Activity Of Mn2 Research Articles

Durable Manganese-Based Li-Excess Electrode Material without Voltage Decay: Metastable and Nanosized Li2MnO1.5F1.5

Li-excess manganese-based oxides have been proposed as high-capacity positive electrode materials, but voltage decay associated with gradual oxygen loss hinders its use for practical applications. Herein, Li-excess manganese oxides with different fluorine contents are synthesized by high-energy mechanical milling. Although Li2MnOF2 with only divalent manganese ions cannot be synthesized, Li2MnO2F and Li2MnO1.5F1.5 are successfully synthesized. When the samples are charged to 5.0 V, both oxyfluorides deliver large reversible capacities, ∼350 mA h g–1 and ∼1000 mWh g–1. However, insufficient capacity retention is also observed because of the instability of anionic redox. In contrast, better capacity retention and higher energy density (730 mWh g–1) are obtained for Li2MnO1.5F1.5 with a 4.4 V cutoff because of the enrichment of fluoride ions and activation of Mn2+/Mn4+ cationic redox. Moreover, electrode durability is significantly improved by using a highly concentrated electrolyte, and good capacity retention without voltage decay is achieved for >180 cycles.

The High Activity of Mn2+-Rich Co-Mn-O Solid Solution Catalyst for Low-Temperature Methane Combustion

The High Activity of Mn2+-Rich Co-Mn-O Solid Solution Catalyst for Low-Temperature Methane Combustion

Enhanced Photocatalytic Activity of ZnS:Mn2+ Quantum Dots

The photocatalytic activity of Mn2+ doped ZnS quantum dots stabilized by glutathione capping agent in aqueous media was studied in situ by photoluminescence spectroscopy. The methylene blue was chosen as model organic dye for photodecomposition under excitation in near UV-range. It is shown that the rate of photodegradation of the methylene blue depends strictly on the concentration of the manganese activator ions and the presence of its own intrinsic defects in the host ZnS crystal lattice. It is found that the most effective photocatalyst are ZnS quantum dots doped with 0.25 at % of Mn2+ providing the total dye decolorization within 5 minutes.

Manganese in the shell of the bivalve Mytilus edulis: Seawater Mn or physiological control?

Manganese in the shell calcite of marine bivalves has been suggested to reflect ambient seawater Mn concentrations, thus providing a high-resolution archive of past seawater Mn concentrations. However, a quantitative relationship between seawater Mn and shell Mn/Ca ratios, as well as clear understanding of which process(es) control(s) shell Mn/Ca, are still lacking. Blue mussels, Mytilus edulis, were grown in a one-year duration field experiment in the Menai Strait, U.K., to study the relationship between seawater particulate and dissolved Mn2+ concentrations and shell calcite Mn/Ca ratios.Shell Mn/Ca showed a well-defined intra-annual double-peak, with maximum values during early spring and early summer and low values during autumn and winter. Seawater particulate Mn peaked during winter and autumn, with a series of smaller peaks during spring and summer, whereas dissolved Mn2+ exhibited a marked single maximum during late-spring to early-summer, being low during the remainder of the year. Consequently, neither seawater particulate Mn nor dissolved Mn2+ concentrations explain the intra-annual variation of shell Mn/Ca ratios.A physiological control on shell Mn/Ca ratios is evident from the strong similarity and timing of the double-peaked intra-annual variations of Mn/Ca and shell growth rate (SGR), the latter corresponding to periods of increased metabolic activity (as indicated by respiration rate). It is thus likely that in M. edulis SGR influences shell Mn/Ca by altering the concentration or activity of Mn2+ within the extra-pallial fluid (EPF), by changing the flux of Mn into or the proportion of protein bound Mn within the EPF. By linking shell Mn/Ca ratios to the endogenous and environmental factors that determine growth and metabolic activity, this study helps to explain the lack of a consistent relationship between shell Mn/Ca in marine bivalve shell calcite and seawater particulate and dissolved Mn2+ concentrations.The use of Mn content from M. edulis shell calcite as a proxy for the dissolved and/or particulate Mn concentrations, and thus the biogeochemical processes that control them, remains elusive.

