Distribution Of Divalent Cations Research Articles

Experiments on Distribution of Divalent Metal Cations between Olivine Solid Solutions and Aqueous Chloride Solutions at 700 °C and 100 MPa

Experiments on divalent cation distribution between Mg–Fe olivine solid solutions and 1 mol/L (Ni2+, Mg2+, Co2+, Zn2+, Fe2+, Mn2+)Cl2 aqueous solutions were carried out at 700 °C and 100 MPa. Regardless of the composition of the Mg–Fe olivine solid solutions, the tendency of divalent cation distribution into the olivine solid solutions against the aqueous chloride solutions was in the order of Ni2+ > Mg2+ > Co2+ > Mn2+ > Fe2+ > Zn2+. Excluding Zn2+, this order corresponds to the order of the sixfold coordinated ionic radius in olivine. This indicates that a smaller ionic radius allows the cation to more easily enter the olivine solid solutions. However, Zn2+ showed a negative distribution anomaly and did not easily enter the sixfold coordinated site of the olivine solid solutions, regardless of the ionic radius. This is because Zn2+ has a strong preference for fourfold coordinated sites. The Mg–Fe olivine solid solutions with more fayalite endmembers have smaller differences in the distribution coefficient of cations. This means that the gradient of the PC–IR curve becomes smaller as the content of fayalite endmembers increases. This trend indicates that fayalite consisting of a large cation (Fe2+) tends to exchange other cations more easily than forsterite consisting of a small cation (Mg2+).

Influence of mixing time during glycine–nitrate process on the structural properties and reducibility of a dual-phase Ni–Cu–Mn spinel catalyst

The potential of Ni–Cu–Mn spinels as methane reforming catalysts for hydrocarbon-fueled solid oxide fuel cell (SOFC) applications is highly dependent on its catalytic properties, particularly reducibility. The reducibility of a spinel-structured catalyst is often correlated with its structural properties and fabrication processes. In this work, the structural properties and reducibility of a Ni–Cu–Mn spinel catalyst was evaluated on the basis of mixing time during the glycine–nitrate process. Phase analysis results showed that Ni 0.4 Cu 0.6 Mn 2.0 O 4 and (Cu, Mn) 3 O 4 in normal or inversed spinel structures were observed in GNP-produced Ni–Cu–Mn spinel catalyst powders. Distortion in inverse spinel structures enhanced the reducibility of the spinel catalyst. Morphological analysis results showed that complete nitrate binding occurred at a minimum mixing time of 24 h and resulted in homogenous particle size distribution and uniform elemental distribution. Furthermore, the Ni–Cu–Mn spinel catalyst produced after 24 h of mixing was fully reduced at 450 °C. The reducing pattern of the Ni–Cu–Mn spinel catalyst produced after 24 h of mixing time showed strong metal–support interaction and the fast adsorption of reactants. These effects were due to either the distribution of divalent cations in octahedral sites or large amounts of bulk pores. In conclusion, a minimum mixing time of 24 h is sufficient to produce the desired structural properties and reducibility of Ni–Cu–Mn spinel catalysts for SOFC applications.

Infrared spectroscopic study of the synthetic Mg–Ni talc series

Five talc samples [(Mg,Ni)3Si4O10(OH)2] covering the entire Mg–Ni solid solution were synthesized following a recently developed and patented process (Dumas et al., Process for preparing a composition comprising synthetic mineral particles and composition, 2013a; Procede de preparation d’une composition comprenant des particules minerales synthetiques et composition, 2013b), which produces sub-micron talc particles replying to industrial needs. Near- and mid-infrared spectra were collected and compared to infrared spectra modeled from first-principles calculations based on density functional theory. The good agreement between experimental and theoretical spectra allowed assigning unambiguously all absorption bands. We focused in particular on the four main OH stretching bands, which represent good probes of their local physical and chemical environment. The description of the vibrational modes at the origin of these absorption bands and the theoretical determination of absorption coefficients provide a firm basis for quantifying the talc chemical composition from infrared spectroscopy and for discussing the distribution of divalent cations in the octahedral sheet. Results confirm that these synthetic talc samples have a similar structure as natural talc, with a random distribution of Mg and Ni atoms. They only differ from natural talc by their hydrophilic character, which is due to their large proportion of reactive sites on sheet edges due to sub-micronic size of the particles. Therefore, the contribution on infrared spectra of hydroxyls adsorbed on edge sites has also been investigated by computing the infrared signature of hydroxyls of surface models.

