Magnesium chloride crystalline forms

The enzyme was purified from Candida utilis in 1965 by Rosen et al. (8Q). Dried yeast was allowed to autolyze in phosphate buffer at pH 7.5 for 48 hr, and the enzyme was isolated in crystalline form from these autolysates by a procedure which included heating to 55° at pH 5.0, fractionation with ammonium sulfate, and purification on phospho-cellulose columns from which the enzyme was specifically eluted with malonate buffer containing 2.0 mM FDP. Crystallization was carried out by addition of ammonium sulfate in the presence of mM magnesium chloride. The Candida enzyme was more active than the mammalian FDPases at room temperature and pH 9.5 the crystalline protein catalyzed the hydrolysis of 83 /nnoles of FDP per minute per milligram of protein. The enzyme was completely inactive with other phosphate esters, including sedoheptulose diphosphate, ribulose diphosphate, and fructose 1- or fructose 6-phosphates. Nor was the activity of the enzyme inhibited by any of these compounds. Optimum activity was observed at concentrations of FDP between 0.05 and 0.5 mM higher concentrations of FDP (5 mM) were inhibitory. 

Potassium magnesium ferrocyanide, K2MgFe(CN)6, is obtained in the anhydrous condition by mixing cold concentrated solutions of potassium ferrocyanide and magnesium chloride.3 After a short time a white micro-crystalline precipitate is formed, which is not affected by heating to 120° C. When moist the salt soon becomes cream-coloured, owing to slight decomposition, possibly under the influence of atmospheric carbon dioxide. 

Experiment 158. — (a) To a solution of magnesium sulphate or chloride add successively solutions of ammonium chloride, ammonium hydroxide, and disodium phosphate. A precipitate of ammonium magnesium phosphate is formed, NH MgPO. It is voluminous at first, but finally crystalline. It is soluble in acids. Try it. 

Dehua and Chuanmei (1999) consider that the formation of the magnesium oxychloride phases are produced in the following reaction sequence the MgO first dissolves in the magnesium chloride solution followed by the formation of the polynuclear complexes [Mgx(0H)J(H20)z]2x y. These complexes then further react with the chloride ion to form a continuous phase or hydrogel, which subsequently converts to the crystalline phases. 

The dehydration of moist inorganic salts with water of crystallization content is, in general, a complex task. The loss of crystalline water usually consists of several components with different temperature or residence time requirements for each case. In the course of dehydration, the material to be processed (e.g., ZnCl2 or MnCy may form undesirable compounds. In numerous cases, as with magnesium chloride and iron chloride, oxygen impedes the full loss of crystal water as a result of heat effects. On the basis of these problems, publications dealing with successful dehydration experiments conducted in spouted bed equipment are of particular interest. 

Aggregation (non-crystalline) and orientation (crystalline) are both influenced by supersaturation and temperature, but the type of species is also very important. For example, strongly polar salts, such as lead iodide, silver chloride and barium sulphate, invariably precipitate in crystalline form. Carbonates of calcium and barium and hydroxides of magnesium and zinc do likewise, but there is evidence in some of these cases of the prior precipitation of hydrated short-lived precursor phases (Mullin et al., 1989 Brecevic and Nielsen, 1990). Hydrous oxides like hydrous ferric oxide (o-ferric hydroxide) are generally amorphous, especially when precipitated from cold solution. 

Catalysts more than a thousand times as active as the original Ziegler-Natta systems have now been developed. In one form magnesium chloride, which has a similar layer lattice to a-TiCl, is milled with ethyl benzoate and then treated with TiCl. The resulting solid retains about 1% titanium and ester it is activated with EtjAl. Polymerization of propene is carried out in the liquid phase under pressure (55°C/20atm) and of ethene, in the gas phase. The reaction is strongly exothermic (p. 124). Such low concentrations of these modern supported catalysts are required that no removal of catalyst residues from the product is necessary. Moreover such highly crystalline polypropene is produced that there is no need to separate unwanted atactic material. 

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