Earth Cations, Particularly Calcium

The Interaction between the Alkali Earth Cations, Particularly Calcium, and Proteins... 

Orthophosphate salts are generally prepared by the partial or total neutralization of orthophosphoric acid. Phase equiUbrium diagrams are particularly usehil in identifying conditions for the preparation of particular phosphate salts. The solution properties of orthophosphate salts of monovalent cations are distincdy different from those of the polyvalent cations, the latter exhibiting incongment solubiUty in most cases. The commercial phosphates include alkah metal, alkaline-earth, heavy metal, mixed metal, and ammonium salts of phosphoric acid. Sodium phosphates are the most important, followed by calcium, ammonium, and potassium salts. 

The ion selectivities displayed by these antibiotics are lower than those of the neutral ionophores, and are given in Table 11. Many studies have been made on the properties of these ionophores, particularly with reference to the calcium-transporting abilities of A 23187 (146) and lasolocid (145). The search for new antibiotics is ongoing and there is constant addition to a list of about 50 distinct polyether antibiotics which have been isolated from various streptomycetes. Representative structures will be discussed here to illustrate the nature of complexation with alkali and alkaline earth metal cations. 

The reversible190 exchange of alkyl chlorides with metal bromides in a two-phase system, under PTC, has been reported to depend on the nature of the metal cation and the concentration of the aqueous phase. Most effective bromide donors are lithium191 and calcium bromides192 particularly when applied in the presence of a small amount of water. Interestingly, both the equilibrium composition and the rate in the reaction of various alkali and alkali earth bromides with -octyl chloride catalyzed by tetra- -hexylammonium bromide are strongly dependent on the amount of water present in the system193,194. 

Calcium bis[tetrahydroborate(l-)] may be prepared from sodium tetra-hydroborate( 1 -) and calcium dichloride by cation exchange11 in a suitable solvent such as dimethylformamide,12 an amine13,14 or an alcohol.13,14 A particularly good preparation of very pure Ca[BH4]2 involves the reaction of calcium dihydride with the triethylamine-borane adduct.15,16 This method may also be used for the preparation of other tetrahydroborates of alkali and alkaline earth metals. The triethylamine-borane adduct17 may be synthesized in a variety of ways, e.g., from triethylamine, sodium tetrahydro-borate(l —), and trichloroborane 18 from a trialkoxyborane, aluminum metal, and hydrogen in the presence of triethylamine 19 or by hydrogenation under pressure of a mixture of triethylborane and triethylamine.20 The triethylamine-borane adduct is a colorless liquid (mp — 2°). It is stable to air and moisture at room temperature and it is easily purified by vacuum distillation (bp 95-96°/12 torr). 

Both As(V) and As(III) may precipitate within soils and sediments, but the constituents inducing precipitation vary dramatically. Arsenate, similar to phosphate, tends to precipitate with hard multivalent cations such as aluminum and ferric iron under acidic conditions and calcium and magnesium under alkaline conditions arsenate may also replace 804 or, in particular, PO4 in minerals due to similar size and charge characteristics (Smedley and Kinniburgh, 2002). Various heavy metals (e.g., Mn, Cd, Pb) and alkali earth metals (Ca, Mg, Ba) also have... 

Like their neighbors sodium and potassium, magnesium and calcium are relatively abundant on Earth and in seawater and are essential for living organisms as cations in ionic compounds. Calcium is particularly important for growth and maintenance of bones and teeth. 

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