Transport trivalent cations

The apparent failure of trivalent and tetravalent cations to enter plants could result from the interaction of the cations with the phospholipids of the cell membranes. Evidence for such interactions is provided by the use of lanthanum nitrate as a stain for cell membranes (143) while thorium (IV) has been shown to form stable complexes with phospholipid micelles (144). However, it is possible that some plant species may possess ionophores specific to trivalent cations. Thomas (145) has shown that trees such as mockernut hickory can accumulate lanthanides. The proof of the existence of such ionophores in these trees may facilitate the development of safeguards to ensure that the actinides are not readily transported from soil to plants. 

The metallic properties observed for the d7 compounds listed in Table I are also consistent with the Goodenough model. The rhodium-selenium system is of particular interest and demonstrates clearly the important relationships between structure and transport properties. Cations may be removed from the superconducting compound (Tc = 6°K), RhSe2. The pyrite structure is maintained as the eg band is gradually emptied, and at the composition Rh2/3Se2 (RhSe3), all cations are trivalent—i.e., have the configuration 4d6. It is not known yet if the ideal... 

The redox system does not depend on endosomal acidification but needs TfR. Fe2Tf first binds to TfR which is located in close proximity to the proton-and electron-pumping NADHiTf oxidoreductase. The Fe—Tf bond is destabilized by proton efflux, making Fe3+ susceptible to reduction. Fe2+ is trapped by a plasma membrane binder and can be transported by a translocator [4]. As Al is a simple trivalent cation incapable of redox changes, it may be theoretically impossible that Al bound to Tf is taken up by a redox mechanism. Actually, no reports on a redox-mediated process of Al bound to Tf have been made. 

There is not much information on the hydration of these trivalent cations. Estimates made on the basis of the calculated entropies of hydration suggest a hydration number of about 7 (5, 6a). But an estimate made by extrapolation of data for electrophoretic transport measurements on the ions of some heavier actinides indicate a hydration number of about 12.7, with nine water molecules in the first coordination sphere (66),... 

Compounds in the P/P" family permit not only fast Na ion diffusion but also rapid transport of other monovalent ions (e.g., K, Ag, Cu", Cs, Rb ), hydronium ions (HsO ), divalent ions (e.g., Ca ", Ba " ) and trivalent cations . As it turns out, the Na ion has the highest mobility in these two structures. The sodium -alumina and /)"-alumina compounds are nonstoichiometric aluminates that are derivatives of the yet unknown stoichiometric sodium aluminate, NaAlnOi (Na20 IIAI2O3), with an excess of Na20. 

Trivalent cation conduction in molybdates with the Sc2(WO4)3-type structure, M2(MoO4)3, was also investigated. The transport of trivalent + in molybdates was higher than that in tungstates (Figure 8.11), due to the smaller radius of Mo +... 

Indanomycin (X-14547 A) [S. antibioticus] 493.69 ethyl acetate, methanol ionophore particularly for K but Rb and Cs are transported across the membrane as well binding mono-, di-, and trivalent cations... 

Schwartz JH, Flamenbaum W (1976) Heavy metal-induced alterations in ion transport by turtle urinary bladder. Am J Physiol 230 1582-1589 Sheets MF, Hanck DA (1992) Mechanisms of extracellular divalent and trivalent cation block of the sodium current in canine cardiac purkinje cells. J Physiol (Lond) 454 299-320... 

In order to overcome these stability problems a wide-range of alternative dopants have been studied in an effort to reproduce the transport properties of LISICON whilst eliminating the problems of aging. The introduction of trivalent cations into the basic lithium germanate structure can cause an adjustment in the lithium concentration, but in this case it is possible to introduce additional, interstitial, lithium cations or vacancies on the lithium position. Which of these types of doping occurs depends on the nature of the substitution that occurs. This can be most clearly illustrated by looking at the introduction of aluminium cations. These can enter the structure in place of and so introduce an interstitial lithium cation ... 

Whilst it is clear that introducing trivalent cations into the octahedral site can modify the transport properties of the material it must be stressed that a change in lithium ion conductivity cannot be used as a proof of incorporation of a dopant cation into the structure. A detailed comparative study of the effect of Sc and on the properties of LiTi2(P04)3 showed that both Lii+,room temperature conductivity for dopant levels In the case of the optimum composition in the yttrium system, Li1.3Y0.3Ti3 7(P04)3, the conductivity was an order of magnitude... 

In the P" phase, trivalent cations like Eu + can also be substituted for Na+. For instance, when a slab of this crystal is heated in EuClj powder for 24 h, almost all the Na is replaced by Eu. This vapor-phase ion exchange utihzing fast ion transport is a typical example of materials synthesis by soft chemistry. Unfortimately, rare earth P"-aluminas are not good ionic conductors, but they are promising candidates as crystals for solid state lasers. ... 

Kruczek and Matsuura in their studies on characterization of gas separation properties of SPPO films have reported similar trends for permeabilities and permselectivities for O2 and N2. They have also reported CO2/CH4 permeability ratio of 43 corresponding to CO2 permeability of 11 Barrer for SPPO. The authors have conducted a detailed study on the effect of mono-, di- and trivalent cation substitutions of SPPO membranes on their gas separation performances. The thus substituted polymers were more permeable to gases than the hydrogen form of SPPO without any loss in the permeability ratios. The improved gas transport properties (separation factor for O2/N2 of 7.65 corresponding to 67.3% of O2 in the permeate when the membrane was used for oxygen enrichment of air) of SPPO with a degree of substitution of 18.5% and in the Mg " form for O2/N2 gas pair placed the polymer above the upper-bound line. 

The activity was transported to ARCA II with a He(KCl) gas-jet within about 3 s. After deposition on a titanium slider it was dissolved and washed through the 1.6x8 mm column (filled with the cation-exchange resin Aminex A6, 17.5 2 pm) a flow rate of 1 mL/min with 0.1 M HNOj/5-10 4 M HF. 85% of the W elute within 10 s. Neither divalent or trivalent metal ions nor group-4 ions are eluted within the first 15 s. Also the pseudo-homologue uranium, in the form of U022+, is completely retained on the column. 

The ionic transport properties of fluorite-type oxide phases (see Chapter 2), another important family of solid electrolytes, are also discussed in subsequent chapters. Briefly, for the well-known zirconia electrolytes, Zr itself is too small to sustain the fluorite structure at moderate temperatures doping with divalent (Ca + ) or trivalent (e.g., Y " ", St " ", Yb " ") cations stabilizes the high-temperature polymorph with the cubic fluorite-type structure. Due to the electroneutrahty condition, anion vacancies are formed ... 

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