Alkali metal transport

Catoptromers —. see Enantiomers Cell division calcium, 6.595 Cell membranes alkali metal transport, 3, 54 Cells labelled... 

Alkali metal transport in biochemistry is a vital process in maintenance of cell membrane potentials of use, for example, in nerve signal transduction and is at the core of some of the early work on artificial ionophores that mimic natural ion carriers such as valinomycin. Ionophore mediated ion transport is much slower than transport through cation and anion ion channel proteins, however. 

Kirch and Lehn have studied selective alkali metal transport through a liquid membrane using [2.2.2], [3.2.2], [3.3.3], and [2.2.C8] (146, 150). Various cryptated alkali metal picrates were transported from an in to an out aqueous phase through a bulk liquid chloroform membrane. While carrier cation pairs which form very stable complexes display efficient extraction of the salt into the organic phase, the relative rates of cation transport were not proportional to extraction efficiency and complex stability (in contrast to antibiotic-mediated transport across a bulk liquid membrane). Thus it is [2.2.Ca] which functions as a specific potassium ion carrier, while [2.2.2] is a specific potassium ion receptor (Table VI). 

The idea of developing a zwitterionic liquid (ZIL) for alkali metal transport has led to the consideration of a new cation conductive material. As shown in Chapter 20, an increase in cation conduction occurs when LiTFSI is added to ZILs. An equimolar mixture of ZIL and LiTFSI may give us a new model, namely on imidazolium cation containing two tethered anions. This novel system, called triple ion-type imidazolium salt, consists of three charges. Scheme 21.3 shows the structure of such triple ion-type imidazolium salts. These salts are prepared by the reaction of an imidazole analogue with an alkane sultone (see Chapter 20). Besides the imidazolium cation having two tethered sulfonate anions, this salt has a target carrier cation... 

Other approaches to self-assembling receptors have been reported in recent years. A self-assembling, trimeric palladium complex based on the bis(benzimidazole) ligand (17) was designed by Williams and coworkers [4]. The complex contains a hydrophobic cavity that in the X-ray structure has included a molecule of acetonitrile. In a different context, Schepartz and McDevitt [70] have used the chelation of nickel(n) by A,7V -bis(salicylaldehy-de)ethylenediamine (salen) derivatives to control the position of K -binding glyme chains, and it has been shown that these self-assembled ionophores influence alkali metal transport across liquid membranes [71]. Also, Shinkai and coworkers [72] and Schneider and Ruf [73] have used metal chelation to induce an allosteric effect on binding at a second site. 

Carrier Chemistry. The use of structurally modified macrocycllc polyethers (crown ethers) as CcU rlers In bulk, emulsion, and Immobilized liquid membranes Is the subject of the chapter by Bartsch et al. (111). They discuss the use of lonlzable crown ethers for the coupled transport of alkali metal cations. The lonlzable carboxylic and phosphonlc acid groups on the macrocycles eliminate the need for an anion to accompany the catlon-macrocycle complex across the liquid membrcuie or for an auxiliary complexlng agent In the receiving phase. The influence of carrier structure on the selectivity and performance of competitive alkali metal transport across several kinds of liquid membranes Is presented. 

Crown ether carboxylic acids and alkyl esters are novel reagents port of alkali metal cations membranes. Metal Ion transport transport of protons. The in variation within the ionizabl molecule upon the selectivity petitive alkali metal transport liquid surfactant (emulsion) liquid membranes is assessed. 

In the present paper, we examine the influence of structural variation within series of crown ether carboxylic acid and crown ether phosphonic acid monoalkyl ester carriers upon the selectivity and efficiency of alkali metal transport across three types of liquid organic membranes. Structural variations within the carriers include the polyether ring size, the lipophilic group attachment site and the basicity of ethereal oxygens. The three membrane types are bulk liquid membranes, liquid surfactant (emulsion) membranes and polymer-supported liquid membranes. 

The results provided above demonstrate that considerable selectivity can be achieved in alkali metal transport across bulk chloroform membranes by appropriately-structured ionizable crown ether carrier molecules. Although such bulk liquid membrane... 

Figure 10. Competitive Alkali Metal Transport Across a Polymer-supported Liquid Membrane by an Analog of 5.

Roland W. Oshe, ed.. Handbook of Thermodynamic and Transport Properties of Alkali Metals, lUPAC, Blackwell Scientific Publications, Oxford, U.K., 1985. 

Chemical Reactivity - Reactivity with Water No reaction Reactivity with Common Materials May attack some forms of plastics Stability During Transport Stable Neutralizing Agents for Acids and Caustics Not pertinent,- Polymerization Hazardous polymerization unlikely to occur except when in contact with alkali metals or metallo-organic compounds Inhibitor of Polymerization 10 -20 ppm tert-butylcatechol. 

In mimicking this type of function, noncyclic artificial carboxylic ionophores having two terminal groups of hydroxyl and carboxylic acid moieties were synthesized and the selective transport of alkali metal cations were examined by Yamazaki et al. 9 10). Noncyclic polyethers take on a pseudo-cyclic structure when coordinating cations and so it is possible to achieve the desired selectivity for specific cations by adjusting the length of the polyether chain 2). However, they were not able to observe any relationship between the selectivity and the structure of the host molecules in an active transport system using ionophores 1-3 10). (Table 1)... 

By considering the stability constant and the lipophilicity of host molecules, Fyles et al. synthesized a series of carboxylic ionophores having a crown ether moiety and energetically developed the active transport of alkali metal cations 27-32). Ionophores 19-21 possess appropriate stability constants for K+ and show effective K+-selective transports (Fig. 5). Although all of the corresponding [15]crown-5 derivatives (22-24) selectively transport Na+, their transport rates are rather slow compared with... 

On the other hand, Bartsch et al. have studied cation transports using crown ether carboxylic acids, which are ascertained to be effective and selective extractants for alkali metal and alkaline earth metal cations 33-42>. In a proton-driven passive transport system (HC1) using a chloroform liquid membrane, ionophore 31 selectively transports Li+, whereas 32-36 and 37 are effective for selective transport of Na+ and K+, respectively, corresponding to the compatible sizes of the ring cavity and the cation. By increasing the lipophilicity from 33 to 36, the transport rate is gradually... 

Table 6. Maximum molar ratios of transported alkali metal ions to crown ether carrier for several separation techniques...

Fig. 6. Proton-driven transport of alkali metal ions through a membrane formed from 12-crown-4 polymer (43 n = 1) (crown ether content of about 30%). M+], and (M+fc refer to metal ion concentrations at time - i and 0, respectively. (Cited from Ref.471)...

A certain crown ether having additional coordination sites for a trasition metal cation (71) changes the transport property for alkali metal cations when it complexes with the transition metal cation 76) (Fig. 13). The fact that a carrier can be developed which has a reversible complexation property for a transition metal cation strongly suggests that this type of ionophore can be applied to the active transport system. 

Alkali metal ion transport and biochemical activity. P. B. Chock and E. Titus, Prog. Inorg. Chem., 1973,18, 287-382 (450). 

The T dependence of the solubility of CsH in Cs differs significantly from those for solutions of the hydrides in the other alkali metals. Distillation leaves behind involatile impurity salts, but oxygen transport from distilland to receiver has been observed. Oxygen can be carried over with the distillate in the form of COj or CO, the former being produced by decomposition of carbonate and the latter by reduction of oxides with a carbon impurity under dry conditions near the end of distillation. The identification of CO among the noncondensable gases during the distillation of Cs lends support to this. ... 

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