Search results for "Magnesium"
showing 10 items of 490 documents
Sulfur isotope ratio measurements of individual sulfate particles by NanoSIMS
2008
Abstract The sulfur isotopic compositions of barite (BaSO4), anhydrite (CaSO4), gypsum (CaSO4·2H2O), mascagnite ((NH4)2SO4), thenardite (Na2SO4), boetite (K2SO4), epsomite (MgSO4·7H2O), magnesium sulfate (MgSO4·xH2O) and cysteine (an amino acid) were determined with a Cameca NanoSIMS 50 ion microprobe employing a Cs+ primary ion beam and measuring negative secondary ions. This ion microprobe permits the analysis of sulfur isotope ratios in sulfates on 0.001–0.5 ng of sample material, enabling the analysis of individual S-bearing particles with diameters as small as 500 nm. The grain-to-grain reproducibility of measurements is typically 5‰ (1σ) for micron-sized grains,
The effect of ions at the surface of calcium oxalate monohydrate crystals on cell-crystal interactions
2003
Magnesium is an abundant ion in biologic systems, including renal tubular fluid; however, the precise role of magnesium during the interaction of calcium oxalate crystals with cells has not been previously defined. In addition, the respective roles of calcium and hydrogen ions during the cell-crystal bonding interaction remain poorly defined. Here we report an atomic level three-dimensional study of a single crystal of calcium oxalate monohydrate (COM; whewellite) which was bathed in a solution of magnesium hexahydrate for 1 year. Magnesium was not incorporated into the structure of whewellite to any significant degree. Instead, COM accepted magnesium primarily as an adsorbate in a binding …
Goldschmidt Abstracts 2010 – F
2010
We report on two novel procedures for the determination of several trace elements in seawater, including elements characterized by very low abundance (sub-0.1 to 1 ng l-1) in the ocean, such as REEs, Hf, and Th. Our methods are based on the procedure developed recently by Bayon et al. [1], and applied successfully to a wide range of geological samples. It involves addition of a Tm spike and pre-concentration using co-precipitation, prior to analysis by inductively coupled plasma-sector field mass spectrometry (ICP-SFMS). The addition of a small amount of Tm to the sample produces a positive Tm anomaly in the resulting REE pattern, which allows calculation of precise trace element concentrat…
Mg/BOX complexes as efficient catalysts for the enantioselective Michael addition of malonates to β-trifluoromethyl-α,β-unsaturated ketones and their…
2021
Abstract Magnesium (II)-BOX complexes catalyze the enantioselective Michael addition of malonates to β-trifluoromethyl enones and their N-sulfonyl imines to give ketones or (E)-enamines bearing a trifluoromethylated stereogenic center, respectively, with good yields and high enantiomeric excesses. Magnesium complexes proved to be more active and stereoselective than zinc and copper analogues in these reactions.
Mass determination, subunit organization and control of oligomerization states of keyhole limpet hemocyanin (KLH).
1997
Analytical dark-field scanning transmission electron microscopy (STEM) of freeze-dried unstained specimens of keyhole limpet hemocyanin (KLH; from Megathura crenulata, a prosobranch gastropod) gave a molecular mass of 400 kDa for the subunit of KLH1 and of 345 kDa for the subunit of KLH2, which confirms our published values from SDS/PAGE. Within the 400-kDa KLH1 subunit we identified, by limited proteolysis, isolation of fragments and N-terminal sequencing, eight distinct 45-60 kDa functional domains (termed 1a through 1h) and determined their sequential arrangement. The KLH1 domains differ biochemically and immunologically from each other and from the previously characterized seven domains…
Switch between tyrosinase and catecholoxidase activity of scorpion hemocyanin by allosteric effectors
2008
AbstractPhenoloxidases and hemocyanins have similar type 3 copper centers although they perform different functions. Hemocyanins are oxygen carriers, while phenoloxidases (tyrosinase/catecholoxidase) catalyze the initial step in melanin synthesis. Tyrosinases catalyze two subsequent reactions, whereas catecholoxidases catalyze only the second one. Recent results indicate that hemocyanins can also function as phenoloxidases and here we show for the first time that hemocyanin can be converted to phenoloxidase. Furthermore, its substrate specificity can be switched between catecholoxidase and tyrosinase activity depending on effectors such as hydroxymethyl-aminomethan (Tris) and Mg2+-ions. Thi…
Local tunneling study of three-dimensional order parameter in the pi band of Al-doped MgB2 single crystals
2007
We have performed local tunneling spectroscopy on high quality Mg$_{1-x}$Al$_x$B$_2$ single crystals by means of Variable Temperature Scanning Tunneling Spectroscopy (STS) in magnetic field up to 3 Tesla. Single gap conductance spectra due to c-axis tunneling were extensively measured, probing different amplitudes of the three-dimensional $\Delta_\pi$ as a function of Al content. Temperature and magnetic field dependences of the conductance spectra were studied in S-I-N configuration: the effect of the doping resulted in a monotonous reduction of the locally measured $T_C$ down to 24K for x=0.2. On the other hand, we have found that the gap amplitude shows a maximum value $\Delta_\pi= 2.3$ …
Synthesis, structural studies and reactivity of vanadium complexes with tridentate (OSO) ligand
2007
The direct reaction between [VCl(3)(thf)3] or [VO(OEt)3] and 2,2'-thiobis{4-(1,1,3,3-tetramethyl-butyl)phenol (tbopH(2)) leads to the formation of [V(2)(micro-tbop-kappa(3)O,S,O)2Cl(2)(CH(3)CN)(2)] (1).4CH(3)CN or [V(2)(micro-OEt)2(O)2(tbop-kappa(3)O,S,O)2] (2), respectively, in high yield. Compounds 1 and 2 were characterized by chemical and physical techniques including X-ray crystallography and variable temperature magnetic susceptibility studies (J = -29.1 cm(-1)) for 1. Complexes 1 and 2 were supported on MgCl2 and when activated with aluminium alkyls, were found to effectively polymerize ethene to produce polyethylene with a narrow molecular weight distribution M(w)/M(n) approximately…
In-process tool rotational speed variation with constant heat input in friction stir welding of AZ31 sheets with variable thickness
2017
In the present work, friction stir welding experiments on AZ31 magnesium alloy sheets, characterized by a variable thickness along the welding line, were carried out. The approach adapted during welding consisted in maintaining constant the heat input to the joint. To this purpose, the rotational speed of the pin tool was increased with decreasing thickness and decreased with increasing thickness in order to obtain the same temperatures during welding. The amount by which the rotational speed was changed as a function of the sheet thickness was defined on the basis of the results given by FEM simulations of the FSW process. Finally, the effect of the in-process variation of the tool rotatio…
A simulation tool for ion exchange membrane crystallization of magnesium hydroxide from waste brine
2021
Abstract Increasing attention is nowadays paid to the management and valorisation of industrial waste brines aiming also at the recovery of raw materials. Magnesium has been listed as a Critical Raw Material by EU, prompting researchers to investigate novel routes for its recovery. Within this framework, a novel Crystallizer with Ion Exchange Membrane (CrIEM), is proposed as an innovative way to recover magnesium from industrial waste brines exploiting low-cost alkaline reactants. In the present work, a novel mathematical model of the CrIEM process is proposed to provide a useful tool for its design in different working conditions. Batch and feed & bleed continuous configurations have been …