stoichiometry, and investigate how the structural and stoichiometric difference influences electrochemical reaction. The distorted Na2/3MnO2 delivers 216 mAh g−1 as a 3 V class positive electrode, reaching 590 Wh (kg oxide)−1 with excellent cycle stability in a non‐aqueous Na cell and demonstrates better electrochemical behavior compared to undistorted Na2/3MnO2. Furthermore, reversible phase transitions correlated with CJTD are found upon (de)sodiation for distorted Na2/3MnO2, providing a new insight into utilization of the MnIII/IV redox couple for positive electrodes of Na‐ion batteries.

Correction to Enhanced Supercapacitor Performance for Equal Co–Mn Stoichiometry in Colloidal Co3-xMnxO4 Nanoparticles, in Additive-Free Electrodes

Correction to Enhanced Supercapacitor Performance for Equal Co–Mn Stoichiometry in Colloidal Co_3-xMn_<i>x</i>O₄ Nanoparticles, in Additive-Free Electrodes

Mn(III)acetate-Induced Electron Transfer in Pentaammine Cobalt(III)Complexes of α-Amino Acids in Micellar Medium

A micellar catalyzed oxidation of pentaamminecobalt(III) complexes of α-amino acids by Mn(III)acetate in acidic medium yielding nearly 100% Co(II) and about 100% carbonyl compounds are ultimate products. The unbound amino acids yield about 100% of carbonyl compound in presence of micelles. The effect of variation of sulphuric acid has been carried. The decrease in UV-Visible absorbance at λ=502 nm for Co(III) complex corresponds to nearly 100% of the initial absorbance. In spite of the stoichiometry of Mn(III) to unbound ligand is 2:1, the ratio of Mn(III) to cobalt(III) complex is 1:1 accounting for about 100% reduction at the cobalt(III) centre. The kinetic and stoichiometric results have been accounted. A suitable mechanism consistent with the experimental findings has been proposed by involving a radical cation intermediate.

Reaction Medium pH Dependent Existence of MnII Bound [ON] Donor Zwitterionic Chelating Ligand and Self‐Assembly of Hydroxido‐Bridged MnII4 Cluster

AbstractA mononuclear MnN4O2 complex with two zwitterionic ligands and a centrosymmetric tetranuclear μ3‐OH‐bridged self‐assembled Mn4 cluster were synthesized and characterized by using the [NO(H)N] ligand HOPhbip [2,6‐bis(phenylmethyliminomethyl)‐4‐methylphenol]. The reaction in MeOH in the presence of NH4SCN and a lower stoichiometry of Mn(OAc)2·4H2O without any added base produces [MnII(HNbip)2(NCS)2]·CH3CN (1·CH3CN). In the presence of NaOH and NH4SCN in MeOH, the cluster [MnII4(μ‐bip)2(μ3‐OH)2(NCS)4] (2), featuring a stepped‐cubane, was obtained through hydroxido‐bridge‐driven dimerization of two μ3‐OH‐bridged [Mn2] fragments derived from 1·CH3CN.

Reconstruction Control of Magnetic Properties during Epitaxial Growth of FerromagneticMn3−δGaon Wurtzite GaN(0001)

Binary ferromagnetic Mn(3-delta)Ga (1.2<3-delta< or =1.5) crystalline thin films have been epitaxially grown on wurtzite GaN(0001) surfaces using rf N-plasma molecular beam epitaxy. The film structure is face-centered tetragonal with CuAu type-I (L1(0)) ordering with (111) orientation. The in-plane epitaxial relationship to GaN is nearly ideal with [110](MnGa) parallel[1100](GaN) and [112](MnGa) parallel[1120](GaN). We observe magnetic anisotropy along both the in-plane and out-of-plane directions. The magnetic moments are found to depend on the Mn/(Mn+Ga) flux ratio and can be controlled by observation of the surface reconstruction during growth, which varies from 1x1 to 2x2 with increasing Mn stoichiometry.

