Cations, monovalent/divalent

In such systems as (M, Mj (i/2))X (M, monovalent cation Mj, divalent cation X, common anion), the much stronger interaction of M2 with X leads to restricted internal mobility of Mi. This is called the tranquilization effect by M2 on the internal mobility of Mi. This effect is clear when Mj is a divalent or trivalent cation. However, it also occurs in binary alkali systems such as (Na, K)OH. The isotherms belong to type II (Fig. 2) % decreases with increasing concentration of Na. Since the ionic radius of OH-is as small as F", the Coulombic attraction of Na-OH is considerably stronger than that of K-OH. 

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. 

To circumvent the above problems with mass action schemes, it is necessary to use a more general thermodynamic formalism based on parameters known as interaction coefficients, also called Donnan coefficients in some contexts (Record et al, 1998). This approach is completely general it requires no assumptions about the types of interactions the ions may make with the RNA or the kinds of environments the ions may occupy. Although interaction parameters are a fundamental concept in thermodynamics and have been widely applied to biophysical problems, the literature on this topic can be difficult to access for anyone not already familiar with the formalism, and the application of interaction coefficients to the mixed monovalent-divalent cation solutions commonly used for RNA studies has received only limited attention (Grilley et al, 2006 Misra and Draper, 1999). For these reasons, the following theory section sets out the main concepts of the preferential interaction formalism in some detail, and outlines derivations of formulas relevant to monovalent ion-RNA interactions. Section 3 presents example analyses of experimental data, and extends the preferential interaction formalism to solutions of mixed salts (i.e., KC1 and MgCl2). The section includes discussions of potential sources of error and practical considerations in data analysis for experiments with both mono- and divalent ions. 

Benzene sulfonic acid Si-O-Si-C CHsCH -SOiH Ion exchange Separates cations, with divalent ions more strongly retained than monovalent ions phosphate buffer systems are often used, sometimes with low concentrations of polar nonaqueous modifiers added the presence of the benzene group on the benzenesulfonic acid moiety gives this phase a dual nature, and the ability to separate based upon nonpolar interactions... 

Movement of monovalent cations—Monovalent cations move faster in zeolites and have lower activation energies than divalent cations [5,23],... 

C. Surfaces that exhibit pH-dependent electrical potential show various degrees of selectivity for the same cation. For example, kaolinite or kaolinitic soils at high pH (high negative surface electrical potential) shows increasing preference for divalent cations than monovalent cations, while at low pH (low negative electrical potential), kaolinite, or kaolinitic soils show increasing preference for monovalent cations than divalent cations. 

Exchange Reactions. Exchange reactions in soils commonly involve monovalent-monovalent (e.g., IC-NKQ, monovalent-divalent (e.g., K+-Ca, Na+-Ca2+), movova-lent-trivalent (e.g., K+-A13+), or divalent-trivalent (e.g., Ca2+-Al3+) cations. The... 

Protein Ca2+ channels are highly permeant to Ca2+, Sr2+, and Ba2+. In the presence of these divalent cations, they select strongly against monovalent cations, such as K+ and Na+84 however, the channels become highly permeable to these monovalent cations when all divalent cations are removed. These characteristics are shared by the Ca2+channels formed in bilayers by E. coli or synthetic PHB128/polyP complexes. The channels are selective for divalent over monovalent cations, permeant to Ca2+, Sr24, and Ba2+, and become permeable to monovalent cations when divalent cations are absent.27,28... 

Although it is not currently included in the pharmacopeias, a specification for hydroxypropyl starch is included in the Japanese Pharmaceutical Excipients (JPE) 2004 see Table I. Hydroxypropyl starch is compatible with cationic ingredients (monovalent, divalent), oils, emollients, and silicone. 

The Gapon equation is widely recognized as empirical in nature and thermodynamically dubious (e.g., see references 7 and 24) but has nonetheless often been used successfully to fit cation-exchange data. We will demonstrate later that the Gapon equation can indeed describe monovalent-divalent exchange under conditions in which sorption in the diffuse layer is minor in comparison with chemisorption. 

Equation 3.108 predicts a higher local concentration of cations near a negatively charged clay surface than in bulk solution, and a lower concentration of anions near the surface than in solution. Figure 3.24 shows this predicted distribution of monovalent cations and anions near the clay surface for two different concentrations of electrolyte in solution. More modem statistical mechanical models of this clay interfacial region have predicted that ion-ion correlation (electrostatic) effects should cause deviations from this classical picture, such as the positive adsorption of anions at intermediate distances from the surface when the cation is divalent or multivalent. 

Do both by replacing monovalent cation with divalent alternatives. 

Another aspect of catalysis at metal ion sites on enzymes is the selectivity exhibited by some enzymes for the type of cation (monovalent versus divalent) and/or the oxidation state (-l- 2 versus + 3) of the cation. Model studies of metal ion-assisted reactions and of metal-ligand structures will be reviewed to establish trends for these types of reactions and features that direct metal ion preference for certain ligand environments. 

For cation chromatography there are basically two eluent systems used. In the case of monovalent cations, the normal eluent is 0.005M HC1. However, the concentrations of hydrogen ion required for divalent cations are such that hydrogen ion is impractical eluent for divalent cations. Instead, the preferred cation for divalent cations like the alkaline earth cations is m-phenylenediamine dihydrochloride. The divalent nature of m-phenylenediamine makes it an efficient eluent for other divalent cations, while its weakly basic character results in very little conductivity when it is converted to the free base form in the suppressor. 

The thermodynamic selectivity series for zeolite T is Cs > Rb > Ag > K > NH4 > Ba >> Na > Ca > Li. One of the most interesting results of this work is that this zeolite prefers many monovalent cations to divalent ones. This behavior is not often observed and is unexpected... 

For all preceding chalcogenide compounds prepared in supercritical amines, the metal centers are always monovalent. This includes both the alkali metal and the transition metal. In attempts to make more electronically interesting compounds, the inclusion of polyvdent metal ions with open shells in the chalcogenide framework was attempted. This was done by replacing the alkali metal cations with divalent cations or trivalent rare earth cations. However,... 

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