Magnesium, Calcium and Zinc

Mg ions activate some enzymes which hydrolyze phosphoric acid ester bonds (e. g. phosphatases cf. Table 2.4) or transfer phosphate residues from ATP to a suitable acceptor (e. g. kinases cf. Table 2.4). In both cases, Mg ions act as an electrophilic Lewis acid, polarize the P—O-linkage of the phosphate residue of the substrate or cosubstrate and, thus, facilitate a nucleophilic attack (water with hydrolases ROH in the case of kinases). An example is the hexokinase enzyme (cf. Table 2.16) which, in glycolysis, is involved in catalyzing the phosphorylation of glucose to glucose-6-phosphate with ATP as cosubstrate. The effect of a Mg ion within the enzyme-substrate complex is obvious from the following formulation  

Ca2 ions are weaker Lewis acids than Mg ions. Therefore, the replacement of Mg by Ca may result in an inhibition of the kinase enzymes. Enhancement of the activity of other enzymes by Ca is based on the ability of the ion to interact with the negatively charged sites of amino acid residues and, thus, to bring about stabilization of the enzyme conformation (e. g. a-amylase cf. 4.4.4.5.1). The activation of the enzyme may be also caused by the involvement of the Ca ion in substrate binding (e. g. lipase cf. 3.7.1.1). 

The Zn ion, among the series of transition metals, is a cofactor which is not involved in redox reactions under physiological conditions. As a Lewis acid similar in strength to Mg , Zn participates in similar reactions. Hence, substituting the Zn ion for the Mg ion in some enzymes is possible without loss of enzyme activity. Both metal ions can function as stabilizers of enzyme conformation and their direct participation in catalysis is readily revealed in the case of alcohol dehydrogenase. This enzyme isolated from horse liver consists of two identical polypeptide chains, each with one active site. Two of the four Zn ions in the enzyme readily dissociate. Although this dissociation has no effect on the quaternary structure, the enzyme activity is lost. As described under section 2.3.1.1, both of these Zn ions are involved in the formation of the active site. In catalysis they polarize the substrate s C—O linkage and, thus, facilitate the transfer of hydride ions from or to the cosubstrate. Unlike the dissociable ions, removal of the two residual Zn ions is possible only under drastic conditions, namely disruption of the enzyme s quaternary structure which is maintained by these two ions. 

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Cationic diorganoaluminum species with non-coordinating anions are activators in the high-temperature polymerization of olefins, while mixtures of AlEt3/B(C6F5)3 also show moderate activity for the polymerization of ethylene. Neutral magnesium, calcium, and zinc compounds, in turn, have been used as catalysts for the polymerization of... 

Rutgers and Hendrikx (126) have reviewed existing hydration numbers and have provided some new values for the hydration of several cations and anions based on measurements with a membrane transference cell. Their results are hydration numbers higher than those normally assumed. Thus, apparent hydration numbers for lithium, sodium, and potassium were respectively 22, 13, and 7 while for magnesium, calcium, and zinc, values of 36, 20, and 44 were obtained. 

PL Parker, H. E., Magnesium, calcium, and zinc in animal nutrition. Atomic Absorption Newsletter No. 13. Perkin-Elmer Corp., Norwalk, Conn. (May 1963). P2. Paschen, F., Bohr s Heliumlinien. Ann. Physik 50, 901-940 (1916). 

M. Pavlov, P. E. M. Siegbahn, and M. Sandstrom, Hydration of Beryllium, Magnesium, Calcium, and Zinc Ions Using Density Functional Theory, J. Phys. Chem. A 102,219-228 (1998). 

Metal ions with low toxicity that are poorly absorbed by the body, such as iron, magnesium, calcium, and zinc, are attractive candidates. Of these, iron and zinc have been extensively apphed in MOF synthesis, perhaps owing to the kinetic labihty of certain oxidation states and their affinity for carboxyfate donors. Other metafs are also suitable, depending on their toxicity in comparison to necessary dosage, but the toxicity of the MOF itself will originate from its metaboHtes, and so careful scrutiny of the speciation and breakdown of the MOF in the hmnan body is obviously required. 