Structural Basis for the Metal-Selective Activation of the Manganese Transport Regulator of Bacillus subtilis,

The manganese transport regulator (MntR) of Bacillus subtilis is activated by Mn(2+) to repress transcription of genes encoding transporters involved in the uptake of manganese. MntR is also strongly activated by cadmium, both in vivo and in vitro, but it is poorly activated by other metal cations, including calcium and zinc. The previously published MntR.Mn(2+) structure revealed a binuclear complex of manganese ions with a metal-metal separation of 3.3 A (herein designated the AB conformer). Analysis of four additional crystal forms of MntR.Mn(2+) reveals that the AB conformer is only observed in monoclinic crystals at 100 K, suggesting that this conformation may be stabilized by crystal packing forces. In contrast, monoclinic crystals analyzed at room temperature (at either pH 6.5 or pH 8.5), and a second hexagonal crystal form (analyzed at 100 K), all reveal the shift of one manganese ion by 2.5 A, thereby leading to a newly identified conformation (the AC conformer) with an internuclear distance of 4.4 A. Significantly, the cadmium and calcium complexes of MntR also contain binuclear complexes with a 4.4 A internuclear separation. In contrast, the zinc complex of MntR contains only one metal ion per subunit, in the A site. Isothermal titration calorimetry confirms the stoichiometry of Mn(2+), Cd(2+), and Zn(2+) binding to MntR. We propose that the specificity of MntR activation is tied to productive binding of metal ions at two sites; the A site appears to act as a selectivity filter, determining whether the B or C site will be occupied and thereby fully activate MntR.

General Synthesis of Di-μ-oxo Dimanganese Complexes as Functional Models for the Oxygen Evolving Complex of Photosystem II

A series of complexes with the formula [Mn(III/IV)2(mu-O)2(L)2(X)2]3+ have been prepared in situ from Mn(II)LCl2 precursors by a general preparative method (L = terpy, Cl-terpy, Br-terpy, Ph-terpy, tolyl-terpy, mesityl-terpy, t Bu3-terpy, EtO-terpy, py-phen, dpya, Me2N-terpy, or HO-terpy, and X = a labile ligand such as water, chloride, or sulfate). The parent complex, where L = terpy and X = water, is a functional model for the oxygen-evolving complex of photosystem II (Limburg, et al. J. Am. Chem. Soc. 2001, 123, 423-430). Crystals of Mn(II)(dpya)Cl2, Mn(II)(Ph-terpy)Cl2, Mn(II)(mesityl-terpy)Cl2, and an organic-soluble di-mu-oxo di-aqua dimanganese complex, [Mn(III/)(IV)2(mu-O)2(mesityl-terpy)2(OH2)2](NO3)3, were obtained and characterized by X-ray crystallography. Solutions of the in situ-formed di-mu-oxo dimanganese complexes were characterized by electrospray mass spectrometry, EPR spectroscopy, and UV-visible spectroscopy, and the rates of catalytic oxygen-evolving activity were assayed. The use of Mn(II)LCl2 precursors leads to higher product purity of the Mn dimers while achieving the 1:1 ligand to Mn stoichiometry appropriate for catalytic activity assay. These methods can be used to screen the catalytic activity of other di-mu-oxo dimanganese complexes generated by using a ligand library.

Oxidation of 3‐(3,4‐dihydroxy phenyl)‐l‐alanine (levodopa) and 3‐(3,4‐dihydroxy phenyl)‐2‐methyl‐l‐alanine (methyl dopa) by manganese(III) in pyrophosphate media: Kinetic and mechanistic study

AbstractManganese(III) (Mn(III)) has been stabilized in weakly acidic solution by means of pyrophosphate and the nature of the complex was elucidated spectrophotometrically. Stoichiometry of Mn(III)‐oxidation of levodopa and methyl dopa in pyrophosphate medium was established in the pH range 2.5–4.0 by iodometric and spectrophotometric methods. The reaction shows a distinct variation in kinetic order with respect to [Mn(III)], a first‐order dependence in the pH range 1.9–2.6, decreasing to fractional order above pH 3. Other common features include first‐order dependence on [dopa], positive fractional order dependence on [H+], and inverse first‐order dependence on [Mn(III)] in the pH range studied. The effects of varying ionic strength and solvent composition were studied. Added ions such as SO42− and ClO4− alter the reaction rate, probably due to the change in the formal redox potential of Mn(III)–Mn(II) couple because of the changes in coordination environment of the oxidizing species. Evidence for the transient existence of the free radical intermediate is given. Cyclic voltametric sensing of levodopa and methyl dopa has ruled out the formation of dopaquinones as oxidation products in the pH range studied. Activation parameters have been evaluated using the Arrhenius and Erying plots. Mechanisms consistent with the kinetic data have been proposed and discussed. These studies are expected to throw some light on dopa metabolism. © 2001 John Wiley &amp; Sons, Inc. Int J Chem Kinet 33: 449–457, 2001

Evidence for the Proximity of Calcium to the Manganese Cluster of Photosystem II: Determination by X-ray Absorption Spectroscopy