Cation exchange in a glacial till drumlin at a road salt storage facility

We use laboratory and field data to calibrate existing geochemical and transport models of cation exchange induced by contamination of an unconfined aquifer at a road salt storage facility built upon a glacial till drumlin in eastern Massachusetts. A Gaines and Thomas selectivity coefficient K models the equilibrium sodium and divalent cation distribution in the groundwater and solid matrix, while an existing method of characteristics model describes the advective transport of total dissolved cations and sorbed sodium. Laboratory isotherms of split spoon soil samples from the drumlin calibrate K with an average value of 0.0048 (L/g) 1/2 for a measured cation exchange capacity of 0.057 meq/g dry soil. Ten years of monitoring well data document groundwater flow and the advection of conservative chloride due to outdoor storage and handling of road salt at the site. The monitoring well cation data and retarded transport model offer an independent K calibration of 0.0040 to 0.0047 (L/g) 1/2: the consistency of the field and laboratory selectivity coefficient calibrations endorse this application of the Gaines and Thomas and method of characteristics models. The advancing deicing agent plume releases divalent cations from the till into the groundwater, so that monitoring well samples do not reflect the chemical composition of the road salt. In this regard, dissolved divalent cation milliequivalent concentrations are as high as 80% of the total dissolved cationic concentrations in the salt contaminated monitoring well samples, far greater than their 2.5% level in the road salt stored at the site. Cation exchange can thus obscure attempts to hindcast stored road salt sodium water table concentration from monitoring well sample stoichiometry, or to predict sodium impacts on groundwater or receiving stream quality downgradient of the well.

Divalent cation distribution in dinoflagellate chromosomes imaged by high-resolution ion probe mass spectrometry

From a variety of analytical electron microscopy experiments, the chromosomes of dinoflagellates are known to contain sizeable amounts of cations, the latter thought to contribute to the neutralization of the negative charge carried by the phosphate groups in the DNA backbone. From previous Ca and Mg chelation experiments, it is also known that these cations are necessary for the compaction and preservation of the chromosome architecture. Similar conclusions have been recently presented by our group concerning mammalian mitotic chromosomes, in studies based on secondary ion mass spectrometry (SIMS) carried out with the University of Chicago high-resolution scanning ion microprobe (UC-SIM). We have now applied this instrument to image the distribution of DNA-bound Ca 2+ and Mg 2+ in dinoflagellate chromosomes, a goal that could not be attained earlier by analytical electron microscopy. Analyzed quantitatively and imaged here by SIMS for the first time, through their cation content, are the chromosomes of the dinoflagellates Prorocentrum micans, Gymnodinium mikimotoi and Gymnodinium dorsum. The cell nuclei were isolated and prepared for SIMS analysis with a minimal protocol (mechanical fractionation in culture medium followed by ethanol drying), which did not expose the samples to artifact-creating, alien chemical agents. By this approach, we have confirmed the earlier findings by several authors, and contributed new structural information provided by our ion probe capability to erode the sample surface layer by layer (SIMS tomography). Dinoflagellates, due to the absence of histones, represent an ideal model system where cations may bind directly with DNA, allowing comparisons to be made with recently reported X-ray crystallography results at atomic resolution. Such comparisons yielded quantitative confirmation that the Ca 2++Mg 2+ concentrations found for e.g. P. micans are consistent with those anticipated to provide complete charge neutralization of naked DNA by cations, also resulting in maximal DNA compaction.

