Membrane transport systems. V. Coupled countertransport of alkaline earth cations and protons

Dulyea, Lynn M.; Fyles, Thomas M.; Whitfield, Dennis M.

doi:10.1139/v84-083

Cited by 51 publications

(35 citation statements)

References 25 publications

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“…Infrared spectra of various carriers at concentrations up to lo-' M failed to indicate any dimerization (2650 cm-', 920 cm-' dimer bands) (24,25). This result is consistent with kinetic studies (8,10) where the rate is a first order process in carrier; higher nonintegral orders would be expected for aggregrated species.…”

Section: Degree Of Aggregrationsupporting

confidence: 85%

“…Together with the differences in ligand, solvent, conditions, and method, these results are reconciled with previous observations. T o place the potentiometric results in the context of bulk membrane transport experiments (7,10) it is essential to note that, even in relatively polar media (methanol-water), electrostatic effects dominate metal ion complexation. In the less polar membrane solvent chloroform, the electrostatic effects will be even more pronounced; hence a very close association between cations and the carrier carboxylate is highly likely.…”

Section: Complex Formation In Methanol/water Solutionmentioning

confidence: 99%

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Membrane transport systems. VI. Complexation of cations by lipophilic crown ether carboxylic acids

Fyles¹,

Whitfield²

1984

Can. J. Chem.

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. J. Chem. 62, 507 (1984).The complexation of alkali metal and alkaline earth cations by crown ether carboxylic acids has been studied by potentiometric titration and by infrared and nuclear magnetic resonance spectroscopy. Complexation in methanol-water solution is governed by the electrostatic interactions between the cation and the carboxylate, hence discrimination among cations on the basis of ionic radius is poor. The isomers syrz and anti (8NH)218-6A2 exhibit differing complexation behaviour towards cations with the anti isomer giving the stronger complexes. Interaction between the carboxylates across the face of the macrocycle of syn (8NH)?18-6Az can be inferred from the potentiometric data. Combined infrared and nuclear magnetic resonance studies of the complexes in chloroform solution show that the cation is held as an asymmetric tight ion pair with the carboxylate. The dimeric salt (4NH18-6)>Ca exhibits both a tight and a symmetric or loose ion pair between the cation and the two carboxylates. The substituents on the macrocycle are pseudoaxially disposed and in some cases gauche ethylenedioxy units can be recognized from the spectra. The complexes are monomeric in solution and in most cases the conformations are unaffected by small amounts of water in the chloroform solution. The discovery of the complexing properties of synthetic macrocyclic polyethers (crown ethers) has sparked a wide range of activity in fields ranging from synthesis of related compounds to analytical applications (1-3). An important property of crown ethers is their ability to dissolve ionic solids in nonpolar media leading to solutions of "naked anions" for synthetic applications (1, 2) to phase transfer catalysis (4) and to cation extraction and membrane transport across artificial membranes (5). The structures of the ligands and their complexes in the solid state and in solutions have been the subject of numerous studies (1,2). In a "typical" complex the metal ion occupies a site in the center of the macrocycle with ligating donor atoms from the ring providing a full or partial inner coordination sphere for the ion. The exterior of the complex is lipophilic to provide for dissolution in the nonpolar solvent.Our interest in crown ethers centers on a series of lipophilic crown ether carboxylic acids (6-10) which are capable of mediating cation-proton coupled countertransport (1 1). Representative structures of the carriers examined to date are shown below together with a line notation (10) indicating structural features. A simple schematic mechanism for the net countertransport of monocations and protons is given in Fig. 1. At the basic interface, the carrier gives up a proton in exchange for a cation from the aqueous phase. The resultant complex is neutral and readily traverses the membrane phase to the acidic interface, whereupon the reverse ion exchange process occurs. The net result is the exchange of a cation for a proton across the membrane barrier. As long as the proton gradient exceeds the cation gradient the system will "...

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Section: Degree Of Aggregrationsupporting

confidence: 85%

Section: Complex Formation In Methanol/water Solutionmentioning

confidence: 99%

Membrane transport systems. VI. Complexation of cations by lipophilic crown ether carboxylic acids

Fyles¹,

Whitfield²

1984

Can. J. Chem.