The photosynthetic oxygen-evolving complex contains a cluster of four manganese atoms and requires both Ca and Cl for activity. The question of Ca proximity to the Mn cluster has been investigated by performing Mn X-ray absorption experiments on native samples of photosystem II (PS II) and on samples depleted of Ca and reconstituted by either Ca or Sr. Analysis of X-ray K-edge spectra demonstrates no significant differences in oxidation state or symmetry between Ca- and Sr-reactivated preparations. Differences are observed in the extended X-ray absorption fine structure (EXAFS). The amplitude of a Fourier transform peak due to scatters at distances greater than 3 A is larger for samples reactivated with strontium than for calcium-reactivated samples. Taking into account the stoichiometry of Mn and Ca atoms in PS II, and considering physically reasonable structures, curve-fitting analyses of the EXAFS data using FEFF5-calculated parameters favor a model where both manganese and calcium (or strontium) scatterers contribute to the Fourier peak at approximately 3 A. Other models for the approximately 3 A peak with multiple Mn-Mn interactions or multiple Mn-Ca(Sr) interactions can also be fit to the data, but are considered less likely. This result provides confirmation for the structural proximity of Ca to the Mn cluster suggested previously [Yachandra, V. K., et al. (1993) Science 260, 675-679]. Possible structural arrangements for a calcium-binding site are discussed.

First volatile alkylgallyl manganese complexes; structure of [(CO5)Mn]2Ga[(CH2)3NMe2]. Molecular control of the stoichiometry of Mn–Ga thin films grown by low-pressure MOCVD

The Mn–Ga complexes of the general formula {L(CO)4Mn}a[GaR3–a(Do)](L = CO, R = alkyl; Do =N-Lewis-donor) are obtained in yields 90% and used as volatile single source precursors for the gas-phase deposition of thin Mn–Ga alloy films.

Characterization of reactions catalyzed by manganese peroxidase from Phanerochaete chrysosporium

Manganese peroxidase (MnP) is one of two extracellular peroxidases believed to be involved in lignin bio-degradation by the white-rot basidiomycete Phanerochaete chrysosporium. The enzyme oxidizes Mn(II) to Mn(III), which accumulates in the presence of Mn(III) stabilizing ligands. The Mn(III) complex in turn can oxidize a variety of organic substrates. The stoichiometry of Mn(III) complex formed per hydrogen peroxide consumed approaches 2:1 as enzyme concentration increases at a fixed concentration of peroxide or as peroxide concentration decreases at a fixed enzyme concentration. Reduced stoichiometry below 2:1 is shown to be due to Mn(III) complex decomposition by hydrogen peroxide. Reaction of Mn(III) with peroxide is catalyzed by Cu(II), which explains an apparent inhibition of MnP by Cu(II). The net decomposition of hydrogen peroxide to form molecular oxygen also appears to be the only observable reaction in buffers that do not serve as Mn(III) stabilizing ligands. The nonproductive decomposition of both Mn(III) and peroxide is an important finding with implications for proposed in vitro uses of the enzyme and for its role in lignin degradation. Steady-state kinetics of Mn(III) tartrate and Mn(III) malate formation by the enzyme are also described in this paper, with results largely corroborating earlier findings by others. Based on a comparison of pH effects on the kinetics of enzymatic Mn(III) tartrate and Mn(III) malate formation, it appears that pH effects are not due to ionizations of the Mn(III) complexing ligand.

Effect of the conformation of concanavalin A on its affinity for manganous ion

The stoichiometry of Mn 2+ binding to concanavalin A at pH 6.4–7 which had been established in two independent studies [ J. A. Sophianopoulos, A. J. Sophianopoulos, and W. C. MacMahon (1983) Arch. Biochem. Biophys. 223, 350–359; D. J. Christie, G. R. Munske, and J. A. Magnuson (1979) Biochemistry 18, 4638–4644] was challenged [ C. F. Brewer, R. D. Brown, III, and S. H. Koenig (1983) Biochemistry 22, 3691–3702] on grounds of possible experimental errors. Additional evidence is presented in this study in support of the previous finding that at pH 6.4 only one Mn 2+ binds per concanavalin A monomer of M r 25,550. Also, evidence is presented showing that the results of Sophianopoulos et al. could not have been due to contamination by Ca 2+. A comparison is made of the results in the three studies cited above which indicates that the concanavalin A used by Brewer et al. had decreased affinity for Mn 2+ and it contained an appreciable fraction of concanavalin A incompetent of binding saccharides.

Metal ion complexes of apoferritin. Evidence for initial binding in the hydrophilic channels.

