Alkaline earth cations, effect

The addition of various alkali and alkaline earth cations to the cyclooligomerization of ethylene oxide by Dale and Daasvatn also provides strong presumptive evidence for the template effect. Recently, Reinhoudt, de Jong and Tomassen utilized several metal fluorides to effect crown formations . The reaction rates were found to be in the order Cs > Rb > > Na LE. Such an order would be expected on the basis of binding... 

We have not attempted to cover all or even most aspects of crown chemistry and some may say that the inclusions are eclectic. We felt that anyone approaching the field would need an appreciation for the jargon currently abounding and for the so-called template effect since the latter has a considerable bearing on the synthetic methodology. We have, therefore, included brief discussions of these topics in the first two chapters. In chapters 3—8, we have tried to present an overview of the macrocyclic polyethers which have been prepared. We have taken a decidedly organic tack in this attempting to be comprehensive in our inclusion of alkali and alkaline earth cation binders rather than the compounds of use in transition metal chemistry. Nevertheless, many of the latter are included in concert with their overall importance. 

Chesniuk et al. studied the transfer of alkali and alkaline-earth cations across phospholipid monolayers at water-1,2-DCE macrointerfaces by cyclic voltammetry. These authors considered the effect of the cation nature, the concentration of the transferring ion, and the applied potential (at the positive end of the polarization window), and noticed either an enhancement of the current or a blocking of the transfer process [13,14]. The enhancement factors observed were very much larger than in other studies, especially at... 

Crown polyethers. Macrocyclic effects involving complexes of crown polyethers have been well-recognized. As for the all-sulfur donor systems, the study of the macrocyclic effect tends to be more straightforward for complexes of cyclic polyethers especially when simple alkali and alkaline earth cations are involved (Haymore, Lamb, Izatt Christensen, 1982). The advantages include (i) the cyclic polyethers are weak, uncharged bases and metal complexation is not pH dependent (ii) these ligands readily form complexes with the alkali and alkaline earth cations... 

CEC and fine silt and clay component (FC) have similar effects on rice s BAC. The competitive uptake of the alkaline-earth cations may result in a reduced heavy metal BAC for rice. Soils with higher percentage of fine silt and clay provided more CEC so that it has similar effect on the BAC. 

Diaza-18-crown-6 substituted with 5-chloro-8-hydroxyquinoline exhibits very interesting complexing properties. For instance, M-6 is very selective for Ba2+ over other alkaline earth cations and for K+ over Na+ in methanol. Unfortunately, investigation of fluorogenic effects with other cations has not been reported. On the other hand, the fluorescence intensity of M-7 was shown to increase by a factor of 1000 in the presence of Mg2+ (in a mixture of methanol/water 1 1 v/v) whereas other alkaline earth ions have no effect. 

Macropolycyclic ligands containing intramolecular cavities of a three-dimensional nature are referred to as cryptands. The bicyclic cryptands (73) exist in three conformations with respect to the terminal nitrogen atoms, exo-exo, endo-exo and endo-endo 6 these forms can rapidly interconvert via nitrogen inversion but only the endo-endo form has been found in the crystal structures of a variety of complexes372 and for the free ligand ([2.2.2], 73, m = n = / = l).449 In their complexes with alkali and alkaline earth cations, the cryptands exhibit an enhanced stability over the crown ethers and coronands dufe to the macrobicyclic, or cryptate, effect.33 202... 

The relative improvements (reference is particle removal without ozone) are quite variable, but were reported to be about 20-90 % lower turbidities and/or lower particle counts in the filtered water. The presence of dissolved organic matter is frequently essential and DOC should be at least 1 mg L The preozonation effects depend strongly on the presence of alkaline earth cations, especially calcium. 

The Adsorption of Alkaline Earth Cations to Phosphatidyl Choline Bilayer Membranes A Unique Effect of Calcium... 

