Order Of Mg Research Articles

Characterization of colloidal particles by laser-induced plasma spectroscopy (LIPS)

To study the nature and abundance of colloids in aquifer systems Laser-Induced Plasma Spectroscopy (LIPS) was used for elemental analysis of heavy metal colloids with particle diameters between 0.1 and 1 μm. Different experimental approaches to the qualitative and quantitative characterization of inorganic colloids are examined. Some of the inherent problems associated with a direct detection are discussed. A direct detection of colloids in water or a liquid jet without separation between solvent and particles yielded only inadequate spectral resolution and detection limits in the order of mg l −1. Utilization of a miniaturized ultrafiltration system with a 0.1 μm membrane filter gave absolute limits of detection in the ng-range with good reproducibility. Figures of merit are given for representative heavy metal colloids. The filtration device used in this work is suitable for subsurface sampling under flow conditions, which minimizes sampling artifacts. A slightly modified LIPS system will be used for field screening and monitoring.

Regulatory effects of zinc on corn root plasma membrane H+‐ATPase

summaryEffects of divalent metal ions (Zn, Mg, Mn), metal‐ATP complexes, and pH on the activity of the plasma membrane H+‐ATPase were investigated. Both native vesicles, isolated by sucrose gradient centrifugation, and solubilized H+‐ATPase, purified by linear glycerol gradient centrifugation were used. Zn, as well as Mg and Mn, stimulates the activity of H+‐ATPase. Computer calculations of equilibrium concentrations have been used to separate the effects of individual ion complexes and free ionic forms on the enzyme activity. The calculations indicated that Zn as ZnATP+ serves as a substrate of the plasma membrane H+‐ATPase. The possibility of serving as substrate depends on the Zn/ATP ratio and the pH of the medium. The native H+‐ATPase was activated by divalent metal ions in the order of Mg > Mn > Zn at pH 6.5 and in the order of Zn > Mn > Mg at pH 5.5 for total metal ion concentrations not higher than 3.0 mM. A Zn: ATP ratio of 0.6 at pH 5.5 gave more than 100% of the Mg‐dependent ATPase activity (Mg: ATP ratio of 1, pH 5.5). By contrast, free Zn2+ is an effective inhibitor of ATP hydrolysis and H+ transport with a strong dependence upon the pH of the medium. At pH 55 a total ZnSO4 concentration of 1 mM induced no inhibition of ATP hydrolysis, whereas at pH 6.5 the same Zn concentration decreased the activity of the native and purified H+‐ATPase to 49% and 34% (control activity: Mg: ATP ratio of 1, no ZnSO4), respectively. We show that both activation by ZnATP2− and inhibition by free Zn2+ of the native plasma membrane H+‐ATPase and the partially purified enzyme were strongly affected by the pH of the medium. The results provide evidence that Zn, in combination with the pH of the cytoplasm could play a role in regulating the plasma membrane H+‐ATPase and thus in nutrient uptake of plant systems.

Effect of protein kinase-C activation on the Mg 2+-sensitivity of cloned NMDA receptors

The mechanisms responsible for protein kinase-c (PKC) mediated potentiation of NMDA receptors are poorly understood. One hypothesis is that PKC-activation reduces the receptor's characteristic voltage-dependent Mg 2+-blockade. Experiments performed on Xenopus oocytes expressing cloned NMDA receptors demonstrated that PKC-activation induced no change in the sensitivity of ζl ε3 and ζ1 ε4 receptors to Mg 2+-blockade and, even though PKC-activation did induce a small shift in Mg 2+sensitivity for the ζl εl and ζl ε2 receptors, the change seen was not large enough to account for an appreciable increase in NMDA receptor activity. Baseline Mg 2+-sensitivities and levels of PKC-mediated potentiation were also quantified for each of the di-heteromeric NMDA receptors. The order of Mg 2+-sensitivity is ζl ε l (most sensitive) > ζl ε2 > | solζl g34 > l ε3 (least sensitive). PKC-activation caused a 2-fold increase in ζl g4 l currents, a 4-fold increase in 1 ε2 currents and no change in either l ε3 or l ε4 currents. These data suggest that PKC-potentiation of the cloned di-heteromeric NMDA receptors does not involve a reduction in Mg 2+-blockade. The di-heteromeric receptors possess varied properties in regard to PKC-potentiation and Mg 2+-blockade which have been quantified here.