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“…As written, reaction [6] is not an elementary process but results in convenient cancellations (below).…”

Section: Resultsmentioning

confidence: 99%

“…A recent report summarized the predictions of a simple diffusion model and concluded that the narrow range of reported rates was consistent with a diffusion mechanism (4). Our interest in this area has centred on crown ether carboxylic acids which can exhibit cation-proton countertransport across artificial membranes (5,6). This system has been examined in detail and it is clear that under the usual conditions of stirring the transport is not controlled by diffusion (5)(6)(7).…”

mentioning

confidence: 99%

“…Our interest in this area has centred on crown ether carboxylic acids which can exhibit cation-proton countertransport across artificial membranes (5,6). This system has been examined in detail and it is clear that under the usual conditions of stirring the transport is not controlled by diffusion (5)(6)(7). We have identified the rate-limiting processes as adsorption and desorption of the carrier at the interface and have shown, as one.consequence, how the transport selectivity depends on the interfacial surface charge (8).…”

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Extraction and transport of alkali metal salts by crown ethers and cryptands: estimation of extraction constants and their relationship to transport flux

Fyles¹

1987

Can. J. Chem.

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THOMAS MURRAY FYLES. Can. J. Chem. 65, 884 (1987).A method is described for the estimation of two phase extraction constants from stability constants for complexation of alkali metal cations by crown ethers and cryptands. The total free energy change for extraction of alkali metal salts from water to a non-polar organic solvent is evaluated as a sum of free energy terms for complexation, transfers of cation, anion, and complex between solvents, and ion pairing in the non-polar solvent. The method gives satisfactory agreement with a variety of published extraction constants and can be used predictively. As an example, the influence of extraction constant on transport flux was examined using calculated extraction constants and the rate data of Lamb et al. (J. Am. Chem. Soc. 102,6820 (1980)); rates are adequately modelled by a simple analysis of diffusion.THOMAS MURRAY FYLES. Can. J. Chem. 65, 884 (1987). The transport of cations across artificial membranes using synthetic ionophores such as crown ethers or cryptands has received considerable attention over the past decade (1, 2). The focus of such studies varies from the assessment of the complexation selectivity of new ligands to the development of specific separation processes (1-3). The actual mechanism of the transport has received somewhat less attention but it is widely assumed that the transport is controlled by diffusion processes in the unstirred boundary layers adjacent to the organiclwater interfaces. A recent report summarized the predictions of a simple diffusion model and concluded that the narrow range of reported rates was consistent with a diffusion mechanism (4). Our interest in this area has centred on crown ether carboxylic acids which can exhibit cation-proton countertransport across artificial membranes (5, 6). This system has been examined in detail and it is clear that under the usual conditions of stirring the transport is not controlled by diffusion (5-7). We have identified the rate-limiting processes as adsorption and desorption of the carrier at the interface and have shown, as one.consequence, how the transport selectivity depends on the interfacial surface charge (8).In search of other systems which might be controlled by interfacial processes, we set out to compare the literature data with the predictions of the simple diffusion model (4). This search is immediately hampered by the paucity of data on two phase extraction constants. The use of extractions, particularly of metal picrates, to assess cation binding and selectivity has a long tradition in crown ether chemistry (9-1 1). However, such tests are often used qualitatively (% extraction) and, moreover,

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Extraction, Liquid–Liquid

Lo¹,

Baird²

2000

Kirk-Othmer Encyclopedia of Chemical Technology

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Liquid‐liquid extraction, also known as solvent extracting, is a well‐established separation technique that depend on the unequal distribution of a solute between two immiscible liquids. The initial feed liquid containing the solute is brought into contact with a solvent which is selected to have a greater affinity for the solute. The partition of the solute can be enhanced by adding a chemical extractant to the solvent; this practice is widespread in the hydrometallurgical and nuclear industries. Most industrial extractors operate continuously with countercurrent flow of the two phases. In mixer‐settlers, the phases are contacted as a well‐agitated dispersion of drops, which are then sent to settling tanks for phase disengagement. In extraction columns, the dispersed drops move countercurrently against the flow of the second (continuous) phase. The physics, chemistry, and practice of extraction, with brief descriptions of important industrial extraction processes and equipment, are presented. Research on hydrodynamic aspects of process design such as axial mixing, drop dispersion, and coalescence is reviewed. New extraction techniques such as membrane extraction, supercritical exctraction, and two‐phase aqueous extraction are discussed.

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Membrane transport systems. V. Coupled countertransport of alkaline earth cations and protons

Cited by 51 publications

References 25 publications

Membrane transport systems. VI. Complexation of cations by lipophilic crown ether carboxylic acids

Membrane transport systems. VI. Complexation of cations by lipophilic crown ether carboxylic acids

Extraction and transport of alkali metal salts by crown ethers and cryptands: estimation of extraction constants and their relationship to transport flux

Extraction, Liquid–Liquid

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