A similar trend is observed for the alkaline earth cation complexes with 18C6, with Ba2+ (where the radius ratio is approximately one) forming the strongest complex. 6 We note that the alkaline earth complexes have a log K that is several times as large as for the corresponding alkali metal complexes. This difference is not surprising, since the alkaline earth cations have twice the electronic charge of the alkali metal cations. We will discuss this effect in more detail later. 

The ionophoric properties of ( )-37 with a variety of alkaline and alkaline-earth cations have been reported, and K+ ions were found to bind preferentially (effective complex-formation constant log KclT = 5.4 0.2) over the other alkali-metal ions [55],... 

The a-LTX pore is permeable to alkaline earth cations, whose affinities for the channel decrease in the following sequence Mg2+ > Ca2+ > Sr2+ > Ba2+ (Mironov et al. 1986). Transition metal cations (Cd2+ > Co2+ > Ni2+ > Zn2+ > Mn2+) strongly block Ca2+ and K+ currents through a-LTX channels in artificial membranes (Mironov et al. 1986). This block is only effective when the cation is applied from the cfs-side (equivalent to the extracellular side) of the membrane. 

The present review deals mainly with two examples of polyelectrolyte phase behavior as discussed above. As an example for an H-type precipitation, the solution properties of polyvinylpyridinium chains are monitored as function of added inert salt. Here, we focus on the determination of the effective charge density and of the solvent quality parameter which are supposed to play a central role for the understanding of polyelectrolyte solution without specific counterion interactions. The second system under investigation comprises the interaction of polyacrylic acid with alkaline earth cations which exhibit very specific interactions, thus representing an example for type L-precipitation. Here the coil dimensions close to the phase boundary are compared to those close to type H-precipitation with inert added salt. 

The observation of very pronounced inhibition of the sodium dodecyl sulfate-catalyzed hydrolysis of methyl orthobenzoate by inorganic cations is also consistent with the proposed mechanism for the micelle catalyzed reaction (Romsted et al., 1967 Dunlap and Cordes, 1968). For alkali-metal cations, the inhibition was found to increase with increasing ion size, i.e. ionic radius, but for alkaline-earth cations the inhibitory effectiveness was observed to be relatively independent of the ion. For... 

The simple idea involved in the electrostatic theory was very effective in predicting the catalytic activity of various cation-exchanged X and Y catalysts. However, it failed to explain quantitatively the difference in activity between cation-exchanged X and Y, alkaline earth cation X being less active than expected. It did not explain the cause for the similar behavior between cation-exchanged and decationized zeolites, and it did not offer satisfactory chemical evidence for the suggested reaction mechanism. 

The effect of addition of alkaline earth cations to Ga-Sil(26) is shown in Table 1. The addition of such kinds of divalent cations to Ga-Sil(26) did not improve the activity or the selectivity for aromatics formation. The introduction of alkaline earth cation could weaken the acidity of Ga-Sil. In the case of Ga-Sil, the addition of divalent cation including Cu cation would weaken the acidity too much for the aromatization. These results suggest that the addition of Cu cation could control the acidity of HZSM-5. 

This reaction is a well-known acid-catalyzed process 150), and it is apparent from the examples in Table XXVIII that the acidic faujasites are far superior to the alkali- or alkaline earth-cation forms as catalysts for this reaction. Fused alumina is also effective. 

When Ba, Sr, or Ca are substituted for La in La2Cu04, the Cu-0 distance steadily decreases. This happens despite the fact that Ba is much larger than La and thus causes a significant increase in the unit cell volume. It is apparently the inductive effect of the electropositive alkaline earth cation that causes increased covalency of Cu-0 bonds and therefore shorter Cu-0 bonds. (One could argue that A11 substitution causes decreased population of cr states and thus decreased Cu-0 distances. Although this is true, the net effect is still that all Cu-0 distances decrease.) The shorter Cu-0 bonds in turn results in increased Tc s. 

Atkinson G, Ennis M, Pearce FL. 1979. The effect of alkaline earth cations on the release of histamine from rat peritoneal mast cells treated with compound 48/80 and peptide 401. Br J Pharmacol 65 395-402. 

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