Chemiluminescence of Mn 2+-activated Rubisco: temperature and pH responses differ between L2 and L8S8 forms, and inhibitors provide no evidence for involvement of active oxygen species

Chemiluminescence associated with the oxygenase activity of Mn 2+ -activated D-ribulose-1,5- bisphosphate carboxylase/oxygenase (Rubisco) was investigated using the L 8 S 8 enzymes from spinach and Synechococcus PCC6301, and the L 2 enzyme from Rhodospirillum rubrum. Chemi-luminescence was measured with a luminometer and oxygenase activity with an oxygen electrode. The relative luminescence yield (light emitted per oxygenase turnover) in the steady-state at pH 8.1 was highest with spinach Rubisco; the enzymes from Synechococcus and R. rubrum exhibited approximately one half and one fifth, respectively, of the spinach value. The relative luminescence yield from the L 8 S 8 enzymes was unaffected by temperature (20–40°C) and pH (7.6–9.0). In contrast, the luminescence yield of R. rubrum Rubisco varied with temperature and pH, and its O 2 -consuming activity exhibited a lower activation energy than that of the L 8 S 8 enzymes. The singlet O 2 -reactive compounds diazabi-cyclo[ 2.2.2]octane and 10,10′-dimethyl-9,9′-biacridinium dinitrate (lucigenin) had no effect on chemi-luminescence. Other compounds tested inhibited chemiluminescence but also inhibited O 2 consumption. The inhibition of chemiluminescence of spinach Rubisco required several seconds to exert its maximal effect, implying that the inhibitors had access to the active site only at a particular stage of the catalytic cycle. The data are consistent with the Mn 2+ ion at the active site being the source of the luminescence.

Stimulation of Ca2+Release-Activated Ca2+Channels as a Potential Mechanism Involved in Non-Genomic 1,25(OH)2-Vitamin D3-Induced Ca2+Entry in Skeletal Muscle Cells

As in other vitamin D target cells, activation of voltage-dependent Ca2+channels (VDCC) mediates the fast, non-genomic, 1,25(OH)2D3stimulation of Ca2+influx in skeletal muscle cells (SMC). 1,25(OH)2D3has also been shown to rapidly induce the release of Ins(1,4,5)P3in SMC. Experiments were performed to investigate whether Ca2+release-activated Ca2+channels (CRAC) also participate in the mechanism by which 1,25(OH)2D3regulates Ca2+entry into these cells. In cultured chick SMC loaded with Fura-2/AM the hormone (10−12- 10−8M) induced a rapid (30 sec) followed by a sustained (up to 5 min) increase in intracellular Ca2+concentration ([Ca2+]i) associated to Ca2+mobilization from internal stores and influx of extracellular Ca2+, respectively. Thus, the initial, transient, 1,25(OH)2D3-dependent increment in [Ca2+]icould be observed in Ca2+-free medium and was abolished by the PLC inhibitor U73122. Readdition of Ca2+to cells that had undergone the initial 1,25(OH)2D3-induced [Ca2+]irise in Ca2+free medium resulted in a fast increment in [Ca2+]iindicating the existence of a hormone-activated CRAC entry pathway. The sustained phase of the Ca2+response to 1,25(OH)2D3was only partially (60%) suppressed by nifedipine, whereas lanthanum (10 μM) completely abolished the hormone effects. Accordingly, depletion of intracellular Ca2+stores by thapsigargin reproduced 1,25(OH)2D3-induced Ca2+influx, inhibiting any further response to the sterol. 1,25(OH)2D3increased the rate of quenching of Fura-2 fluorescence by Mn2+, indicating activation of Mn2+permeable channels. Altogether, these results provide the first evidence involving CRAC channels in the rapid modulation of Ca2+entry in animal cells by 1,25(OH)2D3.

Chemisorptive characterization of Mn2+ cation effects on fused iron-catalysts

Volumetric and pulse chemisorptions of carbon monoxide (CO) have been developed to characterize effects of Mn2+ cations on an industrial doubly promoted fused iron catalyst. Addition of Mn2+ cations induces an increase in Fe dispersity, Fe electronic density and stability of the Mn2+-containing iron catalyst, where the same increase is observed by XPS and SEM. These effects explain why the activity of Mn2+-containing iron catalysts is improved.

