Monovalent cations structure

With respect to the carrier mechanism, the phenomenology of the carrier transport of ions is discussed in terms of the criteria and kinetic scheme for the carrier mechanism the molecular structure of the Valinomycin-potassium ion complex is considered in terms of the polar core wherein the ion resides and comparison is made to the Enniatin B complexation of ions it is seen again that anion vs cation selectivity is the result of chemical structure and conformation lipid proximity and polar component of the polar core are discussed relative to monovalent vs multivalent cation selectivity and the dramatic monovalent cation selectivity of Valinomycin is demonstrated to be the result of the conformational energetics of forming polar cores of sizes suitable for different sized monovalent cations. 

The prespective to be gained thus far is that in order to pass through a lipid layer an ion must have an appropriate polar shell provided in large part by the carrier or channel structure which by virtue of its conformation and by also having lipophilic side chains provides for the polar shell to lipid shell transition. While the relative permeability of monovalent vs divalent and trivalent ions can be qualitatively appreciated from the z2 term in Eqn 2, as indicated in Figure 1B, it is essential to know structural and mechanistic detail in order even qualitatively to understand anion vs cation selectivity and to understand selectivity among monovalent cations. 

Some microbial exopolysaccharides contain the inorganic substituents phosphate and sulphate. Phosphate has been found in exopolysaccharide from bacteria of medical importance, including Escherichia coli. Sulphate is far less common than phosphate and has only been found in spedes of cyanobaderia. In addition to these inorganic components, which form part of the structure of some exopolysaccharides, all polyanionic polymers will bind a mixture of cations. Exopolysaccharides are, therefore, purified in the salt form. The strength of binding of the various cations depend on the exopolysaccharide some bind the divalent cations calrium, barium and strontium very strongly, whereas others prefer certain monovalent cations, eg Na ... 

The soft ionization methods, which will be discussed later, most often produce a molecular ion in which a charge-carrying species is attached to the neutral molecule. Typically, an H+ is the attaching species. Many structural classes of compounds, however, show the strong tendency to scavenge and attach monovalent cations—in this case, Na+. 

Although the acidic antibiotics do not show the high selectivity characteristic of the neutral ones, there is still some preference, a strong one for monovalent as compared with divalent cations, and within the monovalent cations a variation from one acid to another. Monensin prefers sodium to potassium. The larger nigeridn, (X7), prefers potassium to sodium its silver, potassium, and sodium salts are isomorphous and anhydrous. Crystal structure determinations on the silver salt were carried out independently by workers in the U.S.A. (78) and in Japan... 

Monophosphabutadienes, 33 281-283 Monophosphacarbodiimides, 33 322 preparation, 33 323 reactivity, 33 322-325 stereoselective reaction, 33 324 Monophosphahexadienes, 33 305, 307-310 Monoterpyridine complexes of copper, 45 288 Monovalent cations hydration shell properties, 34 203-204 structure, 34 202-205... 

At first glance, the standard potentials listed in Table 1 are largely nondescript. All are quite similar, with the possible exception of the sodium couple, which might appear to be anomalously positive. These values are qualitatively consistent with the simple picture that develops upon consideration of the electronic structures of the metals and their oxidized monovalent cations. Each of the metals exhibits an electronic structure that can be symbolized by (noble gas) s, where the principal quantum number (n) ranges from 2 < < 7. For example, the electronic structure for potassium is [Ar]4s, that is, ls 2s 2p 3s 3p 4sk Each of the alkali metals can easily lose one electron to give a stable monovalent metal cation that is isoelectronic with the noble gas... 

Molybdate, MoO2-, is isolated in the form of salts of monovalent, divalent and trivalent cations. The salts of the simple monovalent cations are usually water soluble while salts with larger cations, e.g. N-propylammonium, jV-ethylpyridinium and tetra-n-butyl ammonium may also have solubility in non-aqueous solvents.9 The salts of di- and tri-valent cations are generally insoluble and form three-dimensional structures in the solid state. As discussed below, although many of these maintain the MoO2- structural unit, some salts which stoichiometrically contain Mo04 have octahedral six-coordinate MoVI. 

The third complication in assigning surface composition arises from nonstoichiometric dissolution during approach to equilibrium between the solid and solution. This subject is abundantly reported in the geological literature with regard to weathering (50, 55). It appears reasonably correct to conclude that monovalent cations are quickly replaced by hydrogen ion. Bivalent cations are partially lost, probably by ion exchange with H+, particularly if they do not form part of the structural framework of the solid. 

Octahedral coordination of Tiiv is also present in the titanium silicates ETS-4 and ETS-10. The structure of these materials is reported to be similar to that of zorite, and they can be described as microporous crystals with uniform pores similar in dimensions to classical small- and large-pore zeolites. In ETS-4 and ETS-10, there are two monovalent cations or one divalent cation for each Tilv ion (Kuznicki, 1989, 1990 Kuznicki et al., 1991a, 1991b, 1991c, 1993 Deeba et al., 1994). A recent report of the synthesis of ETS-10 with tetramethyl-ammonium chloride indicates a ratio of monovalent cations to Tilv of 1.6 (Valtchev et al., 1994). The acidic properties of these materials have not been reported. A material modified by the addition of Al3+ has been obtained, ETAS-10, which, after exchange with NH4 salts, exhibits acidic properties but these are due to the presence of Al3+ and not to the Tilv (Deeba et al., 1994). 

The simple integral oxidation state compounds behave as either insulators or semiconductors. The tetracyanoplatinates of monovalent cations form anionic columnar stack structures with conductivities in the range 10-4—10-9 fi 1 cm-1 and a systematic variation of cry with 1 /electrical conductivity can be increased by as much as a factor of 104 by pressures up to 180 kbar.27... 

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