Salts of neodecanoic acid have been used in the preparation of supported catalysts, such as silver neodecanoate for the preparation of ethylene oxide catalysts (119), and the nickel soap in the preparation of a hydrogenation catalyst (120). Metal neodecanoates, such as magnesium, lead, calcium, and zinc, are used to improve the adherence of plasticized poly(vinyl butyral) sheet to safety glass in car windshields (121). Platinum complexes using neodecanoic acid have been studied for antitumor activity (122). Neodecanoic acid and its esters are used in cosmetics as emoUients, emulsifiers, and solubilizers (77,123,124). Zinc or copper salts of neoacids are used as preservatives for wood (125). 

Magnesium is reduced from a mixture of magnesium, calcium, and sodium chlorides. Electrolysis from aqueous solution is also possible zinc, copper, and manganese dissolved as sulfates in water can be reduced electrolytically from aqueous solution. 

Studies were carried out In adult males to determine the effect of phosphorus, magnesium, fluoride and zinc on the availability of calcium for absorption ... 

AAS is used in a number of limit tests for metallic impurities, e.g. magnesium and strontium in calcium acetate palladium in carbenicillin sodium and lead in bismuth subgallate. It is also used to assay metals in a number of other preparations zinc in zinc insulin suspension and tetracosactrin zinc injection copper and iron in ascorbic acid zinc in acetylcysteine lead in bismuthsubcarbonate silver in cisplatinum lead in oxyprenolol aluminium in albumin solution and calcium, magnesium, mercury and zinc in water used for diluting haemodialysis solutions. 

Potatoes are an important source of different dietary minerals. Potato is listed as providing 18% of the RDA of potassium, 6% of iron, phosphorus and magnesium, and 2% calcium and zinc. Retention of most minerals is high in boiled potatoes cooked with skin (True et al., 1979). Baking a potato with the skin is a good cooking method to retain minerals. 

Potassium, phosphoms, calcium, and magnesium concentrations changed with irrigation and fertilization in physiologically mature tubers (Ilin et al., 2002). The total concentration of iron, calcium, and zinc increased with application of fertilizers whereas the content of phosphoms and molybdenum was reduced (Bibak et al., 1999 Frossard et al., 2000). The wide range of mineral content reported in potatoes may not only be due to genotype and environmental factors, but also sampling issues. 

Ground flax seed is rich in protein, B vitamins, vitamin E, beta-carotene, calcium, potassium, magnesium, manganese, and zinc. 

Wine increases the absorption of calcium, magnesium, phosphorus, and zinc. 

If undistilled sample is used, the addition of zinc sulfate in presence of NaOH would precipitate out iron, magnesium, calcium, and sulfide as a heavy flocculent,... 

Measurements will be made of the form and levels of elements in soil, movement of elements to plant roots, uptake of elements by plant roots, and translocation to above-ground, and edible portions of plants. The elements to be studied include magnesium, calcium, potassium, zinc, phosphorous, nitrogen, iron, manganese, copper, and aluminum. 

Metals. Aluminum, calcium powder, copper foil, iron wire, manganese powder, and potassium ignite in dry chlorine gas as do powdered antimony, bismuth, and germanium. Magnesium, sodium, and zinc ignite in the moist gas. Thorium, tin, and uranium ignite on warming.14 21 22... 

Quantitative risk assessments have been performed on a variety of flame-retardants used both in upholstered furniture fabric and foam. The National Research Council performed a quantitative risk assessment on 16 chemicals (or chemical classes) identified by the U.S. Consumer Product Safety Commission (CPSC). The results were published in 2000.88 The 16 flame-retardants included in this NRC study were HBCD, deca-BDE, alumina trihydrate, magnesium hydroxide, zinc borate, calcium and zinc molybdates, antimony trioxide, antimony pentoxide and sodium antimonate, ammonium polyphosphates, phosphonic acid, (3- [hydroxymethyl]amino -3-oxopropyl)-dimethylester, organic phosphonates, tris (monochloropropyl) phosphate, tris (l,3-dichloropropyl-2) phosphate, aromatic phosphate plasticisers, tetrakis (hydroxymethyl) hydronium salts, and chlorinated paraffins. The conclusions of the assessment was that the following flame-retardants can be used on residential furniture with minimal risk, even under worst-case assumptions ... 

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