Activation of soluble guanylate cyclase by carbon monoxide and inhibition by superoxide anion

Human platelet soluble guanylate cyclase activity was studied with respect to the function of its heme-containing regulatory subunit. As an enzyme source, the 10,000 x g supernatant was used and, since its specific activity proved to be too low for inhibition studies, also a partially purified preparation was employed. The partially purified enzyme was stimulated about 2.5-fold by carbon monoxide and this effect was abolished by illumination with visible light. Sodium nitroprusside also increased the basal activity about fourfold, which, however, is much less than the greater than 100-fold stimulation seen with the supernatant. Superoxide anions generated by the xanthine/xanthine-oxidase system were strongly inhibitory in the enriched preparation as well as in the CO-stimulated platelet supernatant (median effector concentration = 0.1 mU/ml). Unlike CO and NO, the effect of superoxide cannot be mediated through the heme-containing regulatory subunit, since heme-free enzyme, which could not be activated by NO or CO, was inhibited to the same extent as the heme-containing enzyme. Superoxide dismutase did not influence the basal activity, but resulted in a synergistic stimulation in the presence of CO. When Mn2+ replaced Mg2+ as a cofactor, the basal activity was higher but superoxide could not inhibit the enzyme, possibly due to the superoxide-dismutase-like activity of Mn2+. Superoxide turned out to be a potent and reversible inhibitor of soluble guanylate cyclase which, together with endothelium-derived relaxing factor, recently identified as NO, could form a physiologically relevant regulatory effector system.

EFFECTS OF CaCO3 AND P ADDITIONS ON CORN (Zea mays L.) GROWTH AND NUTRIENT AVAILABILITY OF A PODZOLIC SOIL

A surface horizon from a Humo-Ferric Podzol was amended with 0 to 6 cmol kg−1 of CaCO3 and 125 to 500 mg P kg−1 to investigate their effects on the elemental composition and growth of corn and on nutrient availability. The addition of CaCO3 decreased the amounts of extractable P and Mn in the soil and the concentrations of P, K, Mn, Mg and Zn in the plants. The addition of P increased the dry matter yields, the amounts of available P in the soil and the concentrations of P and Mg in the plants, but decreased the concentrations of K, Mn and Zn in the seedlings. There were significant CaCO3 × P interactions on the amounts of extractable Mg and Zn in the soil and on the contents of N and Mn in the seedlings. The addition of 0.5 cmol CaCO3 kg−1 was beneficial to dry matter accumulation, but additions greater than 4 cmol kg−1 were excessive. The dry matter yields were most closely related to the amount of extractable P and to the activity of Mn2+ in solution. The concentration of P in the plants was very closely related to the amount of NaHCO3-extractable P in the soil. The concentration of Zn in the seedlings was most closely related to the amounts of DTPA-extractable Zn and of NaHCO3-extractable P. Key words: Liming, P fertilization, Zea mays (L.), plant nutrition, soil solution, Podzol

Estimation of plant available manganese in acidic subsoil horizons

Abstract General agreement does not exist as to the most appropriate method to estimate plant available Mn in soils. In the current investigation soil and soil solution Mn were measured in limed and unlimed treatments of 11 acidic subsoil horizons and related to plant Mn concentrations, Mn uptake and growth of subterranean clover (Trifolium subterraneum L. cv. Mt. Barker) and switchgrass (Panicum virgatum cv. Cave‐in‐Rock). Manganese measurements were taken at planting and harvest and included: Mn extracted by 1M NH4OAc (pH 7), 0.01M CaCl2, 0.05M CaCl2, 0.033M H3PO4, 0.005M DTPA, 0.2% hydroquinone in 1M NH4OAc (pH 7), 0.01M NH2 OH.HCl 4 2 in 0.01M HNO3, total soil solution Mn and concentrations and 2+ activities of Mn2+ calculated from the GEOCHEM program. Measured and calculated values of soil solution Mn generally gave the best correlations with subterranean clover and switchgrass Mn concentrations and Mn uptake. Root Mn concentrations were highly correlated with soil solution Mn measurements taken at h...

