Transport of alkali metal cations

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... 

There are two general classes of naturally-occurring antibiotics which influence the transport of alkali metal cations through natural and artificial membranes. The first category contains neutral macrocyclic species which usually bind potassium selectively over sodium. The second (non-cyclic) group contains monobasic acid functions which help render the alkaline metal complexes insoluble in water but soluble in non-polar solvents (Lauger, 1972 Painter Pressman, 1982). The present discussion will be restricted to (cyclic) examples from the first class. 

Scheme 2 Transport of alkali metal cations across liquid membranes using [1] as a...

Matsushima, K., Kobayashi, H., Nakatsuji, Y., Okahara, M., Rroton driven active-transport of alkali-metal cations by using alkyl monoaza crown ether derivatives, Chem. Lett., 701-704, 1983. 

In the late 1980s, efforts initiated by Fyles in Canada (Carmichael el al., 1989) and by our own group (Nakano et al., 1990) resulted in two different channel models, both of which incorporated crown ethers. Both of these efforts resulted in channels that show significant transport of alkali metal cations through phospholipid bilayers. Both groups (Gokel and Murillo, 1996) have undertaken extensive stmctme-activity studies to characterize their function. 

Strezelbicki, J. and Bartsch, R.A., Transport of alkali metal cations across liquid membranes by crown ether carboxylic acids. J. Membr. ScL, 1982, 10 35 7. 

Fyles et al.39 described their results concerning the transport of alkali metal cations across vesicle bilayers mediated by these ion channels mimics. The relative activities of their most active transports were comparable to valinomycin but were 2- to 20-fold less active than gramicidin. Six examples in their modular series effectively acted as channels four in this series acted as cation carriers. The range of observed transport activities, selectivities, and mechanism indicates that structural regulation of synthetic ion channel mimics is possible with this family of bolaphiles.38... 

Bartsch, R.A. Charewicz, W.A. Kang, S.I. Walkowiak, W. Proton-coupled transport of alkali metal cations across liquid membranes by ionizable crown ethers. In Liquid Membranes Theory and Applications Noble, R.D., Way, J.D., Eds. ACS Symp. Ser. No. 347 American Chemical Society Washington, D.C., 1987 86-97. 

Tlie aim of this chapter is to provide an overview of materials where fast transport of alkali metal cations and protons is observed. A general discussion of factors affecting conductivity and techniques used to study ion migration paths is followed by a review of the large number of cation conductors. Materials with large alkali ions (Na-Cs) are often isostructural and therefore examined as a group. Tire lithium conductors with unique crystal structure types and proton conductors with unique conduction mechanisms are also discussed. 

Table 3. Transport of alkali metal cations by crownophane-dodecanoic acid cooperative carriers ...

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. 

Proton-Coupled Transport of Alkali Metal Cations Across Liquid Membranes by lonizable Crown Ethers... 

Figure 4. Transport of Alkali Metal Cations Across a Bulk Chloroform Membrane (a = single species transport, b = competitive transport). (Adapted with permission from Ref. 9. Copyright 1982 Elsevier.)...

Figure 8. Influence of Polyether Ring Size Upon Competitive Transport of Alkali Metal Cations Across a Liquid Surfactant Membrane by (a) (b) 2, and (c) 3. (Adapted with permission...

Bulk liquid membranes, transport of alkali metal cations, 89-92... 

Table 1. Membrane Transport of Alkali Metal Cations ...

Figure 24 Amounts of metal cations (mol x lO ) transported into the receiving phase versus time (h) for competitive BLM transport of alkali metal cations (0.20 M in each) by 0.010 M 2 in (a) chloroform, (b) dichloromethane, (c) carbon tetrachloride, (d) 1,2-dichloroethane, (e) 1,1,1-trichloroethane, and (f) o-dichlorobenzene. (Reproduced from Ref. 87. Elsevier, 2005.)...

Reusch and Cussler were the first to describe crown ether-mediated transport of alkali metal cations through supported liquid membranes as ion pairs and derived for the initial flux Equation 11. 

The model has been verified experimentally for the transport of alkali metal cations (27) mediated by valinomycin (1), dibenzo-18-crown-6 (2) and calix[4]crown-5 derivative 3 and calix[4]arene tetraester derivative 4 (Chart 1). D , and for the transport of guanidinium ion (22, 23) mediated by calix[6]arene derivatives have been obtained as well. 

Parameters that Affect Diffusion-Limited Transport. Brown et aL varied the length of the alkyl chain of alkyl o-nitrophenyl ether membrane solvents and examined its influence on the proton-coupled transport of alkali metal cations by a crown ether derivative. By comparison of solvent characteristics, such as the dielectric constant, viscosity, and surface tension, they concluded that hexyl o-nitrophenyl ether is a better membrane solvent than NPOE (43), The effect of the solvent on the transport of NaC104 by carrier 4 has been studied by Visser et al (44), Transport parameters and were determined. A series of octyl phenyl ethers containing an electron withdrawing group (NO2, CN) of various positions on the phenyl ring were used. Data are presented in Table 5. 

Facilitated Transport of Alkali Metal Cations Through Supported Liquid Membranes with Fatty Acids... 

Bulk Liquid Membranes (BLM). This is the simplest type of liquid membrane (2-8) and is utilized for fundamental studies of certain aspects of liquid membrane transport processes. In one such process, a beaker-in-a-beaker cell (Figure 1) consists of inner and outer compartments which contain the aqueous feed (F) and strip (S) solutions, respectively. The inner beaker contains the stripping solution and is surroimded by the feed solution. Both aqueous solutions contact the upper organic layer, which is the liquid membrane. Mass transfer takes place from the feed solution through the liquid membrane and into the strip solution. Bartsch et aL studied the transport of alkali metal cations across bulk liquid membranes in which a crown ether carboxylic acid in the organic layer served as the carrier (2,3). 

Measurements were made of the relative rate of the transport of alkali metal cations through a chloroform liquid membrane containing crown ether with the structural formula [338]... 

Cagnoni et al. synthesized cyclopolymers of crown ethers containing of 5 and 7 oxygen atoms (Fig. 9) and used them as ion carriers in transport of alkali metal cations across liquid membranes [7]. The monomers were subjected to free radical polymerization, either thermally or photochemically induced. 

From the comparison of the relative transport rates for monomer and corresponding polymer, it is evident that there are differences between them. In the case of the monomer of 9a, transport rates are higher for sodium cation, but in the case of the corresponding polymer (9a) this selectivity is shifting towards potassium cation. The crown ether (as the monomer) related with 9b polymer was selective for K, while its polymer did not show any selectivity in transport of alkali metal cations. 

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