Second-order nonlinear optical properties of amphiphilic porphyrins in Langmuir-Blodgett monolayer assemblies

Optical second harmonic generation (SHG) from the Langmuir-Blodgett (LB) monolayer assemblies of amphiphilic porphyrin and its some metal complexes has been investigated. Distinct SHG responses were observed with monolayers of amphiphilic 5-(4-N-hexadecylpyridinium)-10,15,20-triphenylporphine bromide (free base: H2 porphyrin) and its magnesium (Mg), copper (Cu), and zinc (Zn) complexes. The efficiency of SHG was in the order of Mg → Zn → Cu → H2-porphyrins, which could be well correlated with the order of the first reduction potential of the porphyrin. The result indicated that SHG was mainly attributed to charge transfer from the porphyrin ring to the pyridinium group. The tilt angle of the molecular hyperpolarizability for the Zn porphyrin was evaluated.

Speciation and genotoxicity of butyltin compounds

The northern part of the Elbe river in Germany is one of the most highly polluted rivers in Europe, in particular with toxic organotin compounds. Two major anthropogenic sources are the Hamburg harbour area with intensive docking activities and a chemical plant in Bitterfeld close to the Mulde river in eastern Germany. Tributyltin is leached from the antifouling paints and enters the water phase. Thus, the Hamburg harbour area is highly contaminated with tributyltin and its degradation products, di- and mono-butyltin. Untreated run-off waters of an organotin plant in Bitterfeld contaminate the Mulde, a tributary of the Elbe, extensively. The Mulde sediments contain butyltin compounds of the order of mg of Sn per kilogram of dry mass. In Raguhun sediments, concentrations of tetrabutyltin and tributyltin were 1.8 ± 0.4 mg of Sn per kilogram of dry mass and 1.1 ± 0.2 mg of Sn per kilogram of dry mass, respectively. Remobilization of the sediments during high water periods transports the contaminants along the Mulde river into the Elbe river. Tetrabutyltin can be detected in the Elbe river as far as Cuxhaven and its estuary. To evaluate the ecological impact, fish tissues were analysed for their butyltin content and the data were correlated with the butyltin content in the surrounding water. The analysis of different fish tissues: liver, kidney, gills and the edible tissue, shows a clear enrichment of the tributyltin species. In the liver, tributyltin concentrations of up to 200 ng of Sn per gram of wet tissue were found. Bioconcentration factors were calculated to be of the order of 4500–9000. Tetrabutyltin could not be found in all the tissues, whereas it is present in water. The low bioavailability of tetrabutyltin is presumably caused by the low amount of tetrabutyltin in the dissolved constituents of water. Up to 99% of the tetrabutyltin content in water is bonded to particulate matter. The butyl groups influence the toxic behaviour of the butyltins. Although the toxic effects of butyltins on different organisms are well investigated, the genotoxic potential of the butyltins has received much less attention. The SOS-Chromotest was used to evaluate their genotoxicity. All the butyltins were found to be genotoxic; dibutyltin was the most genotoxic (10–40 µg of Sn per litre) followed by tri-, tetra- and mono-butyltin. An enhancement of the genotoxicity of all butyltins was observed using spiked lake water instead of distilled water. For the analysis of the butyltin compounds sodium tetraethylborate was used as in situ ethylating agent in the buffered samples. No pre-extraction steps with complexing agents are necessary. The extraction yields of all butyltin compounds are in the range of 82–94% for water; 76–88% for suspended particulate matter, sediment and soil; 80–94% for organisms; and 76–97% for air samples. The limit of detection of GC–AAS is 25 ± 5 pg of Sn per microlitre injected volume (3σ of the baseline noise).

Evolution of medium-range order of Mg 0.5Ni 0.3La 0.2 metallic glass at a supercooled liquid temperature

Mg 0.5Ni 0.3La 0.2 metallic glass is known as having a wide range in which it is in a supercooled liquid state. Changes in structural and thermal properties of Mg 0.5Ni 0.3La 0.2 at the supercooled liquid state (167°C) were studied by small angle X-ray scattering (SAXS) and differential scanning calorimetry (DSC). DSC results show that the amorphous state is stabilized after annealing at 167°C for the period of time before the onset of crystallization. SAXS results suggest that concentration segregation evolves with a relatively large size and low concentration fluctuations after annealing at 167°C for 40 h before onset of crystallization. The interface of the segregated area is diffuse even after the crystallization starts. The crystallization from a supercooled liquid proceeds in spinodal decomposition mode rather than nucleation and growth mode.

