Calcium complexes crown ethers

Calcium-binding proteins, 6, 564, 572, 596 intestinal, 6, 576 structure, 6, 573 Calcium carbonate calcium deposition as, 6, 597 Calcium complexes acetylacetone, 2, 372 amides, 2,164 amino acids, 3, 33 arsine oxides, 3, 9 biology, 6, 549 bipyridyl, 3, 13 crown ethers, 3, 39 dimethylphthalate, 3, 16 enzyme stabilization, 6, 549 hydrates, 3, 7 ionophores, 3, 66 malonic acid, 2, 444 peptides, 3, 33 phosphines, 3, 9 phthalocyanines, 2,863 porphyrins, 2, 820 proteins, 2, 770 pyridine oxide, 3,9 Schiff bases, 3, 29 urea, 3, 9... 

Because of the particular properties of crown ethers and cryptands in forming complexes with alkali and alkaline earth elements, it is understandable that these elements have been exclusively Investigated in respect to isotopic separations. Among these elements the enrichment of heavy calcium isotopes for medical investi-... 

In all experiments an enrichment of the heavy isotope Ca is found in the aqueous phase. Within the limits of error, the experiments No. 1-5 (Table 6) show no dependence on the type of the isomer or on the concentration of the crown ether. The application of DjO instead of H2O also has no influence on the e-value. Experiments where dibenzo[18]crown-6 was used have shown the same trend of enrichment as was found with dicyclohexano[l8]crown-6. However, the measurements were not precise enough to calculate the e-values from this data. For the complete characterization of the discussed extraction systems, one has to know the dependence of the calcium complex distribution of the calcium concentration in the aqueous phase. This dependence is given in Table 7 for dicyclohexano[18]crown-6. 

Calcium, Sr, and Ba can be extracted as crown-ether complexes [10,11], which enable one to separate those elements [12,13]. Ca (and Sr) was also extracted with pyrazolone derivatives and with trioctylphosphine oxide (cyclohexane) [14]. Calcium can be extracted with Cryptand 2.2.2 using Erythrosin as the counter-anion [14a]. 

A very sensitive method for determining calcium is based on the complex of Ca with the chromogenic macrocyclic reagent (formula 14.4) (1,2-dichloroethane, e = 5.5-10 at 406 nm) [65]. Other diaza-crown ethers have been also used in determinations of Ca (and Mg) [66]. Calcium has been determined after extraction (CHCI3 + benzene) with the crown ether and association with Propyl Orange [67]. 

Photoisomerization of azobenzene moieties has been used also to trigger ion transport in photoresponsive membranes.161 A schematic representation of the photoinduced membrane transport of potassium ion is given in Table 2.10 . The bis(crown ether) (16) can form a 1 2 metal/crown ether complex with large metal ions which cannot be accommodated within simple crown ethers. This photoresponsive function of the azobenzene bis(crown ether) accelerates the transport of potassium and calcium cations across liquid membranes under photoirradiation. 

Calcium complexes amino acids, 33 arsine oxides, 9 bipyridyl, 13 crown ethers, 39 dimethylphthalate, 16 hydrates, 7, ionophores, 66 peptides, 33 phosphines, 9 pyridine oxide, 9 Schiff bases, 29 urea,9 Calixarenes... 

Table III Spectral characteristics, stability constants Kg and variation A in internal chemical shift of calcium complexes of 4-substituted phenylaza-15-crown-5 ethers in acetonitrile (Adapted from ref. 11)...

Fluorimetric methods have proven useful for the assay of metal ions in solution (i) for example, in vivo studies of calcium-selective fluorescence probes have been reported by Tsien (2). Most such analytical methods reported to date involve complexation of metal ions with aromatic heterocyclic ligands ("intrinsic" fluoroionophores). In 1977, Sousa described the synthesis of naphthalene-crown ether probes (Figure 1) in which the fluorophore 7C-system is insulated from the... 

Consider isocyanate trimerization as an example. This reaction in the presence of alkali and alkaline-earth metals was described in detail earlier. With crown-ether in contact with the concrete surface, it forms a crown-complex with the calcium cation of calcium oxide... 

More recent work has pressed towards even more selective sensors for calcium, stimulated by a 2 1 ligand calcium stoichiometry found by Petranek and Ryba (129) for a calcium crown ether which exhibited high calcium ion selectivity over magnesium. Thus, Shono and co-workers (130) have studied a bicyclic polyether amide derivative with enhanced selectivity for calcium, while Simon and co-workers (131) have reported a non-crown neutral carrier for calcium which forms a 3 1 ligand calcium complex with very high selectivity for calcium over sodium and potassium, that is, by factors of 10 and 10, respectively. This indicates that macrocyclic systems are not a prerequisite for high selectivity. 

Macrocyclic polyethers (or crown ethers) also possess attractive cation complexing abilities resulting in the formation of lipophilic species. Not surprisingly, such ionophores have been studied with respect to calcium sensors (32-34), and two examples are shown in Table 3.12. The macrobicyclic polyether-amide (7) provides a better calcium ISE than its monocyclic analogue (8). 

When PEO is intercalated from acetonitrile solutions into montmorillonite and hectorite (122,124-126), the resulting nanocomposites present characteristics that depend on the nature of the interlayer cation in a similar way to that observed for intercalation of crown ethers into smectites (44,46,49,127,128). Such behavior implies the existence of ion-dipole interactions between the oxygen atoms of the polymer and certain interlayer cations, as occurs for PEO-salt complexes (129). The fact that the synthesis is carried out in nonaqueous solutions determines that the polymer may replace the hydration shell usually accompanying the interlayer cations, as shown by IR spectroscopy (124). The effectiveness of such a process is related to the hydration energy of the cation. When this energy is high (calcium... 

In these electrodes, the active material is a large organic molecule capable of interacting specifically with an anion or cation. Typical of these materials are the phosphate diesters (R0)2P02, used for calcium ion electrodes, metal complexes used for anion electrodes and the neutral macrocyclic crown ethers which are suitable for alkali-electrodes. The active organic molecule is adsorbed onto an inert porous support or dissolved in an organic solvent, and indeed their selectivity can be aflected by the choice of medium. Some typical electrodes are shown in Table 12.4. 

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