Manganese Phosphate Equilibrium Relationships in Soils

AbstractSolubility diagrams were developed using log K° values for MnHPO4·3H2O, Mn3(PO4)2·3H2O, Mn5H2(PO4)4·4H2O and MnPO4·1.5H2O. The latter mineral was found to be more stable than hydroxyapatite and thus capable of controlling soil‐solution P at pH values <7.2 and pe + pH values between 13.5 and 17. Controlled redox cells were used to maintain suspensions of several soils at fixed redox levels above pe + pH = 13.5. After 28, 56, 84, and 140 d, samples were taken, and the clear filtrates were analyzed. The activities of Mn2+ and H2PO‐4 were calculated by speciating total Mn and P in solution. Ionic activity products were calculated and compared to the activity products of pure Mn phosphates. This study helps to explain the beneficial effects of phosphate in alleviating Mn toxicities and the importance of Mn phosphates as reaction products of Mn and P fertilizers in soils.

The Effect of Redox on the Solubility and Availability of Manganese in a Calcareous Soil

Soil suspensions were maintained at various fixed redox levels to assess the effect of redox on the solubility and availability of Mn. After 4 weeks of incubation, the liquid phase of the suspensions was analyzed, and the activity of Mn2+ was calculated. The results indicated that Mn solubility was controlled by MnCO3 (rhodocrosite) below pe + pH = 16. Literature findings also suggest the presence of MnCO3 when Mn2+ activities were calculated and plotted as a function of redox. When rice plants (Oryza sativa) were grown in the controlled redox suspensions, the uptake of Mn by rice plants was highly correlated with the activity of Mn2+ in solution. The study demonstrates the usefulness of chemical equilibrium relationships to predict the solubility of Mn in the soil and its availability to plants.

The effect of calmodulin, trifluoperazine and other psychoactive drugs on the activity of the Mn2+-dependent adenylyl cyclase (AC) in testicular germ cells.

This paper is concerned with the effects of calmodulin and different psychoactive drugs on the activity of the rat germ cell Mn2+‐dependent adenylyl cyclase (Mn‐AC) of various degrees of purity. Trifluoperazine inhibited the enzyme activity in a dose‐dependent manner (ID50∼50–70 μM) irrespective of the degree of purification. Calmodulin, on the other hand, elicited little or no activation of the Mn‐AC except for a marginal stimulation (20–30%) of the most purified enzyme preparation. The dose of calmodulin required to achieve this effect was extremely high (ED50∼ 3 μg ml). The trifluoperazineinhibition of a partly purified Mn‐AC was not substantially counteracted by the presence of calmodulin (20 μg/ml). We have also, by kinetic analyses, examined the mode by which trifluoperazine inhibits the Mn‐AC activity. Increasing concentrations of the drug decreased the maximal velocity (Vmax) (Ki∼ 50 μM), but did not influence the apparent affinity (Kma) for MnATP2‐. In contrast, the Kma for Mn2+ was decreased, and double reciprocal plots (1/V vs 1/Mn2+ free) were parallel and compatible with uncompetetive inhibition (Ki∼ 55μM). Other psychoactive agents (pimozide, trifluoperazine, medazepam, promethazine, chlordiazepoxide, haloperidol and chlorpromazine‐sulfoxide), all known to inhibit calmodulin‐activated cAMP phosphodiesterase with varying potencies (ID50s), inhibited the germ cell Mn‐AC with ID50s which parallelled those for cAMP phosphodiesterase inactivation. An exception was haloperidol (a potent phosphodiesterase inhibitor) which exerted a very low effect on the Mn‐AC activity (ID50∼ 2500 μM). The present results indicate that calmodulin or a calmodulin‐like protein may be associated with the Mn‐AC. Another possibility is that trifluoperazine and other psychoactive drugs may bind directly to the Mn‐AC molecule and prevent Mn2+‐activation.

Change of ribonuclease H activity from rat liver nuclei by thioacetamide: Preferential increase in the activity of magnesium-dependent ribonuclease H

The specific activity of Mg2+-dependent ribonuclease H (RNase H) from rat liver nuclei increased three- to four-fold within 24 h of a single injection of thioacetamide, and decreased to normal values 48 h after administration. The response of RNase H activity to thioacetamide was very similar to that of RNA polymerase I after treatment. The activities of Mn2+-dependent RNase H from nuclei and RNase H from soluble fractions were relatively unaffected.