Phase behaviour of blends of nylon 6 and lightly sulfonated polystyrene ionomers

Mixtures of nylon 6 and lightly sulfonated polystyrene ionomers (M-SPS, where MLi, Mg, Zn or Mn) exhibit lower critical solution temperature ( LCST) phase behaviour. Miscibility was a consequence of specific complex formation between the metal sulfonate and amide groups. The interactions were strongest when the cation was Zn 2+ or a transition metal such as Mn 2+. The LCST increased as the sulfonation level increased and as the cation was changed in the order of Mg 2+ + < Li + < Zn 2+ < Mn 2+. Despite large differences in the molecular weights of the two polymers, the liquid-liquid phase diagrams were symmetric about the 50/50 composition. The glass transition temperature of miscible blends showed a positive synergism due to the physical network resulting from intermolecular complex formation. Although both polymers were hygroscopic, the blends exhibited less water absorption than either of the two components alone, which was a consequence of the complex removing sites for hydrogen bonding of water. The amount of water absorption decreased when the cation was varied in the order of Mgt + > Li + > Zn2+.

The characterization of iron based Fe−M ultrafine particle (UFP) catalysts. II. Effect of second metal component (M=Mn, Zn, Mg)

The effect of second metal component on the structural characteristic of Fe M UFP catalysts was investigated by in situ Mossbauer spectroscopy. The incorporation of second metal component hinders, the reduction and carburization of iron containing phase in the presence of H2 and CO, and the degree of hindrance is in the order of Mg Mn Zn due to the interaction between iron and the second metal component. Consequently, the formation of light olefinic products is in the order of Fe Mg>Fe−Mn·Fe−Zn catalysts consistent with the F-T synthesis performance.

Chelation of divalent cations by ATP, studied by titration calorimetry

Thermodynamic parameters and stoichiometry for the formation of complexes of ATP with Mg 2+, Ca 2+, and Sr 2+ were determined by titration calorimetry. In each case, 1:1 stoichiometry was observed and complex formation was entropy driven. Binding constants for formation of complexes decreased in the order of Mg 2+ > Ca 2+ > Sr 2+, as expected from charge density considerations. Monovalent cations hindered complex formation with Mg 2+, apparently by competing with the divalent cation for complexation with ATP. Analysis of this competitive effect provided estimates of the binding constants for complexes of ATP with monovalent cations, which decreased in the order expected from charge density considerations (Li + > Na + > K +).

Comparative study of injection into a pneumatic nebuliser and tungsten coil electrothermal vaporisation for the determination of rare earth elements by inductively coupled plasma optical emission spectrometry

Injection into a pneumatic nebuliser and vaporisation using a tungsten coil electrothermal vaporisation system, with a 3-kW argon-nitrogen inductively coupled plasma (ICP), are compared for the determination of the rare earth elements. The sampling efficiency and thus also the absolute power of detection of the tungsten coil ICP optical emission spectrometric (ICP-OES) technique are better by two orders of magnitude, than the injection technique. The absolute detection limits for the rare earth elements are at the pg level; for the refractory rare earth elements (Er, La, Lu and Y), they are lower than those obtained by graphite furnace atomic absorption spectrometry, whereas for the other rare earth elements (Eu, Sc, Tm and Yb), the detection limits are comparable. With injection of samples into a pneumatic nebuliser and ICP-OES, matrix effects are low and absolute amounts of the order of mg of the rare earth matrix can be tolerated, giving relative detection limits down to 1 µg g–1. The amount of rare earth matrix that can be tolerated with the tungsten-coil atomiser is two orders of magnitude lower. Thus the relatively detection limits of the two methods are of the same order, although the matrix effects are considerably higher with the tungsten coil.

Reaction of metal vapors with gem-dihalides of the methane and cyclopropane series

1. In the reaction of Mg vapors with 1,1-dibromo-2,2-dimethylcyclopropane at 77°K in a medium of solvating solvents, debromination of the starting gem-magnesium dibromide by a radical mechanism with subsequent cleavage of hydrogen atoms from the solvent by the radicals formed is the basic direction of the reaction. 2. The capacity of metal vapors to debrominate gem-dibromocyclopropanes decreased in the order of Mg, Al, Zn. 3. In the reaction of Cr, Ti, Fe, and Cu vapors with CH2Cl2 and CH2Br2 at 77°K, cleavage of one halogen atom and recombination of the ·CH2X radicals generated occurred with formation of 1,2-dihalogenated ethanes.