Transcriptional control of Nramp1: a paradigm for the repressive action of c-Myc

Slc11a1/Nramp1 (solute carrier family 11 member a1/murine natural resistance-associated macrophage protein 1 gene) encodes a divalent cation transporter that resides within lysosomes/late endosomes of macrophages. Nramp1 modulates the cellular distribution of divalent cations in response to cell activation by intracellular pathogens. Nramp1 expression is repressed and activated by the proto-oncogene c-Myc and Miz-1 (c-Myc-interacting zinc finger protein 1) respectively. Here we demonstrate, using a c-Myc mutant (V394D, Val(394)-->Asp) that is incapable of binding Miz-1, that c-Myc repression of Nramp1 transcription is dependent on its interaction with Miz-1. An oligo pull-down assay demonstrates specific binding of recombinant Miz-1 to the Nramp1 Miz-1-binding site or initiator element(s), and Miz-1-dependent c-Myc recruitment.

Pressure effect on the divalent cation distribution in nonideal solid solution of forsterite and fayalite

The divalent cation distribution in olivine (Mg, Fe)2SiO4 under high pressure and temperature was studied to clarify the detailed state of olivine in the mantle. Single crystal samples were heated for a sufficient period of time for the cations to migrate and quenched fast enough to preserve the equilibrated state under high pressures, and the crystal structure was determined with X-ray method. The pressure effect on the distribution coefficient KD[= (Fe/Mg)M1/(Fe/Mg)M2] was determined for the first time; dKD/dP≅0.02 GPa−1. A set of five thermodynamic parameters required to describe the regular solution model was determined from data concerning the pressure dependence and the known temperature and compositional effects. As a result we have shown how KD depends on pressure, temperature, and composition. The notable feature clarified is the very large contribution of nonideality in the olivine solid solution. The KD of olivine crystals in the mantle is predicted; KD increases to ∼ 2.2 at the depth of 400 km, in contrast to 0.9 ∼ 1.2 of natural samples available at the surface of the Earth.

Magnetic properties of X-type Ba2Me2Fe28O46 (Me=Fe, Co, and Mn) hexagonal ferrites

Polycrystalline samples of X-type Ba2Me2Fe28O46 (Me2-X, Me=Fe, Co, and Mn) hexagonal ferrite have been prepared by the classic ceramic method. Low-temperature magnetic properties, Curie temperatures, and distribution of divalent cations were studied. The substitution of Fe2+ ions with Co2+ and Mn2+ ions causes a decrease of the spontaneous moment μ and the Curie temperature Tc of X-type hexaferrites. The lower μ and Tc of Co2-X hexaferrite originate from the smaller magnetic moment of Co2+ ions. In the case of Mn2-X, the lower μ may be due to the valence state of Mn and the lower Tc may be caused by the fact that the space distribution of 3d electrons of Mn is different from that of Fe. In the Co2-X and Fe2-X compounds the Co2+ and Fe2+ ions enter the octahedral sites of spinel S blocks.

Infrared studies on the behavior in oxygen of cobalt-substituted magnetites: Comparison with zinc-substituted magnetites

Infrared spectroscopic measurements were carried out on the cobalt-substituted magnetites (Fe 3+) A(Co 2+ x Fe 2+ 1− x Fe 3+) BO 2− 4, pretreated in oxygen, to investigate as a function of temperature the defect phases γ and their transformation to hematite. It has been found that the defect spinels for which x < 0.30 show a partial vacancy ordering on octahedral sites. Referring to the disappearance of the 720-cm −1 absorption band of the defect phases γ or the appearance of the 470-cm −1 absorption band of αFe 2O 3, we show that the transition temperature γ → α increases with cobalt substitution. By comparison with zinc-substituted magnetites, the divalent cation distribution is shown to be important to vacancy ordering and to setting the temperature of hematite precipitation.

Studies on the ionophorous antibiotics. XVI. The ionophore-mediated calcium transport and concomitant osmotic swelling of mitochondria.

