Polyvalent cation effect

Electrolytes affect dispersed polysaccharides through water inactivation, specific ion binding, and polyanion neutralization. Each effect is valence-dependent, but is less on neutral polysaccharides than on ionic polysaccharides. Di- and polyvalent cations gel or precipitate a constant amount of polysacchride at much lower concentrations than do monovalent cations. The precipitation reaction is used to advantage in isolating pectin with alkaline Al3+, because this cation and polymeric forms of Al(OH)3 readily precipitate and entrain pectinic acid from apple tissue homogenates. Other di- and polyvalent cation effects are crosslinking (Prud homme et al., 1989) and an increased rate of (3 elimination over monovalent cations (Sajjaanan-... 

Ghelants and Precipitation Inhibitors vs Dispersants. Dispersants can inhibit crystal growth, but chelants, such as ethylenediaminetetraacetic acid [60-00-4] (EDTA), and pure precipitation inhibitors such as nitrilotris(methylene)tris-phosphonic acid [6419-19-8], commonly known as amino trismethylene phosphonic acid (ATMP), can be more effective under certain circumstances. Chelants can prevent scale by forming stoichiometric ring stmctures with polyvalent cations (such as calcium) to prevent interaction with anions (such as carbonate). Chelants interact... 

The formation of a single complex species rather than the stepwise production of such species will clearly simplify complexometric titrations and facilitate the detection of end points. Schwarzenbach2 realised that the acetate ion is able to form acetato complexes of low stability with nearly all polyvalent cations, and that if this property could be reinforced by the chelate effect, then much stronger complexes would be formed by most metal cations. He found that the aminopolycarboxylic acids are excellent complexing agents the most important of these is 1,2-diaminoethanetetra-aceticacid (ethylenediaminetetra-acetic acid). The formula (I) is preferred to (II), since it has been shown from measurements of the dissociation constants that two hydrogen atoms are probably held in the form of zwitterions. The values of pK are respectively pK, = 2.0, pK2 = 2.7,... 

In the present experiments, MTX markedly increased the tissue Ca content, Ca uptake, and intracellular free Ca concentration of smooth or cardiac mus cles. These Ca -mobilizing effects of MTX as well as its vasoconstrictive, cardio tonic, and cardiotoxic effects were profoundly suppressed or abolished by Ca entry blockers, polwalent cations, or Ca -free medium. It has been reported that MTX produces Ca -dependent excitatory effects on neuronal (10,11,18) or pituitary (26) cells and smooth (12,13), cardiac (14,15,17), or skeletal (16) muscles, and that all these actions of MTX were antagonized by Ca antagonists or polyvalent cations. These observations suggest that the enhanced Ca influx and the subsequent increase in cytoplasmic free Ca concentration play a dominant role in the excitatory effects of MTX. 

There is no major advance which can be reported in our knowledge of protopectinases. The possibility of the existence of a protopectinase different from PG seems now somewhat more remote than it was ten years ago. As stated above, the trend in thinking about protopectin is definitely in the direction that protopectin is not a specific cellulose-pectinic acid compound but pectinic acid which is insoluble either on account of large molecular size or due to the effect of polyvalent cations or both. In this sense there is really no need to assume the existence of a separate protopectinase. There is little doubt that this uncertainty is in a large degree attributable to the lack of precise knowledge of protopectin. 

Without considering the aomplexity of additional interactions of phytate and Ca2+ with other polyvalent cations, proteins, and fiber, Figures 3 and 4 predict that the progressive elimination of bran in Table II lowers the concentration of soluble Ca2+. This effect is especially pronounced in the bread, where part of the remaining phytate was hydrolyzed by yeast phytase during leavening (Table II). These conclusions and their implications... 

The fact that most triphosphates of polyvalent cations which are difficultly soluble in water are soluble in excess of triphosphate, and that such polyvalent cations (e.g. Ca++) are either not precipitated or not quantitatively precipitated by the usual reagents from solutions of their salts containing triphosphate, has become of great commercial importance in water softening (90). The term sequestration is used in this connection. Numerous publications have appeared which are not mentioned in detail here, and which attempt to determine this property quantitatively. In general, the effect is attributed to the formation of relatively stable ion pairs or complexes, the stability of which is defined by the formation constants K or K. ... 

The ability of water molecules to promote a reaction depends on many factors. In most cases, zeolites with monovalent cations have low activity. However, the addition of water molecules to X and Y zeolites with monovalent ions increased the isomerization of cyclopropane (63). De-cationized zeolites can be promoted readily with water, and the process is reversible (2, 60, 64). It was shown (2) that the promoting ability of water molecules in faujasites is less when the Si02/Al203 increases. Dealu-minated faujasites are even more difficult to promote. For erionite and mordenite the maximum effect of water was observed only after treatment with liquid water and subsequent heating (2). The effect of water on zeolites saturated with polyvalent cations is less pronounced (65, 66, 67). However, the presence of multivalent cations stabilizes the catalytic activity. Water and alcohols were reported to promote ion exchanged zeolites for n-pentane isomerization (68) and n-hexadecane hydrocracking (69). 

The resin capacity for americium was only a few percent of theoretical due to large concentrations of other polyvalent cations. The resin capacity was increased by adding one to two moles of oxalic acid per mole of iron in the feed. Less than 10% of the iron was retained by the resin. Addition of oxalic acid to both the feed and wash solution effectively separated 98% of the iron as well as >98% of the trace Zr, Nb, and Pu ions. 

Equilibrium exchange of some typical monovalent and polyvalent cations were studied mainly at 25°C, with a few cases at 75°C, to show the effect of temperature on the equilibrium. All the results are presented in the form of ion exchange isotherms, Figures 3 to 11. In these figures, the ordinate, Zx, is the equivalent fraction of the ingoing ion X in the zeolite phase and the abscissa, Sx, is that of the exchange solution phase. The equivalent... 

Polycations are strongly retained by the bare silica capillary wall, since they can ion-pair at multiple sites on the anionic wall. Since all electrostatic bonds must be broken to free the solute, this problem becomes increasingly severe as the number of positive charges increases. Polycations may include small molecules such as tetrazoles and even small peptides. Either permanently coated or charged-reversed capillaries are usually required to separate polyvalent cations. Monovalent cations show some wall effects, but these do not preclude the bare silica capillary from being used. Polyanions and monovalent anions can usually be separated on bare silica. 

Solubility practically insoluble in cold ethanol (95%) and in cold water. Starch swells instantaneously in water by about 5-10% at 37°C. Polyvalent cations produce more swelling than monovalent ions, but pH has little effect. Specific surface area ... 

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