Divalent metal cations, extraction

ABSTRACT. The introduction of acetic acid units on p.t-butylealix [4] arene, in a controlled way, leads to a series of new lipophilic complexones (3,5,7) with different structures and properties. The tetraacid derivative (3) shows a cone structure and its alkali and ammonium salts are soluble in water whereas the other two ligands (5) and (7) show a "flattened cone" structure. All new ligands are able to extract divalent metal cations from water to methylene chloride. 

Another example of stereochemical control on cation complexation has been observed in calix[4]arene dicarboxylic acid derivatives 15-17 which were designed for the selective extraction of divalent metal cations. 

The 2-(AuC1)4 and 2-(PtCl2SMe2)4 complexes (see above), show extractability properties vs. alkali metal ions, with a greater affinity for than for other alkali metal ions [48]. No structural data were available and the nature of the binding in the formation of these complexes was not investigated. Similarly, the anionic complexes [2-Cu4(/t-Cl)4(/t3-Cl)] and [2-Ag4(/t-Cl)4(/t4-Cl)] have been shown to act as host for the selective binding of alkali metal cations and divalent metal ions like or Pb. Both complexes... 

Not all MIPS enzymes from thermophiles may have divalent metal ion-dependent activities. While crude protein extracts of A. fulgidus exhibited a MIPS activity that absolutely required divalent metal ions and was totally inhibited by 1 mM EDTA, the production of I-l-P from G-6-P (carried out >75 °C) by protein extracts from M. igneus and T. maritima was observed in the presence of 1 mM EDTA. This observation (Chen and Roberts, unpublished results) suggests that either the MIPS from these particular archaea is not divalent metal ion-dependent or that the metal ions bind very tightly and are not easily removed. None of the MIPS activities from thermophiles are affected by the addition ofNELt-1". Since the divalent cation in A. fulgidus MIPS has been suggested to aid in the aldol condensation and since this is supposedly done by NH4+ in the yeast enzyme, it is of interest how this step occurs in the other archaea and bacteria. 

For a cation-exchanging extractant HR, which extracts a divalent metal ion M2+ according to reaction (8.2-3), a chemical-reaction mode) of the phase equilibrium wonld be the mass-action equilibrium expression... 

Extraction equilibrium data are summarized in TABLE IV, together with the reported values of diameter and heat of hydration of alkali and alkaline earth metal cations. The ten-membered cyclic dimer extracted neither monovalent cations nor divalent cations above a detectable limit. On the contrary, the twenty-membered cyclic tetramer and the twenty -five-membered cyclic pentamer bound, more or less, monovalent and divalent cations, the latter showing somewhat higher Kg values than the former for any ions examined. No significant difference in ion extraction ability between racemic and optically active cyclic oligomers was observed. 

FIGU RE 5.7 Extraction of some divalent base metal cations and Fe(III) from chloride solution by Alamine 336 hydrochloride. (From Nicol, M. J. et al. 1987. In Comprehensive coordination chemistry, vol. 6, Oxford Pergamon. With permission.)... 

Ionophores, or polyether (PET) antibiotics, produced by various species of Streptomyces, possess broad spectrum anticoccidial activities. They are chemically characterized by several cyclic esters, a single terminal carboxylic acid group, and several hydroxyl groups. Representative members of this class include salinomycin (SAL), monensin (MON), lasalocid (LAS), narasin (NAR), maduramicin (MAD), and semduramicin (SEM). The main chemical properties of interest in the extraction methodology are their low polarities and instability under acidic conditions. They are able to form stable complexes with alkaline cations. All of these compounds, with the exception of LAS, bind monovalent cations (e.g., Na+ and K+). Lasalocid has a tendency to form dimers and can form complexes with divalent cations such as Mg2+ and Ca2+. The formation of metal complexes results in all of these compounds adopting a quasi-cyclic formation consequent to head-to-tail hydrogen bonding. No MRLs have yet been set by the EU for any of the carboxylic acid PETs (98). 

The influence of the dose was quite low (see Figure 8.8), and the efficiency of the solvent for the extraction of actinides (III, IV, and VI) and back-extraction of divalent cations was maintained up to 0.6-0.7 MGy. No precipitation was observed after contact of radiolyzed solutions with metallic ions. 

Mill (140, 141) isolated two exo-polygalacturonases from mycelial extracts of Aspergillus niger which diflFered in pH optima, stability, and activation by metal ions. Exopolygalacturonase I had a pH optimum of 4.5 and was fully active only in the presence of Hg ions. A ninefold increase in activity occurred in the presence of IfxM HgCb the Km was 6.2 X lO M. Dialysis against 2,3-dimercaptopropanol removed all activity in absence of Hg Various other divalent cations and chloride ion did... 

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