The effects of various carboxylic ionophores on divalent metal cation translocation in mitochondria have been investigated. High levels of divalent cation ionophores lysocellin and lasalocid A (10 approximately 50 micrometer) produced mitochondrial osmotic swelling in Ca2+ or Mg2+ medium, which was associated with an increase of cation influx. The extent of swelling was a function of both the ionophore and cation concentrations in the medium. This effect was larger in mitochondria de-energized by treatment with antimycin A and oligomycin than in respiring mitochondria. On the other hand, the monovalent cation ionophores carriomycin and etheromycin at concentrations of 50 approximately 100 micrometer also induced mitochondrial swelling in Ca2+ medium but were ineffective in Mg2+ medium. Addition of ruthenium red reversed divalent cation ionophore-induced swelling and released Ca2+ from preloaded mitochondria. In contrast, ruthenium red increased monovalent cation ionophore-induced swelling. In a divalent cation-free medium, lysocellin and lasalocid A caused depletion of membrane-bound Ca2+ and released endogenous Ca2+ and Mg2+ from mitochondria, while carriomycin and etheromycin exerted only a limited effect. These results indicate that the divalent cation ionophores affect divalent cation distribution in mitochondria by increasing both influx and efflux of the cations through the inner membrane.

H+/site ratio and steady state distribution of divalent cations in mitochondria.

H+/site ratio and steady state distribution of divalent cations in mitochondria.

The coupling of electrical ion fluxes in rat liver mitochondria

Although the molecular mechanism of the mitochondrial proton pump is not understood [ 11, the ion fluxes driven by the proton pump are phenomenologically distinguished into two groups: (a) the electrical fluxes, whereby strong acids and bases come into equilibrium with A$ and (b) the electroneutral fluxes whereby weak acids and bases come into equilibrium with ApH [2]. Two questions arise. First, this scheme has difficulties to cope with the observation that intact mitochondria catalyze both the active uptake and extrusion of strong electrolytes (i.e. KCl) without inversion of the membrane polarity [3,4]. Second, the notation of the fluxes of strong acids and bases as electrical, leaves still open the dilemma as to whether the coupling of the fluxes involve long range or short range interactions (delocalized or localized potentials). We have examined the effect of divalent cation transport inhibitors on the steady state distribution of divalent cations and on the active divalent cation extrusion [S] . The two processes possess properties which can be explained by assuming a tight coupling of the fluxes. The view is therefore discussed that electrical fluxes may be microscopically coupled through short range interactions (localized potentials).

Barium accumulation in rat pancreatic B cells.

Barium has been used as an electron-opaque substitute for calcium in a study of the distribution of divalent cations between organelles in homogenates or intact rat islets of Langerhans. These were incubated in the presence of barium acetate. Accumulation of electron-opaque deposits was stimulated during incubation of islets in the presence of high glucose concentrations and was diminished in conditions in which intracellular cyclic AMP levels were raised. Mitochondria were found to be the principal sites of accumulation of electron-opaque deposits. Addition of dinitrophenol to homogenates or intact islets abolished mitochondrial barium accumulation. X-ray microanalysis of the deposits in frozen sections showed them to consist predominantly of barium and phosphate. These experiments serve to emphasize further the critical role of mitochondria in the regulation of divalent cation accumulation in B cells, and to confirm that a direct effect on intracellular distribution of divalent cations may represent one important mechanism of action of cyclic AMP in regulating insulin secretion.

Direct evidence for intracellular divalent cation redistribution associated with platelet shape change

Chlortetracycline was used as a fluorescent probe to monitor shifts in divalent cation distribution when blood platelets were induced to change shape. Human platelets in their native plasma were incubated at 25°C with 50 μM chlortetracycline. It was found that when platelet shape change was stimulated by ADP or the divalent cation ionophore A 23187, a significant decrease in platelet-chlortetracycline fluorescence occurred. This fluorescence shift was consistent with the time course for the change in platelet shape. ATP, which inhibits ADP-induced shape change, also inhibited the decrease in platelet-chlortetracycline fluorescence.

Solvent extraction of salicylates—II: The distribution of divalent cations between aqueous solution and tributyl-phosphate in the presence of salicylic acid

The extraction of beryllium(II), manganese(II), zinc(II), and copper(II) into tributyl phosphate (TBP) by salicylic acid has been examined. Beryllium(II) extracts as Be(OC 6H 4COO)·2H 2O, zinc(II) and manganese(II) extract as species of formula M(HO·C 6H 4COO) 2·2TBP, while copper(II) extracts as species of both these types. The mode of extraction depends on the magnitude of the formation constant of the monosalicylato-metal(II) chelates.