Metal binding to the iron storage protein apoferritin is the first step in the process by which iron accumulates within the protein shell. In the present study, the stoichiometry of metal binding to apoferritin in solution has been examined using the probe ions Mn(II), VO(IV), and Cd(II) in conjunction with EPR spectroscopic and cadmium ion selective electrode measurements. Binding studies were carried out with the individual ions, in competition with one another, and in competition with Fe(II), Fe(III), and Tb(III). All three probe ions show binding stoichiometries near 0.3 and 0.7 metal ion per subunit, close to the theoretically predicted values of 0.33 and 0.67 for the binding of one and two metal ions, respectively, per three subunits. These results in conjunction with other data are consistent with the binding of one, and possibly two, metal ions within each of the eight hydrophilic channels which are located on 3-fold axes leading to the interior of the protein. Pairs of cadmium binding sites have been located in these channels by x-ray crystallography (Rice, D. W., Ford, G. C., White, J. L., Smith, J. M. A., and Harrison, P. M. (1983) Adv. Inorg. Biochem. 5, 39-49). The possibility that some metal binding occurs elsewhere on the protein is not precluded by the present data, however. In competition experiments between various metal ions, approximately 0.3 metal ion per subunit is readily displaced implying common binding sites in the channels for all of them. The stoichiometry of Mn(II) displacement by Fe(II) is less clear. Oxidation of Fe(II) to Fe(III) by molecular oxygen in the presence of Mn(II) regenerates some Mn(II) binding on the protein, suggesting migration of iron(III) to other protein sites, or perhaps to core.

Glutamine Synthetase: The Major Mn(II) Enzyme in Mammalian Brain

Ovine brain glutamine synthetase (GS) has been found to exist in vivo with four Mn(II) ions very tightly bound per octameric native enzyme. Both Mn(II) and GS are essential for normal brain function. Titrations by electron spin resonance (ESR) and kinetics indicate that there exist four additional sites for Mn(II) per octamer with Κ D = 0.56 or 2.6 μM with adenosine triphosphate (ATP) absent or present, respectively. This chapter discusses the distribution and physiology of Mn(II) in mammalian tissues, especially the brain cells . The chapter also discusses the distribution and metabolism of GS in mammalian tissues, especially the brain cells. The quantitative study of the stoichiometry of Mn (II) binding to Mn 4 E by ESR titrations in the presence and absence of added ATP is also discussed. The chapter also describes the interaction of bound Mn(II) with substrate sites by ESR. The ESR studies indicate that considerable perturbation of the environment of bound Mn(II) occurs with ATP but not with L-methionine- S -sulfoximine [MSOX or Met(O)(NH)] alone, in contrast to the effects seen for the E. coli enzyme namely; sharpening and enhanced hyperfine structure with MSOX but not ATP.

Milk alkaline phosphatase. Stimulation by Mg 2+ and properties of the Mg 2+ site

Milk alkaline phosphatase (orthophosphoric-monoester phosphohydrolase (alkaline optimum), EC 3.1.3.1) is an enzyme which requires two types of metals for maximal activity: zinc, which is essential, and magnesium, which is stimulatory. The main features of the Mg 2+ stimulation have been analyzed. Mg 2+ binding to native alkaline phosphatase is characterized by a dissociation constant of 30 μM at pH 8.5, 25°C. The stimulation is pH dependent and is observed mainly between pH 7.8 and 10.2. Both the rate constants of association, k a , and of dissociation, k d , have low values and are respectively 9M −1 · s −1 and 3.2 · 10 −1 · s −1 at pH 8.5, 25°C. Mg 2+ can be replaced at its specific site by Mn 2+, Co 2+, Ni 2+ and Zn 2+. Zinc binding to the Mg 2+ site inhibits the native alkaline phosphatase. The dissociation constant of Zn 2+ from the Mg 2+ site is 0.3 μM at pH 8.5, 25°C. Mn 2+, Co 2+, Cd 2+ and Ni 2+ also bind to the Mg 2+ site with a stimulatory effect which is lower than that of Mg 2+. Mn 2+ is the stimulatory cation which binds most tightly to the Mg 2+ site; the dissociation constant of the Mn 2+ milk phosphatase complex is 2 μM at pH 8.5. The stoichiometry of Mn 2+ binding has been found to be 1 equiv. of Mn 2+ per mol of dimeric milk phosphatase. The native enzyme displays absolute half-site reactivity for Mn 2+ binding. The properties of the Mg 2+ site to milk alkaline phosphatase are very similar to those of bovine kidney phosphatase Mg 2+ site