Transport across liquid membranes

Lazarova Z and Boyadzhiev L. Kinetic aspects of copper(II) transport across liquid membrane containing LIX-860 as a carrier. J Mem Sci, 1993 78(3) 239-245. 

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. 

A. Pannggio, "An Investigation of Some Factors Connolling Solute Transport Across Liquid Membranes. Fb.D. Thesis, University of Rhode Island, Kingston, 1982. 

Oxidation of receptor 1 was found to decrease its binding affinity for alkali metal cations, due to electrostatic repulsion between 1 and the cation. Thus, the ferrocene unit not only enables redox sensing of alkali metal cations, but also allows the host guest interaction to be switched on and off depending on the oxidation state of the receptor. Saji has also demonstrated that this phenomenon can be used in electrochemical ion transport across liquid membranes. ... 

Due to their pronounced selectivity in metal ion ccmplexation (6), crown ethers (macrocyclic polyethers) and related macrocyclic multidentate ligands are attractive mobile carriers for metal ion transport across liquid membranes. As summarized in recent reviews of macrocycle-facil itated transport of ions in liquid membrane systems (7,8), most studies have been conducted with macrocyclic carriers which do not possess ionizable groups. For such carriers, metal ions can only be transported down their concentration gradients unless some type of auxiliary complexing agent is present in the receiving aqueous phase. 

Becauce of their biological relevance, most of the work published in this field refers to the recognition, and the elosely related problem of transport across liquid membranes. of the zwitterionic form of amino acids, which is the most abundant form in solution at pH values around neutrality (see Eq. 1 below). 

The chelation of small molecules described above may be extended to metal ions. The convergence of the carboxyls within the molecular clefts provides a microenvironment ideal for divalent metals. A special structural feature of the new ligands involves stereoelectronic effects at carboxyl oxygen. Classical chelates such as EDTA present the less anti lone pairs to the metal ion, but the new structures offer the more basic syn lone pairs. Metals such as Ca and Mg are tightly bound and readily transported across liquid membranes (Scheme 6). In addition, the mode of binding within the new ligands is exclusively trans, a feature which is likely to lead to altered reactivity of the bound metal ions as catalysts. 

U-tube An apparatus to measure transport across liquid membranes consisting of a U-shaped tube containing a heavy membrane solvent with lighter source and receiving-phase solvents in the arms of the U. 

New Multidentate ligand Carriers for Macroqrcle-Facilitated Metal Ion Transport Across Liquid Membranes... 

Several types of acyclic amides have been synthesized and evaluated as carriers for metal ion transport across liquid membranes. The abilities of oligoamides containing 8-quinolyl groups to transport heavy metal ions, such as copper(II), mercury(n), silver(I), etc., across bulk chloroform membranes are assessed. Among the different types of amides, malonamide and glutaramide derivatives are found to exhibit high selectivity for copper(II) transport and different methionine derivatives for mercury(II) and for silver(I) transport. The relationship between the structure of the ionophore and its transport behavior is discussed. 

On the other way, to obtain higher selectivity and efficiency of metal ions removal in ion exchange processes those macrocycles are polimerized. In this way macrocycles obtained are more hydrophobic. They can be used as ion carriers for separation of metal ions from dilute aqueous solutions, especially in transport across plasticizer and liquid membranes [4]. For example, calixcrown oligomers used as ion carriers in the transport across liquid membranes exhibit the high selectivity for alkali metal cations. Also the application of crown ethers and calixarenes as the liquid membrane carriers is presented. The structures of monomers and polymers determines recognition and selectivity for metal ions. 

The well known complexing properties of macrocyclic compounds towards metal ions have led to their incorporation into polymeric matrices. Polymer-supported crown ethers have many advantages, such as easy handling and recoverability when used for the removal of the toxic metal ions from the environment. Crown ether-, calixarene-, calixcrown- and cyclodextrin- based polymers have been recently receiving attention as the new polymers and may be processed into materials suitable as the extractant (solvent extraction), collector (ion flotation) or the ion carrier (transport across liquid membranes or ion selective electrodes). 

Light-driven membrane transport. Cations may be transported through liquid membranes using crown ethers. For example, a typical system is of the type water-phase(I)/organic-phase/water-phase(II). The metal ion is added to water-phase(I) and the crown ether to the organic phase (to yield the liquid membrane). The crown acts as carrier for metal ions from water-phase(I) across the liquid membrane phase into water-phase(II). There have now been a very large number of studies of this type reported and a fuller discussion of this topic is given in Chapter 9. 

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

Pervaporation is a membrane separation process in which a dense, non-porous membrane separates a liquid feed solution from a vapour permeate (Fig. 19.2c). The transport across the membrane barrier is therefore based, generally, on a solution-difliision mechanism with an intense solute-membrane interaction. It... 

Evans, D. F., Cussler, E. L. Selective Transport of Ions across Liquid Membranes, in 14). 

Some fundamentals of micelle formation and of the solubilization of water-insoluble substances by micelles are reviewed. The accelerating effect of micellization upon the rate of dissolution and of transport of solubilizate through bulk liquid is then considered. Membranes present an obstacle to transport. A larger fraction of the total driving force can be brought to bear upon this obstacle as other resistances are reduced by solubilization. Hence, transport across a membrane will, in general, be accelerated whether micelles are effective within the membrane or not. It is now possible to determine also this contribution of micelles to the transport within the membrane. In a specific case it was found to be negligible. 

Membrane. In discussing transport across a membrane, we consider only the case where the pressures on both sides of the membrane are substantially the same so that no liquid is being pressed across it and there is no transport by convection. Diffusion is then the only mechanism... 

A membrane can essentially be defined as a barrier that separates two phases and selectively restricts the transport of various chemicals. It can be homogenous or heterogeneous, symmetric or asymmetric in structure, solid or liquid, and can carry a positive or negative charge, or be neutral or bipolar. Transport across a membrane can take place by convection or by diffusion of individual molecules, or it can be induced by an electric field or concentration, pressure or temperature gradient. The membrane thickness can vary from as little as 100 p.m to several millimeters. 

Pietraszkiewicz M, Kozbial M, and Pietraszkiewicz O. Transport studies of inorganic and organic cations across liquid membranes containing Mannich-base calix[4]resorcinarenes. Pol J Chem, 1998 72(5) 886-892. 

This chapter deals with the transport of actinide ions across liquid membranes resulting in their recovery/separation from complex matrices. The transport behavior of lanthanides is also discussed in many places, which has chemical similarity with the trivalent actinides and are often used as their homologs. The transport behavior of actinides/lanthanides across other membranes such as ceramic/metallic and grafted membranes is also included. Table 31.1 gives a summary of the extractants discussed in this chapter. 

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. 

In these devices polymer materials containing specific ingredients constitute the backbone of the film covering the electrochemical transducer. Here we deal with a liquid membrane, because the organic solvent provides the medium in which the ions permeate across the membrane. The polymer membrane ion-selective electrodes (ISE) and their ion transport across the membrane function similarly as the ion transport across the membranes of living cells (Figure 8.29). We follow the presentation given by Widmer (1993). 

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. 

Christensen JJ, Lamb LD, Izatt SR, Starr SE, Weed GC, Astin MS, Stitt BD, Izatt RM, Effect of anion type on rate of facihtated transport of cations across liquid membranes via neutral macrocychc carriers. J. Am. Chem. Soc. 1978 100, 3219-3220. 

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