Magnetic Field Structure of Star Forming Regions: VLBI Spectral Line Results

Magnetic fields play a major role in the general dynamics of astronomical phenomena and particularly in the process of star formation. The magnetic field strength in galactic molecular clouds is of the order of few tens of μG. On a smaller scale, OH masers exhibit fields of the order of mG and these can probably be taken as representative of the magnetic field in the dense regions surrounding protostars. The OH molecule has been shown to emit highly circular and linearly polarized radiation. That it was indeed the action of the magnetic field that would give rise to the highly polarized spectrum of OH has been shown by the VLBI observations of Zeeman pairs of the 1720 and 6035 MHz by Lo et. al. and Moran et. al. VLBI observations of W3 (OH) revealed that the OH emission was coming from numerous discrete locations and that all spots fell within the continuum contours of the compact HII region. The most detailed VLBI aperture synthesis experiment of the 1665 MHz emission from W3 (OH) was carried out by Reid et. al. who found several Zeeman pairs and a characteristic maser clump size of 30 mas. In this work, we report the results of a 5 station VLBI aperture synthesis experiment of the 1665 MHz OH emission from W3 (OH) with full polarization information. We produced VLBI synthesis maps of all Stokes parameters of 16 spectral features that showed elliptical polarization. The magnitude and direction of the magnetic field have been obtained by the detection of 7 Zeeman pairs. The three dimensional orientation of the magnetic field can be obtained, following the theoretical arguments of Goldreich et. al., from the observation of π and σ components.

Accurate assay of lithium by isotope dilution mass spectrometry.

A need for accurate assay of lithium exists in a number of different fields, e.g. in the nuclear field and in clinical chemistry. Stable isotope dilution mass spectrometry is a well established technique that can be used successfully for this purpose. The technique has an inherent accuracy which is constant over a wide dynamic concentration range. This work reports on the assay of lithium in LiF deposits of amounts of the order of mg and in human serum with lithium concentration in the ppm range. In both cases the assay has been achieved to an accuracy of 0.5 percent.

Experimental and theoretical studies of low-voltage electronluminescence of ZnS single crystals

Sub-critical crack growth in various kinds of metaphosphate glasses was investigated by using DCDC (Double Cleavage Drilled Compression) technique. The crack growth measurements were only being made in Region III, or in an inert environment. In order to evaluate intrinsic crack growth behaviors in Region III, crack propagation tests were performed in dehydrated heptane, and the crack velocity, v, was plotted as a function of the stress intensity factor, KI. Fracture toughness of glass was also estimated from a stress intensity factor at a given crack velocity. For binary metaphosphate glasses (50MO · 50P2O5, M = Zn, Mg, Ca, Ba), fracture toughness increases in the order of Mg > Ca > Zn > Ba. However, the slope of KI–v curve is almost unchanged. In the case of aluminum containing metaphosphate glasses, with increasing aluminum content, fracture toughness increases and the slope of KI–v curve becomes smaller, regardless of the type of divalent cations in glass. It is concluded that an addition of aluminum ions into metaphosphate glass results in both high toughness and easy fatigue. In addition, the structural role of aluminum ions on the intrinsic sub-critical crack growth is discussed in terms of the models of atomistic bond rupture.

STUDY ON SPINNING MECHANISM OF VISCOSE

Effsects of some ions on the mutual diffusion of NaOH-H2SO4 system through a cellophane film as a basic study on the spinning mechanism of viscose were studied and the following results were obtained:(1) S-- ion in the alkali solution and Zn++ ion in the spin bath solution restrict the diffusion of the spin bath components into the alkali solution and allow the diffusion of the alkali components into the spin bath solution.(2) The restrictive effects of the diffusion of the spin bath components into the alkali solution by some metalic ions in the spin bath solution have a relationship with the precipitating pII of these metalic sulfides or hydroxides, in the order of Mg++, Fe+++, Al+++, Mn++, Fe++, Zn++, the precipitating pH of metalic sulfide or hydroxide is lower and the restrictive effects of the diffusion of the spin bath components into the alkali solution is larger. These results were discussed in relation to the spinning mechanism of viscose.