Permeability metal cations

For the alkali metal cations, the stability (14) and permeability (43) sequences for dicyclohexyl-18-crown-6 have been found to be the same (K+ > Rb+ > Cs+ > Na+ > Li+). Thus, a direct relationship exists between the ability of a macrocyclic compound to complex a particular cation (as measured by the log K value for complex formation) and its influence on the biological transport of that cation. Furthermore, it would appear that the biological ion-transport mechanism may in part be due to the complexation properties of the macrocyclic carrier molecules. This subject with respect to cyclic antibiotics has been treated extensively by Si wow and co-workers (2). 

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. 

Y. Teraoka, T. Nobunaga, K. Okamoto, N. Miura and N. Yamazoe, Influence of constituent metal cations in substituted LaCoOs on mixed conductivity and oxygen permeability. Solid State Ionics, 48 (1991) 207-212. 

Hille B (1972) The permeability of the sodium channel to metal cations in myelinated nerve. J Gen Physiol 59 637-658... 

Ion-selective membranes attain their permselectivity from ion-exchange, dissolution, or complexation phenomena. Different types of membranes are available for the construction of ion-selective electrodes glass and other solid state rods (crystals), liquid or polymer ion ecchangers, or dissolved ionophores. Many electrodes are commercially available with selec-tivities for different ions, mainly H, alkali metal cations, heavy metal ions, and halides or pseudohalides. Also gas-sensing electrodes may be constructed from an ion-selective electrode and a gas-permeable membrane [182]. Ion selective electrodes and gas-selective electrodes... 

The silicate anion, in all its many forms, has specific properties which make it a valuable component in the various enhanced recovery processes. Among these properties are its ability to sequester multi-valent metal cations to act as a sacrificial agent in the adsorption process by clays to maintain water-wettability to reduce permeability in high permeability areas to improve sweep and to aid in reducing IFT at the oil/water interface. Each of these properties depends on the size, charge, and basicity of the silicate molecule, which can be varied by changing ratio and concentration. 

Issues Regarding Metal Cation Transport in Hydrogen-permeable Membrane Materials... 

Let us formulate the conditions for thermodynamic equUibrium at the metal -solution interface. To this end, consider a solution of the Me + type, where Me + denotes ions of metal (cations) with charge z+ and denotes ions of the solution (anions) with charge z. The metal-solution interface is impermeable for X and permeable for Me +. On the cathode interface, the incoming Me + ions lose their charge, thansforming back into atoms. At the anode interface, the transition of Me + ions from the lattice into the solution takes place. By analogy with (7.2), one can write the last reaction as... 

Y. Wu and N. A. Mummallah, Microbiocidal Anionic Sequesterants with Polyvalent Metal Cations for Permeability Correction Process, United States Patent 4,552,217, Nov. 12 (1985). 

In spite of being permeable to oxygen and water, paints can protect metals by the barrier effect provided they are impermeable to anions and gaseous pollutants. Atmospheric corrosion is an electrochemical phenomenon (Chapter 8) and requires the presence of an electrolyte at the metal surface. If no anions arrive there, no electrolyte can be formed with the dissolving metal cations and no corrosion takes place. 

At BAM, from 1987 to 1997, investigations were carried out into permeation of metal salts, metal cations and nitrate anion, through HDPE geomembranes (Muller et al. 1997a). At this time no indication was found by the measurements for any permeation and a comparison of test and control experiment with pure water. From the test times and test conditions an upper limit can be estimated for the permeation rate. For example the permeability for cadmium is estimated to be less than 1.310 mVs. R. K. Rowe and collaborators (Rowe et al. 1995b) report on similar experiments about chloride permeation through an HDPE geomembrane. An upper limit could be specified for the permeability as 3-lO m /s from their test conditions. 

Teraoka Y, Nobunaga T, Okamoto K, Miura N, Yamazoe N, Influence of Constituent Metal Cations in Substituted LaCoOs on Mixed Conductivity And Oxygen Permeability, Solid State Ionics, 4S, 207-212(1991). 

The ability of toxic metals to increase membrane permeability to cations, and in particular to K, is well established (Rothstein 1970) however, it is not known whether these cation-selective pathways also function to transport the toxic metals across the membrane. Changes in cation permeability appear to be the result of an interaction of toxic metals with sulfhydryl groups of membrane proteins that modulate cation permeability (Ballatori et al. 1988 Jungwirth et al. 1991a,b Kone et al. 1988, 1990). These proteins have not yet been identified. 

A third major class of physical separation is molecular separation, which is often based on membrane processes in which dissolved contaminants or solvents pass through a size-selective membrane under pressure. The products are a relatively pure solvent phase (usually water) and a concentrate rich in the solute impurities. Membrane processes including the special case of reverse osmosis to remove salts from water are discussed for the treatment of water in Chapter 5, Section 5.10. Electrodialysis, employing membranes alternately permeable to cations and to anions and driven by the passage of an electrical current (see Chapter 5, Section 5.10), is sometimes used to concentrate metal plating wastes and to reclaim dissolved metals. 

Investigations of membrane-transport properties of amino phosphor-ylic carriers in relation to metals ions of I-IV groups that have been previously conducted, allows determining that factors defining the efficiency of metals ions transfer can be different except the molecular structure of membrane-extracting agents. First of all, this is the concentration of a carrier in membrane phase, concentration of metal cations and anions in donating phase, the nature of added anion and, as pointed above, the nature of used solvent and others The influence of some of these factors to the values of membrane permeability has been studied on the example of membrane transport of ion Nd . 

Control of water permeability by mechanochemical contraction of PMAA-grafted PVA membranes was studied by Osada et al. [58]. The permeability of the membranes decreased dramatically upon increase in solution pH. In the presence of NaCI permeability at all pH values was high. Furthermore, addition of metal cations or PEG increased the membrane permeability. The chemical valve action was attributed to blockage of PVA pores by highly expanded forms of PMAA. When PMAA was Induced to contract by complexation with PEG or metal cations, or by screening by NaCI, the pores opened up, resulting in high permeability. 

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